Boron isotopes as a proxy of weathering mechanisms and balance in soil minerals

The objective of this thesis is to estimate the ability of boron and its isotopes to evaluate mineral weathering budgets and mechanisms in soils. In this goal, 3 different approaches were conducted: 1) an experimental approach during which a test-mineral (biotite) undergoes the action of different weathering agents, representative of those found in soils. 2) an in-situ approach in an acid soil profile led on different minerals (biotite, muscovite, K-feldspar and albite) handpicked at various depths and weathering state (Breuil-Chenue forest experimental site, France). The objective of this study is to determine the sensitivity of boron to soil formation processes. 3) a second in-situ approach conducted on the same study site but this time on sub-surface horizons (horizon A and Al-oxi-hydroxides accumulation horizon), which aim is to evaluate the sensitivity of boron and its isotopes to mechanisms in close vicinity to vegetation (seasonal variations, vicinity of the roots). B and its isotopes able, thanks to its high reactivity during weathering mechanisms in comparison to major elements that constitute the crystallographic network (observed in experimental as well as in in-situ approaches), to trace with a great sensitivity primary minerals dissolution or transformation mechanisms, and opens new insights for the comprehension of soils. (author)