Basin-scale environmental changes in the Okhotsk Sea over the last 30,000 years

The Sea of Okhotsk, situated at the northern boundary of the East Asian summer monsoon's domain, represents the southernmost region in the Northern Hemisphere where perennial sea ice develops year-round. It serves as a critical source of ventilation for modern North Pacific Intermediate Water and is highly sensitive to global climate change, making it an ideal natural laboratory for studying environmental changes. Despite its importance, our understanding of the basin-scale environmental evolution of the Sea of Okhotsk remains limited. This study addresses these gaps by compiling paleoenvironmental records from several sediment cores in the Sea of Okhotsk. We recalibrated the age models of these cores to reconstruct the histories of sea surface temperature (SST), sea ice activity, surface productivity, and intermediate water ventilation since 30 ka. Based on the reconstruction, we propose the conceptual modes of environmental evolution: the "glacial type," dominated by sea ice, and the "interglacial type," controlled by both sea ice and ocean currents. During the Last Glacial period (30 - 18 ka), the Sea of Okhotsk experienced low SSTs, extensive sea ice coverage, weak intermediate water ventilation, and reduced surface productivity. In contrast, the Late Holocene (< 6 ka) was characterized by higher SSTs, diminished sea ice, robust intermediate water ventilation, and increased surface productivity, with siliceous ooze being the dominant sediment component. Notably, during the Bølling-Allerød (14.7 - 13 ka) and Preboreal (11 - 9.7 ka) warm periods, the marine environment resembled the "interglacial type" but featured anoxic intermediate waters. During Heinrich Stadial 1 (18 - 14.7 ka) and the Younger Dryas (13 - 11.7 ka), environmental regimes were generally similar to the "glacial type" but with enhanced intermediate water ventilation. Since 30 ka, the evolution of environmental factors in the Sea of Okhotsk has been shaped by external forcings, internal feedbacks, and climate processes at both high and low latitudes, underscoring the complex interplay of factors influencing this dynamic region.