Ocean Acidification Impacts on Sea-Surface Biology, Biogeochemistry and Climate

Lead Research Organisation: University of Oxford
Department Name: Earth Sciences


The burning of fossil fuels is releasing vast quantities of extra carbon dioxide to the Earth's atmosphere. Much of this stays in the atmosphere, raising CO2 levels, but much also leaves the atmosphere after a time, either to become sequestered in trees and plants, or else to become absorbed in the oceans. CO2 staying in the atmosphere is a greenhouse gas, causing global warming; CO2 entering the sea makes it more acidic, and the ongoing acidification of seawater is seen in observational records at various sites where time-series data are collected. The changing chemistry of seawater due to ocean acidification is mostly well understood and not subject to debate. What is much less well known 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 climate. We will look to investigate these questions in terms of how the surface waters of the world's oceans, and the life within, will respond to ocean acidification. Most of what we know about biological impacts, and the source of the current concern about the impact on marine life, comes from experimental studies in which individual organisms (e.g. single corals) or mono-specific populations (e.g. plankton cultures) have been subjected to elevated CO2 (and the associated lower pH) in laboratory experiments. These laboratory experiments have the advantage of being performed under controlled conditions in which everything can be kept constant except for changes to CO2. So if a response is observed, then the cause is clear. However, there are also limitations to laboratory studies. For instance, organisms have no time to adapt evolutionarily, and there is no possibility of shifts in species composition away from more sensitive forms towards more acid-tolerant forms, as might be expected to occur in nature. Another shortcoming is the absence of food-web complexity in most experiments, and therefore the absence of competition, predation, and other interactions that determine the viability of organisms in the natural environment. We seek to advance the study of ocean acidification by collecting more observations of naturally-occurring ecosystems in places where the chemistry of seawater is naturally more acidic, and/or where it naturally holds more carbon,as well as locations which are not so acidic, and/or hold more usual amounts of carbon. 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 3 cruises to places with strong gradients in seawater carbon and pH: to the Arctic Ocean, around the British Isles, and to the Southern Ocean. As well a making observations we will also conduct a large number of experiments, in which we will bring volumes of natural seawater from the ocean surface into containers on the deck of the ship, together with whatever life is contained within, and there subject them to higher CO2 and other stressors. We will monitor the changes that take place to these natural plankton communities (including to biogeochemical and climate-related processes) as the seawater is made more acidic. 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 experiments on the naturally-occurring community may represent more accurately the future response of the surface ocean to ocean acidification. In order to carry out this experimental/observational work programme we have assembled a strong UK-wide team with an extensive track record of successfully carrying out sea-going scientificresearch projects of this type.


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Crowhurst S (2018) Carbonate ions, orbits and Mg/Ca at ODP 1123 in Geochimica et Cosmochimica Acta

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McClelland HL (2017) The origin of carbon isotope vital effects in coccolith calcite. in Nature communications

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Rickaby R (2016) Environmental carbonate chemistry selects for phenotype of recently isolated strains of Emiliania huxleyi in Deep Sea Research Part II: Topical Studies in Oceanography

Description We have discovered that the acidic polysaccharide used for mediating calcification, differs in its structure between morphotype of coccolithophore.
We have also discovered that the carbon concentrating mechanism likely employed by coccolithophores is starting to be relaxed in response to rising CO2 levels already introduced into the environment through fossil fuel burning.
Coccolithophorid algae, particularly Emiliania huxleyi, are prolific biomineralisers that, under many conditions, dominate communities of marine eukaryotic plankton. Their ability to photosynthesise and form calcified scales (coccoliths) has placed them in a unique position in the global carbon cycle. Contrasting reports have been made with regards to the response of E. huxleyi to ocean acidification. Therefore, there is a pressing need to further determine the fate of this key organism in a rising CO2 world. In this paper, we investigate the phenotype of newly isolated, genetically diverse, strains of E. huxleyi from UK Ocean Acidification Research Programme (UKOA) cruises around the British Isles, the Arctic, and the Southern Ocean. We find a continuum of diversity amongst the physiological and photosynthetic parameters of different strains of E. huxleyi morphotype A under uniform, ambient conditions imposed in the laboratory. This physiology is best explained by adaptation to carbonate chemistry in the former habitat rather than being prescribed by genetic fingerprints such as the CMM motif. To a first order, the photosynthetic capacity of each strain is a function of both aqueous CO2 availability, and calcification rate, suggestive of a link between carbon concentrating ability and calcification. The calcification rate of each strain is related linearly to the natural environmental [CO32-] at the site of isolation, but a few exceptional strains display low calcification rates at the highest [CO32-] when calcification is limited by low CO2 availability and/or a lack of a carbon concentrating mechanism. We present O2-electrode measurements alongside coccolith oxygen isotopic composition and the uronic acid content (UAC) of the coccolith associated polysaccharide (CAP), that act as indirect tools to show the differing carbon concentrating ability of the strains. The environmental selection revealed amongst our recently isolated strain collection points to the future outcompetition of the CCM-lacking, slow growing morphotypes B/C and R by more rapidly photosynthesising, and lightly calcified strains of morphotype A but with their rate of calcification highly dependent on the surface ocean saturation state.
Exploitation Route Provides a new non-subjective method for morphotype identification
Have provided a framework for thinking about selection of coccolithophorid by environmental carbonate chemistry during ongoing ocean acidification
Sectors Environment

Description Evidence for ocean acidification impacts on coccolithophores from the natural environment but in terms of elevating carbon availability for photosynthesis. novel marker for coccolithophore morphotype.
First Year Of Impact 2013
Sector Environment
Impact Types Cultural

Description ERC Advanced Grant
Amount € 2,423,564 (EUR)
Funding ID H2020 - ERC-2020-AdG n. 101019146 SCOOBi 
Organisation European Research Council (ERC) 
Sector Public
Country Belgium
Start 12/2022 
End 11/2027
Description WOWHOW Science exhibit at the Oxford Natural History Museum 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? Yes
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Engagement of public with algae

Year(s) Of Engagement Activity 2012,2013,2014