The Intensifying Role of High Wind Speeds on Air‐Sea Carbon Dioxide Exchange

Abstract

While it has been known that wave breaking and bubble generation at high wind speeds enhance air‐sea carbon dioxide (CO2) exchange rates (F), quantification of their contribution at the global scale remains a formidable challenge. There is urgency to make progress on this issue as a significant uptick in both magnitude and frequency of high wind events (HW) has been documented over the last 3 decades. Using a wind‐wave dependent expression for gas transfer velocity (k) that explicitly considers bubbles and a widely used wind‐only parameterization, the spatial pattern of k at high winds can be explained by sea surface temperature distribution. The HW, which represent some 3% of wind conditions, contribute disproportionally to the global F (18%) with an increasing trend. Approximately 50% of the global F at high winds is attributed to bubble contribution. The findings are of significance to quantifying CO2 transfer to the ocean interior.

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

“…However, relying solely on wind speed to calculate the gas transfer velocity at the sea surface increases the uncertainty of CO 2 flux estimation (Woolf, 1993). Recent studies have shown that the generation and breaking of ocean waves also significantly affect the gas exchange process at the sea-air interface (Zappa et al, 2007;Gu et al, 2021). Observations in the Southern Indian Ocean sector of the Antarctic Circumpolar Current (ACC) show that large quantities of bubbles produced by wave breaking enhance the intensity of under-surface turbulence by up to three orders of magnitude and hence expand the gas contact area (Li et al, 2021).…”

“…And the contribution of bubbles and the dependence of the ocean state vary greatly on regional and seasonal scales, generally supporting the ocean to absorb approximately 40% of the CO 2 (Reichl and Deike, 2020). Gu et al (2021) investigated a new expression of gas transfer velocity that coupled with wind-wave and showed that about 50% of the global CO 2 fluxes at high wind speeds are attributable to bubblemediated contributions. However in these studies, 'wind-wave' represents total waves and using these to modulate gas transfer velocity may exaggerate their impacts.…”

Gas Fluxes and Steady State Saturation Anomalies at Very High Wind Speeds

“…At more moderate wind speeds, such as those between ∼10 and 30 m s −1 , the discrepancy between CO 2 and DMS in eddy covariance experiments (Bell et al., 2017; Blomquist et al., 2017; Zavarsky et al., 2018) is often attributed to bubble fluxes being important for CO 2 but not DMS. Recent studies suggest that 18%–40% of the air‐sea CO 2 flux overall is mediated through bubbles (Gu et al., 2021; Reichil & Deike, 2020). Thus, a better understanding of bubble fluxes is crucial in order to accurately predict CO 2 fluxes at high wind speeds as well as for calculating gas fluxes of less soluble gases such as O 2 and the noble gases.…”

“…Very few studies investigate air‐sea gas exchange at high wind speeds (>25 m s −1 ) in the field (D'Asaro & McNeil, 2007; Liang et al., 2020; McNeil & D'Asaro, 2007) due to safety and technological challenges of sampling during hurricane force winds. Even though wind speeds greater than 25 m s −1 do not occur globally often (Figure S1 in Supporting Information , Ricciardulli & Wentz, 2016), the expected high fluxes associated with such wind speeds (Gu et al., 2021) and the predicted increase in frequency of high wind conditions (Young & Ribal, 2019; I. R. Young et al., 2011) make it important to study gas exchange at high wind speeds. Most experiments at high wind speeds have been done in wind‐wave tanks (Krall & Jaehne, 2014; Krall et al., 2019; Mesarchaki et al., 2015), controlled environments where wind is produced by large fans and waves are produced by wave paddles.…”

“…Very few studies investigate air-sea gas exchange at high wind speeds (>25 m s −1 ) in the field Liang et al, 2020; due to safety and technological challenges of sampling during hurricane force winds. Even though wind speeds greater than 25 m s −1 do not occur globally often (Figure S1 in Supporting Information S1, Ricciardulli & Wentz, 2016), the expected high fluxes associated with such wind speeds (Gu et al, 2021) and the predicted increase in frequency of high wind conditions (Young & Ribal, 2019;I. R. Young et al, 2011) make it important to study gas exchange at high wind speeds.…”