Sp. Dhakar et Dj. Burdige, COUPLED, NONLINEAR, STEADY-STATE MODEL FOR EARLY DIAGENETIC PROCESSESIN PELAGIC SEDIMENTS, American journal of science, 296(3), 1996, pp. 296-330
A steady state, coupled, non-linear model has been developed for early
diagenetic processes in pelagic and hemi-pelagic marine sediments. Mo
del results show that the occurrence of oxic and sub-oxic diagenetic p
rocesses is significantly affected by variations in parameters such as
the sedimentation rate, bioturbation coefficient, sediment porosity,
and organic matter flux to the sediments. Increases in the sedimentati
on rate or the bioturbation coefficient increase organic matter oxidat
ion by sub-oxic processes, whereas an increase in sediment porosity de
creases organic matter oxidation by sub-oxic processes. Sediment data
from three contrasting MANOP sites are fit reasonably well with the mo
del. The resulting best-fit organic cat;bon, oxygen, and nitrate fluxe
s at the sediment-water interface and depth-integrated organic carbon
oxidation rates for these sites are also within the range of independe
nt estimates of these quantities. Model results show that the internal
redox cycling of manganese in sediments leads either to the formation
of a Mn-peak near the sediment redox boundary or to surficial Mn-rich
oxic sediments, depending on the depth zonation of manganese oxidatio
n and bioturbation. In sediments with a shallow redox boundary (<5 cm)
, upward diffusion of pore water manganese into the oxic sediments dom
inates over manganese oxidation near the redox boundary. The majority
of the manganese oxidation therefore occurs in the surficial, bioturba
ted sediments, and as a result, manganese-rich oxic sediments are form
ed. In contrast, in sediments with a deeper redox boundary (>10 cm), m
anganese oxidation near the sediment redox boundary dominates over por
e water manganese diffusion into the overlying oxic sediments. Here, m
ajority of the manganese oxidation occurs below the zone of active bio
turbation (assumed to be the upper 8-10 cm of sediment), and in this c
ase, a well developed Mn-peak forms near the sediment redox boundary.
Previous models explained the occurrence of this Mn-peak by neglecting
bioturbation or suggested that this peak could not occur in bioturbat
ed sediments due to this sediment mixing.