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North Pacific deglacial hypoxic events linked to abrupt ocean warming
Praetorius, S.K.; Mix, A.C.; Walczak, M.H.; Wolhowe, M.D.; Addison, J.A.; Prahl, F.G. (2015). North Pacific deglacial hypoxic events linked to abrupt ocean warming. Nature (Lond.) 527(7578): 362-366. http://hdl.handle.net/10.1038/nature15753
In: Nature: International Weekly Journal of Science. Nature Publishing Group: London. ISSN 0028-0836; e-ISSN 1476-4687, meer
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  • Praetorius, S.K.
  • Mix, A.C.
  • Walczak, M.H.
  • Wolhowe, M.D.
  • Addison, J.A.
  • Prahl, F.G.

Abstract
    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. The mechanisms driving this hypoxia remain under debate. We present a new high-resolution alkenone palaeotemperature reconstruction from the Gulf of Alaska that reveals two abrupt warming events of 4–5 degrees Celsius at the onset of the Bølling and Holocene intervals that coincide with sudden shifts to hypoxia at intermediate depths. The presence of diatomaceous laminations and hypoxia-tolerant benthic foraminiferal species, peaks in redox-sensitive trace metals, and enhanced 15N/14N ratio of organic matter, collectively suggest association with high export production. A decrease in 18O/16O 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.

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