The High Arctic glacial ecosystem: new insights from nutrient budgets

This paper describes detailed budgets of water, Cl), dissolved Si and both inorganic and organic forms of nitrogen and phosphorus for two small glacier basins in Arctic Svalbard (Midre Lovenbreen and AustreBroggerbreen). Rates of nutrient deposition are modest, dominated by inorganic nitrogen and episodically enhanced by extreme events. Hence deposition rates are also variable, ranging from 20 to 72 kg NO3- N km(-2) a(-1) and 10 - 37 kg NH4- N km(-2) a(-1) over just two consecutive years. Deposition of dissolved organic and particulate forms of nitrogen ( DONand PN respectively) also appears significant and therefore requires further investigation ( 3 - 8 kg DON-N km(-2) and 7 - 26 kg PN-N km(-2) during winter - no summer data are available). Evidence for microbially mediated nutrient cycling within the glacial system is clear in the nutrient budgets, as is the release of large phosphorus, Si and organic/particulate nitrogen fluxes by subglacial erosion. The latter is entirely dependent upon the presence of subglacial drainage, promoting silicate mineral dissolution and the erosion of largely unweathered apatite. The large DON and PN fluxes are surprising and may relate to young organic nitrogen associated with microbial life within the glaciers. This is because wide spread assimilation of NH4+ and perhaps even nitrification occurs on the glacier surface, most likely within abundant cryoconite holes. Further microbial activity also occurs at the glacier bed, where denitrification and sulphate reduction is now known to take place. Thus a two component 'glacial ecosystem' is proposed that is highly sensitive to climate change.