Sea ice dynamics across the Mid-Pleistocene transition in the Bering Sea.

Sea ice and associated feedback mechanisms play an important role for both long- and short-term climate change. Our ability to predict future sea ice extent, however, hinges on a greater understanding of past sea ice dynamics. Here we investigate sea ice changes in the eastern Bering Sea prior to, across, and after the Mid-Pleistocene transition (MPT). The sea ice record, based on the Arctic sea ice biomarker IP25 and related open water proxies from the International Ocean Discovery Program Site U1343, shows a substantial increase in sea ice extent across the MPT. The occurrence of late-glacial/deglacial sea ice maxima are consistent with sea ice/land ice hysteresis and land-glacier retreat via the temperature-precipitation feedback. We also identify interactions of sea ice with phytoplankton growth and ocean circulation patterns, which have important implications for glacial North Pacific Intermediate Water formation and potentially North Pacific abyssal carbon storage

Late quaternary sea-ice and sedimentary redox conditions in the eastern Bering Sea – Implications for ventilation of the mid-depth North Pacific and an Atlantic-Pacific seesaw mechanism

On glacial-interglacial and millennial timescales, sea ice is an important player in the circulation and primary productivity of high latitude oceans, affecting regional and global biogeochemical cycling. In the modern North Pacific, brine rejection during sea-ice freezing in the Sea of Okhotsk drives the formation of North Pacific Intermediate Water (NPIW) that ventilates the North Pacific Ocean at 300 m to 1000 m water depth. Glacial intervals of the late Quaternary, however, experienced a deepening of glacial NPIW to at least 2000 m, with the strongest ventilation observed during cold stadial conditions of the last deglaciation. However, the origin of the shifts in NPIW ventilation is poorly understood. Numerical simulations suggest an atmospheric teleconnection between the North Atlantic and the North Pacific, in response to a slowdown or shutdown of the Atlantic meridional overturning circulation. This leads to a build-up of salinity in the North Pacific surface ocean, triggering deep ventilation. Alternatively, increased sea-ice formation in the North Pacific and its marginal seas may have caused strengthened overturning in response to enhanced brine rejection. Here we use a multi-proxy approach to explore sea-ice dynamics, sedimentary redox chemistry, and benthic ecology at Integrated Ocean Drilling Program Site U1343 in the eastern Bering Sea across the last 40 ka. Our results suggest that brine rejection from enhanced sea-ice formation during early Heinrich Stadial 1 locally weakened the halocline, aiding in the initiation of deep overturning. Additionally, deglacial sea-ice retreat likely contributed to increased primary productivity and expansion of mid-depth hypoxia at Site U1343 during interstadials, confirming a vital role of sea ice in the deglacial North Pacific carbon cycle

Orbital-scale benthic foraminiferal oxygen isotope stratigraphy at the northern Bering Sea Slope Site U1343 (IODP Expedition 323) and its Pleistocene paleoceanographic significance

A continuous composite oxygen isotope (δ18O) stratigraphy from benthic foraminifera in the Bering Sea was reconstructed in order to provide insight into understanding sea-ice evolution in response to Northern Hemisphere Glaciation. Oxygen isotope records from multiple species of benthic foraminifera at Integrated Ocean Drilling Program (IODP) Expedition 323 Site U1343 (54°33.4'N, 176°49.0'E, water depth 1950 m) yield a highly refined orbital-scale age model spanning the last 1.2 Ma, and a refined age model between 1.2 and 2.4 Ma. An inter-species calibration was used to define species offsets and to successfully obtain a continuous composite benthic δ18O record, correlated with the global composite benthic δ18O stack curve LR04 to construct an orbital-scale age model. The consistency of the benthic δ18O stratigraphy with biostratigraphy and magnetostratigraphy confirms the reliability of both methods for constraining age. The time difference between cyclic changes in sedimentary physical properties and glacial–interglacial cycles since 0.8 Ma is notable, and suggests that physical properties alone cannot be used to construct an orbital-scale age model. Amplitude changes in physical properties and a significant drop in the linear sedimentation rate during glacials after 0.9 Ma indicate that the glacial sea-ice edge extended beyond the Bering Sea Slope (Site U1343) at this time