Toward a universal relationship between wind speed and gas exchange: Gas transfer velocities measured with³He/SF₆during the Southern Ocean Gas Exchange Experiment

Abstract

Two 3He/SF6 dual-gas tracer injections were conducted during the Southern Ocean Gas Exchange Experiment (SO GasEx) to determine gas transfer velocities. During the experiment, wind speeds of up to 16.4 m s -1 were encountered. A total of 360 3He and 598 SF 6 samples were collected at 40 conductivity-temperature-depth (CTD) rosette casts and two pumped stations. The gas transfer velocity k was calculated from the decrease in the observed 3He/SF6 ratio using three different approaches. Discrete points of wind speed and corresponding k were obtained from the change in 3He/SF6 ratio over three time intervals. The results were also evaluated using an analytical model and a 1-D numerical model. The results from the three approaches agreed within the error of the estimates of about ±13%-15% for Patch 1 and ±4% for Patch 2. Moreover, 3He/SF6 dual-tracer results from SO GasEx are similar to those from other areas in both the coastal and open ocean and are in agreement with existing parameterizations between wind speed and gas exchange. This suggests that wind forcing is the major driver of gas exchange for slightly soluble gases in the ocean and that other known impacts are either intrinsically related to wind or have a small effect (<20% on average) on time scales of the order of days to weeks. The functionality of the wind speed dependence (quadratic or cubic) cannot be unequivocally determined from SO GasEx results. Copyright 2011 by the American Geophysical Union.