Salinity Transport in the Florida Straits

Abstract

submarine cable across the Florida Straits yields a time series of volume and temperature transports using previously determined calibrations, and here a calibration is defined for salinity transport using data not yet compared to the cable. Since 2001, 32 transects were collected with conductivity?temperature?depth (CTDs) sensors and lowered acoustic Doppler current profilers (LADCPs). Calibrations for volume and temperature transports using CTD/LADCP data are consistent with previous studies. A salinity calibration is obtained by regressing salinity transport against volume transport, where salinity transport is calculated relative to the basin-averaged salinity at 26°N (Sref = 35.156 psu). On average, the transect-derived salinity transport is 33.0 Sv psu (1 Sv ≡ 106 m3 s?1), has a standard deviation of 2.8 Sv psu, and has a 90th percentile range of 29.1?37.4 Sv psu. The cable-derived salinity transport has a root-mean-square error of 2.2 Sv psu compared to the CTD/LADCP transects. Inherent spatial fluctuations and their covariability in the Florida Straits are responsible for noise in the calibrations and for slight increases in accuracy from salinity to temperature to volume calibrations. Salinity fluctuations are strongest in middepth waters of intermediate salinity, where velocity is neither particularily fast nor variable. In contrast, temperature is highly stratified and warm near-surface waters coincide with fast and variable velocities. Temperature additionally exhibits seasonality near the surface, whereas no robust seasonality is found for salinity or velocity. Temperature and salinity transports are largely driven by volume transport, which in turn, because of a large average electrical conductivity, is closely related to the conductivity-weighted velocity that generates the cable-measured voltage.