Measuring and understanding the biogeochemical impact of Greenland ice sheet melt

Increased ice sheet is increasing freshwater input to the oceans. The implications of this increasing flux are widespread, both regionally and globally, since meltwater transports bioavailable compounds and chemical weathering products that can influence global biogeochemical cycles. Quantifying these outputs is demanding: glacier meltwaters are remote, experience freeze-thaw, low temperatures, high concentrations of suspended sediment, low concentrations of major ions and turbid and varying flows that challenge conventional sampling techniques. New sensing technologies enable high resolution, continuous assessment of biogeochemically significant parameters, which, when combined with high quality sampling programmes, can reveal how glacier melt impacts on downstream systems. Data from two contrasting catchments in Greenland show that meltwaters were undersaturated with respect to atmospheric CO₂ for the vast majority of the melt season. Undersaturated meltwaters drawdown CO₂ from the atmosphere; however, this is balanced by CO₂ returned to the atmosphere via marine carbonate precipitation. Meltwater from the contemporary Greenland ice sheet therefore has the potential to provide a carbon feedback mechanism to the global system.