How much does the Gulf of Mexico Contribute to the Gulf Stream?

What is Gulf Stream?
The Gulf Stream is a narrow ribbon of high velocity (~2 m/s) and warm (>20 °C) water meandering through the gaps along the continental shelf flowing northward along the east coast of North America until leaving the coastline near Cape Hatteras in North Carolina.

How much of the Gulf of Mexico water contributes to the Gulf stream?
Despite the name, very little water from the Gulf of Mexico contributes to the Gulf Stream. To show the percentage of contribution from the Gulf, we run an experiment. The experiment is performed using NASA’s ocean model called ECCO2. The model combines ocean general circulation simulation with observed global ocean datasets. To do this experiment, we fill the Gulf (from surface to a depth of ~3000 m) with 115000 virtual particles, allowing them to move with the ocean’s three dimensional velocity field. We track their path, and count those that make their way to the meandering Gulf stream.

What are some properties of the water contributing to the Gulf Stream from the Gulf?
Most of the water that is squeezed through Florida Strait from the Gulf is warm and shallow. The Gulf Stream extends from the surface to a depth of 300 m. Particle temperatures are usually higher than 20 °C and salinities are higher than 36 salinity units. As the Gulf stream meanders along the continental shelf, coherent eddies with diameters ~100–300 km are formed and get separated from the main currents. These are called Gulf stream rings. Often, the rings that separate to the North of the meandering stream rotate clockwise and those separating to the south of the stream rotate counter clockwise (e.g. see the two rings to the north and south of the stream along NYC's longitude line, ~ -73.5 ° longitude, between March 16^th-20^th in Animation 1 and Image 1). These eddies act to stir the flow, decreasing temperature gradients across the Gulf stream.

Why can running such experiments be useful? One can think of the Gulf of Mexico and Florida straits as a big reservoir and a dam system. A dam controls the overflow of water in a somewhat similar way that the gaps of Florida straits constrict the flow of currents. The loop current in the Gulf of Mexico (the very large eddy persisting in the Gulf, see animations 1 and 2) that bring the warm and highly saline Caribbean water into the Gulf can constrict the water entering the Gulfstream through Florida states.
Luckily in May 2010, the loop current broke the connection between the Deepwater Horizon oil spill site and the Florida current, limiting the contamination from entering the Gulf Stream. Running such particle tracking experiments with the ocean circulation models helps with understanding how and where tracers (such as environmental contaminants) can spread and it helps with improving emergency responses.

So where does the Gulfstream come from if it’s not mainly supplied by the Gulf of Mexico?
Most of the water flowing through the Florida Straits originally comes from the southern half of the North Equatorial Current, and in part from a branch of the South Equatorial Current (which splits off from the South Atlantic by Brazil’s wedgelike coastline). This is not shown here.

References
The Gulf Stream: A Physical and Dynamical Description. Henry Stommel, University of California Press, 1965
Liu, Y.Y., Weisberg, R.H.R.H., Hu, C.C. and Zheng, L.L. (2011). Trajectory Forecast as a Rapid Response to the Deepwater Horizon Oil Spill. In Monitoring and Modeling the Deepwater Horizon Oil Spill: A Record-Breaking Enterprise (eds Y. Liu, A. Macfadyen, Z.-G. Ji and R.H. Weisberg). https://doi.org/10.1029/2011GM001121