Patrizia Ziveri – Institut de Ciència i Tecnologia Ambientals Universitat Autònoma de Barcelona (ICTA – UAB)
More than a quarter of the anthropogenic CO2 emissions are absorbed by the ocean, changing the ocean chemistry and resulting in ‘ocean acidification’. Anthropogenic CO2 emission leads also to a rise in global average temperatures, including sea surface temperature at an unprecedented pace. The risks posed by warming and acidification are expected to become more acute in the next decades, as CO2 emissions into the atmosphere are accelerating.
Coccolithophores are a very abundant marine calcifying phytoplankton group that plays a major role in biogeochemical cycles and in the regulation of climate. These tiny algae measuring a few thousands of a millimeter, form the base of the marine trophic web, and through calcification and photosynthesis contribute to the regulation of the atmospheric and oceanic CO2 levels. The effects of acidification – and in particular warming – are rarely considered for the organism itself, and there is very little knowledge on how warming and acidification combined may affect their adaptation and evolution.
Culture experiments were conducted on Mediterranean Sea and North Pacific Ocean strains of Emiliania huxleyi, the most abundant coccolitophore species. A main aim was to detect the effects of temperature, and secondarily of acidification, on the coccolithophore calcification and sinking rates.
Using scanning electron microscopy, an increase in malformed and incomplete coccoliths in a warmer and more acidified ocean was shown. This will hamper the evolutionary success of these calcifiers and their role in regulating atmospheric carbon. In addition, using a novel approach to calculate sinking rate from cell-architecture, the studies showed that a warmer and more acidic ocean will lead to an increase in their cell sinking rate. The faster sinking of this group of calcifying phytoplankton can have an impact on their survival.