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  • 1. Acosta, R. P.
    et al.
    Burls, N. J.
    Pound, M. J.
    Bradshaw, C. D.
    de Boer, Agatha M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Stockholms universitet, Naturvetenskapliga fakulteten, Bolincentret för klimatforskning (tills m KTH & SMHI).
    Herold, N.
    Huber, M.
    Liu, X.
    Donnadieu, Y.
    Farnsworth, A.
    Frigola, A.
    Lunt, D. J.
    von der Heydt, A. S.
    Hutchinson, D. K.
    Knorr, G.
    Lohmann, G.
    Marzocchi, A.
    Prange, M.
    Sarr, A. C.
    Li, X.
    Zhang, Z.
    A Model-Data Comparison of the Hydrological Response to Miocene Warmth: Leveraging the MioMIP1 Opportunistic Multi-Model Ensemble2024Ingår i: Paleoceanography and Paleoclimatology, ISSN 2572-4517, E-ISSN 2572-4525, Vol. 39, nr 1, artikel-id e2023PA004726Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Miocene (23.03-5.33 Ma) is recognized as a period with close to modern-day paleogeography, yet a much warmer climate. With large uncertainties in future hydroclimate projections, Miocene conditions illustrate a potential future analog for the Earth system. A recent opportunistic Miocene Model Intercomparison Project 1 (MioMIP1) focused on synthesizing published Miocene climate simulations and comparing them with available temperature reconstructions. Here, we build on this effort by analyzing the hydrological cycle response to Miocene forcings across early-to-middle (E2MMIO; 20.03-11.6 Ma) and middle-to-late Miocene (M2LMIO; 11.5-5.33 Ma) simulations with CO2 concentrations ranging from 200 to 850 ppm and providing a model-data comparison against available precipitation reconstructions. We find global precipitation increases by similar to 2.1 and 2.3% per degree of warming for E2MMIO and M2LMIO simulations, respectively. Models generally agree on a wetter than modern-day tropics; mid and high-latitude, however, do not agree on the sign of subtropical precipitation changes with warming. Global monsoon analysis suggests most monsoon regions, except the North American Monsoon, experience higher precipitation rates under warmer conditions. Model-data comparison shows that mean annual precipitation is underestimated by the models regardless of CO2 concentration, particularly in the mid- to high-latitudes. This suggests that the models may not be (a) resolving key processes driving the hydrological cycle response to Miocene boundary conditions and/or (b) other boundary conditions or processes not considered here are critical to reproducing Miocene hydroclimate. This study highlights the challenges in modeling and reconstructing the Miocene hydrological cycle and serves as a baseline for future coordinated MioMIP efforts. This study looks at Earth's hydrological cycle during the Miocene (23-5 million years ago). During this period, the Earth's climate was 3-7 degrees C warmer than today, with carbon dioxide (CO2) estimates ranging between 400 and 850 ppm. Understanding how the hydrological cycle responded during warmer climate conditions can give us insight into what might happen as the Earth gets warmer. We analyzed a suite of Miocene paleoclimate simulations with different CO2 concentrations in the atmosphere and compared them against fossil plant data, which gives an estimate of the average annual rainfall during the period. We found that during the Miocene global rainfall increased by about 2.1%-2.3% for each degree of warming. The models agree that the tropics, mid- and high-latitude, became wetter than they are today but have lower agreement on whether subtropical areas got wetter or drier as they warmed. Compared to proxies, models consistently underestimated how much rain fell in a year, especially in the mid- to high-latitude. This illustrates the challenges in reconstructing the Miocene's hydrological cycle and suggests that the models might not fully capture the range of uncertainties associated with changes in the hydrological cycle due to warming or other factors that differentiated the Miocene. A multi-model comparison of the hydrological cycle in early-to-middle and middle-to-late Miocene simulations is conductedModels generally agree on wetter than modern tropics, middle and high latitudes, but not on the sign of subtropical precipitation changesModel-data comparison shows mean annual precipitation is underestimated by the models, particularly in the mid- to high-latitudes

  • 2.
    Adler, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Studier av geomorfologi på Mani, Peloponnesos, Grekland2013Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Halvön Mani i södra Peloponnesos, Grekland, ligger enbart 50 km från subduktionszonen Hellenic arc. Det medför att aktiva tektoniska processer påverkar geomorfologin. Genom fjärranalys, analys av digital terrängmodell samt genom ett fem dagars fältarbete har en del av södra halvöns geomorfologi studerats. Recenta processer som idag skapar landformer har identifierats. Av dessa är det främst kemisk vittring och tektonik som dominerar. Även relikta landformer studerades för att skapa en komplettare bild över området. Två stycken stenfält upptäcktes på en av uddarna, som troligen skapats innan udden lyfts upp till nivån den befinner sig idag. Ett konglomerat överlagrade kalkstenen i en av vikarna och vittnar om stora massrörelser som skett då markytan även här var lägre än idag. Ett pediment finns på den västra sidan av berget Sagias. Asymmetrin beror troligen på en kombination av tektonik och havsnivåförändringar.

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  • 3.
    Afrifa, Yamoah Kweku Kyei
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Reconstruction of the Southeast Asian hydro-climate using biomarkers and their hydrogen isotopic composition2015Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Southeast Asia is characterized by a monsoonal climate, with distinct wet and dry seasons. This has great impact on societies, agriculture and infrastructures. Despite the critical importance to understand the mechanisms that influence the variability of the Asian Monsoon, there is scarcity of both historical and paleoclimate proxy data from Southeast Asia. For this reason, two lakes from Thailand, Lake Pa Kho (LPK) and Lake Nong Thale Pron (NTP), which are located in the northeastern and southern part of Thailand, respectively, were cored. The region also offers the opportunity to study the potential influence of climate on the Angkor civilization. Overall, this project seeks to improve our understanding of the mechanisms that contribute to Asian monsoon variability and how the variability influenced Angkor Civilization. Here I present results on a 2000-years sediment record from LPK. The most important part of the work presented here consists of compound-specific hydrogen isotope ratios (δD), which are used to infer past changes in the hydrological cycle of Southeast Asia. This approach is based on the premise that δD of lipid biomarkers from plants, algae and microorganisms deposited in sediments reflects the δD of their source water, which in turn is influenced by local hydrology. A rapid increase in precipitation is inferred from ca. 700 to ca. 850 AD, after a long dry phase. The inferred shift to wet conditions likely contributed to the rise of the Angkor Civilization, by boosting agriculture. However, gradual drying occurred at around 900 AD until the 19th century. This long-term decline in precipitation, favoring ever more frequent occurrences of severe droughts, likely also contributed to the demise and fall of the Angkor, around 1400 AD. Comparison with other hydroclimate proxy records revealed that wet conditions in tropical SE Asia corresponded to a dry Western Pacific, wet conditions in the East Pacific, and vice versa - a pattern that can be explained by opposing centers of convection and subsidence. Moreover, our tropical record also appears to be anti-correlated with the subtropical East Asian Monsoon, possibly caused by rainout effects along moisture trajectories. These long-term rainfall shifts closely match patterns observed during periods of strong El Niño, and suggests a central role for Pacific Walker circulation as a driver of centennial-scale hydroclimatic change. Besides these results from LPK oriented towards reconstructing hydroclimate, I also present some initial results concerning the evolution of the plant community of LPK, based on compound specific 13C analysis, as well as first biomarker results from NTP.

  • 4. Andresen, Camilla S.
    et al.
    Karlsson, Nanna B.
    Straneo, Fiammetta
    Schmidt, Sabine
    Andersen, Thorbjørn J.
    Eidam, Emily F.
    Bjørk, Anders A.
    Dartiguemalle, Nicolas
    Dyke, Laurence M.
    Vermassen, Flor
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Gundel, Ida E.
    Sediment discharge from Greenland's marine-terminating glaciers is linked with surface melt2024Ingår i: Nature Communications, E-ISSN 2041-1723, Vol. 15, nr 1, artikel-id 1332Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Sediment discharged from the Greenland Ice Sheet delivers nutrients to marine ecosystems around Greenland and shapes seafloor habitats. Current estimates of the total sediment flux are constrained by observations from land-terminating glaciers only. Addressing this gap, our study presents a budget derived from observations at 30 marine-margin locations. Analyzing sediment cores from nine glaciated fjords, we assess spatial deposition since 1950. A significant correlation is established between mass accumulation rates, normalized by surface runoff, and distance down-fjord. This enables calculating annual sediment flux at any fjord point based on nearby marine-terminating outlet glacier melt data. Findings reveal a total annual sediment flux of 1.324 + /- 0.79 Gt yr-1 over the period 2010-2020 from all marine-terminating glaciers to the fjords. These estimates are valuable for studies aiming to understand the basal ice sheet conditions and for studies predicting ecosystem changes in Greenland's fjords and offshore areas as the ice sheet melts and sediment discharge increase. 

  • 5.
    Ardung, Ola
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Closed To Open Sourve GIS: First Steps In Reverse Engineering ESRI's Layer Defintion File Format2017Självständigt arbete på avancerad nivå (masterexamen), 30 poäng / 45 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Visualization of digital geographic data is often accomplished through custom symbology that is saved in a proprietary format called a layer file (.lyr). The sharing of free geographical information system (GIS) data can be limited as the symbology data is bound inthe .lyr file format. This makes it harder and more tedious to work with open software tools since it is not possible to convert or open the .lyr file in free and open GIS software and thus limits the distribution of free GIS data. The aim of this thesis is to increase the interoperability of .lyr data between proprietary and free and open GIS software. This was done by revers eengineering the .lyr file format to document the file structure and to distribute the knowledge and metadata gained from this project to the open source community. Reverse engineering the.lyr format provided a well needed metadata and documentation about the format which increases the interoperability and enable future work to continue to lessen the gap between open source and commercial software. This groundwork can therefore, enable a continued development of data interoperability between proprietary and free and open GIS software.

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  • 6.
    Backman, Jan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Moran, Kathryn
    University of Rhode Island.
    Expanding the Cenozoic paleoceanographic record in the central Arctic Ocean: IODP Expedition 302 synthesis2009Ingår i: Central European Journal of Geosciences, E-ISSN 1896-1517, Vol. 1, nr 2, s. 157-175Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Arctic Coring Expedition (ACEX) proved to be one of the most transformational missions in almost 40 year of scientific ocean drilling. ACEX recovered the first Cenozoic sedimentary sequence from the Arctic Ocean and extended earlier piston core records from ≈1.5 Ma back to ≈56 Ma. The results have had a major impact in paleoceanography even though the recovered sediments represents only 29% of Cenozoic time. The missing time intervals were primarily the result of two unexpected hiatuses. This important Cenozoic paleoceanographic record was reconstructed from a total of 339 m sediments. The wide range of analyses conducted on the recovered material, along with studies that integrated regional tectonics and geophysical data, produced surprising results including high Arctic Ocean surface water temperatures and a hydrologically active climate during the Paleocene Eocene Thermal Maximum (PETM), the occurrence of a fresher water Arctic in the Eocene, ice-rafted debris as old as middle Eocene, a middle Eocene environment rife with organic carbon, and ventilation of the Arctic Ocean to the North Atlantic through the Fram Strait near the early-middle Miocene boundary. Taken together, these results have transformed our view of the Cenozoic Arctic Ocean and its role in the Earth climate system.

