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  • 1. Abbott, P. M.
    et al.
    Austin, W. E. N.
    Davies, S. M.
    Pearce, N. J. G.
    Rasmussen, T. L.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Brendryen, J.
    Re-evaluation and extension of the Marine Isotope Stage 5 tephrostratigraphy of the Faroe Islands region: The cryptotephra record2014In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 409, p. 153-168Article in journal (Refereed)
    Abstract [en]

    Previous studies of marine sequences from the Faroe Islands region have identified a series of coarse-grained tephra horizons deposited during Marine Isotope Stage (MIS) 5. Here we reassess the MIS 5 tephrostratigraphy of the Faroe Islands region and focus on the cryptotephra deposits preserved within the fine-grained fraction of marine core LINK 16. We also extend the record to encompass the late MIS 6 and early MIS 4 periods. A density separation technique, commonly used for tephra investigations in lacustrine settings but rarely applied to marine sediments, is utilised to explore the fine-grained material and EPMA and LA-ICP-MS are employed to determine the major and trace element composition of individual tephra shards. In total, 3 basaltic and 3 rhyolitic Icelandic cryptotephra deposits with homogeneous geochemical compositions are identified - all of which have the potential to act as isochronous tie-lines. Geochemical results highlight that the Grimsvotn volcanic system of Iceland is the predominant source of the basaltic horizons and the Oraefajokull or Torfajokull systems are the likely sources of the rhyolitic deposits. Three of the horizons have been previously recognised in Faroe Islands region marine sequences, with two of these deposits traceable into a Norwegian Sea sequence. An early MIS 4 rhyolitic horizon is the most widespread deposit as it can be traced into the Norwegian Sea and to the south into a record from the Rockall Trough. Basaltic and rhyolitic horizons deposited during late MIS 6 have not been recognised in other sequences and represent new additions to the regional tephrostratigraphy.

  • 2. Cohen, Timothy
    et al.
    Nanson, Gerald
    Jansen, John
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jones, Brian
    Jacobs, Zenobia
    Larsen, Joshua
    May, Jan-Hendrick
    Treble, Pauline
    Price, David
    Smith, Andrew
    Late Quaternary mega-lakes fed by the northern and southern river systems of central Australia: varying moisture sources and increased continental aridity2012In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 356, no Special Issue, p. 89-108Article in journal (Refereed)
    Abstract [en]

    Optically stimulated and thermoluminescence ages from relict shorelines, along with accelerator mass spectrometer 14C ages from freshwater molluscs reveal a record of variable moisture sources supplied by northern and southern river systems to Lake Mega-Frome in southern central Australia during the late Quaternary. Additional lacustrine, palynological and terrestrial proxies are used to reconstruct a record that extends back to 105 ka, confirming that Lakes Mega-Frome and Mega-Eyre were joined to create the largest system of palaeolakes on the Australian continent as recently as 50–47 ka. The palaeohydrological record indicates a progressive shift to more arid conditions, with marked drying after 45 ka. Subsequently, Lake Mega-Frome has filled independently at 33–31 ka and at the termination of the Last Glacial Maximum to volumes some 40 times those of today. Further sequentially declining filling episodes (to volumes 25–10 those of today) occurred immediately prior to the Younger Dryas stadial, in the mid Holocene and during the medieval climatic anomaly. Southern hemisphere summer insolation maxima are a poor predictor of palaeolake-filling episodes. An examination of multiple active moisture sources suggests that palaeolake phases were driven independently of insolation and at times by some combination of enhanced Southern Ocean circulation and strengthened tropical moisture sources.

  • 3. Ekblom, Anneli
    et al.
    Gillson, Lindsey
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Chidoub, Zara
    Rainfall variability and vegetation dynamics of the lower Limpopo Valley, Southern Africa, 500 AD to present2012In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 363, p. 69-78Article in journal (Refereed)
    Abstract [en]

    The long-term responses of vegetation to climate variability are of relevance for predicting present and future vegetation change, and have implications for the management of savanna and riparian ecosystems. This paper explores the links between regional rainfall, hydrology and vegetation dynamics in the savannas and riverine forests of the lower Limpopo Valley, southern Africa, from 800 AD to the present, reviewing palaeoecological data (fossil pollen, spores, diatoms and lithology) from several hydrological systems in Kruger National Park (KNP), South Africa and Limpopo National Park (PNL), Mozambique. The PNL-KNP records show that riverine arboreal taxa expanded during wetter periods, including 800-1400 AD and after 1800 AD. Between 1400 and 1800 AD, grasses, savanna taxa and generalist taxa were favored over riparian taxa, a change that is linked with the onset of dry spells in the region (corresponding to the so-called Little Ice Age). The most extreme drought events around 1700 AD resulted in a marked decline of riparian forest taxa near Lake Mapimbi, KNP. In contrast, many water-scarce sequences away from the riverine environment, such as Radio Pan, Mafayeni Pan, Malahlapanga Pan and Lake Makwadzi show stable grassland vegetation throughout the last 1200 years. The results demonstrate the resilience of the grassland-savanna ecosystems to projected climate change with warmer and overall drier climate. The riverine forests are predicted to be more vulnerable especially as more extreme weather events are projected.

  • 4.
    Finné, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Bar-Matthews, Miryam
    Geological Survey of Israel.
    Rapid climatic shifts in southern Greece during Marine Isotope Stages 5a-3In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616XArticle in journal (Refereed)
    Abstract [en]

    We present a speleothem based stable isotope (δ13C, δ18O) record from southern Greece covering a period from 79±5.8 ka to 37±3 ka, i.e. the end of Marine Isotope Stage (MIS) 5a and large parts of MIS 4 and MIS 3. The record from Glyfada Cave provides a U-Th dated proxy paleoclimate record from Greece, covering this time period, and shows that the climate over the Peloponnese rapidly responded to interstadial and stadial conditions over Greenland. During stadial (interstadial) conditions colder (warmer) and drier (wetter) conditions are reflected by depleted (enriched) δ13C-values in the speleothems from Glyfada Cave. Depositional hiatuses in Glyfada Cave correspond to periods of severe cold conditions in the northern Hemisphere and reduced precipitation over the Peloponnese most likely due to a southward displacement of Mediterranean cyclone tracks due to expanding northern ice sheets and increased snow cover over the European continent. By comparing our independently dated record with previously published pollen studies from Greece a time lag between the records from Ioannina and Megali Limni and Glyfada is evident. The match in time between the Glyfada speleothem record and the Tenaghi Philippon pollen record, when tuned to NGRIP, is rather precise.

