According to a new study, meltwater lakes that develop at glacier margins cause ice to ebb relatively further and quicker than glaciers that end on land.
However, current ice loss models do not reflect the impacts of these glacial lakes, warned the authors of the study. Therefore, estimates of the recession rates as well as the loss of ice mass from lake-terminating glaciers in the days to come might be underestimated.
Several mountain glaciers end in these lakes, which developed as meltwater became stuck behind the ridges of glacier debris. They are called proglacial lakes.
Globally, climate change has increased the rate of glacier melt and this has consequently resulted in a significant rise in the number and size of proglacial lakes. However, the impacts of proglacial lakes on the speed of deglaciation and also on glacier behavior were poorly understood before.
Under the guidance of the University of Leeds, an international research team has now measured the impact of proglacial lakes on mountain glaciers through computer simulations, for the first time.
The team discovered that the existence of a proglacial lake causes a glacier to subside further by more than four times and speed up the ice flow by up to eight times in comparison to the same glacier that terminates on land under the same climatic condition.
Recently published in the Geophysical Research Letters journal, the findings demonstrate that a land-terminating glacier took 1000 years to yield to the same proportion of recession as a lake-terminating glacier experienced in 100 years.
Dr Jenna Sutherland, the study’s lead author, performed this study while she was a PhD candidate in the School of Geography at the University of Leeds.
An ice cube in a bowl of water is going to melt much more quickly than an ice cube sitting on a table, and the effect proglacial lakes have on glacier ice is roughly the same.
Dr Jenna Sutherland, Study Lead Author, University of Leeds
“The simulations show that the influence of a proglacial lake on a glacier predominantly takes place over decades to centuries rather than over millennia, meaning the glacier recedes much faster than it ever could from climatic changes alone,” Dr Sutherland added.
Our findings suggest that simulations of past, contemporary or future glaciers ignore the effects of ice-contact lakes and will likely mis-represent the timing and rate of recession, especially the changes to the timing and rate that will occur once a proglacial lake forms.
Dr Jonathan Carrivick, Study Co-Author and Senior Lecturer in Geomorphology, University of Leeds
Dr Carrivick continued, “This effects need to be included in all future models and simulations if we are to have an accurate global picture of glacial ice loss.”
Using the BISICLES ice-flow model, the researchers investigated the impacts of a proglacial on the Pukaki Glacier located in New Zealand, at the time of recession from the end of the previous ice age.
While this study focussed on New Zealand, proglacial lakes are prevalent during glacial retreat worldwide and this paper should therefore be of global interest and importance.
James Shulmeister, Study Co-Author and Professor, University of Canterbury
He continued, “This study is also critical because the timing of ice retreat is often used to determine the synchrony or lack thereof of in climate events globally. Major inferences have been made about the roles of phenomena like oceanic circulation in affecting the global climate system from glacial retreat timings.”
“If the timings are wrong, the relationship between these processes may need to be re-examined,” Shulmeister concluded.
Sutherland, J. L., et al. (2020) Proglacial Lakes Control Glacier Geometry and Behavior During Recession. Geophysical Research Letters. doi.org/10.1029/2020GL088865.