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The G as T ransfer through P olar S ea ice experiment: Insights into the rates and pathways that determine geochemical fluxes
Author(s) -
Lovely A.,
Loose B.,
Schlosser P.,
McGillis W.,
Zappa C.,
Perovich D.,
Brown S.,
Morell T.,
Hsueh D.,
Friedrich R.
Publication year - 2015
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2014jc010607
Subject(s) - sea ice , carbon dioxide , ice shelf , chemistry , cryosphere , geology , atmospheric sciences , oceanography , organic chemistry
Sea ice is a defining feature of the polar marine environment. It is a critical domain for marine biota and it regulates ocean‐atmosphere exchange, including the exchange of greenhouse gases such as CO 2 and CH 4 . In this study, we determined the rates and pathways that govern gas transport through a mixed sea ice cover. N 2 O, SF 6 , 3 He, 4 He, and Ne were used as gas tracers of the exchange processes that take place at the ice‐water and air‐water interfaces in a laboratory sea ice experiment. Observation of the changes in gas concentrations during freezing revealed that He is indeed more soluble in ice than in water; Ne is less soluble in ice, and the larger gases (N 2 O and SF 6 ) are mostly excluded during the freezing process. Model estimates of gas diffusion through ice were calibrated using measurements of bulk gas content in ice cores, yielding gas transfer velocity through ice ( k ice ) of ∼5 × 10 −4 m d −1 . In comparison, the effective air‐sea gas transfer velocities ( k eff ) ranged up to 0.33 m d −1 providing further evidence that very little mixed‐layer ventilation takes place via gas diffusion through columnar sea ice. However, this ventilation is distinct from air‐ice gas fluxes driven by sea ice biogeochemistry. The magnitude of k eff showed a clear increasing trend with wind speed and current velocity beneath the ice, as well as the combination of the two. This result indicates that gas transfer cannot be uniquely predicted by wind speed alone in the presence of sea ice.