PIANO

The accelerated melting of the Antarctic ice sheet due to global warming profoundly influences adjacent marine ecosystems. The delivery of fresh water from the ice sheet potentially represents a new source of key nutrients, including iron (Fe), a micronutrient known to limit phytoplankton primary production and the biological pump of CO2 in the Southern Ocean. But the bioavailability of Fe, provided mainly in the form of colloids and particles by glacial ice, is poorly understood. The main objectives of PIANO are to elucidate the role of marine prokaryotes as key engineers in the transformation of Fe delivered by Antarctic ice sheet melting and its consequences on their interactions with phytoplankton. PIANO aims to elucidate 1- the processes by which prokaryotes transform and acquire glacial Fe 2- the response of phytoplankton to Fe processed by prokaryotes and 3- the nature and strength of the Fe-mediated prokaryote-phytoplankton interactions. To fill these knowledge gaps the multidisciplinary team of PIANO will combine experimental observations using model organisms of prokaryotes and phytoplankton, a mechanistic model, and in situ observations throughout one year at a coastal Antarctic site influenced by ice melting. This latter will be achieved by the deployment of two innovative autonomous samplers. The identification of the pathways involved in the acquisition of glacial Fe by prokaryotes and the resulting interactions with phytoplankton together with the seasonal in situ dynamics of the respective genes and transcripts will provide original insights to the metabolic routes and microbial taxa involved in this key process. PIANO will thereby provide a better understanding of a key mechanism likely to influence the Southern Ocean ecological trajectory under climate change conditions.