Trends and drivers in global surface ocean pH over the past 3 decades
We report global long-term trends in surface ocean pH using a new pH data set computed by combining <i>f</i>CO<sub>2</sub> observations from the Surface Ocean CO<sub>2</sub> Atlas (SOCAT) version 2 with surface alkalinity estimates based on temperature and salinit...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-03-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/12/1285/2015/bg-12-1285-2015.pdf |
| Summary: | We report global long-term trends in surface ocean pH using a new pH data
set computed by combining <i>f</i>CO<sub>2</sub> observations from the Surface Ocean
CO<sub>2</sub> Atlas (SOCAT) version 2 with surface alkalinity estimates based on
temperature and salinity. Trends were determined over the periods 1981–2011
and 1991–2011 for a set of 17 biomes using a weighted linear least squares
method. We observe significant decreases in surface ocean pH in
~70% of all biomes and a mean rate of decrease of
0.0018 ± 0.0004 yr<sup>−1</sup> for 1991–2011. We are not able to calculate a
global trend for 1981–2011 because too few biomes have enough data for this.
In half the biomes, the rate of change is commensurate with the trends
expected based on the assumption that the surface ocean pH change is only
driven by the surface ocean CO<sub>2</sub> chemistry remaining in a transient
equilibrium with the increase in atmospheric CO<sub>2</sub>. In the remaining
biomes, deviations from such equilibrium may reflect that the trend of
surface ocean <i>f</i>CO<sub>2</sub> is not equal to that of the atmosphere, most notably
in the equatorial Pacific Ocean, or may reflect changes in the oceanic buffer (Revelle)
factor. We conclude that well-planned and long-term sustained observational
networks are key to reliably document the ongoing and future changes in
ocean carbon chemistry due to anthropogenic forcing. |
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| ISSN: | 1726-4170 1726-4189 |