Circulation and Associated Variability in the Intra-Americas Sea: the Role of Loop Current Intrusion and Caribbean Eddies

Abstract

Circulation and associated variability in the Intra-Americas Sea (IAS) are examined using observations and numerical models. Vertically integrated transport variations through the Yucatan Channel in the model are found to be related to the intrusion of the Loop Current into the Gulf of Mexico. We argue that the transport variations are part of a “compensation effect” by which transport variations through the Yucatan Channel are at least partly compensated by flow around Cuba. Numerical experiments show that the transport variations result from the interaction between the density anomalies associated with the Loop Current intrusion and the variable bottom topography. The compensation effect is found to be associated with baroclinic (2-layer) flow through the Yucatan Channel at timescales longer than a month, while at shorter timescales (less than a month) the vertical structure of the flow is barotropic. An index, that can be computed from satellite data, is proposed for measuring the impact of the Loop Current intrusion on the transport variability through the Yucatan Channel. This index is shown to be significantly correlated at low frequencies (cutoff 120 days) with the cable estimates of transport between Florida and the Bahamas. We argue that it is the geometric connectivity between the Yucatan Channel and the Straits of Florida between Florida and the Bahamas that accounts for the relationship. A three-dimensional, data-assimilative, ocean circulation model is developed in order to simulate circulation, hydrography and associated variability in the IAS from 1999 to 2002. The model performance is assessed by comparing model results with various observations made in the IAS during this period. Model results are used to study the role played by Caribbean eddies in the dynamics of monthly to seasonal (with timescales of 30-120 days) circulation variability in the IAS. It is shown that the variations in vertically integrated transport between Nicaragua and Jamaica are linked to the interaction of Caribbean eddies with the Nicaraguan Rise. The mechanism can be explained in terms of the form drag effect acting across the Nicaraguan Rise.