Volume transport variability through the Florida Keys tidal channels

Shipboard measurements of volume transports through the passages of the middle Florida Keys are used together with time series of moored transports, cross-Key sea level slopes and local wind records to investigate the mechanisms controlling transport variability. Predicted tidal transport amplitudes ranged from ±6000 m3/s in Long Key Channel to ±1500 m3/s in Channel 2. Subtidal transport variations are primarily due to local wind driven cross-Key sea level slopes. Subtidal transports through Long Key Channel ranged from +1000 m3/s inflow to Florida Bay to −2500 m3/s outflow to the reef tract. Wind directions oriented toward 190–315° will cause a positive cross-Key sea level slope and inflow to Florida Bay. All other wind directions will tend to cause a negative cross-Key slope of sea level and Gulf to Atlantic outflow toward the reef tract. Seasonal variation in local wind forcing results in maximum outflows from Florida Bay in the winter when increased winds toward the SE and S occur following cold front passages. Minimum outflow occurs in fall when winds toward the SW and W are more frequent and inflows to Florida Bay can persist for several days. The long-term mean flow is toward the southeast and the reef tract and is estimated at –740 m3/s for the combined flows of the major channels in the middle Keys, with 7-Mile Bridge Channel accounting for about 50% of this flow, Long Key Channel carries about 35% of the flow and Channels 5 and 2 account for about 7% each. The mean Gulf to Atlantic flow is supported by sea level standing higher in western Florida Bay and the eastern Gulf than in the Keys Atlantic coastal zone.