As we continue to expand our understanding of climate change, it is crucial to study its effects on both short- and long-term time scales. Seasonality is the study of sub-annual patterns in data that are significant to long-term data trends. Here, I present my main PhD work on the seasonality of outlet glaciers in Greenland and a side project on the seasonality of firn, which led me to do fieldwork in Antarctica!

The Greenland Ice Sheet (GrIS) is losing mass due, in part, to the recent speedup of many of the outlet glaciers that line the ice sheet [1]. Mass loss from outlet glaciers can be characterized by (1) retreat of the glacier’s frontal position, or terminus, via calving and ocean melting, and (2) speedup, characterized by an increase in ice velocity, leading to ice draining from the ice sheet more quickly.

The Graubard Fellowship in the Program on Climate Change has allowed me to analyze one of the most dramatic examples of outlet glacier change, observed at Zachariæ Isstrøm (ZI). ZI is one of three large glaciers that comprise the Northeast Greenland Ice Stream (NEGIS), a notable feature of fast-flowing ice that drains ~12% of the ice sheet by area [2]. After its floating ice tongue collapsed in 2013, ZI underwent pronounced seasonal changes, causing ZI to lose more mass due to glacial retreat than any other outlet glacier in Greenland [3].

Multiple environmental and glacial processes likely contribute to the observed seasonality, and these relationships must be well constrained before future projections of seasonality can be made. These variables include (1) the summertime production and discharge of meltwater, which can impact glacier sliding speeds as it drains and alters pressure at the ice bed [4], and (2) proglacial mélange (the mixture of calved icebergs and sea ice that can form in glacier-fed fjords) which can impact the timing of glacier advance and retreat by buttressing the terminus [5]. However, the relative impact of these variables on glacier flow and factors determining their impact remain unclear [6].

Understanding fluctuations in seasonality in relation to terminus changes and due to meltwater and mélange forcing is necessary for understanding ZI’s changing dynamics and predicting future mass loss. My work focuses on ZI and its NEGIS neighbor, Nioghalvfjerdsfjorden (79N), which is one of the few Greenland glaciers with a long (~80 km) floating ice tongue. I use machine learning and explainable artificial intelligence to quantify and compare the sensitivity of ZI and 79N, two glaciers in the same region with vastly different geometries and seasonalities. I aim to provide a deeper understanding of the evolving sensitivity and response of Greenland outlet glaciers to changing environmental conditions.

The Graubard Fellowship is also providing me with the flexibility to expand my research to the Southern Hemisphere, where I conducted field work in Antarctica! I spent a month at Taylor Dome, Antarctica, to study firn: partially compacted snow that has survived a melt season and is on its way to becoming fully compacted glacial ice. This work is part of a project aimed at resolving uncertainty surrounding firn compaction and supplying observational data to numerical firn compaction models. Current firn models use steady-state firn compaction rates measured from firn cores. However, these models perform poorly in scenarios outside of the firn core calibration range since they rely on an assumption (the Clausius-Clapeyron relation) that is not unique everywhere or during all timescales. Taylor Dome is an ideal study area because there is a fairly consistent annual temperature across the dome, despite wildly different annual accumulation rates (2-25 cm/yr across our four field sites). Since temperatures are relatively consistent, we can determine the reasoning behind the large changes in accumulation rate across the dome and improve numerical firn models by supplying them with quantitative information.

At Taylor Dome, I collected ice-penetrating radar data, including profiling and stationery radar. I helped deploy Autonomous Phase-Sensitive Radio Echo Sounding (ApRES) stations, which will be left to collect data for up to two years. The ApRES stations will collect data on firn compaction every 12 hours by measuring changes in snow, firn, and ice layers from the surface to the bedrock at millimeter-scale precision. I hope to use these data to aid in our understanding of firn compaction on a seasonal scale across different accumulation rates.

Written by Claire Jensen. Claire is a second-year PhD student in the Earth and Space Sciences (ESS) department. She studies glacier seasonality in Greenland using remote sensing and machine learning and has completed a season of field work in Antarctica using ice-penetrating radar to study seasonal snow compaction. She is a member of the ESS Inclusive Excellence committee and is an ESS Graduate Student Representative.