Early diagenetic processes in recent sediments of the Gulf of St-Lawrence: phosphorus, carbon and iron burial rates

Abstract

Selective extraction procedures were used to quantify different forms of solid-phase phosphorus, carbon and iron in marine sediments, and to evaluate the impact of authigenic formation of mineral forms such as carbonate fluorapatite (CFA), calcium carbonate (CaCO 3) and pyrite (FeS 2) on major elemental cycles during early diagenesis. Detrital P and Fe phases were successfully used as indicators of the constancy or variability of detrital inputs to several sedimentary environments from the deep channels of the Gulf of St-Lawrence. In cores characterized by near steady state influx rates, solid-phase P, C and Fe data and sediment burial rates indicate that CFA, CaCO 3 and probably FeS 2 are currently forming in the sediments of the Gulf. However, high concentrations and/or formation of CaCO 3 in marine sediments appear to inhibit the formation of authigenic CFA. On the other hand, the formation of FeS 2 does not influence authigenic CFA precipitation. In the deep troughs of the Gulf of St-Lawrence, total P burial rates range from ≈ 50 to 500 mgP/m 2/yr. Truly authigenic precipitation of CFA, when observed, may represent up to ≈ 25% of the total burial rate of P. Bioturbation of sub-surface sediments reduces the potential for authigenic precipitation of CFA and CaCO 3, thus affecting immobilization reactions that have a strong impact on the global oceanic cycles of C and P. The spatial heterogeneity of diagenetic reactions precludes the establishment of an accurate quantification of P removal on the scale of a continental shelf such as the Gulf of St-Lawrence.