The long arm of global warming may reach down into the ocean floor, interrupting the flow of nutrients from shallow waters to the deep ocean. These nutrients, in the form of organic matter, jointly with coarse sediment, are funneled down into the deep ocean through vast steep-sided submarine canyons, driven by the formation of dense water over continental shelves through cooling by wind and evaporation. In the Gulf of Lions, the Dense Shelf Water Cascading (DSWC) currents deliver up to 15,000 tones of highly nutritive, fresh organic matter per day. As global warming increases sea surface temperatures, it could cause major decreases in dense water formation (Somot et al., 2006). In addition, carbon storage in the deep ocean is going to be dramatically affected. The effect has been underestimated and, given the large number of ocean sites where DSWC has been reported (Ivanov et al., 2004), it will deserve the attention of GRACCIE scientists, who are pioneering research on the impacts of DSWC (Canals et al., 2006).

Global warming is also altering the properties of ocean water masses (e.g. salinity, temperature, density) and therefore their behaviour. Marginal seas, like the Mediterranean, significantly influence nearby ocean regions through the export of modified water outflows (Lopez-Jurado et al., 2005) and are particularly sensitive to these climate variations. Ocean gateways like the Strait of Gibraltar play a key role in water, matter and energy exchange. A system of proven acoustic transmitters and receivers to track tagged marine animals (including endangered species) passing through an Ocean Tracking Network (OTN) of listening curtains for monitoring the structure and movements of water masses and their alterations due to climate change will be deployed at the Strait of Gibraltar. GRACCIE funding will be very timely to support such an exciting and promising experience, which is an absolute novelty worldwide.