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Guillerm C. (2016). Campagne Nivmer 16-ddu, R2/Janvier 2016.
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Calzas M., C Guillerm and A Guillot. (2016). Nivmer CWB, janvier 2016.
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L. Lescarmontier, B. Legresy, N. W. Young, R. Coleman, L. Testut, C. Mayet, P. Lacroix. (2015). Rifting processes and ice-flow modulation observed on Mertz Glacier, East Antarctica (Vol. 61).
Abstract: We investigated the evolution of two major rifts cutting across Mertz Glacier Tongue, East Antarctica, using a combination of satellite images and 60 day sets of GPS data from two stations deployed either side of the western rift in 2007. The eastern rift began to open in the early 1990s, and the western rift initiated in 2002 in conjunction with the collision of a large iceberg with the tongue. Velocity time series derived from the 2007 GPS data exhibited strong variations at tidal periods modulated by sea-surface height and sea-surface slope and reproduced here with a conceptually simple model. We found that opening of the western rift in 2002 leads to a dramatic change in behavior of the tongue as the large range in velocity (700–2400 m a−1) observed in 2000 was largely reduced (1075–1225 m a−1) in 2007. Opening of the western rift decoupled the glacier from the transverse loading on the tongue driven by east–west tidal circulation. This loading previously induced time-varying lateral drag, which caused the large velocity range. Our results suggest changes in the mechanical behavior of an ice tongue impact the dynamics of the outlet glacier system and should be considered in longer-term mass-balance evaluations.
Keywords: Antarctic glaciology calving crevasses glacier flow glacier mechanics
Programme: 688
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Laurent Testut, Virginie Duvat, Valérie Ballu, Rui M. S. Fernandes, Frédéric Pouget, Camille Salmon, Jérome Dyment. (2015). Shoreline changes in a rising sea level context: The example of Grande Glorieuse, Scattered Islands, Western Indian Ocean (Vol. 72).
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.
Keywords: Climate change French overseas territories Indian Ocean Observatory Reef islands Scattered Islands Sea level rise Shoreline changes Vertical land movement
Programme: 688
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L. Testut, A. S. Unnikrishnan. (2015). Improving Modeling of Tides on the Continental Shelf off the West Coast of India (Vol. 32).
Abstract: Testut, L. and Unnikrishnan, A.S., 2016. Improving modeling of tides on the continental shelf off the west coast of India. Global tidal solutions are sometimes inaccurate in coastal regions. This is particularly true in some regions of the northern Indian Ocean, which are characterized by wide continental shelves and large tidal ranges. We show that these global solutions are inaccurate on the shelf region off Mumbai, off the west coast of India. In this region, the shelf is very wide, and it opens into the Gulf of Khambhat, where large tides are observed. Moreover, in regions of large semidiurnal tides in the Bay of Bengal, such as the head Bay, Gulf of Martaban, etc., global tidal solutions are not accurate. In the present work, we focus on the shelf region off the west coast of India. We used a new approach in developing a high-resolution hydrodynamic tidal model for the inner shelf region (8°N to 22°N). The open boundary of the model is aligned to the altimetry tracks, which allowed us to prescribe boundary conditions obtained directly from observations. We show that the tidal solutions at the coast are much improved compared with those obtained from the global solutions and that on the wide shelf portion and the Gulf of Khambhat the improvement has been considerable.
Programme: 688
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Christopher S. Watson, Neil J. White, John A. Church, Matt A. King, Reed J. Burgette, Benoit Legresy. (2015). Unabated global mean sea-level rise over the satellite altimeter era (Vol. 5).
Abstract: The rate of global mean sea-level (GMSL) rise has been suggested to be lower for the past decade compared with the preceding decade as a result of natural variability1, with an average rate of rise since 1993 of +3.2 ± 0.4 mm yr−1 (refs 2, 3). However, satellite-based GMSL estimates do not include an allowance for potential instrumental drifts (bias drift4,5). Here, we report improved bias drift estimates for individual altimeter missions from a refined estimation approach that incorporates new Global Positioning System (GPS) estimates of vertical land movement (VLM). In contrast to previous results (for example, refs 6, 7), we identify significant non-zero systematic drifts that are satellite-specific, most notably affecting the first 6 years of the GMSL record. Applying the bias drift corrections has two implications. First, the GMSL rate (1993 to mid-2014) is systematically reduced to between +2.6 ± 0.4 mm yr−1 and +2.9 ± 0.4 mm yr−1, depending on the choice of VLM applied. These rates are in closer agreement with the rate derived from the sum of the observed contributions2, GMSL estimated from a comprehensive network of tide gauges with GPS-based VLM applied (updated from ref. 8) and reprocessed ERS-2/Envisat altimetry9. Second, in contrast to the previously reported slowing in the rate during the past two decades1, our corrected GMSL data set indicates an acceleration in sea-level rise (independent of the VLM used), which is of opposite sign to previous estimates and comparable to the accelerated loss of ice from Greenland and to recent projections2,10, and larger than the twentieth-century acceleration2,8,10.
Programme: 688
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Testut L. (2015). Sea Level Variations over the recording era: A focus on the Southern Ocean.
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Bonnefond P., P. Exertier, O. Laurain, M. Bergé-Nguyen, S. Calmant, J.-F. Crétaux, L. Testut, F. Perosanz, V. Ballu, C. Brachet, M. Calzas, C. Drezen, B. Haines. (2015). La mesure du niveau de l'eau par GNSS pour les besoins de l'étalonnage de la mesure altimétrique par satellite – quelques avancées récentes.
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Brachet C., M. Calzas, C. Drezen, L. Fichen, A. Guillot, P. Téchiné, L. Testut, P. Bonnefond, O. Laurain. (2015). Towed and static GPS buoys for CAL/VAL and SSH.
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Brachet C., M. Calzas, C. Drezen, L. Fichen, A. Guillot, P. Téchiné, L. Testut, P. Bonnefond, O. Laurain. (2015). Towed and static GPS buoys for CAL/VAL and SSH.
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