On the ventilation of the Gulf of Mexico

Abstract

Long term in-situ observations reveal that at equivalent depths, the waters of the Gulf of Mexico below the Yucatan Sill are warmer than the Caribbean and Atlantic water. Using long-term regional simulations of the Gulf of Mexico at 1/12° horizontal resolution and a water-mass transformation analysis we show that these warmer conditions are sustained by a downward flux of heat controlled to first order by interactions between deep currents and topography, with large contributions below the Loop Current and along the Sigsbee escarpment. The analysis reveals that tides, high-frequency winds, and geothermal heat flux have little effect, and points to interactions between geostrophic currents and topography as the primary category of processes responsible for deep-water mixing. This is in contrast to the paradigm for the global deep ocean which attributes buoyancy sources mostly to tidal vertical mixing. Consequences for the evolution of the water masses of the Gulf of Mexico and the exchanges with the Caribbean Sea are explored using a passive dye tracer designed to be representative of waters coming from the Caribbean. The tracer propagation experiment provides estimates of the age of Gulf of Mexico water masses. Results suggest that in the upper 1500 meters, waters are renewed on timescales of roughly 50 years, while below 1500 meters, the timescale for a 90% renewal of Gulf waters reaches about 350 years. The analysis also reveals age differences of approximately 50 years between the eastern and western parts of the Gulf.