  • 5. Fritz, Michael
    et al.
    Wetterich, Sebastian
    Schirrmeister, Lutz
    Meyer, Hanno
    Lantuit, Hugues
    Preusser, Frank
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Pollard, Wayne H.
    Eastern Beringia and beyond: Late Wisconsinan and Holocene landscape dynamics along the Yukon Coastal Plain, Canada2012In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 319, p. 28-45Article in journal (Refereed)
    Abstract [en]

    Terrestrial permafrost archives along the Yukon Coastal Plain (northwest Canada) have recorded landscape development and environmental change since the Late Wisconsinan at the interface of unglaciated Beringia (i.e. Komakuk Beach) and the northwestern limit of the Laurentide Ice Sheet (i.e. Herschel Island). The objective of this paper is to compare the late glacial and Holocene landscape development on both sides of the former ice margin based on permafrost sequences and ground ice. Analyses at these sites involved a multi-proxy approach including: sedimentology, cryostratigraphy, palaeoecology of ostracods, stable water isotopes in ground ice, hydrochemistry. and AMS radiocarbon and infrared stimulated luminescence (IRSL) dating. AMS and IRSL age determinations yielded full glacial ages at Komakuk Beach that is the northeastern limit of ice-free Beringia. Herschel Island to the east marks the Late Wisconsinan limit of the northwest Laurentide Ice Sheet and is composed of ice-thrust sediments containing plant detritus as young as 16.2 cal ka BP that might provide a maximum age on ice arrival. Late Wisconsinan ice wedges with sediment-rich fillings on Herschel Island are depleted in heavy oxygen isotopes (mean delta O-18 of -29.1 parts per thousand); this, together with low d-excess values, indicates colder-than-modern winter temperatures and probably reduced snow depths. Grain-size distribution and fossil ostracod assemblages indicate that deglaciation of the Herschel Island ice-thrust moraine was accompanied by alluvial, proluvial. and eolian sedimentation on the adjacent unglaciated Yukon Coastal Plain until similar to 11 cal ka BP during a period of low glacio-eustatic sea level. The late glacial-Holocene transition was marked by higher-than-modern summer temperatures leading to permafrost degradation that began no later than 11.2 cal ka BP and caused a regional thaw unconformity. Cryostructures and ice wedges were truncated while organic matter was incorporated and soluble ions were leached in the thaw zone. Thermokarst activity led to the formation of ice-wedge casts and deposition of thermokarst lake sediments. These were subsequently covered by rapidly accumulating peat during the early Holocene Thermal Maximum. A rising permafrost table. reduced peat accumulation, and extensive ice-wedge growth resulted from climate cooling starting in the middle Holocene until the late 20th century. The reconstruction of palaeolandscape dynamics on the Yukon Coastal Plain and the eastern Beringian edge contributes to unraveling the linkages between ice sheet. ocean, and permafrost that have existed since the Late Wisconsinan.

  • 6. Gilg, H. Albert
    et al.
    Hall, Adrian M.
    University of St Andrews, Scotland, UK.
    Ebert, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Cool kaolins in Finland2013In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 392, p. 454-462Article in journal (Refereed)
    Abstract [en]

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

  • 7.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Late Glacial and Holocene paleoceanography in the Skagerrak from high-resolution grain size records2005In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 222, no 3-4, p. 344-369Article in journal (Refereed)
    Abstract [en]

    High-resolution grain size analyses of the AMS 14C-dated, 32 m long core MD99-2286 from the northeastern Skagerrak were performed in order to study late Glacial and Holocene paleoceanographic and sedimentary changes. All ages in this study are given in calibrated thousand years before present (= AD 1950), abbreviated ‘kyr’, unless otherwise noted.

    The distinct ending of IRD (ice rafted debris) in core MD99-2286, which was retrieved from a location down current from the final calving ice margin in the region, indicates that iceberg calving in the Skagerrak ended between 10.6 and 10.2 kyr.

    A clay-rich sequence in core MD99-2286, deposited between 11.3 and 10.3 kyr, is attributed to outflow from the Baltic basin across south central Sweden. The sequence is correlated to similar units from cores along the Swedish west coast. The onset of this clay-rich deposition occurs progressively later in cores further south along the coast, supporting a previous hypothesis that differential glacio-isostatic uplift caused a southward migration of the Baltic outflow from the Otteid-Stenselva to the Göta Älv outlet.

    A distinct coarsening towards younger sediments in core MD99-2286 indicates a hydrographic shift at 8.5 kyr, which is correlated to a shift previously reported in the Skagerrak, Kattegat and the Norwegian Channel. This shift reflects the establishment of the modern circulation system in the eastern North Sea, as a consequence of the opening of the English Channel and the Danish straits and increased Atlantic water inflow, and the subsequent development of the South Jutland Current. A general trend of coarsening, poorer sorting and increasing variability from 8.5 kyr until the present indicates increasing strength and influence of the variable South Jutland Current.

    A series of changes from ca. 6.3 to ca. 3.8 kyr in core MD99-2286 reflects strengthening of the Jutland Current towards the present day sedimentation system in the Skagerrak–Kattegat. These changes are correlated to previously reported hydrographic shifts at 5.5 14C years BP in the Skagerrak and at 4.0 14C years BP in the Kattegat. It is suggested that these shifts were separate features of a transitional period related to strengthening of the current system. The resulting changes are differently manifested in different parts of the Skagerrak–Kattegat, due to the complex circulation system.

