The following is a re-post from the Antarctic folder (from the WAIS Collapse thread, Feb. 7 2015):
While the linked reference (with a free access pdf) address a hydro-thermodynamic feedback from summer surface ice melt resulting in the surge of calving from a marine terminating glacier in Svalbard; the abstract & conclusions (see extract below) indicate that this newly identified feedback mechanism may soon accelerate ice mass loss from both marine terminating glaciers in Greenland and from marine glaciers in Antarctica (potentially both East and West Antarctica). While the postulated hydro-thermodynamic feedback mechanism (see the attached image and the associated caption) is less dynamic than the hydro-fracturing and cliff failure mechanism discussed by Pollard et al 2015; it is alarming nevertheless because it appears to be effect at destabilizing and successively mobilizing otherwise stagnant ice regions such as those currently plugging the gateways of such critical glacial drainage basins as the Byrd Subglacial Basin (Thwaites) and the Wilkes Subglacial Basin. With continuing global warming the postulated hydro-thermodynamic feedback followed by the postulated hydro-fracturing / cliff failure mechanism could deliver a deadly one-two punch to marine terminating, and marine, glaciers in both Greenland and Antarctic sooner than any research thought possible only a few month ago:
Dunse, T., Schellenberger, T., Hagen, J. O., Kääb, A., Schuler, T. V., and Reijmer, C. H.: Glacier-surge mechanisms promoted by a hydro-thermodynamic feedback to summer melt, The Cryosphere, 9, 197-215, doi:10.5194/tc-9-197-2015, 2015.
http://www.the-cryosphere.net/9/197/2015/tc-9-197-2015.htmlAbstract: "Mass loss from glaciers and ice sheets currently accounts for two-thirds of the observed global sea-level rise and has accelerated since the 1990s, coincident with strong atmospheric warming in the polar regions. Here we present continuous GPS measurements and satellite synthetic-aperture-radar-based velocity maps from Basin-3, the largest drainage basin of the Austfonna ice cap, Svalbard. Our observations demonstrate strong links between surface-melt and multiannual ice-flow acceleration. We identify a hydro-thermodynamic feedback that successively mobilizes stagnant ice regions, initially frozen to their bed, thereby facilitating fast basal motion over an expanding area. By autumn 2012, successive destabilization of the marine terminus escalated in a surge of Basin-3. The resulting iceberg discharge of 4.2±1.6 Gt a−1 over the period April 2012 to May 2013 triples the calving loss from the entire ice cap. With the seawater displacement by the terminus advance accounted for, the related sea-level rise contribution amounts to 7.2±2.6 Gt a−1. This rate matches the annual ice-mass loss from the entire Svalbard archipelago over the period 2003–2008, highlighting the importance of dynamic mass loss for glacier mass balance and sea-level rise. The active role of surface melt, i.e. external forcing, contrasts with previous views of glacier surges as purely internal dynamic instabilities. Given sustained climatic warming and rising significance of surface melt, we propose a potential impact of the hydro-thermodynamic feedback on the future stability of ice-sheet regions, namely at the presence of a cold-based marginal ice plug that restricts fast drainage of inland ice. The possibility of large-scale dynamic instabilities such as the partial disintegration of ice sheets is acknowledged but not quantified in global projections of sea-level rise."
Extract from the Conclusions: "We propose a hydro-thermodynamic feedback mechanism triggered by surface melt reaching a growing fraction of the glacier bed. Intrusion of surface melt to the glacier bed provides an efficient heat source through CHW, facilitating a thermal switch from cold to temperate basal conditions, permitting for basal motion. Initiation of hydraulic lubrication, along with rising pore-water pressure within subglacial sediments, further enhances basal motion, eventually destabilizing the overlying ice.
…
Given continued climatic warming and increasing surface melt, we hypothesize that the hydro-thermodynamic feedback may gain significance in other glaciated areas, including the ice sheets. In light of recent record melt and rising ELA of the Greenland Ice Sheet, the proposed mechanism has the potential to lead to a long-term enhancement of outlet glacier discharge and calving loss, as earlier proposed by Phillips et al. (2013). Our expectation contrasts with recent studies that indicate limited effects of surface-melt-induced acceleration on the future net mass balance of the Greenland Ice Sheet (Nick et al., 2013; Shannon et al., 2013). Surface melt in Antarctica is presently mainly constrained to the ice shelves (Comiso, 2000). Given strong continued warming, surface melt will increasingly occur over coastal areas of Antarctica, making the grounded ice-sheet margins vulnerable to the hydro-thermodynamic feedback."
Caption: "Figure 5. Schematic illustration of the proposed hydro-thermodynamic feedback to summer melt, imbedded within the surge cycle of Basin-3, Austfonna. The approximate start of each phase is indicated at the bottom. Phase 1 follows from long-term changes in glacier geometry, i.e. build-up of a reservoir, and associated changes in driving stress and basal thermal regime. The hydro-thermodynamic feedback loop operates over several years during phase 2 and 3, each loop coinciding with consecutive summer melt periods. Successive mobilization and destabilization initiates the surge. Dynamic thinning, reduction in driving stress and basal heat dissipation eventually terminate the surge.
