Glider observations of productivity in the Alboran Sea (GOPITAS)

Marine plants contribute about half of the global net primary production and thus sustain fisheries and world food supplies. Current climate change caused by anthropogenic greenhouse gas emissions is likely to affect this production through changes in temperature, ocean circulation, pH, nutrient and light availability. Understanding what drives production is therefore a key problem of marine science. Here, we propose a pilot study involving UEA's three ocean gliders, to make a significant contribution to improving this understanding by observing the physical, chemical and biological processes driving production in the Alboran Sea, western Mediterranean. In the temperate and polar oceans, winter overturning provides nutrients for surface production, but in the subtropical gyres this mechanism is too weak to overcome nutrient limitation. The gyres of the Alboran Sea behave like the subtropical gyres, but are much smaller and therefore easier to study. In such regions, smaller-scale processes are likely to contribute significantly, e.g., wind/turbulence interactions at the mesoscale (10-100 km) and submesoscale (1-10 km). Resolving these small-scale processes through traditional ship-board surveys is expensive and technically challenging. Recently developed autonomous platforms and sensors can significantly enhance traditional ship-based work. For example, a fleet of >3000 Argo floats now take regular temperature and salinity profiles of the upper 2 km of the world's oceans (www.argo.ucsd.edu) and help improve our understanding of oceanic heat budgets and circulation. Biological and chemical sensors add further dimensions to these technologies. In particular, oxygen sensors can measure net community production, i.e. the balance between oxygen-producing photosynthesis and oxygen-consuming respiration. Continuous measurements of key parameters and processes have thus become possible on a global scale. Floats can only vertically in the water column and are otherwise drifting passively. Gliders have been developed to partly overcome the limited manoeuvrability of floats. These autonomous vehicles can be interactively piloted in the vertical as well as horizontal direction and acquire depth profiles of marine physical and biogeochemical parameters with high resolution in space and time. They can 'see' where satellites cannot penetrate the surface, work for months at a time and are much cheaper than traditional oceanographic cruises. We propose the use of three gliders for simultaneous measurements of physical, chemical and biological parameters in the Alboran Sea, a small seasonally oligotrophic gyre system in the western Mediterranean Sea, adjacent to two frontal zones. Our overall goal is to establish how to best use gliders to improve our understanding of processes sustaining biological production, on all temporal and spatial scales. The GOPITAS pilot study will bring a biogeochemical component to the international REP10 Alboran Sea experiment organised by the NATO Undersea Research Centre (NURC) involving up to 15 gliders. The Small Grant is sufficient to enable GOPITAS thanks to the generous support in kind from our project partners, including free access to the ships HMS Roebuck (UK Navy) and NRV Alliance (NATO) as well as deployment and technical support from the glider manufacturer (iRobot). This will be one of the first deployments worldwide of three biogeochemical gliders simultaneously.