Ocean acidification state in western Antarctic surface waters: controls and interannual variability
During four austral summers (December to January) from 2006 to 2010, we investigated the surface-water carbonate system and its controls in the western Antarctic Ocean. Measurements of total alkalinity (<i>A</i><sub>T</sub>), pH and total inorganic carbon (<i>C</i>...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-01-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/11/57/2014/bg-11-57-2014.pdf |
| Summary: | During four austral summers (December to January) from 2006 to 2010, we
investigated the surface-water carbonate system and its controls in the
western Antarctic Ocean. Measurements of total alkalinity (<i>A</i><sub>T</sub>),
pH and total inorganic carbon (<i>C</i><sub>T</sub>) were investigated in
combination with high-frequency measurements on sea-surface temperature
(SST), salinity and Chl <i>a</i>. In all parameters we found large interannual
variability due to differences in sea-ice concentration, physical processes
and primary production. The main result from our observations suggests that
primary production was the major control on the calcium carbonate saturation
state (Ω) in austral summer for all years. This was mainly reflected
in the covariance of pH and Chl <i>a</i>. In the sea-ice-covered parts of the
study area, pH and Ω were generally low, coinciding with low Chl <i>a</i>
concentrations. The lowest pH in situ and lowest aragonite saturation
(Ω<sub>Ar</sub> ~ 1.0) were observed in December 2007 in the
coastal Amundsen and Ross seas near marine outflowing glaciers. These low
Ω and high pH values were likely influenced by freshwater dilution.
Comparing 2007 and 2010, the largest Ω<sub>Ar</sub> difference was
found in the eastern Ross Sea, where Ω<sub>Ar</sub> was about 1.2 units
lower in 2007 than in 2010. This was mainly explained by differences in Chl
<i>a</i> (i.e primary production). In 2010 the surface water along the Ross Sea
shelf was the warmest and most saline, indicating upwelling of nutrient and
CO<sub>2</sub>-rich sub-surface water, likely promoting primary production leading
to high Ω and pH. Results from multivariate analysis agree with our
observations showing that changes in Chl <i>a</i> had the largest influence on the
Ω<sub>Ar</sub> variability. The future changes of Ω<sub>Ar</sub>
were estimated using reported rates of the oceanic uptake of anthropogenic
CO<sub>2</sub>, combined with our data on total alkalinity, SST and salinity
(summer situation). Our study suggests that the Amundsen Sea will become
undersaturated with regard to aragonite about 40 yr sooner than predicted by
models. |
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| ISSN: | 1726-4170 1726-4189 |