  • 7.
    Barrientos, Natalia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Arctic Ocean benthic foraminifera preservation and Mg/Ca ratios: Implications for bottom water palaeothermometry2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Reconstructions of Arctic Ocean palaeotemperatures are needed to disentangle natural variability from anthropogenic changes and understand the role of ocean heat transport in forcing or providing feedbacks on Arctic climate change. Despite known complications with calcareous microfossil preservation in Arctic Ocean sediments, calcareous benthic foraminifera can be common in interglacial sequences. However, thus far they have been underutilized in palaeoceanographic studies. This thesis explores the application of the Mg/Ca palaeothermometry proxy for reconstructing bottom water temperatures (BWT) in the Arctic Ocean during the late Quaternary. This method, which is supported by previous empirical studies demonstrating a strong temperature control on trace Mg inclusion into foraminiferal shell calcite, has been applied in many ocean regions and time intervals. Until now its application in the Arctic Ocean has been sparingly explored.

    The results of this doctoral thesis are based on benthic foraminifera retrieved from marine sediment cores covering a wide geographical Arctic Ocean area including both the shallow and vast continental shelves and slopes to the intermediate-to-deep waters of the Lomonosov Ridge and Morris Jesup Rise. These provide the first benthic foraminifera Mg/Ca ratios from the central Arctic Ocean region. In the first study, mechanisms that could affect Mg incorporation in Arctic benthic foraminifera are investigated using oceanographic field data and six 'live' modern Arctic species (Elphidium clavatum, Nonionella labradorica, Cassidulina neoteretis, Oridorsalis tener, Cibicidoides wuellerstorfi and Quinqueloculina arctica). The result is new species-specific Mg/Ca–BWT field calibrations that provide important constraints at the cold end of the BWT spectrum (-2 to 1°C) (Paper I). Using the new Mg/Ca–BWT equation for E. clavatum, a palaeotemperature record was generated for the late Holocene (past ca. 4100 yr) from the western Chukchi Sea. The data showed BWT fluctuations from -2 to 1°C that are interpreted as showing pulses of warmer Pacific water inflow at 500–1000 yr periods, thus revealing multi-centennial variability in heat transport into the Arctic Ocean driven by low latitude forcings (Paper II). Complications with foraminiferal calcite preservation that limit Mg/Ca palaeothermometry in the Arctic were discovered and these are tackled in two additional papers. Anomalously high Mg content in benthic foraminifera from the central Arctic Ocean is linked to diagenetic contamination as a result of the unique oceanographic, sedimentary and geochemical environment (Paper III). Lastly, the dramatic post-recovery dissolution of foraminifera from a Chukchi Shelf sediment core during core storage is investigated and attributed to acidification driven by sulphide oxidation in this organic rich and calcite poor shelf setting (Paper IV).

    The findings of this thesis demonstrate that benthic foraminiferal Mg/Ca-palaeothermometry can be applied in the Arctic Ocean and capture small BWT change (on the order of -2 to 2°C) even at low temperatures. In practice, preservational complexities can be limiting and require special sample handling or analysis due to the high potential for diagenetic contamination in the central Arctic Ocean and rapid post coring calcite dissolution in the seasonally productive shelf seas. This Ph.D. project is a component of the multidisciplinary SWERUS-C3 (Swedish-Russian-US Arctic Ocean Climate-Cryosphere- Carbon Interactions) project that included an expedition with Swedish icebreaker Oden to the East Siberian Arctic Ocean.

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  • 8.
    Barrientos, Natalia
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Coxall, Helen
    Lear, Caroline
    O'Regan, Matt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Mörth, Carl-Magnus
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Mg/Ca ratios in late Quaternary benthic foraminifera from the central Arctic OceanManuskript (preprint) (Övrigt vetenskapligt)
  • 9.
    Barrientos, Natalia
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Mörth, Carl-Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Pearce, Christof
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Miller, Clint
    O'Regan, Matt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Brüchert, Volker
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Johansson, Carina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Coxall, Helen
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Post-recovery dissolution of calcareous microfossils in sediments from a highly productive Arctic marine environmentManuskript (preprint) (Övrigt vetenskapligt)
  • 10.
    Bergman, Helena
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Piazolo, Sandra
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    The recognition of multiple magmatic events and pre-existing deformation zones in metamorphic rocks as illustrated by CL signatures and numerical modelling: examples from the Ballachulish contact aureole, Scotland2012Ingår i: International journal of earth sciences, ISSN 1437-3254, E-ISSN 1437-3262, Vol. 101, nr 5, s. 1127-1148Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The combination of cathodoluminescence (CL) analysis, temperature and temperature-time calculations, and microstructural numerical modelling offers the possibility to derive the time-resolved evolution of a metamorphic rock. This combination of techniques is applied to a natural laboratory, namely the Ballachulish contact aureole, Scotland. Analysis of the Appin Quartzite reveals that the aureole was produced by two distinct magmatic events and infiltrated by associated fluids. Developing microstructures allow us to divide the aureole into three distinct regions. Region A (0-400 m, 663A degrees C < T (max) < 714A degrees C) exhibits a three-stage grain boundary migration (GBM) evolution associated with heating, fluid I and fluid II. GBM in region B (400-700 m, 630A degrees C < T (max) < 663A degrees C) is associated with fluid II only. Region C (> 700 m of contact, T (max) < 630A degrees C) is characterised by healed intragranular cracks. The combination of CL signature analysis and numerical modelling enables us to recognise whether grain size increase occurred mainly by surface energy-driven grain growth (GG) or strain-induced grain boundary migration (SIGBM). GG and SIGBM result in either straight bands strongly associated with present-day boundaries or highly curved irregular bands that often fill entire grains, respectively. At a temperature of similar to 620A degrees C, evidence for GBM is observed in the initially dry, largely undeformed quartzite samples. At this temperature, evidence for GG is sparse, whereas at similar to 663A degrees C, CL signatures typical for GG are commonplace. The grain boundary network approached energy equilibrium in samples that were at least 5 ka above 620A degrees C.

  • 11.
    Berntsson, Annika
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Kaislahti Tillman, Päivi
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Risberg, Jan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Bilaga 18. Miljöförändringar kring Gamla Älvsborgs fästning baserade på diatoméstratigrafi, samt analyser av svavel och organiskt kol, i sediment avsatta i vallgraven2011Ingår i: Gamla Älvsborg i nytt ljus: Arkeologiska undersökningar 2004-2006 / [ed] Ulf Ragnesten, Mölnlycke: Elanders , 2011Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 12. Björk, Alexandra
    et al.
    Skånes, Helle
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    The Need for Awareness of Semantic Plasticity in International Harmonization of Geographical Information: Seen from a Nordic Forest Classification Perspective2015Ingår i: Land Use and Land Cover Semantics: Principles, Best Practices and Prospects / [ed] Ola Ahlqvist, Dalia Varanka, Steffen Fritz, Krzysztof Janowicz, Boka Raton: CRC Press, 2015, s. 41-58Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    The aim of this chapter is to address and clarify the important issues and challenges of semantic plasticity when it comes to forest classification and geographical information. Necessary improvements for international data harmonization and implementation are highlighted along with the need for increased awareness of the consequences for ecological modeling. We envisage a combination of thoroughly described metadata and controlled vocabularies as a means to ensure the future use of a wide range of regional and national classification systems in an ontological framework that enables crosswalks between classification systems and spatial comparisons between existing data sets. This would allow for a wide range of old, contemporary, and future data sets to be used together in landscape-related analyses.

  • 13.
    Björkvald, Louise
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi. Geokemi.
    Borg, Hans
    Institutionen för tillämpad miljövetenskap (ITM).
    Laudon, Hjalmar
    Mörth, Carl-Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Influence of landscape type on trace metals in small boreal catchments2007Ingår i: Geochimica et cosmochimica acta 71 (15) A95 Suppl. S. Aug 2007, 2007, s. A95-Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    We studied temporal and spatial variations of trace metal (TM) concentrations (As, Cd, Co, Cr, Cu, Ge, La, Ni, Pb, Rb, Sc, and Y) in stream water and their correlation with catchment properties (i.e. coverage of wetland and forest), but also with Fe and Mn. During 2004 and 2005 water samples were collected from 10 streams (0.13 km2 to 67 km2) in the Krycklan Catchment Study, a boreal stream network in northern Sweden. Since spring snowmelt is the most important hydrological event, the monthly sampling was intensified during spring flood (April-May) when samples were collected every second day. Total and dissolved (<0.4µm) concentrations of Fe and Mn were determined by ICP-OES. Dissolved concentrations of TM were determined by ICP-MS.

    Preliminary results show a seasonal variation for all TM, in particular during spring flood. In forested catchments most TM concentrations increased at spring flood, but for Rb and Sc a decrease was observed. Conversely, in wetland influenced catchments the opposite seasonal variation was observed, i.e. concentrations of all TM decreased by a factor of 2 to 3. The seasonal variation of Fe shows a similar pattern to many TM, due to the association of TM to Fe oxyhydroxides. In particular, Fe correlates significantly with Cr and Pb in a forested headwater stream (r2=0.77 and r2=0.71, respectively, p<0.05). In the wetland headwater stream similar correlations between Fe and TM are found, but DOC also correlates significantly with As, Cd, Ni, and Pb (r2=0.92, p<0.05).

    A significant negative correlation (p<0.05) was observed between coverage of wetlands and average concentrations of Cr, Cu, Ge, Ni, Sc and Y. The results indicate that wetlands act as sinks for these elements. Alternatively, there is a source limitation in wetlands and that increased concentrations during base flow are due to mineral groundwater influence. Positive correlation with wetland coverage was only observed for Pb (r2=0.79, p<0.05), indicating that wetlands acts as a source for this element. Sulfate concentrations correlated negatively (r2=0.97, p<0.05) with increasing coverage of wetlands, which highlights the importance of sulfate reduction within wetland areas.

    This study emphasizes the importance of considering stream water chemistry from a landscape perspective.

