Scientists have discovered that the strength of the Florida Current, which marks the beginning of the Gulf Stream system and plays a crucial role in the global Atlantic Meridional Overturning Circulation (AMOC), has remained consistent over the last forty years.
A recent research study conducted by scientists at the Cooperative Institute for Marine and Atmospheric Studies (CIMAS), part of the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science, NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML), and the National Oceanography Centre, indicates that the strength of the Florida Current has stayed stable for the past four decades.
The AMOC is drawing increased interest from both scientists and the public. This intricate system of ocean currents functions like a “conveyor belt,” distributing heat, salt, nutrients, and carbon dioxide throughout the oceans. Variations in the strength of the AMOC could lead to significant changes in global and regional climates, weather patterns, sea levels, precipitation, and marine life.
This research included adjustments for long-term changes in the Earth’s magnetic field to assess the Florida Current, known as one of the fastest ocean currents and a vital part of the AMOC, which has remained quite stable over the past four decades.
Published in the journal Nature Communications, the study involved a re-evaluation of 40 years’ worth of data on Florida Current volume transport, gathered from a now-removed submarine telecommunications cable that runs across the bottom of the sea between Florida and the Bahamas. The Earth’s magnetic field induces a measurable voltage in the cable as salt ions carried by the Florida Current flow over it. These cable readings were combined with data from regular hydrographic surveys that directly assess the volume transport and properties of water masses. Additionally, transport data was derived from differences in cross-stream sea levels measured by altimetry satellites.
“While this study does not deny the possibility of an AMOC slowdown, it demonstrates that the Florida Current, crucial to the AMOC in the subtropical North Atlantic, has shown stability over the more than four decades of observations,” explained Denis Volkov, the lead author of the study and a scientist at CIMAS at the Rosenstiel School. “With the corrected and updated time series for Florida Current transport, the downward trend in AMOC transport is indeed lessened, but not completely eliminated. The current observational data is just beginning to reveal longer-term variability, and we require many more years of consistent monitoring to determine if a genuine decline in AMOC is occurring.”
Grasping the condition of the Florida Current is vital for establishing systems that forecast coastal sea levels and for evaluating local weather and its impacts on ecosystems and communities.
Since 1982, NOAA’s Western Boundary Time Series (WBTS) project and its earlier iterations have tracked the movement of the Florida Current between Florida and the Bahamas at latitude 27°N, using a 120-kilometer long submarine cable along with regular hydrographic surveys in the Florida Straits. This nearly uninterrupted monitoring effort has resulted in the longest existing observational record of a boundary current. Since 2004, the WBTS project has collaborated with the UK’s Rapid Climate Change program (RAPID) and the University of Miami’s Meridional Overturning Circulation and Heatflux Array (MOCHA) programs to create the first trans-basin AMOC observation network at approximately 26.5°N.
This study received support from NOAA’s Global Ocean Monitoring and Observing program (grant #100007298), NOAA’s Climate Variability and Predictability program (grant #NA20OAR4310407), the Natural Environment Research Council (grants #NE/Y003551/1 and NE/Y005589/1), as well as the National Science Foundation (grants #OCE-1332978 and #OCE-1926008).
