Paleoenvironmental reconstructions of the Laptev Sea during the postglacial sea-level rise are based on fossil assemblages of planktic and benthic foraminifers investigated in three AMS¹⁴C dated cores from mid-outer shelf and upper continental slope, water depth range 45-270 m. Fossil assemblages display time dependent changes in the total abundance, diversity, and relative abundance of species and ecological groups distinguished in the arctic seas in relation to offshore changes in water depth and river runoff influence (river-proximal, river-intermidiate and river-distal ones, Polyak et al., 2002). The index species to trace the subsurface penetration of Atlantic-derived waters (ADW) is Cassidulina neoteretis (Lubinski et al., 2001).

The basal part of the core from the upper continental slope (ca. 17 cal.ka, extrapolated) contains rare tests of C. neoteretis and abundant small-sized subpolar planktic foraminifers evidencing strong, but short-lived intrusions of ADW. Constant inflow of subsurface ADW is recorded 15.4-12 cal.ka.

Increasing river runoff influence with extreme freshwater event at 13 cal.ka is expressed in the highest total abundance of C. reniforme. Further Holocene flooding and climate warming created freshened shelf water masses which caused disappearance of C. neoteretis between 12 and 5 cal.ka. Surface water warming and enhanced primary productivity 12-10 cal. ka due to water stratification and proximity to the summer sea-ice margin are indicated by the occurrence of Nonion labradoricum, Islandiella spp., Pyrgo williamsoni.

Establishment of modern-like conditions is evidenced by the growing abundance of Melonis barleeanus and re-appearance of C. neoteretis since 5 cal.ka. Simultaneous increase in river-proximal species and angular rock fragments which were ice-rafted to the site from the nearshore regions gives evidence for the Late Holocene climate cooling.

Foraminireral records from the shelf cores show time transgressive changes from impoverished nearshore environments (Elphidium clavatum and river-proximal species) to the present outer shelf settings (river-intermediate and river-distal species).