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  • 901. Wang, Lixin
    et al.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Ravi, Sujith
    Riveros-Iregui, Diego
    Caylor, Kelly
    Dynamic interactions of ecohydrological and biogeochemical processes in water-limited systems2015In: Ecosphere, ISSN 2150-8925, E-ISSN 2150-8925, Vol. 6, no 8, article id 133Article in journal (Refereed)
    Abstract [en]

    Water is the essential reactant, catalyst, or medium for many biogeochemical reactions, thus playing an important role in the activation and deactivation of biogeochemical processes. The coupling between hydrological and biogeochemical processes is particularly evident in water-limited arid and semi-arid environments, but also in areas with strong seasonal precipitation patterns (e.g., Mediterranean) or in mesic systems during droughts. Moreover, this coupling is apparent at all levels in the ecosystems-from soil microbial cells to whole plants to landscapes. Identifying and quantifying the biogeochemical hot spots'' and hot moments'', the underlying hydrological drivers, and how disturbance-induced vegetation transitions affect the hydrological-biogeochemical interactions are challenging because of the inherent complexity of these interactions, thus requiring interdisciplinary approaches. At the same time, a holistic approach is essential to fully understand function and processes in water-limited ecosystems and to predict their responses to environmental change. This article examines some of the mechanisms responsible for microbial and vegetation responses to moisture inputs in water-limited ecosystems through a synthesis of existing literature. We begin with the initial observation of Birch effect in 1950s and examine our current understanding of the interactions among vegetation dynamics, hydrology, and biochemistry over the past 60 years. We also summarize the modeling advances in addressing these interactions. This paper focuses on three opportunities to advance coupled hydrological and biogeochemical research: (1) improved quantitative understanding of mechanisms linking hydrological and biogeochemical variations in drylands, (2) experimental and theoretical approaches that describe linkages between hydrology and biogeochemistry (particularly across scales), and (3) the use of these tools and insights to address critical dryland issues of societal relevance.

  • 902.
    Wang, Tongmei
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hannachi, Abdel
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hirooka, Toshihiko
    Hegglin, Michaela I.
    Tropical water vapour in the lower stratosphere in ERA5 and its relationship to tropical/extra-tropical dynamic processesManuscript (preprint) (Other academic)
  • 903.
    Wang, Tongmei
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology . Stockholm University, Faculty of Science, Department of Physical Geography.
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hannachi, Abdel
    Stockholm University, Faculty of Science, Department of Meteorology .
    Lin, Yihua
    Hirooka, Toshihiko
    On the dynamics of the spring seasonal transition in the two hemispheric high-latitude stratosphere2019In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 71, no 1, article id 1634949Article in journal (Refereed)
    Abstract [en]

    The seasonal transition is one of the main features of the atmospheric general circulation and is particularly manifest in the high-latitude stratosphere. To explore the dynamics of stratospheric seasonal transition in both hemispheres, the observational features of the annual cycle and seasonal transition in high-latitude stratosphere are investigated using the 38-year ERA-interim reanalysis. Climatological analysis shows that tropospheric planetary waves propagate to the stratosphere and affect significantly the winter-to-summer stratospheric seasonal transition over both hemispheres, but with a much stronger wave activity in austral spring than its boreal counterpart. The austral spring seasonal transition occurs first at the stratopause then propagates down to the lower stratosphere due to enhanced planetary wave breaking, weakening the westerlies. In boreal spring, the seasonal transition occurs simultaneously across the depth of the stratosphere, mainly due to the solar radiation and weaker planetary wave activity. Interannual variability analysis shows that the timing of stratospheric seasonal transition is closely linked to the intensity of upward propagation of planetary wave activity, i.e. the stronger the upward propagation of planetary wave activity in high-latitudes in spring the earlier the stratospheric seasonal transition. Transition indexes are defined and the probability distributions of the indexes show that there are two types of transition in both hemispheres: synchronous/asynchronous in the Northern Hemisphere (NH), and steep/moderate transitions in the Southern Hemisphere (SH). A composite analysis shows that before the transition, stronger wave activity leads to asynchronous rather than synchronous transition in the NH, which propagates downward from the stratopause. In the SH, a moderate rather than steep transition is obtained, which occurs earlier and takes longer to propagate from the upper to lower stratosphere.

  • 904.
    Wang, Tongmei
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology . Stockholm University, Faculty of Science, Department of Physical Geography.
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kuilman, Maartje
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hannachi, Abdel
    Stockholm University, Faculty of Science, Department of Meteorology .
    Response of stratospheric water vapour to CO2 doubling in WACCM2020In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 54, p. 4877-4889Article in journal (Refereed)
    Abstract [en]

    Stratospheric water vapour (SWV), as a greenhouse gas, modulates the radiative energy budget of the climate system. It is sensitive to, and plays a significant role in the climate change. In this study, we investigate the SWV response to CO2 increase with the Whole Atmosphere Community Climate Model (WACCM). In addition, we study its possible feedback on stratospheric temperature and relevant mechanisms. In our model experiments, the CO2 concentration and sea surface temperature (SSTs) are changed at the same time, as well as separately, to enable separating the radiative-photochemical and dynamical response to CO2 doubling scenarios. The model results show that the response of SWV to CO2 doubling is dominated by the changes in the SSTs, with an increase of the SWV concentration by similar to 6 to 10% in most of the stratosphere and more than 10% in the lower stratosphere, except for winter pole in the lower stratosphere, where the CO2 doubling decreases water vapour. The increase of SWV is mostly due to a dynamical response to the warm SSTs. Doubled CO2 induces warm SSTs globally and further leads to moist troposphere and a warmer tropical and subtropical tropopause, resulting in more water vapour entering stratosphere from below. As a greenhouse gas, large increase of SWV in the lower stratosphere, in turn, affects the stratospheric temperature, resulting in a warming of the tropical and subtropical lower stratosphere, offsetting the cooling caused by CO2 doubling.

  • 905.
    Wang, Tongmei
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kuilman, Maartje
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hannachi, Abdel
    Stockholm University, Faculty of Science, Department of Meteorology .
    Response of stratospheric water vapour to CO2 doubling in WACCMManuscript (preprint) (Other academic)
  • 906.
    Wang, Tongmei
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. Stockholm University, Faculty of Science, Department of Meteorology .
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Lossow, Stefan
    Chafik, Léon
    Risi, Camille
    Murtagh, Donal
    Hannachi, Abdel
    Stockholm University, Faculty of Science, Department of Meteorology .
    Stable Water Isotopologues in the Stratosphere Retrieved from Odin/SMR Measurements2018In: Remote Sensing, ISSN 2072-4292, E-ISSN 2072-4292, Vol. 10, no 2, article id 166Article in journal (Refereed)
    Abstract [en]

    Stable Water Isotopologues (SWIs) are important diagnostic tracers for understanding processes in the atmosphere and the global hydrological cycle. Using eight years (2002-2009) of retrievals from Odin/SMR (Sub-Millimetre Radiometer), the global climatological features of three SWIs, (H2O)-O-16, HDO and (H2O)-O-18, the isotopic composition D and O-18 in the stratosphere are analysed for the first time. Spatially, SWIs are found to increase with altitude due to stratospheric methane oxidation. In the tropics, highly depleted SWIs in the lower stratosphere indicate the effect of dehydration when the air comes through the cold tropopause, while, at higher latitudes, more enriched SWIs in the upper stratosphere during summer are produced and transported to the other hemisphere via the Brewer-Dobson circulation. Furthermore, we found that more (H2O)-O-16 is produced over summer Northern Hemisphere and more HDO is produced over summer Southern Hemisphere. Temporally, a tape recorder in (H2O)-O-16 is observed in the lower tropical stratosphere, in addition to a pronounced downward propagating seasonal signal in SWIs from the upper to the lower stratosphere over the polar regions. These observed features in SWIs are further compared to SWI-enabled model outputs. This helped to identify possible causes of model deficiencies in reproducing main stratospheric features. For instance, choosing a better advection scheme and including methane oxidation process in a specific model immediately capture the main features of stratospheric water vapor. The representation of other features, such as the observed inter-hemispheric difference of isotopic component, is also discussed.

  • 907. Wartenburger, Richard
    et al.
    Seneviratne, Sonia
    Hirschi, Martin
    Chang, Jinfeng
    Ciais, Philippe
    Deryng, Delphine
    Elliott, Joshua
    Folberth, Christian
    Gosling, Simon N.
    Gudmundsson, Lukas
    Henrot, Alexandra-Jane
    Hickler, Thomas
    Ito, Akihiko
    Khabarov, Nikolay
    Kim, Hyungjun
    Leng, Guoyong
    Liu, Junguo
    Liu, Xingcai
    Masaki, Yoshimitsu
    Morfopoulos, Catherine
    Müller, Christoph
    Müller Schmied, Hannes
    Nishina, Kazuya
    Orth, Rene
    Stockholm University, Faculty of Science, Department of Physical Geography. Max Planck Institute for Biogeochemistry, Germany.
    Pokhrel, Yadu
    Pugh, Thomas A. M.
    Satoh, Yusuke
    Schaphoff, Sibyll
    Schmid, Erwin
    Sheffield, Justin
    Stacke, Tobias
    Steinkamp, Joerg
    Tang, Qiuhong
    Thiery, Wim
    Wada, Yoshihide
    Wang, Xuhui
    Weedon, Graham P.
    Yang, Hong
    Zhou, Tian
    Evapotranspiration simulations in ISIMIP2a-Evaluation of spatio-temporal characteristics with a comprehensive ensemble of independent datasets2018In: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 13, no 7, article id 075001Article in journal (Refereed)
    Abstract [en]

    Actual land evapotranspiration (ET) is a key component of the global hydrological cycle and an essential variable determining the evolution of hydrological extreme events under different climate change scenarios. However, recently available ET products show persistent uncertainties that are impeding a precise attribution of human-induced climate change. Here, we aim at comparing a range of independent global monthly land ET estimates with historical model simulations from the global water, agriculture, and biomes sectors participating in the second phase of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP2a). Among the independent estimates, we use the EartH2Observe Tier-1 dataset (E2O), two commonly used reanalyses, a pre-compiled ensemble product (LandFlux-EVAL), and an updated collection of recently published datasets that algorithmically derive ET from observations or observations-based estimates (diagnostic datasets). A cluster analysis is applied in order to identify spatio-temporal differences among all datasets and to thus identify factors that dominate overall uncertainties. The clustering is controlled by several factors including the model choice, the meteorological forcing used to drive the assessed models, the data category (models participating in the different sectors of ISIMIP2a, E2O models, diagnostic estimates, reanalysis-based estimates or composite products), the ET scheme, and the number of soil layers in the models. By using these factors to explain spatial and spatio-temporal variabilities in ET, we find that the model choice mostly dominates (24%-40% of variance explained), except for spatio-temporal patterns of total ET, where the forcing explains the largest fraction of the variance (29%). The most dominant clusters of datasets are further compared with individual diagnostic and reanalysis-based estimates to assess their representation of selected heat waves and droughts in the Great Plains, Central Europe and western Russia. Although most of the ET estimates capture these extreme events, the generally large spread among the entire ensemble indicates substantial uncertainties.

