Rapid deep ocean deoxygenation and acidification threaten life on Northeast Pacific seamounts

Anthropogenic climate change is causing our oceans to lose oxygen and become more acidic at an unprecedented rate, threatening marine ecosystems and their associated animals. In deep‐sea environments, where conditions have typically changed over geological time scales, the associated animals, adapted to these stable conditions, are expected to be highly vulnerable to any change or direct human impact. Our study coalesces one of the longest deep‐sea observational oceanographic timeseries, reaching back to the 1960s, with a modern visual survey that characterizes almost two vertical‐kilometers of benthic seamount ecosystems. Based on our new and rigorous analysis of the Line P oceanographic monitoring data, the upper 3000 m of the Northeast Pacific has lost 15% of its oxygen in the last 60 years. Over that time, the oxygen minimum zone (OMZ), ranging between approximately 480 and 1700 m has expanded at a rate of 3.0±0.7 m/year (due to deepening at the bottom). Additionally, carbonate saturation horizons above the OMZ have been shoaling at a rate of 1‐2 m/year since the 1980s. Based on our visual surveys of four Northeast Pacific seamounts, these deep‐sea features support ecologically important taxa typified by long lifespans, slow growth rates, and limited mobility, including habitat‐forming cold‐water corals and sponges, echinoderms, and fish. By examining the changing conditions within the narrow realized bathymetric niches for a subset of vulnerable populations, we resolve chemical trends that are rapid in comparison to the lifespan of the taxa and detrimental to their survival. If these trends continue as they have over the last 3‐6 decades, they threaten to diminish regional seamount ecosystem diversity and cause local extinctions. This study highlights the importance of mitigating direct human impacts as species continue to suffer environmental changes beyond our immediate control.

Ross T., Preez C. D. & Ianson D., in press. Rapid deep ocean deoxygenation and acidification threaten life on Northeast Pacific seamounts. Global Change Biology. Article (subscription required).

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