Does the heating of the oceans due to greenhouse effect negate the acidification due to increased CO2 levels?

Question

As I understand, the dissolving of carbon dioxide leads to increased acidification of the oceans, and thus increased atmospheric CO₂ levels would lead to more dissolution in the oceans and thus increased levels of carbonic acid.

However, also as CO₂ is a gas, it's solubility decreases with temperature, thus as atmospheric CO₂ increase leads to higher surface ocean temperatures via greenhouse effect, does this reduce the solubility of CO₂ in the oceans to any degree, in some sense limiting the effect of increased gas concentrations on the acidification.

Furthermore on a slight tangent, surely the carbonate buffering system of the ocean is large enough to withstand the effects of more dissolved atmospheric carbon dioxide to maintain a constant pH?

Answer 1

This is a very complex issue, and therefore I'm not entirely convinced I am qualified to answer that, considering how little I understand chemistry, but I'll give it a try.

The Flux of CO₂ can be expressed as follows (see e. g. Wanninkhof et al. 2009):

$$F = kK_0(p_{\mathrm{CO}_2sea} - p_{\mathrm{CO}_2air})$$

By convention a negative $F$ means a flux from the atmosphere to the ocean.
$k$ is the transfert velocity and $K_0$ is the solubility which indeed decreases with temperature, as you noted.
$p_{\mathrm{CO}_2sea}$ and $p_{\mathrm{CO}_2air}$ are respectively the partial pressure of CO₂ in the sea and in the atmosphere.
Now, with $T$ increasing, $K_0$ (and also $k$ I believe) decreases, but, as long as the partial pressure of CO₂ is larger in the atmosphere than in the ocean there still is a flux toward the ocean.

So worst case scenario, increasing temperature slows down the absorption of CO₂ by the ocean but does not negate it. However of course, if the temperature increase to begin with, it is because $p_{\mathrm{CO}_2air}$ is increasing, so this is a bit of a moot point anyway.

As far as the ocean buffer goes, we're talking here of an uptake of ca. 2 Pg (i.e. $2\times10^{15}$g) of carbon dioxide per year (the preindustrial uptake being ca. 0.5 Pg according to Takahashi et al. 2009), which is too much to be buffered. For comparison, phytoplankton net primary productivity is ca. 50 Pg of fixed carbon per year (Falkowski et al. 1998).

_{Falkowski, P. G., Barber, R. T., Smetacek, V., 1998. Biogeochemical Controls and Feedbacks on Ocean Primary Production. Science, 281: 200-207.
Takahashi, T., et al. 2009. Climatological mean and decadal change in surface ocean pCO2, and net sea–air CO2 flux over the global oceans. Deep Sea Research II, 56: 554-577.
Wanninkhof, R., et al. 2009. Advances in Quantifying Air-Sea Gas Exchange and Environmental Forcing. Annual Review of Marine Science, 1: 213-244.}