TY - JOUR
T1 - Upper ocean O2 trends
T2 - 1958–2015
AU - Ito, Takamitsu
AU - Minobe, Shoshiro
AU - Long, Matthew C.
AU - Deutsch, Curtis
N1 - Funding Information:
We are thankful for the support from the Scientific Visitor Program of the Climate and Global Dynamics Laboratory at the National Center for Atmospheric Research (NCAR) as this study started, while the authors were visiting NCAR during the summer of 2016. NCAR is supported by the National Science Foundation. T.I. is partially supported by the NSF (OCE-1357373) and NOAA grant (NA16OAR4310173). S.M. is supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI (26287110, 26610146, and 15H01606). All data sets supporting the conclusions of this study are available in the public domain as referenced within the paper. Data analysis products used to generate the figures and tables are available from the corresponding author upon request.
Publisher Copyright:
©2017. American Geophysical Union. All Rights Reserved.
PY - 2017/5/16
Y1 - 2017/5/16
N2 - Historic observations of dissolved oxygen (O2) in the ocean are analyzed to quantify multidecadal trends and variability from 1958 to 2015. Additional quality control is applied, and the resultant oxygen anomaly field is used to quantify upper ocean O2 trends at global and hemispheric scales. A widespread negative O2 trend is beginning to emerge from the envelope of interannual variability. Ocean reanalysis data are used to evaluate relationships with changes in ocean heat content (OHC) and oxygen solubility (O2,sat). Global O2 decline is evident after the 1980s, accompanied by an increase in global OHC. The global upper ocean O2 inventory (0–1000 m) changed at the rate of −243 ± 124 T mol O2 per decade. Further, the O2 inventory is negatively correlated with the OHC (r = −0.86; 0–1000 m) and the regression coefficient of O2 to OHC is approximately −8.2 ± 0.66 nmol O2 J−1, on the same order of magnitude as the simulated O2-heat relationship typically found in ocean climate models. Variability and trends in the observed upper ocean O2 concentration are dominated by the apparent oxygen utilization component with relatively small contributions from O2,sat. This indicates that changing ocean circulation, mixing, and/or biochemical processes, rather than the direct thermally induced solubility effects, are the primary drivers for the observed O2 changes. The spatial patterns of the multidecadal trend include regions of enhanced ocean deoxygenation including the subpolar North Pacific, eastern boundary upwelling systems, and tropical oxygen minimum zones. Further studies are warranted to understand and attribute the global O2 trends and their regional expressions.
AB - Historic observations of dissolved oxygen (O2) in the ocean are analyzed to quantify multidecadal trends and variability from 1958 to 2015. Additional quality control is applied, and the resultant oxygen anomaly field is used to quantify upper ocean O2 trends at global and hemispheric scales. A widespread negative O2 trend is beginning to emerge from the envelope of interannual variability. Ocean reanalysis data are used to evaluate relationships with changes in ocean heat content (OHC) and oxygen solubility (O2,sat). Global O2 decline is evident after the 1980s, accompanied by an increase in global OHC. The global upper ocean O2 inventory (0–1000 m) changed at the rate of −243 ± 124 T mol O2 per decade. Further, the O2 inventory is negatively correlated with the OHC (r = −0.86; 0–1000 m) and the regression coefficient of O2 to OHC is approximately −8.2 ± 0.66 nmol O2 J−1, on the same order of magnitude as the simulated O2-heat relationship typically found in ocean climate models. Variability and trends in the observed upper ocean O2 concentration are dominated by the apparent oxygen utilization component with relatively small contributions from O2,sat. This indicates that changing ocean circulation, mixing, and/or biochemical processes, rather than the direct thermally induced solubility effects, are the primary drivers for the observed O2 changes. The spatial patterns of the multidecadal trend include regions of enhanced ocean deoxygenation including the subpolar North Pacific, eastern boundary upwelling systems, and tropical oxygen minimum zones. Further studies are warranted to understand and attribute the global O2 trends and their regional expressions.
KW - biogeochemical cycling
KW - climate change
KW - climate impacts
KW - data analysis
KW - global warming
KW - marine chemistry
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U2 - 10.1002/2017GL073613
DO - 10.1002/2017GL073613
M3 - Article
AN - SCOPUS:85019085051
SN - 0094-8276
VL - 44
SP - 4214
EP - 4223
JO - Geophysical Research Letters
JF - Geophysical Research Letters
IS - 9
ER -