Ocean acidification around the UK and Ireland

11 January 2023

Ocean acidification is a pressing global issue, but what are its impacts more locally to the UK and Ireland? A report led by scientists at Plymouth Marine Laboratory highlights just this, with concerning findings. 

 

What is ocean acidification? 

The term ocean acidification is used to describe the ongoing decrease in ocean pH caused by human carbon dioxide (CO2) emissions, such as the burning of fossil fuels. 

The carbon dioxide goes up into the atmosphere, but it doesn’t stay there. It is absorbed by the ocean, it dissolves into the sea water, and it reacts with the chemistry of the seawater and creates carbonic acid. 

Regardless of where it is emitted, anthropogenic CO2 is mixed throughout the Earth’s atmosphere by wind and weather. The increasing amount of CO2 taken up by the oceans and corresponding pH decline are therefore global phenomena. 

 

What are the impacts of ocean acidification on a global level? 

On a global level, atmospheric CO2 exceeded 414 parts per million (ppm) in 2021 - a 49% increase above pre-industrial levels - and this has continued to increase by approximately 2.4 ppm per year over the last decade. This ongoing increase is primarily due to CO2 release by fossil fuel combustion, cement production and land-use change (mainly deforestation). 

Dr Helen Findlay, Biological Oceanographer at Plymouth Marine Laboratory, who led the study, said: 

“Ocean acidification can influence marine species in a number of ways, including direct impacts on internal physiology or indirectly through changes to food webs and processes.” 

“Some species are already showing effects from ocean acidification when exposed to short-term fluctuations, and these could be used as indicator species for long-term impacts on marine ecosystems.” 

“Our studies have shown that ocean acidification can have either positive, neutral or negative impacts depending on the process, population, or species that is being investigated.” 

“For example, many phytoplankton, seaweed and algae species, show a positive or neutral response to elevated CO2, as a result of using those higher levels of carbon dioxide to utilise for photosynthesis. However, for marine invertebrates, and some fish species, the direct response to lowered pH and elevated CO2 is generally either neutral or negative.” 

“It's not just about the lower pH - the altered seawater chemistry also changes the ease at which calcium carbonate minerals are made and dissolve. Calcium carbonate is vital to many marine organisms that use it to build their skeletons or shell structures, such as corals, shellfish and several important groups of plankton. These marine organisms are at increased risk from ocean acidification, and it’s important to remember that shell-based animals are an incredibly important part of the food web, so ocean acidification has much wider implications on all marine life.” 

 

What are the impacts to the UK and Ireland? 

More locally, the North Atlantic Ocean - bordering the west of the United Kingdom and Ireland - contains more anthropogenic CO2 than any other ocean basin. This is due to the deep-water formation that occurs there, which effectively transfers CO2 from the surface into the ocean interior.  

Whilst ocean acidification has been primarily considered a surface-water issue, it is spreading throughout the water column.  

This has the potential to impact marine species and ecosystems at greater depths, such as cold-water coral reefs, which occur around the UK shelf and northeast Atlantic at depths from 200 m to 1500 m. 

Dr Findlay adds, “There is also evidence of ocean acidification affecting the shell integrity of plankton calcifiers, raising concern on the potential consequences for bivalve and crustacean populations in the North Sea and for future implications for the shellfish and aquaculture industry.” 

 

What could happen in the future? 

Dr Yuri Artioli, Marine Ecosystem Modeller at PML, who also contributed to the paper, said: 

“We use a forecasting model to project anticipated impacts of ocean acidification in the future. Our models have projected that the average continental shelf seawater pH will continue to decline to year 2050 at similar rates to the present day, with rates then increasing in the second half of the century, depending on the emissions scenario.” 

“The rate of pH decline in coastal areas is projected to be faster in some areas (e.g. Bristol Channel) than others, such as the Celtic Sea, therefore impacts on marine life will be felt more strongly in some areas than others.” 

“Under high-emission scenarios, it is projected that around 60% of bottom waters on the North-West European Shelf seas could become permanently corrosive to more soluble forms of calcium carbonate (aragonite), and episodic corrosive conditions are projected to begin by as soon as 2030.” 

“High levels of nearshore variability in carbonate chemistry may mean that some coastal species have developed a higher adaptative capacity than others. However, all species are at increased risk from extreme exposure episodes.” 

To find out more, you can access the full report here >>