The efficiency of the biological pump strongly depends on the composition and susceptibility to bacterial degradation of the Particulate Organic Matter (POM). Earth system models usually assume that the primary production gets recycled within the water column following a pre-established remineralisation profile. However, the shape of this profile, which depends on the origin and lability of the POM, has a great impact on the final amount of organic carbon that reaches the deep ocean and sediments. With relatively large cell sizes and mineral covers that protect and ballast the cells, diatoms and coccolithophorids greatly contribute to carbon export in silica rich and silica depleted environments, respectively. With the aim of assessing the remineralisation of POM in the mesopelagic zone, a series of degradation experiments with POM of different origin were performed. By enriching surface seawater with two sets of nutrients (one with silica and one without), blooms of diatoms and coccolithophorids were induced in the lab. The POM produced by each bloom was then transferred to dark containers with bacterial assemblages from mesopelagic waters (200m) and the remineralisation process was followed for 3 weeks. Inorganic nutrients concentration, abundance of prokaryotes, bacterial extracellular enzyme activity, particulate and dissolved organic carbon concentration, optical characteristics of the dissolved organic matter, pH and alkalinity were among the measurements used to monitor the process. We will discuss the importance of phytoplankton composition on POM remineralisation efficiency in the context of ocean carbon sequestration

1st Iberian Ecological Society Meeting (2019); XIV Congreso Nacional de la Asociación Española de Ecología Terrestre (AEET), Ecology: an integrative science in the Anthropocene, 4-7 February 2019, Barcelona, Spain

Peer Reviewed