Variations in pelagic input rates over abyssal hill areas cannot be
inferred easily from sedimentation rate variations between cores because
of redistribution by down-slope gravity processes and bottom currents.
Some spatial averaging or adjustment for sediment transport is required.
Relatively accurate mean sedimentation rates may be obtained,
however, by regressing sediment thickness with distance from a mid-
ocean ridge spreading centre, where the regression averages out the
variations due to local redistribution. This is shown using sediment
profiler records from the Galapagos spreading centre (SC) at 1û N in the
eastern Pacific. Physical property data from Deep Sea Drilling Project
(DSDP) Leg 70 are used to correct sediment thicknesses for compaction
and to convert sedimentation rates to mass accumulation rates (MARs),
which are ~2 g cm-2 Ka-1 in this region. These high MARs are due to
enhanced equatorial productivity of pelagic organisms, which is also
reflected in a ~6% higher MAR for the ridge flank closest to the
equator, corresponding to a rate of change of MAR with latitude of
~16% per degree. The equatorial high productivity zone in the Panama
Basin lies further south then in the central Pacific (Moore et al. 1973);
peak sedimentation along the Ocean Drilling Program (ODP) Leg 138
transect (110û W) occurs near 1û N so has nearly zero gradient at this
latitude, but has comparable gradient to the Galapagos SC north of 2û
N. The zone of peak enhancement at 86û W in the Panama Basin may
therefore be 1û or more further south than at 110û W. Some further
sedimentation characteristics of the Galapagos spreading centre are also
described, such as a scaling of thickness variability and the possibility
of dating seafloor using sediment thickness.
Mitchell, N. C., Sediment accumulation rates from Deep Tow profiler records and
DSDP Leg 70 cores over the Galapagos Spreading Centre, in: A. Cramp, C.J. MacLeod,
S.V. Lee and E.J.W. Jones (Eds.) The Geological Evolution of Ocean Basins: Results
From the Ocean Drilling Program, Spec. Publ. Geol. Soc. Lond., 131, 199-209, 1998.