| Summary: | The modern North Pacific Ocean is one major region of the world ocean where only mid-depth water layers are ventilated and re-supplied with nutrients which are mainly sourced from the subarctic Okhotsk Sea and precondition the North Pacific as substantial natural CO2 sink. Fundamental regional environmental changes like sea ice decrease, transformations of nutrient inventories, and oxygenation were detected in the Okhotsk Sea based on relatively short instrumental records. Such changes are often attributed to global climate change. However, knowledge about the natural long-term variability beyond instrumental time series is extremely limited. The extension into past, warmer-than-present times by using palaeoceanographic, proxy-based time series thus helps establishing baselines of natural variations against which potential anthropogenic changes can be evaluated and local vs. larger regional patterns can be assessed. Our proxy data-based study focuses on a collection of sediment records covering the last ca. 15,000 years with high temporal and spatial resolution. We decipher rapid changes in North Pacific Intermediate Water on centennial to millennial time scales and show that the current benign ventilation of the mid-depth North Pacific has only been prevalent for the last 2 ka. We provide evidence for a shift around 4-6 ka that changes the mid-depth Pacific oxygen character-istics, and ascribe the observed variations to intensity changes of the SE Asian Monsoon dynamics. Additionally, changes in flow speed and patterns of the Atlantic Meridional Overturning Circulation are reflected in our records of North Pacific mid-depth water mass dynamics, thus indicating a hemispheric teleconnection pattern between the Atlantic and Pacific realm during the Holocene.
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