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Titre : Seasonally resolved paleoclimate records derived from fossil giant clam shells (Tridacna spp.) from the Western Pacific Warm Pool: reconstructions of past ENSO
Nom du conférencier : Mary Elliot
Son affiliation : Professeur à l'Université de Nantes
Laboratoire organisateur : LOCEAN
Date et heure : 30-06-2020 11h00
Lieu : Séminaire en ligne - voir infos ci-après
Résumé :


El Niño Southern Oscillation (ENSO) is the main source of interannual climate variability and is associated with significant changes of Tropical ocean temperature, rainfall patterns and global atmospheric temperatures. The evolution of ENSO in response to future global warming remains uncertain and paleoclimate studies provides information required to assess the response of ENSO to different background states and full range of natural variability of this climate phenomenon.

Fossil shells of marine bivalves such as giant Tridacna provide information on past environments with seasonal resolutions. Similarly to corals, changes in mean seasonal cycles and inter-annual variability can be reconstructed by sequentially analyzing the annual layers of calcium carbonate. Inter-comparison studies conducted on modern material show that seasonally resolved records derived from marine bivalves (Tridacna gigas) and corals (Porites) provide similar information. This step has been necessary in order to combine these data sets into global databases. This presentation will focus on paleoclimate reconstructions from several sites around the Western Pacific Warm Pool which cover the last 130ka. We have conducted calibration studies of modern Tridacna gigas and Tridacna squamosa which have been collected in several localities around Indonesia. Stable isotope (del-18O) and trace element profiles (Mg/Ca, Ba/Ca) are measured and compared to local hydrology : sea surface temperature, rainfall and productivity. T. squamoza Mg/Ca and SST exhibit a clear linear relationship with similar equations regardless of the area of sampling. Comparison of measured and estimated del-18O confirm that both species precipitates their shells in isotopic equilibrium. The results from calibration experiments are used to compare modern and fossil samples collected from the Huon Peninsula, Sulawesi and Belitung Island located in the Western Pacific Warm pool.

This talk will focus on two studies : 1) Fossil samples from the Huon Peninsula provide information on past ENSO. Results show that the intensity and the frequency of modern ENSO at this locality is rarely observed in the past. 2) Samples from Belitung Island in the Java Sea shows that the mid-Holocene period, around 6ka, was slightly colder (mean temperature difference was 1°C) and lower salinity compared to modern conditions. Results are compared to model studies and other coral based data collected from nearby locations. It is suggested that during the Holocene a northward displacement of the Intertropical Convergence zone increased rainfall rates over land and reduced precipitation in the Southern region of the South China Sea.

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