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Abstract The air‐sea exchange of oxygen (O2) is driven by changes in solubility, biological activity, and circulation. The total air‐sea exchange of O2has been shown to be closely related to the air‐sea exchange of heat on seasonal timescales, with the ratio of the seasonal flux of O2to heat varying with latitude, being higher in the extratropics and lower in the subtropics. This O2/heat ratio is both a fundamental biogeochemical property of air‐sea exchange and a convenient metric for testing earth system models. Current estimates of the O2/heat flux ratio rely on sparse observations of dissolved O2, leaving it fairly unconstrained. From a model ensemble we show that the ratio of the seasonal amplitude of two atmospheric tracers, atmospheric potential oxygen (APO) and the argon‐to‐nitrogen ratio (Ar/O2), exhibits a close relationship to the O2/heat ratio of the extratropics (40–). The amplitude ratio,/, is relatively constant within the extratropics of each hemisphere due to the zonal mixing of the atmosphere./is not sensitive to atmospheric transport, as most of the observed spatial variability in the seasonal amplitude ofAPO is compensated by similar variations in(Ar/). From the relationship between/heat and/in the model ensemble, we determine that the atmospheric observations suggest hemispherically distinct/heat flux ratios of 3.30.3 and 4.70.8 nmolbetween 40 andin the Northern and Southern Hemispheres respectively, providing a useful constraint forand heat air‐sea fluxes in earth system models and observation‐based data products.
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The Sensitivity of Southern Ocean Air‐Sea Carbon Fluxes to Background Turbulent Diapycnal Mixing Variability
Abstract The Southern Ocean (SO) connects major ocean basins and hosts large air‐sea carbon fluxes due to the resurfacing of deep nutrient and carbon‐rich waters. While wind‐induced turbulent mixing in the SO mixed layer is significant for air‐sea fluxes, the importance of the orders‐of‐magnitude weaker background mixing below is less well understood. The direct impact of altering background mixing on tracers, as opposed to the response due to a longer‐term change in large‐scale ocean circulation, is also poorly studied. Topographically induced upward propagating lee waves, wind‐induced downward propagating waves generated at the base of the mixed layer, shoaling of southward propagating internal tides, and turbulence under sea ice are among the processes known to induce upper ocean background turbulence but typically are not represented in models. Here, we show that abruptly altering the background mixing in the SO over a range of values typically used in climate models (m2 s−1–m2 s−1) can lead to a ∼70% change in annual SO air‐sea CO2fluxes in the first year of perturbations, and around a ∼40% change in annual SO air‐sea CO2fluxes over the 6‐year duration of the experiment, with even greater changes on a seasonal timescale. This is primarily through altering the temperature and the dissolved inorganic carbon and alkalinity distribution in the surface water. Given the high spatiotemporal variability of processes that induce small‐scale background mixing, this work demonstrates the importance of their representation in climate models for accurate simulation of global biogeochemical cycles.
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- PAR ID:
- 10491609
- Publisher / Repository:
- AGU
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Oceans
- Volume:
- 128
- Issue:
- 9
- ISSN:
- 2169-9275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1029/2023JC019756