  • 908.
    Wastegård, Stefan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Gudmundsdóttir, Esther R.
    Lind, Ewa M.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Timms, Rhys G. O.
    Björck, Svante
    Hannon, Gina E.
    Olsen, Jesper
    Rundgren, Mats
    Towards a Holocene tephrochronology for the Faroe Islands, North Atlantic2018In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 195, p. 195-214Article in journal (Refereed)
    Abstract [en]

    The Faroe Islands hold a key position in the North Atlantic region for tephra studies due to their relative proximity to Iceland. Several tephras have been described over the last 50 years in peat and lake sediment sequences, including the type sites for the Saksunarvatn and Mjauvotn tephras. Here we present a comprehensive overview of Holocene tephras found on the Faroe Island. In total 23 tephra layers are described including visible macrotephras such as the Saksunarvatn and Hekla 4 tephras and several cryptotephras. The importance of tephras originally described from the Faroe Islands is highlighted and previously unpublished results are included. In addition, full datasets for several sites are published here for the first time. The Saksunarvatn Ash, now considered to be the result of several eruptions rather than one major eruption, can be separated into two phases on the Faroe Islands; one early phase with two precursor eruptions with lower MgO concentrations (4.5-5.0 wt%) than the main eruption and a later phase with higher MgO concentrations (5.5-6.0 wt%), including the visible Saksunarvatn Ash. The Tjornuvik Tephra, previously considered to be a primary deposit, is now interpreted as a reworked tephra with material from at least two middle Holocene eruptions of Hekla. Several of the tephras identified on the Faroe Islands provide useful isochrons for climate events during the Holocene.

  • 909.
    Wastegård, Stefan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Johansson, Hans
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Pacheco, José M.
    New major element analyses of proximal tephras from the Azores and suggested correlations with cryptotephras in North-West Europe2020In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 35, no 1-2, p. 114-121Article in journal (Refereed)
    Abstract [en]

    The Azores Archipelago is one of the most active volcanic areas in the North Atlantic region. Approximately 30 eruptions have been reported over the last 600 years with some major VEI 5 (Volcanic Explosivity Index) eruptions further back in time. The geochemical composition of associated tephra-derived glass, however, is not well characterized. An Azorean origin of cryptotephras found in distal areas such as North Africa, the British Isles and Greenland has been suggested, but proximal data from the Azores are scarce and the correlations have only been tentative. These tephras have a traychtic composition, which excludes an Icelandic origin. In a previous study, we presented major element analyses of proximal tephra-derived glass from five Holocene eruptions on the Azores Islands. There is a striking geochemical similarity between tephras from volcanoes on Sao Miguel and Irish cryptotephras, and especially with eruptives from the Furnas volcano. Here we present new analyses of proximal tephras that confirm and strengthen a link between Furnas and cryptotephras found in south-west Ireland. We also suggest a correlation between a previously unsourced tephra found in a Swedish bog with an eruption of the Sete Cidades volcano c. 3880 a cal BP.

  • 910. Watson, E. J.
    et al.
    Swindles, G. T.
    Lawson, I. T.
    Savov, I. P.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    The presence of Holocene cryptotephra in Wales and southern England2017In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 32, no 4, p. 493-500Article in journal (Refereed)
    Abstract [en]

    There have been few detailed studies into the tephrostratigraphy of southern Britain. We report the tephrostratigraphy of two sites, one in southern England (Rough Tor, Cornwall) and one in Wales (Cors Fochno, west Wales). Our study extends the known southernmost reach of Icelandic cryptotephra in northern Europe. Given the large distance between sites in southern England and eruptive sources (e.g. Iceland 1500-1700km distant), most of the cryptotephra layers consist of sparse numbers of shards, even by the standards of distal tephrostratigraphy (as low as 3 shards cm(-1)), each layer spanning only 1 or 2cm in depth. We identify multiple cryptotephra layers in both sites, extending the known distribution of several tephra layers including the MOR-T4 tephra (approximate to AD 1000) most probably of Icelandic origin, and the AD 860 B tephra correlated to an eruption of Mount Churchill, Alaska. The two sites record contrasting tephrostratigraphies, illustrating the need for the inclusion of multiple sites in the construction of a regional tephrostratigraphic framework. The tephra layers we describe may provide important isochrons for the dating and correlation of palaeoenvironmental sequences in the south of Britain.

  • 911.
    Webber, Luke
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Differential Interferometry and Multiple-Aperture Interferometry for Retrieving Three-Dimensional Measurements of Glacial Surface Velocity2016Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
    Abstract [en]

    The measurement and monitoring of glacial surface velocity is important for many aspects of glaciology, such as determining the mass balance, for characterising the stability or instability of glaciers, or the identification of potential hazards from surging glaciers or Jökulhlaups, a type of glacial outburst flood. Predominately measurements of glacial surface velocity have been produced using either differential interferometry (DInSAR) applied to radar data, or offset-tracking applied to either optical or radar data. Both of these methods have their own set of limitations, notably the one-dimensional nature of DInSAR measurements, and the relatively low accuracy of offset-tracking. Instead using DInSAR and multiple-aperture interferometry (MAI) applied to ERS-1/2 Tandem SAR data, measurements of glacial surface displacements were obtained in the line-of-sight (LOS) and along-track directions respectively. Then using a weighted-least squares adjustment, the method for producing the full three-dimensional surface velocity field is presented and applied to the Svartisen glacial system, Norway and the Petermann Glacier, Greenland. The advantages and disadvantages of applying such a method were explored, of which interferometric coherence is found to be the largest factor in retrieving accurate measurements using MAI. Low interferometric coherence due to temporal decorrelation resulted in the inability to extract the full three-dimensional surface velocity field over the Bagley Icefield, Alaska, and the Mýrdalsjökull & Eýjafjallajökull ice caps, Iceland. A feasibility analysis into the use of Sentinel-1 data, revealed that the current revisit period is too large to maintain interferometric coherence between acquisitions, preventing the application of either DInSAR or offset-tracking in order to measure the surface velocity of the Blåmannsisen Glacier, Norway. Despite the limitations encountered, in part due to the selection of source data, MAI in tandem with DInSAR has been shown to be capable of measuring the three-dimensional surface velocity to a higher accuracy than offset-tracking when coherence is high. The methods used within have been developed to work with pre-processed single look complex (SLC) SAR data rather than raw unfocused SAR data, in an effort to improve their adoption and enable more accurate estimates of glacial surface velocity. 

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  • 912. Weiberg, Erika
    et al.
    Unkel, Ingmar
    Kouli, Katerina
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Avramidis, Pavlos
    Bonnier, Anton
    Dibble, Flint
    Finné, Martin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Izdebski, Adam
    Katrantsiotis, Christos
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Stocker, Sharon R.
    Andwinge, Maria
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Baika, Kalliopi
    Boyd, Meighan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Heymann, Christian
    The socio-environmental history of the Peloponnese during the Holocene: Towards an integrated understanding of the past2016In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 136, p. 40-65Article in journal (Refereed)
    Abstract [en]

    Published archaeological, palaeoenvironmental, and palaeoclimatic data from the Peloponnese in Greece are compiled, discussed and evaluated in order to analyse the interactions between humans and the environment over the last 9000 years. Our study indicates that the number of human settlements found scattered over the peninsula have quadrupled from the prehistoric to historical periods and that this evolution occurred over periods of climate change and seismo-tectonic activity. We show that societal development occurs both during periods of harsh as well as favourable climatic conditions. At some times, some settlements develop while others decline. Well-known climate events such as the 4.2 ka and 3.2 ka events are recognizable in some of the palaeoclimatic records and a regional decline in the number and sizes of settlements occurs roughly at the same time, but their precise chronological fit with the archaeological record remains uncertain. Local socio-political processes were probably always the key drivers behind the diverse strategies that human societies took in times of changing climate. The study thus reveals considerable chronological parallels between societal development and palaeoenvironmental records, but also demonstrates the ambiguities in these correspondences and, in doing so, highlights some of the challenges that will face future interdisciplinary projects. We suggest that there can be no general association made between societal expansion phases and periods of advantageous climate. We also propose that the relevance of climatic and environmental regionality, as well as any potential impacts of seismo-tectonics on societal development, need to be part of the interpretative frameworks.

