The coccolithophores: Actors and recorders of climate change – CARCLIM

As we head into the future with uncertainty regarding the effects that the emission of greenhouse gas will have on our climate, there is an increasing desire to better understand and model carbon fixation by oceanic phytoplankton – a prominent component of the carbon cycle and Earth’s climate system. There is indeed a pressing need to constrain the response of marine phytoplankton ecosystems and the biological pump to increased sea surface temperatures, surface ocean carbonation and consecutive decreased seawater pH. The overarching objective of this project is to establish an unprecedented bulk response of photosynthetic and calcification efficiency through laboratory culture of a prominent biological group, the coccolithophores, subjected to a series of perturbation experiments mimicking the environmental conditions of our future, present and past oceans (spanning the IPCC2014 RCP conditions to greenhouse conditions of the Cenozoic). This project will seek a mechanistic understanding of the modulation of calcification of their biominerals, using the isotopic composition of the coccoliths as tracers of the dynamics of physiological-relevant reactions enabling intracellular calcification. As such, it will unravel a still elusive link between the chemistry and morphometrics of the coccoliths. Conducting laboratory cultures of coccolithophores will enable constraining the environmental control on their ability to calcify and developing a biologically-grounded understanding of these vital effects with ramifications for the use of the geochemistry of the coccolith in palaeoceanography. For decades, palaeoceanographers have struggled to tackle the biological origin of the sedimentary archive, which is still regarded as a black box-type problem and remains a large source of uncertainty in climate reconstruction. Yet, it is of paramount importance to deconvolve the biological vs. environmental forcing on the geochemistry of sediments. The vital effects have been regarded as the villain in the palaeoceanographic world for more than 60 years. Integrated via modelling, this project will provide a valuable biogeochemical framework for the fate of coccolithophore production in our Anthropocene World, and set the stage to a novel means of fingerprinting fluctuations in temperatures, ambient CO2 concentrations and pH in the past by exploiting the magnitude of the vital effects. The CARCLIM project extends well beyond the proxy development, but aims at a conceptual advance in (palae)oceanography with the establishment of a ground-breaking and multidisciplinary approach that will ultimately serve to augment current understanding of the influence of organic and inorganic carbon fixation by the coccolithophores on ocean chemistry and Earth’s climate.