Airborne radar evidence for tributary flow switching in Institute Ice Stream, West Antarctica: Implications for ice sheet configuration and dynamics

Abstract

Despite the importance of ice streaming to the evaluation of West Antarctic Ice Sheet (WAIS) stability we know little about mid-to long-term dynamic changes within the Institute Ice Stream (IIS) catchment. Here we use airborne radio echo sounding to investigate the subglacial topography, internal stratigraphy, and Holocene flow regime of the upper IIS catchment near the Ellsworth Mountains. Internal layer buckling within three discrete, topographically confined tributaries, through Ellsworth, Independence, and Horseshoe Valley Troughs, provides evidence for former enhanced ice sheet flow. We suggest that enhanced ice flow through Independence and Ellsworth Troughs, during the mid-Holocene to late Holocene, was the source of ice streaming over the region now occupied by the slow-flowing Bungenstock Ice Rise. Although buckled layers also exist within the slow-flowing ice of Horseshoe Valley Trough, a thicker sequence of surface-conformable layers in the upper ice column suggests slowdown more than~4000 years ago, so we do not attribute enhanced flow switch-off here, to the late Holocene ice-flow reorganization. Intensely buckled englacial layers within Horseshoe Valley and Independence Troughs cannot be accounted for under present-day flow speeds. The dynamic nature of ice flow in IIS and its tributaries suggests that recent ice stream switching and mass changes in the Siple Coast and Amundsen Sea sectors are not unique to these sectors, that they may have been regular during the Holocene and may characterize the decline of the WAIS.

Holocene Formation of Henry Ice Rise, West Antarctica, Inferred From Ice‐Penetrating Radar

“…Future work should aim to place the regrounding of HIR in context with other Holocene changes in this sector, such as the transition at Korff Ice Rise, from North‐South flow to stable ice‐divide flow prior to 2.5 kyr BP (Brisbourne et al, ; Kingslake et al, ), the potential retreat of WAIS GL inland of its current position (Bradley et al, ; Kingslake et al, ; Siegert et al, ), and other flow switching in the Institute and M ller ice stream system (Bingham et al, ; Winter et al, ). There is also no current dating constraint on the formation and evolution of DIR, which may be significant for controlling the GL position of ice rises and the main ice sheet.…”

Major Ice Sheet Change in the Weddell Sea Sector of West Antarctica Over the Last 5,000 Years

“…The IIS has three tributaries to the south and west of the Ellsworth Mountains, occupying the Horseshoe Valley, Independence Trough, and Ellsworth Trough (Bamber et al, ; Ross et al, ; Winter et al, ). The Horseshoe Valley trough, around 20‐km wide and 1.3‐km below sea level at its deepest point, is located downstream of the steep mountains of the Heritage Range.…”

“…The Ellsworth Trough (Ross et al, ) is aligned with the Independence Trough; both are orthogonal to the orientation of the Amundsen‐Weddell ice divide, dissecting the Ellsworth Subglacial Highlands northwest to southeast. The Ellsworth Trough is considered to be the largest and deepest trough‐controlled tributary of the IIS (Ross et al, ; Winter et al, ), measuring ~34 km in width and ~260 km in length. At its deepest point, the Ellsworth Trough extends ~2 km below sea level.…”

Topographic Steering of Enhanced Ice Flow at the Bottleneck Between East and West Antarctica

“…The bottleneck region contains a major West Antarctic ice divide, separating ice catchments in the Weddell and Ross Sea sectors (Figure 1), which could be susceptible to migration driven by ice dynamics. Although ice flow switching (Conway et al, 2002;Siegert et al, 2013;Winter et al, 2015), complex internal dynamics (Joughin & Alley, 2011), and enhanced "onset" ice flow (Beem et al, 2017;Bingham et al, 2007;Studinger et al, 2001) in the bottleneck region has the potential to impact mass discharge from the Antarctic interior, field site inaccessibility and the orbits of Earth observation satellites have previously restricted our understanding of basal topography and ice flow conditions in this area. This paper uses new aerogeophysical survey data acquired across the bottleneck zone during the 2015/2016 austral summer (PolarGAP survey data: https://earth.esa.int/web/guest/campaigns), complemented by ice thickness data acquired in 2010-2011 (Jeofry et al, 2018;Ross et al, 2012) and recent satellite-derived surface ice velocity measurements Rignot et al, 2017;Figure 1b) to assess the controls on ice flow at the bottleneck zone.…”