Alan C. Mix Maureen H. Davies Matthew D Wolhowe Jason A. Addison Frederick G Prahl Summer K Praetorius 2015 <p><span>Marine sediments from the North Pacific document two episodes of expansion and strengthening of the subsurface oxygen minimum zone (OMZ) accompanied by seafloor hypoxia during the last deglacial transition</span>^{<a id="ref-link-34" title="Mix, A. C. et al. Rapid climate oscillations in the Northeast Pacific during the last deglaciation reflect Northern and Southern Hemisphere sources, in Mechanisms of global climate change at millennial time scales, American Geophysical Union, edited by P.U. Clark et al., Geophysical Monograph 112, 127–148 (1999)" href="https://www.nature.com/nature/journal/v527/n7578/full/nature15753.html#ref1" data-mce-href="https://www.nature.com/nature/journal/v527/n7578/full/nature15753.html#ref1">1</a>,<span>&nbsp;</span><a id="ref-link-35" title="Davies, M. H. et al. 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The presence of diatomaceous laminations and hypoxia-tolerant benthic foraminiferal species, peaks in redox-sensitive trace metals</span>^{<a id="ref-link-49" title="Barron, J. A., Bukry, D., Dean, W. E., Addison, J. A. &amp; Finney, B. Paleoceanography of the Gulf of Alaska during the past 15,000 years: results from diatoms, silicoflagellates, and geochemistry. Mar. Micropaleontol. 72, 176–195 (2009)" href="https://www.nature.com/nature/journal/v527/n7578/full/nature15753.html#ref12" data-mce-href="https://www.nature.com/nature/journal/v527/n7578/full/nature15753.html#ref12">12</a>,<span>&nbsp;</span><a id="ref-link-50" title="Addison, J. A. et al. Productivity and sedimentary δ15N variability for the last 17,000 years along the northern Gulf of Alaska slope. Paleoceanography 27, PA1206 (2012)" href="https://www.nature.com/nature/journal/v527/n7578/full/nature15753.html#ref13" data-mce-href="https://www.nature.com/nature/journal/v527/n7578/full/nature15753.html#ref13">13</a>}<span>, and enhanced&nbsp;</span>¹⁵<span>N/</span>¹⁴<span>N ratio of organic matter</span>^{<a id="ref-link-51" title="Addison, J. A. et al. Productivity and sedimentary δ15N variability for the last 17,000 years along the northern Gulf of Alaska slope. Paleoceanography 27, PA1206 (2012)" href="https://www.nature.com/nature/journal/v527/n7578/full/nature15753.html#ref13" data-mce-href="https://www.nature.com/nature/journal/v527/n7578/full/nature15753.html#ref13">13</a>}<span>, collectively suggest association with high export production. A decrease in&nbsp;</span>¹⁸<span>O/</span>¹⁶<span>O values of benthic foraminifera accompanying the most severe deoxygenation event indicates subsurface warming of up to about 2 degrees Celsius. We infer that abrupt warming triggered expansion of the North Pacific OMZ through reduced oxygen solubility and increased marine productivity via physiological effects; following initiation of hypoxia, remobilization of iron from hypoxic sediments could have provided a positive feedback on ocean deoxygenation through increased nutrient utilization and carbon export. Such a biogeochemical amplification process implies high sensitivity of OMZ expansion to warming.</span></p> application/pdf 10.1038/nature15753 en Nature North Pacific deglacial hypoxic events linked to abrupt ocean warming article