  • 913.
    Weiss, Niels
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Permafrost carbon in a changing Arctic: On periglacial landscape dynamics, organic matter characteristics, and the stability of a globally significant carbon pool2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Organic matter (OM) in arctic permafrost ground contains about twice as much carbon (C) as is currently present in the atmosphere. Climate change is particularly strong in the Arctic, and could cause a considerable part of the OM in permafrost to thaw out, decompose, and be released as greenhouse gases; further enhancing global warming. The exact size of the northern circumpolar C pool remains unclear, and processes that control decomposition and mineralization rates are even more uncertain. Superimposed on the long-term release of C through microbial decomposition of OM in the gradually deepening active layer, is the rapid release of currently sequestered OM through geomorphological processes. This thesis considers the quantity, quality, and availability of permafrost C, and explores interactions and common controls.

    To better understand the potential effects of thawing permafrost, it is vital to: i) obtain more accurate size and distribution estimates of permafrost C stocks, and develop methods to accurately and efficiently implement these in models, ii) identify OM characteristics that control decomposition, specifically for permafrost material, and iii) determine and quantify key geomorphological processes that cause large amounts of OM to become available for rapid decomposition.

    Detailed C quantifications are valuable to increase our fundamental understanding of permafrost soil processes and C sequestration, but including high levels of heterogeneity in models is challenging. Simple upscaling tools based on e.g. elevation parameters (Paper I) can help to bridge the gap between detailed field studies and global C models.

    Permafrost OM quality is controlled by different factors than those commonly observed in temperate soils (without permafrost). We observed an unexpected (significant) correlation in upper permafrost samples, where material that is generally considered more recalcitrant showed the highest CO2 production rates per g C, indicating high lability (Paper II). In ancient Pleistocene permafrost, labile samples related significantly to OM that was enriched in decomposed microbial remains, whereas less-decomposed plant material was more stable (Paper III). Investigation of multiple incubation datasets revealed that the unusual relationship between %C and CO2 production occurred in contrasting field sites throughout the Arctic, indicating important permafrost-specific controls over OM quality (Paper IV). We discuss several possible explanations for the observed high lability of permafrost OM, such as a pool of labile dissolved organic C in the upper permafrost, or increased lability caused by past decomposition. In order to conclusively identify causal relationships, and to answer the question whether or not the same mechanisms control OM quality in different environments, further investigation of permafrost-specific OM quality is required.

    Geomorphology plays a key role in C reworking and OM decomposition. Vast amounts of OM can be released abruptly (e.g. in thaw slumps and thermokarst lakes, Paper II), resulting in C turnover that will likely outweigh decomposition through gradual active layer deepening. Climate change could enhance this rapid release of C, and changes in surface hydrology and increased fire activity are expected to become the largest contributors to C loss from permafrost regions. Together with C quantity and quality, availability through gradual and abrupt processes must be parameterized and included in models in order to accurately assess the potential permafrost C climate feedback.

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  • 914.
    Weiss, Niels
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Blok, Daan
    Elberling, Bo
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Juncher Jorgensen, Christian
    Siewert, Matthias Benjamin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Thermokarst dynamics and soil organic matter characteristics controlling initial carbon release from permafrost soils in the Siberian Yedoma region2016In: Sedimentary Geology, ISSN 0037-0738, E-ISSN 1879-0968, Vol. 340, p. 38-48Article in journal (Refereed)
    Abstract [en]

    This study relates soil organic matter (SOM) characteristics to initial soil incubation carbon release from upper permafrost samples in Yedoma region soils of northeastern Siberia, Russia. Carbon (C) and nitrogen (N) content, carbon to nitrogen ratios (C:N), delta C-13 and delta N-15 values show clear trends that correspond with SOM age and degree of decomposition. Incubation results indicate that older and more decomposed soil material shows higher C respiration rates per unit incubated C than younger and less decomposed samples with higher C content. This is important as undecomposed material is often assumed to be more reactive upon thawing. Large stocks of SOM and their potential decomposability, in combination with complex landscape dynamics that include one or more events of Holocene thaw in most of the landscape, are of consequence for potential greenhouse gas release from permafrost soils in the Yedoma region.

  • 915.
    Weiss, Niels
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Faucherre, Samuel
    Blok, Daan
    Elberling, Bo
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Jørgensen, Christian J.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Vulnerabilityof organic matter in upper permafrost from contrasting northern circumpolar regionsManuscript (preprint) (Other academic)
  • 916.
    Weiss, Niels
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Faucherre, Samuel
    Lampiris, Nikos
    Wojcik, Robin
    Elevation-based upscaling of organic carbon stocks in high arctic permafrost terrain: a storage and distribution assessment for Spitsbergen, SvalbardManuscript (preprint) (Other academic)
  • 917.
    Weiss, Niels
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Faucherre, Samuel
    Lampiris, Nikos
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Wojcik, Robin
    Stockholm University, Faculty of Science, Department of Physical Geography. German Research Centre for Geoscience, Germany.
    Elevation-based upscaling of organic carbon stocks in High-Arctic permafrost terrain: a storage and distribution assessment for Spitsbergen, Svalbard2017In: Polar Research, ISSN 0800-0395, E-ISSN 1751-8369, Vol. 36, article id 1400363Article in journal (Refereed)
    Abstract [en]

    Accurate quantity and distribution estimates of permafrost soil organic carbon (SOC) stocks are needed to project potential feedbacks to climate, following warming. Still, upscaling from local field observations to regional estimates to circumarctic assessments remains a challenge. Here we explore elevation-based upscaling techniques for High-Arctic permafrost SOC stocks. We combine two detailed, high-resolution SOC inventories on Spitsbergen (Svalbard) with regional validation data. We find a clear relationship between elevation and SOC content, and use this observed exponential correlation, as well as discrete elevation classes, as upscaling models for Spitsbergen. We estimate the total amount of permafrost SOC currently present in soils on Spitsbergen to be 105.36 Tg (0.11 Pg), with a mean SOC content of 2.84 +/- 0.74 kg C m(-2) (mean +/- 95% confidence interval). Excluding glaciers and permanent snowfields, exposed land is currently estimated to contain 6.26 +/- 1.47 kg C m(-2).

  • 918.
    Weiss, Niels
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kaal, Joeri
    Characterization of labile organic matter in Pleistocene permafrost (NE Siberia), using Thermally assisted Hydrolysis and Methylation (THM-GC-MS)Manuscript (preprint) (Other academic)
  • 919.
    Weiss, Niels
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kaal, Joeri
    Characterization of labile organic matter in Pleistocene permafrost (NE Siberia), using Thermally assisted Hydrolysis and Methylation (THM-GC-MS)2018In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 117, p. 203-213Article in journal (Refereed)
    Abstract [en]

    Pleistocene yedoma sediments store large amounts of soil organic matter (SOM) and are vulnerable to permafrost degradation. Here we contribute to our understanding of yedoma SOM dynamics and potential response to thaw, by molecular characterization of samples from a 5.7 m yedoma exposure, as well as upper permafrost samples that were previously incubated, using Thermally assisted Hydrolysis and Methylation (THM-GC-MS). In general, the SOM is derived from aliphatic material (including cutin and suberin), phenols (lignin, sphagnum acid), polysaccharides and N-containing components (largely microbial SOM). Soil organic carbon (SOC) content and molecular SOM composition follow a sawtooth pattern where local maxima in SOC coincide with lignin and aliphatic material that experienced only slight degradation, and minima with degraded plant-derived SOM and microbial tissue, representing a stratified cryopedolith. The SOC-depleted top 0.9 m (active layer and transition zone) is enriched in microbial SOM probably due to recent thawing. Comparison with CO2 respiration rates indicates that SOM of microbial origin (low C/N) is more labile than aliphatic SOM from well-preserved plant tissue (high C/N). However, we argue that the more stable aliphatic SOM in SOC-rich layers might also be vulnerable to decay, which could, due to its abundance in SOC-rich layers, dominate overall Yedoma C losses due to thermal erosion.

  • 920. Wemple, Beverley C.
    et al.
    Browning, Trevor
    Ziegler, Alan D.
    Celi, Jorge
    Chun, Kwok Pan (Sun)
    Jaramillo, Fernando
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Leite, Nei K.
    Ramchunder, Sorain J.
    Negishi, Junjiro N.
    Palomeque, Ximena
    Sawyer, Derek
    Ecohydrological disturbances associated with roads: Current knowledge, research needs, and management concerns with reference to the tropics2018In: Ecohydrology, ISSN 1936-0584, E-ISSN 1936-0592, Vol. 11, no 3, article id e1881Article, review/survey (Refereed)
    Abstract [en]

    Roads are a pervasive form of disturbance with potential to negatively affect ecohydrological processes. Some of the most rapid growth in road networks is occurring in developing countries, particularly in the tropics, where political agendas are often focused on strengthening the economy, improving infrastructure, bolstering national security, achieving self-sufficiency, and increasing citizen well-being, often at the expense of the environment. We review what is known about road impacts on ecohydrological processes, focusing on aquatic systems, both temperate and tropical. We present seven cases that represent the broader trends of road development and impacts in tropical settings. Many of these process dynamics and impacts are not different from those experienced in temperate settings, although the magnitude of impacts in the tropics may be amplified with intense rainfall and lack of best management practices applied to road construction/maintenance. Impacts of roads in tropical settings may also be unique because of particular organisms or ecosystems affected. We outline a set of best practices to improve road network management and provide recommendations for adopting an agenda of research and road management in tropical settings. Importantly, we call for incorporation of transdisciplinary approaches to further study the effects of roads on ecohydrological processes in the tropics. Specific emphasis should also be placed on collaboration with governments and developers that are championing road development to help identify the drivers of road expansion and thresholds of negative impact, as well as methods of sustainable road construction and maintenance.

