Multivariate objective analysis of the coastal circulation of Barbados, West Indies: implication for larval transport

Abstract

A multivariate spatial objective analysis (MVOA) assimilating high spatio-temporal resolution of hydrographic (CTD) and acoustic (ADCP) observations near Barbados provided a comprehensive view of the local surface circulation (0–100 m) during early spring of two consecutive years (1996 and 1997). Significant submesoscale fluctuations of the velocity and salinity fields exhibit a very dynamic environment. In the middle of each cruise, low-salinity water originating from the Amazon and entrained by a North Brazil Current Ring (NBCR) intruded from offshore and persisted on the west coast of Barbados throughout the rest of the survey. Principal component analysis (PCA) of velocity relative to the vertical structure and temporal factors in the study area demonstrated that the local circulation was mostly baroclinic and was dominated by a strong salinity front impinging on the island and large amplitude current reversals with a periodicity of ca. 20 d. During transition times, indicated by a change of the sign of the amplitude of the empirical orthogonal function (EOF), the flow became barotropic. This situation produced strong southward currents followed by the onset of vertical velocity shear. Most of the flow variability occurred in the upper 40 m of the water column, which was also found to be the depth of penetration of the low-salinity lenses. These results indicate that the NBCR structure was retained during both intrusions. Lagrangian trajectories using the MVOA currents were found to be consistent with in situ drifter trajectories, suggesting that the analyzed flow field is representative of the near-shore circulation. Tracking of particles released in the surface layer (0–20 m) from the reef shows a maximum residence time of 18 d indicating the possibility of larval retention within the island-scale flow field. Finally, our results suggest that MVOA, within its limitations, is a powerful tool that can be applied elsewhere to infer circulation and larval transport, even in situations when forcing is unknown.