Shoreline changes in a rising sea level context: The example of Grande Glorieuse,Scattered Islands,Western Indian Ocean |
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| Affiliation: | 1. LIENSs UMR7266, University of La Rochelle-CNRS, Institut du Littoral et de l’Environnement, 2 rue Olympe de Gouges, 17000, La Rochelle, France;2. LEGOS UMR5566 (CNRS/CNES/IRD/UPS), 14 Av. Edouard Belin, Toulouse, France;3. Instituto Dom Luiz, University of Beira Interior, Rua Marquês d''Ávila e Bolama, 6201-001 Covilhã, Portugal;4. Institut de Physique du Globe de Paris, Sorbonne Paris Cité, 1 rue Jussieu, 75005, Paris, France;5. Delft Institute for Earth-Oriented Space Research, TU Delft, Kluyverweg 1, 2629 HS Delft, Netherlands;1. Université de Polynésie Française, UMR-EIO, LabEx-CORAIL, BP 6570, 98702 Faa''a, Tahiti, French Polynesia;2. Agence pour la Recherche et la Valorisation Marines (ARVAM), CYROI, La Technopole, 2 rue Maxime Rivière, 97490 Sainte Clotilde, La Réunion, France;3. Biological Science Center, Boston University, 5 Cummington Street, Boston, MA 02215, USA;1. National Laboratory for Civil Engineering, Estuaries and Coastal Zones Division, Av. do Brasil, 101, 1700-066 Lisbon, Portugal;2. UMR 7266 LIENSs, CNRS – Université de La Rochelle, 2 rue Olympe de Gouges, 17000 La Rochelle Cedex, France;3. Centro Tecnológico del Mar, Vigo, Spain;1. Ecomar, Université de La Réunion, 97715 La Réunion, France;2. Département Milieux et Peuplements Aquatiques, MNHN, 47 rue Cuvier, 75005 Paris, France;3. BIORECIF, 3 ter rue de l''albatros, 97434 La Réunion, France;4. Swedish Museum of Natural History, Frescativägen 40, 114 18 Stockholm, Sweden;5. IRD, BP 50172, 97492 Ste Clotilde, La Réunion, France;1. Centre d''Etudes Biologiques de Chizé (CEBC), UMR7372 CNRS, Université de La Rochelle 79360 Villiers-en-Bois, France;2. ENTROPIE, UMR 9220 UR CNRS/IRD, Université de La Réunion, CS 92003, 97744 Saint Denis Cedex 9, Ile de La Réunion, France;3. LOCEAN-IPSL, Sorbonne Universités, UPMC Univ Paris 06/CNRS/MNHN, UMR 7159, F-75005 Paris, France |
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| Abstract: | This paper provides baseline data on absolute and relative sea level variations and shoreline changes in the Scattered Islands region of the Indian Ocean, based on aerial image analysis, satellite altimetry and field observations and in situ measurements from the 2009 and 2011 TAAF scientific expeditions. The analysis shows the importance of regular observations and monitoring of these islands to better understand reef island responses to climate stressors. We show that Grande Glorieuse Island has increased in area by 7.5 ha between 1989 and 2003, predominantly as a result of shoreline accretion: accretion occurred over 47% of shoreline length, whereas 26% was stable and 28% was eroded. Topographic transects and field observations show that the accretion is due to sediment transfer from the reef outer slopes to the reef flat and then to the beach. This accretion occurred in a context of sea level rise: sea level has risen by about 6 cm in the last twenty years and the island height is probably stable or very slowly subsiding. This island expansion during a period of rising sea level demonstrates that sea level rise is not the primary factor controlling the shoreline changes. This paper highlights the key role of non-climate factors in changes in island area, especially sediment availability and transport. We also evidence rotation of the island, underscoring the highly dynamic nature of reef islands. |
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| Keywords: | Reef islands Climate change Sea level rise Shoreline changes French overseas territories Indian Ocean Observatory Vertical land movement Scattered Islands |
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