  • 921.
    Westerberg, Lars-Ove
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hagberg, Emilia
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Geomorphology and pedology of the Engaruka archaeological environment, Tanzania, and the effects of the 1997-1998 El Nino flash-flood2018In: Catena (Cremlingen. Print), ISSN 0341-8162, E-ISSN 1872-6887, Vol. 163, p. 244-256Article in journal (Refereed)
    Abstract [en]

    Here we analyse geomorphic, pedologic and hydrologic processes of relevance to archaeological research on the pre-colonial irrigation system at Engaruka, Tanzania. Although archaeological studies have been carried out in Engaruka for several decades; geophysical processes have not been in focus, despite having the potential to contribute to the understanding of both the ancient irrigation system and the current land use in Engaruka. Geomorphology and pedology were explored through field surveys and mapping using air photos and satellite images. The effects of the flash-flood during the 1997-1998 El Nino were mapped and quantified in the field. Maximum flash-flood discharge in Engaruka River was estimated using Marming's Equation. The geomorphic study revealed that Engaruka is an environment where high-magnitude processes (debris flows, flash-floods, rock slides) dominate landform development. Low-magnitude processes (sheet-wash, wind erosion), transfer fine-textured sediment to low terrain, causing successive coarsening of soil texture in fields of the ancient irrigation system. Andisol occurrence in the dry environment is associated with current irrigation, indicating incremental improvement of arable land resulting from human land use. Andisols appear transient; discontinuation of irrigation has caused a reversion to Entisols, as water retention and structure deteriorate upon drying. A flash-flood during the 1997-1998 El Nino caused destruction of parts of the archaeological remains, with severe impact on current land use and settlements. Approximately 80 ha (4%) of the total area of the ancient remains were covered by debris flow deposits and alluvium, or scoured by new drainage lines of the water courses. The denudation caused by the single flash-flood is estimated to 9 mm in the catchment of Engaruka River. Manning's Equation yielded a least possible maximum discharge in Engaruka River, in the order of 270 m(3)/s, some 600-700 times higher than normal, dry season discharge.

  • 922.
    Wiborgh, Hanna
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Where do the nutrients come from?: A case study from the agricultural landscape of Sibou village2015Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
    Abstract [en]

    This study investigates the source of nutrients in an agricultural landscape in Kenya. Kapshoi furrow has its intake from Embobut River and flows through the village of Sibou until it reaches the plots in the lowland in Keu. The pH, electrical conductivity (EC), sediment transport, total nitrogen (N) mass flux and total phosphorus (P) mass flux all change when the furrow flows through the village. The most possible cause for the nutrients peaks is the farmers' goats, sheep and cows that walk freely in and around the furrow. This is counter to some existing local theories. The likely cause for the pH decrease and the EC increase are inflow of groundwater (springs) to the furrow. To secure safe drinking water it would be good to uphold the old rules in Sibou of (1) not to live in close proximity of the furrows and (2) not to bathe or do the dishes in the furrow water. This might be difficult due to a fast growing population. 

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  • 923.
    Widgren, Mats
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Human Geography.
    Maggs, Tim
    Plikk, Anna
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Schoeman, Maria H.
    Westerberg, Lars-Ove
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Precolonial agricultural terracing in Bokoni, South Africa: Typology and an exploratory excavation2016In: Journal of African Archaeology, ISSN 1612-1651, E-ISSN 2191-5784, Vol. 14, no 1, p. 33-53Article in journal (Refereed)
    Abstract [en]

    Earlier work on the terraced settlements of the Bokoni area (16th to 19th century, Mpumalanga province, South Africa) focussed on the homesteads, their contents, layout and chronology. This paper suggests a terminology and typology of agrarian structures in Bokoni in order to improve comparative approaches in Africa and beyond. The typology and an excavation of the terracing have made possible preliminary conclusions relevant for the further analysis of the terracing and stone-walling in Bokoni. The terracing developed incrementally, whereby cultivation, stone-clearing and terracing were intermixed processes. This is supported both by the organic content in a section of a terrace and by a phytolith analysis. The phytolith analysis furthermore indicated that maize was cultivated on the terraces, but this should be seen as a pilot study only, and presence of maize in Bokoni must be tested with other archaeobotanical methods.

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  • 924.
    Widström, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Migration av gummigranulat från konstgräsplaner: En förbisedd miljöfarlig verksamhet2017Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Pitches with artificial turf can be used at all hours and all year. They are therefore very space efficient and become increasingly common. But questions have been raised about the environmental issues that may arise from them. It has previously been known that artificial turf is a source of unwanted chemicals and recently they have been identified as the second biggest source of leakage of micro-plastic particles in Sweden. Such particles could affect biota negatively if they are released into nature. Since the state of knowledge was uncertain about migration of micro-plastic particles from artificial turf via their drainage, tests were made in draining wells at a selected number of artificial turf fields in municipality of Södertälje. To be able to answer if artificial turf is considered to have an environmentally damaging effect, a review of requirements and laws related to them were also made. Estimated quantities of granulate found during tests showed small amounts and conclusions were made that there must be another migration than through the drainage that contributes to the large leakage of micro particles of plastic from artificial turf. However, the study shows that the granulate can migrate through the drainage system and thus make it through to aquatic environments. Review of requirements and laws showed that environmental aspects linked to artificial turf several times are undefined and unclear and sometimes completely missing. Questions are raised if artificial turf should be seen as an activity where notification, authorization and supervision based on the environmental perspective are used, and which parties who have the responsibility in the matter. With additional information about that part of the filling material produced in Sweden and thus posted on artificial turf fields around the country are classified as waste, again raises questions about responsibility but also about governing agencies and their position on the subject. Concluding proposals are given for measures that could help to municipalities' efforts to minimize the risk of migration of rubber granules to nature.

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  • 925.
    Wild, Birgit
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. University of Vienna, Austria; Austrian Polar Research Institute, Austria; University of Gothenburg, Sweden; .
    Alves, Ricardo J. Eloy
    Bárta, Jiři
    Čapek, Petr
    Gentsch, Norman
    Guggenberger, Georg
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography. Stanford University, United States of America.
    Knoltsch, Anna
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Lashchinskiy, Nikolay
    Mikutta, Robert
    Palmtag, Juri
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Prommer, Judith
    Schnecker, Jörg
    Shibistova, Olga
    Takriti, Mounir
    Urich, Tim
    Richter, Andreas
    Amino acid production exceeds plant nitrogen demand in Siberian tundra2018In: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 13, no 3, article id 034002Article in journal (Refereed)
    Abstract [en]

    Arctic plant productivity is often limited by low soil N availability. This has been attributed to slow breakdown of N-containing polymers in litter and soil organic matter (SOM) into smaller, available units, and to shallow plant rooting constrained by permafrost and high soil moisture. Using N-15 pool dilution assays, we here quantified gross amino acid and ammonium production rates in 97 active layer samples from four sites across the Siberian Arctic. We found that amino acid production in organic layers alone exceeded literature-based estimates of maximum plant N uptake 17-fold and therefore reject the hypothesis that arctic plant N limitation results from slow SOM breakdown. High microbial N use efficiency in organic layers rather suggests strong competition of microorganisms and plants in the dominant rooting zone. Deeper horizons showed lower amino acid production rates per volume, but also lower microbial N use efficiency. Permafrost thaw together with soil drainage might facilitate deeper plant rooting and uptake of previously inaccessible subsoil N, and thereby promote plant productivity in arctic ecosystems. We conclude that changes in microbial decomposer activity, microbial N utilization and plant root density with soil depth interactively control N availability for plants in the Arctic.

  • 926.
    Wild, Birgit
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Andersson, August
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Bröder, Lisa
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Vrije Universiteit, Amsterdam, The Netherlands.
    Vonk, Jorien
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    McClelland, James W.
    Song, Wenjun
    Raymond, Peter A.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Rivers across the Siberian Arctic unearth the patterns of carbon release from thawing permafrost2019In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 116, no 21, p. 10280-10285Article in journal (Refereed)
    Abstract [en]

    Climate warming is expected to mobilize northern permafrost and peat organic carbon (PP-C), yet magnitudes and system specifics of even current releases are poorly constrained. While part of the PP-C will degrade at point of thaw to CO2 and CH4 to directly amplify global warming, another part will enter the fluvial network, potentially providing a window to observe large-scale PP-C remobilization patterns. Here, we employ a decade-long, high-temporal resolution record of C-14 in dissolved and particulate organic carbon (DOC and POC, respectively) to deconvolute PP-C release in the large drainage basins of rivers across Siberia: Ob, Yenisey, Lena, and Kolyma. The C-14-constrained estimate of export specifically from PP-C corresponds to only 17 +/- 8% of total fluvial organic carbon and serves as a benchmark for monitoring changes to fluvial PP-C remobilization in a warming Arctic. Whereas DOC was dominated by recent organic carbon and poorly traced PP-C (12 +/- 8%), POC carried a much stronger signature of PP-C (63 +/- 10%) and represents the best window to detect spatial and temporal dynamics of PP-C release. Distinct seasonal patterns suggest that while DOC primarily stems from gradual leaching of surface soils, POC reflects abrupt collapse of deeper deposits. Higher dissolved PP-C export by Ob and Yenisey aligns with discontinuous permafrost that facilitates leaching, whereas higher particulate PP-C export by Lena and Kolyma likely echoes the thermokarst-induced collapse of Pleistocene deposits. Quantitative C-14-based fingerprinting of fluvial organic carbon thus provides an opportunity to elucidate large-scale dynamics of PP-C remobilization in response to Arctic warming.

