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Abstract The Weddell Gyre mediates carbon exchange between the abyssal ocean and atmosphere, which is critical to global climate. This region also features large and highly variable freshwater fluxes due to seasonal sea ice, net precipitation, and glacial melt; however, the impact of these freshwater fluxes on the regional carbon cycle has not been fully appreciated. Using a novel budget analysis of dissolved inorganic carbon (DIC) mass in the Biogeochemical Southern Ocean State Estimate, we highlight two freshwater‐driven transports. Where freshwater with minimal DIC enters the ocean, it displaces DIC‐rich seawater outwards, driving a lateral transport of 75 ± 5 Tg DIC/year. Additionally, sea ice export requires a compensating import of seawater, which carries 48 ± 11 Tg DIC/year into the gyre. Though often overlooked, these freshwater displacement effects are of leading order in the Weddell Gyre carbon budget in the state estimate and in regrouped box‐inversion estimates, with implications for evaluating basin‐scale carbon transport.
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Quantifying Net Community Production and Calcification at Station ALOHA Near Hawai'i: Insights and Limitations From a Dual Tracer Carbon Budget Approach
Abstract A budget approach is used to disentangle drivers of the seasonal mixed layer carbon cycle at Station ALOHA (A Long‐term Oligotrophic Habitat Assessment) in the North Pacific Subtropical Gyre (NPSG). The budget utilizes data from the WHOTS (Woods Hole—Hawaii Ocean Time‐series Site) mooring, and the ship‐based Hawai'i Ocean Time‐series (HOT) in the NPSG, a region of significant oceanic carbon uptake. Parsing the carbon variations into process components allows an assessment of both the proportional contributions of mixed layer carbon drivers and the seasonal interplay of drawdown and supply from different processes. Annual net community production reported here is at the lower end of previously published data, while net community calcification estimates are 4‐ to 7‐fold higher than available sediment trap data, the only other estimate of calcium carbonate export at this location. Although the observed seasonal cycle in dissolved inorganic carbon in the NPSG has a relatively small amplitude, larger fluxes offset each other over an average year. Major supply comes from physical transport, especially lateral eddy transport throughout the year and entrainment in the winter, offset by biological carbon uptake in the spring. Gas exchange plays a smaller role, supplying carbon to the surface ocean between Dec‐May and outgassing in Jul‐Oct. Evaporation‐precipitation (E‐P) is variable with precipitation prevailing in the first half and evaporation in the second half of the year. The observed total alkalinity signal is largely governed by E‐P with a somewhat stronger net calcification signal in the wintertime.
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- Award ID(s):
- 1756517
- PAR ID:
- 10435636
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Global Biogeochemical Cycles
- Volume:
- 37
- Issue:
- 7
- ISSN:
- 0886-6236
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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