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| Titel |
Multiproxy study of the environmental conditions during the last Interglacial in NE Siberia (Dmitry Laptev Strait, East Siberian Sea) |
| VerfasserIn |
Sebastian Wetterich, Larisa Frolova, Larisa Nazarova, Andrei Andreev, Lutz Schirrmeister, Frank Kienast |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250041736
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| Zusammenfassung |
| In course of the IPY ’Past permafrost’ fieldwork was undertaken at coastal permafrost
sections of the Dmitry Laptev Strait in summer 2007. Late Quaternary permafrost deposits
were sampled for further cryolithological, sedimentological, and micro-palaeontological
analyses to reconstruct landscape dynamics during several climate cycles (Wetterich et al.
2009).
Records of environmental changes from the penultimate Glacial (MIS 6) to the last
Interglacial (MIS 5e; ca. 130 - 115 kyr BP) are preserved in ice-wedge casts exposed along
the studied coasts. Due to climate warming the transition from glacial to interglacial
conditions induced extensive thawing of ice-rich permafrost (thermokarst) and the formation
of ice-wedge casts. Evolving thermokarst depressions transformed formerly frozen ground
into taberal (thawed and refrozen) deposits. Overlying lacustrine deposits are fossil-rich and
retain evidence of changes in environmental conditions. Pollen records reflect changes from
early-interglacial grass-sedge dominated tundra to shrub tundra during the thermal
optimum followed by late-interglacial grass-sedge tundra. The findings of Larix
(larch) pollen and macro-remains in mid-interglacial deposits from the south coast
of the Dmitry Laptev Strait, and their absence in similar deposits from the north
coast indicate the location of the northern tree line during the interglacial thermal
optimum.
Species composition and dominant taxa of cladocerans remains indicate the warmer
temperature during the last Interglacial in comparison to modern conditions. Among the
identified sub-fossil Cladocera taxa are those that are now found on the border of the
modern tree-line and to the south of it. The rich cladoceran assemblages have been
represented by various ecological groups among which most frequent are littoral
phytophilic and truly planktonic organisms, presented in particular by genera Bosmina
sp.
The investigated chironomid community is diverse, with stable and evenly distributed
structure (Shennon Index is 2,40, Pielou Index is 0,86). Littoral taxa form the basis of the
investigated community and indicate temperate lacustrine conditions with shallow water and
pronounced zone of macrophytes. Findings of steam and leaf mining taxa indicates presence
of some submerged coarse vegetation, most probably remains of trees and shrubs. Majority of
the taxa are inhabitants of hygropertic, which is indicative for unstable conditions, fluctuating
water level and heterogeneous habitat controlled by complex factors, such as air exposure,
insolation, unstable water temperature and dissolved oxygen concentration, etc.
These conclusions are confirmed by mean July air temperature and water depth
reconstructions performed with Yakutian chironomid based inference models (Nazarova
et al. in press). Air T july reconstructed for the interglacial thermal optimum is
12,90±0,9oC.
Rich fossil ostracod records reflecting shallow lakeshore conditions can be correlated
with the thermal optimum.
The last interglacial palaeoenvironmental records reflect three landscape development
stages according to changes in the climatic setting: (1) thermokarst-induced formation of
basins, (2) accumulation of lacustrine sequences, and (3) transformation of lake-dominated
areas into polygonal tundra. The stages are considered to be of stratigraphical significance. |
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