    The last 800 years are characterised by poorly sorted sediments with a relatively high and variable proportion of coarse material, reflecting a circulation system significantly modified by regional climatic conditions, especially the general wind directions and storm frequency over the southern North Sea.

  • 8.
    Hall, Adrian
    et al.
    University of St Andrews, Scotland, UK.
    Ebert, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Cenozoic microfossils in northern Finland: Local reworking or distant wind transport?2013In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 388, p. 1-14Article in journal (Refereed)
    Abstract [en]

    Allochthonous Cenozoic microfossils have been reported from Late Pleistocene lake and mire host sediments across an area of > 30,000 km2 in northern Finland. Two main groups of microfossils are recognised: Palaeogene marine diatoms, silicoflagellates and ebridians that include taxa from around the time of the Palaeocene–Eocene Thermal Maximum and Pliocene to early Pleistocene freshwater diatoms. The presence of these microfossils has been regarded as evidence that Eocene marine and late Neogene freshwater sediments formerly existed on the shield surface. Both groups have been referred to frequently in reconstructions of the sea level, tectonic and erosion history of the northern Fennoscandian shield. The questions raised by the presence of allochthonous Cenozoic microfossils in northern Finland are, however, strongly resonant of the debate over the biota, origin and age of the Pliocene Sirius Group in Antarctica where competing hypotheses have been put forward of local deposition and reworking versus distant wind transport of marine diatoms from the continental shelf.

    This review explores alternative origins for the allochthonous Cenozoic microfossils in northern Finland. Local reworking of Palaeogene marine sediments during Pleistocene glaciation is unlikely, as no source rocks of Palaeogene age are known from the shield surface or from surrounding sedimentary basins in the Baltic and White Sea. Moreover, at all sites except Akanvaara, the marine diatom taxa cover wide age ranges and occur only as minor components in diatom assemblages that are dominated by Quaternary freshwater taxa. Local reworking of Pliocene–Pleistocene freshwater diatoms is, however, compatible with the widespread survival of pre-Pleistocene deep weathering although no in situ or unmixed, ice-rafted Pliocene–Pleistocene lacustrine sediment has yet been found. An alternative origin for the marine Palaeogene microfossils by distant wind transport is proposed. In this hypothesis, Palaeogene diatomites on the Barents Sea shelf were exposed to deep glacial and fluvioglacial erosion during the Pliocene and Early Pleistocene and in low sea level stages of the Middle and Late Pleistocene. Intense wind action acting on comminuted mudstones on outwash plains carried dust including microfossils into northern Fennoscandia to be deposited by rain-out in lakes and wetlands. This material may have been later further recycled by glacial and meltwater transport and more localised wind action, processes that also may help to account for the distribution of Eemian marine diatoms well beyond Eemian shorelines. The distant wind transport hypothesis implies that the presence of marine Palaeogene diatoms on the shield surface in northern Finland cannot be regarded as vestiges of former marine sediments and so do not constrain the tectonic and geomorphic history of the northern Fennoscandian shield in the Cenozoic.

  • 9.
    Hall, Adrian M.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Gilg, H. Albert
    Fallick, Anthony E.
    Merritt, Jon W.
    Kaolins in gravels and saprolites in north-east Scotland: Evidence from stable H and O isotopes for Palaeocene-Miocene deep weathering2015In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 424, p. 6-16Article in journal (Refereed)
    Abstract [en]

    Stable isotope ratios can provide important evidence for estimating groundwater temperatures during the formation of clay minerals in response to chemical weathering of rocks at the landsurface. In this paper, we investigate weathering kaolins found in Buchan, NE Scotland. Stable oxygen and hydrogen isotopes for kaolins from weathered clasts in post-Cretaceous fluvial gravels and from clay-rich saprolites developed in Dalradian metamorphic and Caledonian igneous rocks indicate weathering under warm groundwater temperatures of 23 +/- 5 degrees C. Comparisons with Cenozoic palaeotemperatures derived from North Sea sediments indicate that weathering took place under humid tropical climates of the Palaeocene-Eocene. The >25 m deep weathering profiles in the Buchan Gravels indicate that these coarse, quartzite- and flint-bearing gravels are older than previously thought and were likely deposited by rivers which also fed thick Palaeocene-Early Eocene deep-water sand fans in the western North Sea basin. A later phase of kaolin weathering at lower temperatures of 15 +/- 5 degrees C took place in the Middle Miocene. Kaolinitic weathering remnants are largely confined to elevations of >100 m in eastern Buchan and define a well-preserved, deeply weathered Cenozoic landscape in north-east Scotland.

  • 10. Hints, Olle
    et al.
    Delabroye, Aurelien
    Nolvak, Jaak
    Servais, Thomas
    Uutela, Anneli
    Wallin, Åsa
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Biodiversity patterns of Ordovician marine microphytoplankton from Baltica: Comparison with other fossil groups and sea-level changes2010In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 294, no 04-mar, p. 161-173Article in journal (Refereed)
    Abstract [en]

