West Antarctic Ice Sheet retreat in the Amundsen Sea driven by decadal oceanic variability

Abstract

Mass loss from the Amundsen Sea sector of the West Antarctic Ice Sheet has increased in recent decades, suggestive of sustained ocean forcing or ongoing, possibly unstable response to a past climate anomaly. Lengthening satellite records appear incompatible with either process, however, revealing both periodic hiatuses in acceleration and intermittent episodes of thinning. Here we use ocean temperature, salinity, dissolved-oxygen and current measurements taken from 2000-2016 near Dotson Ice Shelf to determine temporal changes in net basal melting. A decadal cycle dominates the ocean record, with melt changing by a factor of ~4 between cool and warm extremes via a non-linear relationship with ocean temperature. A warm phase that peaked around 2009 coincided with ice shelf thinning and retreat of the grounding line, which readvanced during a post-2011 cool phase. Those observations demonstrate how discontinuous ice retreat is linked with ocean variability, and that the strength and timing of decadal extremes is more influential than changes in the longer-term mean state. The non-linear response of melting to temperature change heightens the sensitivity of Amundsen Sea ice shelves to such variability, possibly explaining the vulnerability of the ice sheet in that sector, where subsurface ocean temperatures are relatively high.

Upper Ocean Distribution of Glacial Meltwater in the Amundsen Sea, Antarctica

“…As our pWW endpoints in Θ, S A , and c (O 2 ) are similar to those used by Jenkins et al. () to the west of PIIS in front of Dotson Ice Shelf for 2014 data, this suggests that the pWW endpoint used here is reliable over a reasonable geographic area (approximately 20° longitude) but is likely to be variable on time scales greater than a year.…”

“…Using this knowledge, we extrapolate the existing WW endpoint down to the freezing temperature line (Figure 2a; red dot). For this data set, this provides a new Θ and S A endpoint for pWW of −1.86°C and 34.32 g/kg, which is comparable to values used by Jenkins et al (2018).…”

Instantaneous Antarctic ice sheet mass loss driven by thinning ice shelves

“…Again, while the magnitudes of calculated flux perturbation for each catchment basin (see Figure S7 in SI for definition of catchment basins) changed with the magnitude of the applied thickness change, the relative spatial pattern was unaffected. We stress that observations of ice shelf velocities and horizontal divergence, as well as estimates and modeling of ice shelf surface mass balance, show that the recent thickness changes over ice shelves are almost entirely due to ocean-induced melt (Jenkins et al, 2018;Turner et al, 2017). We stress that observations of ice shelf velocities and horizontal divergence, as well as estimates and modeling of ice shelf surface mass balance, show that the recent thickness changes over ice shelves are almost entirely due to ocean-induced melt (Jenkins et al, 2018;Turner et al, 2017).…”

How Accurately Should We Model Ice Shelf Melt Rates?

“…Freezing is likely an artifact of our Lagrangian tracking, since Crosson is heavily rifted in these regions, and freezing is unlikely given nearby observed ocean temperatures (Jenkins et al, 2018;Randall-Goodwin et al, 2015). Freezing is likely an artifact of our Lagrangian tracking, since Crosson is heavily rifted in these regions, and freezing is unlikely given nearby observed ocean temperatures (Jenkins et al, 2018;Randall-Goodwin et al, 2015).…”