The intensifying role of high wind speeds on air‐sea carbon dioxide exchange

Type Article
Date 2021-03
Language English
Author(s) Gu YuanyuanORCID1, 2, Katul Gabriel G.ORCID3, 4, Cassar NicolasORCID1, 5
Affiliation(s) 1 : Division of Earth and Ocean Sciences Nicholas School of the Environment Duke University Durham, USA
2 : College of Oceanography Hohai University Nanjing, China
3 : Nicholas School of the Environment Duke University Box90328 Durham NC ,USA
4 : Department of Civil and Environmental Engineering Duke University Durham NC ,USA
5 : CNRS ,Univ Brest IRD, Ifremer, LEMAR F‐29280 Plouzané ,France
Source Geophysical Research Letters (0094-8276) (American Geophysical Union (AGU)), 2021-03 , Vol. 48 , N. 5 , P. e2020GL090713 (10p.)
DOI 10.1029/2020GL090713
Abstract

While it has been known that wave breaking and bubble generation at high wind speeds enhance air‐sea 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 three 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.

Plain Language Summary

Studies on air‐sea carbon dioxide (CO2) exchange seek to determine how rapidly CO2 molecules traverse the air‐water interface. This exchange impacts a plethora of processes related to ocean biogeochemistry, oceanic carbon cycling, and CO2 buildup in the atmosphere. At high wind speeds, both conventional aerodynamic transfer processes and bubbles generated by wave breaking are expected to enhance air‐sea CO2 gas exchange. Yet the impact of bubbles in isolation on global and regional CO2 exchange remains a subject of inquiry and speculation. There is some urgency to make progress on this topic because the magnitude and frequency of high wind events (HW) have been steadily increasing over the last three decades. The work here demonstrates that bubbles contribute as much as 50% of CO2 gas exchange under high wind speeds conditions, which rarely occur over the ocean (less than 3% of the time). Yet, HW contribute disproportionally to the global air‐sea CO2 gas exchange (about 18%).

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