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Strategically positioned along the western margin of the North Atlantic, Irish shelf and offshore waters play a crucial role in the global thermohaline circulation and regional and global climate cycles. The main objective of this study was to investigate the biogeochemical characteristics of the main water masses in the region to generate information on how the marine environment is changing with time. Dissolved oxygen, nutrient and carbon data, collected across the Rockall Trough in February 2009 and 2010, proved useful as chemical tracers of water masses in the region and highlighted processes that could not have been identified using hydrographic data alone. Inorganic carbon data from 2009 and 2010 were compared with WOCE data collected across the Trough in the 1990s to assess the temporal evolution of anthropogenic carbon (Cant) in the region over 2 decades. Two methods were used to calculate Cant between surveys, CT-abio and extended multiple linear regression, both of which resulted in similar rates of increase in Cant through the water column, with subsequent decrease in pH and saturation state of calcium carbonate minerals. Between 1991 and 2010, pH in subsurface waters has decreased by 0.040±0.003 units and by 0.029±0.002 units in Labrador Sea Water. Net community production (NCP) was calculated along the western shelf edge between 49.8-55.4ºN. Generally maximum NCP was measured in surface waters over the 500-750m contours, decreasing in both offshore and shallower on-shelf surface waters. Where calculated, there was a net CO2 uptake from the atmosphere suggesting this region is a CO2 sink during the productive season. Due to its influence on the buffer capacity of the surface ocean, the distribution of total alkalinity (AT) in Irish coastal and shelf waters was investigated. The AT distribution in outer estuarine and coastal waters is more complex than along the western shelf and through the centre of the Irish Sea due to varying river inputs. Rivers with limestone bedrock catchments had relatively high AT concentrations which influence the buffer capacity, and hence rate of pH change, of the surrounding coastal waters. Results indicate that the algorithm produced by Lee et al. (2006) to calculate AT from temperature and salinity should not be used in Irish coastal waters due to variable but substantial riverine inputs of AT.

Lead Partner: National University of Ireland Galway. Project Partner: Marine Institute, Ocean pH is a function of the seawater carbonate system, which is a function of both the influx of CO2 from the atmosphere and the resulting concentration of CO2 in the water (i.e. pCO2). Uptake of anthropogenic carbon dioxide from the atmosphere is reducing ocean pH; a phenomenon referred to as ocean acidification. It is estimated that there has been a decrease of 0.1 pH units in the surface waters of the world’s oceans since the start of the industrial revolution with a reduction of 0.3 – 0.5 forecast by 2100. There is growing concern over the potential consequences of ocean acidification for marine ecosystems and the services they provide for mankind. This project was aimed at enabling the capability and developing the expertise within Ireland to measure and quantify the flux of CO2 into (or out of) the ocean; to monitor seasonal trends in pCO2 and CO2 fluxes; to determine the current baseline state and variability of the carbonate system; and to evaluate the potential impact of future changes on ecosystems with the ultimate aim of contributing to more informed policy development., This project (Grant-Aid Agreement No. SS/CC/07/001(01)) was carried out under the Sea Change strategy with the support of the Marine Institute and the Marine Research Sub-Programme of the National Development Plan 2007–2013. Support was also provided by NUI Galway College Fellowship and by the EPA Fellowship 2006-PhD-AQ-2., Funder: Marine Institute