Mapping Subglacial Discharge Plumes and Estimating Suspended Sediment Concentrations in South Greenland Fjords

The interface between marine-terminating glaciers and fjord waters is a key part of the Greenland cryosphere and marine systems. The discharge of glacial meltwater interacts with fjord conditions by affecting water circulation, heat budget and ecosystem dynamics. Sediment-laden plumes are clear visual evidence of this interaction. The plumes occur when meltwater from a marine-terminating glacier is discharged into a fjord at depth. The meltwater then forms buoyant, sediment-laden plumes that reach the fjord water surface, making them detectable by satellite. Although the presence of plumes is well-documented, direct observational evidence is sparse, and only a few in-situ observations exist. More observations are needed to improve our understanding of the driving mechanisms of the plumes, including their spatiotemporal extent.

In this study, we apply Random Forest Classification to high-resolution optical imagery from Sentinel-2 to automatically map the extent of the plumes in front of glaciers in South Greenland. Based on surface reflectance, we estimate the suspended sediment concentration in the plumes, and we assess the performance of Random Forest compared to more commonly used regression methods.

Our results provide the basis for future work of constructing a comprehensive dataset of subglacial discharge plumes and sediment concentration for all marine-terminating glaciers across Greenland, offering new insights into their extent and properties.