UC Irvine

Totten Glacier, East Antarctica, a glacier that holds a 3.9 m sea level change equivalent, has thinned and lost mass for decades. Change in surface elevation calculated from high- resolution DEM differencing shows significant surface lowering rates concentrated in areas of fast flow, hence is probably of dynamic origin. A 26-year long ice velocity time series (1989-2015) consisting of 13 maps is developed from Landsat and interferometric synthetic aperture radar (InSAR) data. We find significant speed-up in ice velocity, especially in 2002-2007, followed by a period of slow decrease in 2010-2014. Comparing the ice discharge with surface mass balance suggests that the glacier mass balance was already negative in 1996 and became more negative into the 2000s. Grounding line mapping using differential InSAR, combined with high resolution topographies of the ice surface and ice draft, reveals a 1,500-2,300 m deep grounding zone. The grounding line extends 15 km inland along two prominent side lobes. Immediately upstream of the grounding line, there is an ice plain which is slightly grounded, only 15-50 m above hydrostatic equilibrium. At the glacier center, we detect a retreat of the grounding line up to 2.6±0.1 km by comparing differential InSAR data acquired 17 years apart. The retreat is asymmetrical along the two lobes, but consistently indicates a total thinning of 11.9±1.5 m from 1996 to 2013. On the ice plain, the glacier is prone to rapid retreat around a region about 7 km long, but inland the bed elevation rises. Sustained thinning will cause further retreat and speed up, but will not be conducive to a marine ice sheet instability. The ultimate cause of the changes is not known, but probably of oceanic origin. Comparison of the velocity time series and reanalysis sub-surface ocean temperatures indicates that Totten Glacier may be very sensitive to oceanic perturbations.