  • 14.
    Bonaglia, Stefano
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Hylén, Astrid
    Rattray, Jayne E.
    Kononets, Mikhail Y.
    Ekeroth, Nils
    Roos, Per
    Thamdrup, Bo
    Brüchert, Volker
    Hall, Per O. J.
    The fate of fixed nitrogen in marine sediments with low organic loading: an in situ study2017Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 14, nr 2, s. 285-300Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Over the last decades, the impact of human activities on the global nitrogen (N) cycle has drastically increased. Consequently, benthic N cycling has mainly been studied in anthropogenically impacted estuaries and coasts, while in oligotrophic systems its understanding is still scarce. Here we report on benthic solute fluxes and on rates of denitrification, anammox, and dissimilatory nitrate reduction to ammonium (DNRA) studied by in situ incubations with benthic chamber landers during two cruises to the Gulf of Bothnia (GOB), a cold, oligotrophic basin located in the northern part of the Baltic Sea. Rates of N burial were also inferred to investigate the fate of fixed N in these sediments. Most of the total dissolved fixed nitrogen (TDN) diffusing to the water column was composed of organic N. Average rates of dinitrogen (N-2) production by denitrification and anammox (range: 53-360 mu mol Nm(-2) day(-1)) were comparable to those from Arctic and subarctic sediments worldwide (range: 34-344 mu mol Nm(-2) day(-1)). Anammox accounted for 18-26% of the total N2 production. Absence of free hydrogen sulfide and low concentrations of dissolved iron in sediment pore water suggested that denitrification and DNRA were driven by organic matter oxidation rather than chemolithotrophy. DNRA was as important as denitrification at a shallow, coastal station situated in the northern Bothnian Bay. At this pristine and fully oxygenated site, ammonium regeneration through DNRA contributed more than one-third to the TDN efflux and accounted, on average, for 45% of total nitrate reduction. At the offshore stations, the proportion of DNRA in relation to denitrification was lower (0-16% of total nitrate reduction). Median value and range of benthic DNRA rates from the GOB were comparable to those from the southern and central eutrophic Baltic Sea and other temperate estuaries and coasts in Europe. Therefore, our results contrast with the view that DNRA is negligible in cold and well-oxygenated sediments with low organic carbon loading. However, the mechanisms behind the variability in DNRA rates between our sites were not resolved. The GOB sediments were a major source (237 kt yr(-1), which corresponds to 184% of the external N load) of fixed N to the water column through recycling mechanisms. To our knowledge, our study is the first to document the simultaneous contribution of denitrification, DNRA, anammox, and TDN recycling combined with in situ measurements.

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    fulltext
  • 15.
    Bonow, Johan M.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Lidmar-Bergström, Karna
    Institutionen för naturgeografi och kvartärgeologi.
    Japsen, Peter
    Chalmers, James A.
    Green, Paul F.
    Elevated erosion surfaces in central West Greenland and southern Norway: their significance in integrated studies of passive margin development2007Ingår i: Norwegian Journal of Geology, ISSN 0029-196X, Vol. 87, s. 197-206Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Elevated erosion surfaces were used as an independant data set in an integrated study of the landscape development in central West Greenland. The study resulted in a time-constrained model describing multiple episodes of post-rift uplift, erosion and burial on a passive margin. The model is based on full integration of three data sets: analysis of large-scale landforms, apatite fission track analysis (AFTA) of samples from outcrops and deep boreholes, and the geological record. These data are equally important as they record specific an unique parts of the landscape history. The relative chronology obtained from the landform record is constrained by geology, which gives the maximum age of an erosin surface, and AFTA that records the cooling history of the subsurface rock. This combined approach validates the interpretation of erosion surface as having been goverened by different base levels in the past, and shows that erosion surfaces can be used to reconstruct tectonic events. Geomorphological key observations for the landscapes of southern Norway are presented and the similarities with landscapes in central West Greenland emphasised, especially the elevated plateaux and the Mesozoic etch surfaces. This similarity suggests that it may be possible to construct a time-constrained model for the landscape development of southern Norway based on our West Greenland approach.

  • 16. Booth, Adam D.
    et al.
    Mercer, Andrew
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Clark, Roger
    Murray, Tavi
    Jansson, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Axtell, Charlotte
    A comparison of seismic and radar methods to establish the thickness and density of glacier snow cover2013Ingår i: Annals of Glaciology, ISSN 0260-3055, E-ISSN 1727-5644, Vol. 54, nr 64, s. 73-82Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We show that geophysical methods offer an effective means of quantifying snow thickness and density. Opportunistic (efficient but non-optimized) seismic refraction and ground-penetrating radar (GPR) surveys were performed on Storglaciaren, Sweden, co-located with a snow pit that shows the snowpack to be 1.73 m thick, with density increasing from similar to 120 to similar to 500 kg m(-3) (with a +50 kg m(-3) anomaly between 0.73 and 0.83 m depth). Depths estimated for two detectable GPR reflectors, 0.76 +/- 0.02 and 1.71 +/- 0.03 m, correlate extremely well with ground-truth observations. Refraction seismic predicts an interface at 1.90 +/- 0.31 m depth, with a refraction velocity (3730 +/- 190 m s(-1)) indicative of underlying glacier ice. For density estimates, several standard velocity-density relationships are trialled. In the best case, GPR delivers an excellent density estimate for the upper snow layer (observed = 321 +/- 74 kg m(-3), estimated = 319 +/- 10 kg m(-3)) but overestimates the density of the lower layer by 20%. Refraction seismic delivers a bulk density of 404 +/- 22 kg m(-3) compared with a ground-truth average of 356 +/- 22 kg m(-3). We suggest that geophysical surveys are an effective complement to mass-balance measurements (particularly for controlling estimates of snow thickness between pits) but should always be validated against ground-truth observations.

  • 17.
    Bovin, Mattias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Utveckling av biotopdatabas och tillämpning av landskapsekologisk analys i Huddinge kommun2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    På grund av ökad urbanisering och exploatering av grönområden i stadsnära miljöer fragmenteras och reduceras arters habitat vilket bland annat ligger till grund för den globalt minskade biologiska mångfalden. För att stärka och förbättra arters möjlighet till spridning i landskapet, och därmed säkra en hög biologisk mångfald, efterfrågas insamling av data och utveckling av nya metoder för att identifiera ekologiska kärnområden och för att analysera habitatnätverk. Syftet med den här studien är därför att 1) kartera och sammanställa biotoper i en biotopdatabas utifrån tolkning av infraröda flygbilder med digital stereofotogrammetri, 2) undersöka olika metoder att samla in data med hjälp av laser- och höjddata, och 3) att tillämpa landskapsekologisk analys på underlag i biotopkarteringen.

    Resultatet validerar att tolkning av infraröda flygbilder med digital stereofotogrammetri är en utmärkt källa för att kartera biotoper som medför en tolkningsnoggrannhet på 86 %. Valideringen av kateringen genomfördes med fältkontroller som utvärderades i felmatriser. En metod har även undersökts baserat på tidigare studier för att uppskatta busk- och krontäckning med hjälp av laserdata, men eftersom det saknas validering av resultatet bör den användas som en indikator för att visuellt uppskatta busk- och krontäckning i dagsläget. Fortsättningsvis har ett topografiskt fuktighetsindex (TWI) tillämpats med hjälp av höjddata för att uppskatta fuktighet i vegetationstäckta områden. Eftersom det saknas validering och tröskelvärden för att avgöra hur TWI ska klassificera olika fuktighetsgradienter, bör verktyget endast användas som en indikator för att visuellt uppskatta fuktighet tillsammans med tolkning av infraröda flygbilder. Om metoderna valideras med fältmätningar kan de bidra med att förbättra kvaliteten och tidseffektivisera kartering av biotoper.

    Biotopkarteringen fungerar som ett bra underlag vid tillämpning av landskapsekologisk analys. Med hjälp av MatrixGreen var det möjligt att modellera potentiella habitatnätverk för två olika arter inom studieområdet. På grund av en del problem med modelleringen i MatrixGreen bör resultaten beaktas med ett kritiskt angreppssätt, men kan eventuellt användas som ett underlag för framtida artinventeringar.

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    Utveckling av biotopdatabas och tillämpning av landskapsekologisk analys i Huddinge kommun
  • 18. Brandefelt, J.
    et al.
    Kjellstrom, E.
    Naslund, J. -O
    Strandberg, G.
    Voelker, A. H. L.
    Wohlfarth, Barbara
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    A coupled climate model simulation of Marine Isotope Stage 3 stadial climate2011Ingår i: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 7, nr 2, s. 649-670Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a coupled global climate model (CGCM) simulation, integrated for 1500 yr to quasi-equilibrium, of a stadial (cold period) within Marine Isotope Stage 3 (MIS 3). The simulated Greenland stadial 12 (GS12; similar to 44 ka BP) annual global mean surface temperature (T(s)) is 5.5 degrees C lower than in the simulated recent past (RP) climate and 1.3 degrees C higher than in the simulated Last Glacial Maximum (LGM; 21 ka BP) climate. The simulated GS12 is evaluated against proxy data and previous modelling studies of MIS3 stadial climate. We show that the simulated MIS 3 climate, and hence conclusions drawn regarding the dynamics of this climate, is highly model-dependent. The main findings are: (i) Proxy sea surface temperatures (SSTs) are higher than simulated SSTs in the central North Atlantic, in contrast to earlier simulations of MIS 3 stadial climate in which proxy SSTs were found to be lower than simulated SST. (ii) The Atlantic Meridional Overturning Circulation (AMOC) slows down by 50% in the GS12 climate as compared to the RP climate. This slowdown is attained without freshwater forcing in the North Atlantic region, a method used in other studies to force an AMOC shutdown. (iii) El-Nino-Southern Oscillation (ENSO) teleconnections in mean sea level pressure (MSLP) are significantly modified by GS12 and LGM forcing and boundary conditions. (iv) Both the mean state and variability of the simulated GS12 is dependent on the equilibration. The annual global mean T(s) only changes by 0.10 degrees C from model years 500-599 to the last century of the simulation, indicating that the climate system may be close to equilibrium already after 500 yr of integration. However, significant regional differences between the last century of the simulation and model years 500-599 exist. Further, the difference between simulated and proxy SST is reduced from model years 500-599 to the last century of the simulation. The results of the ENSO variability analysis is also shown to depend on the equilibration.

