Müller-Lupp, Thomas (2002) Short- and long-term environmental change in the Laptev Sea/Siberian Arctic during the Holocene / Kurz- und langfristige Umweltveränderungen in der Laptev-See (sibirische Arktis) während des Holozäns. . AWI, 85 pp.

Preview	Text BerPolarforsch2002424.pdf - Reprinted Version Download (2MB) | Preview
	Text Diss_Müller-Lupp_T_2001.pdf - Reprinted Version Restricted to Registered users only Available under License German copyright act UrhG. Download (13MB)

Abstract

Given the variability of seasonal, annual, and in particular langer time-scales, the dispersal and fate of the
river discharge and its influence on the hydrographical and sedimentological settings are the central tasks
in understanding the Holocene history of the Laptev Sea shelf. The main goal of this study was to
investigate short- and long-term environmental changes in the strongly coupled land-shelf system of the
Laptev Sea using isotopic evidence in sediments and biogenic carbonates.
In order to trace the modern spatial distribution of terrestrial organic matter, which is strongly affected by
the riverine input and the thermal erosion of the ice-rich permafrost coast, stable carbon isotope ratios of
total organic carbon in surface sediments were analyzed. The stable carbon isotope composition of surface
sediments reveal a dominant impact of terrestrial organic matter on the modern depositional environment
of the Laptev Sea shelf with distinct south to north and east to west gradients. Based on downcore 8 13Carg
records in radiocarbon-dated sediment cores the spatial and temporal deposition of terrestrial organic
matter during the past 12.7 ka is specified and can be related to depositional changes which occurred after
the last glacial maximum when this region became flooded due to a global rising sea level. The major
changes in the deposition of terrestrial organic matter occurred between 11 and 7 ka BP and comprise the
main phase of the southward retreat of the coastline and river depocenters due to the postglacial sea level
rise.
Stable oxygen and carbon isotope profiles from recent and fossil bivalve shells were investigated in order
to trace modern and past hydrographical conditions and their changes during the postglacial history of the
Laptev Sea. The serial dissection of bivalve shell valves along their growth axis from the umbo towards
the ventral margin provides an isotopic record of hydrographical and physiological changes during the life
of the individual specimen. The oxygen isotopic profiles of modern bivalve species of Astarte borealis
exhibit amplitude cycles interpreted as recording annual hydrographical cycles. Regarding the well-known
relationship between the carbonate 8 180, temperature, and the isotopic composition of water (8180w), it is
possible to relate isotopic phases to seasonal hydrographical phases like summer and winter. The within
shell isotopic variations are mainly attributed to variations in the isotopic composition and in the salinity
of bottom waters in the Laptev Sea. Seasonal temperature changes can be regarded of minor importance.
Using a modern linear relationship between 8 180w and salinity of 0.50 %0/salinity, salinity records are
reconstructed from the oxygen isotope records of the bivalve shells and can be directly compared with
hydrographical parameters at the investigated sites.
Carbon isotope profiles from modern specimens reveal a correspondence to the river breakup and to
seasonal phytoplankton productivity. Trends towards lighter 8 13 C values through ontogeny suggest the
effects of metabolic changes from a juvenile into a mature adult. Differences in the 8 13C of shell carbonate
between the sites appear to reflect the regional distribution of the ö 13C of sedimentary organic matter.
Given a good conformance between isotope profiles from modern bivalve shells and oceanographic
observations, oxygen isotope profiles of radiocarbon bivalve shells from a sediment core from northeast
off the Lena Delta are usecl to obtain in formation about passt hydrological conditions. Although isotope
profiles from fossil bivalves of the Laptev Sea shelf reflect only a brief interval of time, they may offer
new important insights into the paleohydrography during snapshots of the last 8.4 ka and their relation to
the Holocene transgression.
A reconstructed bottom water salinity of 29.5 at 8.4 ka BP indicates that the particular site was much more
affectecl by riverine water than nowaclays causecl by the proximity to the coastline and to the paleo-1iver
mouth. Due to the continuing southward retreat of the coastline ancl the Lena River mouth relative to the
study site an increase in the bottom water salinity at 7.3 ka BP is reconstructecl. The oxygen isotope shell profile at 7.3 ka BP gives an evidence of a bottom water hydrography which is characterized by a high
variability of summer and winter conditions on the level of modern bottom water conditions. The
following time slices at 3.6 ka and 1.6 ka BP reveal that modern hydrological conditions are fully
established.
The presented salinity reconstruction enables us to make further presurnptions on the relative proximity of
the study site to the coast and to the river rnouth during snapshot views of the Holocene history and thus
can be related to the postglacial transgression of the Laptev Sea shelf.

Actions (login required)

View Item