An investigation of sediment-laden meltwater plumes using in-situ and remote sensing techniques, Kongsfjorden, Svalbard

The Arctic is warming at least two times faster than the rest of the Earth. Increased warming results in the melting and retreat of glaciers and ice caps, a reduction in sea ice extent and thickness, and changes to the region’s hydrological cycle, altering the balance of precipitation. In glaciated basins throughout the Arctic, increased atmospheric temperatures result in the production of greater volumes of meltwater. Meltwater can be delivered to fjords and coastal areas by marine-terminating glaciers at depth or via terrestrial glacier-fed rivers. These systems entrain and transport the products of glacial erosion, sediment, in suspension. When this entrained material reaches the fjord, a sediment-laden meltwater plume is formed, as the denser freshwater sits on the fjord surface. These plumes impact upon fjord circulation, biogeochemical cycling and glaciomarine sedimentation, and at marine-terminating systems can also increase iceberg calving and enhance melt. However, the spatial and temporal evolution of plumes from both terrestrial glacier-fed rivers and marine-terminating glaciers are thus far poorly understood, resulting in uncertainties for glaciomarine landscape evolution and sedimentary models and in predicting future sea level rise.

This research focuses on two sites in Kongsfjorden, north-west Svalbard: the Bayelva catchment on the Brøggerhalvøya peninsula, and Blomstrandbreen, a marine-terminating glacier that drains into the northern side of the fjord. Meltwater produced by ablation of the Austre and Vestre Brøggerbreen glaciers, along with non-glacial sources, converges to form Bayelva. The river drains through a small delta into a sheltered section on the southern side of Kongsfjorden, known as Kolhamna, where a small sediment-laden meltwater plume is formed. At Blomstrandbreen, sediment-laden meltwater is transported at the bed of the glacier, and delivered at depth into the fjord, forming its plume.

Simulated bandwidths of various research and commercial satellites were calibrated using in-situ measurements of suspended sediment concentration and spectral reflectance to quantify the variability of the two contrasting plume systems within a melt season and from year-to-year. Plume outlines at Blomstrandbreen were mapped using every cloud-free image available between the months of May and October for every year between 2016 and 2021, using Sentinel-2 data and analysed in relation to changes in glacial runoff and retreat. Particle size in the Bayelva plume is compared over two melt seasons to determine the sources and drivers of sediment variability within the plume. Results of the research conducted reveal that empirical relationships of suspended sediment concentration and spectral reflectance are not spatially or temporally transferable, with a clear contrast in relationships between the two sites and between melt seasons. Glacial runoff drives sediment plume magnitude at Blomstrandbreen, but the frequency of plumes remains constant throughout the study period. Particle size is not wholly impacted by changes in melt and runoff, rather the source of sediment and precipitation events impact the particle size composition of the Bayelva sediment plume.

Sediment-laden meltwater plumes are driven primarily by changes in glacial runoff, allowing them to be used to quantify glacier hydrology and investigate sediment transfer processes from source to sink. This research furthers the understanding of sediment-laden meltwater plumes in a fast-changing high Arctic environment and will be beneficial for refining glaciomarine landscape evolution and sedimentary models, and more accurately predicting the nature of future sea level rise.