Marine particles play a key role in the control of the ocean chemistry and in the export of organic carbon towards the deep ocean. 230Th and 231Pa are natural chronometers of these particles. The development of new mass spectrometers (MC-ICPMS) allows to solve the analytical difficulties which limited the use of 230Th and 231Pa until now and have allowed the implementation of the international program GEOTRACES (www.geotraces.org) for which one of the objectives is to obtain a global mapping of these tracers. The purpose of this thesis is to improve and to develop new protocols for the chemical separation and isotopic analysis of Pa and Th, who will allow to obtain high-resolution profiles compatible with the GEOTRACES sampling strategy. The data obtained will allow to understand the cycle of the marine particles. The project is based on a cooperation between LSCE and LIG (Stockholm, Sweden) and will include work in both laboratories. This thesis will provide a state-of-the-art training in the field of the trace element chemistry and mass spectrometry in an international environment.