Impacts of Increased Atmospheric CO2 on Ocean Chemistry and Ecosystems

Lead Partner: National University of Ireland Galway. Project Partner: Marine InstituteOcean 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 Institut

Chemical oceanography of Irish waters, with particular emphasis on ocean acidification

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

Chemical characteristics of water masses in the rockall trough

NOTICE: this is the author’s version of a work that was accepted for publication in Deep Sea Research Part I: Oceanographic Research Papers. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Deep Sea Research Part I: Oceanographic Research Papers, [In Press (December 2011)] doi:10.1016/j.dsr.2011.11.007 http://www.sciencedirect.com/science/article/pii/S0967063711002111peer-reviewedDirect observations of physical and chemical data in the Rockall Trough during February of 2008, 2009 and 2010 are presented. Results are compared to a similar WOCE transect, AR24, completed in November/December 1996. Temperature and salinity data have been used to identify the water masses present in the Trough, and have been combined with nutrient (nitrate, nitrite, phosphate, silicate) and oxygen data to produce a table outlining the chemical characteristics of each of the water masses. Eastern North Atlantic Water (ENAW) moving north through the Trough gains nutrients from a branch of the North Atlantic Current (NAC). Mediterranean Water (MW) was identified as a warm saline core, with characteristically low oxygen and low preformed nutrients along the Irish continental shelf break near 53°N. Found at a similar density level at the southern entrance to the Trough, Sub Arctic Intermediate Water (SAIW) has relatively high oxygen and preformed nutrients, likely entrained from the subpolar gyre when it was formed. LSW was identified as a prominent water mass between 1500–2000 m deep, with characteristically high oxygen content. Lower silicate, and to a lesser extent preformed nitrate, in 2009 coincide with a freshening of Labrador Sea Water (LSW) relative to other years, and could indicate a stronger influence from the Labrador Current when it was formed. Finally, traces of Antarctic Bottom Water (AABW) were found as far north as 53°N, indicated by a sharp increase in nutrient concentrations, particularly silicate in the deepest parts of the Trough

Local drivers of the seasonal carbonate cycle across four contrasting coastal systems

Four contrasting coastal systems in Ireland, each with shellfish production activities, were studied to provide a first evaluation of the spatial and seasonal influences on the local carbonate system. The study sites included; (1) a coastal system with sandstone bedrock and minimal freshwater sources, (2) an estuarine system with a catchment limestone bedrock, (3) an estuarine system with a catchment granite bedrock, and (4) a karst groundwater-fed estuary. The type of bedrock was the dominant control on regional carbonate chemistry, where the calcium carbonate catchment bedrock was a strong source of both dissolved inorganic carbon and total alkalinity input in the two limestone regions, which are supersaturated with respect to atmospheric CO2 throughout the year. Primary production played an important role in the non-limestone regions, where both systems were CO2-undersaturated during productive months. Minimum aragonite saturation () was observed at all sites during winter when productivity is lowest; surface winter is 2 in the inner estuary. The substrate-to-inhibitor ratio (SIR), an alternative indicator of ecosystem vulnerability to acidification, was positively correlated to in all systems, however with more variability in the two limestone regions. Results highlight challenges of assessing local ecosystem vulnerability to future acidification and the importance of understanding the local spatio-temporal biogeochemistry

Diurnal to interannual variability in the Northeast Atlantic from hydrographic transects and fixed time-series across the Rockall Trough

The southern entrance to the Rockall Trough is subject to a complex set of dynamic processes, influenced by Atlantic gyre interactions, the North Atlantic Current, slope boundary currents, variable wind stress forcing, mesoscale activity, and a changing supply of modified water masses formed elsewhere in the Atlantic. These processes drive large temporal and spatial variations, and mixing of surface and intermediate water mass properties that advect through the Trough and drive variations in the deeper waters circulating around it. Here, we investigate variability across the southern and central Rockall Trough from standard hydrographic sections (2006–2022) and deepwater moored subsurface measurements, to better understand changes in water column characteristics and water mass modification during advection through the Rockall Trough and track the aftermath of recent freshening events. Rapid and longer-term physical changes are assessed along with spatial variability and watermass interaction. Interannual variability is large across intermediate depths, deeper circulations are regenerated and a salinity core associated with the eastern boundary current is detailed. Establishing, maintaining, monitoring and analysis of observational ocean time-series datasets are a fundamental requirement for managing and conserving crucial biological resources and are key to understanding oceanic and earth system change