Upslope Sediment Transport on Continental Margins: A Process-Oriented
Numerical Study
Abstract
Using the method of process-oriented hydrodynamic modelling, this work
investigates the dispersal of particles in stratified fluids on
continental margins. The focus is placed on steady-state density
distributions that are governed by an advective-diffusive balance. In
this case, particles can still be advected across isopycnal surfaces,
given that turbulent fluctuations do generally not offset the advective
displacement of a particle. The validity of this fundamental principle
is demonstrated here with the diapycnal upslope sediment transport in a
bottom Ekman layer that forms under a stratified geostrophic slope
current. Similarly, this study demonstrates that interaction between
slope currents with a submarine channel can facilitate a continuous
diapycnal upslope flux of particles, confined to the lowermost 10-20 m
of the water column. Velocity anomalies that facilitate this upslope
sediment flux are the signature of standing topographic Rossby waves,
that can only develop for slope currents that are left-bounded
(right-bounded) by shallower water in the northern (southern)
hemisphere. Findings of sensitivity studies confirm the existence of
up-channel flows for a wide range of parameter values. Under the
assumption that particles remain suspended in the water column, the
inclusion of gravitational settling significantly increases the
up-channel sediment flux. Sediment settling operates to trap particles
close to the seafloor within the core of bottom-intensified up-channel
flow. The author postulates that this mechanism plays an important role
in biogeochemical cycles at continental margins.