Complex evolving patterns of mass loss from Antarctica’s largest glacier

Abstract

Pine Island Glacier has contributed more to sea level rise over the last four decades than any other glacier in Antarctica. Model projections indicate that this will continue in the future but at conflicting rates. Some models suggest that mass loss could dramatically increase over the next few decades, resulting in a rapidly growing contribution to sea level, and fast retreat of the grounding line, where the grounded ice meets the ocean. Other models indicate more moderate losses. Resolving this contrasting behaviour is important for sea level rise projections. Here, we use high resolution satellite observations of elevation change since 2010 to show that thinning rates are now highest along the slow-flow margins of the glacier and that the present-day amplitude and pattern of elevation change is inconsistent with fast grounding line migration and the associated rapid increase in mass loss over the next few decades. Instead, our results support model simulations that imply only modest changes in grounding line location over that timescale. We demonstrate how the pattern of thinning is evolving in complex ways both in space and time and how rates in the fast-flowing central trunk have decreased by about a factor five since 2007.

Rapid Viscoelastic Deformation Slows Marine Ice Sheet Instability at Pine Island Glacier

“…These glaciers are particularly vulnerable to collapse because they have retrograde slopes and are grounded well below sea level (Pattyn, 2018). Such a collapse may already be underway at Thwaites Glacier (Joughin et al, 2014; Waibel et al, 2018) and, although Pine Island may have recently stabilized (Bamber & Dawson, 2020; Medley et al, 2014), it remains at risk for further future unstable retreat. As the catchment area of these and connected glaciers contains ice that would raise globally averaged sea level by 1.2 m (Rignot et al, 2019) and provide a pathway to much larger losses (>2.5 m, Martin et al, 2019), understanding the processes that contribute to (or mitigate) their instability is essential to assessing the impact of future changes.…”

The regional-scale surface mass balance of Pine Island Glacier, West Antarctica, over the period 2005–2014, derived from airborne radar soundings and neutron probe measurements

“…While spaceborne observations indicate that this acceleration has levelled off recently (Rignot et al, 2019), they also support model projections suggesting modest changes in mass balance, i.e. the resulting net ice loss after accounting for all loss and gain processes, for the next decades to come (Bamber and Dawson, 2020). The dynamic ice loss is mainly responsible for the negative mass balance of Pine Island Glacier (PIG).…”

Drivers of Pine Island Glacier retreat from 1996 to 2016

“…Based on our analysis of Sentinel and Landsat satellite images, there is no obvious indication of recent changes in the surface morphology in these areas. Either significant and wide-spread changes in the thermal and mechanical properties have occurred beneath the surface, or the observed speed-up and thinning in these areas, as previously reported by Bamber and Dawson (2020), cannot be convincingly attributed to changes in the rate factor.…”

“…Evidence from indirect observations have indicated that changes in ice shelf thickness have occurred since at least some decades before the 1970s (Jenkins et al, 2010;Smith et al, 2017;Shepherd et al, 2004;Pritchard et al, 2012). Within the last two decades, thinning of the grounded ice (Shepherd et al, 2001;Pritchard et al, 2009;Bamber and Dawson, 2020), intermittent retreat of the grounding line (Rignot et al, 2014), changes in calving front position (Arndt et al, 2018) and the partial loss of ice shelf integrity (Alley et al, 2019) have all been reported in considerable detail. At the same time, numerical simulations of ice flow have confirmed the strong link between ice-shelf thinning, which reduces the buttressing forces, and the increased discharge across the grounding line (Schmeltz et al, 2002;Payne et al, 2004;Favier et al, 2014;Arthern and Williams, 2017;Reese et al, 2018;Gudmundsson et al, 2019).…”

“…We consider how calving, ice shelf thinning, the induced dynamic thinning upstream of the grounding line and potential changes in ice-internal and basal properties have caused a different dynamic response across the ice shelf, the glacier's main trunk, the margins and tributaries. Initial observations indicated that the speed-up of PIG was primarily confined to its fast-flowing central trunk (Rignot et al, 2002;Rignot, 2008), though more complex, spatiotemporal patterns of change have emerged more recently (Bamber and Dawson, 2020). The rapid and spatially diverse acceleration of the flow is an expression of the glacier's dynamic response to changes in the force balance, and it is imperative that numerical ice flow models are capable of reproducing this complex behavior in response to the correct forcing.…”