Constraining Recent Ice Flow History at Korff Ice Rise, West Antarctica, Using Radar and Seismic Measurements of Ice Fabric. Issue 1 (25th January 2019)

• Record Type: Journal Article
• Authors: Brisbourne, A. M.; Martín, C.; Smith, A. M.; Baird, A. F.; Kendall, J. M.; Kingslake, J.
• Is Part Of: Journal of geophysical research. Volume 124:Issue 1(2019)
• Page Start: 175
• Page End: 194
• Publication Date: 2019-01-25
• Subjects: Antarctica -- anisotropy -- fabric -- ice sheet history -- seismic -- radar; Geomorphology -- Periodicals; 551.3
• DOI: 10.1029/2018JF004776
• Languages: English
• ISSNs: 2169-9003

Abstract

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. Key Points: Backscatter power anomaly and phase difference in polarimetric radar data have been used to constrain ice fabric variation with depth Fabric derived from seismic observations is consistent with the fabric derived from radar measurements Fabric at Korff Ice Rise indicates a previous episode of grounded north‐south ice flow prior to ice divide formation