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

1
Center for Marine Sensors, Institute for Chemistry and Biology of the Marine Environment, Carl von Ossietzky University Oldenburg, 26129 Wilhelmshaven, Germany
2
Climate and Environmental Physics, Physics Institute, and Oeschger Centre for Climate Change Research, University of Bern, 3012 Bern, Switzerland
3
Centre for Ocean and Atmospheric Sciences, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK
*
Author to whom correspondence should be addressed.
Geosciences 2019, 9(5), 230; https://doi.org/10.3390/geosciences9050230
Received: 15 March 2019 / Revised: 6 May 2019 / Accepted: 13 May 2019 / Published: 20 May 2019
(This article belongs to the Special Issue Ocean-Atmosphere Interaction)
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Abstract

Carbon dioxide (CO2) fluxes between the ocean and atmosphere (FCO2) are commonly computed from differences between their partial pressures of CO2pCO2) 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 pCO2 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 ΔpCO2 between the ocean and atmosphere. Such conditions occur frequently in the Tropics. View Full-Text
Keywords: gas transfer velocity; low wind speed; carbon dioxide; ocean-atmosphere CO2 flux; carbon cycle gas transfer velocity; low wind speed; carbon dioxide; ocean-atmosphere CO2 flux; carbon cycle
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Ribas-Ribas, M.; Battaglia, G.; Humphreys, M.P.; Wurl, O. Impact of Nonzero Intercept Gas Transfer Velocity Parameterizations on Global and Regional Ocean–Atmosphere CO2 Fluxes. Geosciences 2019, 9, 230.

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