Flow disruption resulting from interactions between currents and abrupt topography
can have important consequences for biological processes in the ocean. A highresolution
three-dimensional hydrodynamic model is used to study topographically
influenced flow at the Flower Garden Banks, two small but thriving coral reef
ecosystems in the northwest Gulf of Mexico. Flow past the modeled banks is
characterized by vortex shedding, turbulent wake formation and strong return velocities
in the near-wake regions. The speed of the oncoming current, strength of water-column
stratification, and level of topographic detail used in the model each serve to modulate
these basic flow characteristics.
Larval retention and dispersal processes at the Flower Garden Banks, and
specifically the dependence of these processes on the nature of flow disruption, are
explored by coupling a Lagrangian particle-tracking algorithm to the hydrodynamic
model. Passive particles released from the tops of the modeled banks as mimics of coral
larvae can remain trapped in the wake regions very close to the banks on time scales of
hours to days, depending primarily on the speed of the free-stream current. Most
particles are swept quickly downstream, however, where their trajectories are most
strongly influenced by the topography of the continental shelf. Modeled dispersal
patterns suggest that there is an ample supply of larvae from the Flower Garden Banks to
nearby oil and gas platforms, which can provide suitable benthic habitat for corals. The flow disturbances generated by the modeled banks result in the mixing of
nutrients from deeper water into shallower, nutrient-depleted layers in the wakes of the
banks. The ability of the planktonic system to respond to such an injection of nutrients is
tested by embedding a simple nutrient-phytoplankton-zooplankton ecosystem model into
the hydrodynamic model. Plankton biomass in the flow-disturbed wakes is shown to
increase in response to the additional nutrients.
This study shows how flow-topography interactions at the Flower Garden Banks can
exert critical control over local larval transport processes and plankton dynamics. More
generally, it demonstrates the usefulness and feasibility of using numerical models as
tools to uncover important mechanisms of physical-biological interaction in the ocean.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/3236 |
| Date | 12 April 2006 |
| Creators | Francis, Simone |
| Contributors | Jackson, George A. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 3895342 bytes, electronic, application/pdf, born digital |
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