Publications
Sedimentation rates and fluxes in the continental shelf mud fields in the Bay of Biscay (France)
Bibliographie
Lesueur, P; Jouanneau, JM; Boust, D; Tastet, JP; Weber, O.
Continental Shelf Research, 21, p.1383-1401 (2001)
Summary
TexteZone1
Sedimentation rates in shelf mud fields of the Bay of Biscay (the Gironde shelf
mud patches and "La Grande Vasiere") were investigated for a 100-yr time scale,
using Pb-210 geochronology of nine cores. The distribution of apparent
sedimentation rates reveals a general trend along the terrigenous dispersal
system from the Gironde outlet of: no or negligible (<0.1 cm yr(-1)) cumulative
sedimentation in the inner zone of the mud fields; 0.1-0.2 cm yr(-1) in the
outer zone where the supply is reduced; and a maximum value of about 0.5 cm
yr(-1) in the depocentre of the main mud field. Except for the latter value, the
Pb-210 sedimentation rates are of the same magnitude as longer-term rates based
on C-14, and although slightly higher, are in good agreement with an earlier
estimation determined for the rate of accumulation of surficial sediments, using
pollen analyses. These differences are interpreted as being due to an increase
in the supply of fine-grained sediment over the last century (from 0.2 to 0.5 cm
yr(-1)), perhaps as a result of an intensification of estuarine suspended matter
supply to the shelf. Compilation of a sediment budget shows that about one third
of the annual Gironde solid discharge is trapped in the Gironde nearshore shelf
mud fields. The mid-shelf muddy belt (i.e. "La,Grande Vasiere") is the site of
accumulation of fine-grained material from various terrigenous sources (mainly
from the Gironde and Loire rivers). Two cores from the latter area yielded a
maximum rate of sedimentation of 0.2 cm yr(-1). Mixing processes dominate in
this open middle shelf, due to the periodic sediment removal by long-period
swells and bioturbation.