How will ocean acidification affect surface ocean biology and processes?

The burning of fossil fuels is releasing vast quantities of extra carbon dioxide (CO₂) to the Earth's atmosphere. A proportion of this stays in the atmosphere, raising atmospheric CO₂ levels, but much leaves the atmosphere after a time, either to become sequestered in trees and plants or to become absorbed in the oceans. CO₂ staying in the atmosphere is a greenhouse gas, causing global warming; whereas CO₂ entering the sea lowers pH and increases acidity. The changing chemistry of seawater due to ocean acidification is mostly well understood and not subject to debate. What is much less well known and more strongly debated is the impact that the changing chemistry will have on marine organisms and ecosystems, on biogeochemical cycling in the sea, and on how the sea interacts with the atmosphere to influence global climate.

Most work to date has consisted of experimental studies in which organisms have been subjected to elevated CO₂ (and the associated lower pH/increased acidity) in tanks or flasks. An advantage of these laboratory experiments is control; everything is kept constant except for the changes to CO₂ and pH, so if a response is observed the cause is clear. However, there are also limitations to such studies. For instance, there is no time for organisms to adapt evolutionarily or for there to be shifts in species composition, away from more affected forms towards more acid-tolerant forms, as might occur in nature. We aim instead to study the response of real-world plankton to acidification and provide an increased mechanistic and quantitative understanding of the effects of ocean acidification on organism physiology, variation in shell size and shape, biogeochemical rates, plankton biodiversity and community structure, food webs and climate-affecting processes. We will thus advance understanding of how the surface waters of the world's oceans, and the life within, will respond to ocean acidification.

(Inter)national governmental environment and climate change departments (e.g. the European Union, UK Met Office, UK government departments, such as DEFRA and DECC ) as well as international bodies and NGOs (Intergovernmental Panel on Climate Change, environmental and fisheries charities, pressure groups) are interested in ocean acidification and the way in which marine ecosystems can be managed, protected and any undesirable changes predicted and mitigated against. Improved understanding of oceanic consequences of elevated CO₂ will allow policy forming bodies to refine their CO₂ emission and mitigation strategies and policies. Ocean acidification is part of the Living With Environmental Change programme.

We will advance the study of ocean acidification by collecting and comparing more observations of marine ecosystems which are naturally more acidic or alkaline.

We will also conduct a large number of experiments in which we will bring volumes of natural seawater from the ocean surface into ship deck-containers and subject the organisms within to higher CO₂ and other stressors such as increased temperature. We will monitor the changes that take place within these natural communities, including biogeochemical and climate-related processes, as the seawater acidity is increased to controlled levels that may be expected in the future oceans at current CO₂ emission rates. A major strength of such studies is the inclusion of natural environmental variability and complexity that is difficult or impossible to capture in laboratory experiments. Thus, the responses measured during these controlled experiments on the naturally-occurring community may represent more accurately the future response of the surface ocean to acidification.

By contrasting the two sets of observations, we will gain an improved understanding of how acidification affects organisms living in their natural environment, after assemblage reassortments and evolutionary adaptation have had time to play out.

Most of the planned work will be carried out on three cruises to locations with strong gradients in seawater carbon chemistry and pH; the Arctic Ocean, around the British Isles and the Southern Ocean.