Biogeochemical Role of Subsurface Coherent Eddies in the Ocean: Tracer Cannonballs, Hypoxic Storms, and Microbial Stewpots?

Ivy Frenger, Daniele Bianchi, Carolin Stührenberg, Andreas Oschlies, John Dunne, Curtis Deutsch, Eric Galbraith, Florian Schütte

Research output: Contribution to journalArticleResearchpeer-review

14 Citations (Scopus)

Abstract

©2018. American Geophysical Union. All Rights Reserved. Subsurface eddies are known features of ocean circulation, but the sparsity of observations prevents an assessment of their importance for biogeochemistry. Here we use a global eddying (0.1°) ocean-biogeochemical model to carry out a census of subsurface coherent eddies originating from eastern boundary upwelling systems (EBUS) and quantify their biogeochemical effects as they propagate westward into the subtropical gyres. While most eddies exist for a few months, moving over distances of hundreds of kilometers, a small fraction (<5%) of long-lived eddies propagates over distances greater than 1,000 km, carrying the oxygen-poor and nutrient-rich signature of EBUS into the gyre interiors. In the Pacific, transport by subsurface coherent eddies accounts for roughly 10% of the offshore transport of oxygen and nutrients in pycnocline waters. This “leakage” of subsurface waters can be a significant fraction of the transport by nutrient-rich poleward undercurrents and may contribute to the well-known reduction of productivity by eddies in EBUS. Furthermore, at the density layer of their cores, eddies decrease climatological oxygen locally by close to 10%, thereby expanding oxygen minimum zones. Finally, eddies represent low-oxygen extreme events in otherwise oxygenated waters, increasing the area of hypoxic waters by several percent and producing dramatic short-term changes that may play an important ecological role. Capturing these nonlocal effects in global climate models, which typically include noneddying oceans, would require dedicated parameterizations.
Original languageEnglish
Pages (from-to)226-249
JournalGlobal Biogeochemical Cycles
Volume32
Issue number2
DOIs
Publication statusPublished - 1 Feb 2018

Keywords

  • coherent
  • eddies
  • hypoxic
  • ocean
  • subsurface
  • transport

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