Large changes in seasonal sea ice distribution and productivity in the Sea of Okhotsk during the deglaciations

Abstract

Changes in the surface environment of the central Sea of Okhotsk were reconstructed using TEX86 paleothermometry, facilitated by the BIT index, in order to investigate paleoenvironmental changes during the glacial-interglacial cycles. The core top TEX86-derived temperature is the same as the present-day summer sea surface temperature (SST), suggesting that TEX86 records seasonal rather than annually averaged SSTs in this region. The TEX86 record reveals ̃3°C lower summer SST during glacial maxima than during interglacial periods and significant warming during the deglaciations (15-10 ka and 136-130 ka). This is consistent with previous inferences of more expanded and persistent seasonal sea ice during the glacial periods than the present-day and its substantial retreat during the deglaciation. Timing of the deglacial warming also coincided with a distinct increase in coccolithophorid productivity, suggesting a causal relationship between sea surface warming and coccolithophorid blooms during the deglaciations. The relationship could reflect an increase in the supply of fresh and warm water from the Amur River during deglaciation, which significantly impacted hydrology by facilitating sea surface stratification, which in turn promoted production of coccolithophids.