Abstract
Abstract. The Beaufort Gyre (BG) and the Bering Strait inflow (BSI) are important elements of the Arctic Ocean circulation system and major controls on the distribution of Arctic sea ice. We report records of the quartz ∕ feldspar and chlorite ∕ illite ratios in three sediment cores from the northern Chukchi Sea, providing insights into the long-term dynamics of the BG circulation and the BSI during the Holocene. The quartz ∕ feldspar ratio, interpreted as a proxy of the BG strength, gradually decreased during the Holocene, suggesting a long-term decline in the BG strength, consistent with an orbitally controlled decrease in summer insolation. We propose that the BG rotation weakened as a result of the increasing stability of sea-ice cover at the margins of the Canada Basin, driven by decreasing insolation. Millennial to multi-centennial variability in the quartz ∕ feldspar ratio (the BG circulation) is consistent with fluctuations in solar irradiance, suggesting that solar activity affected the BG strength on these timescales. The BSI approximation by the chlorite ∕ illite record, despite a considerable geographic variability, consistently shows intensified flow from the Bering Sea to the Arctic during the middle Holocene, which is attributed primarily to the effect of higher atmospheric pressure over the Aleutian Basin. The intensified BSI was associated with decrease in sea-ice concentrations and increase in marine production, as indicated by biomarker concentrations, suggesting a major influence of the BSI on sea-ice and biological conditions in the Chukchi Sea. Multi-century to millennial fluctuations, presumably controlled by solar activity, were also identified in a proxy-based BSI record characterized by the highest age resolution.
Highlights
The Arctic currently faces rapid climate change caused by global warming (e.g., Screen and Simmonds, 2010; Harada, 2016)
Kobayashi et al (2016) indicate that both the / illite and chlorite / illite ratios (CK / I and C / I ratios, respectively) are higher in the Bering Sea and decrease northward throughout the Chukchi Sea, reflecting the diminishing strength of the Bering Strait inflow (BSI) (Fig. 2). These results are consistent with earlier studies showing that illite is a common clay mineral in Arctic sediments (Kalinenko, 2001; Darby et al, 2011), whereas chlorite is more abundant in the Bering Sea and the Chukchi shelf areas influenced by the BSI (Naidu and Mowatt, 1983; Kalinenko, 2001; Nwaodua et al, 2014; Kobayashi et al, 2016)
The Q / F ratio showed a westward decreasing trend from the eastern Beaufort Sea to the East Siberian Sea and its offshore area (Fig. 2d). This supports a notion that quartzrich but feldspar-poor sediments are derived from the North American margin by the Beaufort Gyre (BG) circulation, whereas feldsparrich sediments are delivered to the Chukchi Sea from the Siberian margin by currents along the East Siberian slope (Vogt, 1997; Stein, 2008; Darby et al, 2011; Kobayashi et al, 2016)
Summary
The Arctic currently faces rapid climate change caused by global warming (e.g., Screen and Simmonds, 2010; Harada, 2016). Inflow of warm Pacific water through the Bering Strait (hereafter Bering Strait inflow – BSI) is suggested to have caused catastrophic changes in sea-ice stability in the western Arctic Ocean (Shimada et al, 2006). A dramatic strengthening of the BG circulation occurred during the last two decades (Shimada et al, 2006; Giles et al, 2012) This change was attributed to a recent reduction in sea-ice cover along the margin of the Canada Basin, which caused a more efficient transfer of the wind momentum to the ice and underlying waters in the BG (Shimada et al, 2006). This anomalous heat flux into the western part of the Canada Basin retarded sea-ice formation during winter, further accelerating overall sea-ice reduction
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