Observing relationships between sediment-laden meltwater plumes, glacial runoff and a retreating terminus at Blomstrandbreen, Svalbard

Sediment-laden meltwater plumes are a common occurrence at the margins of marine-terminating glaciers in Svalbard and are useful proxies for inferring the glacial hydrological system and meltwater runoff. Plumes can influence calving rates, marine biogeochemistry and fjord circulation. However, little is known about how their dynamics will evolve in a warmer, wetter Arctic with increasing melt rates and retreating glacier margins. To determine the temporal magnitude and frequency evolution of sediment-laden meltwater plumes, we manually delineated plume outlines in every available Sentinel-2 image at Blomstrandbreen, Kongsfjorden, Svalbard, between 2016 and 2021. While the frequency of plumes upwelling on the fjord surface remained stable in each melt season, their surface area increased significantly by almost an order of magnitude between the beginning and end of the study period, owing primarily to glacial runoff. This significant change was a result of several large plumes (>2 km²) mapped in 2020 and 2021. The rate of glacier terminus change throughout the study period has little-to-no influence on plume surface area. However, a notable event concerning the terminus retreating into an overdeepening between 2017 and 2018 may have impacted plume magnitude, allowing for larger plume migration across the calving front after 2018. Seasonal supraglacial lakes on Blomstrandbreen are found to be small in both area and volume which have limited influence on plumes surfacing between 2016-2021. Our findings suggest with increased runoff, plumes upwelling at the glacier terminus may increase in size, transporting greater volumes of sediment into the surrounding local marine environment. These changes could be exacerbated by projected increases in glacier mass loss and retreat expected to occur across Svalbard throughout this century and beyond, making the study of plumes and their impacts key to constraining the transport of water and sediment from a terrestrial to a marine environment as demonstrated at Blomstrandbreen.