Wind-Driven Control of Shelf-Sea CO2 Sinks

Abstract

Continental shelf surface waters are considered a variable but increasing sink of atmospheric carbon dioxide (CO₂), but the mechanisms controlling these increasing sinks are unclear. We identify that the winter wind-driven surface atmosphere-ocean CO₂ gas exchange and wind-driven movement of water onto (or off of) shelf seas are consistent with the atmospheric CO₂ uptake tendency of many shelf seas. A 20-year observational-based analysis shows that geostrophic, wind and wave driven currents all contribute to the surface shelf break water velocities, but the dominance of each is location and season dependent. Analyzing these flows for fourteen shelf-seas based on their 20-year long-term gradient in air-sea partial pressure of carbon dioxide (their atmospheric CO₂ uptake tendency) identifies significant relationships between uptake tendency and winter (r² = 0.72 ± 0.03, p < 0.01, n = 14) and autumn (r² = 0.57 ± 0.05, p < 0.01, n = 14) wind-driven surface flows. These signals are most strong in winter, but the results are consistent at annual scales. Including the wintertime wind-driven air-sea CO₂ gas exchange further enhances this result, and collectively they describe 82% of the variance in the atmospheric CO₂ uptake tendency data (r² = 0.82 ± 0.06, p < 0.01, n = 14). These findings identify that long-term wind-driven water flow and surface gas exchange are key mechanisms for controlling their chemical evolution and their status as CO₂ sinks. This observational-based evidence highlights the need for these wind-driven processes to be resolved within methods used to predict or understand continental shelf-sea carbonate system state and ocean health.