Fig. 8 Sulphur in LGM and LPM sediments. (a) Normative sulphide-bound Fe in percent of Fetotal; pyrite as the only sulphide phase and absence of organic-bound sulphur is considered for the estimate. (b, c) Analytical determined elemental sulphur in percent of Stotal for LGM and LPM sediments. (d) Excess Fe in LPM sediments balanced for an assumed Fe/Al mass ratio of 0.75 for the siliciclastic debris. Littoral sediments of the modern LGM show slightly higher Stotal contents than the sediments from the lake centre (Fig. 5n), documenting overall higher H2S production in the shallow water area of LGM. Pore water dissolved H2S is fixed in the sediments mainly by reaction with reactive Fe or oxidation to elemental sulphur. The above mass balance estimates show that the sedimentary Fe inventory is most claimed in shallow water sediments of LGM. Pyrite genesis in the shallow water sediments is favoured by distinct seasonal change between oxic and anoxic conditions in the surface sediments. In LGM sediments from the 23 m sampling site and in sediments of the meromictic LPM a high proportion of elemental sulphur was detected in the freeze-dried samples. The real elemental sulphur contents may be overestimated due to oxidation of S2− to elemental sulphur during freeze-drying and sample handling
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