Coccolithophore, unicellular calcifying microalgae, significantly impact the atmosphere-ocean CO2 exchanges and the carbon cycle since geological time (Monteiro et al., 2016). Despite being only 1% of the Earth photosynthetic biomass, they store as much carbon as terrestrial plants thanks to their fast renovation time (Falkowski, 2012), assessing up to 10% of the global C fixation (Poulton et al., 2013). Among the 200 living species of coccolithophores, this project focuses on Helicosphaera carteri a species considered resistant to many environmental stressors (Šupraha et al., 2015) including highly polluted waters (Dimiza et al., 2014). Through a pilot study, we observed that H. Carteri cultivated under high CO2 level (700 ppm) reaches faster growth rates showing better preserved and bigger coccospheres than experiments at lower CO2. Thus, the CaCO3 production, the C uptake and storage, increase with increased CO2 levels. It has been demonstrated that small alterations of growth rate can affect the calcite production up to 50% (Sheward et al., 2017) with significant differences in the geometry and number of coccoliths on the coccosphere. As growth rate and cell size are the main drivers of calcite production, it is very important to understand which environmental parameter mainly affects them, and thus the cellular physiology. Being CO2 the main climate variable attracting the scientific and public interest, in this research we will deepen the CO2 effects on coccolithophore physiology exploring coccolithophores potential towards CO2 biofixation and biomass production under controlled CO2 conditions, studying the impact of climate change on future scenarios for the calcite production and export.To do so, we will reconstruct the morphological, and thus physiological, variations of H. Carteri induced by different levels of CO2. A 3D reconstruction of the coccosphere and its coccoliths would allow to identify different cellular development under low to high CO2 scenarios. We will also deepen on past and future climate/environmental drivers studying the geochemical information extracted from cultured H. Carteri. Geochemical analyzes of the trace elements will be performed on coccoliths in collaboration with Elettra synchrotron of Trieste (proposal already approved). The acquisition of the element maps will provide new evidences on the specific-element distribution on the coccolith which is still poorly known, shedding light on both the physiological processes involved in the elements’ incorporation and the relationships with the surrounding environmental and climate conditions.By knowing in depth the repercussions of environmental parameters on physiology will it be possible to understand the impact of future climate change for the production and export of calcite and the role of coccolithophores in the global carbon cycle.

Successful candidates are expected to have a background in geology, marine biology or ocean chemistry with interest in biogeochemistry and climate changes. Previous research experience with coccolithophores will be a plus. We are looking for a candidate who knows how to work both in a team and independently, and he/she is willing to test him/herself with pioneering and transdisciplinary researches.

The selected candidate will be employed for three years at the University of Pavia (Italy) in a young and dynamic team. The PhD candidate will have access to facilities concerning the study of deep marine sediments in the coccolith content at both optical and electronic microscope. Moreover, he/she is expected to collaborate with national and international outstanding institutions such as the National Institute of Oceanography and Applied Geophysics (OGS) of Trieste, the Elettra synchrotron of Trieste or the Tongji University of Shanghai.