Study of marine particles in the Austral Ocean, the Barents Sea and the Mediterranean Sea using the Thorium isotopes

• Main Author: Coppola, Laurent
• Other Authors: Laboratoire d'études en Géophysique et océanographie spatiales (LEGOS), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS), Université Paul Sabatier - Toulouse III, M. Matthieu Roy-Barman
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2002
• Subjects: thorium; particule marine; Antares; pièges à particules; [SDU]Sciences of the Universe [physics]; Antarc*; Antarctic; Austral Ocean; Barents Sea; Mer de Barents; NADW; North Atlantic Deep Water; North Atlantic; Southern Ocean
• Online Access: https://theses.hal.science/tel-00606517; https://theses.hal.science/tel-00606517/document; https://theses.hal.science/tel-00606517/file/THESE_L.Coppola.pdf

This work is based on thorium (Th) isotopes to quantify the particles fluxes and exchange between dissolved and particulate phase in three distinct environments. In the shelf region of the Barents Sea, the 234Th fluxes in the water column suggest that the sediment traps have a good catchment efficiency. To estimate the export of Particulate Organic Carbon (POC), we need to use a POC/234Th ratio. It is 10 times lower in the large trapped particles than in the suspended particles. This is due to a preferential remineralization of POC vs 234Th and also to a large quantity of fecal pellets in traps. These results show us the importance of the large particles in the vertical fluxes and suggest that data estimated in previous studies based on the composition of suspended particles in other Arctic regions have been overestimated. In the Indian sector of the Southern Ocean, the export of POC is higher in the Polar Front Zone (PFZ). The 230Th profiles in the water column indicate a rapid renewal rate of deep water (1-15 y) by the North Atlantic Deep Water (NADW) and the Antarctic Bottom Water (AABW) in the site of study. From 234Th-230Th coupling, we are able to constrain the dynamic processes of marine particles in the upper layer. The results suggest that the settling speed of the filtered large particles are lower in the north of the Agulhas Front (AF). Moreover, we note that the desorption and the disaggregation are higher. This could be explained by the presence of detrital organic matter and/or an efficient microbial loop limiting the export of organic matter to the deep layers. In the Mediterranean studies, we have used 232Th and 230Th to estimate the degradation of large marine particles during in vitro experiments. This results suggests that the aggregation of filtered large particles requires to take into account in the particles dynamic models. 230Th-232Th budget of the western Mediterranean Sea indicates that the refractory elements fluxes are dominated by the dissolution of the continental particles stored ...