ALBERT

Description: Nature Geoscience 8, 294 (2015). doi:10.1038/ngeo2388 Authors: J. S. Greenbaum, D. D. Blankenship, D. A. Young, T. G. Richter, J. L. Roberts, A. R. A. Aitken, B. Legresy, D. M. Schroeder, R. C. Warner, T. D. van Ommen & M. J. Siegert Totten Glacier, the primary outlet of the Aurora Subglacial Basin, has the largest thinning rate in East Antarctica. Thinning may be driven by enhanced basal melting due to ocean processes, modulated by polynya activity. Warm modified Circumpolar Deep Water, which has been linked to glacier retreat in West Antarctica, has been observed in summer and winter on the nearby continental shelf beneath 400 to 500 m of cool Antarctic Surface Water. Here we derive the bathymetry of the sea floor in the region from gravity and magnetics data as well as ice-thickness measurements. We identify entrances to the ice-shelf cavity below depths of 400 to 500 m that could allow intrusions of warm water if the vertical structure of inflow is similar to nearby observations. Radar sounding reveals a previously unknown inland trough that connects the main ice-shelf cavity to the ocean. If thinning trends continue, a larger water body over the trough could potentially allow more warm water into the cavity, which may, eventually, lead to destabilization of the low-lying region between Totten Glacier and the similarly deep glacier flowing into the Reynolds Trough. We estimate that at least 3.5 m of eustatic sea level potential drains through Totten Glacier, so coastal processes in this area could have global consequences.

Description: The impact of localized regions of elevated geothermal heat flux on ice sheet dynamics is largely unknown. Simulations of ice dynamics are produced using poorly resolved and low resolution estimates of geothermal heat flux. Observations of crustal heat production within the continental crust underneath the Lambert-Amery glacial system in East Antarctica indicate high heat flux regions of at least 120 mWm −2 exist. Here we investigate the influence of simulated but plausible, localized regions of elevated geothermal heat flux on ice dynamics using a numerical ice sheet model of the Lambert-Amery glacial system. We find that high heat flux regions have a significant effect across areas of slow moving ice with the influence extending both upstream and downstream of the geothermal anomaly, while fast moving ice is relatively unaffected. Our results suggest that localized regions of elevated geothermal heat flux may play an important role in the organization of ice sheet flow.

Description: Repeated large-scale retreat and advance of Totten Glacier indicated by inland bed erosion Nature 533, 7603 (2016). doi:10.1038/nature17447 Authors: A. R. A. Aitken, J. L. Roberts, T. D. van Ommen, D. A. Young, N. R. Golledge, J. S. Greenbaum, D. D. Blankenship & M. J. Siegert Climate variations cause ice sheets to retreat and advance, raising or lowering sea level by metres to decametres. The basic relationship is unambiguous, but the timing, magnitude and sources of sea-level change remain unclear; in particular, the contribution of the East Antarctic Ice Sheet (EAIS) is ill defined, restricting our appreciation of potential future change. Several lines of evidence suggest possible collapse of the Totten Glacier into interior basins during past warm periods, most notably the Pliocene epoch, causing several metres of sea-level rise. However, the structure and long-term evolution of the ice sheet in this region have been understood insufficiently to constrain past ice-sheet extents. Here we show that deep ice-sheet erosion—enough to expose basement rocks—has occurred in two regions: the head of the Totten Glacier, within 150 kilometres of today’s grounding line; and deep within the Sabrina Subglacial Basin, 350–550 kilometres from this grounding line. Our results, based on ICECAP aerogeophysical data, demarcate the marginal zones of two distinct quasi-stable EAIS configurations, corresponding to the ‘modern-scale’ ice sheet (with a marginal zone near the present ice-sheet margin) and the retreated ice sheet (with the marginal zone located far inland). The transitional region of 200–250 kilometres in width is less eroded, suggesting shorter-lived exposure to eroding conditions during repeated retreat–advance events, which are probably driven by ocean-forced instabilities. Representative ice-sheet models indicate that the global sea-level increase resulting from retreat in this sector can be up to 0.9 metres in the modern-scale configuration, and exceeds 2 metres in the retreated configuration.

