For our assignment, we are required to analyse and compare the $\ce{CO2}$ level (in both ocean and air) of two different sites. Theoretically, shouldn't the $\ce{CO2}$ level of a colder region (e.g., Alaska) be higher due to $\ce{CO2}$ being more soluble in colder temperatures?

I've looked at the data (I'm comparing Alaska and the Equator) and the carbon dioxide concentration is higher for the equator. What could explain this? The data can be found at NOAA's PMEL Carbon Data Observation Data page.*

* The US National Oceanic and Atmospheric Administration / Pacific Marine Environmental Laboratory


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    $\begingroup$ One fast guess is that the warmer water has higher conductivity (diffusion and infusion is faster when molecules move faster), which makes it to faster suck the CO2 from the atmosphere and faster reach higher oxidification, despite the capacity of the colder water is higher. Fear the moment when the CO2 reserves in the water reach their limit, causing the CO2 release instead of consumption and the following climate catastrophe. $\endgroup$ – Little Alien Aug 14 '16 at 11:07
  • $\begingroup$ Wouldn't seasonality also play a strong part in the measured CO2 level of polar latitudes? $\endgroup$ – Trevor J. Smith Aug 14 '16 at 20:05
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    $\begingroup$ It's a complicated question and I'm not sure the answer, but plankton remove CO2 from the ocean. The amount of CO2 in the ocean at any given point is in equilibrium with atmospheric absorption, any added from rain (which tends to have a higher concentration of CO2), and rate it's removed from the ocean either by plankton or released into the air. Rate of absorption from the atmosphere and percentage dissolved may not go hand in hand, but I'm just speculating. $\endgroup$ – userLTK Aug 14 '16 at 20:44

From Sabine, et al., 2004:

The capacity for ocean waters to take up anthropogenic CO2 from the atmosphere is inversely proportional to the value of the Revelle Factor, hence the lower the Revelle Factor, the higher the oceanic equilibrium concentration of anthropogenic CO2 for a given atmospheric CO2 perturbation.

The Revelle Factor is, "the ratio of instantaneous change in carbon dioxide to the change in total dissolved inorganic carbon (DIC)"

Therefore, the controlling factor for CO$_2$ absorption in seawater is presence of DIC and buffering. If you add CO$_2$ and a relatively small portion of it becomes other DIC species such as HCO$_3^{-}$ or CO$_3^{2-}$, then you have a low Revelle factor and high uptake of atmospheric CO$_2$. Alkaline waters (lower pH) can absorb more CO$_2$ because they have less of the acidic CO$_3^{2-}$ and neutral buffering HCO$_3^{-}$.


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