TY - JOUR
T1 - Biogeochemical Role of Subsurface Coherent Eddies in the Ocean
T2 - Tracer Cannonballs, Hypoxic Storms, and Microbial Stewpots?
AU - Frenger, Ivy
AU - Bianchi, Daniele
AU - Stührenberg, Carolin
AU - Oschlies, Andreas
AU - Dunne, John
AU - Deutsch, Curtis
AU - Galbraith, Eric
AU - Schütte, Florian
N1 - Funding Information:
We are indebted to many scientists at NOAA GFDL for developing and providing access to the CM2.6 high-resolution model simulation. We thank Rena Czeschel and Lothar Stramma for providing the mooring data presented in Figure 2c, and Alexis Chaigneau and Rudnick et al. (2017) (data doi: 10.21238/S8SPRAY7292) for the undercurrent data presented in Figure 5. We thank Sören Thomsen for discussions and Stephen Griffies for valuable comments on the manuscript. D. B. acknowledges support from the U.S. National Science Foundation (NSF) grant OCE-1635632 and F. S. from the Collaborative Research Centre 754 (SFB 754) “Climate-Biogeochemistry Interactions in the Tropical Ocean”, funded by the German Research Foundation (DFG). The code of CM2.6 is based on ESM2M, available at https://www.gfdl.noaa.gov/earth- system-model and includes the simple marine biogeochemical model miniBLING. Solutions from CM2.6 with its high-resolution ocean component require large storage capacities. The solution analyzed here is available via the SOCCOM project upon request (https://soccom.princeton.edu), and results of analyses of this project from the authors upon request.
Publisher Copyright:
©2018. American Geophysical Union. All Rights Reserved.
PY - 2018/2
Y1 - 2018/2
N2 - 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.
AB - 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.
KW - coherent
KW - eddies
KW - hypoxic
KW - ocean
KW - subsurface
KW - transport
UR - http://www.scopus.com/inward/record.url?scp=85042108957&partnerID=8YFLogxK
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U2 - 10.1002/2017GB005743
DO - 10.1002/2017GB005743
M3 - Article
AN - SCOPUS:85042108957
SN - 0886-6236
VL - 32
SP - 226
EP - 249
JO - Global Biogeochemical Cycles
JF - Global Biogeochemical Cycles
IS - 2
ER -