Coccolithophore biodiversity controls carbonate export in the Southern Ocean

• Published in: Biogeosciences
• Main Authors: Hernandez, ASR, Trull, TW, Nodder, SD, Flores, JA, Bostock, H, Abrantes, F, Eriksen, RS, Sierro, FJ, Davies, DM, Ballegeer, AM, Fuertes, MA, Northcote, LC
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus GmbH 2020
• Subjects: coccolithophore; biodiversity; carbonate export; Southern Ocean
• Online Access: https://eprints.utas.edu.au/36493/; https://eprints.utas.edu.au/36493/1/143555%20-%20Coccolithophore%20biodiversity%20controls%20carbonate%20export.pdf

Southern Ocean waters are projected to undergo profound changes in theirphysical and chemical properties in the coming decades. Coccolithophoreblooms in the Southern Ocean are thought to account for a major fraction ofthe global marine calcium carbonate (CaCO3) production and export tothe deep sea. Therefore, changes in the composition and abundance ofSouthern Ocean coccolithophore populations are likely to alter the marinecarbon cycle, with feedbacks to the rate of global climate change. However,the contribution of coccolithophores to CaCO3 export in the SouthernOcean is uncertain, particularly in the circumpolar subantarctic zone thatrepresents about half of the areal extent of the Southern Ocean and wherecoccolithophores are most abundant. Here, we present measurements of annualCaCO3 flux and quantitatively partition them amongst coccolithophorespecies and heterotrophic calcifiers at two sites representative of a largeportion of the subantarctic zone. We find that coccolithophores account fora major fraction of the annual CaCO3 export, with the highest contributionsin waters with low algal biomass accumulations. Notably, our analysisreveals that although Emiliania huxleyi is an important vector for CaCO3 export to thedeep sea, less abundant but larger species account for most of the annualcoccolithophore CaCO3 flux. This observation contrasts with thegenerally accepted notion that high particulate inorganic carbon accumulations during the australsummer in the subantarctic Southern Ocean are mainly caused by E. huxleyi blooms. Itappears likely that the climate-induced migration of oceanic fronts willinitially result in the poleward expansion of large coccolithophore speciesincreasing CaCO3 production. However, subantarctic coccolithophorepopulations will eventually diminish as acidification overwhelms thosechanges. Overall, our analysis emphasizes the need for species-centredstudies to improve our ability to project future changes in phytoplanktoncommunities and their influence on marine biogeochemical cycles.