Quantifying changes in glacier dynamics of marine-terminating glaciers retreating and transitioning to land between 1943 and 2025 in South Greenland fjords

Expedition Location: Qalerallit Imaat and Sermilik Fjord, South Greenland

Expedition Dates: Jun 11 to 16, 2025

Field Team Members: Mathilde Børch, Kristin Schild, Lee Karp-Boss, Allie Berry, Kayla Guthrie, Miranda Seixas, Wyatt Stanley, and Seth Campbell

Funding Support: The Robert and Judith Sturgis Family Foundation, and NSF SAUNNA NRT

Background and Significance:

Today, glaciers worldwide are retreating under our warming climate. However, a critical and yet under-explored aspect of this global retreat, which could significantly influence future sea-level rise projections, is the transition of hundreds of glaciers from marine- to land-terminating. When a marine-terminating glacier retreats and the glacier terminus loses contact with the ocean it is classified as land-terminating. With the new terminus environment the dominant controls on the glacier dynamics shifts, and forces such as friction, plays a stronger role. As a consequence, a decrease in flow velocity would be expected, and if accounted for in calculations, reduce the contribution to sea level rise predictions.

Transitioning glaciers are widespread but remain poorly understood, as marine- and land-terminating glaciers have largely been studied as two distinct systems rather than along a continuum. This field work is part of a Master’s thesis work to investigate the dynamics and flow of four transitioning glaciers in South Greenland, to better recognise transitioning glaciers and their importance, thereby filling a critical gap in our understanding. The work studies glaciers in Qalerallit Imaat and Sermilik Fjord in South Greenland and spans the period from 1943 to 2025 by combining historical aerial photographs, satellite imagery and present day in situ measurements.

Field Report:

In June 2025, the team went to Qalerallit Imaat and Sermilik Fjord, two fjords in South Greenland where field work by UMaine has been conducted for several years as part of the SAUNNA NRT research week. At the head of the two neighbouring fjords are four glaciers in different terminus environments: marine-terminating, transitioning and land-terminating. The long record of available remote sensing records from aerial surveys and satellites together with the present day variable terminus positions makes the area ideal to study the change in glaciers as they transition from one terminal environment to another.

The field objective was to measure the depth of the fjord in the areas the glaciers once had covered while being marine-terminating since 1943. If we have the depth of the fjord we can calculate an estimated ice thickness. The ice thickness is used in our force balance approach to understand the dynamics and flow of the glaciers. The force balance is the balance between forces moving the glacier forward (driving stress) and holding the glacier back (resistive stress).

We lived in Tasermiut’s tent glacier camp and from there sampled by zodiac the fjords to map out their depths. These depth measurements will be used together with DEM made from historical aerial photographs to quantify the changes in the driving stress as the glaciers transitions from marine-terminating to land-terminating.

Initial interpretations of our data reveal variable fjord bathymetry that contrasts with the smoother estimates provided by the IceBridge BedMachine Greenland, Version 5 which is a bathymetry map of Greenland with a 150 m spatial resolution. The depth measurements we collected in the field provide a more accurate representation of past ice thickness.

The work of a previous UMaine Master’s student, Sydney Baratta, had suggested the presence of a bedrock high in the fjord. Our field work confirmed and mapped this feature, lending support to her findings. We also verified that our remote sensing classification of glacier type (land-terminating, marine-terminating, or transitioning) was consistent with field observations. Overall, the field season was very successful.

This fieldwork completed the dataset needed to calculate changes in driving stress, which is the basis for my thesis. It will be the first study to document and quantify changes in driving stress as glaciers transition from marine- to land-terminating.

Acknowledgements:

This project was possible thanks to the assistance of the Robert and Judith Sturgis Family Foundation Exploration Fund and NSF SAUNNA NRT.