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Early diagenesis in a marine sapropel, Mangrove Lake, Bermuda
Author(s) -
Boudreau Bernard P.,
Canfeld Donald E.,
Mucci Alfonso
Publication year - 1992
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1992.37.8.1738
Subject(s) - diagenesis , sapropel , aragonite , geology , carbonate , sediment , loss on ignition , mixed layer , pore water pressure , mineralogy , diffusion , organic matter , mangrove , oceanography , environmental chemistry , chemistry , calcite , geomorphology , mediterranean climate , ecology , geotechnical engineering , thermodynamics , organic chemistry , physics , biology
The pore waters of a marine sapropel in Mangrove Lake (Bermuda) have been analyzed for a suite of diagenetically sensitive species, i.e. pH, SO 4 2− , ∑H 2 S, Ca 2+ , ∑CO 2 , ∑NH 4 , ∑P0 4i Fe 2+ , and Mn 2+ . We have also measured a 210 Pb depth profile (suggesting a burial velocity of 0.94 cm yr −1 ) and experimentally determined the rate constant for sulfate reduction (0.062 yr −1 ). Waves and turbulence have mixed sediment and pore waters to a depth of 15 cm. However, both stoichiometric and transport‐reaction models argue that molecular diffusion dominates solute transport beneath this mixed zone and that the pore waters are open to diffusion despite rapid burial. Diagenetic modeling shows further that diffusion accounts for 95% of the SO 4 2− , ∑H 2 S, and ∑CO 2 fluxes below the mixed layer. Comparison of model results with sulfur burial fluxes indicates that at least 94% of the generated ∑H 2 S diffuses out of the sediments. The pore‐water ∑CO 2 is also within 5% of that predicted by our models. The : N ratio of the decaying organic matter is calculated to be between 3.86 and 6.87, which is less than half that obtained by analysis of the solids. The carbonate chemistry of the pore waters suggests that they are nearly saturated with respect to aragonite in the mixed zone, even though this mineral has not been identified in the solids. Precipitation in the mixed zone is confirmed by comparing the observed dissolved Ca profile with that expected for conservative behavior.