Partitioning the CO2 Flux Mediated by Droplets Released from Breaking Waves

摘要

The CO2 flux from spume droplets occurs in two steps. First, the initial droplet-air gas concentration gradient del C is immediately removed with no change in the droplet solubility. Then, the solubility changes with droplet temperature T and radius r evolution, but the flux maintains the condition del C = 0. The gas content of a droplet can be determined by del C = 0 since the parameters T and r are known. Therefore, the net gas influx of a droplet depends on the values of T and r in its return to the sea. In the second step, the droplet temperature T evolves to an equilibrium temperature T-eq, and the radius r is then reduced by evaporation at constant T-eq. For the droplet spectrum, a cut-off radius r(cut) is used to separate short-lived (r > r(cut), returning to the sea before T = T-eq) and long-lived r <= r(cut) conditions. The net influx is split into three contributions: the first (S-2S) is mediated by short-lived mechanisms, and the second and the third by long-lived (S-2L) mechanisms that are further separated into temperature-varying (S-2L(T)) and radius-varying (S-2L(R)) stages. The results show that, in the cases with large air-sea temperature differences, the first stage S-2S dominates the net gas input, but its importance decreases as the value of r(cut) increases. The temperature-varying stage S-2L(T) is dominant in cases with both large values of r(cut) and large temperature differences, while the radius-varying stage S-2L(R) increases as either the temperature difference decreases or as the value of r(cut) increases.