Living in a crazy ocean: calcareous nannoplankton response to Oceanic Anoxic Event 2 and comparison with living coccolithophores algae

Coccolithophores algae are phytoplanktonic organisms that play a fundamental role in the ocean food web and in the global carbon cycle. They produced some tiny calcium carbonate plate, coccoliths, that surround the cell and therefore they actively contribute to the marine carbonate cycling. Nowadays the ocean is facing an alteration of seawater carbonate chemistry due to anthropogenic release of carbon dioxide. Laboratory experiments suggest that coccolithophores are very sensitive to seawater pH, dissolved CO2, temperature and nutrient concentration all of which are impacted by human CO2 emissions. Some species might have the ability to adapt but coccolithophores responses to environmental stress in culture experiments are not straightforward. Furthermore studies on large volcanic eruptions, demonstrate that metals contained in volcanic ashes, such as Cd, Cu, Pb and Zn, can have both fertilizing and toxic effects on marine phytoplankton species (diatoms and coccolithophores algae) which will ultimately lead to changes in species composition with implications for community productivity. The geological record is imprinted with numerous examples of natural global perturbations of the global carbon cycle and climate changes some of which are characterized by large-scale release of natural CO2 and ocean acidification. The selected case history we analyzed is the Cenomanian-Turonian Oceanic Anoxic Event (OAE2), during which the formation of the Carribean Plateau Large Igneous Provinces (LIP), induced the degassing of large amounts of CO2 and associated environmental consequences of warming, lower oxygen minimum zone and possibly ocean acidification. Here we present biometric data of 4 coccolith species mostly dominant in the Cenomanian and Turonian. The morphometric analyses showed a species-specific response to the perturbation: W. barnesiae, the most cosmopolitan species, doesn’t show any significant variation in size through all the event. On the contrary the other eutrophic species, respectively B. constans, D. rotatorius and Z. erectus, display a strong reduction in sizes. Dwarfism affected both length and width and mimics the p CO2 fluctuations: a progressive increase in size take place when pCO2 start to decrease while dwarf coccolith are coeval with a strong increase in CO2. Notably the maximum reduction in size occurs with the highest CO2 concentration, very high sea surface temperature and a remarkable biolimiting metal peak. However there is difficulty in unequivocally attributing deformities and size reduction during OAE2 to a single parameter, given the covariation of environmental changes. To better understand which parameter/s influence coccolith formation the most, we performed several culture experiments on four species of living coccolithophores algae taking in account toxic metal content, carbonate chemistry, nutrient content and light intensities. Here we present some preliminary results.