Relationship between wind speed and gas exchange over the ocean

Abstract

Relationships between wind speed and gas transfer, combined with knowledge of the partial pressure difference of CO2 across the air-sea interface are frequently used to determine the CO2 flux between the ocean and the atmosphere. Little attention has been paid to the influence of variability in wind speed on the calculated gas transfer velocities and the possibility of chemical enhancement of CO2 exchange at low wind speeds over the ocean. The effect of these parameters is illustrated using a quadratic dependence of gas exchange on wind speed which is fit through gas transfer velocities over the ocean determined by the natural-14C disequilibrium and the bomb-14C inventory methods. Some of the variability between different data sets can be accounted for by the suggested mechanisms, but much of the variation appears due to other causes. Possible causes for the large difference between two frequently used relationships between gas transfer and wind speed are discussed. To determine fluxes of gases other than CO2 across the air-water interface, the relevant expressions for gas transfer, and the temperature and salinity dependence of the Schmidt number and solubility of several gases of environmental interest are included in an appendix.

Evaluation of a near-global eddy-resolving ocean model

“…The iron, oxygen, and carbon cycles are linked to the phosphate uptake and remineralisation through a constant Redfield ratio, and the formation of calcium carbonate is a constant fraction of organic carbon production. The atmospheric iron deposition is set by a seasonal climatology (Mongin et al, 2011); and the air-sea exchange of carbon dioxide is a function of wind speed (Wanninkhof, 1992) and climatological sea ice concentration (Matear and Lenton, 2008). Phytoplankton growth is limited by light, phosphate and iron, with the minimum of these three terms limiting growth.…”

Enhanced methane emissions from oil and gas exploration areas to the atmosphere – The central Bohai Sea

“…To determine k, the revised empirical equation of Wanninkhof (1992) by Sweeney et al (2007) was used, that is,…”

“…where S c is the Schmidt number in seawater (Wanninkhof, 1992), and u 10 is the wind speed at 10 m height (unit: m s À1 ), recorded by onboard meteorological sensors.…”

Air–sea exchange of gaseous mercury in the tropical coast (Luhuitou fringing reef) of the South China Sea, the Hainan Island, China

“…Briefly, the air-sea Hg(0) exchange flux (F) is calculated by F = K(Hg(0) water − Hg(0) air / H′), where F (ng m −2 h −1 ) is the Hg(0) emission flux from (+) or deposition flux into (-) the surface water. The gas transfer coefficient (K) is calculated by Wanninkhof (1992), K = 0.31u 10 2 (Sc Hg / 600) 0.5 , where u 10 is the wind speed (m s −1 ) at 10 m above the sea surface and the Sc Hg is the temperature-and salinity-dependent dimensionless Schmidt number of Hg (0) for seawater. The Sc Hg is defined as v / D, where v is the kinematic viscosity (cm 2 s −1 ) of seawater and D is the aqueous diffusion coefficient (cm 2 s −1 ) of Hg(0).…”

“…The Sc Hg is defined as v / D, where v is the kinematic viscosity (cm 2 s −1 ) of seawater and D is the aqueous diffusion coefficient (cm 2 s −1 ) of Hg(0). The v and D are calculated according to Wanninkhof (1992) and Kuss et al (2009), respectively. H′ is the dimensionless Henry's law constant: H′ = exp(-2404.3 / T + 6.92) (Andersson et al 2008a), where T is the surface water temperature (K).…”