The pelagic record of ocean acidification since the beginning of industrialisation

The planet's oceans are absorbing a substantial fraction of the CO2 released by anthropogenic fossil fuel and biomass burning. As a consequence the pH of seawater is dropping; a process called ocean acidification. The concern is that these changes will have a profound impact on marine biota by affecting both species range of habitat and the calcification of their skeletons and shells. At the current rate of CO2 uptake, the average surface ocean pH will be lower than that experienced by marine organisms at any time over the last several million years. The most vulnerable ecosystems are in the polar regions and hence we will focus on the northern North Atlantic. Here seawater is corrosive to carbonate minerals and so organisms that calcify in these waters will be particularly sensitive to any acidification. We have selected representative groups of marine plankton that live at the surface in the top metres of the ocean (foraminifers and coccolithophores) and hence in habitats already altered by the 0.1 pH drop since the start of the industrial period in the late 19th Century. Foraminifers and coccolithophores are single-celled organisms. We have selected these groups because they are 1) key carbonate producers and hence contribute to global carbon cycle, and 2) significant components of the planktic ecosystem. How can we test if the seawater pH and carbonate ion changes over the last 150 years have influenced organisms with carbonate skeletons? Changes have already been suggested in the scientific literature for these calcifiers and so it is important to test these results using a larger number of species and different groups of organisms at the same location to assess possible ecosystem impacts. The project will focus on high resolution sediment cores which will allow us to study marine plankton at decadal resolution. We will be able to determine both, natural variability within these ecosystems over the last 1000 years and quantify OA changes over the last 150 years. We will compare and contrast foraminifers and coccolithophores. We are expecting possible differences as the former are zooplankton, live much longer before reproducing and encapsulate sea water to calcify. The contrast, the latter are phytoplankton and hence calcification and photosynthesis will be influenced by the changes in surface water chemistry, they divide daily instead of bi-weekly to monthly and they calcify in an internal vesicle. Changes in calcification will be determined for both groups, determining their weight (just foraminifers) and thickness. As foraminifers grow by adding chambers, we can analyse the entire life history and see if possible changes in size are related to changes in timing of development. We has, using detailed scanning electron analysis and morphometics, determine these changes not just for the traditional 'geological species' but for more subtle 'morphotypes' which have been recognised to have specific environmental adaptation and potentially different reactions to OA. All of this work will be done in a framework of well dated material, analysed for sedimentological alterations (winnowing) to ascertain the comparability of the results. Environmental information will additionally help to interpret the data. These results will determine if the base of the marine food chain and the major contributors to the global carbon cycle, have already altered their calcification due to ocean acidification. All this information is needed to improve predictions of how vulnerable marine ecosystems are to ocean acidification, how likely they are able to adapt and support effective advice to policy makers and managers of marine bioresources on the possible size and timescale of risks of ocean acidification to marine ecosystems.