Transport and diffusion on the southwestern Puerto Rican shelf

Kioroglou, Sotiris (1992) Transport and diffusion on the southwestern Puerto Rican shelf. Masters thesis, Memorial University of Newfoundland.

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Abstract

In 1988 and 1989 drifter tracking experiments were conducted on the Southwestern Puerto Rican shelf. Surface drifters were used as surrogates for buoyant fish eggs, in order to determine the dependence of the egg trajectory on the spawning site and time. Data analysis of the drifters shows that the mean trajectory depends on the spawning time and the season of drifter release. Trajectories from adjacent spawning and nonspawning sites have no significant difference, however. Both the current and the wind tend to have an along-shore and westward direction. The high correlation between wind and current indicates that the wind drives the current in a direction parallel to the shore. Flow reversals (to the East) are common in periods of light winds, which occur most frequently in the wet season, from July to December. The data analysis agrees with the hypothesis that the flow reversals might be caused by a eastward pressure gradient opposing the wind. The predominant tidal harmonics on the reef are the diurnal K1 and the semidiurnam M2, that can be modelled as across-shelf standing waves. Scale analysis showed that the associated velocity amplitudes are insignificant on the reef. The seiche of occuring on the reef, is important for the currents in the area. -- The flow is highly variable, especially in the along-shore direction. The flow variability can be modelled as a random walk for the cross-shore component. Statistical analysis of motion relative to the cluster centroid, indicates that a patch of drifters is elongated in a direction parallel to the coastline at all the times. This indicates that the horizontal shearing of the mean flow velocity plays a dominant role in the relative diffusion processes of the area. The data analysis also indicates that there is much more variability in the paths of the clusters, than in the paths of the drifters within a cluster.

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