High-Resolution Sensors Reveal Nitrate and Dissolved Silica Dynamics in an Arctic Fjord

Abstract

Subglacial weathering releases biologically important nutrients into meltwaters that have the potential to influence downstream ecosystems. There is a need to understand how accelerated glacial retreat could impact biogeochemical cycling in coastal regions in the near future. However, fjords—important gateways connecting the Greenland ice sheet and coastal oceans—are highly heterogeneous environments both in space and time. Here, we investigate temporal variability of nutrient dynamics in a glacier-fed fjord (Nuup Kangerlua, Greenland) using a high resolution record of nitrate + nitrite (∑NO_x) and dissolved silica (DSi), coupled with temperature and salinity, using submersible in situ sensors. During a 3-month monitoring period (14th June to 13 September 2019), ∑NO_x varied between 0.05 and 10.07 μM (±0.2 μM), whereas DSi varied between 0.35 and 14.98 μM (±0.5 μM). Both nutrients started low (following the spring bloom) and increased throughout the monitoring period. Several large peaks in both nutrients were observed, and these can largely be associated with meltwater runoff and upwelling events. Peaks in DSi were likely the direct result of glacial meltwater pulses, whereas elevated ∑NO_x concentrations in the fjord system were likely the result of meltwater-induced upwelling of marine sources. However, we did not observe a case of simple conservative mixing, suggesting that other processes in the fjord system (e.g., differential biological uptake and remineralization) may decouple the relationship between the two nutrients. This data set was used to investigate the biogeochemical impact of changes in glacier meltwater input throughout the melt season.