  • 19. Castillo, Miguel
    et al.
    Bishop, Paul
    Jansen, John D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Knickpoint retreat and transient bedrock channel morphology triggered by base-level fall in small bedrock river catchments: The case of the Isle of Jura, Scotland2013Ingår i: Geomorphology, ISSN 0169-555X, E-ISSN 1872-695X, Vol. 180, s. 1-9Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A sudden drop in river base-level can trigger a knickpoint that propagates throughout the fluvial network causing a transient state in the landscape. Knickpoint retreat has been confirmed in large fluvial settings (drainage areas > 100 km(2)) and field data suggest that the same applies to the case of small bedrock river catchments (drainage areas < 100 km(2)). Nevertheless, knickpoint recession on resistant lithologies with structure that potentially affects the retreat rate needs to be confirmed with field-based data. Moreover, it remains unclear whether small bedrock rivers can absorb base-level fall via knickpoint retreat. Here we evaluate the response of small bedrock rivers to base-level fall on the isle of Jura in western Scotland (UK), where rivers incise into dipping quartzite. The mapping of raised beach deposits and strath terraces, and the analysis of stream long profiles, were used to identify knickpoints that had been triggered by base-level fall. Our results indicate that the distance of knickpoint retreat scales to the drainage area in a power law function irrespective of structural setting. On the other hand, local channel slope and basin size influence the vertical distribution of knickpoints. As well, at low drainage areas (similar to 4 km(2)) rivers are unable to absorb the full amount of base-level fall and channel reach morphology downstream of the knickpoint tends towards convexity. The results obtained here confirm that knickpoint retreat is mostly controlled by stream discharge, as has been observed for other transient landscapes. Local controls, reflecting basin size and channel slope, have an effect on the vertical distribution of knickpoints; such controls are also related to the ability of rivers to absorb the base-level fall.

  • 20.
    Chabangborn, Akkaneewut
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    The Asian monsoon - 50-7 ka BP2012Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The Asian monsoon is one of the largest climatic systems on Earth. It covers an area from the Arabian Sea to the South China Sea and from northern Australia to northern China with the world’s highest population density. Moreover, the Asian monsoon transports heat energy and humidity to higher latitudes. In order to better understand the behaviour of the Asian monsoon and its environmental impact, its variability between 50 and 7 ka BP is analysed using paleo-data compilation, data-model comparisons, and lake sediment analysis.

    The main results presented here are from the compilation of the Asian monsoon variability during the last glacial maximum (LGM) (23 - 19 ka BP) which is presumed to be under persistence cool and dry climatic conditions. The pattern of reconstructed and simulated precipitation agrees well in most of the region. However, the data-model discrepancies show in some areas, which may come from low resolution of the model or the local topographic effect. The reconstructed SSTs are well correlation with simulated SSTs, except in the Arabian Sea. The LGM Asian monsoon changes around 20 – 19 ka BP. The simulated ITCZ varies between 5°N and 15°N in the west and the east of the Asian monsoon region. However, the reconstructed ITCZ is ~5°N in the Arabian Sea, shifts northward in the Bay of Bengal, reaches ~30°N over central of China and migrates southward in the South China Sea. The ITCZ is likely shift northward after 20 ka BP. The climatic change might have been triggered by several factors, e.g., an increased land-sea thermal contrast and a variation of Pacific water inflow.

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    Akkaneewut
  • 21.
    Chakrawal, Arjun
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Herrmann, Anke M.
    Santrručková, Hana
    Manzoni, Stefano
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Quantifying Microbial Metabolism in Soils Using Calorespirometry — A Bioenergetics Perspective2020Ingår i: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 148, artikel-id 107945Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Microbial carbon use efficiency (CUE) measures the partitioning between anabolic and catabolic processes. While most work on CUE has been based on carbon (C) mass flows, the roles of organic C energy contents and microbial energy demand on CUE have been rarely considered. Thus, a bioenergetics perspective could provide new insights on how microorganisms utilize C and ultimately allow evaluating their role in C stabilization in soils. Recently, the calorespirometric ratio (CR)— the ratio of heat dissipation and respiration— has been used to characterize the efficiency of microbial growth in soils. Here, we formulate a coupled mass and energy balance model for microbial growth and provide a generalized relationship between CUE and CR. In the model, we consider two types of organic C in soils: an added substrate (e.g., glucose) and the native soil organic matter (SOM), to also account for priming effects. Furthermore, we consider both aerobic and fermentation metabolic pathways. We use this model as a framework to generalize previous formulations and generate hypotheses on the expected variations in CR as a function of substrate quality, metabolic pathways, and microbial traits (specifically CUE). In turn, the same equations can be used to estimate CUE from measured CR. Our results confirm previous findings on CR and show that without microbial growth, CR depends only on the rates of the different metabolic pathways, while CR is also a function of the growth yields for these metabolic pathways when microbial growth occurs. Under strictly aerobic conditions, CUE increases with increasing CR for substrates with a higher degree of reduction than that of the microbial biomass, while CUE decreases with increasing CR for substrates with a lower degree of reduction than the microbial biomass. When aerobic reactions and fermentation occur simultaneously, the relation between CUE and CR is mediated by (i) the degree of reduction of the substrates, (ii) the rates and growth yields of all metabolic pathways, and (iii) the contribution of SOM priming to microbial growth. Using the proposed framework, calorespirometry can be used to evaluate CUE and the role of different metabolic pathways in soil systems.

  • 22. Charkin, A. N.
    et al.
    Dudarev, O. V.
    Semiletov, I. P.
    Kruhmalev, A. V.
    Vonk, J. E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Sanchez-Garcia, L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Karlsson, Emma
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Gustafsson, Örjan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Seasonal and interannual variability of sedimentation and organic matter distribution in the Buor-Khaya Gulf: the primary recipient of input from Lena River and coastal erosion in the southeast Laptev Sea2011Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 8, nr 9, s. 2581-2594Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Climate warming is amplified in the land-sea system of the East Siberian Arctic, which also holds large pools of vulnerable carbon in permafrost. This coastal area is strongly influenced by sediment and carbon transport from both its large rivers and extensive erosion of Pleistocene permafrost along its coastline. This study is investigating the coastal fate of the sediment and organic carbon delivered to the Buor-Khaya Gulf, which is the first recipient of the overwhelming fluvial discharge from the Lena River and is additionally receiving large input from extensive erosion of the coastal ice-complex (permafrost a. k.a. Yedoma; loess soil with high organic carbon content). Both water column suspended particulate matter (SPM) and surface sediments were sampled at about 250 oceanographic stations in the Gulf in this multi-year effort, including one winter campaign, and analyzed for the distribution and sorting of sediment size, organic carbon content, and stable carbon isotope signals. The composition of the surface sediment suggests an overwhelmingly terrestrial contribution from both river and coastal erosion. The objective of this paper is to improve our understanding of the seasonal (i.e., winter vs summer) and interannual variability of these coastal sedimentation processes and the dynamics of organic carbon (OC) distribution in both the water column SPM and the surface sediments of the Buor-Khaya Gulf. Based on data collected during several years in the period 2000-2008, two different sedimentation regimes were revealed for the Buor-Khaya Gulf, the relative importance of each at a given time depend on hydrometeorological conditions, the Lena River water discharge and sea-ice regime: Type 1 erosion-accumulation and Type 2 accumulation. The Type 1 erosion-accumulation sedimentation regime is typical (2000-2006) for the ice-free period of the year (here considered in detail for August 2005). Under such conditions terrigenous sources of SPM and particulate organic carbon (POC) stem predominantly from river discharge, thermal erosion of coastal ice-complex and remobilized bottom sediments. The Type 2 accumulation sedimentation regime develops under ice-covered conditions, and only occasionally during the ice-free period (August 2008). In Type 2 winter, combined terrigenous and marine-biogenic SPM and POC sources are dominating due to relatively low overall terrigenous input (April 2007). In Type 2 summer, river alluvium becomes the major SPM and POC source (August 2008). The water column SPM and POC loadings vary by more than a factor of two between the two regimes. This study underscores the necessity of multi-year investigations to better understand the functioning of the primary recipient of terrestrially expulsed matter in the East Siberian Arctic.

  • 23.
    Chibeya, Doubt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    How do African ElephantsUtilize the Landscape DuringWet Season?: A Habitat Connectivity Analysis for Sioma Ngwezi Landscape in Zambia2019Självständigt arbete på avancerad nivå (masterexamen), 30 poäng / 45 hpStudentuppsats (Examensarbete)
    Abstract [en]

    How environmental factors influence distribution and persistence of African elephants(Loxodonta africana) is pertinent to policy makers and managers to formulate balanced plansfor different landuse types (i.e. wildlife management, forestry). The study focuses on movementof elephants and how they utilize foraging areas in Sioma Ngwezi landscape in Zambia. Theanalysis was based on telemetry data (global position system radio collars) acquired from 8elephants (5 matriarchs and 3 bulls) between February and July in 2018. The followingenvironmental variables were analysed; land cover, topographic wetness index, normalizeddifference vegetation index, proximity to roads and proximity to settlements. MaximumEntropy (MaxEnt) and linkage mapper were the novel tools used to predict habitat suitability,movement corridors and barriers in the landscape during the wet season. Landscapepermeability and habitat suitability were explored by using resistance raster. The studyidentified elevation, land cover and Normalized Difference Vegetation Index (NDVI) as themost important environmental predictors that modifies the dispersal of elephants in thelandscape during the wet season. Additionally, a total of 36 potential wet season corridors wereidentified connecting 15 core areas mainly used for foraging and protection from poachers inthe landscape. Of these, 24 corridors were highly utilized and are suggested as priority corridorsfor elephant movement in the landscape. The identified wet season habitats and functionalcorridors may help to combat elephant poaching by patrolling areas with high relativeprobability of elephant presence. The findings may also help abate human elephant conflictsuch as crop raiding by managing identified corridors that run into agriculture zones in the gamemanagement area. Finally, management of these corridors has massive potential to increasemovement of elephants in the region especially since Sioma landscape is strategically locatedin the Kavango-Zambezi Trans-frontier Conservation Area (KAZA TFCA) connecting thesource (Hwange, Chobe and Bwabwata national parks) and the sink (the Greater Kafue andLuangwa ecosystems) linking elephants from Zambia, Zimbabwe, Angola, Namibia and Botswana.

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    fulltext
  • 24.
    Clason, Caroline C.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Applegate, Patrick
    Holmlund, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Modelling Late Weichselian evolution of the Eurasian ice sheets forced by surface meltwater-enhanced basal sliding2014Ingår i: Journal of Glaciology, ISSN 0022-1430, E-ISSN 1727-5652, Vol. 60, nr 219, s. 29-40Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We simulated the Late Weichselian extent and dynamics of the Eurasian ice sheets using theshallow-ice approximation ice-sheet model SICOPOLIS. Our simulated Last Glacial Maximum ice-sheetextents closely resemble geomorphological reconstructions, and areas of modelled fast flow areconsistent with the known locations of palaeo-ice streams. Motivated by documented velocity responseto increased meltwater inputs on Greenland, we tested the sensitivity of the simulated ice sheet to thesurface meltwater effect (SME) through a simple parameterization relating basal sliding to local surfacemelt rate and ice thickness. Model runs including the SME produce significantly reduced ice volumeduring deglaciation, with maximum ice surface velocities much greater than in similar runs that neglectthe SME. We find that the simple treatment of the SME is not applicable across the whole ice sheet;however, our results highlight the importance of the SME for dynamic response to increased melting.The southwest sector of the Scandinavian ice sheet is most sensitive to the SME, with fast flow in theBaltic ice stream region shutting off by 15 kaBP when the SME is turned on, coincident with a retreat ofthe ice-margin position into the Gulf of Bothnia.

