Constraining Recent Ice Flow History at Korff Ice Rise, West Antarctica, Using Radar and Seismic Measurements of Ice Fabric

Abstract

The crystal orientation fabric of ice reflects its flow history, information which is required to better constrain projections of future ice sheet behavior. Here we present a novel combination of polarimetric phase-sensitive radar and seismic anisotropy measurements to provide independent and consistent constraints on ice fabric at Korff Ice Rise, within the Weddell Sea sector of West Antarctica. The nature and depth distribution of fabric in the ice column is constrained using the azimuthal variation in (1) the received power anomaly and phase difference of polarimetric vertical radar soundings and (2) seismic velocities and shear wave splitting measurements. Radar and seismic observations are modeled separately to determine the nature and strength of fabric within the ice column. Both methods indicate ice fabric above 200-m depth which is consistent with present-day ice-divide flow. However, both measurements also indicate an oblique girdle fabric below 230-m depth within the ice column, inconsistent with steady state divide flow. Our interpretation is that this deeper fabric is a remnant fabric from a previous episode of flow, which is currently being overwritten by ongoing fabric development associated with the present-day flow regime. The preexisting fabric is consistent with ice flow from the south prior to ice-divide formation, in agreement with models of Holocene ice sheet evolution. These findings apply new constraints to the flow history at Korff Ice Rise prior to divide formation and demonstrate the capacity of radar and seismic measurements to map fabric and thus constrain past ice flow.Plain Language Summary When ice flows its crystals become oriented in specific ways dependent on the way the ice is flowing, forming what we call a fabric. When this occurs in an ice stream the form of this fabric is determined by the flow direction and geometry of the ice stream bed. These fabrics remain imprinted within the ice but can become overwritten by new fabrics which result from a subsequent flow pattern. The study site here is Korff Ice Rise, which is an isolated area of grounded ice within the floating Ronne Ice Shelf in the Weddell Sea, West Antarctica. Here the ice flows in a very specific way, forming a characteristic fabric. We can measure this fabric using radar and seismic measurements. We also see an older fabric which must have formed when the ice was flowing differently. This older fabric is consistent with a time when the ice sheet was much thinner and ice was flowing from the continent of Antarctica further upstream, and over the current site. This study shows how measurements of fabric within Antarctic ice help us look at how the ice sheet behaved in the past. This past behavior would have affected global sea levels.

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

“…Future geophysics campaigns could seek englacial features in ice rises in the Ross Ice Sea similar to those observed in HIR for dating constraints and mechanistic explanations for the readvance of the GL here, as reported by Kingslake et al (2018) and to build on the work of Fahnestock et al (2000), Catania et al (2006), and Hulbe et al (2013) in conjunction with estimates of GL retreat through the sector (Conway et al, 1999;Martín et al, 2006). 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, 2019;Kingslake et al, 2016), the potential retreat of WAIS GL inland of its current position (Bradley et al, 2015;Kingslake et al, 2018;Siegert et al, 2013), and other flow switching in the Institute and Möller ice stream system Winter et al, 2015). 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.…”

“…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.…”

“…However, recent evidence suggests that the WAIS has readvanced in the Ross and Weddell Sea sectors following a post-LGM maximum retreat (Bradley et al, 2015;Kingslake et al, 2018;Siegert et al, 2013). Other work points to a reconfiguration of ice flow within the last 10 kyr in these sectors Brisbourne et al, 2019;Catania et al, 2005Catania et al, , 2006Fahnestock et al, 2000;Hulbe & Fahnestock, 2004;Kingslake et al, 2016;Winter et al, 2015). Groundingline (GL) retreat upstream of its present-day location in the Weddell Sea sector of West Antarctica was hypothesized by (Siegert et al, 2013), who used airborne ice-penetrating radar data as evidence for previous fast flow in a currently slow-flowing grounded region.…”

Estimation of ice fabric within Whillans Ice Stream using polarimetric phase-sensitive radar sounding

“…The ApRES was originally designed to estimate basal melt and vertical strain rates (Nicholls and others, 2015) and has since been used to investigate englacial water storage (Kendrick and others, 2018), englacial layer geometry (Young and others, 2018), and to invert for ice flow velocities (Kingslake and others, 2016). The ApRES has recently been used to conduct polarimetric radar sounding measurements in complex flow regions, with Brisbourne and others (2019) focusing on ice rises in the Weddell sea sector of Antarctica.…”

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

“…Beneath the ice divide on KIR a prominent Raymond Arch suggests stable flow here during at least the past 2–3 kyr (Kingslake et al, ). Further north along the KIR divide, polarmetric phase‐sensitive radar and active seismic surveys reveal a transition in englacial fabric at around 200‐ to 230‐m depth (Brisbourne et al, ). These authors interpret the fabric beneath this depth as evidence of a change in past flow conditions.…”