Unravelling warm water pathways below Antarctica’s ice shelves

Master internship (4 to 6 months) - IGE Grenoble - glaciology

Laboratoire(s) de rattachement : Institut des Geosciences de l’Environnement, Grenoble
Encadrant(s) : Jeremie Mouginot
Co-encadrant(s) : Romain Millan
Contact(s) : romain.millan univ-grenoble-alpes.fr ; jeremie.mouginot univ-grenoble-alpes.fr
Lieu : IGE, Grenoble
Niveau de formation & prérequis : notions de base en glaciologie et dynamique glaciaire, programmation python/bash, notions de base en géophysique/gravimétrie
Mots clés : Antarctique,ice-ocean interactions,ice shelves

Scientific context
Glaciers and ice caps are the two major contributors to sea level rise. Between 2006 and 2015, they contributed more than 50% of its rise, exceeding the contribution related to ocean thermal expansion [SROCC., 2019]. In Antarctica, the outflowing glaciers of the ice sheet flow into the ocean and starts to float, forming ice shelves. The shelves are thus the first elements in contact with the warming ocean waters, constituting the stabilizing buttresses of 90% of the upstream ice [Rignot et al., 2013 ; Fürst et al., 2016]. Currently, 90% of Antarctic mass loss is related to the weakening of the shelves as a result of ocean warming : the shelves are therefore the most vulnerable parts of the ice sheets. The future evolution of Antarctica is therefore determined by the future of ice shelves.

To better constrain the future contribution of Antarctica to sea level, it is therefore essential to better understand ice-ocean interactions. In particular, it is crucial to know the topography of the ocean floor beneath the ice shelves, which controls the passage of warm ocean waters, with the presence or absence of submarine obstructions, and thus the melting beneath the shelves [Schodlok et al., 2012]. Mapping the bathymetry in Antarctica has always been a challenge. The most direct methods are the use of field measurements, such as seismic reflection or refraction, but these remain limited due to the high cost of field campaigns, and the relatively small spatial coverage. Because of the lack of direct observations, bathymetry under floating platforms is the result of rough and unrealistic mathematical interpolations. Despite its fundamental importance, the pathways of warm water under Antarctic ice shelves remain unknown to this day.

More recently, the use of multi-sensor gravity inversions has proven to be an effective way to reconstruct bathymetry [Millan et al., 2017 ; Tinto et al., 2011]. During an acquisition campaign, the gravimeter records, after a series of corrections, a gravity anomaly correlated to the average density, which depends on the distribution and density of the different geologic layers that make up the terrain beneath the instrument. By combining data from the NASA Operation Icebridge mission, and the Antarctic Gravity Grid database [Scheinert et al., 2016], it is now possible to have a complete coverage of the bathymetry under floating platforms, and thus improve the way we model ice-ocean interactions in Antarctica.

Goal of the internship
The goal of this internship is to use these gravity databases to better understand the pathways of warm waters under the Antarctic platforms. The candidate will use the processing chain implemented at IGE and at the University of California, Irvine to invert geophysical data and infer bedrock elevation. The candidate will compare the results with in-situ data (radar, seismic) to better quantify the errors on the calculated models. Using a database of CTD measurements, he will identify the sectors that are the most exposed to warm oceanic waters, and therefore the most vulnerable. At the end of this internship, the candidate will be part of a scientific publication of rank A, in collaboration with foreign institutes (University of California, Irvine, NASA’s Jet Propulsion Laboratory, Tongji University).

We are looking for a Master student in Earth Sciences, with good knowledge in programming (python, bash) and geophysics. The duration of this internship will be 4 to 6 months, and will take place at the Institut des Géosciences de l’Environnement, Grenoble under the supervision of Romain Millan (romain.millan univ-grenoble-alpes.fr) and Jeremie Mouginot (jeremie.mouginot univ-grenoble-alpes.fr).

References :
Rignot, E. et al. (2013). Ice-Shelf Melting Around Antarctica. Science, 341(6143), 266–270. https://doi.org/10.1126/science.1235798
Fürst, J. J., et al. (2016). The safety band of Antarctic ice shelves. Nature Climate Change, 6(5), 479–482. https://doi.org/10.1038/nclimate2912
Millan, R et al. (2017). Bathymetry of the Amundsen Sea Embayment sector of West Antarctica from Operation IceBridge gravity and other data. Geophysical Research Letters, 44(3), 1360–1368. https://doi.org/10.1002/2016GL072071
Tinto, K. J., & Bell, R. E. (2011). Progressive unpinning of Thwaites Glacier from newly identified offshore ridge : Constraints from aerogravity. Geophysical Research Letters, 38(20). https://doi.org/10.1029/2011GL049026
Schodlok, M et al. (2012). Sensitivity of the ice-shelf/ocean system to the sub-ice-shelf cavity shape measured by NASA IceBridge in Pine Island Glacier, West Antarctica. Annals of Glaciology, 53(60), 156–162. https://doi.org/10.3189/2012AoG60A073
Scheinert, M. et al. (2016). New Antarctic gravity anomaly grid for enhanced geodetic and geophysical studies in Antarctica. Geophysical Research Letters, 43(2), 600–610. https://doi.org/10.1002/2015GL067439