Variability of sea ice cover in the Chukchi Sea (western Arctic Ocean) during the Holocene

Abstract

[1] Dinocysts from cores collected in the Chukchi Sea from the shelf edge to the lower slope were used to reconstruct changes in sea surface conditions and sea ice cover using modern analogue techniques. Holocene sequences have been recovered in a down-slope core (B15: 2135 m, 75°44 0 N, sedimentation rate of $1 cm kyr À1 ) and in a shelf core (P1: 201 m, 73°41 0 N, sedimentation rate of $22 cm kyr À1 ). The shelf record spanning about 8000 years suggests high-frequency centennial oscillations of sea surface conditions and a significant reduction of the sea ice at circa 6000 and 2500 calendar (cal) years B.P. The condensed offshore record (B15) reveals an early postglacial optimum with minimum sea ice cover prior to 12,000 cal years B.P., which corresponds to a terrestrial climate optimum in Bering Sea area. Dinocyst data indicate extensive sea ice cover (>10 months yr À1 ) from 12,000 to 6000 cal years B.P. followed by a general trend of decreasing sea ice and increasing sea surface salinity conditions, superimposed on large-amplitude millennial-scale oscillations. In contrast, d 18 O data in mesopelagic foraminifers (Neogloboquadrina pachyderma) and benthic foraminifers (Cibicides wuellerstorfi) reveal maximum subsurface temperature and thus maximum inflow of the North Atlantic water around 8000 cal years B.P., followed by a trend toward cooling of the subsurface to bottom water masses. Sea-surface to subsurface conditions estimated from dinocysts and d 18 O data in foraminifers thus suggest a decoupling between the surface water layer and the intermediate North Atlantic water mass with the existence of a sharp halocline and a reverse thermocline, especially before 6000 years B.P. The overall data and sea ice reconstructions from core B15 are consistent with strong sea ice convergence in the western Arctic during the early Holocene as suggested on the basis of climate model experiments including sea ice dynamics, matching a higher inflow rate of North Atlantic Water.

Holocene dynamics in the Bering Strait inflow to the Arctic and the Beaufort Gyre circulation based on sedimentary records from the Chukchi Sea

“…8;de Vernal et al, 2005de Vernal et al, , 2008de Vernal et al, , 2013Farmer et al, 2011;Polyak et al, 2016). This pattern contrasts with reconstructions from other Arctic regions that show lower sea-ice concentrations in the early Holocene (de Vernal et al, 2013).…”

“…Sea-ice concentrations in the Chukchi Sea during the Holocene were reconstructed by dinoflagellate cysts (de Vernal et al, 2005(de Vernal et al, , 2013Farmer et al, 2011) and biomarker IP 25 Stein et al, 2017).…”

The Arctic sea ice biomarker IP25: a review of current understanding, recommendations for future research and applications in palaeo sea ice reconstructions

“…Such semi-quantitative interpretations contrast those derived from other proxies, such as dinocyst assemblages, where the application of transfer functions has yielded more quantitative estimates of sea ice cover (e.g. months/year; de Vernal et al, 2001Vernal et al, , 2005Ledu et al, 2008;McKay et al, 2008;Bonnet et al, 2010). As the potential to use IP 25 content to reconstruct past Arctic sea ice conditions has become more widely recognized, more recent research has aimed to calibrate abundances with known sea ice conditions, with the overall objective of making the interpretations of IP 25 abundance data more quantitative (e.g.…”

Large mammal biomass predicts the changing distribution of hunter-gatherer settlements in mid-late Holocene Alaska

“…We use modern sea-ice limits as a proxy for estimating the seasonal extent of ice-obligate marine mammal species ranges. We recognize that climate change in the past affected the extent and duration of the ice in a given area (Crockford and Frederick, 2007;de Vernal et al, 2005), and this may have played a role in the shortterm appearance and disappearance of ASTt in southwest Alaska coastal areas at different times.…”