Millennial-Scale Changes of Intermediate Water Ventilation, Productivity and Nutrient Supply in the Okhotsk Sea and Subarctic North Pacific During the Last 18,000 Years

Abstract

A reconstruction of North Pacific mid-depth water ventilation and biogenic productivity variations over the last 18,000 years is presented, based on sediment cores from the source region (Okhotsk Sea) of modern intermediate water (IW) ventilation. I reconstructed transient decreases in IW oxygenation during deglacial warm phases, likely tied to rapid, significantly enhanced organic matter remineralization within the IW, in line with evidence for maxima in primary productivity. Investigations of upper ocean stratification and sea surface temperatures revealed a link between upper mixed layer stratification maxima and ventilation minima during interstadial deglacial phases in large swaths of the Northwest Pacific. Analysis of Holocene cores showed the modern pattern of IW ventilation to be a relatively recent feature of only the last 2,000 years. During the warmer than present early-mid-Holocene, active ventilation was significantly decreased. Estimated O2 concentrations of Okhotsk Sea IW reached only 50-60 % of modern values, and the region turned from an early Holocene O2-sink into the modern O2-source around 6,000 years ago.