    Based on the extensive literature on Ordovician acritarchs, biodiversity curves of marine microphytoplankton of the palaeocontinent Baltica have been compiled. The dataset is derived from more than 100 publications and includes over 600 species whose ranges can be used in diversity analysis. Stratigraphically well-constrained data from the Rapla and Mannamaa boreholes, northern Estonia, are analysed separately in order to provide additional information on the Middle to Late Ordovician microphytoplankton evolution on shallow shelf settings. The total species diversity and normalised diversity curves based on range-through data show a slight decrease from the Tremadocian to Floian, which may partly be attributed to limited data available. A continuous increase in diversity from the base of the Dapingian to late Darriwilian - early Katian can be observed, with highest total diversity approaching 250 species in the Keila Regional Stage. The highest appearance rates are recorded in the Dapingian and Darriwilian. Diversity progressively diminished after the early Katian with a more pronounced decrease in the upper Ordovician Porkuni Regional Stage, corresponding to the Hirnantian. A significant faunal turnover took place in the uppermost Ordovician Pirgu and Porkuni stages, with high extinction rates as well as the appearance of many acritarch taxa that are typical of the Silurian floras. The phytoplankton diversity curves match rather well with those of several other fossil groups in Baltica, notably brachiopods and ostracods. Comparison with other palynomorphs reveals both similarities and differences. The chitinozoans show the highest diversities in the upper Darriwilian, but their later decline predates that of acritarchs. A rapid diversification of scolecodonts (jawed polychaetes) can also be observed in the upper Darriwilian. However, unlike acritarchs or chitinozoans, their diversity continues to increase until the uppermost Katian. The acritarch diversity changes are analysed and discussed in the context of palaeogeographic (northwards drifting of Baltica) and palaeoclimatologic changes (rising sea levels up to the middle part of the Upper Ordovician). The increasing diversity of the phytoplankton not only roughly correlates with the Baltic and global sea-level changes, but also with the diversification of marine invertebrate groups.

  • 11. Houben, Alexander J. P.
    et al.
    van Mourik, Caroline A.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Montanari, Alessandro
    Coccioni, Rodolfo
    Brinkhuis, Henk
    The Eocene-Oligocene transition: Changes in sea level, temperature or both?2012In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 335, p. 75-83Article in journal (Refereed)
    Abstract [en]

    The Eocene-Oligocene Transition (EOT similar to 34 Ma) reflects the onset of major Antarctic glaciation. The primary geochemical signature of the EOT is two similar to 300 kyr spaced shifts in increasing deep-sea oxygen isotope values, possibly reflecting both global cooling a nd/or increasing ice volume. A way to assess the respective contribution of continental ice is to quantify concomitant glacio-eustatic sea level change. This is usually expressed in relatively shallow marine depositional settings. One potentially suitable region is in the Vicentinian Alps, NE Italy, where marginal marine deposits document sea level changes during the;EOT. By correlating stable isotope-, bio- and magnetostratigraphic information between three distant regions, we are able to relate the shallow marine sections to the Pacific oxygen isotope record from Ocean Drilling Program (ODP) Site 1218 of Coxall et al. (2005). Microfacies, sedimentological, and biotic analysis suggests that associated with the first isotope shift (EOT-1) sea level fell similar to 20 m, and with the ultimate shift, the Oligocene Isotope Event 1 (Oi-1) sea level fell some 50-60 m. Distribution patterns of temperature sensitive dinoflagellates from a coeval central Italian section reveal that the early stages of the EOT were accompanied by sea surface cooling, whereas no sustained cooling is noted in association with the Oi-1. This suggests that the initial EOT shift(s) reflect a mixed signal of ice volume and temperature whereas the Oi-1 primarily reflects expansion of the Antarctic cryosphere.

  • 12.
    Kaislahti Tillman, Päivi
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holzkämper, Steffen
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Sannel, A. Britta K.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Loader, Neil J.
    Robinson, Iain
    Long-term climate variability in continental subarctic Canada: A 6200-year record derived from stable isotopes in peat2010In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 298, no 3, p. 235-246Article in journal (Refereed)
    Abstract [en]

    The rapid warming of arctic regions during recent decades has been recorded by instrumental monitoring, but the natural climate variability in the past is still sparsely reconstructed across many areas. We have reconstructed past climate changes in subarctic west-central Canada. Stable carbon and oxygen isotope ratios (δ13C, δ18O) were derived from a single Sphagnum fuscum plant component; α-cellulose isolated from stems. Periods of warmer and cooler conditions identified in this region, described in terms of a “Mediaeval Climatic Anomaly” and “Little Ice Age” were registered in the temperature reconstruction based on the δ13C record. Some conclusions could be drawn about wet/dry shifts during the same time interval from the δ18O record, humification indices and the macrofossil analysis. The results were compared with other proxy data from the vicinity of the study area. The amplitude of the temperature change was similar to that in chironomid based reconstructions, showing c. 6.5±2.3°C variability in July temperatures during the past 6.2 ka.

  • 13.
    Leon-Rodriguez, Lizette
    et al.
    Dept Earth Science, Rice University, Texas.
    Dickens, Gerald R.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Constraints on ocean acidification associated with rapid and massive carbon injections: The early Paleogene record at ocean drilling program site 1215, equatorial Pacific Ocean2010In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 298, p. 409-420Article in journal (Refereed)
    Abstract [en]

    Massive amounts of 13C-depleted carbon rapidly entered the ocean more than once during the Early Paleogene, providing a geological framework for understanding future perturbations in carbon cycling, including ocean acidification. To assess the number of events and their impact on deep-sea carbonate accumulation, we investigated a 42 m thick unit of Upper Paleocene–Lower Eocene carbonate ooze, which was deposited on a subsiding flank of the East Pacific Rise. Age control was established using calcareous nannofossils and planktonic foraminifera, as well as stable carbon isotopes of bulk carbonate. Carbonate content, foraminiferal test fragmentation, and planktonic/benthic foraminiferal ratio were measured to ascertain changes in carbonate dissolution. Based on these analyses, carbonate preservation generally increased from the late Paleocene (55.4 Ma) through the early Eocene (51.4 Ma), after which it became poor to negligible. This trend was punctuated by three (and probably four) short-term intervals characterized by carbonate dissolution and negative δ13C excursions. These horizons almost assuredly correspond to the PETM (~55.5 Ma), H1/ETM-2 (~53.7 Ma), I1 (~53.2 Ma), and K/X (~52.5 Ma) events. Carbonate preservation also increased within 200 kyr after two and perhaps all four intervals. We suggest the lysocline and calcite compensation depth (CCD) generally deepened between 55.4 and 51.4 Ma but shoaled and subsequently overcompensated during and after three and likely four intervals of rapid and massive carbon injection. Oxygen isotope data further suggests these intervals were times of anomalous warmth. 