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    Clason_etal_2014
  • 25. Cohen, T. J.
    et al.
    Nanson, G. C.
    Jansen, John D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Gliganic, L. A.
    May, J. -H.
    Larsen, J. R.
    Goodwin, I. D.
    Browning, S.
    Price, D. M.
    A pluvial episode identified in arid Australia during the Medieval Climatic Anomaly2012Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 56, s. 167-171Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Optically stimulated luminescence (OSL) ages from a relict shoreline on Lake Callabonna record a major pluvial episode in southern central Australia between 1050  70 and 1100  60 Common Era (CE), within the Medieval Climatic Anomaly (MCA). During this pluvial interval Lake Callabonna filled to 10e12 times the volume of the largest historical filling (1974) and reached maximum depths of 4e5 m, compared to the 0.5e1.0 m achieved today. Until now there has been no direct evidence for the MCA in the arid interior of Australia. A multi-proxy, analogue-based atmospheric circulation reconstruction indicates that the pluvial episode was associated with an anomalous meridional atmospheric circulation pattern over the Southern extratropics, with high sea-level pressure ridges in the central Indian Ocean and Tasman Sea, and a trough extending from the Southern Ocean into central Australia. A major decline in the mobility of the Australian aboriginal hunter-gatherer coincides with this MCA period, in southern central Australia.

  • 26.
    Corell, Hanna
    et al.
    Univ Gothenburg, Dept Biol & Environm Sci, Gothenburg, Sweden.
    Döös, Kristofer
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Difference in Particle Transport Between Two Coastal Areas in the Baltic Sea Investigated with High-Resolution Trajectory Modeling2013Ingår i: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 42, nr 4, s. SI 455-463Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A particle-tracking model based on high-resolution ocean flow data was used to investigate particle residence times and spatial distribution of settling sediment for two geo-morphologically different Swedish coastal areas. The study was a part of a safety assessment for the location of a future nuclear-waste repository, and information about the particle-transport patterns can contribute to predictions of the fate of a possible leakage. It is also, to our knowledge, the first time particle-transport differences between two coastal areas have been quantified in this manner. In Forsmark, a funnel-shaped bay shielded by a number of islands, the average residence time for clay particles was 5 times longer than in the modeled part of Simpevarp, which is open to the Baltic Sea. In Forsmark, < 10 % of the released particles left the domain compared to 60-80 % in Simpevarp. These site-specific differences will increase over time with the differences in land uplift between the areas.

  • 27.
    Crang, William
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Petrological, geochemical and structural evidence of fluid-rock interaction in the Siljan Ring2024Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The Siljan Ring in Dalarna, Sweden is the site of the largest meteor impact crater in Europe and has long been a topic of discussion regarding methane production. However, the source of this methane and the timing of production in relation to the impact remain unclear. An outcrop of red Ordovician limestone preserved on the edge of a downfaulted zone encircling the crater’s central plateau is crosscut by fractures surrounded by pale-coloured reduction haloes within which precipitates can be observed. These haloes suggest interaction with a reducing agent mobilised within a fluid flow, of which methane would be a prime candidate. A field study was subsequently undertaken to establish the reaction whereby these haloes were formed, as well as the timing of their formation relative to the Siljan impact based upon petrological, geochemical, and structural data obtained in the field. Results from this study show that a methane-bearing hydrothermal fluid mobilised within the fractures has preserved the original mineralogy of the limestone within the reaction haloes whilst the country rock beyond was being oxidised. Pyrite is shown to be preserved within the pale reaction haloes, whilst its oxidation within the country rock is shown to be the source of the limestone’s distinct red colouring. Fracture and bedding orientation at the study site suggest the hydrothermal event to have been simultaneous with the meteor impact, with the fractures forming part of a wider complex network of impact features. Whilst mobilisation associated with the meteor impact is a likely cause of methane release, the exact source of the methane active at the study site is unclear.

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  • 28. Cronin, T. M.
    et al.
    Dwyer, G. S.
    Farmer, J.
    Bauch, H. A.
    Spielhagen, R. F.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Nilsson, Johan
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Briggs, W. M., Jr.
    Stepanova, A.
    Deep Arctic Ocean warming during the last glacial cycle2012Ingår i: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 5, nr 9, s. 631-634Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the Arctic Ocean, the cold and relatively fresh water beneath the sea ice is separated from the underlying warmer and saltier Atlantic Layer by a halocline. Ongoing sea ice loss and warming in the Arctic Ocean(1-7) have demonstrated the instability of the halocline, with implications for further sea ice loss. The stability of the halocline through past climate variations(8-10) is unclear. Here we estimate intermediate water temperatures over the past 50,000 years from the Mg/Ca and Sr/Ca values of ostracods from 31 Arctic sediment cores. From about 50 to 11 kyr ago, the central Arctic Basin from 1,000 to 2,500 m was occupied by a water mass we call Glacial Arctic Intermediate Water. This water mass was 1-2 degrees C warmer than modern Arctic Intermediate Water, with temperatures peaking during or just before millennial-scale Heinrich cold events and the Younger Dryas cold interval. We use numerical modelling to show that the intermediate depth warming could result from the expected decrease in the flux of fresh water to the Arctic Ocean during glacial conditions, which would cause the halocline to deepen and push the warm Atlantic Layer into intermediate depths. Although not modelled, the reduced formation of cold, deep waters due to the exposure of the Arctic continental shelf could also contribute to the intermediate depth warming.

  • 29.
    Dahlke, Helen E.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Lyon, Steve W.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Early melt season snowpack isotopic evolution in the Tarfala valley, northern Sweden2013Ingår i: Annals of Glaciology, ISSN 0260-3055, E-ISSN 1727-5644, Vol. 54, nr 62, s. 149-156Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study investigated the stable water isotopic (delta O-18 and delta D) evolution of two snowpacks located at the same elevation on a north-facing (Nf) and a south-facing (Sf) slope within the Tarfala research catchment, northern Sweden, and the potential impact of pre-freshet snowpack melt on streamflow. Our results indicate that over the study period the Sf snowpack showed a more enriched isotopic composition, especially in the top of the profile, and contributed more snowmelt to streamflow than the Nf slope. The Sf snowpack also showed a significantly higher variability in snowpack delta O-18 levels and snowpack snow water equivalent (SWE) over time. Comparing snowpack and snowmelt isotopic values it was seen that the Sf slope experienced earlier snowmelt from upslope positions due to greater insolation that subsequently enhanced the meltwater flux at the base of downslope snowpacks. In contrast, the Nf slope primarily underwent changes within the snowpack and experienced relatively minimal melt. Detailed field-based isotopic snowmelt studies such as this highlight the potential importance of incorporating spatio-temporal runoff generation concepts into distributed energy-balance models, which could allow for more accurate prediction with regard to the spatio-temporal dynamics associated with the snowmelt ion pulse.

  • 30.
    Darby A., Dennis
    et al.
    Old Dominion University.
    Myers, Wesley B.
    Old Dominion University.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Rigor, Ignatius
    University of Washington.
    Modern dirty sea ice characteristics and sources: The role of anchor ice2011Ingår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, nr C09008Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Extensive dirty ice patches with up to 7 kg m−2 sediment concentrations in layers of up to 10 cm thickness were encountered in 2005 and 2007 in numerous areas across the central Arctic. The Fe grain fingerprint determination of sources for these sampled dirty ice floes indicated both Russian and Canadian sources, with the latter dominating. The presence of benthic shells and sea weeds along with thick layers (2–10 cm) of sediment covering 5–10 m2 indicates an anchor ice entrainment origin as opposed to suspension freezing for some of these floes. The anchor ice origin might explain the dominance of Canadian sources where only narrow flaw leads occur that would not favor suspension freezing as an entrainment process. Expandable clays, commonly used as an indicator of a Kara Sea origin for dirty sea ice, are present in moderately high percentages (>20%) in many circum-Arctic source areas, including the Arctic coasts of North America. Some differences between the Russian and the North American coastal areas are found in clay mineral abundance, primarily the much higher abundance of chlorite in North America and the northern Barents Sea as opposed to the rest of the Russian Arctic. However, sea ice clay mineralogy matched many source areas, making it difficult to use as a provenance tool by itself. The bulk mineralogy (clay and non-clay) does not match specific sources possibly due to reworking of the sediment in dirty floes through summer melting or the failure to characterize all possible source areas.

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  • 31.
    Darracq, Amelie
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Destouni, Georgia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Persson, Klas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Prieto, Carmen
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Jarsjö, Jerker
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Scale and model resolution effects on the distributions of advective solute travel times in catchments2010Ingår i: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 24, nr 12, s. 1697-1710Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Advective solute travel times and their distributions in hydrological catchments are useful descriptors of the dynamics and variation of the physical mass transport among and along the different source-to-recipient pathways of solute transport through the catchments. This article investigates the scale dependence and the effects of model and data resolution on the quantification of advective travel times and their distributions in the Swedish catchment areas of Norrström and Forsmark. In the surface water networks of the investigated (sub)catchments, the mean advective travel time increases with (sub)catchment scale, whereas the relative travel time variability around the mean value (coefficient of variation, CV) is scale-invariant and insensitive to model resolution. In the groundwater and for the whole (sub)catchments, both the mean value and the CV of travel times are scale-invariant, but sensitive to model resolution and accuracy. Such quantifications and results of advective travel times constitute important steps in the development of improved understanding and modelling of nutrient, pollutant and tracer transport through catchments.

