Future Projections of Petermann Glacier Under Ocean Warming Depend Strongly on Friction Law

Abstract

Basal friction heavily controls the dynamics of fast‐flowing glaciers. However, the best approach to modeling friction is unclear, increasing uncertainties in projections of future mass loss and sea‐level rise. Here, we compare six friction laws and evaluate them for Petermann Glacier in northern Greenland, using a higher order three‐dimensional ice‐sheet model. We model glacier retreat and mass loss under an ocean‐only warming until year 2300, while not considering the effects of a future warmer atmosphere. Regardless of the friction law, we find that breakup of Petermann's ice shelf is likely to occur within the next decades. However, future grounding‐line retreat differs by 10s of km and estimates of sea‐level rise may quadruple, depending on the friction law employed. A bedrock ridge halts the retreat for four of the laws, and Petermann retreats furthest when applying a Budd or a Coulomb‐type “till law.” Depending on the friction law, sea‐level contributions differ by 133% and 282% by 2300 for 2°C and 5°C ocean warming scenarios, respectively.

Petermann ice shelf may not recover after a future breakup

“…We start all our Petermann recovery simulations from a future retreated model state (year 2300 AD; Fig 1 c), which is attained as a response to a 2 °C ocean-only warming relative to present-day 19 . This corresponds to a ~3 °C ocean warming relative to pre-industrial times (before c. 1850).…”

“… Evolution of Petermann’s a ice-shelf calving front, b grounding line and c grounding-line flux, for the forcings compared in Fig. 1 during the 2 °C ocean warming 19 and recovery experiments. An ocean cooling alone does not lead to recovery, neither does ocean cooling + increased surface mass balance (SMB).…”

“…2 a (see ref. 19 for details), thus lowering ice-shelf basal melt rates back to those associated with present-day ocean conditions (Section “Ocean forcing”; Fig. S2) .…”

“…1 a), using the Ice-sheet and Sea-level System Model (ISSM; 18 ). We examine the climate conditions required for Petermann to recover to its present-day (2008) state after an ice-shelf breakup and grounding-line retreat 19 . Petermann is the largest glacier by area in northern Greenland, drains about 4% of the entire Greenland Ice Sheet by area 20 , 21 and has one of the northern hemisphere’s few remaining ice shelves.…”

“…Note that Petermann’s ice shelf is confined in a fjord (sometimes referred to as an ice tongue), in contrast to many topographically unconfined ice shelves in Antarctica. Over the last decade, Petermann has lost ~40% of its ice shelf 22 , 23 and concerns have been raised that further breakup would lead to grounded-ice speedup, retreat and accelerated mass loss 19 , 24 – 26 . Similar scenarios have been put forward for ice-shelf-glacier systems in West Antarctica in response to ongoing and future ocean warming (e.g.…”