  • 14.
    Löwemark, Ludvig
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Nara, Masakazu
    Morphology, ethology and taxonomy of the ichnogenus Schaubcylindrichnus: Notes for clarification2010In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 297, no 1, p. 184-187Article in journal (Refereed)
    Abstract [en]

    Two recent publications dealing with the trace fossil Schaubcylindrichnus (Frey and Howard, 1981) in Cenozoic outcrops have been published independently in the same year (Löwemark and Hong, 2006; Nara, 2006). The two studies came to similar conclusions regarding morphology, somewhat different conclusions with respect to the behavior of the trace maker, and diametrically opposed conclusions regarding the ichnotaxonomy. The two studies (Löwemark & Hong, 2006; Nara, 2006) were published in parallel without taking the other into consideration. During the 2nd International Ichnological Congress in Krakow 2008 the authors had the opportunity to compare their results (Löwemark and Nara, 2008). We therefore feel that a clarifying note is timely.

    Morphologically, S. coronus is shown to typically consist of three distinct parts: a bundle of thickly lined, often crossing tubes that have been constructed after each other, a feeding funnel connected to one end of the burrow system, and a fecal mound connected to the other end (Nara, 2006). Löwemark & Hong (2006) introduced a new ichnospecies, S. formosus, based on the differences in morphology to the original description of S. coronus that outlined a congruent bundle as the typical form. However, subsequent comparison of S. formosus with Nara's (2006) descriptions of S. coronus showed that the former can be accommodated in the latter. S. formosus therefore should be considered as a junior synonym of S. coronus and be abandoned.

  • 15.
    Löwemark, Ludvig
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hanebuth, T.J.J.
    Alfred Wegener Institute for Polar and Marine Research.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Late Quaternary spatial and temporal variability in Arctic deep-sea bioturbation and its relation to Mn cycles2012In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 365-366, p. 192-208Article in journal (Refereed)
  • 16. Margalef, O.
    et al.
    Martínez Cortizas, A.
    Kylander, Malin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pla-Rabes, S.
    Cañellas-Boltà, N.
    Pueyo, J. J.
    Sáez, A.
    Valero-Garcés, B. L.
    Giralt, S.
    Environmental processes in Rano Aroi (Easter Island) peat geochemistry forced by climate variability during the last 70 kyr2014In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 414, p. 438-450Article in journal (Refereed)
    Abstract [en]

    We analyze the geochemistry of Rano Aroi mire record (Easter Island) using bulk peat composition (C, N, S) and stable isotopes (delta C-13, delta N-15, delta S-34) and major, minor and trace elemental compositions obtained by ICP-AES (Al, Ti, Zr, Sc, V, Y, Fe, Mn, Th, Ba, Ca, Mg and Sr). Peat geochemistry and the pollen record are used to reconstruct the environmental changes during the last 70 kyr BP. Principal component analysis on ICP-AES data revealed that three main components account for the chemical signatures of the peat. The first component, characterized by lithogenic elements (combined signal of V. Al, Sc, Y, Cr, Cd, Ti, Zr and Cu), evidences long-term changes in the basal fluxes of mineral material into the mire. This component, in combination with stable isotopes and pollen data suggests a link between soil erosion and vegetation cover changes in the Rano Aroi watershed. The second component is identified by the signal of Fe, Mn, Th, Ba, Zr and Ti, and is indicative of strong runoff events during enhanced precipitation periods. The third component (tied mainly to Ca, Sr and Mg) reflects a strong peat oxidation event that occurred during an arid period with more frequent droughts, sometime between 39 and 31 kyr BP. Correlation coefficients and a multiple regression model (PCR analysis) between peat organic chemistry and the principal components of ICP-AES analysis were calculated. Isotope chemistry of the peat organic matter further contributes to define Rano Aroi environmental history: delta C-13 data corroborates a vegetation shift documented by the palynological record from C-4 to C-3 between 55 and 45 cal kyr BP; the delta N-15 record identifies periods of changes in mire productivity and denitrification processes, while the delta S-34 peat signature indicates a marine origin of S and significant diagenetic cycling. The geochemical and environmental evolution of Rano Aroi mire is coherent with the regional climatic variability and suggests that climate was the main forcing in mire evolution during the last 70 kyr BP. The coupling of geochemical and biological proxies improves our ability to decipher depositional processes in tropical and subtropical peatlands and to use these sequences for paleoenvironmental and paleoclimate reconstructions.

  • 17.
    Massuanganhe, Elidio A.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. Universidade Eduardo Mondlane, Moçambique.
    Berntsson, Annika
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Westerberg, Lars-Ove
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Christiansson, Marie
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Preusser, Frank
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Bjursäter, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Achimo, Mussa
    Palaeogeography and dynamics of the deltaic wetland of Save River, Mozambique2018In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 489, p. 64-73Article in journal (Refereed)
    Abstract [en]

    Many mangrove wetland systems in deltaic environments are negatively affected by massive sedimentation fromriver inflows. In this paper we use the example of the Save River delta to assess the palaeogeographic distributionof mangrove wetlands and to analyze their dynamics. To track past occurrences of mangrove wetlands in thestudy area we have integrated sedimentological data with siliceous microfossil analysis combined with AMSradiocarbon and OSL dating. The results show a fine-grained deposit with an approximate thickness of 2 m,present at different sampling sites. In the upper deltaic plain, the deposit is interbedded between sand layers,while in the lower deltaic plain the deposit occupies the uppermost stratigraphic position. In most of thesampling sites the deposit shows a succession with brackish-marine diatoms at the bottom of the sequence whilethe upper part shows only scattered occurrences. Based on sedimentological and microfossil characteristics wehave interpreted the layer to represent a mangrove wetland deposit. The development of the deposit in the studyarea is suggested to have been initiated around 3100 cal. yr BP, induced by sea-level rise. Thereafter, the developmentfollowed the combined effect of a sea-level fall and delta progradation processes. In some areas,particularly in the proximal part of the delta, the mangrove deposit has developed progressively on top of thedelta-front. From around 1300 years ago (OSL) onwards, massive alluvial sedimentation impacted the mangroveecosystem. However, the retreat of mangrove wetland coincided with a regional fall of sea level. At the edges ofthe alluvial deposit, the current mangrove ecosystem has reclaimed the habitat in some sectors where gullyerosion has exposed the once extinct mangrove habitat.

