Mesoscale Temporal Wind Variability Biases Global Air–Sea Gas Transfer Velocity of CO2 and Other Slightly Soluble Gases

Abstract

The significance of the water-side gas transfer velocity for air–sea CO2 gas exchange (k) and its non-linear dependence on wind speed (U) is well accepted. What remains a subject of inquiry are biases associated with the form of the non-linear relation linking k to U (hereafter labeled as f(U), where f(.) stands for an arbitrary function of ), the distributional properties of (treated as a random variable) along with other external factors influencing k, and the time-averaging period used to determine k from . To address the latter issue, a Taylor series expansion is applied to separate f(U) into a term derived from time-averaging wind speed (labeled as ⟨U⟩ where indicates averaging over a monthly time scale) as currently employed in climate models and additive bias corrections that vary with the statistics of . The method was explored for nine widely used f(U) parameterizations based on remotely-sensed 6-hourly global wind products at 10 m above the sea-surface. The bias in k of monthly estimates compared to the reference 6-hourly product was shown to be mainly associated with wind variability captured by the standard deviation around or, more preferably, a dimensionless coefficient of variation [...]

Spatiotemporal distributions of air-sea CO2 flux modulated by windseas in the Southern Indian Ocean

“…It is clear that after considering the impact of windseas, the gas transfer velocity is improved nearly for all times. An average 5%-15% enhancement is seen, which is lower than the enhancement caused by total waves shown in Gu et al (2020). This is in line with expectations, as increasing evidence has indicated that mass transfer, such as CO 2 , is factually influenced by the surface turbulent process associated with the wave field (Liang et al, 2013;Brumer et al, 2017;Lenain and Melville, 2017).…”

Response of Surface Ocean pCO2 to Tropical Cyclones in Two Contrasting Basins of the Northern Indian Ocean

“…$$$\delta {F}_{{CO}_{2}}=\sqrt{{(0.2)}^{2}+{(0.003)}^{2}+{{(0.057)}^{2}+(0.0006)}^{2}}\approx 0.2$$$ In the process of calculating CO 2 air‐sea flux, many algorithms have been put forth which relate the gas transfer velocities to a variety of factors regulating the transfer of gases across the air‐sea boundary (Garbe et al., 2014; Gutierrez‐Loza et al., 2022; Leighton et al., 2018; Ribas‐Ribas et al., 2018; Yang et al., 2021). Empirical formulations which relate transfer velocities to wind speeds have reported quadratic (Wanninkhof 2014; Prytherch & Yelland 2021) or higher dependencies and even other functionalities (Deiki & Melville 2018; Frankignoulle, 1988; Gu et al., 2021b; Li et al., 2021; Monahan & Spillane 1984; Wanninkhof & McGillis, 1999; Wanninkhof et al., 2009; Yang et al., 2022). Wanninkhof (1992) showed that a quadratic dependence exists between gas transfer velocities and wind speeds within the range of global wind speeds of 0–30 m/s determined at intervals of 0.5 m/s.…”