The inorganic carbon chemistry in coastal and shelf waters around Ireland

The wintertime spatial distribution of carbonate parameters in outer estuarine and coastal waters around Ireland is described from total alkalinity (TA) and dissolved inorganic carbon (DIC) data collected between 2010 and 2013. Due to predominantly limestone bedrock of their river catchments, the River Shannon and Barrow, Nore and Suir River system export high concentrations (>3800 μmol kg−1) of TA to their estuarine and inshore coastal waters where estuarine alkalinity decreases with increasing salinity. TA is lower in rivers with a non-calcareous bedrock, with positively correlated alkalinity-salinity relationships in both the Lee and Foyle outer estuaries. Winter pCO2 in the Shannon, Barrow/Nore/Suir and Lee estuaries is supersaturated relative to atmospheric CO2, while pCO2 in the outer Liffey estuary is slightly lower than atmospheric CO2 in three consecutive winters, indicative of a CO2 sink. Winter pCO2 is close to atmospheric equilibrium along the western shelf and through the centre of the Irish Sea, while it is a CO2 sink across the North Channel. While aragonite was supersaturated in most Irish waters, it was close to undersaturation in both the Lee estuary, attributed to its low alkalinity freshwater source, and Barrow/Nore/Suir estuary related to the flux of high concentrations of DIC from this river system. The seasonal impacts on inorganic carbon chemistry was also investigated by comparing winter and summer data collected between 2009 and 2013 along two transects in western coastal waters and along the western shelf edge. DIC was ~60 μmol kg−1 lower in summer relative to winter in the coastal transects and 39 μmol kg−1 lower along the shelf edge, accompanied by depleted nutrients and supersaturation of dissolved oxygen during summer, indicative of primary production. TA was generally higher in summer relative to winter corresponding with a decrease in nitrate, indicating that primary production dominated the TA distribution over calcification. An exception to this was at two stations along the shelf edge where TA was lower in summer relative to winter (51 μmol kg−1) and coincides with high reflectance in satellite images from a coccolithophore bloom at the time of sampling. While pCO2 was close to atmospheric equilibrium along the shelf edge during winter, this area was a CO2 sink during summer, apart from the stations where calcification was likely occurring resulting in elevated CO2 relative to atmospheric concentrations.

McGrath T., McGovern E., Cave R. R. & Kivimäe C., in press. The inorganic carbon chemistry in coastal and shelf waters around Ireland. Estuaries and Coasts. Article (subscription required).

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