Description: Empirical data as well as modelling experiments show that the stability of the Arctic cryosphere is today under threat due to global warming. Along the circum-arctic ocean periphery this cryosphere is comprised of terrestrial permafrost. However, during Quaternary times this frozen landscape was repeatedly changed due to global sea-level fluctuations which particularly affected the wide and shallow Siberian shelves. As western part of the Beringian landmass the entire Laptev Sea shelf was subaerially exposed in last glacial times. During the ensuing postglacial global sea-level rise this region gradually changed from a terrestrial permafrost landscape into a shallow marine shelf environment. Various geochemical, micropaleontological, palynological, and sedimentological data obtained from both conventional gravity cores and drill cores reveal the strong influence of this tranformation process on the shelf environment. Our previous scientific drilling campaign (2000), conducted to the outer Laptev Sea shelf with the goal to recover pre-Holocene sediments from acoustically transparent sections, confirmed the existence of frozen, and ice-bearing terrestrial sediments below a soft, marine sediment package of Holocene age. However, oxygen isotope composition of the ice unveiled that these frozen sediments must have been altered by re-freezing processes during and after the transgression. This assumption seems now corroborated by new high-resolution acoustic data from the mid- to inner shelf region gained during the latest expeditions in 2004. Although the overall scenario of shelf transformation for the time since the last sea level rise seems to be reasonably well understood now, there is no information available so far from older climatic intervals with conditions comparable to the Holocene. But such information from Holocene-like climate intervals will contribute useful insight for predictive purposes, since these records would then provide a longer time frame within which to evaluate natural variability in general, and means to examine the response of the Arctic system to future changes in particular. The Laptev shelf seas is a crucial area for such paleo-evaluation studies due to its highly changeable environment, both seasonally as well as on longer timescales (decadal to millennial to glacial-interglacial).

Description: Large amounts of carbon are stored in permafrost-affected soils of the Arctic tundra. The quantity, distribution and composition of this carbon are important, because much of the carbon is likely to be released as a result of global warming. We have studied soils of the central Siberian Arctic to determine the carbon content and the nature of the organic matter by density fractionation, and 13C-NMR- and 13C-stable-isotope analyses. There are pronounced differences in the profile and variations from place to place in the quantity and nature of soil organic matter. We estimated that the mean stock of carbon was 14.5 kg m–2 within the active layer. We found a total of about 30.7 kg C m–3 in the entire upper metre of the soils. Carbon of the tussock tundra showed strong vertical differentiation, with a large proportion comprising decomposed, recalcitrant compounds. We identified within the soil several zones of aerobe and anaerobe decomposition. Mobile carbon fractions have precipitated under the influence of low temperatures.

Description: High resolution oxygen isotope profiles of aragonitic bivalve shells (Astarte borealis) collected alive in different years are used to trace hydrographical changes on the Laptev Sea shelf, which are mainly forced by changes in riverine freshwater discharge and arctic atmospheric circulation patterns. By merging individual isotope profiles, a high resolution time series of relative changes in bivalve δ18O is obtained for the eastern Laptev Sea for the period 1969 to 1998. The resulting pattern in the δ18O time series reflects seasonal bottom-water salinity changes in the Laptev Sea, which is dominated by the peak input of freshwater discharged by the Lena River onto the Laptev Sea shelf during summer. The relative changes in summer bottom-water salinity, deduced from the δ18O values in the bivalves and the discharge anomaly of the Lena River, show a significant negative correlation. It is therefore suggested that the annual and subdecadal variations of the riverine freshwater and its influence on the shelf hydrography are imprinted in the bivalve shells. Moreover, we note that extreme summer precipitation anomalies in the Lena River catchment area affect the river discharge characteristics, events which are detectable in the δ18O time series. This all implies that δ18O records of bivalve shells have the potential to build long-term records of atmospheric-forced changes in arctic circulation.