A Holocene palynological record from the northeastern Laptev Sea and its implications for palaeoenvironmental research

摘要

A 844 cm long core PS51/118-3 (77°53.54′N; 132°11.92′E) recovered from the upper slope (122 m water depth) of the Laptev Sea (Russian Arctic) has been studied for pollen, spores and aquatic palynomorphs, including freshwater green algae and cysts of marine dinoflagellates. The age model was established on the basis of radiocarbon dates obtained on marine bivalve mollusk shells. The available dates suggest that the analyzed sediment was accumulated during the last ca. 10.8 cal. ka and reveal two intervals with markedly different sedimentation rates, reflecting the sedimentary regime changes of the Laptev Sea shelf during postglacial sea-level rise. Very high sedimentation rates (ca. 4.7 mm per year) in the lower part of the core (120-866 cm) between ca. 9.2 and 10.8 cal. ka BP reflect lower-than-present sea levels, high erosion activity and much closer position of the palaeo-shoreline with the Lena and Yana river mouths to the core site. Dramatic decrease in sedimentation rates (ca. 0.1 mm per year) during the middle and late Holocene interval reflects high sea-level and decreased amount of suspended material transported to the outer shelf by rivers. Despite the location of the core site at the continental slope and far away from the modern coastline pollen, spores and fresh-water algae constitute a major part of the microfossils throughout the whole record, indicating great impact of the Lena and Yana rivers and possibly prevalent wind regime on the pollen and non-pollen-palynomorph (NPP) assemblages. Although a number of short-term (decadal to multi-century) oscillations deviate from the mean Holocene values, pollen taxa percentages and pollen-based numerical biome reconstructions do not show very clear trends. The latter is likely a result of the mixed environmental signal and complex pollen contribution of several large environmental regions and vegetation zones of Siberia drained by the Lena and Yana rivers. The greater pollen contribution of the forested regions to the PS51/118-3 record reflects higher pollen production of the boreal trees and shrubs over the low-productive Arctic vegetation. The intervals of the relative increase in the tundra biome scores in the PS51/118-3 record reflect decreased arboreal pollen production or/and increased landscape openness within the pollen source area and can be correlated (within the uncertainty of the age models) with the cold episodes observed in the Greenland ice and North Atlantic sediment records.