Enhanced ocean deoxygenation in the Bering Sea during MIS 11c

Accelerated Arctic warming has raised concerns about future environmental conditions in the Bering Sea, one of the world's most productive marine ecosystems. Marine Isotope Stage (MIS) 11 (424–374 ka), a period with orbital parameters similar to those of the current interglacial (Holocene), is thought to be a suitable analog to predict future marine environments. Here, we reconstruct paleoredox changes in the Bering Sea over the last 800 kyr using high-resolution U/Th ratios from four sites, which were sampled by the Integrated Ocean Drilling Program (IODP) Expedition 323. During the early stages of MIS 11 (MIS11c), four IODP Expedition 323 sites (U1339, U1340, U1343, and U1345) with different water depths (1100–1900 m) had highly elevated U/Th ratios, indicating a substantial loss of dissolved oxygen (O₂) in the intermediate waters of the Bering Sea. High U/Th ratios were closely associated with extremely high %biogenic opal in the Bering Sea and an exceptionally warm Arctic climate. We speculate that during this period, the highest amplitude deglacial warming led to the onset of a super interglacial (MIS 11c) in the Arctic regions, via Arctic amplification. The exceptionally warm Arctic climate resulted in particularly high export productivity in the Bering Sea via physiological effects, a reduction in sea ice, and increased river discharge. Due to high productivity, increased organic matter degradation caused severe hypoxia in the intermediate waters of the Bering Sea. Our study shows that severe hypoxia may also appear in the Bering Sea if Arctic warming accelerates in the future.