Resolving glacier–fjord interactions using observations of 3-dimensional fjord circulation, plume activity, and glacier dynamics

Interactions between tidewater glaciers and fjord waters play a key role in Greenland Ice Sheet mass loss. However, many of the underlying processes remain hidden beneath the fjord surface. In particular, the coupling between subglacial meltwater discharge, plume formation, fjord circulation, ice mélange conditions, and glacier dynamics is poorly constrained due to the difficulty of obtaining temporally and spatially highly resolved observations in these environments. This lack of observations limits our ability to resolve glacier-fjord interactions, resulting in considerable uncertainties in mass loss projections.

We address this challenge using an extensive time series of terrestrial radar interferometry (TRI) observations collected at the tidewater glacier Eqalorutsit Kangilliit Sermiat in South Greenland. Using this dataset, we analyse meltwater plume activity, ice mélange conditions in the fjord, glacier motion, calving activity, and 3-dimensional fjord circulation at minute-scale temporal resolution over several weeks, presenting an integrated observational view of the glacier–fjord system, including processes occurring below the waterline.

Fjord circulation is inferred using an autonomous iceberg-tracking framework that derives 3-dimensional flow patterns from the motion of icebergs spanning a wide range of sizes. Combining trajectory data with iceberg drafts, estimated from TRI-derived elevation models, allows circulation to be resolved across different water-depth layers within the ~300 m deep fjord. These observations are evaluated alongside fjord stratification measured by CTD profiles. The results reveal a highly complex circulation that varies strongly with water depth, time, and location in the fjord. Icebergs can even move in opposite directions depending on their draft and the dominant current acting on them. These observations are consistent with modelled fjord circulation, placing the measurements within a process-based framework.

Subglacial meltwater discharge and plume dynamics are investigated using a newly developed autonomous plume-detection algorithm applied to terrestrial radar data. Temporal changes in plume surface area are combined with melt modelling and subglacial hydrological routing to estimate meltwater fluxes entering the fjord. In parallel, ice mélange conditions are quantified using time-lapse imagery and radar backscatter, providing insight into mélange rigidity, its temporal evolution, and its influence on calving and terminus dynamics. On short (subdaily) timescales, plume area does not directly reflect discharge magnitude, as ice mélange conditions strongly control whether meltwater reaches the surface. Over longer (daily) timescales, however, plume size evolution generally agrees with estimated discharge variability.

Overall, these results advance our understanding of how subglacial discharge–driven circulation influences ocean-driven melting and glacier terminus stability, with important implications for projecting Greenland Ice Sheet mass loss and assessing fjord ecosystem responses under ongoing climate change.