Controls of sediment-bound and dissolved nutrient transport from a glacierised metasedimentary catchment in the high Arctic

Abstract

Rapid warming in polar and alpine areas is causing significant glacier mass loss and resulting in increasing freshwater delivery to the oceans. Recent research indicates that higher meltwater water runoff is likely to increase solute and sediment transport, which will include nutrients, to downstream environments. This enhanced delivery may drive a negative feedback effect on atmospheric CO₂ concentrations by stimulating primary production in fjords and near-coastal regions. Labile sediment-bound nutrient species constitute a high proportion of the total nutrient yield from glacierised catchments, but studies that investigate their source and behaviour are sparse. Here we determine sediment-bound and dissolved nutrient (Si, Fe, P) delivery from a polythermal glacier in SW Spitsbergen. Suspended sediment and dissolved samples were collected from subglacial outflows and a downstream site. Our results show high spatial variability in chemical weathering processes resulting in differences in sediment-bound nutrient concentration. Sulphide oxidation and carbonate dissolution appear more important in a channelised system underlain by rocks metamorphosed in green schist facies, and silicate mineral weathering appears more important in smaller subglacial outflows underlain by rocks undergone intense metamorphism in amphibolite facies. Sediments from the channelised outlet have two times higher content of sediment-bound highly reactive iron (∼0.29 % dry weight, hereafter d.w.) than the minor subglacial outflows. In contrast, sediment-bound amorphous silica (ASi) is almost double in the minor subglacial outflows compared to the channelised outlet (∼0.17 % d.w. vs ∼0.10 % d.w.). The yield of sediment-bound Fe and Si (2.3 and 1.3 10³ kg km⁻² yr⁻¹, respectively) was several times higher than the dissolved flux of those elements. Sediment-bound Fe yields were in the range of values noted previously for the Greenland Ice Sheet. Our data reinforces the critical role of sediment-bound nutrients on elemental cycling in glacierised basins of the high Arctic.