TY - JOUR
T1 - Ventilation Pathways for the North Pacific Oxygen Deficient Zone
AU - Margolskee, A.
AU - Frenzel, H.
AU - Emerson, S.
AU - Deutsch, C.
N1 - Funding Information:
This work was supported by funding from the University of Washington School of Oceanography GSFEI and the National Science Foundation (OCE-1458888). We would like to acknowledge high-performance computing support from Yellowstone (ark:/85065/d7wd3xhc) and Cheyenne (doi:10.5065/D6RX99HX) provided by NCAR's Computational and Information Systems Laboratory, sponsored by the National Science Foundation. We thank J. Gula for providing Pyticles code (https://github.com/Mesharou/Pyticles) and B. Qiu for Argo velocity data. SODA data are available from the University of Hawaii APDRC (http://apdrc.soest.hawaii.edu/data/data.php), Argo data are available from the US-Godae (ftp://usgodae.org/pub/outgoing/argo), and NODC hosts WOD13 and WOA13 data sets at the https://www.nodc.noaa.gov/OC5/indprod.html website. ROMS output related to this work is deposited at figshare (https://doi.org/10.6084/m9.figshare.8097620). The constructive suggestions of Anand Gnanadesikan and an anonymous reviewer are gratefully acknowledged.
Publisher Copyright:
©2019. The Authors.
PY - 2019
Y1 - 2019
N2 - Oxygen deficient zones (ODZs) in the tropical ocean exert a profound influence on global biogeochemical cycles, but the factors that regulate their long-term structure and sensitivity to oceanic change remain poorly understood. We analyzed hydrographic observations and a high-resolution physical/biogeochemical model to diagnose the primary pathways that ventilate the tropical Pacific ODZs. Historical and recent autonomous observations reveal pronounced and widespread O2 peaks, termed secondary oxygen maxima (SOMs), within the depths of the broader O2 minimum layer, especially at the equatorward edge of both northern and southern ODZs. In the northern ODZ, Lagrangian particle tracking in an eddy-permitting numerical model simulation attributes these features to intrusions of the Northern Subsurface Countercurrent along the equatorial edge of the ODZ. Zonal subsurface jets also ventilate the poleward edge of the northern ODZ but induce a smaller O2 flux and do not yield detectable SOMs. Along the ODZ's eastern boundary, oxygenation is achieved by the seasonal cycle of upwelling of low-O2 water onto the continental shelf, followed by downwelling of O2-replenished near-surface waters back into the ODZ. Waters entering the northern Pacific ODZ originate from the extratropics in both hemispheres, but two thirds are from the Southern Hemisphere and arrive later and with a wider range of transit times. These results suggest that predicting future changes in the large Pacific ODZs will require a better understanding of the climate sensitivity of the narrow zonal jets and seasonal dynamics of coastal upwelling that supply their O2.
AB - Oxygen deficient zones (ODZs) in the tropical ocean exert a profound influence on global biogeochemical cycles, but the factors that regulate their long-term structure and sensitivity to oceanic change remain poorly understood. We analyzed hydrographic observations and a high-resolution physical/biogeochemical model to diagnose the primary pathways that ventilate the tropical Pacific ODZs. Historical and recent autonomous observations reveal pronounced and widespread O2 peaks, termed secondary oxygen maxima (SOMs), within the depths of the broader O2 minimum layer, especially at the equatorward edge of both northern and southern ODZs. In the northern ODZ, Lagrangian particle tracking in an eddy-permitting numerical model simulation attributes these features to intrusions of the Northern Subsurface Countercurrent along the equatorial edge of the ODZ. Zonal subsurface jets also ventilate the poleward edge of the northern ODZ but induce a smaller O2 flux and do not yield detectable SOMs. Along the ODZ's eastern boundary, oxygenation is achieved by the seasonal cycle of upwelling of low-O2 water onto the continental shelf, followed by downwelling of O2-replenished near-surface waters back into the ODZ. Waters entering the northern Pacific ODZ originate from the extratropics in both hemispheres, but two thirds are from the Southern Hemisphere and arrive later and with a wider range of transit times. These results suggest that predicting future changes in the large Pacific ODZs will require a better understanding of the climate sensitivity of the narrow zonal jets and seasonal dynamics of coastal upwelling that supply their O2.
KW - Regional Ocean Modeling System
KW - oxygen deficient zone
KW - secondary oxygen maxima
KW - ventilation
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U2 - 10.1029/2018GB006149
DO - 10.1029/2018GB006149
M3 - Article
AN - SCOPUS:85069916481
SN - 0886-6236
VL - 33
SP - 875
EP - 890
JO - Global Biogeochemical Cycles
JF - Global Biogeochemical Cycles
IS - 7
ER -