Impacts and effects of mesoscale ocean eddies on ocean carbon storage and atmospheric pCO₂

Abstract

An idealized numerical ocean model is used to investigate the sensitivity of the partial pressure of atmospheric carbon dioxide (pCO2) to changes in surface wind stress when mesoscale eddies are permitted in the flow. When wind stress increases, pCO_2 increases, and vice versa. The introduction of mesoscale eddies reduces the overall sensitivity of pCO2 by changing the sensitivity of ocean carbon storage due to the saturation state of carbon dioxide, the net air‐sea disequilibrium, soft tissue carbon, and the carbonate pump. However, a full carbon pump decomposition shows different responses for different ocean carbon storage terms. For example, air‐sea disequilibrium is actually more sensitive to increased winds at eddy‐permitting resolution, whereas soft tissue carbon is much less sensitive to wind changes in an eddy‐permitting ocean. Changes in pycnocline depth and the strength of both upper and lower cells of the meridional overturning circulation affect this sensitivity.

Southern Ocean carbon-wind stress feedback

“…However the magnitude of the change is slightly increased. When eddies are partially resolved, the magnitude of the pCO o 2 response to SO is seen to be reduced (Munday et al 2014), without fundamentally changing its character. The set of wind stress perturbation experiments with a 30% stronger Gent-McWilliams eddy diffusivity parameter described earlier exhibit a similar SO 1∕2 dependence (Fig.…”

“…3, we employ the MITgcm (Marshall et al 1997) in an idealised set-up designed to represent the Atlantic and Southern Oceans. The set-up is similar to Munday et al (2014) at 2…”

“…1c, d), which broadly match the observed distributions in the Atlantic. The model parameters are as in Munday et al (2014). The same model was used in Bronselaer et al (2016) to demonstrate the effect of Southern Ocean winds on the North Atlantic air-sea carbon flux.…”

“…These wind-induced changes in atmospheric CO 2 levels are generally driven by large changes in pre-formed (or abiotic) and regenerated (or biological) ocean carbon reservoirs (Broecker 1974), that nearly but not exactly compensate each other (Lauderdale et al 2013;Munday et al 2014). Consideration of pre-formed and regenerated carbon reservoirs have proven fruitful in understanding how ocean circulation impacts atmospheric pCO 2 .…”

“…In an abiotic ocean, it is sufficient to predict the pycnocline depth in order to understand the atmospheric carbon dioxide concentration for both wind and vertical mixing changes (Ito and Follows 2003). The inclusion of biology, and the additional carbon reservoirs this gives rise to, breaks this strong connection and the details of how the ocean is ventilated and how the overturning circulation varies also become important (Toggweiler et al 2003;Munday et al 2014). This can be 1 3 summarised in terms of what fraction of the ocean is filled by water from different end members, such as the Southern Ocean or North Atlantic, and their relative carbon content (Marinov et al 2008a, b).…”