Geochemical study of carbonate precipitation by soil freezing process in natural environment (Brögger peninsula, Spitsbergen)

The precipitation conditions of soil secondary calcites under the current periglacial climate are defined using 18 O and 2 H contents of soil waters, hydrochemical data, SEM obsevations, 13 C and 14 C contents of the calcitic coatings. An experimental site has been equiped near Ny Alesund (79 o N, 12 0 E) on a fluvio-glacial terrace. During the first stage of the freezing period, the ionic species contents increase in the residual water according to the distribution coefficient between water and ice. Calcite precipitation occurs in a second stage as indicated by the simultaneous decrease of the calcite saturation index and increase of the concentration of non-interactive element. Under such conditions, in a silicated active layer, secondary calcites are present as coatings below pebbles. The stable isotopes (δ 18 O= -5.5 to -7.3 %c and δ 13 C= +1 to -3% o vs PDB) indicate a calcite precipitation from continental water in apparent non-equilibrium with biogenic carbon. The isotopic values result from a mixing between recent calcites and “old calcites”. The low radiocarbon activities (10 to 45%) confirm that the “old calcites” have precipitated during the last interglacial or interstadial period.