Impact of Nonzero Intercept Gas Transfer Velocity Parameterizations on Global and Regional Ocean-Atmosphere CO2 Fluxes

Type Article
Date 2019-05
Language English
Author(s) Ribas-Ribas MarianaORCID1, Battaglia Gianna2, 3, Humphreys Matthew P.4, Wurl Oliver1
Affiliation(s) 1 : Carl von Ossietzky Univ Oldenburg, Ctr Marine Sensors, Inst Chem & Biol Marine Environm, D-26129 Wilhelmshaven, Germany.
2 : Univ Bern, Climate & Environm Phys, Phys Inst, CH-3012 Bern, Switzerland.
3 : Univ Bern, Oeschger Ctr Climate Change Res, CH-3012 Bern, Switzerland.
4 : Univ East Anglia, Sch Environm Sci, Ctr Ocean & Atmospher Sci, Norwich NR4 7TJ, Norfolk, England.
Source Geosciences (2076-3263) (Mdpi), 2019-05 , Vol. 9 , N. 5 , P. 230 (22p.)
DOI 10.3390/geosciences9050230
Note This article belongs to the Special Issue Ocean-Atmosphere Interaction
Keyword(s) gas transfer velocity, low wind speed, carbon dioxide, ocean-atmosphere CO2 flux, carbon cycle

Carbon dioxide (CO2) fluxes between the ocean and atmosphere (FCO2) are commonly computed from differences between their partial pressures of CO2 (pCO(2)) and the gas transfer velocity (k). Commonly used wind-based parameterizations for k imply a zero intercept, although in situ field data below 4 m s(-1) are scarce. Considering a global average wind speed over the ocean of 6.6 m s(-1), a nonzero intercept might have a significant impact on global FCO2. Here, we present a database of 245 in situ measurements of k obtained with the floating chamber technique (Sniffle), 190 of which have wind speeds lower than 4 m s(-1). A quadratic parameterization with wind speed and a nonzero intercept resulted in the best fit for k. We further tested FCO2 calculated with a different parameterization with a complementary pCO(2) observation-based product. Furthermore, we ran a simulation in a well-tested ocean model of intermediate complexity to test the implications of different gas transfer velocity parameterizations for the natural carbon cycle. The global ocean observation-based analysis suggests that ignoring a nonzero intercept results in an ocean-sink increase of 0.73 Gt C yr(-1). This corresponds to a 28% higher uptake of CO2 compared with the flux calculated from a parameterization with a nonzero intercept. The differences in FCO2 were higher in the case of low wind conditions and large pCO(2) between the ocean and atmosphere. Such conditions occur frequently in the Tropics.

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