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CYCLOPS:- Cycling of Phosphorus in the Mediterranean

Problem to be solved

The Mediterranean in general, and the eastern basin in particular, is the largest body of water in the world that is thought to be phosphorus limited. However, all the evidence for this conclusion is indirect, based on chemical measurements and a limited number of bottle experiments.

It is well known that the Mediterranean is an extremely vulnerable marine ecosystem especially regarding nutrient inputs. As a result of its unusual anti-estuarine circulation, it exports nutrients into the North Atlantic making it highly oligotrophic. Relatively small changes in the fluxes of nutrients have a disproportionate effect on the marine ecosystem structure in the region. Although the Barcelona treaty and subsequent EC regulations severely restrict the nature and amount of waste that can be disposed of within the Mediterranean, anthropogenic inputs of nutrients continue to reach the basin in large amounts. These nutrients are introduced via the atmosphere, river discharges and dredge spoils, as well as directly from activities such as mariculture, which is an expanding industry in the region. In order to reduce the impact on the marine ecosystem it is necessary to understand the P cycling in detail.

Scientific objectives and approach

The aim of CYCLOPS is to confirm directly that P is the growth-limiting nutrient in the Eastern Mediterranean, using a novel field strategy that avoids the limitations of bottle experiments. Detailed measurements will be made to determine how small additions of phosphate change the structure of the microbial ecosystem and increase biomass and productivity. In the first year, we will carry out a set of microcosm experiments, involving the addition of P, N, and Si to define the changes that we will expect to see during the field experiments. In year 2 we will carry out a cruise in which phosphate and an inert SF6 tracer will be dispersed in a 4 km2 patch of surface water within the stable structure of the Cyprus eddy. The experiment is designed to mimic natural processes and the total amount of phosphorus added will be similar to a natural dust event, consisting of less than 20% of the natural winter turnover. Our novel techniques for P, tracer and microbiological assays are sensitive enough to track these small P additions, ensuring our experiments are reversible, localized and have negligible ecosystem effects. This is ideal for (1) biogeochemical budgeting of P and (2) compliance with the Barcelona convention and all other relevant EC regulations and directives regarding nutrient inputs to the Mediterranean. Between this experiment and a second enrichment experiment, we will carry out 2 short cruises to determine the natural state and seasonal variability of the system. In the second field experiment we will add phosphate 3 times successively to the same patch of water, in order to determine the change in biomass, ecosystem structure and phosphorus speciation by detailed biological and chemical measurements.

Expected impacts

The scientific understanding developed during this study will be used to develop a quantitative understanding of the P cycle that will be used to calibrate nutrient & ecosystem models including the Mediterranean Forecasting system, a model currently being developed to provide real-time oceanographic predictions across the basin. The results of this project will be used to update directives and regulations, to further protect the Mediterranean from ecosystem damage. New technologies will be developed to solve environmental problems. For example, the new technology of non-polluting intensive mariculture systems will be targeted to remove P from the effluent as well as the present N, if we can show that P is the critical nutrient in the region.

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