  • 927. Wild, Birgit
    et al.
    Gentsch, Norman
    Capek, Petr
    Diakova, Katerina
    Alves, Ricardo J. Eloy
    Barta, Jiri
    Gittel, Antje
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Knoltsch, Anna
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Lashchinskiy, Nikolay
    Mikutta, Robert
    Palmtag, Juri
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Schleper, Christa
    Schnecker, Jörg
    Shibistova, Olga
    Takriti, Mounir
    Torsvik, Vigdis L.
    Urich, Tim
    Watzka, Margarete
    Santruckova, Hana
    Guggenberger, Georg
    Richter, Andreas
    Plant-derived compounds stimulate the decomposition of organic matter in arctic permafrost soils2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 25607Article in journal (Refereed)
    Abstract [en]

    Arctic ecosystems are warming rapidly, which is expected to promote soil organic matter (SOM) decomposition. In addition to the direct warming effect, decomposition can also be indirectly stimulated via increased plant productivity and plant-soil C allocation, and this so called priming effect might significantly alter the ecosystem C balance. In this study, we provide first mechanistic insights into the susceptibility of SOM decomposition in arctic permafrost soils to priming. By comparing 119 soils from four locations across the Siberian Arctic that cover all horizons of active layer and upper permafrost, we found that an increased availability of plant-derived organic C particularly stimulated decomposition in subsoil horizons where most of the arctic soil carbon is located. Considering the 1,035 Pg of arctic soil carbon, such an additional stimulation of decomposition beyond the direct temperature effect can accelerate net ecosystem C losses, and amplify the positive feedback to global warming.

  • 928. Wilhelms, Frank
    et al.
    Miller, Heinrich
    Gerasimoff, Michael D.
    Druecker, Cord
    Frenzel, Andreas
    Fritzsche, Diedrich
    Grobe, Hannes
    Hansen, Steffen Bo
    Hilmarsson, Sverrir A. E.
    Hoffmann, Georg
    Hörnby, Kerstin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Jaeschke, Andrea
    Jakobsdottir, Steinunn S.
    Juckschat, Paul
    Karsten, Achim
    Karsten, Lorenz
    Kaufmann, Patrik R.
    Karlin, Torbjorn
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kohlberg, Eberhard
    Kleffel, Guido
    Lambrecht, Anja
    Lambrecht, Astrid
    Lawer, Gunther
    Schaermeli, Ivan
    Schmitt, Jochen
    Sheldon, Simon G.
    Takata, Morimasa
    Trenke, Marcus
    Twarloh, Birthe
    Valero-Delgado, Fernando
    Wilhelms-Dick, Dorothee
    The EPICA Dronning Maud Land deep drilling operation2014In: Annals of Glaciology, ISSN 0260-3055, E-ISSN 1727-5644, Vol. 55, no 68, p. 355-366Article in journal (Refereed)
    Abstract [en]

    We report on the EPICA Dronning Maud Land (East Antarctica) deep drilling operation. Starting with the scientific questions that led to the outline of the EPICA project, we introduce the setting of sister drillings at NorthGRIP and EPICA Dome C within the European ice-coring community. The progress of the drilling operation is described within the context of three parallel, deep-drilling operations, the problems that occurred and the solutions we developed. Modified procedures are described, such as the monitoring of penetration rate via cable weight rather than motor torque, and modifications to the system (e.g. closing the openings at the lower end of the outer barrel to reduce the risk of immersing the drill in highly concentrated chip suspension). Parameters of the drilling (e.g. corebreak force, cutter pitch, chips balance, liquid level, core production rate and piece number) are discussed. We also review the operational mode, particularly in the context of achieved core length and piece length, which have to be optimized for drilling efficiency and core quality respectively. We conclude with recommendations addressing the design of the chip-collection openings and strictly limiting the cable-load drop with respect to the load at the start of the run.

  • 929.
    Wilhelmsson, Emelie
    Stockholm University, Faculty of Science, Department of Physical Geography.
    3D-positionering till havs efter bearbetning med PPK- och PPP-lösning och kontroll av fartygets dynamiska rörelser2017Independent thesis Advanced level (degree of Master (Two Years)), 40 credits / 60 HE creditsStudent thesis
    Abstract [en]

    This project investigates whether 3D-positioning at sea can be improved by processing real-time positioning data. SWEPOS-based RTK (accurate GNSS) was used to log positions data on a hydrographic survey vessel along Sweden’s east and north coast for 7 days. However, because of the long distance between the vessel and the reference stations the positioning solutions do not always have high accuracy. This problem generates a large interest to research how processing real-time data could improve position accuracy. Processing positioning data is done through Applanix IN-fusion PPK (Post-Processed Kinematic) and PPP (Precise Point Positioning) loosely coupled concept. The positioning accuracy of these methods are compared against one another and against collected data in real-time (RTK). The vertical component are being assessed further in detail to evaluate the accuracy of these methods and the data is presented in respect to vertical positioning and height. However, solely processing the vessels positioning according to the PPP or PPK concept is not enough to get a good positioning vertically, as the vessels positioning height also depends on the vessels dynamic movements. Including the vessel’s dynamic movement’s leads not only to a higher positioning accuracy but also to a more accurate description of the shape of the water surface. The shape of the water surface is an important component for the modelling of the geoid, as the water mass distribution affects gravitational measurements and calculations by water mass variations. The future goal, is that vessels should be able to collect data which can be used to correct the present geoid model, only by using GNSS technique and water level corrections from reference stations. Furthermore, good hydrographic data and accurate GNSS height provides preconditions to introduce a 3D-navigational system. A system like this could calculate if the present draught is compatible with the future depth conditions along the route. The system can thereby support the navigator with suggestions of speed adjustments at optimal moments to avoid running aground.

    Initially, the different post-processing methodology’s ability to improve position accuracy are evaluated. The observations presented in this project indicate that position accuracy varies depending on which method is used. The results show that the vertical measurement uncertainty (RMS) values are lowest when using the processing methods based on the PPK concept. The RMS mean value using PPP processing methodology show a higher value than the real-time solutions. In this case, by adjusting the real-time solutions by processing according to the PPK method, the vessels vertical position can be corrected with a mean value of 5 cm. In the secondary process, the GNSS height from the PPK processing methodology was used together with static and dynamic corrections to approximate the actual water level. This project demonstrates the potential of using this type of process to get a more accurate picture of the present water surface.

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  • 930. Wilson, R.
    et al.
    Anchukaitis, K.
    Andreu-Hayles, L.
    Cook, E.
    D'Arrigo, R.
    Davi, N.
    Haberbauer, L.
    Krusic, Paul
    Stockholm University, Faculty of Science, Department of Physical Geography. University of Cambridge, UK.
    Luckman, B.
    Morimoto, D.
    Oelkers, R.
    Wiles, G.
    Wood, C.
    Improved dendroclimatic calibration using blue intensity in the southern Yukon2019In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 29, no 11, p. 1817-1830Article in journal (Refereed)
    Abstract [en]

    In north-western North America, the so-called divergence problem (DP) is expressed in tree ring width (RW) as an unstable temperature signal in recent decades. Maximum latewood density (MXD), from the same region, shows minimal evidence of DP. While MXD is a superior proxy for summer temperatures, there are very few long MXD records from North America. Latewood blue intensity (LWB) measures similar wood properties as MXD, expresses a similar climate response, is much cheaper to generate and thereby could provide the means to profoundly expand the extant network of temperature sensitive tree-ring (TR) chronologies in North America. In this study, LWB is measured from 17 white spruce sites (Picea glauca) in south-western Yukon to test whether LWB is immune to the temporal calibration instabilities observed in RW. A number of detrending methodologies are examined. The strongest calibration results for both RW and LWB are consistently returned using age-dependent spline (ADS) detrending within the signal-free (SF) framework. RW data calibrate best with June-July maximum temperatures (Tmax), explaining up to 28% variance, but all models fail validation and residual analysis. In comparison, LWB calibrates strongly (explaining 43-51% of May-August Tmax) and validates well. The reconstruction extends to 1337 CE, but uncertainties increase substantially before the early 17th century because of low replication. RW-, MXD- and LWB-based summer temperature reconstructions from the Gulf of Alaska, the Wrangell Mountains and Northern Alaska display good agreement at multi-decadal and higher frequencies, but the Yukon LWB reconstruction appears potentially limited in its expression of centennial-scale variation. While LWB improves dendroclimatic calibration, future work must focus on suitably preserved sub-fossil material to increase replication prior to 1650 CE.

  • 931. Wilson, R.
    et al.
    Loader, N. J.
    Rydval, M.
    Patton, H.
    Frith, A.
    Mills, C. M.
    Crone, A.
    Edwards, C.
    Larsson, L.
    Gunnarson, Björn E.
    Stockholm University, Faculty of Science, Department of Physical Geography. Swedish University of Agricultural Sciences, Sweden.
    Reconstructing Holocene climate from tree rings: The potential for a long chronology from the Scottish Highlands2012In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 22, no 1, p. 3-11Article in journal (Refereed)
    Abstract [en]

    Despite promising research in the 1980s showing the potential of Scots pine (Pinus sylvestris L.) for the reconstruction of past summer temperatures in the Scottish Highlands, little dendroclimatic work has been attempted in this region since. This reflects, in part, the limited number of sparsely distributed remnant natural/ semi-natural pine woodlands in the Scottish Highlands and the lack of old growth forest therein. On average, most of the pine trees dated in this region are around 225 years in age. Here, we present the first results of an ongoing interdisciplinary initiative to develop a long Scottish chronology through the acquisition of modern, historical and subfossil pine material from the native pinewoods, historic structures and lakes of the Scottish Highlands. Radiocarbon dating of 25 subfossil pine timbers recovered from lake sediments identified the presence of preserved material covering the last 8000 years with initial clusters focused on the last two millennia and early-mid Holocene. Although developing a well-replicated 8000 year pine chronology will take many years, this preliminary study indicates that a millennial length pine chronology from the northwest Cairngorm region is a feasible and realistic objective in the near future. The importance of such a record in this climatically important sector of northwest Europe cannot be underestimated.