  • 18. Mays, Chris
    et al.
    Steinthorsdottir, Margret
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stilwell, Jeffrey D.
    Climatic implications of Ginkgoites waarrensis Douglas emend. from the south polar Tupuangi flora, Late Cretaceous (Cenomanian), Chatham Islands2015In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 438, p. 308-326Article in journal (Refereed)
    Abstract [en]

    The flora of the Cenomanian-Turonian (ca. 96-90 Ma) Tupuangi Formation, Chatham Islands, New Zealand, was inhabiting a region well within the south polar circle (similar to 70-80 degrees S) during the early Late Cretaceous, an interval characterised by extreme global greenhouse conditions. The Tupuangi flora offers a unique perspective into an ecological and environmental setting which has no extant analogue, whilst providing proxies of polar palaeoclimatic conditions during a phase of extreme global warming. Ginkgoites waarrensis Douglas, 1965 (emended herein), a species known previously from a single occurrence in Australia, is an abundant element of the Tupuangi flora. Forty-five leaf samples from three localities are reported, and a systematic treatment of this species revealed a wide morphological range. In contrast to the exclusively riparian niche of more recent members of Ginkgoales, associated sedimentological and palaeoecological data suggest that this species had an ecological preference for regularly disturbed, coastal deltaic settings. Herein, we review the geographic and stratigraphic distributions of Cretaceous Gondwanan ginkgoalean leaf taxa. An increasing diversity of this group from the Early Cretaceous to the early Late Cretaceous supports a broader trend of floral provincialisation throughout this interval, most likely driven by concurrent global transgression and active tectonic extension across southern Gondwana. Carbon dioxide has been inferred as a primary proximate cause of the mid-Cretaceous global greenhouse. The leaf cuticles of Ginkgoites waarrensis were utilised to approximate atmospheric carbon dioxide (pCO(2)) during the Cenomanian. Stomatal index (SI) data were collected from ten specimens, and the stomatal ratio method yielded a semi-quantitative pCO(2) estimate of 1150-1350 ppmv, which is consistent with modelled and proxy estimates of the Cenomanian. The present study explores the inherent limitations of the transfer function method for estimating CO2 when applied to taxa with very low SI values, such as G. waarrensis. In addition to pCO(2), temperature and irradiance are identified as environmental variables which may have systematically promoted the low SI of G. waarrensis, but their combined influence is likely mitigated by the relatively high temperature of this region during the mid-Cretaceous and the high summer insolation at polar latitudes.

  • 19.
    Moberg, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Brattström, Gudrun
    Stockholm University, Faculty of Science, Department of Mathematics.
    Prediction intervals for climate reconstructions with autocorrelated noise: An analysis of ordinary least squares and measurement error methods2011In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 308, no 3-4, p. 313-329Article in journal (Refereed)
    Abstract [en]

    The estimation of past climate variations is a statistical prediction problem, where climate proxy data are calibrated against instrumental observations. Although noise is always present in both instrumental and proxy data, motivating the use of so-called errors-in-variables or measurement error methods, such methods have not yet been widely accepted by palaeoclimatologists. We define a univariate measurement error model that allows for white noise in instrumental and red noise in proxy data, and derive new formulae to construct prediction intervals for past climate values. The new method can be applied to either unsmoothed data or to data smoothed after calibration. Using synthetic simulated data, we demonstrate that the new formulae perform well for noise levels and calibration period lengths typical of many palaeoclimate series, in particular tree-rings and other annually resolved data. With an example, using a recently published 500-year long temperature reconstruction, we demonstrate that conclusions about the statistical significance of the difference between the present and past climates may be incorrect if the noise is not adequately modeled.

  • 20.
    Plikk, Anna
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Helmens, Karin F.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Fernández-Fernández, María
    Kylander, Malin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Löwemark, Ludvig
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Salonen, J. Sakari
    Väliranta, Minna
    Weckström, Jan
    Development of an Eemian (MIS 5e) Interglacial palaeolake at Sokli (N Finland) inferred using multiple proxies2016In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 463, p. 11-26Article in journal (Refereed)
    Abstract [en]

    A 12 m long lacustrine record from Sokli, N Finland, was analyzed for diatoms, non-pollen palynomorphs, macrofossils, pollen and geochemistry in order to reconstruct the development of a high-latitude Eemian lake and investigate the influence of climatic and environmental changes on the lake ecosystem. Based on this multi-proxy dataset we distinguished five major lake phases in the lake's evolution. An initial minerogenic, glacio-lacustrine phase was followed by an organic-rich early Eemian lake phase characterized by anoxic bottom waters, high seasonality and rising nutrient levels. A long open water season, pronounced summer stratification and high productivity characterized the following early mid-Eemian lake phase, corresponding to the Eemian thermal maximum. During the late mid-Eemian lake phase decreasing water depths due to infilling and extensive mixing of the water column resulted in less stable summer stratification and decreased anoxia. The late-Eemian lake phase was characterized by shallow and dynamic conditions and a cooling climate. Superimposed on these general trends are two events characterized by colder and more arid conditions, that possibly match cold and arid events registered in palaeolimnological records on the European continent. In general, the multi-proxy record reflects a nutrient rich lake, where changes in mixing regime associated with climatic forcing and lake level changes asserted a major impact on the aquatic assemblages. The changes in the aquatic assemblages reflect the major patterns of climate change that took place during the Eemian in northern Europe; i.e. a rapid warming and high seasonality during the early Eemian, decreased seasonality during the mid Eemian and a cooling late Eemian with increased seasonality. The high latitude Sokli Eemian palaeolake record lengthens the latitudinal extent of Eemian terrestrial records across Europe, adding to the understanding of climatic gradients and drivers over Europe.

