La datation des archives glaciaires

Les glaces en Antarctique et au Groenland sont une archive de premier plan pour reconstruire le climat du Quaternaire. Une datation précise est nécessaire pour exploiter cette archive. Les méthodes de datation peuvent être tirées de l'analyse de la glace, des bulles d'air piégées, de la comparaison à d'autres archives ou aux variations des paramètres orbitaux de la Terre, ou de la modélisation du processus de sédimentation glaciaire. Ces méthodes étant complémentaires, un modèle probabiliste a été développé pour les combiner de manière optimale. Ice samplings from Antarctica or Greenland form an exceptional archive to reconstruct the Quaternary climate. An accurate chronology is necessary to exploit this archive. Dating methods can be derived from the analysis of ice, or enclosed air bubbles, from the comparison to other archives or to variations of orbital parameters of the Earth, or from the modelling of the glacial sedimentation process. These methods being complementary, a probabilistic model has been developed to combine them in an optimal manner.

Recent distribution of Echinodermata species in Spitsbergen coastal waters

Thirty-two species of echinoderms from epibenthic sledges, dredges, scuba diving, and other samples (in total: 467 samples and c. 20 000 specimens) from fjords and coastal waters off Spitsbergen were analysed between 1996 and 2014. The most numerous group of echinoderms in the coastal waters off Spitsbergen is brittle stars (78% of the total individuals). The echinoderms do not form any clear assemblages according to depth or distance from glacial sedimentation and substrate. Some species prefer hard bottom (Strongylocentrotus droebachiensis) or water free from glacial suspensions (Ophiopholis aculeata). In contrast to the species listed above, we also found opportunistic species such as the starfish Urasterias lincki and the brittle star Ophiocten sericeum. These two species are distributed quite uniformly, regardless of the environmental factors. The majority of the species prefer a soft bottom below 200 m.

Observation of a living macroalga at 166 m in a high Arctic fjord

Still photos of the seafloor in Raudfjorden, Spitsbergen, recorded in 2011, showed an abundant macroalga at a depth of 166 m. The macroalga was observed attached to stones of varying size and streaming in the bottom current, which would imply that the alga was alive and growingin situ. The alga likely experiences very low-light conditions, as it is present in a turbid fjord influenced by glacial sedimentation. Arctic macroalgae are often adapted to low-light conditions, but to the authors’ knowledge, the present report is the deepest record of living macroalgae in the high Arctic.