Holocene hydrographical changes of the eastern Laptev Sea (Siberian Arctic) recorded in δ18O profiles of bivalve shells

Oxygen isotope profiles along the growth axis of fossil bivalve shells of Macoma calcarea were established to reconstruct hydrographical changes in the eastern Laptev Sea since 8400 cal yr B.P.. The variability of the oxygen isotopes (delta(18)O) in the individual records is mainly attributed to variations in the salinity of bottom waters in the Laptev Sea with a modem ratio of 0.50parts per thousand/salinity. The high-resolution delta(18)O profiles exhibit distinct and annual cycles from which the seasonal and annual salinity variations at the investigated site can be reconstructed. Based on the modem analogue approach oxygen isotope profiles of radiocarbon-dated bivalve shells from a sediment core located northeast of the Lena Delta provide seasonal and subdecadal insights into past hydrological conditions and their relation to the Holocene transgressional history of the Laptev Sea shelf. Under the assumption that the modem relationship between delta(18)O(w) and salinity has been constant throughout the time, the delta(18)O of an 8400-cal-yr-old bivalves would suggest that bottom-water salinity was reduced and the temperature was slightly warmer, both suggesting a stronger mixture of riverine water to the bottom water. Reconstruction of the inundation history of the Laptev Sea shelf indicates local sea level similar to27 m below present at this time and a closer proximity of the site to the coastline and the Lena River mouth. Due to continuing sea level rise and a southward retreat of the river mouth, bottom-water salinity increased at 7200 cal yr B.P. along with an increase in seasonal variability. Conditions comparable to the modem hydrography were achieved by 3800 cal yr B.P. (C) 2003 University of Washington. All rights reserved.