Wind, convection and fetch dependence of gas transfer velocity in an Arctic sea‐ice lead determined from eddy covariance CO 2 flux measurements
The air‐water exchange of trace gases such as CO2 is usually parameterized in terms of a gas transfer velocity, which can be derived from direct measurements of the air‐sea gas flux. The transfer velocity of poorly soluble gases is driven by near‐surface ocean turbulence, which may be enhanced or su...
Published in: | Global Biogeochemical Cycles |
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2021
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Online Access: | http://nora.nerc.ac.uk/id/eprint/529464/ https://nora.nerc.ac.uk/id/eprint/529464/7/2020GB006633.pdf https://doi.org/10.1029/2020GB006633 |
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ftnerc:oai:nora.nerc.ac.uk:529464 2023-05-15T14:26:17+02:00 Wind, convection and fetch dependence of gas transfer velocity in an Arctic sea‐ice lead determined from eddy covariance CO 2 flux measurements Prytherch, J. Yelland, M. J. 2021-02-01 text http://nora.nerc.ac.uk/id/eprint/529464/ https://nora.nerc.ac.uk/id/eprint/529464/7/2020GB006633.pdf https://doi.org/10.1029/2020GB006633 en eng https://nora.nerc.ac.uk/id/eprint/529464/7/2020GB006633.pdf Prytherch, J.; Yelland, M. J. orcid:0000-0002-0936-4957 . 2021 Wind, convection and fetch dependence of gas transfer velocity in an Arctic sea‐ice lead determined from eddy covariance CO 2 flux measurements. Global Biogeochemical Cycles, 35 (2), e2020GB006633. https://doi.org/10.1029/2020GB006633 <https://doi.org/10.1029/2020GB006633> cc_by_4 CC-BY Publication - Article PeerReviewed 2021 ftnerc https://doi.org/10.1029/2020GB006633 2023-02-04T19:51:38Z The air‐water exchange of trace gases such as CO2 is usually parameterized in terms of a gas transfer velocity, which can be derived from direct measurements of the air‐sea gas flux. The transfer velocity of poorly soluble gases is driven by near‐surface ocean turbulence, which may be enhanced or suppressed by the presence of sea ice. A lack of measurements means that air‐sea fluxes in polar regions, where the oceanic sink of CO2 is poorly known, are generally estimated using open‐ocean transfer velocities scaled by ice fraction. Here, we describe direct determinations of CO2 gas transfer velocity from eddy covariance flux measurements from a mast fixed to ice adjacent to a sea‐ice lead during the summer‐autumn transition in the central Arctic Ocean. Lead water CO2 uptake is determined using flux footprint analysis of water‐atmosphere and ice‐atmosphere flux measurements made under conditions (low humidity and high CO2 signal) that minimise errors due to humidity cross‐talk. The mean gas transfer velocity is found to have a quadratic dependence on wind speed: k660 = 0.179 U102 which is 30% lower than commonly used open‐ocean parameterizations. As such, current estimates of polar ocean carbon uptake likely overestimate gas exchange rates in typical summertime conditions of weak convective turbulence. Depending on the footprint model chosen, the gas transfer velocities also exhibit a dependence on the dimension of the lead, via its impact on fetch length and hence sea state. Scaling transfer velocity parameterizations for regional gas exchange estimates may therefore require incorporating lead width data. Article in Journal/Newspaper Arctic Arctic Arctic Ocean Sea ice Natural Environment Research Council: NERC Open Research Archive Arctic Arctic Ocean Global Biogeochemical Cycles 35 2 |
institution |
Open Polar |
collection |
Natural Environment Research Council: NERC Open Research Archive |
op_collection_id |
ftnerc |
language |
English |
description |
