HR: 1330h
AN: OS23A-01    [Abstracts]
TI: Enhanced Turbulent Mixing Over the Pinnacles on the Mississippi/Alabama Shelf
AU: * Jarosz, E
EM: ewa.jarosz@nrlssc.navy.mil
AF: Naval Research Laboratory, Stennis Space Center, MS 39529 United States
AU: Teague, W J
EM: teague@nrlssc.navy.mil
AF: Naval Research Laboratory, Stennis Space Center, MS 39529 United States
AU: Mitchell, D A
EM: doug.mitchell@nrlssc.navy.mil
AF: Naval Research Laboratory, Stennis Space Center, MS 39529 United States
AU: Field, R L
EM: bob.field@nrlssc.navy.mil
AF: Naval Research Laboratory, Stennis Space Center, MS 39529 United States
AB: Topographic features, such as submarine canyons and banks, are often present on shelves and are known to enhance mixing at least one order of magnitude greater than mixing on shelves with gradually varying bathymetry. Such topographic features can easily alter ambient motion, intensify density gradients, accelerate mean currents, and modify vertical shear. Associated topographically induced turbulence may account for an appreciable fraction of the total shelf mixing and can exert a large bottom stress and dissipate considerable energy. The Pinnacles are an extensive system of drowned fossil reefs ranging from 5 to 15 m in height and 100 to 500 m in width covering an area approximately 8 by 20 km in 80 to 110 m of water on the shelf just west of the Desoto Canyon. This region is characterized by fairly vigorous currents, and it is thought that at times, these currents are energetic enough to induce hydraulically controlled flow over the Pinnacles. This flow, in turn, can produce strong turbulence in the bottom layer. A 24-hour time series of the currents and density measurements collected during NRL's first SEED cruise in the Pinnacles region suggest that such conditions may have occurred in May, 2004. The energetic flow was observed twice in the 20 to 40-m thick layer just above the bottom with speeds larger than 60 cm/s, while in the upper part of the water column, current speeds did not exceed 25 cm/s. Estimates of the composite internal Froude (>2.7) and Richardson (<0.35) numbers suggests that hydraulically control flow and enhanced turbulence may have been present during these two events.
DE: 4219 Continental shelf processes
DE: 4512 Currents
DE: 4546 Nearshore processes
DE: 4568 Turbulence, diffusion, and mixing processes
DE: 4572 Upper ocean processes
SC: Ocean Sciences [OS]
MN: 2005 Joint Assembly