EARLY DIAGENETIC PROCESSES IN RECENT SEDIMENTS OF THE GULF OF ST-LAWRENCE - PHOSPHORUS, CARBON AND IRON BURIAL RATES

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 (CaCO3) and pyrite (Fe S2) on major elemental cycles during early diagenesis. Detrital P and Fe phases were successfully used as indicators of the constancy or var iability of detrital inputs to several sedimentary environments from t he 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 sedi ment burial rates indicate that CFA, CaCO3 and probably FeS2 are curre ntly forming in the sediments of the Gulf. However, high concentration s and/or formation of CaCO3 in marine sediments appear to inhibit the formation of authigenic CFA. On the other hand, the formation of FeS2 does not influence authigenic CFA precipitation. In the deep troughs o f the Gulf of St-Lawrence, total P burial rates range from approximate to 50 to 500 mgP/m(2)/yr. Truly authigenic precipitation of CFA, when observed, may represent up to approximate to 25% of the total burial rate of P. Bioturbation of sub-surface sediments reduces the potential for authigenic precipitation of CFA and CaCO3, thus affecting immobil ization reactions that have a strong impact on the global oceanic cycl es of C and P. The spatial heterogeneity of diagenetic reactions precl udes the establishment of an accurate quantification of P removal on t he scale of a continental shelf such as the Gulf of St-Lawrence. (C) 1 997 Elsevier Science B.V. All rights reserved.