Frank Sansone - Permeable Sediments

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 the 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 production/consumption rates.

For more 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.