Extreme flows and unusual water levels near a Caribbean coral reef: was this a case of a “perfect storm”?

Abstract

Observations of currents aimed to study the flow near a spawning aggregation reef, Gladden Spit off the coast of Belize, reveal unusually strong currents on 19–20 October 2009 (the current speed was over 1 m s−1, when the mean and standard deviation are 0.2 ± 0.12 m s−1). During this short time, the water level was raised by 60–70 cm above normal in one place, but lowered by 10–20 cm in another location just 2 km away. The temperature dropped by over 2°C within a few hours. Analyses of local and remote sensing data suggest that a rare combination of an offshore Caribbean cyclonic eddy, a short-lived local tropical storm, and a Spring tide, all occurred at the same time and creating a “perfect storm” condition that resulted in the unusual event. High-resolution simulations and momentum balance analysis demonstrate how the unique shape of the coral reef amplified the coastal current through nonlinear flow–topography interactions. The suggested mechanism for the water level change is different than the classical wind-driven storm surge process. The study has implications for the influence of external forcing on mixing processes and physical–biological interactions near coral reefs.