Écologie des foraminifères benthiques en domaine arctique dans un contexte de changements climatiques : cas des mers de Chukchi, Barents et Baffin

Abstract : Benthic foraminifera are widely used in oceanography as paleoclimate and paleoenvironmental bio-indicators due to their presence in all marine environments, their sensitivity to environmental changes and their great capacity to fossilize. However, the use of benthic foraminifera as paleoenvironmental proxies requires a good knowledge of the ecological conditions and the parameters controlling species distribution. Although knowledges about the ecology of benthic foraminifera are improving, they remain sporadic in Arctic area, a complex ecosystem characterized by multiple interactions between the atmosphere, the ocean and the cryosphere and particularly sensitive to change and vulnerable to global warming. Temperatures in the Arctic have risen twice as fast as the global average over the past decades, a phenomenon that has been dubbed the “polar amplification of global warming”. In this context, this thesis aims at better understanding the ecology of living benthic foraminifera in Arctic regions and at defining the importance of environmental controls on fauna such as water mass properties, primary productivity, organic matter flux as well as sea-ice dynamics. Living benthic foraminifera were identified in the first centimetres of 21 surface sediment cores collected in three Arctic areas during summer in 2014 and 2015: Baffin Bay and the Barents and Chukchi Seas. These three regions present specific characteristics in terms of sea-ice cover, water mass circulation or primary productivity. Our results suggest that these factors influence the distribution of benthic foraminifera. The flux of organic matter resulting from primary productivity intensified during spring and summer periods near hydrographic polar fronts, sea-ice edges (marginal ice zones) and in the north water polynya (Baffin Bay) increases the fauna’s densities and diversity and favours the development of specific species. Nonionellina labradorica in cold Arctic waters and Cassidulina neoteretis associated with Atlantic waters respond to fresh supply of organic matter while Melonis barleeanus is found in environment rich in degraded organic matter. In deeper oligotrophic environments, Oridorsalis tenerus is a ubiquitous species associated with Cibicidoides wuellerstorfi on the west continental margin of Barents Sea and Ioanella tumidula in the deeper basin in the north of the Chukchi Sea. Physical and chemical water mass properties also affect the distribution of living benthic foraminifera. In the Baffin Bay and the continental shelf of the Chukchi Sea, corrosive waters lead to carbonate dissolution, favouring the dominance of agglutinated species. This thesis hence contributes to calibrate the benthic foraminifera to their environment and to improve their application as paleoclimate and paleoenvironmental proxies in the Arctic. Finally, a preliminary study about fossil benthic foraminifera in three cores of Barents Sea allowed to show variations of environmental conditions during the last two centuries.
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Calypso Racine. Écologie des foraminifères benthiques en domaine arctique dans un contexte de changements climatiques : cas des mers de Chukchi, Barents et Baffin. Milieux et Changements globaux. Université de Bordeaux, 2019. Français. ⟨NNT : 2019BORD0008⟩. ⟨tel-02303043⟩

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