  • 932. Wilson, Rob
    et al.
    Wilson, David
    Rydval, Milos
    Crone, Anne
    Buntgen, Ulf
    Clark, Sylvie
    Ehmer, Janet
    Forbes, Emma
    Fuentes, Mauricio
    Gunnarson, Björn E.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Linderholm, Hans W.
    Nicolussi, Kurt
    Wood, Cheryl
    Mills, Coralie
    Facilitating tree-ring dating of historic conifer timbers using Blue Intensity2017In: Journal of Archaeological Science, ISSN 0305-4403, E-ISSN 1095-9238, Vol. 78, p. 99-111Article in journal (Refereed)
    Abstract [en]

    Dendroarchaeology almost exclusively uses ring-width (RW) data for dating historical structures and artefacts. Such data can be used to date tree-ring sequences when regional climate dominates RW variability. However, the signal in RW data can be obscured due to site specific ecological influences (natural and anthropogenic) that impact crossdating success. In this paper, using data from Scotland, we introduce a novel tree-ring parameter (Blue Intensity BI) and explore its utility for facilitating dendrohistorical dating of conifer samples. BI is similar to latewood density as they both reflect the combined hemicellulose, cellulose and lignin content in the latewood cell walls of conifer species and the amount of these compounds is strongly controlled, at least for trees growing in temperature limited locations, by late summer temperatures. BI not only expresses a strong climate signal, but is also less impacted by site specific ecological influences. It can be concurrently produced with RW data from images of finely sanded conifer samples but at a significantly reduced cost compared to traditional latewood density. Our study shows that the probability of successfully crossdating historical samples is greatly increased using BI compared to RW. Furthermore, due to the large spatial extent of the summer temperature signal expressed by such data, a sparse multi -species conifer network of long BI chronologies across Europe could be used to date and loosely provenance imported material.

  • 933. Winsa, Marie
    et al.
    Öckinger, Erik
    Bommarco, Riccardo
    Lindborg, Regina
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Roberts, Stuart P. M.
    Wärnsberg, Johanna
    Bartomeus, Ignasi
    Sustained functional composition of pollinators in restored pastures despite slow functional restoration of plants2017In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 7, no 11, p. 3836-3846Article in journal (Refereed)
    Abstract [en]

    Habitat restoration is a key measure to counteract negative impacts on biodiversity from habitat loss and fragmentation. To assess success in restoring not only biodiversity, but also functionality of communities, we should take into account the re-assembly of species trait composition across taxa. Attaining such functional restoration would depend on the landscape context, vegetation structure, and time since restoration. We assessed how trait composition of plant and pollinator (bee and hoverfly) communities differ between abandoned, restored (formerly abandoned) or continuously grazed (intact) semi-natural pastures. In restored pastures, we also explored trait composition in relation to landscape context, vegetation structure, and pasture management history. Abandoned pastures differed from intact and restored pastures in trait composition of plant communities, and as expected, had lower abundances of species with traits associated with grazing adaptations. Further, plant trait composition in restored pastures became increasingly similar to that in intact pastures with increasing time since restoration. On the contrary, the trait composition of pollinator communities in both abandoned and restored pastures remained similar to intact pastures. The trait composition for both bees and hoverflies was influenced by flower abundance and, for bees, by connectivity to other intact grasslands in the landscape. The divergent responses across organism groups appeared to be mainly related to the limited dispersal ability and long individual life span in plants, the high mobility of pollinators, and the dependency of semi-natural habitat for bees. Our results, encompassing restoration effects on trait composition for multiple taxa along a gradient in both time (time since restoration) and space (connectivity), reveal how interacting communities of plants and pollinators are shaped by different trait-environmental relationships. Complete functional restoration of pastures needs for more detailed assessments of both plants dispersal in time and of resources available within pollinator dispersal range.

  • 934.
    Winterdahl, Mattias
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. Swedish University of Agricultural Sciences, Sweden; Uppsala University, Sweden.
    Laudon, Hjalmar
    Lyon, Steve W.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Pers, Charlotta
    Bishop, Kevin
    Sensitivity of stream dissolved organic carbon to temperature and discharge: Implications of future climates2016In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 121, no 1, p. 126-144Article in journal (Refereed)
    Abstract [en]

    Dissolved organic carbon (DOC) is a significant constituent in aquatic ecosystems with concentrations in streams influenced by both temperature and water flow pathway dynamics associated with changes in discharge (streamflow). We investigated the sensitivity of DOC concentrations in 12 high-latitude headwater streams to changes in temperature and discharge using a mathematical model. The implications of differences in sensitivities were explored by using downscaled projections of air temperature and discharge to simulate possible trajectories of DOC concentrations in a changing climate. We found two distinct responses: (i) catchments where stream DOC sensitivity was high to temperature but low to discharge and (ii) catchments where stream DOC sensitivity was low to temperature but high to discharge. Streams with strong seasonal DOC dynamics were more sensitive to temperature changes than nonseasonal systems. In addition, stream DOC sensitivity to discharge was strongly correlated with vertical soil water DOC differences in the near-stream zone. Simulations of possible future changes in DOC concentrations indicated median increases of about 4-24% compared to current levels when using projections of air temperature and discharge but even larger increases were observed for base flow concentrations (13-42%). Streams with high-temperature sensitivity showed the largest increases in DOC concentrations. Our results suggest that future climatic changes could bring significant increases in surface water DOC concentrations in boreal and hemiboreal areas but that the response ultimately is dependent on vertical soil solution DOC differences and soil organic carbon distribution.

  • 935.
    Winterdahl, Mattias
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Wallin, Marcus B.
    Huseby Karlsen, Reinert
    Laudon, Hjalmar
    Öquist, Mats
    Lyon, Steve W.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Decoupling of carbon dioxide and dissolved organic carbon in boreal headwater streams2016In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 121, no 10, p. 2630-2651Article in journal (Refereed)
    Abstract [en]

    Streams and rivers emit large quantities of carbon dioxide (CO2) to the atmosphere. The sources of this CO2 are in-stream mineralization of organic carbon (OC) and CO2 input via groundwater inflow, but their relative importance is largely unknown. In this study, we quantified the role of in-stream OC mineralization as a source of CO2 in a number of nested boreal headwater streams. The results showed that mineralization of stream OC contributed 3% of CO2 supersaturation at time scales comparable to the estimated water travel times in the streams (<24h). Mass balances showed that downstream losses of OC were 3% in low-order streams, whereas up to 16% of the OC was lost in the largest (fourth order) streams. In contrast, 85% of the CO2 was lost along the stream network (longest total stream length=17km). Under the assumption that in-stream OC mineralization was the main source of stream CO2, higher rates of OC mineralization (6% of OC) than those reported across the literature (0.7% of OC) would be required to sustain observed CO2 supersaturation. Further, model results indicated that groundwater inflows were sufficient to sustain observed stream CO2 concentrations. We hence conclude that in-stream OC mineralization was a minor source of CO2 in these boreal headwater systems and that the main source of stream CO2 was inflowing groundwater transporting CO2 originating from soil respiration.

  • 936.
    Wojcik, Robin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Palmtag, Juri
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Weiss, Niels
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Land cover and landform-based upscaling of soil organic carbon stocks on the Brogger Peninsula, Svalbard2019In: Arctic, Antarctic and Alpine research, ISSN 1523-0430, E-ISSN 1938-4246, Vol. 51, no 1, p. 40-57Article in journal (Refereed)
    Abstract [en]

    In this study we assess the total storage, landscape distribution, and vertical partitioning of soil organic carbon (SOC) stocks on the Brogger Peninsula, Svalbard. This type of high Arctic area is underrepresented in SOC databases for the northern permafrost region. Physico-chemical, elemental, and radiocarbon (C-14) dating analyses were carried out on thirty-two soil profiles. Results were upscaled using both a land cover classification (LCC) and a landform classification (LFC). Both LCC and LFC approaches provide weighted mean SOC 0-100 cm estimates for the study area of 1.0 +/- 0.3 kg C m(-2) (95% confidence interval) and indicate that about 68 percent of the total SOC storage occurs in the upper 30 cm of the soil, and about 10 percent occurs in the surface organic layer. Furthermore, LCC and LFC upscaling approaches provide similar spatial SOC allocation estimates and emphasize the dominant role of vegetated area (4.2 +/- 1.6 kg C m(-2)) and solifluction slopes (6.7 +/- 3.6 kg C m(-2)) in SOC 0-100 cm storage. LCC and LFC approaches report different and complementary information on the dominant processes controlling the spatial and vertical distribution of SOC in the landscape. There is no evidence for any significant SOC storage in the permafrost layer. We hypothesize, therefore, that the Brogger Peninsula and similar areas of the high Arctic will become net carbon sinks, providing negative feedback on global warming in the future. The surface area that will have vegetation cover and incipient soil development will expand, whereas only small amounts of organic matter will experience increased decomposition due to active-layer deepening.

