Climate change impact on ecosystems of Prince Edward Islands : role of oceanic mesoscale processes

• Main Author: Asdar, Sarah
• Other Authors: Laboratoire d'Océanographie Physique et Spatiale (LOPS), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Université de Bretagne occidentale - Brest, University of Cape Town, Pierrick Penven
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2018
• Subjects: Subantarctic islands; Mesoscale eddy; Subantarctic front; Climate change; Idealised ocean modelling; Îles subantarctiques; Tourbillon mésoéchelle; Front subantarctique; Changement climatique; Modélisation idéalisée; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Antarctic; The Antarctic; Indian; Antarc*; Antarctique*; Prince Edward Islands
• Online Access: https://theses.hal.science/tel-01892140; https://theses.hal.science/tel-01892140/document; https://theses.hal.science/tel-01892140/file/These-2018-SML-Oceanographie_physique-ASDAR_Sarah.pdf

The subantarctic Prince Edward Islands lie in the Antarctic Circumpolar Current, between the Subantarctic Front (SAF) and the Polar Front (PF). These fronts positions were found to be highly variable at interannual and monthly time scales and revealed a significant long-term southward trend in the region. The intense mesoscale activity, observed upstream the islands at the South West Indian Ridge, also showed an interannual and intra-annual variability as well a decrease in eddy kinetic energy over 24 years. At a more local scale, we highlighted that the archipelago’s environment was impacted by the mesoscale features produced upstream.Tides appeared to be another important driver of variability of the circulation in between the two islands.An idealised model configuration was designed for the Prince Edward Islands region to study the mesoscale eddy properties and the physical mechanisms of their formation at the ridge. The Eddy Available Potential Energy revealed a maximum of energy around 800 m depth, confirming the deep reaching characteristic of the eddy originated in the region and suggested the presence of a local energy source at this depth. This eddies activity was shown to be the result of a combination of barotropic and baroclinic instabilities occurring at the ridge.Finally, we investigated on the potential consequences of a southward shift of the SAF in the region of the islands.Because the model was idealised, it allowed us to simulate an SAF southward shift by shifting the initial and boundary conditions. The main result was the clear decrease of mesoscale activity in the region which could potentially impact the ecosystems of the Prince Edward Islands. L’archipel du Prince Édouard est situé dans le Courant Circumpolaire Antarctique, entre le Front Subantarctique (SAF) et le front polaire (PF). Les positions de ces fronts se sont révélées très variables aux échelles interannuelles et mensuelles et ont montré une tendance à long terme à migrer vers le sud dans la région. L'activité ...