UMR CNRS 5805 EPOC
Environnements et Paléoenvironnements
Océaniques et Continentaux

        

Consignes de Sécurité et Numéros d'Urgence
(à l'usage des personnels du laboratoire)

April 30, 2020

Eleanor GEORGIADIS

Jacques Giraudeau / Guillaume Massé (Université de Laval, Canada)

Mme Marit-Solveig SEIDENKRANTZ, Professeur, University of Aarhus, DK - Rapporteur
M. Jochen KNITZ, Dir. Rech., Geol. Survey of Norway - University of Tromsoe, NO - Rapporteur
Mme Carlota ESCUTIA DOTTI, Dir. Rech, Spanish National Research Council, Univ. Granada, SP - Examinatrice
M. Patrick LAJEUNESSE, Professeur, Université Laval, Québec, CA - Examinateur
Mme Marie-Alexandrine SICRE, Dir. Rech. CNRS, UMR LOCEAN, Sorbonne Université, Paris, FR - Examinatrice
M. Philippe MARTINEZ, Professeur, UMR EPOC, Université de Bordeaux, FR - Examinateur
Mme Sofia RIBEIRO, Sen. Sc., Geological Survey of Denmark, Copenhagen, DK - Invitée
M. Guillaume MASSE, CR CNRS, UMI Takuvik, Université Laval, CA - Co-Directeur
M. Jacques GIRAUDEAU, DR CNRS, UMR EPOC, Université de Bordeaux, FR - Co-Directeur

Nares Strait is one of the three channels of the Canadian Arctic Archipelago (CAA), which connect the Arctic Ocean to Baffin Bay. The CAA throughflow is a major component of ocean circulation in western Baffin Bay. Nares Strait borders the CAA to the east, separating Ellesmere Island from Greenland, and is 80% covered in sea ice 11 months of the year. The heavy sea ice cover is constituted of (1) arctic (multi-year) sea-ice having entered the strait by the north, and (2) locally formed first year sea ice, which consolidates the ice cover. The hydrological history of the area is intimately linked to the formation of land-fast sea ice in the strait, constituting ice arches. The sea-ice cover in Nares Strait regulates freshwater (liquid and solid) export towards Baffin Bay, and is integral to the formation of an area of open water in northernmost Baffin Bay: the North Water polynya.
Nares Strait has been at the heart of major geomorphological changes over the past 10,000 years. Its deglacial and post-glacial history is marked by (1) rapid retreat of the Greenland and Innuitian ice-sheets which coalesced along Nares Strait during the Last Glacial Maximum, (2) post-glacial shoaling associated to isostatic rebound, and (3) variable multi-year and seasonal sea ice conditions. Little is known about the evolution of these three environmental components of the Nares Strait history, and they are poorly constrained in terms of chronology and synchronism with other regional changes. Nares Strait and its eventful Holocene history provide a unique case study of the response of the marine and continental cryosphere to rapid climate change, such as that affecting Arctic regions in modern times.
The marine sediment archives that were retrieved during the ANR GreenEdge and ArcticNet (2014 and 2016) cruises of the CCGS Amundsen offer a unique opportunity to investigate the Deglacial to Late Holocene history of Nares Strait. Our reconstructions are based on a multi-proxy study of these cores, including sedimentological (grain size and lithofacies), geochemical (XRF), mineralogical (q-XRD) micropaleontological (planktic and benthic foraminiferal assemblages), and biogeochemical (sea ice biomarkers IP25 and HBI III) indicators.
Our results include an age for the deglacial opening of Nares Strait between 9.0 and 8.3 cal. ka BP, with the event likely occurring closer to the later bracket of the timeframe (i.e. ca 8.4-8.3 cal. ka BP). This event established the throughflow from the Arctic Ocean towards northernmost Baffin Bay. Environmental conditions were highly unstable in the Early Holocene, and marine primary productivity was limited. A period of minimum sea ice cover occurred from ca 8.1 to 7.5 cal. ka BP, during the Holocene Thermal Maximum, when atmospheric temperatures were higher than today in Nares Strait. Sea ice cover became more stably established as a seasonal feature around 7.5 cal. ka BP and primary productivity related to ice edge blooms increased. Eventually, the duration of the ice arches increased and they were present in spring and into the summer from 5.5 to 3.7 cal. ka BP, which allowed the inception of the North Water polynya. The North Water reached its maximal potential between 4.5 and 3.7 cal. ka BP, when warmer Atlantic-sourced water upwelled in the polynya, providing nutrients for primary productivity. The establishment of a near-perennial ice arch in northern Nares Strait prevented export of multi-year sea ice into Nares Strait and hindered the formation of the southern ice arch, ultimately resulting in a less productive polynya over the past ca 3.0 cal. ka BP.

En raison de la crise sanitaire, cette soutenance se tiendra en visio-conférence intégrale, sous contrôle de l'Ecole Doctorale Sciences et Environnement de l'Université de Bordeaux, et après autorisation de l'Université de Bordeaux et de l'Université Laval.
Conformément à la réglementation, pour des raisons techniques liées à la gestion des connexions, il n'est malheureusement pas possible d'associer un public invité à assister à cette soutenance.

ice-sheet ; sea ice ; climate ; Holocene ; Arctic ; paleoenvironments