  • 21.
    Raúl Sitoe, Sandra
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. University of Eduardo Mondlane, Mozambique.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Norström, Elin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Westerberg, Lars-Ove
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Late Holocene sea-level changes and paleoclimate recorded in Lake Lungué, southern Mozambique2017In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 485, p. 305-315Article in journal (Refereed)
    Abstract [en]

    We report on late Holocene paleoenvironmental and sea-level changes in southern Mozambique, based on analysis of diatom stratigraphy, mineral magnetic susceptibility, Saturation Isothermal Remnant Magnetization (SIRM) and organic carbon content in a sediment core from Lake Lungué, located ca. 30 km north of Xai Xai City in the Limpopo River floodplain. Eleven radiocarbon dates performed on terrestrial shells allowed establishment of an age-depth model. High content of brackish-marine taxa, especially Diploneis suborbicularis and Navicula yarrensis, suggests that the Lake Lungué basin was part of the Indian Ocean coastal zone between ca. 740 and 910 CE, suggesting higher relative sea-level during this phase. A similar diatom distribution in older parts of the sequence, of unknown age, indicates that the site was connected to the Indian Ocean also at some stage prior to 740 CE. Between ca. 910 and 1130 CE the basin was under a combined effect of sporadic marine water influx and Limpopo River actions. A freshwater lake was established sometime between 1130 and 1360 CE, when the basin became less affected by marine influences due to lower sea-levels. Instead, the lake system was more influenced by Limpopo River meandering dynamics and flooding events, and eventually isolated into a more or less independent lake ecosystem where diatom diversity most likely responded to lake levels fluctuations driven by shifts in relative humidity and rainfall amounts within the floodplain and also from upstream sources. During this phase, high abundance of freshwater planktonic species, i.e. Aulacoseira granulata and A. ambigua, indicates high lake levels and wetter conditions dated to ca. 1360–1560 CE. From 1560 CE until present, the lake has been subject to drier conditions and higher evaporation as indicated by lower lake levels, reported by a decline in freshwater planktonic taxa and increase in brackish taxa, e.g. Amphora robusta.

  • 22. Rodriguez-Tovar, Francisco J.
    et al.
    Löwemark, Ludvig
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pardo-Iguzquiza, Eulogio
    Zoophycos cyclicity during the last 425 ka in the northeastern South China Sea: Evidence for monsoon fluctuation at the Milankovitch scale2011In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 305, no 1-4, p. 256-263Article in journal (Refereed)
    Abstract [en]

    In a deep-sea piston core, covering the last 425 ka from the northeastern South China Sea, power spectrum analysis of several core data from sediment parameters has been conducted and compared with that obtained from time-series analysis of the distribution of the trace fossil Zoophycos through the core. Power spectra show a more or less well developed cyclical pattern, with similar cyclostratigraphic patterns for sand and carbonate content, oxygen isotopes and Zoophycos distribution, but different for carbon isotopes and total organic carbon content (TOC). Temporal calibration allows the recognition of Milankovitch orbital-scale cycles, with a duration of 111-100 ka for short-term eccentricity, 63-55 ka for the combined effect of both precession and obliquity, 42-40 ka for the obliquity cycle, and 28-21 ka for the precessional cycle band. The variable Milankovitch-scale cyclicity suggests the influence of a complex interaction of variable processes. East Asian monsoon variability at the Milankovitch orbital-scale cycles could determine variations in environmental conditions, including changes in the organic material reaching the sea floor, and in turn influencing the cyclical occurrence of the Zoophycos trace makers. The cyclicity of Zoophycos is of special interest to basin analysis, where Zoophycos has the potential of being used as a proxy for cyclical monsoon fluctuations at the Milankovitch scale.

  • 23.
    Steinthorsdottir, Margret
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jeram, Andrew J.
    McElwain, Jennifer C.
    Extremely elevated CO(2) concentrations at the Triassic/Jurassic boundary2011In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 308, no 3-4, p. 418-432Article in journal (Refereed)
    Abstract [en]

    Although progress has been made in recent years in reconstructing the environmental conditions at the Triassic/Jurassic Boundary (TJB), published records of atmospheric CO(2) concentrations have been of low resolution and/or based on multi-taxon estimates. This is addressed here by reconstructing CO(2) concentrations across the TJB using stomatal frequencies of four phylogenetically and ecologically distinct plant groups from two depositionally, geographically and taphonomically separate boundary sections in East Greenland and Northern Ireland, with stomatal proxy methods and regression analysis. The resulting CO(2) records then are compared with an additional existing TJB record from a geological section in Sweden. The final results indicate that pre-TJB (Rhaetian), the CO(2) concentration was approximately 1000 ppm, that it started to rise steeply pre-boundary and had doubled to around 2000-2500 ppm at the TJB. The CO(2) concentration then remained elevated for some time post-boundary, before returning to pre-TJB levels in the Hettangian. These results are in very good accordance with published C-isotope, fire and leaf dissection records, and clearly indicate steeply rising and lingering CO(2) concentration at the TJB.

