Irish Ocean and Climate Status Report

The Irish Ocean Climate and Ecosystems Status Report 2023 is the first to build upon its 2009 predecessor. This report assesses observational datasets covering a host of Essential Ocean Variables (EOVs) and includes recommendations across areas including: atmospheric changes, ocean warming, sea level rise, acidification, plankton and fish distributions and abundance, and seabirds. This report should be considered a guide to climate adaptation policy for the public. The 2023 status report notes the following key findings in the Irish context:

• Sea-level rises of between 2-3 mm per annum since the 1990s
• A rise of ~0.5C in sea surface temperatures on Ireland’s north coast over the past ten years.
• Identification of surface water acidification
• Identification of a year-round presence of harmful algal species

This report is intended to summarise the current trends in Ireland’s ocean climate. Use has been made of archived marine data held by a range of organisations to make clear some of the key trends observed in phenomena such as atmospheric changes, ocean warming, sea level rise, acidification, plankton and fish distributions and abundance, and seabirds. The report aims to summarise the key findings and recommendations in each of these areas as a guide to climate adaptation policy and for the public.

The ocean is important to Ireland and its citizens with many livelihoods and activities supported by marine sectors including fisheries, aquaculture, ocean energy, shipping, tourism and leisure. In Ireland, about 40% of the population live within 5 km of the coast. Hence, it is critical to understand how our ocean is being affected by climate change and the implications this may have on how the ocean is used by humans.

The ocean and atmosphere are intricately linked elements of the Earth system. Changing dynamics in the atmosphere have a direct effect on oceans and their ecosystems. The North Atlantic Oscillation (NAO) is the leading mode of climate variability in the North Atlantic. A positive NAO leads to warm, wet and stormy weather over northern Europe. Other important atmospheric modes are the East Atlantic (EA) and Scandinavian (SCA) patterns.

The Atlantic Meridional Overturning Circulation (AMOC) or Gulf Stream system is key to Ireland’s mild climate. This system is predicted to decline due to climate change. Irish waters have warmed since the 1980s, with 2007 temperatures over 0.8°C above the 1960–1990 average however recent years have seen a cooling trend of -0.3°C/decade. Overall sea surface temperatures remain 0.4°C warmer in the 21st century relative to 1960–1990. Sea levels continue to rise globally with notably larger sea level rise observed in Cork and Dublin compared to global estimates.

The ocean takes up over a quarter of anthropogenic CO2 emissions each year hence, understanding the magnitude, variability and limitations of the ocean as a carbon sink is critical to climate science. CO2 uptake is altering seawater chemistry, a phenomenon referred to as “Ocean Acidification” (OA). Irish offshore waters have become more acidic with an overall reduction in pH of 0.02 units per decade. The reduction in pH is also evident in deeper waters (1500–2000 m) when 2010 is compared to the 1990s. OA also results in reduced calcium carbonate saturation states, which impacts the ability of organisms to form shells and skeletons.

Phytoplankton are the base of the marine food chain and include several harmful algal species that impact the seafood sector and potentially humans. An expansion of the phytoplankton growth season has been observed for some species in Irish waters. Diatom cell abundance has increased nationally while many dinoflagellates have declined in terms of monthly cell abundance. Significant regional variation in some of the trends is observed. Alexandrium species have increased from June to August and their geographic range has extended around the south west coast in recent years. Karenia mikimotoi blooms appear to occur slightly later in the year when comparing the most recent decade with 2001 to 2010.

There are many significant commercial fisheries in the Irish Exclusive Economic Zone (EEZ) with stock trajectories varying by species. Declines in over-exploited stocks may be further exacerbated by climate change however, disentangling climate effects from other pressures, including fishing, remains a challenge. There is evidence of increasing Lusitanian (warm water) species southern Irish waters which may allow for new fishing opportunities e.g. boarfish and anchovy. Increases in some species may be due to natural long-term fluctuations in abundance, e.g. snake pipefish. It is imperative that new and existing fishing opportunities are managed effectively and sustainably.

Half of all seabird species globally have declining population trends. Eighty-nine percent of seabirds affected by climate change are also affected by other threats e.g. overfishing, incidental capture, hunting/trapping and disturbance. Similar to fisheries, it is difficult to disentangle the precise effects of each threat on the seabird population. Northward shifts in the copepod prey of sandeels have been observed with important implications for the diet of many seabird species. Sea level rise is likely to impact populations such as Little Terns and Ringed Plover that nest on coastal beaches.

Ireland’s land mass is connected to the surrounding ocean therefore, the terrestrial and ocean environments should be studied in tandem. The terrestrial ecosystems of Ireland are strongly coupled to variability in the ocean, particularly in terms of hydrology. The Marine Institute Burrishoole catchment provides an ideal natural laboratory for such research. Comparison of CO2 levels in Lough Feeagh and Lough Furnace show that Lough Furnace emits far less CO2 than Lough Feeagh and can be a net sink of CO2 at certain times of the year. Regional inputs of nutrients and carbon from watersheds should be coupled with scenarios of global CO2 emissions to assess local impacts on coastal ecosystems.

While this report is primarily focused on the current state of the ocean, this chapter is dedicated to summarising some of the key marine climate projections for the 21st century.

• Wave heights
• Mean sea level
• Sea surface temperatures
• Stratification of the Celtic Sea water column
• Salinity

The Essential Ocean Variables (EOVs) that form the basis for many of the chapters in this report are collected by an array of marine infrastructures and monitoring programmes in Irish waters. Marine infrastructure includes marine platforms or observatories and land based specialised equipment and laboratories. These infrastructures are key to gathering long-term evidence in a changing climate and require specialised training, knowledge and skill to operate to ensure they are operated correctly.