Hauck, Judith, Arrigo, K. R., Hoppema, Mario, van Dijken, G. L., Völker, Christoph and Wolf-Gladrow, Dieter (2012) Dissolution of Antarctic shelf carbonates: an insignificant feedback to acidification. [Talk] In: EGU General Assembly 2012. , 22.-27.04.2012, Vienna, Austria .

Abstract

Dissolution of calcium carbonate neutralizes anthropogenic CO2. An upward shift of the calcite and aragonite
saturation horizons exposes carbonate deposits to dissolution which is an important carbon sink reaction on a time
scale of several thousand years for the world oceans.
In the Southern Ocean, the surface calcite and aragonite saturation states are naturally low due to cold temperatures.
They are further reduced by the uptake of anthropogenic carbon which is strongest in the top 1000 m.
Undersaturation at the surface might occur even before the underlying water column is completely undersaturated.
Therefore, carbonate sediments on Antarctic shelves are likely to be be among the first to dissolve due to man-made
acidification.
Obviously, we need to know the inventory of CaCO3 in the bioturbated layer of the Antarctic shelf sediments
to quantify the capacity of this negative feedback mechanism. Here, we present a technique that allows us to
spatially interpolate CaCO3 data on the Antarctic shelves. We derive quantitative relationships between nearly
400 measurements of CaCO3 on the Antarctic shelves, water depth and satellite-derived primary production in the
overlying water column. This confirms that primary production mainly determines the CaCO3 distribution on the
Antarctic shelves: On the one hand, there is hardly any CaCO3 production when primary production is low. On
the other hand, dissolution due to CO2 produced by remineralization of organic matter dominates in high primary
production regions; this constrains CaCO3 accumulation and preservation to regions with an optimum primary
production level.
These relationships between sedimentary CaCO3, primary production, and water depth are then applied to produce
a map of CaCO3 on all Antarctic shelves. The inventory, calculated from this interpolated map of CaCO3, amounts
to 4 Pg CaCO3, capable to neutralize about 0.5 Pg C. This, however, is in the same range as estimates of the annual
anthropogenic CO2 uptake in the Southern Ocean. The dissolution of CaCO3 is limited by slow reaction kinetics,
otherwise CaCO3 could disappear from the Antarctic shelves in only one to a few years. Our analysis suggests that
deposits of CaCO3 will dissolve without releasing a significant buffering signal and that Antarctic acidification
will proceed without being slowed down by dissolution of carbonates from Antarctic shelves.

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