Talks by John Goodge and Mathieu Casado

13.00 JOHN GOODGE will give a talk on:
Exploring Antarctica’s ice sheets and subglacial geology with a rapid access ice drill
Read abstract below
John Goodge is professor at Dept. of Earth & Environmental Sciences

13.30 Coffee break

13.45 MATHIEU CASADO will give a talk on:
What is actually archived by water isotopic composition of ice on the East Antarctic Plateau?
Read abstract below
Mathieu Casado is PhD from LSCE


Exploring Antarctica’s ice sheets and subglacial geology with a rapid access ice drill
By John Goodge

ABSTRACT A Rapid Access Ice Drill (RAID) is being developed that will penetrate the Antarctic ice sheets in order to core in deep ice, the glacial bed, and bedrock below. This new technology will provide a critical first look at the interface between major ice caps and their subglacial geology. Currently in development for the U.S. Antarctic Program, RAID is a mobile drilling system capable of making several long boreholes in a single field season in Antarctica. RAID is interdisciplinary and will allow access to polar paleoclimate records in ice >1 Ma, direct observation at the base of the ice sheets, and recovery of rock cores from the ice-covered East Antarctic craton. RAID is based on a diamond rock-coring system as used in mineral exploration. Threaded drill-pipe with hardened metal bits will cut through ice using reverse circulation of ESTISOL 140 for pressure-compensation, maintenance of temperature, and removal of ice cuttings. Near the bottom of the ice sheet, a wireline bottom-hole assembly will enable diamond coring of ice, the glacial bed, and bedrock below. Once complete, boreholes will be kept open with fluid, capped, and made available for future down-hole measurement of thermal gradient, heat flow, ice chronology, and ice deformation. RAID will also sample for extremophile microorganisms. RAID is designed to penetrate up to 3,300 meters of ice in less than 48 hours and take sample cores. This rapid performance will allow completion of a borehole and coring in about 10 days before moving to the next drilling site. RAID is unique because it can provide fast borehole access through thick ice; take short ice cores for paleoclimate study; sample the glacial bed to determine ice-flow conditions; take cores of subglacial bedrock for age dating and crustal history; and create boreholes for use as an observatory in the ice sheets. Together, the rapid drilling capability and mobility of the drilling system, along with ice-penetrating imaging methods, will provide a unique 3D picture of the interior Antarctic ice sheets.

What is actually archived by water isotopic composition of ice on the East Antarctic Plateau?
By Mathieu Casado

ABSTRACT The oldest ice core records are obtained on the East Antarctic plateau.  The composition in stable isotopes of water permits to reconstruct past climatic conditions over the ice sheet and at the evaporation source. Paleothermometer accuracy relies on good knowledge of processes affecting the isotopic composition of surface snow in Polar Regions. Both simple models and global atmospheric models with isotopes provide good prediction of precipitation isotopic composition in East Antarctica but post deposition processes can alter isotopic composition on site, in particular exchanges with local vapour. To quantitatively interpret the isotopic composition of water archived in ice cores, it is thus essential to study the continuum water vapour – precipitation – surface snow – buried snow.

Using the new developments of infrared spectrometers measuring isotopic composition directly on the field even at low humidities, we present here a compilation of new water isotopic results from the East Antarctic Plateau: snow surface measurements on several transects documenting the spatial variability of δ18O-temperature relationship, precipitations over several years documenting the temporal variability at the seasonal scale, water vapour isotopic composition in parallel with snow surface in Dome C over several years documenting the post deposition effects and snow pits from different sites documenting the processes influencing the archiving of water isotopic signal in deep ice cores. All these results highlight the importance of the direct exchanges between water vapour and snow at the surface in between precipitation events and raise the question of what is actually archived in the ice core isotopic composition.

Casado M, Landais A, Masson-Delmotte V, Genthon C, Kerstel E, Kassi S, et al. Continuous measurements of isotopic composition of water vapour on the East Antarctic Plateau, Atmos Chem Phys Discuss, 2016:1-26, (2016)
Ekaykin AA, Lipenkov VY, Barkov NI, Petit JR, Masson-Delmotte V. Spatial and temporal variability in isotope composition of recent snow in the vicinity of Vostok station, Antarctica: implications for ice-core record interpretation. Annals of Glaciology;35(1):181-6, (2002)
Münch T, Kipfstuhl S, Freitag J, Meyer H, Laepple T. Regional climate signal vs. local noise: a two-dimensional view of water isotopes in Antarctic firn at Kohnen station, Dronning Maud Land. Clim Past Discuss;11(6):5605-49 (2015)
Touzeau A, Landais A, Stenni B, Uemura R, Fukui K, Fujita S, et al. Acquisition of isotopic composition for surface snow in East Antarctica and the links to climatic parameters, The Cryosphere Discuss ;9(6):6275-313, (2015)