  • 32. De Frenne, Pieter
    et al.
    Graae, Bente J.
    Brunet, Joerg
    Shevtsova, Anna
    De Schrijver, An
    Chabrerie, Olivier
    Cousins, Sara A. O.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Decocq, Guillaume
    Diekmann, Martin
    Hermy, Martin
    Heinken, Thilo
    Kolb, Annette
    Nilsson, Christer
    Stanton, Sharon
    Verheyen, Kris
    The response of forest plant regeneration to temperature variation along a latitudinal gradient2012Ingår i: Annals of Botany, ISSN 0305-7364, E-ISSN 1095-8290, Vol. 109, nr 5, s. 1037-1046Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The response of forest herb regeneration from seed to temperature variations across latitudes was experimentally assessed in order to forecast the likely response of understorey community dynamics to climate warming. Seeds of two characteristic forest plants (Anemone nemorosa and Milium effusum) were collected in natural populations along a latitudinal gradient from northern France to northern Sweden and exposed to three temperature regimes in growth chambers (first experiment). To test the importance of local adaptation, reciprocal transplants were also made of adult individuals that originated from the same populations in three common gardens located in southern, central and northern sites along the same gradient, and the resulting seeds were germinated (second experiment). Seedling establishment was quantified by measuring the timing and percentage of seedling emergence, and seedling biomass in both experiments. Spring warming increased emergence rates and seedling growth in the early-flowering forb A. nemorosa. Seedlings of the summer-flowering grass M. effusum originating from northern populations responded more strongly in terms of biomass growth to temperature than southern populations. The above-ground biomass of the seedlings of both species decreased with increasing latitude of origin, irrespective of whether seeds were collected from natural populations or from the common gardens. The emergence percentage decreased with increasing home-away distance in seeds from the transplant experiment, suggesting that the maternal plants were locally adapted. Decreasing seedling emergence and growth were found from the centre to the northern edge of the distribution range for both species. Stronger responses to temperature variation in seedling growth of the grass M. effusum in the north may offer a way to cope with environmental change. The results further suggest that climate warming might differentially affect seedling establishment of understorey plants across their distribution range and thus alter future understorey plant dynamics.

  • 33. de Souza, Claudio M. D.
    et al.
    Carneiro, Cristine E. A.
    Bau, Joao Paulo T.
    da Costa, Antonio C. S.
    Ivashita, Flavio F.
    Paesano, Andrea, Jr.
    di Mauro, Eduardo
    de Santana, Henrique
    Holm, Nils G.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Neubeck, Anna
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Zaia, Cassia T. B. V.
    Zaia, Dimas A. M.
    Interaction of forsterite-91 with distilled water and artificial seawater: a prebiotic chemistry experiment2013Ingår i: International Journal of Astrobiology, ISSN 1473-5504, E-ISSN 1475-3006, Vol. 12, nr 2, s. 135-143Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present work, the interactions between forsterite-91 with distilled water and forsterite-91 with artificial seawater were studied at two pHs (2.0 and 8.0) using different techniques. A large increase in pH was observed for samples incubated at an initially acidic pH (2.0) due to the dissolution of forsterite-91 in distilled water and artificial seawater. Thus, in acidic hydrothermal vents, an increase in the amount of hydrocarbons and magnetite should be expected due to the release of Fe(II). The pH(PZC) decreased and the pH(IEP) increased when forsterite-91 was treated with distilled water and artificial seawater. The ions from the artificial seawater had an effect on zeta potential. Scanning electron microscopy (SEM) images and X-ray diffractograms showed halite in the samples of forsterite-91 mixed with artificial seawater. The presence of halite or adsorption of ions on the surface of forsterite-91 could affect the synthesis of magnetite and hydrocarbons in hydrothermal vents, due to a decrease in the dissolution rates of forsterite-91. The dissolution of forsterite-91 yields low concentrations of Fe(III) and Mn(II) as detected by electron paramagnetic resonance (EPR) spectroscopy. Microanalysis of forsterite-91 showed a higher amount of Mn, with an oxidation that was likely not + II, as Mn in supernatant solutions was only detected by EPR spectroscopy after mixing with artificial seawater at pH 2.0. As Fe(III) and Mn(II) are catalyst constituents of magnetite and manganese oxide, respectively, their presence is important for synthesis in hydrothermal vents. Etch pits were observed only in the forsterite-91 sample mixed with distilled water at pH 8.0. Na, Cl, S, Ca and K were detected in the samples mixed with artificial seawater by SEM-EDS. Si, Mg, Fe and Al were detected in almost all supernatant samples due to forsterite-91 dissolution. Cr was not dissolved in the experiments, thus Cr in the mineral could serve as an effective catalyst for Fischer Tropsch Types (FTT) reactions in hydrothermal vent systems. X-ray diffractograms of the original forsterite-91 also showed peaks arising from zeolites and clinochlore. After the samples were treated with artificial seawater, X-ray diffractograms showed the dissolution of zeolite. Experiments should be performed in the natural environment to verify the potential for zeolites to act as a catalyst in hydrothermal vents.

  • 34. Dehnert, Andreas
    et al.
    Kracht, Oliver
    Preusser, Frank
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Akcar, Naki
    Kemna, Hans Axel
    Kubik, Peter W.
    Schlüchter, Christian
    Cosmogenic isotope burial dating of fluvial sediments from the Lower Rhine Embayment, Germany2011Ingår i: Quaternary Geochronology, ISSN 1871-1014, E-ISSN 1878-0350Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cosmogenic isotope burial dating, using 10Be and 26Al, was applied to PlioePleistocene fluvial successionsfrom the Lower Rhine Embayment, Germany. The approach consists of three principal steps: (1)measurement of cosmogenic nuclides in depth profiles, (2) modelling of hypothetical nuclide concentrationsbased on a first-order conceptualisation of the geological context and the principal succession ofdepositions and subsequent erosional and burial phases, and (3) using parameter estimation to identifyvalues for the a priori unknown model parameters (burial age, initial nuclide concentrations, terraceerosion rates) that result in minimal disagreement between hypothetical and measured nuclideconcentrations.

  • 35.
    Dessirier, Benoît
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Numerical modeling of groundwater and air flow between compacted bentonite and fractured crystalline rock2016Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The geological repository for final storage of spent nuclear fuel, envisioned by the Swedish Nuclear Fuel and Management Company (SKB), relies on several barriers: copper canisters deposited in holes in the floor of underground tunnels in deep bedrock, embedded in a buffer of compacted bentonite. The initially unsaturated buffer would take up water from the surrounding rock mass and swell to seal any potential gap. This initial two-phase (gas and liquid) regime with two components (air and water) may impact the final density, swelling pressure and biogeochemical conditions in the buffer. A main objective of this work is to identify factors and mechanisms that govern deposition hole inflow and bentonite wetting under the prevailing two-phase flow conditions in sparsely fractured bedrock. For this purpose, we use the numerical code TOUGH2 to perform two-phase flow simulations, conditioned by a companion field experiment (the Bentonite Rock Interaction Experiment or BRIE) performed in a 417 m deep tunnel of the Äspö Hard Rock Laboratory in southeastern Sweden. The models predict a significant de-saturation of the rock wall, which was confirmed by field data. To predict the early buffer wetting rates and patterns, the position of local flowing fractures and estimates of local rock matrix permeability appear more important than the total open hole groundwater inflow. A global sensitivity analysis showed that the buffer wetting time and the persistence of unsaturated conditions over extended periods of time in the rock depend primarily on the local fracture positions, rock matrix permeability, ventilation conditions in the tunnel and pressure far in the rock. Dismantling photographs from BRIE were used to reconstruct a fine-scale snapshot of saturation at the bentonite/rock interface, showing tremendous spatial variability. The high level of heterogeneity in the rock generates complex two-phase flow phenomena (air trapping, dissolution), which need to be accounted for in buffer design and rock suitability criteria. In particular, results suggest that uncertainties regarding two-phase flow behavior are relatively high close to residual air saturation, which may also have important implications for other applications involving two-phase flows, such as geological storage of carbon dioxide.

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  • 36.
    Dessirier, Benoît
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Frampton, Andrew
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Jarsjö, Jerker
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    A global sensitivity analysis of two-phase flow between fractured crystalline rock and bentonite with application to spent nuclear fuel disposal2015Ingår i: Journal of Contaminant Hydrology, ISSN 0169-7722, E-ISSN 1873-6009, Vol. 182, s. 25-35Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Geological disposal of spent nuclear fuel in deep crystalline rock is investigated as a possible long term solution in Sweden and Finland. The fuel rods would be cased in copper canisters and deposited in vertical holes in the floor of deep underground tunnels, embedded within an engineered bentonite buffer. Recent experiments at the Äspö Hard Rock Laboratory (Sweden) showed that the high suction of unsaturated bentonite causes a de-saturation of the adjacent rock at the time of installation, which was also independently predicted in model experiments. Remaining air can affect the flow patterns and alter bio-geochemical conditions, influencing for instance the transport of radionuclides in the case of canister failure. However, thus far, observations and model realizations are limited in number and do not capture the conceivable range and combination of parameter values and boundary conditions that are relevant for the thousands of deposition holes envisioned in an operational final repository.

    In order to decrease this knowledge gap, we introduce here a formalized, systematic and fully integrated approach to study the combined impact of multiple factors on air saturation and dissolution predictions, investigating the impact of variability in parameter values, geometry and boundary conditions on bentonite buffer saturation times and on occurrences of rock de-saturation. Results showed that four parameters consistently appear in the top six influential factors for all considered output (target) variables: the position of the fracture intersecting the deposition hole, the background rock permeability, the suction representing the relative humidity in the open tunnel and the far field pressure value. The combined influence of these compared to the other parameters increases as one targets a larger fraction of the buffer reaching near-saturation. Strong interaction effects were found, which means that some parameter combinations yielded results (e.g., time to saturation) far outside the range of results obtained by the rest of the scenarios. This study also addresses potential air trapping by dissolution of part of the initial air content of the bentonite, showing that neglecting gas flow effects and trapping could lead to significant underestimation of the remaining air content and the duration of the initial aerobic phase of the repository.

