In the recent geological past, it appears that in this region there were natural (not influenced by humans) changes in the ventilation dynamics, even when the upper water layers became “only” two degrees warmer. For comparison: in the last 50 years, the North Sea has become 1.7 degrees warmer. Even within the announced limits for anthropogenic global warming, in the future it’s possible that oxygen minimum zones will increase. “Until now, it has only been only possible to quantify oxygen depletion associated with ventilation changes to a limited extent. But our first estimations indicate that an oxygen loss of 25-50 % compared to today’s levels could be expected if it becomes warmer,” says Lembke-Jene. This would lead to episodic oxygen deficiency in large parts of the intermediate waters in the subpolar Pacific. This in turn could have a negative impact on the food web, including the economically important fishing grounds in the Bering Sea. To better understand the effects on the Pacific and to investigate the background and causes, this summer scientists from the AWI and the GEOMAR Helmholtz Centre for Marine Research are embarking on a joint expedition to the Northwest Pacific on board the research vessel Sonne.
Lester Lembke-Jene, Ralf Tiedemann, Dirk Nürnberg, Xun Gong, and Gerrit Lohmann: A Rapid Shift and Millennial-scale Variations in Holocene North Pacific Intermediate Water Ventilation. Proceedings of the National Academy of Sciences of the United States of America (PNAS). doi/10.1073/pnas.1714754115