Ireland's State of the Environment Report 2024

227 Chapter 9: The Marine Environment Figure 9.8  Global (blue) and Irish waters (green) sea surface temperature (SST) anomaly (top). Global (blue) and Irish waters (green) ocean heat content (OHC) anomaly (bottom). Anomalies are calculated relative to the period 1960-1990. Inset highlights in green the ‘Real Map of Ireland’ – the limits of Irish waters used here ˜ SST anomaly global ˜ SST anomaly Ireland ˜ OHC anomaly global ˜ OHC anomaly Ireland -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 2020 2000 1980 1960 1940 1920 1900 -250 -200 -150 -100 -50 0 50 100 150 200 250 2020 2000 1980 1960 1940 1920 1900 OHC Anomaly (zettajoules) SST Anomaly (°C) Year Year -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 Source: Nolan et al. , 2023 The uptake by the oceans of anthropogenic carbon dioxide emissions also leads to acidification. The pH (the scale used to specify the acidity or basicity of an aqueous solution) of Irish waters has been declining over the last four decades (McGovern et al. , 2023). Ocean acidification will continue and even accelerate under the higher carbon dioxide emission scenarios. Certain marine organisms that build calcium shells or skeletons, such as shellfish and cold-water coral ( Desmophyllum pertusum ) reefs, will be vulnerable to ocean acidification. There have been changes in marine ecosystems, such as in the seasonality and abundance of many species including phytoplankton and zooplankton at the base of the food web. Globally, climate change is leading to a poleward expansion of many species. There is evidence of an increase in the presence of warm-water species to the south of Ireland. However, for fish and seabirds, disentangling climate effects from other pressures on populations, including fishing, remains a challenge (Nolan et al. , 2023; Vaughan et al. , 2023). Nutrient enrichment The assessment of nutrient enrichment in marine waters shows that eutrophication is not an issue in our offshore waters. However, in the seas closer to shore this is not always the case. Assessment under the WFD has shown that 64% of our estuaries are at moderate status. In particular, no estuaries on the south coast are at a status higher than moderate (EPA, 2021). The primary driver of environmental status is nutrient enrichment. The OSPAR Inputs of Nutrients to the OSPAR Maritime Area programme has been tracking the loads of different parameters from land-based activities reaching the marine environment since the 1990s (Axe, 2022). For Ireland, large decreases in nitrogen and phosphorous inputs were observed, and these continued to decline until around 2013 (EPA, 2024). Since then, the inputs of nutrients have increased (Figure 9.9), and these are largest in the rivers entering the sea along the south and south-east coasts of Ireland.