Synthesis of North Pacific oxygen fluctuations during the climate transitions of the last 20,000 years
Abstract
Here we produce the most comprehensive and regionally specific reconstructions of intermediate and abyssal hypoxia in the North Pacific, and these results can be used to evaluate mechanistic hypotheses such as oceanic gateways, circulation and surface ocean productivity. Of the 1,249 sedimentary cores recovered in the North Pacific and marginal seas, we used 55 primary cores (and 56 auxiliary cores) that have both high-resolution chronologies (primarily developed with radiocarbon dating and planktic foraminiferal oxygen isotopes stratigraphy) and seafloor oxygenation proxies. North Pacific oxygen concentrations in intermediate waters were abruptly reduced at the warming events of Glacial Terminations IA (14.7 ka) and IB (11.7 ka). Deep intermediate waters in Subarctic Pacific (1,400-1,600 m) exhibit early deoxygenation at 16-17.6 ka. Termination IA co-occurs with the maximum vertical extent of hypoxia in the Alaskan Gyre (78-1,515 m) and the Western Subarctic Pacific (870-1,107 m). Maximum vertical extent of hypoxia in the Bering Sea (14 ka; 732-1,867 m), and the Sea of Okhotsk (14 ka; 770-1,835 m) is delayed by 700 years as compared to the Subarctic Pacific interior. The Younger Dryas initiates a Pacific-wide, ephemeral return to oxic intermediate waters, and Termination IB (11.7) is expressed as a secondary, abrupt expansion of hypoxic intermediate waters. The Alaskan Gyre, Bering Sea, Western Subarctic Pacific and Sea of Okhotsk oscillate in synchrony and reveal broad-scale and coherent patterns in oceanic oxygenation. The Sea of Japan, however, demonstrates an anomalous, out-of-phase oxygenation pattern wherein the glacial Sea of Japan (17-20 ka) was hypoxic ([O2] < 0.1 ml/L) from upper intermediate waters to the basin center (677-2,764 m), due to sea level high stands and the absence of circulation through shallow gateways to the Western Pacific. Subsurface oxygenation was restored at 17 ka, and this is mechanistically attributed to sea level rise. The Sea of Japan then oscillated at Termination IB back to a hypoxic state, in synchrony with the rest of the North Pacific. This secondary event was driven by atmosphere and surface ocean processes (altering productivity and carbon export) and not by oceanic gateway limitations.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMPP13C..08M
- Keywords:
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- 1605 Abrupt/rapid climate change;
- GLOBAL CHANGEDE: 1616 Climate variability;
- GLOBAL CHANGEDE: 1620 Climate dynamics;
- GLOBAL CHANGEDE: 4901 Abrupt/rapid climate change;
- PALEOCEANOGRAPHY