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Abstract There is limited information on how the nutrient and freshwater input affects water column carbonate chemistry in the estuaries along the northern Gulf of Mexico. In this study, we assess the seasonal and spatial variability in carbonate chemistry in the Barataria Basin, a eutrophic estuary adjacent to the mouth of the Mississippi River. Eleven stations were sampled along a salinity gradient during the winter (January), spring (April), summer (July), and fall (October) of 2021. Surface and bottom water samples were collected for the analyses of dissolved inorganic carbon (DIC); total alkalinity (TA); and nitrite plus nitrate (NO2 + NO3), phosphate (PO4), and dissolved silica (SiO4). Dissolved CO2(pCO2) was measured in the surface water. Seasonal surface DIC and TA values ranged from 1553 to 2582 μmol kg−1and 1217 to 2217 μmol kg−1, respectively. DIC and TA varied seasonally and showed an increasing trend from fresh stations to saline stations. The highest DIC and TA values were observed during the fall season, likely due to the increased contribution of DIC and TA from adjacent marshes as a result of enhanced porewater exchange. In contrast to DIC and TA, pCO2decreased with the increase of salinity. The seasonal and spatial patterns in carbonate chemistry could not be explained solely by physical mixing and reflected complex interactions between biogeochemical processes driven by nutrient supply and temperature as well as tidal flushing and material exchanges with adjacent marshes.
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Inorganic Carbon and p CO 2 Variability During Ice Formation in the Beaufort Gyre of the Canada Basin
Abstract Solute exclusion during sea ice formation is a potentially important contributor to the Arctic Ocean inorganic carbon cycle that could increase as ice cover diminishes. When ice forms, solutes are excluded from the ice matrix, creating a brine that includes dissolved inorganic carbon (DIC) and total alkalinity (AT). The brine sinks, potentially exporting DIC andATto deeper water. This phenomenon has rarely been observed, however. In this manuscript, we examine a ~1 yearpCO2mooring time series where a ~35‐μatm increase inpCO2was observed in the mixed layer during the ice formation period, corresponding to a simultaneous increase in salinity from 27.2 to 28.5. Using salinity and ice based mass balances, we show that most of the observed increases can be attributed to solute exclusion during ice formation. The resultingpCO2is sensitive to the ratio ofATand DIC retained in the ice and the mixed layer depth, which controls dilution of the ice‐derivedATand DIC. In the Canada Basin, of the ~92 μmol/kg increase in DIC, 17 μmol/kg was taken up by biological production and the remainder was trapped between the halocline and the summer stratified surface layer. Although not observed before the mooring was recovered, this inorganic carbon was likely later entrained with surface water, increasing thepCO2at the surface. It is probable that inorganic carbon exclusion during ice formation will have an increasingly important influence on DIC andpCO2in the surface of the Arctic Ocean as seasonal ice production and wind‐driven mixing increase with diminishing ice cover.
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- PAR ID:
- 10457805
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Oceans
- Volume:
- 124
- Issue:
- 6
- ISSN:
- 2169-9275
- Page Range / eLocation ID:
- p. 4017-4028
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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