  • 937.
    Wood, Heather
    Stockholm University, Faculty of Science, Department of Physical Geography.
    EU tree density limits in wooded pastures and their effects on bat populations within traditional agricultural landscapes2016Independent thesis Advanced level (degree of Master (Two Years)), 40 credits / 60 HE creditsStudent thesis
    Abstract [en]

    The European Union’s Common Agricultural Policy (CAP) recommends subsidies are only granted for wooded pastures with less than 100 trees per hectare. This arbitrary guidance exists despite these habitats being among the most biodiverse in rural Europe. To date, most biodiversity research in agricultural landscapes has focused on plants, birds and invertebrates. Bats are also important bio-indicators of agricultural landscapes, but to my knowledge no study has explicitly focused on bat diversity in relation to this policy. In this thesis, I investigate how bat activity, foraging and species richness is affected in twenty-six wooded pastures along a gradient of tree density, from open to dense pastures. In parallel, nearby open fields and deciduous woodlands were sampled, creating a triplet of habitats being surveyed simultaneously. Bat species were divided into feeding guilds to explore how functional diversity affects response to habitat and landscape configuration. The overall contribution of wooded pastures to the species pool of bats within a heterogeneous, low intensity agricultural landscape was also explored. I found a consistent increase in bat activity and species richness within wooded pastures along the tree density gradient and across most feeding guilds. This in combination with shrub density was the strongest predictor of total bat activity and foraging; whilst structural diversity of pastures was most strongly correlated with species richness. Wooded pastures contributed more to total species richness than forested habitats. Interestingly, higher activity levels of forest feeding specialists were observed in pastures compared to forests. At the landscape level, amount of water and deciduous forest were the strongest predictors of bat activity. This study demonstrates that tree density within wooded pastures is not a limiting factor of bat activity and that other habitat and landscape parameters are important. Wooded pastures may also be an important component of current landscapes with little remaining deciduous forest. In conclusion, focusing solely on tree density limits will not help to preserve the ecological requirements for bats within agricultural landscapes.

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  • 938.
    Wood, Heather
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Lindborg, Regina
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Jakobsson, Simon
    Stockholm University, Faculty of Science, Department of Physical Geography.
    European Union tree density limits do not reflect bat diversity in wood-pastures2017In: Biological Conservation, ISSN 0006-3207, E-ISSN 1873-2917, Vol. 210, p. 60-71Article in journal (Refereed)
    Abstract [en]

    The European Union's Common Agricultural Policy (CAP) recommends subsidies are only granted for wood-pastures with < 100 trees/ha. This guidance exists despite these habitats being among the most biodiverse in boreal Europe and currently under threat due to land conversion. Bats are important bio-indicators of agricultural landscapes, but bat diversity has not explicitly been studied in relation to this policy. We investigate how bat activity, foraging, species richness and functional groups are affected in twenty-six wood-pastures along a gradient of tree density, from open to dense. In parallel, open fields and deciduous forests were sampled and the effect of the surrounding landscape configuration was explored. Our results show a consistent increase in total bat activity, foraging activity and species richness within wood-pastures along the tree density gradient. We find optimal tree densities within wood-pastures are higher than values reported in previous studies, and suggest thresholds might depend on the landscape context. Shrub density was a strong predictor of total bat activity and foraging; whilst structural variation of tree size in wood-pastures was most strongly correlated with species richness. We show that wood-pastures are an important habitat and in comparison to forests they contribute to higher bat species richness and activity levels. Interestingly, higher activity levels of forest feeding specialists were observed in wood-pastures compared to forests. At the landscape level, amount of water in the landscape was the strongest predictor of bat activity whilst deciduous forest mostly influenced foraging activity. This study demonstrates that tree density within wood-pastures is not a limiting factor of bat activity and foraging and that other habitat and landscape parameters are important. Thereby focusing solely on tree density limits will not help to promote the ecological requirements for bats. Instead we suggest that a results based approach to CAP payments would be preferable.

  • 939. Wu, Zhendong
    et al.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography. Stanford University, USA.
    Luo, Yiqi
    Smith, Benjamin
    Xia, Jianyang
    Fensholt, Rasmus
    Lehsten, Veiko
    Ahlström, Anders
    Approaching the potential of model-data comparisons of global land carbon storage2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 3367Article in journal (Refereed)
    Abstract [en]

    Carbon storage dynamics in vegetation and soil are determined by the balance of carbon influx and turnover. Estimates of these opposing fluxes differ markedly among different empirical datasets and models leading to uncertainty and divergent trends. To trace the origin of such discrepancies through time and across major biomes and climatic regions, we used a model-data fusion framework. The framework emulates carbon cycling and its component processes in a global dynamic ecosystem model, LPJ-GUESS, and preserves the model-simulated pools and fluxes in space and time. Thus, it allows us to replace simulated carbon influx and turnover with estimates derived from empirical data, bringing together the strength of the model in representing processes, with the richness of observational data informing the estimations. The resulting vegetation and soil carbon storage and global land carbon fluxes were compared to independent empirical datasets. Results show model-data agreement comparable to, or even better than, the agreement between independent empirical datasets. This suggests that only marginal improvement in land carbon cycle simulations can be gained from comparisons of models with current-generation datasets on vegetation and soil carbon. Consequently, we recommend that model skill should be assessed relative to reference data uncertainty in future model evaluation studies.

  • 940. Xu, Guobao
    et al.
    Liu, Xiaohong
    Wu, Guoju
    Chen, Tuo
    Wang, Wenzhi
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Zhang, Youfu
    Zeng, Xiaomin
    Qin, Dahe
    Sun, Weizhen
    Zhang, Xuanwen
    Tree ring O-18's indication of a shift to a wetter climate since the 1880s in the western Tianshan Mountains of northwestern China2015In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, no 13, p. 6409-6425Article in journal (Refereed)
    Abstract [en]

    Central Asian droughts have drastically and significantly affected agriculture and water resource management in these arid and semiarid areas. Based on tree ring O-18 from native, dominant Schrenk spruce (Picea schrenkiana Fisch. et Mey.), we developed a 300year (1710-2010) standard precipitation-evaporation index (SPEI) reconstruction from January to August for China's western Tianshan Mountains. The regression model explained 37.6% of the variation in the SPEI reconstruction during the calibration period from 1950 to 2010. Comparison with previous drought reconstructions confirmed the robustness of our reconstruction. The 20th century has been a relatively wet period during the past 300years. The SPEI showed quasi 2, 5, and 10year cycles. Several pluvials and droughts with covariability over large areas were revealed clearly in the reconstruction. The two longest pluvials (lasting for 12years), separated by 50years, appeared in the 1900s and the 1960s. The most severe drought occurred from 1739 to 1761 and from 1886 to 1911 was the wettest period since 1710. Compared to previous investigations of hydroclimatic changes in the western Tianshan Mountains, our reconstruction revealed more low-frequency variability and indicated that climate in the western Tianshan Mountains shifted from dry to wet in 1886. This regime shift was generally consistent with other moisture reconstructions for the northeastern Tibetan Plateau and northern Pakistan and may have resulted from a strengthened westerly circulation. The opposite hydrological trends in the western Tianshan Mountains and southeastern Tibetan Plateau reveal a substantial influence of strengthened westerlies and weakening of the Indian summer monsoon.

  • 941. Xu, Guobao
    et al.
    Liu, Xiaohong
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Zhang, Qiang
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hudson, Amy
    Trouet, Valerie
    Century-scale temperature variability and onset of industrial-era warming in the Eastern Tibetan Plateau2019In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 53, no 7-8, p. 4569-4590Article in journal (Refereed)
    Abstract [en]

    To improve our understanding of climate variability in the Tibetan Plateau (TP) and its sensitivity to external forcings, recent temperature changes need to be placed in a long-term historical context. Here, we present two tree-ring based temperature reconstructions: a 1003-year (1000-2002 CE) annual temperature reconstruction for the northeastern TP (NETP) based on seven series and a 522-year (1489-2010 CE) summer (June-July-August) temperature reconstruction for the southeastern TP (SETP) based on 11 series. Our reconstructions show six centuries of generally warm NETP temperatures (1000-1586 CE), followed by a transition to cooler temperatures (1587-1887 CE for NETP and 1588-1930 CE for SETP). The transition from the Medieval Climate Anomaly to the Little Ice Age thus happened in the 1580s in NETP and SETP, which is about 150 years later than in larger-scale (e.g. Asia and the Northern Hemisphere) temperature reconstructions. We found that TP temperature variability, especially in SETP, was influenced by the Atlantic multi-decadal oscillation and that the twentieth century was the warmest on record in NETP and SETP. Our reconstructions and climate model simulations both show industrial-era warming trends, the onset of which happened earlier in NETP (1812 CE) compared to SETP (1887 CE) and other temperature reconstructions for Western China, East Asia, Asia, and the Northern Hemisphere. The early NETP onset of industrial-era warming can likely be explained by NETP's faster warming rate and by local feedback factors (i.e., ice-snow cover-albedo). Comparisons between climate model simulations and our reconstructions reveal that cooler TP temperatures from 1600 to 1800 CE might be related to land-use and land-cover change.

  • 942.
    Yanda, Pius Zebhe
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Temporal and spatial variations of soil degradation in Mwisanga Catchment, Kondoa, Tanzania1995Doctoral thesis, monograph (Other academic)
  • 943. Yang, Haijun
    et al.
    Zhao, Yingying
    Liu, Zhengyu
    Li, Qing
    He, Feng
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Heat Transport Compensation in Atmosphere and Ocean over the Past 22,000 Years2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, article id 16661Article in journal (Refereed)
    Abstract [en]

    The Earth's climate has experienced dramatic changes over the past 22,000 years; however, the total meridional heat transport (MHT) of the climate system remains stable. A 22,000-year-long simulation using an ocean-atmosphere coupled model shows that the changes in atmosphere and ocean MHT are significant but tend to be out of phase in most regions, mitigating the total MHT change, which helps to maintain the stability of the Earth's overall climate. A simple conceptual model is used to understand the compensation mechanism. The simple model can reproduce qualitatively the evolution and compensation features of the MHT over the past 22,000 years. We find that the global energy conservation requires the compensation changes in the atmosphere and ocean heat transports. The degree of compensation is mainly determined by the local climate feedback between surface temperature and net radiation flux at the top of the atmosphere. This study suggests that an internal mechanism may exist in the climate system, which might have played a role in constraining the global climate change over the past 22,000 years.