Description: Climate variations cause ice sheets to retreat and advance, raising or lowering sea level by metres to decametres. The basic relationship is unambiguous, but the timing, magnitude and sources of sea-level change remain unclear; in particular, the contribution of the East Antarctic Ice Sheet (EAIS) is ill defined, restricting our appreciation of potential future change. Several lines of evidence suggest possible collapse of the Totten Glacier into interior basins during past warm periods, most notably the Pliocene epoch, causing several metres of sea-level rise. However, the structure and long-term evolution of the ice sheet in this region have been understood insufficiently to constrain past ice-sheet extents. Here we show that deep ice-sheet erosion-enough to expose basement rocks-has occurred in two regions: the head of the Totten Glacier, within 150 kilometres of today's grounding line; and deep within the Sabrina Subglacial Basin, 350-550 kilometres from this grounding line. Our results, based on ICECAP aerogeophysical data, demarcate the marginal zones of two distinct quasi-stable EAIS configurations, corresponding to the 'modern-scale' ice sheet (with a marginal zone near the present ice-sheet margin) and the retreated ice sheet (with the marginal zone located far inland). The transitional region of 200-250 kilometres in width is less eroded, suggesting shorter-lived exposure to eroding conditions during repeated retreat-advance events, which are probably driven by ocean-forced instabilities. Representative ice-sheet models indicate that the global sea-level increase resulting from retreat in this sector can be up to 0.9 metres in the modern-scale configuration, and exceeds 2 metres in the retreated configuration.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Aitken, A R A -- Roberts, J L -- van Ommen, T D -- Young, D A -- Golledge, N R -- Greenbaum, J S -- Blankenship, D D -- Siegert, M J -- England -- Nature. 2016 May 18;533(7603):385-9. doi: 10.1038/nature17447.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉School of Earth and Environment, University of Western Australia, Perth, Western Australia 6008, Australia. ; Australian Antarctic Division, Kingston, Tasmania 7050, Australia. ; Antarctic Climate &Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, Tasmania 7005, Australia. ; University of Texas Institute for Geophysics, University of Texas at Austin, Austin, Texas 78758, USA. ; Antarctic Research Centre, Victoria University of Wellington, Wellington 6140, New Zealand. ; GNS Science, Avalon, Lower Hutt 5011, New Zealand. ; The Grantham Institute and Department of Earth Science and Engineering, Imperial College London, London SW7 2AZ, UK.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/27193684" target="_blank"〉PubMed〈/a〉

Description: Sedimentary basins beneath the East Antarctic Ice Sheet (EAIS) have immense potential to inform models of the tectonic evolution of East Antarctica and its ice-sheet. However, even basic characteristics such as thickness and extent are often unknown. Using airborne geophysical data, we resolve the tectonic architecture of the Knox Subglacial Sedimentary Basin in western Wilkes Land. In addition, we apply an erosion restoration model to reconstruct the original basin geometry for which we resolve geometry typical of a transtensional pull-apart basin. The tectonic architecture strongly indicates formation as a consequence of the rifting of India from East Gondwana from ca. 160-130 Ma, and we suggest a spatial link with the western Mentelle Basin offshore western Australia. The erosion restoration model shows that erosion is confined within the rift margins, suggesting that rift structure has strongly influenced the evolution of the Denman and Scott ice streams.

Description: Future global mean sea level (GMSL) change is dependent on the complex response of the Antarctic Ice Sheet to ongoing changes and feedbacks in the climate system. The Lambert-Amery glacial system has been observed to be stable over the recent period yet is potentially at risk of rapid grounding line retreat and ice discharge given a significant volume of its ice is grounded below sea level, making its future contribution to GMSL uncertain. Using a regional ice sheet model of the Lambert-Amery system, we find that under a range of future warming and extreme scenarios, the simulated grounding line remains stable and does not trigger rapid mass loss from grounding line retreat. This allows for increased future accumulation to exceed the mass loss from ice dynamical changes. We suggest the Lambert-Amery glacial system will remain stable, or gain ice mass and mitigate a portion of potential future sea level rise over the next 500 years, with a range of +3.6 to -117.5 mm GMSL-equivalent.

Description: The second generation Antarctic magnetic anomaly compilation for the region south of 60°S includes some 3.5 million line-km of aeromagnetic and marine magnetic data that more than doubles the initial map’s near-surface database. For the new compilation, the magnetic data sets were corrected for the International Geomagnetic Reference Field, diurnal effects, and high-frequency errors and leveled, gridded, and stitched together. The new magnetic data further constrain the crustal architecture and geological evolution of the Antarctic Peninsula and the West Antarctic Rift System in West Antarctica, as well as Dronning Maud Land, the Gamburtsev Subglacial Mountains, the Prince Charles Mountains, Princess Elizabeth Land, and Wilkes Land in East Antarctica and the circumjacent oceanic margins. Overall, the magnetic anomaly compilation helps unify disparate regional geologic and geophysical studies by providing new constraints on major tectonic and magmatic processes that affected the Antarctic from Precambrian to Cenozoic times.