Frank Sansone -
My research group has
been working with
permeable (i.e., sandy) sediments since the mid-1980s; these are
sediments with grains coarser than ~80 um. This work was originally
involved with carbonate reef sediments, but it has since broadened to
cover permeable sediments of all kinds.
We are currently
funded by the U.S.
National Science Foundation to study the effects of surface waves on
particle and fluid motion in permeable sediments. My
collaborators on this project are:
Overview of this research:
Surface gravity waves traveling above permeable (sandy) sediments can
induce greatly enhanced (1) mixing across the sediment-water interface,
and (2) transport of water and particles within the sediment.
These processes can be expected to (1) substantially increase the rates
of biochemical processes occurring in sediments by increasing the
supply of oxygen and particulate matter to the sediment, and (2)
significantly increase the rate of return of degradation products such
as nutrients to the water column, thereby increasing water-column and
benthic primary production. However, the rapid transport of
porewater and particles in sandy sediments renders the calculation of
benthic fluxes using conventional diffusion-based models invalid and
thus confounds the interpretation of sediment chemical profiles
collected in coastal areas and on the continental shelf.
Thus, a numerical model of wave-driven porewater motion in permeable
sediments was developed by combining pressure-induced porewater
advection (as derived by Shum) with Webster’s shear dispersion;
the sediment-surface driving pressure is calculated from potential flow
via second-order Stokes wave expansion and conformal mapping over
ripples. As a rough rule of thumb, the daily sediment
ventilation depth approximates the sediment ripple wave length.
Temperature, measured with a sediment-mounted miniature thermistor
chain, was used to verify the model by using the sub-daily sediment
temperature propagation to calculate advective transport to at least 20
cm into the sediment (i.e., over depths where advection dominates over
diffusion). The model’s mapping of porewater motion allows the
estimation of (1) seawater/porewater exchange rates, (2) porewater
residence times, and, when combined with in-situ electrochemical
profiling, (3) porewater chemical fluxes and sediment
information on this project,
please see the pdf-format version of the research proposal.
Also, here is a presentation I recently gave that
describes some of the more interesting current aspects of this research.
My research group is
also an active participant in Coastal Ocean Observing Systems, in
particular the Kilo Nalu Observatory just
offshore of Honolulu.
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