TY - JOUR
T1 - Trend and Variability in Global Upper-Ocean Stratification Since the 1960s
AU - Yamaguchi, Ryohei
AU - Suga, Toshio
N1 - Funding Information:
The authors thank the members of the Physical Oceanography Group at Tohoku University and the participants of Otsuchi Symposium 2018 at the International Coastal Research Center, the University of Tokyo for useful comments and discussions. Also, we would like to express our appreciation to two anonymous reviewers for giving many constructive comments. This work was financially supported through JSPS grant 17J02314. T. S. is financially supported by JSPS through grants 16H04046 and 15H02129. This work also was partly supported by activity of the Core Research Cluster of Disaster Science in Tohoku University (a Designated National University). The processed data used to estimate long‐term trends and variability in this study are publicly available at https://doi.org/10.5281/zenodo.3466122 .
Funding Information:
The authors thank the members of the Physical Oceanography Group at Tohoku University and the participants of Otsuchi Symposium 2018 at the International Coastal Research Center, the University of Tokyo for useful comments and discussions. Also, we would like to express our appreciation to two anonymous reviewers for giving many constructive comments. This work was financially supported through JSPS grant 17J02314. T. S. is financially supported by JSPS through grants 16H04046 and 15H02129. This work also was partly supported by activity of the Core Research Cluster of Disaster Science in Tohoku University (a Designated National University). The processed data used to estimate long-term trends and variability in this study are publicly available at https://doi.org/10.5281/zenodo.3466122.
Publisher Copyright:
© 2019. The Authors.
PY - 2019/12/1
Y1 - 2019/12/1
N2 - Many studies on future climate projection point out that with progressing of global warming, upper-ocean density stratification will strengthen over this century, and consequently, global-averaged ocean primary productivity will decrease. Observed long-term changes in the stratification to date, however, still show large uncertainties of the change itself and its driver. Focusing on the vertical difference in the emergence of the global warming signals, we used only observational profiles to describe the spatiotemporal characteristic of long-term trend and variability in the upper-ocean stratification (defined as the density difference between the surface and 200-m depth). Statistically significant strengthening of the stratification since the 1960s was detected in ~40% of the global ocean area. The global average increase in the stratification corresponds to 3.3–6.1% of the mean stratification. The strengthening trends considerably change depending on the regions and show dominant contribution from the tropical region. In addition to the well-documented explanation of strengthening stratification, namely the surface intensification of global warming signal, we found that changes in subsurface temperature and salinity stratification associated with changes in atmospheric/ocean circulations significantly contribute to the long-term change in the stratification and setting its regional difference. In midlatitude and high-latitude ocean of the Northern Hemisphere, the long-term trend exhibits noteworthy seasonality, which shows faster increase trend in the summer than in the winter. From the detrended time series, interannual variabilities correlated with a particular climate mode are detected in several ocean regions, suggesting that these variabilities are mainly driven by associated sea surface temperature variation.
AB - Many studies on future climate projection point out that with progressing of global warming, upper-ocean density stratification will strengthen over this century, and consequently, global-averaged ocean primary productivity will decrease. Observed long-term changes in the stratification to date, however, still show large uncertainties of the change itself and its driver. Focusing on the vertical difference in the emergence of the global warming signals, we used only observational profiles to describe the spatiotemporal characteristic of long-term trend and variability in the upper-ocean stratification (defined as the density difference between the surface and 200-m depth). Statistically significant strengthening of the stratification since the 1960s was detected in ~40% of the global ocean area. The global average increase in the stratification corresponds to 3.3–6.1% of the mean stratification. The strengthening trends considerably change depending on the regions and show dominant contribution from the tropical region. In addition to the well-documented explanation of strengthening stratification, namely the surface intensification of global warming signal, we found that changes in subsurface temperature and salinity stratification associated with changes in atmospheric/ocean circulations significantly contribute to the long-term change in the stratification and setting its regional difference. In midlatitude and high-latitude ocean of the Northern Hemisphere, the long-term trend exhibits noteworthy seasonality, which shows faster increase trend in the summer than in the winter. From the detrended time series, interannual variabilities correlated with a particular climate mode are detected in several ocean regions, suggesting that these variabilities are mainly driven by associated sea surface temperature variation.
KW - Climate mode
KW - Global warming
KW - Interannual variability
KW - Long-term change
KW - Observational profile
KW - Upper-ocean stratification
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U2 - 10.1029/2019JC015439
DO - 10.1029/2019JC015439
M3 - Article
AN - SCOPUS:85076356879
VL - 124
SP - 8933
EP - 8948
JO - Journal of Geophysical Research: Oceans
JF - Journal of Geophysical Research: Oceans
SN - 2169-9275
IS - 12
ER -