Long-Term Gulf-to-Atlantic Transport Through Tidal Channels in the Florida Keys

Current meter time series collected between 1987 and 1993 from tidal channels in the Middle and Lower Keys quantify long-term net displacement and volume transport between the Gulf of Mexico and Hawk Channel on the Atlantic Ocean side of the Florida Keys. NOAA-supported field studies conducted near Looe Key Marine Sanctuary during autumn, winter and spring months of 1987 and 1988 reveal a quasi-steady nontidal flow into Hawk Channel. Resultant speeds in Newfound Harbor Channel, Bahia Honda Channel and Moser Channel are 0.05, 0.11 and 0.04 m·s⁻¹, respectively. More recent studies of Long Key Channel and Channel No. Five show temporal variability over time scales on the order of 1–2 weeks; seasonal variations are not well defined. The long-term net flow is consistently out of the Gulf of Mexico. Investigations conducted as part of the SEAKEYS program included translating cumulative net displacement into cumulative volume transport. Current profiles at anchor stations under both flood and ebb conditions are used to calibrate two tidal channels. For a 34-day time period in October and November 1990, the resultant volume transport through Bahia Honda Channel is 620 m³·s^−l. The tidal contribution to the total is isolated and found to provide a resultant volume transport of 78 m³·s^−l in the opposite direction— into the Gulf of Mexico. A similar analysis of a one-year record from Long Key Channel indicates a resultant volume transport of 262 m³·s^−l with strongest Gulf-to-Atlantic transport in winter and spring months.