Articles | Volume 11, issue 21
Research article
13 Nov 2014
Research article |  | 13 Nov 2014

Wind-driven changes in the ocean carbon sink

N. C. Swart, J. C. Fyfe, O. A. Saenko, and M. Eby

Abstract. We estimate changes in the historical ocean carbon sink and their uncertainty using an ocean biogeochemical model driven with wind forcing from six different reanalyses and using two different eddy parameterization schemes. First, we quantify wind-induced changes over the extended period from 1871 to 2010 using the 20th Century Reanalysis winds. Consistent with previous shorter-term studies, we find that the wind changes act to reduce the ocean carbon sink, but the wind-induced trends are subject to large uncertainties. One major source of uncertainty is the parameterization of mesoscale eddies in our coarse resolution simulations. Trends in the Southern Ocean residual meridional overturning circulation and the globally integrated surface carbon flux over 1950 to 2010 are about 2.5 times smaller when using a variable eddy transfer coefficient than when using a constant coefficient in this parameterization. A second major source of uncertainty arises from disagreement on historical wind trends. By comparing six reanalyses over 1980 to 2010, we show that there are statistically significant differences in estimated historical wind trends, which vary in both sign and magnitude amongst the products. Through simulations forced with these reanalysis winds, we show that the influence of historical wind changes on ocean carbon uptake is highly uncertain, and the resulting trends depend on the choice of surface wind product.

Short summary
Estimates of ocean carbon uptake from ocean biogeochemical models are key to our understanding of the global carbon cycle. Such estimates suggest that ocean carbon uptake is decreasing due to climate change, and particularly due to strengthening of the Southern Hemisphere winds. We show that these model-based estimates are highly uncertain due to poorly resolved physical processes (mesoscale ocean eddies) and uncertainty in the observed surface wind forcing used to drive the models.
Final-revised paper