Productivity History of the Central Okhotsk Sea and Northeast Russia During the Mid‐Pleistocene Transition

Abstract Biological productivity, shaped by climate and environmental factors, is critical to climate feedback mechanisms and the global carbon cycle. This study investigates the measurement of six phytosterols (β‐sitosterol, stigmasterol, campesterol, dinosterol, epi‐brassicasterol, and 24‐methylene cholesterol) from core MD01‐2414 in the central Okhotsk Sea, covering the past 1.5 million years (Ma). These sterols serve as proxies for terrestrial and marine productivity in the central Okhotsk Sea and northeast Siberia. Sterol concentrations reflect global glacial/interglacial cycles between 1.2 and 0.6 Ma, with higher and lower values during interglacial and glacials intervals, respectively. X‐ray fluorescence (Ba/Ti) and total organic carbon/total nitrogen (TOC/TN) ratios indicate shifts in marine and terrestrial sources, confirming biological productivity as a key driver of sterol deposition. Sterol fluxes, combined with sea surface temperature records from the northwest Pacific and sea ice proxies from the Bering Sea, reveal an extreme cold interglacial (Marine Isotope Stage, MIS 23) and prolonged glacial conditions during MIS 22, which stressed both terrestrial and marine ecosystems. Increased sea ice expansion during this period likely fostered North Pacific Intermediate Water formation, reducing upwelling and CO 2 exchange between bottom waters and the atmosphere. Integration of sterol data with regional records, including pollen, temperature, and sedimentary facies from Lake El'gygytgyn, highlights a warming event at the onset of MIS 32, peaking in late MIS 32. This warming precedes the “super‐interglacial” MIS 31 and coincides with maxima in boreal and austral summer insolation, underscoring its significance in regional climate evolution.