Ice-related environmental changes in Arctic fjords : new insights from benthic foraminifera

• Main Author: Fossile, Eleonora
• Other Authors: Bio-Indicateurs Actuels et Fossiles (BIAF), Université d'Angers (UA), Université d'Angers, Hélène Howa, Meryem Mojtahid, Maria-Pia Nardelli
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2022
• Subjects: Sea ice; Polynya; Tidewater glacier; Bioindicators; Proxy; Svalbard; Polynie; Glacier côtier; Bioindicateurs; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Arctic; Climate change; Foraminifera*; glacier; Kongsfjord*; Kongsfjorden; Storfjorden; Tidewater
• Online Access: https://theses.hal.science/tel-04089929; https://theses.hal.science/tel-04089929/document; https://theses.hal.science/tel-04089929/file/pdffix_these_FOSSILE.pdf

Climate change threatens polar regions with major consequences on ice-related dynamics and linked ecosystems. Predictions of future sea ice cover and glacier retreat rely on paleoenvironmental reconstructions (through proxies’ application) to extend the instrumental period and thus reduce models’ uncertainty. This PhD thesis aimed to develop and test ecological proxies for sea ice formation and glacier melting using benthic foraminifera. In the Storfjorden “sea ice factory”, foraminiferal responses to brine presence (i.e., CO2-enriched waters released during sea ice formation processes) were investigated. The ratio between Agglutinated and Calcareous (A/C) foraminifera was proposed as potential proxy for brine persistence, because of the brine-induced dissolution on calcareous foraminiferal shells. Although the A/C signal was affected by taphonomic processes, the differences between areas of brine persistence and those with intermittent influence was preserved, thus supporting the proxy. Likewise, foraminiferal responses to steep environmental gradients (e.g., water salinity and turbidity, organic fluxes) created by tidewater glacier dynamics in summer, were investigated in Kongsfjorden. The glacier induced disturbance resulted in the establishment of different foraminiferal assemblages and increased taxonomic and functional diversity with increased distance from the glacier front. A combination of diversity metrics was proposed as potential proxy for glacier retreat and its effectiveness was tested on a sedimentary archive covering the last 60 years. The two proxies proposed here are therefore applicable in any similar Arctic environments. Le changement climatique menace les régions polaires avec des conséquences majeures sur la dynamique des glaces et les écosystèmes associés. Les simulations de fonte glaciaire reposent sur des reconstitutions paléo environnementales, qui complètent les mesures directes sur la période actuelle pour réduire l'incertitude des prévisions. Des proxies basés sur l’écologie des ...