One of the major concerns of marine scientists is the extent to which global warming and the associated changes will affect the ability of oceans to mitigate these impacts. The ''biological carbon pump'' (BCP), i.e., biologically driven C sequestration from the atmosphere and surface ocean to the seafloor is one of the most important processes contributing to the mitigation of climate change. A variety of parameters that may affect the effectiveness of the BCP have been studied. The extent to which altered phytoplankton composition would be subject to abiotic (photooxidation) and biological (phycosphere bacteria) degradation, termed bio/degradation, has not yet been studied or considered in climate change scenarios. The predictions are that climate change will lead to lower production of diatoms, which will be compensated for by coccolithophores. Both groups have the potential to sink due to the heavy shells on the cell surface. We plan to grow diatom and coccolithophore under optimal and unfavourable conditions mimicking warming and oligotrophy. Cultures from the stationary growth phase would be subjected to bio/degradation. Using a complex methodological approach, we will analyse the quantity and quality of organic matter (OM), especially lipids, including DOC, POC, SAS, CDOM, FDOM, together with cell morphology, pigments, C, N and P content and gene expression related to lipids. To supplement the results of the laboratory experiments, seawater samples will be taken during the diatom and coccolithophore bloom periods. Lipids are of interest because they are selectively preserved in the deep sea. Our project will provide insight into whether phytoplankton OM, particularly lipids, will be more or less degradable in the future ocean. Our prediction is that the OM, especially lipids, of coccolithophores will be more stable than those of diatoms. Our results will provide additional knowledge for predicting the extent to which global change will affect BCP.