The air‐water exchange of trace gases such as CO2 is usually parameterized in terms of a gas transfer velocity, which can be derived from direct measurements of the air‐sea gas flux. The transfer velocity of poorly soluble gases is driven by near‐surface ocean turbulence, which may be enhanced or suppressed by the presence of sea ice. A lack of measurements means that air‐sea fluxes in polar regions, where the oceanic sink of CO2 is poorly known, are generally estimated using open‐ocean transfer velocities scaled by ice fraction. Here, we describe direct determinations of CO2 gas transfer velocity from eddy covariance flux measurements from a mast fixed to ice adjacent to a sea‐ice lead during the summer‐autumn transition in the central Arctic Ocean. Lead water CO2 uptake is determined using flux footprint analysis of water‐atmosphere and ice‐atmosphere flux measurements made under conditions (low humidity and high CO2 signal) that minimise errors due to humidity cross‐talk. The mean gas transfer velocity is found to have a quadratic dependence on wind speed: k660 = 0.179 U102 which is 30% lower than commonly used open‐ocean parameterizations. As such, current estimates of polar ocean carbon uptake likely overestimate gas exchange rates in typical summertime conditions of weak convective turbulence. Depending on the footprint model chosen, the gas transfer velocities also exhibit a dependence on the dimension of the lead, via its impact on fetch length and hence sea state. Scaling transfer velocity parameterizations for regional gas exchange estimates may therefore require incorporating lead width data. |
format |
Article in Journal/Newspaper |
author |
Prytherch, J. Yelland, M. J. |
spellingShingle |
Prytherch, J. Yelland, M. J. Wind, convection and fetch dependence of gas transfer velocity in an Arctic sea‐ice lead determined from eddy covariance CO 2 flux measurements |
author_facet |
Prytherch, J. Yelland, M. J. |
author_sort |
Prytherch, J. |
title |
Wind, convection and fetch dependence of gas transfer velocity in an Arctic sea‐ice lead determined from eddy covariance CO 2 flux measurements |
title_short |
Wind, convection and fetch dependence of gas transfer velocity in an Arctic sea‐ice lead determined from eddy covariance CO 2 flux measurements |
title_full |
Wind, convection and fetch dependence of gas transfer velocity in an Arctic sea‐ice lead determined from eddy covariance CO 2 flux measurements |
title_fullStr |
Wind, convection and fetch dependence of gas transfer velocity in an Arctic sea‐ice lead determined from eddy covariance CO 2 flux measurements |
title_full_unstemmed |
Wind, convection and fetch dependence of gas transfer velocity in an Arctic sea‐ice lead determined from eddy covariance CO 2 flux measurements |
title_sort |
wind, convection and fetch dependence of gas transfer velocity in an arctic sea‐ice lead determined from eddy covariance co 2 flux measurements |
publishDate |
2021 |
url |
http://nora.nerc.ac.uk/id/eprint/529464/ https://nora.nerc.ac.uk/id/eprint/529464/7/2020GB006633.pdf https://doi.org/10.1029/2020GB006633 |
geographic |
Arctic Arctic Ocean |
geographic_facet |
Arctic Arctic Ocean |
genre |
Arctic Arctic Arctic Ocean Sea ice |
genre_facet |
Arctic Arctic Arctic Ocean Sea ice |
op_relation |
https://nora.nerc.ac.uk/id/eprint/529464/7/2020GB006633.pdf Prytherch, J.; Yelland, M. J. orcid:0000-0002-0936-4957 . 2021 Wind, convection and fetch dependence of gas transfer velocity in an Arctic sea‐ice lead determined from eddy covariance CO 2 flux measurements. Global Biogeochemical Cycles, 35 (2), e2020GB006633. https://doi.org/10.1029/2020GB006633 <https://doi.org/10.1029/2020GB006633> |
op_rights |
cc_by_4 |
op_rightsnorm |
CC-BY |
op_doi |
https://doi.org/10.1029/2020GB006633 |
container_title |
Global Biogeochemical Cycles |
container_volume |
35 |
container_issue |
2 |
_version_ |
1766298780090499072 |