Plume Dispersion on a Fringing Coral Reef

Parameters: Rhodamine WT

A field experiment was conducted on a fringing reef on the South Shore of the island of Oahu, Hawaii, to investigate the dispersion and transport of a nearbed coastal plume. An autonomous dye source released Rhodamine WT fluorescent dye at the sea floor at a constant rate. The horizontal structure of the plume was tracked with a REMUS Autonomous Underwater Vehicle (AUV) [Hydroid, Inc.] with an onboard Turner Designs Cyclops fluorometer (Figure 1a and b; figure 2). The vertical structure of the plume and the ambient stratification was measured using an Ocean Sensors CTD with a Turner Designs Cyclops fluorometer (Figure 3). Experiments incorporated a variety of different surface wave conditions, allowing us to investigate how waves affect cross-reef plume transport (via Stokes' drift) and enhance vertical and horizontal mixing generated by the interaction of the oscillatory flow with the reef roughness.

Figure 1 The Cyclops fluorometer is situated in the nose of REMUS.

Figure 2 Rhodamine WT dye concentration measured by the Cyclops fluorometer. Plume measured centerline vs. that predicted using ADCP data: o's represent measured centerline position. x's represent predicted centerline

Figure 3 Vertical profiles of density and fluorescence illustrate the growth in the height of the plume from roughly 2 m of the bed, 17 m away from the source, to 4 m of the bed, 63 m from the source.

Authors: Nicole Jones, Ryan Lowe, Stephen Monismith, Derek Fong & Geno Pawlak Institution: Stanford University, University of Hawaii Location: South Shore of Oahu, Hawaii, USA