  • 24.
    Steinthorsdottir, Margret
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Vajda, Vivi
    Pole, Mike
    Global trends of pCO(2) across the Cretaceous-Paleogene boundary supported by the first Southern Hemisphere stomatal proxy-based pCO(2) reconstruction2016In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 464, p. 143-152Article in journal (Refereed)
    Abstract [en]

    Reliable reconstructions of atmospheric carbon dioxide concentrations (pCO(2)) are required at higher resolution than currently available to help resolve the relationship between mass extinctions and changes in palaeo-pCO(2) levels. Such reconstructions are needed: 1, at a high temporal resolution for constraining the pre- and post extinction atmospheres; and 2, at a sufficient spatial resolution to constrain potential inter-hemispheric differences. Here we estimate pCO(2) based on fossil Lauraceae leaf cuticle specimens derived from three localities with strata spanning the latest Cretaceous to the mid-Paleocene, including a new Cretaceous-Paleogene boundary (K-Pg) locality, in New Zealand. We use two independent methods of stomatal density-based pCO(2) reconstructions; a transfer function calibrated using herbarium material and the stomatal ratio method, producing three calibration sets. Our results based on the mean values of each of the three calibration methods indicate pCO(2) ranging between ca. 460 and 650 ppm during the latest Cretaceous, falling precipitously to average values between ca. 360 and 430 ppm across the K-Pg boundary, and further to ca. 305-320 ppm in the mid-Paleocene. A 'spike' of extremely high pCO(2) at the K-Pg could not be confirmed, but our results are, nonetheless, consistent with previously published pCO(2) records from the Northern Hemisphere, and show that stomatal density worldwide was responding to significant changes in pCO(2) across the K-Pg.

  • 25.
    Steinthorsdottir, Margret
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Swedish Museum of Natural History, Sweden.
    Vajda, Vivi
    Pole, Mike
    Significant transient pCO(2) perturbation at the New Zealand Oligocene-Miocene transition recorded by fossil plant stomata2019In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 515, p. 152-161Article in journal (Refereed)
    Abstract [en]

    The reorganisation of Earth's climate system from the Oligocene to the Miocene was influenced by complex interactions between Tethyan tectonics, orbital parameters, oceanographic changes, and carbon cycle feedbacks, with climate modelling indicating that pCO(2) was an important factor. Oscillating episodes of climate change during the Oligocene Miocene transition (OMT) have however been difficult to reconcile with existing pCO(2) records. Here we present a new pCO(2) record from the OMT into the early Miocene, reconstructed using the stomatal proxy method with a database of fossil Lauraceae leaves from New Zealand. The leaf database derives from three relatively well-dated sites located in the South Island of New Zealand; Foulden Maar, Mataura River and Grey Lake. Atmospheric pCO(2) values were obtained based on four separate calibrations with three nearest living equivalents, using the stomatal ratio method as well as transfer functions. Our results, based on the mean values of each of the four calibrations, indicate pCO(2) ranging 582-732 ppm (average 650 ppm) at the OMT, falling precipitously to mean values of 430-538 ppm (average 492 ppm) for the earliest Miocene and similar to 454-542 ppm (average 502 ppm) in the early Miocene. The much higher values of pCO(2) at the OMT indicate that pCO played an important role in climate dynamics during this time, potentially including the abrupt termination of glaciations.

  • 26. Yang, Fengmei
    et al.
    Wang, Naiang
    Shi, Feng
    Charpentier Ljungqvist, Fredrik
    Stockholm University, Faculty of Humanities, Department of History.
    Zhao, Sen
    Liu, Ting
    The spatial distribution of precipitation over the West Qinling region, China, AD 1470–20002016In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 443, p. 278-285Article in journal (Refereed)
    Abstract [en]

    The West Qinling Mountains form part of the climatic barrier that separates southern and northern China, and are located at the edge of the region dominated by the Asian summer monsoon. To investigate the spatial distribution of regional hydroclimatic variability in the West Qinling region, the annually resolved spatial field of rainy season (May–June–July–August–September, MJJAS) precipitation anomalies from AD 1470 to 2000 was reconstructed using 39 tree-ring chronologies, as well as 28 dryness/wetness indices derived from historical documentary data. The results indicate that the El Niño–Southern Oscillation (ENSO) and the Tropospheric Biennial Oscillation (TBO) may jointly affect the spatial pattern of precipitation over the West Qinling Mountains at inter-annual timescales. The drought in the 1990s was found to exceed the amplitude and duration of all other periods of drought that have occurred since AD 1470 in this region. The new precipitation field reconstruction assesses the spatial pattern of historical hydroclimatic variability in the West Qinling region and provides an opportunity to test the performance of climate models in simulating regional precipitation variability and change.

  • 27.
    Öberg, Helena
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Norström, Elin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Ryner, Maria Malmström
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Karin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Westerberg, Lars-Ove
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Eddudottir, Sigrun Dogg
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Andersen, Thorbjörn J.
    Muzuka, Alfred
    Environmental variability in northern Tanzania from AD 1000 to 1800, as inferred from diatoms and pollen in Lake Duluti2013In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 374, p. 230-241Article in journal (Refereed)
    Abstract [en]

    Fossil pollen and diatoms have been analyzed in a sediment sequence from a topographically closed crater lake in northern Tanzania (Lake Duluti), with the aim to reconstruct past changes in lake level and vegetation dynamics. The results provide a new paleoenvironmental record from equatorial Africa covering the period c. AD 1000 to AD 1800. Overall, the pollen and diatom records generate comparable stories of dry and wet periods. Dry conditions are inferred at c. AD 1040-1470, c. AD 1510-1640 and C. AD 1650-1670 with the lowest lake levels at c. AD 1260-1290 and AD 1600-1640. Wetter conditions occurred c. AD 1640-1650 and c. AD 1670-1790. The chronology is based on combined analyses of Pb-210 activity and AMS C-14 on bulk sediment, and a Bayesian model was applied to establish the age-depth relationship. The hydroclimatic record from Lake Duluti shows good correlation with several East African lakes in a centennial time perspective, although comparison of high frequency variability in the region is hampered by dating uncertainties.

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