  • 37.
    Dessirier, Benoît
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Frampton, Andrew
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Jarsjö, Jerker
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Impact of near-wall rock characteristics on bentonite buffer wetting: In situ study of nuclear fuel deposition holes in deep bedrockManuskript (preprint) (Övrigt vetenskapligt)
  • 38.
    Destouni, Georgia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Modeling and uncertainty assessment of nutrient runoff from larger catchments2011Ingår i: International Seminar on Pollution runoff from urban and non-urban catchments, Technical University of Denmark (DTU), Copenhagen, March 30, 2011., 2011Konferensbidrag (Övrigt vetenskapligt)
  • 39. Drüke, Markus
    et al.
    Lucht, Wolfgang
    von Bloh, Werner
    Petri, Stefan
    Sakschewski, Boris
    Tobian, Arne
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholm Resilience Centre. Potsdam Institute for Climate Impact Research, Germany.
    Loriani, Sina
    Schaphoff, Sibyll
    Feulner, Georg
    Thonicke, Kirsten
    The long-term impact of transgressing planetary boundaries on biophysical atmosphere–land interactions2024Ingår i: Earth System Dynamics, ISSN 2190-4979, E-ISSN 2190-4987, Vol. 15, nr 2, s. 467-483Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Human activities have had a significant impact on Earth's systems and processes, leading to a transition of Earth's state from the relatively stable Holocene epoch to the Anthropocene. The planetary boundary framework characterizes major risks of destabilization, particularly in the core dimensions of climate and biosphere change. Land system change, including deforestation and urbanization, alters ecosystems and impacts the water and energy cycle between the land surface and atmosphere, while climate change can disrupt the balance of ecosystems and impact vegetation composition and soil carbon pools. These drivers also interact with each other, further exacerbating their impacts. Earth system models have been used recently to illustrate the risks and interacting effects of transgressing selected planetary boundaries, but a detailed analysis is still missing. Here, we study the impacts of long-term transgressions of the climate and land system change boundaries on the Earth system using an Earth system model with an incorporated detailed dynamic vegetation model. In our centennial-scale simulation analysis, we find that transgressing the land system change boundary results in increases in global temperatures and aridity. Furthermore, this transgression is associated with a substantial loss of vegetation carbon, exceeding 200 Pg C, in contrast to conditions considered safe. Concurrently, the influence of climate change becomes evident as temperatures surge by 2.7–3.1 °C depending on the region. Notably, carbon dynamics are most profoundly affected within the large carbon reservoirs of the boreal permafrost areas, where carbon emissions peak at 150 Pg C. While a restoration scenario to reduce human pressure to meet the planetary boundaries of climate change and land system change proves beneficial for carbon pools and global mean temperature, a transgression of these boundaries could lead to profoundly negative effects on the Earth system and the terrestrial biosphere. Our results suggest that respecting both boundaries is essential for safeguarding Holocene-like planetary conditions that characterize a resilient Earth system and are in accordance with the goals of the Paris Climate Agreement.

  • 40.
    Eklund, Carl
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Ståndortsfaktorer och vegetation: En problematiserande litteraturstudie2017Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Ståndort är ett område där ett bestånd av en viss växt finns, ofta avses träd inom skogsproduktion. Förutsättningarna för detta, ståndortsfaktorer, återfinns i markens egenskaper (edafiska faktorer) och klimatet. Dessa påverkar därigenom växtens produktion, något som särskilt är av intresse inom skogsbruket och de skogliga vetenskaperna. Till detta kommer att växter samspelar med andra växter och organismer såsom svampar, bakterier och djur, och även den antropogena påverkan med faktorer såsom husdjursbete, atmosfäriskt nedfall och skogsproduktion har en stark inverkan på vegetationen.

    Utifrån att studera några av de mer kända teorierna om växtsamhällen och -strategier samt olika vinklar av ståndortsfaktorer var hypotesen att det går att få fram en problematiserande bild och hitta störfaktorer (confoundingvariabler), som kan ge felaktiga tolkningar av resultat.

    Ett antal kända verk inom vegetationsklassificering gicks igenom, kompletterat med stödjande litteratur. En artikelsökning genomfördes också, med kombinationer av specifika sökord med anknytning till ståndort. För att begränsa urvalet och ge en mer regional prägel på arbetet ställdes sökfiltren i artikelsökningen in på att enbart visa resultat från Skandinavien och Finland. Artiklarna delades in efter teman och behandlades efter dessa.

    Även om få huvudsakliga faktorer styr vegetationen finns flera variabler som lokalt har en stor betydelse, såsom snö, genetiska egenskaper och symbios med andra organismer. Dessa variabler kan vara svåra att mäta och det finns mycket på detaljnivå som är dåligt undersökt. Markanvändningar påverkar de edafiska faktorerna långt efter att brukandet ändrats eller upphört, men detta har olika stor lokal påverkan. Kvävets och kolets halter och cykler är återkommande osäkerhetsfaktorer i artiklarna, där det atmosfäriska kvävenedfallet spelar en viktig men ojämn roll, och jämförbara mätningar försvåras av skillnader i väder och klimat. Till detta kommer påverkan av markorganismer, vilka har en mycket viktig del i växternas näringsupptag, men är svår att mäta.

    Även om alla aspekter av en växtplats inte kan tas med bör fler felkällor tas i beaktande och modeller ha möjlighet att kalibreras mot olika teorier om växtsamhällen och -strategier. Flera faktorer som traditionellt inte räknas som ståndortsfaktorer, såsom snödjup, symbios med markorganismer och markanvändning, kan vara betydelsefulla att ta med i exempelvis modellering.

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  • 41.
    Fagerlind, David
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholm Resilience Centre.
    Deconstructing the Great Acceleration2018Självständigt arbete på avancerad nivå (masterexamen), 40 poäng / 60 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The Anthropocene is characterized by a strong human influence on the Earth System that is threatening the future prosperity of human societies. A mid-20th century onset of the Anthropocene is being proposed supported by the global phenomenon the Great Acceleration, but much concern has been raised that defining the Anthropocene based on global averages fails to recognize the massive inequalities in humanity’s contribution to current pressures on the Earth System. This study uses increase in growth rate as in indication of system change and conducts a statistical analysis to determine the largest change in the socio-economic domain of the Earth System on both a global and national level. The aim is to examine the empirical support for an unequal Anthropocene from a systems perspective. 814 of these events are identified across all the Great Acceleration indicators. The magnitude of the changes is typically large, with the growth rate increasing by more than 100% in 86% of the identified events. The findings suggest that while there is good evidence for a substantial change in the socio-economic domain of the Earth System the mid-20th century it is not the result of a globally synchronous event, but rather the culmination of a gradual process that display large temporal disparities with these system changes moving like waves across the Earth. The observed disparities show striking similarities to current developmental status suggesting that when deconstructed, the Great Acceleration can be used both to support global patterns and to illustrate inequalities between countries and people, making it a powerful tool to communicate the many facets of the Anthropocene.

  • 42.
    Farineau, Anne
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Diamonds in the Rough: Remote predictive mapping using multispectral satellite imagery for kimberlite exploration on northeast Banks Island, NT2015Självständigt arbete på avancerad nivå (masterexamen), 40 poäng / 60 hpStudentuppsats (Examensarbete)
    Abstract [en]

    This study demonstrates the use and limitations of Remote Predictive Mapping (RPM) as an aid to kimberlite exploration on northeast Banks Island, Northwest Territories, Canada. It focuses on the effectiveness of ASTER and Landsat 8 optical multi-spectral satellite imagery for discerning the spectral properties of different bedrock and surficial materials that outcrop or blanket the regional terrain. Statistical algorithms and digital image enhancement techniques were used to highlight patterns and anomalies within each scene in order to determine the range of materials and specific deposits (e.g., till, glaciofluvial) that could be the source of recovered kimberlite indicator minerals (KIMs) from stream sediment samples. Field inspection and sampling were in part guided by these patterns and anomalies. During the course of fieldwork, numerous outliers of the Pliocene Beaufort Formation fluvial sand and gravel deposits were discovered on upland surfaces in northeastern Banks Island. These outcrops sit well beyond (east) of any previous mapped Beaufort Fm. extents, and it is hypothesized that as they exist within catchments where Industry has recovered KIMs, they could be a source of bedrock-inherited KIMs. Field observations and spectral sampling using a portable spectroradiometer were integrated with ASTER and Landsat data to predict the spatial extents of Beaufort Fm. deposits. Using test and field-validated Beaufort Fm. sites, Spectral Angle Mapper (SAM) whole pixel spectral target detection was compared with Matched Filtering (MF), Mixture-Tuned Matched Filtering (MTMF) sub-pixel spectral target detection methods and Parallelepiped classification for ASTER scenes 1228 and 0686.  Each method was also performed on ASTER scene 0541 to assess the potential for Quaternary sediment discrimination, using pixel ROIs from a field-validated glaciolacustrine deposit. The sub-pixel sensitivity of the MF/MTMF methods was determined to have the best potential for the discrimination of surficial materials on NE Banks Island.  MF/MTMF also had the best results for discriminating Beaufort Fm. in scene 1228, but Parallelepiped classification was the most effective prediction method for scene 0686. These inconsistent results indicate spectral variability between Beaufort Fm. sites, a consideration for any further study in the region.  

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  • 43.
    Fors, Yvonne
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Jalilehvand, Farideh
    Risberg, Emiliana Damian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Bjordal, Charlotte
    Phillips, Ebba
    Sandström, Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Sulfur and iron analyses of marine archaeological wood in shipwrecks from the Baltic Sea and Scandinavian waters2012Ingår i: Journal of Archaeological Science, ISSN 0305-4403, E-ISSN 1095-9238, Vol. 39, nr 7, s. 2521-2532Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Analyses of marine archaeological wood from shipwrecks in the Baltic Sea area, Kronan, Riksnyckeln, Tattran, the Puck Bay Boat and the Ghost wreck, and at the Scandinavian West coast, the Gota wreck, Stora Sofia and the Viking shipwrecks of Skuldelev, show accumulation of sulfur compounds. The penetration profiles of sulfur and iron into the wood and the speciation of characteristic sulfur groups were evaluated by combining X-ray spectroscopic analyses, in particular S K-edge XANES (X-ray absorption near edge structure) and X-ray fluorescence, with ESCA and elemental analyses. The combined analyses support the hypothesis that hydrogen sulfide produced by sulfate-reducing bacteria reacts and accumulates at low iron concentration mainly as organically bound sulfur, which as in previous studies was found by X-ray spectro-microscopy to accumulate in lignin-rich parts of the wood cell walls. The presence of iron(II) ions from corroding iron promotes formation of pyrite and other iron(II) sulfides, which easily oxidise in aerobic conditions with high humidity. No significant differences in sulfur and iron accumulation were found in wood from shipwrecks in the east coast brackish water and the west coast seawater. Sediments from three wreck sites, the Gota wreck, Stora Sofia and Kronan, were analyzed to a depth of a few decimeters and showed especially at the Stora Sofia high sulfur concentrations, exceeding 3 mass%. S K-edge XANES analyses of the sediments showed mainly reduced forms of sulfur, in particular pyrite and iron(II) sulfides together with elemental sulfur.

  • 44. Gallagher, K
    et al.
    Bodin, T
    Sambridge, M
    Weiss, D
    Kylander, Malin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Large, David
    Inference of abrupt changes in noisy geochemical records using transdimensional changepoint models2011Ingår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 311, nr 1-2, s. 182-194Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a method to quantify abrupt changes (or changepoints) in data series, represented as a function of depth or time. These changes are often the result of climatic or environmental variations and can be manifested in multiple datasets as different responses, but all datasets can have the same changepoint locations/timings. The method we present uses transdimensional Markov chain Monte Carlo to infer probability distributions on the number and locations (in depth or time) of changepoints, the mean values between changepoints and, if required, the noise variance associated with each dataset being considered. This latter point is important as we generally will have limited information on the noise, such as estimates only of measurement uncertainty, and in most cases it is not practical to make repeat sampling/measurement to assess other contributions to the variation in the data. We describe the main features of the approach (and describe the mathematical formulation in supplementary material), and demonstrate its validity using synthetic datasets, with known changepoint structure (number and locations of changepoints) and distribution of noise variance for each dataset. We show that when using multiple data, we expect to achieve better resolution of the changepoint structure than when we use each dataset individually. This is conditional on the validity of the assumption of common changepoints between different datasets. We then apply the method to two sets of real geochemical data, both from peat cores, taken from NE Australia and eastern Tibet. Under the assumption that changes occur at the same time for all datasets, we recover solutions consistent with those previously inferred qualitatively from independent data and interpretations. However, our approach provides a quantitative estimate of the relative probability of the inferred changepoints, allowing an objective assessment of the significance of each change.

