Increased West Antarctic and unchanged East Antarctic ice discharge over the last 7 years

Abstract

Abstract. Ice discharge from large ice sheets plays a direct role in determining rates of sea-level rise. We map presentday Antarctic-wide surface velocities using Landsat 7 and 8 imagery spanning 2013-2015 and compare to earlier estimates derived from synthetic aperture radar, revealing heterogeneous changes in ice flow since ∼ 2008. The new mapping provides complete coastal and inland coverage of ice velocity north of 82.4 • S with a mean error of < 10 m yr −1 , resulting from multiple overlapping image pairs acquired during the daylight period. Using an optimized flux gate, ice discharge from Antarctica is 1929 ± 40 Gigatons per year (Gt yr −1 ) in 2015, an increase of 36 ± 15 Gt yr −1 from the time of the radar mapping. Flow accelerations across the grounding lines of West Antarctica's Amundsen Sea Embayment, Getz Ice Shelf and Marguerite Bay on the western Antarctic Peninsula, account for 88 % of this increase. In contrast, glaciers draining the East Antarctic Ice Sheet have been remarkably constant over the period of observation. Including modeled rates of snow accumulation and basal melt, the Antarctic ice sheet lost ice at an average rate of 183 ± 94 Gt yr −1 between 2008 and 2015. The modest increase in ice discharge over the past 7 years is contrasted by high rates of ice sheet mass loss and distinct spatial patters of elevation lowering. The West Antarctic Ice Sheet is experiencing high rates of mass loss and displays distinct patterns of elevation lowering that point to a dynamic imbalance. We find modest increase in ice discharge over the past 7 years, which suggests that the recent pattern of mass loss in Antarctica is part of a longer-term phase of enhanced glacier flow initiated in the decades leading up to the first continent-wide radar mapping of ice flow.

Glacier change along West Antarctica's Marie Byrd Land Sector and links to inter-decadal atmosphere–ocean variability

“…Unlike ocean models or reanalysis data, these products represent quality-controlled, monthly gridded interpolations of all available in situ ocean observations assimilated from the World Ocean Database (WOD09/13), the Global Temperature and Salinity Profile Program (GTSPP), and global Argo float data; Good et al (2013) provide a thorough discussion of these data sources and their interpolation methodologies. While subject to high uncertainty (see Good et al, 2013 for further discussion) and coarse (1 • × 1 • ) spatial resolution, these observations provide an independent first-order impression of changes in the Southern Ocean's vertical hydrography (cf. Miles et al, 2016) to support our climate reanalysis records.…”

“…To supplement our analyses, we also compared these data sets to changes in sub-surface ocean temperature derived from Met Office EN4 objective analysis products (cf. Good et al, 2013). These methods were utilized due to a dearth of high-resolution, spatially, and temporally continuous in situ oceanographical observations within the MBLS during the observational period, with the last comprehensive and publicly available surveys having been carried out in 2000 and 2007 .…”

“…Changes in subsurface potential temperature linked to temporal variability in atmospheric forcing were examined using monthly Met Office EN4 objective analysis solutions for 2000(Good et al, 2013. Unlike ocean models or reanalysis data, these products represent quality-controlled, monthly gridded interpolations of all available in situ ocean observations assimilated from the World Ocean Database (WOD09/13), the Global Temperature and Salinity Profile Program (GTSPP), and global Argo float data; Good et al (2013) provide a thorough discussion of these data sources and their interpolation methodologies.…”

“…Observations of the ice streams and glaciers draining into this sector, in particular Pine Island Glacier and Thwaites Glacier, have revealed rapid grounding-line retreat (cf. Park et al, 2013;Rignot et al 2014;Scheuchl et al, 2016), pronounced icedynamic thinning (Pritchard et al, 2009Konrad et al, 2017), ice-flow-speedup Gardner et al, 2018), and large ice-shelf melting rates (Depoorter et al, 2013;Rignot et al, 2013;Paolo et al, 2015;Gourmelen et al, 2017a). These phenomena have been attributed to oceanic and atmospheric forcing impinging on the West Antarctic margin (e.g.…”

“…D. W. Christie et al: West Antarctic glacier change andforcing, 2003-2015 Whilst the processes driving ice-ocean-atmosphere interactions are being increasingly elucidated for the Amundsen Sea Sector (Jenkins et al, 2016;Asay-Davis et al, 2017;Turner et al, 2017), they remain poorly constrained elsewhere along coastal West Antarctica owing to a dearth of glaciological, oceanographical, and climatological observations. Some recent studies have highlighted accelerated dynamic thinning along the Bellingshausen Sea margin Paolo et al, 2015;Wouters et al, 2015;Christie et al, 2016;Gardner et al, 2018) potentially linked to atmosphere-ocean forcing similar to that at work in the Amundsen Sea Sector (e.g. Holland et al, 2010;Zhang et al, 2016).…”