Thus two completely independent studies, using completely different methods, both find that the early stages
of marine ice sheet instability may be underway in West Antarctica.
Marine ice sheet instability occurs when sub-shelf melt rate is large enough to force the ice sheet grounding line to retreat into an area where the ice is grounded below sea level on an inward - sloping bedrock, then it can become unstable.
It's a positive feedback cycle, a viscious loop that means that future recession of the ice stream is inevitable (
see Marine Ice Sheet Instability and previous post).
The first of these pathways,
marine ice sheet instability, has been studied for decades, but the second, marine ice cliff instability, has only recently been considered as an important contributor to future sea level change.
Grounding line recession here could be irreversible, leading to rapid glacier thinning and recession, and sea level rise — see
Marine Ice Sheet Instability.
Marine ice sheet instability is a classic example of hysteresis.
If they thin and melt away, this support is removed, leading to increase ice discharge, accelerated flow, grounding line recession8, 9, 10, and
marine ice sheet instability.
She has shown, in an ice sheet model with gravitationally self - consistent sea level, there is actually a sea level fall at the grounding line, which acts to stabilize against
the marine ice sheet instability.
The ice sheet in this area is grounded up to 2000 m below sea level, making it intrinsically unstable6 and susceptible to rapid melting at its base, and to rapid migration of the grounding line up the ice stream7 (see
Marine Ice Sheet Instability).
A study using Earth Remote Sensing satellite radar interferometry (EERS - 1 and -2) observations from 1992 through 2011 finds «a continuous and rapid retreat of the grounding lines of Pine Island, Thwaites, Haynes, Smith, and Kohler» Glaciers, and the authors conclude that «this sector of West Antarctica is undergoing
a marine ice sheet instability that will significantly contribute to sea level rise in decades to centuries to come» (Rignot et al. 2014).