The past decade has seen a substantial amount of research on air-sea gas exchange and its environmental controls. These studies have significantly advanced the understanding of processes that control gas transfer, led to higher quality field measurements, and improved estimates of the flux of climate-relevant gases between the ocean and atmosphere. This review discusses the fundamental principles of air-sea gas transfer and recent developments in gas transfer theory, parameterizations, and measurement techniques in the context of the exchange of carbon dioxide. However, much of this discussion is applicable to any sparingly soluble, non-reactive gas. We show how the use of global variables of environmental forcing that have recently become available and gas exchange relationships that incorporate the main forcing factors will lead to improved estimates of global and regional air-sea gas fluxes based on better fundamental physical, chemical, and biological foundations.

The SOLAS Air‐Sea Gas Exchange (SAGE) Experiment was conducted in the western Pacific sector of the Southern Ocean. During SAGE, gas transfer velocities were determined using the 3He/SF6 dual gas tracer technique, and results were obtained at higher wind speeds (16.0 m s−1) than in previous open ocean dual tracer experiments. The results clearly reveal a quadratic relationship between wind speed and gas transfer velocity rather than a recently proposed cubic relationship. A new parameterization between wind speed and gas transfer velocity is proposed, which is consistent with previous 3He/SF6 dual tracer results from the coastal and open ocean obtained at lower wind speeds. This suggests that factors controlling air‐sea gas exchange in this region are similar to those in other parts of the world ocean, and that the parameterization presented here should be applicable to the global ocean.

[1] Air-water gas transfer influences CO 2 and other climatically important trace gas fluxes on regional and global scales, yet the magnitude of the transfer is not well known. Widely used models of gas exchange rates are based on empirical relationships linked to wind speed, even though physical processes other than wind are known to play important roles. Here the first field investigations are described supporting a new mechanistic model based on surface water turbulence that predicts gas exchange for a range of aquatic and marine processes. Findings indicate that the gas transfer rate varies linearly with the turbulent dissipation rate to the 1 = 4 power in a range of systems with different types of forcing -in the coastal ocean, in a macro-tidal river estuary, in a large tidal freshwater river, and in a model (i.e., artificial) ocean. These results have important implications for understanding carbon cycling.

He/SF 6 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 3 He 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 3 He/SF 6 ratio using three different approaches. Discrete points of wind speed and corresponding k were obtained from the change in 3 He/SF 6 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, 3 He/SF 6 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.

[1] Measurements of atmospheric O 2 /N 2 ratios and CO 2 concentrations can be combined into a tracer known as atmospheric potential oxygen (APO % O 2 /N 2 + CO 2 ) that is conservative with respect to terrestrial biological activity. Consequently, APO reflects primarily ocean biogeochemistry and atmospheric circulation. Building on the work of Stephens et al. (1998), we present a set of APO observations for the years 1996-2003 with unprecedented spatial coverage. Combining data from the Princeton and Scripps air sampling programs, the data set includes new observations collected from ships in the low-latitude Pacific. The data show a smaller interhemispheric APO gradient than was observed in past studies, and different structure within the hemispheres. These differences appear to be due primarily to real changes in the APO field over time. The data also show a significant maximum in APO near the equator. Following the approach of Gruber et al. (2001), we compare these observations with predictions of APO generated from ocean O 2 and CO 2 flux fields and forward models of atmospheric transport. Our model predictions differ from those of earlier modeling studies, reflecting primarily the choice of atmospheric transport model (TM3 in this study). The model predictions show generally good agreement with the observations, matching the size of the interhemispheric gradient, the approximate amplitude and extent of the equatorial maximum, and the amplitude and phasing of the seasonal APO cycle at most stations. Room for improvement remains. The agreement in the interhemispheric gradient appears to be coincidental; over the last decade, the true APO gradient has evolved to a value that is consistent with our time-independent model. In addition, the equatorial maximum is somewhat more pronounced in the data than the model. This may be due to overly vigorous model transport, or insufficient spatial resolution in the air-sea fluxes used in our modeling effort. Finally, the seasonal cycles predicted by the model of atmospheric transport show evidence of an excessive seasonal rectifier in the Aleutian Islands and smaller problems elsewhere.

[1] We use continuous and discrete measurements of the dissolved O 2 /Ar ratio in the mixed layer to investigate the dynamics of biological productivity during the Southern Ocean Gas Exchange Experiment in March and April 2008. Injections of SF 6 defined two water masses (patches) that were followed for up to 2 weeks. In the first patch, dissolved O 2 /Ar was supersaturated, indicating net biological production of organic carbon. In the second patch, rapidly decreasing O 2 /Ar could only be reasonably explained if the mixed layer was experiencing a period of net heterotrophy. The observations rule out dominant contributions from vertical mixing, lateral dilution, or respiration in the ship's underway seawater supply lines. We also compare nine different estimates of net community, new, primary, or gross production made during the experiment. Net community and new production estimates agreed well in the first patch but disagreed in the second patch, both during an initial net heterotrophic period but also during the apparently autotrophic period at the end of the observations. Rapidly changing productivity during the second patch complicated the comparison of methods that integrate over daily and several week timescales. Primary productivity values from on-deck 24 h 14 C incubations and gross carbon production values from photosynthesis-irradiance experiments were nearly identical even during highly dynamic periods of net heterotrophy, while gross oxygen production measurements were 3.5-4.2 times higher but with uncertainties in that ratio near AE2. These comparisons show that the photosynthesis-irradiance experiments based on 1-2 h 14 C incubations underestimated gross carbon production.Citation: Hamme, R. C., et al. (2012), Dissolved O 2 /Ar and other methods reveal rapid changes in productivity during a

Specific docking interactions between MAPKs and their activating MAPK kinases (MKKs orMEKs

[1] During the 2007 UK SOLAS Deep Ocean Gas Exchange Experiment in the northeast Atlantic Ocean, we conducted the first ever study of the effect of a deliberately released surfactant (oleyl alcohol) on gas transfer velocities (k w ) in the open ocean. Exchange rates were estimated with the 3 He/SF 6 dual tracer technique and from measured sea-to-air DMS fluxes and surface water concentrations. A total of seven k w estimates derived from 3 He/SF 6 were made, two of which were deemed to be influenced by the surfactant. These exhibited suppression from ∼5% to 55% at intermediate wind speeds (U 10 ) in the range 7.2-10.7 m s −1 . Similarly, k w determined from DMS data (k DMS ) was also depressed by the surfactant; suppression ranged from ∼39% at 5.0 m s −1 to ∼24% at 10.8 m s −1. Surfactant thus has the potential to measurably suppress gas exchange rates even at moderate to high wind speeds.