  • 45.
    Gartz, Mira
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Plantdiversitet på svenska slåtterängar: En GIS-analys med kulturella perspektiv2015Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    En hög plantdiversitet är beroende av ett landskap som erbjuder tillräckligt stora habitat, funktionell konnektivitet och heterogenitet. Habitatförlust och förändrad markanvändning utgör det största hotet mot biodiversitet idag. Det svenska landskapet har inte bara förändrats dramatiskt de senaste 60 åren, det innehåller också några av Europas sista fragment av de mycket värdefulla slåtterängarna. Många av de svenska slåtterängarna är upptagna i Natura 2000-områden. Trots detta finns inga systematiska bevarandestrategier för dessa slåtterängar och arbetet hänger mestadels på volontärer. Den här studien ämnar bidra till en ökad förståelse för hur omgivande landskap påverkar plantdiversiteten på svenska slåtterängar. GIS-analyser av lokala landskap som omger 21 svenska slåtterängar har utförts. Nedslag vid två tidpunkter har gjorts; år 1950 och 2015. Genom digitalisering av kartor från 1950-talet har arean av marktyper kunnat beräknas och sedan jämföras med dagens markanvändning och artdata i samma områden. Resultaten visar att den totala skogsarealen har ökat med 12% sedan 1950-talet och det finns negativa samband mellan både den historiska och den nutida skogsarealen och artrikedomen på ängarna. Arean av åkermark har minskat med 19% i de undersökta områdena, men inga samband med artrikedomen kunde finnas. Däremot visade det sig att den före detta åkermark som fanns på 1950-talet påverkar dagens artrikedomen negativ, både som ensam oberoende variabel och tillsammans med öppen mark. Öppen mark har minskat med mellan 17% och 24%, men inga samband mellan denna landskapskategori och plantdiversiteten fanns. De sammanställda resultaten indikerar att den historiska markanvändningen på lokal skala har större påverkan på dagens plantdiversitet än den nutida markanvändningen. Detta bör tas i beaktande vid utformande av bevarandestrategier och vid fysisk planering.

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  • 46. Gennari, Giordana
    et al.
    Rosenberg, Thomas
    Spezzaferi, Silvia
    Berger, Jean-Pierre
    Fleitmann, Dominik
    Preusser, Frank
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Al-shanti, Mahmoud
    Matter, Albert
    Faunal evidence of a Holocene pluvial phase in Southern Arabia with remarks on the morphological variability of Helenina anderseni2011Ingår i: Journal of Foraminiferal Research, ISSN 0096-1191, E-ISSN 1943-264X, Vol. 41, s. 248-259Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Although foraminifera have been found living in inlandsaline lakes isolated from the sea, this phenomenon has rarelybeen recognized in the fossil record. This study documents theoccurrence of benthic foraminifera in Holocene lake sedimentslocated nearly 500 km inland from the Red Sea, in theAl-Mundafan region of southern Saudi Arabia. The lakeformed during a regional pluvial period, 10,500–6000 yr BP.The presence of foraminifera and brackish charophytes in thestudied section represent an interval when the lake wasslightly brackish due to high evaporation. The studiedsediments yielded a bispecific benthic foraminiferal faunacomprised of Helenina anderseni and Trichohyalus aguayoi,as well as the brackish charophyte genus Lamprothamnium.The benthic foraminifera are species characteristic ofmangrove swamps, salt marshes, and lagoons, which areenvironments currently widespread along the Red Sea coasts.Because the Al Mundafan area was never connected to the seaduring the Quaternary, wading birds must have been thevector that transported the foraminifera to the paleolake

  • 47. Giesler, Reiner
    et al.
    Mörth, Carl-Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Karlsson, Jan
    Lundin, Erik J.
    Lyon, Steve W.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Humborg, Christoph
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Spatiotemporal variations of pCO(2) and delta C-13-DIC in subarctic streams in northern Sweden2013Ingår i: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 27, nr 1, s. 176-186Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Current predictions of climate-related changes in high-latitude environments suggest major effects on the C export in streams and rivers. To what extent this will also affect the stream water CO2 concentrations is poorly understood. In this study we examined the spatiotemporal variation in partial pressure of CO2 (pCO(2)) and in stable isotopic composition of dissolved inorganic carbon (delta C-13-DIC) in subarctic streams in northern Sweden. The selected watersheds are characterized by large variations in high-latitude boreal forest and tundra and differences in bedrock. We found that all streams generally were supersaturated in pCO(2) with an average concentration of 850 mu atm. The variability in pCO(2) across streams was poorly related to vegetation cover, and carbonaceous bedrock influence was manifested in high DIC concentrations but not reflected in either stream pCO(2) or delta C-13-DIC. Stream water pCO(2) values were highest during winter base flow when we also observed the lowest delta C-13-DIC values, and this pattern is interpreted as a high contribution from CO2 from soil respiration. Summer base flow delta C-13-DIC values probably are more affected by in situ stream processes such as aquatic production/respiration and degassing. A challenge for further studies will be to disentangle the origin of stream water CO2 and quantify their relative importance.

  • 48. Gilg, H. Albert
    et al.
    Hall, Adrian M.
    University of St Andrews, Scotland, UK.
    Ebert, Karin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Cool kaolins in Finland2013Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 392, s. 454-462Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We use D/H and 18O/16O ratios to explore the age of kaolins on the Fennoscandian Shield. Sub-Cretaceous kaolins in southern Scandinavia have isotopic compositions indicative of weathering under warm mean annual temperatures (MATs) of > 15 °C. Deep kaolins on the shield surface in Finland previously also have been regarded as products of humid tropical weathering of Mesoproterozoic to Eocene age. New oxygen and hydrogen isotope ratios indicate, however, weathering by cool groundwater under MATs of 13–15 °C. Isotope ratios are also not consistent with deep (> 1 km) burial by cover rocks, indicating that a very old age for the weathering is unlikely. Palaeotemperatures are below Cretaceous MATs, yet substantially above Plio-Pleistocene MATs. Comparisons with palaeotemperatures in N Europe and around the Arctic Ocean indicate that the Finnish kaolins developed on the shield surface in the Palaeogene or, alternatively, Miocene. Deep weathering was selectively developed in highly fractured shield rocks and took place in response to latest Cretaceous and Palaeogene uplift and after stripping of Palaeozoic cover rocks. The cool kaolins in Finland indicate that previous routine attributions of kaolinitic weathering products in the geological record to humid tropical environments should be closely scrutinised.

  • 49. Glimskär, Anders
    et al.
    Skånes, Helle
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Land Type Categories as a Complement to Land Use and Land Cover Attributes in Landscape Mapping and Monitoring2015Ingår i: Land Use and Land Cover Semantics: Principles, Best Practices, and Prospects / [ed] Ola Ahlqvist, Dalia Varanka, Steffen Fritz, and Krzysztof Janowicz, Boca Raton: CRC Press, 2015, s. 171-190Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    The purpose of land cover and land use descriptions varies, and this influences how these concepts are perceived in different contexts. The increasing need for spatial data for multipurpose monitoring and modeling also increases the demands for compatibility, repeatability, detail, and well-documented criteria. We suggest that threshold values along a continuous scale can be used to create nominal classes for a common conceptual framework. However, the exact values of these thresholds need to be based on well-defined functional and systematic criteria. Ecological and environmental gradients are often mosaic and complex, and several types of land use may coexist at the same site. In reality, land use can be seen as a “shifting cloud” of activities varying in both time and space. We advocate the use of strict definitions of land cover as physical structures and land use as human activities, which raises the need for a complementary concept, which we call “land type,” with stable threshold values based on mutually exclusive functional criteria. Such functional criteria often put clear limits to what spatial resolution is appropriate, since the suitability for a certain purpose (e.g., agriculture or forestry) is determined by the user of the land, rather than by the independent observer. Our example of land type categories comprises a two-level hierarchical classification with seven main types and altogether 28 subtypes. As an example, we discuss the overlapping Swedish definitions of forest and arable land. The criteria that define our main land types are less dependent on how the area is managed at a specific moment in time, and they are therefore less sensitive to short-term variation. The land types define the limits for what land cover and land use can be expected at a certain site, given, for example, ground conditions, water, or artificial structures. Since such land types need to incorporate functional and qualitative understanding and interpretation, human visual interpretation is needed, whereas automated remote sensing methods are suitable mainly for the structural aspects of land cover.

  • 50. Goldner, A.
    et al.
    Huber, M.
    Caballero, Rodrigo
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Does Antarctic glaciation cool the world?2013Ingår i: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 9, nr 1, s. 173-189Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study, we compare the simulated climatic impact of adding an Antarctic ice sheet (AIS) to the greenhouse world of the Eocene and removing the AIS from the modern world. The modern global mean surface temperature anomaly (Delta T) induced by Antarctic Glaciation depends on the background CO2 levels and ranges from -1.22 to -0.18 K. The Eocene Delta T is nearly constant at similar to-0.25 K. We calculate an climate sensitivity parameter S[Antarctica] which we define as Delta T divided by the change in effective radiative forcing (Delta Q(Antarctica)) which includes some fast feedbacks imposed by prescribing the glacial properties of Antarctica. The main difference between the modern and Eocene responses is that a negative cloud feedback warms much of the Earth's surface as a large AIS is introduced in the Eocene, whereas this cloud feedback is weakly positive and acts in combination with positive sea-ice feedbacks to enhance cooling introduced by adding an ice sheet in the modern. Because of the importance of cloud feedbacks in determining the final temperature sensitivity of the AIS, our results are likely to be model dependent. Nevertheless, these model results suggest that the effective radiative forcing and feedbacks induced by the AIS did not significantly decrease global mean surface temperature across the Eocene-Oligocene transition (EOT -34.1 to 33.6 Ma) and that other factors like declining atmospheric CO2 are more important for cooling across the EOT. The results illustrate that the efficacy of AIS forcing in the Eocene is not necessarily close to one and is likely to be model and state dependent. This implies that using EOT paleoclimate proxy data by itself to estimate climate sensitivity for future climate prediction requires climate models and consequently these estimates will have large uncertainty, largely due to uncertainties in modelling low clouds.

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