Glacial retreat in the Amundsen Sea sector, West Antarctica – first cosmogenic evidence from central Pine Island Bay and the Kohler Range

Abstract

a b s t r a c tThe Amundsen Sea Embayment of West Antarctica hosts one of the most rapidly changing sectors of the West Antarctic Ice Sheet. With the fastest-flowing ice streams in Antarctica, the region around Pine Island Bay is characterized by rapid ice-sheet thinning and grounding-line retreat. Published surfaceexposure data are limited to a few isolated nunataks making it difficult to assess the long-term deglacial history of the area. To address this, we correlate existing records of lateral ice-stream retreat from marine sediment cores with onshore glacial thinning in two key areas of eastern Marie Byrd Land: the Kohler Range and Pine Island Bay. Our 10 Be surface-exposure ages are the first from the isolated Kohler Range and show that the nunataks there became ice-free between 8.6 and 12.6 ka. This implies a minimum long-term average thinning rate of 3.3 ± 0.3 cm/yr, which is one order of magnitude lower than recent rates based on satellite data. We also present pre-to early Holocene 10 Be surface-exposure ages from two islands located approximately 80 km downstream of the Pine Island Glacier ice-shelf front to constrain the lateral deglacial history in the Pine Island Bay area. This study provides insight into the significance of local ice sheet variations and suggests that the post-LGM history in the Amundsen Sea sector was characterized by glacial thinning as well as lateral retreat in pre-to early Holocene times.

Atmosphere‐ocean‐ice interactions in the Amundsen Sea Embayment, West Antarctica

“…It has also been suggested that some of these basins hosted, at least temporarily, subglacial lakes during the last glacial period [ Nitsche et al ., ; Witus et al ., ]. Surface exposure ages of glacially transported rocks have shown that the LGM surface of the WAIS lay at least ~140 m and 190 m higher than today to the north and to the east of the modern PIG grounding‐line position, respectively [ Johnson et al ., , ], while in the hinterland of the Crosson and Dotson ice shelves the LGM ice sheet was ~300 to 330 m thicker than today [ Johnson et al ., ; Lindow et al ., ].…”

“…Estimates of the time that surface rocks around the ASE have been exposed (see Dunai [] for details of the types of technique used) indicate that significant post‐LGM ice sheet thinning occurred in the hinterland of the Dotson Ice Shelf between 12.6 and 8.6 ka [ Lindow et al ., ] and in the hinterland of the Crosson Ice Shelf between 14.5 and 11.7 ka [ Johnson et al ., ], which is consistent with the reconstructions from the marine sediment cores. However, the data also revealed rapid WAIS thinning in the Pine Island Bay region at ~8 ka, i.e., >3000 years later than the deglaciation of the inner shelf [ Johnson et al ., ].…”

“…Thus, the data suggest either a stoppage of post‐LGM thinning of the WAIS in this area from 6 ka until recently or a local ice sheet thickening during the last few millennia or centuries. Surface exposure ages on an erratic boulder and bedrock collected from islands in inner Pine Island Bay range from 13.8 ka to 2.2 ka, but currently, it is unclear whether these dates indicate the timing of local ice margin retreat or the emergence of the islands above regional sea level caused by glacioisostatic rebound [ Johnson et al ., ; Larter et al ., ; Lindow et al ., ].…”

“…Reliable proxies for ice‐shelf presence (or absence) are also required for evaluating the role of ice‐shelf buttressing for delaying or even halting ice sheet retreat and thinning. In addition, more rock samples for reconstructing the thinning history of the ASE drainage basin by surface exposure age dating are required because currently only a few locations in the hinterland of the ASE have been studied [ Johnson et al ., , ; Larter et al ., ; Lindow et al ., ]. In addition, the recovery and analysis of further marine sediment cores from below the modern ASE ice shelves [e.g., Smith et al ., , ] will help to reconstruct the (sub) recent ice‐ocean and ice‐bed topography interactions.…”

The role of the cryosphere in source-to-sink systems

“…Cosmogenic exposure-age dating, which relies on the measurement of rare nuclides produced in rock surfaces and sediments by cosmic ray bombardment, is now widely used to date both late Pleistocene and Holocene deglaciation ages as well as to quantify subglacial erosion rates via the nuclide concentration in glacially transported boulders and in bedrock exposed during retreat (Balco, 2011). Advances in the use of cosmogenic nuclide isotopes (Miller et al, 2002;Briner et al, 2006;Briner and Kaufman, 2008;Menounos et al, 2009;Balco, 2011;Fastook and Hughes, 2013;Granger et al, 2013;Champagnac et al, 2014;Cofaigh et al, 2014;Hormes et al, 2013;Refsnider et al, 2013;Hodgson et al, 2014;Larter et al, 2014;Lindow et al, 2014;Rother et al, 2014;Winsor et al, 2014) have helped resolve a number of longstanding chronological and process debates in geomorphology, including: topographic relief development (e.g., Tremblay et al, 2014) and the ability of cold-based ice sheets to preserve pre-glacial landscape features (e.g. Stroeven et al, 2002;Briner et al, 2006); complex Holocene glacial exposureburial histories (e.g.…”