Many glaciers and ice shelves along the Antarctic Peninsula have been thinning and retreating leading to collapses, and consequently increasing ice discharge to the ocean. Some authors suggest that the concurrent ocean warming could be related to these collapses and changes in glaciers. However, the timing and magnitude of these changes vary, probably due to regional variation such as changes in the Southern Oscillation Index and El Niño processes. We already know that variation in ocean conditions affects ice loss, but it is necessary to understand the importance of such controls on glacier dynamics. North American researchers recently explored the use of remotely-sensed iceberg melt rates around the Antarctic Peninsula to infer variability in ocean forcing of glacier terminus position, i.e. the end of a glacier at any given time.
This study occurred in eight sites selected with the proximal to glaciers along the Antarctic Peninsula (six along the west side and two on the east side) from 2013 to 2019. Melt rates were calculated for 14 separate observation periods, observing no more than 20 icebergs. They also observed the frontal ablation, that is the glacier mass loss due to calving and submarine melt, calculating the difference between surface speed and the terminus position change rate along each glacier centerline.
There were higher melt rates on the western side of the peninsula (Cadman Glacier between 2018 and 2019) and lower melt rates on the eastern side of the peninsula (Crane Glacier between 2016 and 2017). For Edgeworth Glacier, this rate was significantly higher between 2013 and 2014 than from the other observation periods. Water temperatures are relatively cold as they are sourced from the Weddell Sea, which explains low iceberg melt rates at Edgeworth and Crane Glacier sites. The only exception was the very large melt rates from icebergs proximal to the Edgeworth Glacier where glacial meltwater plumes may exist. Between 2014-2016 and 2019, the Seller Glacier had high mean melt rate, that could be explain by the fact that the inferior part of these icebergs are deep-drafted, reaching warmer subsurface waters.
Crane and Cadman Glaciers advanced more than 3km from 2013 to 2019, while the Edgeworth Glacier advanced until 2017, then retreated back. The other glaciers maintained relatively stable positions and velocities in recent years. However, the speed time suggest that Cadman and Widdowson glaciers accelerated through 2018. Relatively to frontal ablation rates, Seller and Widdowson Glaciers have the highest rates, which tend to be larger in average for faster-flowing glaciers. The frontal ablation rates at Seller and Crane glaciers are a reflection of the long-term dynamic adjustment to ice-shelf collapse.
These results indicate a positive link between iceberg melt rates and regional ocean conditions, indicating that ocean conditions influence frontal ablation of marine-terminating glaciers and the melting is strongly controlled by the velocity of the water mass.
Source: Dryak MC & Enderlin EM (2020). Analysis of Antarctic Peninsula glacier frontal ablation rates with respect to iceberg melt-inferred variability in ocean conditions. Journal of Glaciology, 1-14. doi: 10.1017/jog.2020.21
Author: Inês Ribeiro