PISCES: Patagonian Ice field Shrinkage impacts on Coastal and fjord EcosystemS

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Ocean basins across a large proportion of the Earth's surface receive substantial freshwater and sediment input from glaciers and ice sheets. This freshwater input is increasing and will continue to do so as rising air and ocean temperatures enhance rates of ice melting and stimulate the collapse of floating glacier tongues. This is true of glaciers draining the Patagonian Ice Fields, the largest ice mass in the Southern hemisphere outside of Antarctica, almost all of which have thinned and retreated in recent decades. The physical impacts of Patagonian meltwater discharge on the oceans are becoming better studied, driven by a need to predict future sea level rise and future water supply for human settlements. However, the biological dimension of this freshwater export, is poorly understood. Large fjord systems act as receiving waters for glacial runoff and ice discharge in Patagonia, and together with marine waters, boast highly productive ecosystems and associated fisheries. The impact of glacial freshwater inputs to these ecosystems is likely to be important for several reasons. First, inputs of dilute glacial meltwater create a stable stratified water column for phytoplankton growth, but simultaneously may reduce nutrient supplies from vertical mixing. Second, glacial runoff and icebergs likely act as "fertilisers", being rich in highly bioavailable dissolved organic matter and other major nutrients, such as iron, phosphorus, nitrogen and silicon. Last, the high suspended particulate matter load of glacial runoff is likely to have a dual effect, adding further nutrients but creating light limiting conditions for plankton within inner fjord systems. These impacts on downstream ecosystems are likely to intensify as glacial freshwaer fluxes rise. Key unknowns at present are: 1) the magnitude, character and timing of glacial nutrient and sediment delivery to Patagonian fjord ecosystems; 2) how these inputs may alter in a warming world; and 3) the sensitivity of downstream ecosystem productivity and biodiversity to such inputs. PISCES will test the hypothesis that Patagonian Ice Field FW fluxes have a natural fertilisation impact upon downstream fjord and marine productivity, via a combination of field-based research and biogeochemical modelling. PISCES will generate the first ice-to-ocean dataset of riverine nutrient fluxes and biological response across a broad latitudinal transect in Patagonia. This will provide an important utility for policy makers managing freshwater supply, quality, marine ecosystems and fisheries in the region.