Upper ocean bubble measurements from the NE Pacific and estimates of their role in air‐sea gas transfer of the weakly soluble gases nitrogen and oxygen

Abstract

Simultaneous observations of upper‐ocean bubble clouds, and dissolved gaseous nitrogen (N 2 ) and oxygen (O 2 ) from three winter storms are presented and analyzed. The data were collected on the Canadian Surface Ocean Lower Atmosphere Study (C‐SOLAS) mooring located near Ocean Station Papa (OSP) at 50°N, 145°W in the NE Pacific during winter of 2003/2004. The bubble field was measured using an upward looking 200 kHz echosounder. Direct estimates of bubble mediated gas fluxes were made using assumed bubble size spectra and the upward looking echosounder data. A one‐dimensional biogeochemical model was used to help compare data and various existing models of bubble mediated air‐sea gas exchange. The direct bubble flux calculations show an approximate quadratic/cubic dependence on mean bubble penetration depth. After scaling from N 2 /O 2 to carbon dioxide, near surface, nonsupersaturating, air‐sea transfer rates, K T , for U 10 > 12 m s −1 fall between quadratic and cubic relationships. Estimates of the subsurface bubble induced air injection flux, V T , show an approximate quadratic/cubic dependence on mean bubble penetration depth. Both K T and V T are much higher than those measured during Hurricane Frances over the wind speed range 12 < U 10 < 23 m s −1 . This result implies that over the open ocean and this wind speed range, older and more developed seas which occur during winter storms are more effective in exchanging gases between the atmosphere and ocean than younger less developed seas which occur during the rapid passage of a hurricane.