Florida Current transport

The Florida Current (FC) is the western boundary current for the subtropical gyre of the North Atlantic.  In addition, to transporting water masses originating in the northern hemisphere, the FC advects water from the southern hemisphere that has crossed both the equator and the North Atlantic’s tropical/subtropical gyre boundary. Ultimately, a portion of the FC transport becomes entrained in the subpolar gyre where it contributes to the formation of the deeper water masses.  Beginning in the early 1980's in STACS, submarine cable observations of voltage differences across the Straits have been calibrated with direct current data to estimate FC transport. Recently a new program consisting of weekly observations of velocities started.  Data are collected with an ADCP on the EXPLORER OF THE SEAS (Figure 1.). 

•  Mean annual transport: The mean annual transport of the Florida Current at 27N over the cable record is 32 Sv.  Earlier data collected at 26N during the late 1960's early 1970's observed a mean annual transport of 30Sv (Niiler and Richardson, 1973).  Johns et al. (1999) computed a mean annual transport through the NW Providence Channel (located between the two transport sections) of about 1 to 2 Sv.  Thus over the past 30+-years the mean annual transport of the Florida Current appears stable.

• Decadal signals: A smoothed version of the 20-year time-series is shown in Figure 2. On decadal time-scales, the variability is less than 4Sv (10-15% of the mean annual signal).  This signal in FC transport is visually correlated with an NAO-index with similar time-scales (Figure 2.)

• Annual signal: Using the 1960/1970's data, Niiler and Richardson (1973) estimated an annual signal for FC transport.  Largest transports were in the summer and minimum, in the fall (Figure 3). The amplitude of the annual signal was about 3 SV. However, Behringer and Larsen (2001) found a larger semi-annual component in the more recent transport data than observed in the earlier records (Figure 3.).

• Higher frequency variability: Larger amplitude, shorter duration variability in FC transport is caused by continental shelf waves.  These waves are generated by wind changes (typically frontal passages, with periods of several days in the winter to a week in the summer) and can have amplitudes of some 5 to 7 Sv.  If climate scale changes in FC transport are desired, the effects of these waves can be eliminated from continuous time-series of FC transport.  However, the waves can cause serious aliasing effects if not resolved by isolated cruise data for example.

• Tidal motions: Tidally induced barotropic tides in the Straits of Florida have large amplitudes. These high frequency motions can be removed from transport estimates using existing tide models.       

References:

Baringer, M.O. and J.C. Larsen (2001). Sixteen years of Florida Current transport at 27°N. . Geophys. Res. Lett., 28, 3179-3182.

Johns, E.W., W.D. Wilson and R.L. Molinari (1999). Direct observations of velocity and transport in the passages between the Intra-Americas Sea and the Atlantic Ocean, 1984-1996. J. Geophys. Res., 104, 25,805 - 25,820.

Niiler, P.P. and W.S. Richardson (1973). Seasonal variability of the Florida Current. J. Mar. Res., 31, 144-166.

<< Back