Inferring Florida Current Volume Transport From Satellite Altimetry

The nearly four-decades-long quasi-continuous daily measurements of the Florida Current (FC) volume transport with a submarine cable at about 27 degrees N represents the longest climate record of a boundary current in existence. Given the extremely high utility of this time series for monitoring the Atlantic meridional overturning circulation, as well as for improving understanding and prediction of the regional weather, climate phenomena, coastal sea-level, and ecosystem dynamics, efforts are underway to establish a suitable backup observing system in case the cable becomes inoperable in the future. This study explores the utility of along-track satellite altimetry measurements since 1993 as a potential cable backup by establishing the relationship between the cross-stream sea surface height gradients and the FC volume transport derived from cable measurements and ship sections. We find that despite the lower temporal resolution, satellite altimetry can indeed serve as a decent but limited backup observing system. The FC transport inferred from satellite altimetry captures about 60% of the variability observed in the concurrent cable estimates, and the estimated error bars for the altimetry-derived transport are larger than those of the cable transport (2.1 Sv vs. 1.5 Sv). We nevertheless demonstrate that satellite altimetry reproduces the seasonal, intra-seasonal, and inter-annual variability of the FC transport fairly well, as well as large transport anomalies during extreme weather events, such as tropical storms and hurricanes. The altimetry-derived transport can be provided in near-real time and serve the need to fill in data gaps in the cable record and assess its quality over time. Plain Language Summary Florida Current (FC) is one of the major conduits of heat, salt, carbon, nutrients and other properties in the subtropical North Atlantic, with profound influences on regional weather, climate, sea-level, and ecosystems. Daily monitoring of the FC volume transport with a submarine cable has been maintained nearly continuously since 1982. Because of the extremely high value of these measurements for Earth system studies, efforts are underway to find a suitable backup observing system for the inevitable future when the cable fails. Satellites have been providing accurate measurements of sea level for nearly 3 decades. Due to the Earth's rotation, the direction of major oceanic currents is parallel to the lines of constant sea level, which for the FC translates into sea level near the Bahamas being about 1-m higher than sea level along Florida east coast. Variations in the FC volume transport are linked to changes in the sea surface tilt across the Straits of Florida. This study demonstrates that accounting for the platform-specific limitations, satellite altimetry can serve as a limited but useful cable replacement, with the advantage of not being prone to damage from severe weather, which can often endanger the existing cable-based system.