By Bryn Huxley-Reicher, Harvard University; Joe Silverwood, University of Manchester; Kara Vogler, Dalhousie University; Benjy Getraer, Princeton University; Teddy Reinhardt-Ertman, Carleton College; Gavin McNamara, Dalhousie University; and Max Bond, Dartmouth University.
Hello from the 2017 JIRP Mass Balance team! We are studying the health of the Juneau Icefield by measuring the changing masses of the glaciers over time. This research allows us to contribute to an understanding of how climate change is affecting glaciers, and how glacier melt will affect local ecosystems and the global environment. We do this by digging large pits in the snow and measuring this year’s accumulation. In practice, this means skiing a few miles after breakfast, spending several hours digging pits, and measuring the density of the snow at varying depths.
Caption: JIRPers digging a snow pit on the Llewellyn Glacier. PC: Gavin McNamara.
Caption: Avery Stewart and Max Bond in the bottom of a mass balance pit. PC: Susannah Cooley.
Caption: Max Bond taking snow samples by coring the layers of snow in a pit. PC: Gavin McNamara .
The history of the Mass Balance Team is the history of JIRP: this data collection effort was an original research goal of the program when it was founded in the late 1940s. The record to which JIRP students add each summer is one of the longest continuous records of glacier mass change in the world. To continue this record, we dig pits in the same locations every year: five pits on the Lemon Creek Glacier (one of the smallest glaciers on the icefield), about 20 on Taku Glacier (the largest) and its tributary branches, and a handful on the Llewellyn Glacier. Digging all these pits means the mass balance crew – and any other interested JIRPers – are usually out of camp, exploring many beautiful corners of the Icefield.
Caption: Snow sample holes in the wall of a pit. PC: Gavin McNamara.
This year, in addition to relating the current snowpack to the historical JIRP records, we are trying to compare different methods of observing mass change. First, we are comparing the snowpack measured in pits to the snowpack measured using a ground penetrating radar (GPR). Estimating accumulation based on pit data- single points in a massive expanse of ice- is inherently limiting. GPR shows the different layers of ice and snow beneath the surface in transects across the glacier- profile lines, with much more information than the single-point pits. To check whether our point-based inference of glacier-wide snowpack is valid, we are using GPR to see if the depth of this year’s snowpack across the glacier matches our measurements from the pits.
Caption: JIRPers skiing towards Camp 25 on the Llewellyn Glacier to dig pits as part of a mini expedition. PC: Gavin McNamara.
Second, we are comparing the measured snowpack to the measurements of GRACE, a satellite that tracks changes in Earth’s gravity. The GRACE system is a pair of orbiting satellites that measures the gravitational force exerted on them by the Earth below. An increase in mass below the satellites results in stronger local gravitational force; researchers can use the GRACE measurements to calculate changes in mass. Unfortunately for us, GRACE measures areas of the Earth about the size of the entire Icefield. We are trying to determine whether the GRACE data match our pit measurements of mass balance for a single glacier. Our pits are small and spread out, so they might not fully describe accumulation across the entire glacier.
Our analysis of long term mass balance trends show Taku Glacier was gaining mass from 1946 until the early 1990s, where it stagnated, and has been losing mass ever since. The Lemon Creek Glacier has been losing mass steadily since the start of its mass balance record in 1953.
Figure: Cumulative mass balance for the Taku Glacier and the Lemon Creek Glacier from JIRP records. Long term trends indicate that the Taku’s ~50 year trend of mass gain has stagnated and more recently reversed, and that the Lemon Creek Glacier has been losing mass for the last 60 years.
Additionally, in our comparison of the data from our pits and the GRACE satellites, we have seen that the Taku and Lemon Creek Glaciers both follow the same trends as the GRACE data, but that the satellites are picking up larger changes in mass that must be coming from the other glaciers in the icefield, where we do not dig pits.
Being a part of the mass balance team was a pleasure for all of us and we had a very successful field season. We plan to present our findings at this year’s AGU (American Geophysical Union) conference in New Orleans and are very excited to see our fellow diggers once again! Mass balance field work was a physical and scientific adventure: it took us far across the icefield and taught us about field science and research.
Caption: JIRPers skiing home after a long day of pit digging. PC: Gavin McNamara.