  • 944.
    Yang, Heng
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. China Institute of Water Resources and Hydropower Research, China.
    Wang, Jianhua
    Xiao, Weihua
    Lu, Fan
    Wang, Yan
    Jarsjö, Jerker
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Relationship between hydroclimatic variables and reservoir wetland landscape pattern indices: A case study of the Sanmenxia Reservoir wetland on the Yellow River, China2020In: Journal of earth system science, ISSN 2347-4327, Vol. 129, no 1, article id 83Article in journal (Refereed)
    Abstract [en]

    Reservoir construction has led to the development of numerous wetlands, and these wetlands play an important role in global environmental change. In this paper, we investigate the relationship between reservoir wetlands and hydroclimatic variables. We used the MODIS land cover product to extract the wetland area of the Sanmenxia Reservoir, China. Then, various indices of reservoir wetland landscape patterns were calculated. Principal component analysis was performed to build the Sanmenxia Reservoir wetland comprehensive landscape pattern index (CLPI) to depict the changes in Sanmenxia Reservoir wetlands from 2001 to 2013. Pearson correlation analysis was used to assess their relationship. The following results were obtained. Firstly, the Sanmenxia Reservoir wetland area considerably declined and the landscape heterogeneity decreased from 2001 to 2013, especially in 2004. Secondly, the CLPI is significantly negatively correlated with annual runoff and significantly positively correlated with annual sediment discharge, annual average water level and annual shallow groundwater table in Sanmenxia Reservoir regions. Additionally, due to the decline in the reservoir wetland area, the values of Shannon's diversity index and Simpson's diversity index decreased in the study area. Therefore, the study suggests that maintaining a stable and healthy reservoir wetland area should be the focus of ecological reservoir management.

  • 945.
    Yang, Heng
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. China Institute of Water Resources and Hydropower Research, China.
    Zhao, Yong
    Wang, Jian-Hua
    Xiao, Wei-Hua
    Jarsjö, Jerker
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Huang, Ya
    Liu, Yang
    Wu, Jia-Peng
    Wang, He-jia
    Urban closed lakes: Nutrient sources, assimilative capacity and pollutant reduction under different precipitation frequencies2020In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 700, article id UNSP 134531Article in journal (Refereed)
    Abstract [en]

    Many natural and man-made urban lakes have been developed under urbanization. A unique feature of these lakes is the lack of an outlet; thus, they are defined as urban closed lakes (UCLs). UCLs are facing unexpected eutrophication under climate change and human activities. Our study assessed the trophic state, assimilative capacity (AC) and pollutant reduction of UCLs under different precipitation frequencies in Wuhan, China based on Carlson's Trophic State Index, assimilative capacity modelling, field investigations and observed data. The UCLs in Wuhan are nearly eutrophic in summer. Three primary nutrient sources are atmospheric deposition, pollutants carried in rainfall and nutrients released by sediments. TN and TP in the UCL water column are primarily contributed by surface runoff. The ACs of TN and TP in 2015 for Lingjiao Lake, Yue Lake, and Houxianghe Lake were 3472.07 kg, 13,800.99 kg, and 2805.58 kg, respectively, and 641.66 kg, 8386.79 kg, and 800.14 kg, respectively. The ACs of TN and TP were much higher at a 25% precipitation frequency (wet year) compared with a 50% frequency, and the lowest AC was observed at a 75% precipitation frequency (dry year). A comparison of the pollution load and AC showed that TN and TP reduction was highest in the dry and wet years, respectively. We found that specific meteorological conditions in the early stage led to the algal bloom. These results can facilitate governmental decision making in the future.

  • 946. Yu, Lin
    et al.
    Zanchi, Giuliana
    Akselsson, Cecilia
    Wallander, Håkan
    Belyazid, Salim
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Modeling the forest phosphorus nutrition in a southwestern Swedish forest site2018In: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 369, p. 88-100Article in journal (Refereed)
    Abstract [en]

    In this study, a phosphorus (P) module containing the biogeochemical P cycle has been developed and integrated into the forest ecosystem model ForSAFE. The model was able to adequately reproduce the measured soil water chemistry, tree biomass (wood and foliage), and the biomass nutrient concentrations at a spruce site in southern Sweden. Both model and measurements indicated that the site showed signs of P limitation at the time of the study, but the model predicted that it may return to an N-limited state in the future if N deposition declines strongly. It is implied by the model that at present time, the plant takes up 0.50 g P m(-2) y(-1) of which 80% comes from mineralization and the remainder comes from net inputs, i.e. deposition and weathering. The sorption/desorption equilibrium of P contributed marginally to the supply of bioavailable P, but acted as a buffer, particularly during disturbances.

  • 947.
    Zandén Ljungmark, Mimi
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Razna National Park: - a selection of excursion destinations2012Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Different areas in Latvias youngest National Park Rāzna has been visited and analyzed. One objectivewas to find out if ecotourism is a possibility and what improvements need to be made. Latvia has avery old history of nature conservation. Objectives to protect valuable species and habitats for thefuture are influenced by factors such as economy and politics. The laws and regulations concerningenvironmental care are dependent on the processes and conditions that have contributed to formingthem. What is considered normality in Sweden can be completely different in Latvia eventhough theintentions and wished results are the same. The conclusion is that there is potential for ecotourism,although many factors must be considered and disadvantageous situations be avoided in the natureprotecting process.

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  • 948. Zhang, Aoqi
    et al.
    Chen, Yilun
    Zhang, Xiangdong
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Fu, Yunfei
    Structure of Cyclonic Precipitation in the Northern Pacific Storm Track Measured by GPM DPR2020In: Journal of Hydrometeorology, ISSN 1525-755X, E-ISSN 1525-7541, Vol. 21, no 2, p. 227-240Article in journal (Refereed)
    Abstract [en]

    Despite the long existence of theoretical studies, few statistical studies of precipitation characteristics on the northern Pacific storm track have been reported due to lack of observation. Using data from GPM DPR and ERA-Interim, we examined the precipitation features of extratropical cyclones in the northern Pacific storm-track region. Extratropical cyclones were classified into four categories including developing, mature, dissipating, and short-term based on their life stages. Our results show that extratropical cyclones of all categories had a comma rainband and precipitation mostly occurred to the east of the cyclonic center. The extratropical cyclones promote precipitation to the east of their centers, but suppress precipitation to the west. Precipitation to the east of the extratropical cyclones had larger and more condensed droplets, a stronger intensity, and a higher rain top than the local seasonal average, while the opposite characteristics were seen to the west. Our results suggest that the different types of vertical air motion and moisture content in these two regions induced by the frontal structure of extratropical cyclones play important roles in the different impact of extratropical cyclones. Furthermore, the different life stages of extratropical cyclones had different degrees of impact on precipitation: the highest impact in the developing stage, followed by the mature stage, and the weakest impact in the dissipating stage.

  • 949. Zhang, Haicheng
    et al.
    Goll, Daniel S.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Ciais, Philippe
    Guenet, Bertrand
    Huang, Yuanyuan
    Modeling the effects of litter stoichiometry and soil mineral N availability on soil organic matter formation using CENTURY-CUE (v1.0)2018In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 11, no 12, p. 4779-4796Article in journal (Refereed)
    Abstract [en]

    Microbial decomposition of plant litter is a crucial process for the land carbon (C) cycle, as it directly controls the partitioning of litter C between CO2 released to the atmosphere versus the formation of new soil organic matter (SOM). Land surface models used to study the C cycle rarely considered flexibility in the decomposer C use efficiency (CUEd) defined by the fraction of decomposed litter C that is retained as SOM (as opposed to be respired). In this study, we adapted a conceptual formulation of CUEd based on assumption that litter decomposers optimally adjust their CUEd as a function of litter substrate C to nitrogen (N) stoichiometry to maximize their growth rates. This formulation was incorporated into the widely used CENTURY soil biogeochemical model and evaluated based on data from laboratory litter incubation experiments. Results indicated that the CENTURY model with new CUEd formulation was able to reproduce differences in respiration rate of litter with contrasting C: N ratios and under different levels of mineral N availability, whereas the default model with fixed CUEd could not. Using the model with flexible CUEd, we also illustrated that litter quality affected the long-term SOM formation. Litter with a small C: N ratio tended to form a larger SOM pool than litter with larger C: N ratios, as it could be more efficiently incorporated into SOM by microorganisms. This study provided a simple but effective formulation to quantify the effect of varying litter quality (N content) on SOM formation across temporal scales. Optimality theory appears to be suitable to predict complex processes of litter decomposition into soil C and to quantify how plant residues and manure can be harnessed to improve soil C sequestration for climate mitigation.

  • 950. Zhang, Peng
    et al.
    Linderholm, Hans W.
    Gunnarson, Björn E.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Björklund, Jesper
    Chen, Deliang
    1200 years of warm-season temperature variability in central Scandinavia inferred from tree-ring density2016In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 12, no 6, p. 1297-1312Article in journal (Refereed)
    Abstract [en]

    Despite the emergence of new high-resolution temperature reconstructions around the world, only a few cover the Medieval Climate Anomaly (MCA). Here we present C-Scan, a new Scots pine tree-ring density-based reconstruction of warm-season (April-September) temperatures for central Scandinavia back to 850aEuro-CE, extending the previous reconstruction by 250aEuro-years. C-Scan is based on samples collected in a confined mountain region, adjusted for their differences in altitude and local environment, and standardised using the new RSFi algorithm to preserve low-frequency signals. In C-Scan, the warm peak of MCA occurs ca. 1000-1100aEuro-CE, and the Little Ice Age (LIA) between 1550 and 1900aEuro-CE. Moreover, during the last millennium the coldest decades are found around 1600aEuro-CE, and the warmest 10 and 30aEuro-years occur in the most recent century. By comparing C-Scan with other millennium-long temperature reconstructions from Fennoscandia, regional differences in multi-decadal temperature variability, especially during the warm period of the last millennium are revealed. Although these differences could be due to methodological reasons, they may indicate asynchronous warming patterns across Fennoscandia. Further investigation of these regional differences and the reasons and mechanisms behind them are needed.

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