Research Spotlight: Tackling Ocean Acidification

The Wildlife Trusts’ National Marine Week runs from 25^th July – 9^th August and in celebration of all things marine we are highlighting some of the incredible projects our researchers and students are involved in. Here Sophie Gill, postgraduate student, explains how her research could help us to ensure the future conservation of the oceans by mitigating global warming!

‘I work as part of the OceanBUG research group, led by Prof. Ros Rickaby. We all investigate the evolution and role of marine plankton in the biogeochemical cycles in the ocean, including coccolithophores, one of which, a species called Emiliania huxleyi, is shown in Figure 1. Plankton are the base of the food chain for the entire ocean ecosystem, and produce more oxygen than all plants on land! So understanding the ecological and biogeochemical role of plankton is key to ensuring the future conservation of our oceans.

An individual coccolithophore of the species Emiliania huxleyi, as viewed under the Scanning Electron Microscope (SEM). The intricately shaped plates adorning the outside of this single-celled organism are made out of calcium carbonate.

My DPhil research involves using laboratory culturing experiments to quantify how coccolithophores and foraminifera, two major groups of marine plankton, respond to enhanced ocean alkalinity. Both make their spectacularly intricate shells out of calcium carbonate. Foraminifera are shown in Figure 2, where there are actually two individuals of the species Globigerinella siphonifera. Both the shells at the centre, and the radial spines, are made of calcium carbonate.

Foraminifera as viewed under the light microscope. The species shown in the photo is Globigerinella siphonifera, and there are two individuals here. Calcite chambers are surrounded by calcite spines.

Elevating the natural levels of ocean alkalinity has been proposed as an idea to a) increase the natural CO₂ sequestration capacity of the oceans, helping us to reduce levels of atmospheric CO_2, and b) counteract harmful ocean acidification. Ocean acidification poses severe threats in particular to calcifying organisms like the coccolithophores and foraminifera I work on, because their calcium carbonate shells may be harder to build when the ocean’s acidity increases. Corals are also at significant risk from this threat.

So far, my results show that enhanced ocean alkalinity does not appear to be severely damaging to the growth of coccolithophores or foraminifera. This is promising as an initial result to illustrate that enhanced ocean alkalinity might be safe to implement. However, coccolithophores seem to increase the amount of calcium carbonate they produce when alkalinity is enhanced. Calcium carbonate formation (also called calcification) actually releases CO₂ as a by-product, so this could reverse some of the CO₂ drawdown. The key trade-off to understand is whether CO₂ release through increased calcification by the coccolithophores outweighs CO₂ drawdown by alkalinity enhancement. Resolving this is still a work in progress, but I hope to publish the results soon!’