The oligotrophic ocean, mostly located in subtropical regions occupies ~30% of the Earth surface and has been conventionally regarded as an ocean desert. It is characterized by permanent stratification, nutrient depletion and extremely low net biological production, and hence, contributes little to carbon export from surface to deep waters at per unit area. Emerging evidence has shown that this oceanic system has a much larger dynamic range of nutrient inputs from different sources in addition to those from depth. These differently sourced nutrients withdiffering stoichiometry may stimulate biological productions in different community structures and drive the carbon export at various depth horizons within the sunlit euphotic zone (EZ). Hence, the EZ is better characterized by a two-layered structure with a nutrient nutrient-depleted layer (NDL) above the nutricline and a nutrient replete layer (NRL) across the nutricline to the base of the EZ.

The main objective of the Paris agreement consists in 《 holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change》. Still, if nothing is done to manage the increase of the greenhouse effect tied to human activity, we should see, at the end of this century, a minimum average 4°C global warming which will increase well beyond 2100. The impacts of such a 《 business as usual 》 scenario would be difficult if not impossible to handle. And, even if easier to manage, these difficulties will hold true for a +3 °C climate change a level which could be reached in the current context of the Paris agreement.

Green deal, biodiversity strategy, Farm to fork strategy… the ambitions that the European Union address in 2020 have connections with the ocean. In a world in which interactions are more and more complex, decision-makers need to rely more and more and robust, shared and evolutive science expertise. Relying on the Horizon Europe framework program, the “Starfish 2030” mission proposes to adopt a research strategy in order to fulfill theses ambitions and to give politicians keys for acti ng in the next 10 years in the field of ocean. 5 overarching objectives drive this missions : (i) Filling the knowledge and emotional gap, (ii)regenerating marine and freshwater ecosystems, (iii) zero pollution, (iv) decarbonising our ocean, and waters (v) revampinggovernance.

In 2019 the Intergovernmental Panel on Climate Change (IPCC) approved the Special Report on The Ocean and Cryosphere in a Changing Climate (SROCC) as the third special report of the 6th Assessment Cycle, following the Special Report on GlobalWarming of 1.5°C (SR1.5) and the Special Report on Climate Change and Land (SRCCL). The SROCC addresses climate change phenomena for about 80% of the Earth’s surface as covered by the ocean and the cryosphere, and develops a picture how even these remote areas of the planet are affected by climate change. It also deals with how these changes feedback on human societies, through ice melt and associated sea level rise, or through ocean warming, oxygen loss and acidification impacting marine life and fisheries results. Terrestrial aspects cover the potential exacerbation of climate change and associated impacts through permafrost thaw.

Current emission reduction pledges under the 2015 Paris Agreement are insufficient to keep global temperature “well below +2°C” in 2100 relative to pre-industrial levels and to reach targets of the United Nations Sustainable Development Goals. Even a full and timely implementation of the Paris Agreement will heavily impact the ocean. Increased political ambition is therefore required, as well as enhanced efforts of both mitigation and ecosystem and human adaptation. There is growing evidence highlighting the role the ocean plays in mitigating anthropogenic climate change (i.e., uptake and storage of heat and anthropogenic carbon), and the cascading consequences on its chemistry and physics (ocean warming, acidification, deoxygenation, and sea-level rise), ecosystems and ecosystem services.