ocean flows colored with sea surface temperature data
Source: National Aeronautics and Space Administration (NASA) Scientific Visualization Studio, Gulf Stream Sea Surface Currents and Temperatures
The Atlantic Ocean began to form as the supercontinent Pangea split up 200 million years ago near the end of the Triassic Period. The oldest basalt on the seafloor is next to the East Coast, while the youngest bedrock is forming now in the middle of the ocean at the Mid-Atlantic Ridge. The ocean continue to widen about one inch per year, as lava emerges at the ridge and pushes Europe and North America further apart.1
The currents in the ocean have changed dramatically over 200 million years as the continents have realigned and the seafloor has widened. Today, the Gulf Stream is a current of warm water, sometimes 15-20°F warmer than the adjacent water, flowing north from the equator.
The current warms the eastern edge of the North American continent in winter. That heat exchange is part of the entire Atlantic Meridional Overturning Circulation (AMOC), where cold water from the Arctic and warm water from the tropics transfer energy around the globe.2
ocean flows colored with sea surface temperature data (red pixels are warmer areas approaching 25° C, greens are intermediate values of 12-13° C, and blues are less than 10° C)
Source: National Aeronautics and Space Administration (NASA) Scientific Visualization Studio, Gulf Stream's Brightness Temperature (May 2, 2001)
The flow of the Gulf Stream affects shipping patterns. In 1768, Benjamin Franklin examined why British mail ships were slower than merchant ships that sailed across the Atlantic Ocean. Franklin was serving as Deputy Postmaster General in the colonies, so he had a professional interest as well as scientific curiosity.
Franklin explored the question with his cousin Timothy Folger, a Nantucket ship captain with an understanding of ocean currents from personal experience and from discussions with American whalers. Franklin realized that merchant sea captains minimized the time they spent sailing within the Gulf Stream, while British ship captains responsible for carrying the mail ignored the current.
Franklin and Folger produced an accurate map documenting the location of the Gulf Stream. British mail ship captains reportedly ignored the information since it came from just a "colonial," but in the American Revolution French ship captains took advantage of the map.3
Benjamin Franklin and his cousin Timothy Folger documented that sailing in the Gulf Stream could increase time required to cross the Atlantic Ocean to North America
Source: Library of Congress, Franklin-Folger chart of the Gulf Stream (Benjamin Franklin and Timothy Folger, c.1769-1770)
The Spanish understood the benefits of using the Gulf Stream long before the English. Ponce de Leon may have been the first to recognize and use it, in 1513. Throughout the 16th Century, Spanish treasure fleets sailed through the straights between Florida and the Bahamas, then north past Bermuda, because the current sped the journey eastward towards Seville.4
The Spanish treated their "Padron Real" and other maps as state secrets. As a result, Benjamin Franklin often gets credit for "discovering" the Gulf Stream that many Spanish pilots and ship captains had utilized effectively for over 150 years before Franklin and Folger published their map.5
ship captains sailing east to Europe took advantage of the Gulf Stream current
Source: David Rumsey Historical Map Collection, Chart of the Atlantic Ocean (by John Melish, 1812)
The flow of the Gulf Stream may lower sea level on Virginia's coastline, by pulling ocean water eastward and away from the edge of the continent. In 2015, Hurricane Joaquin slowed the speed of the Florida Current between Florida and the Bahamas. In Hampton Roads, without the Gulf Stream flowing at its normal speed, high tides were as much as 3 feet higher than predicted.6
The Atlantic Meridional Overturning Circulation (AMOC) is not a stable, unchanging pattern. Currents that transport warm and salty water north, such as the Gulf Stream, are affected by global climate change. Freshwater runoff into the North Atlantic changes salinity and temperature. The "conveyor belt" pattern where salty water cools, becomes more dense and sinks, then returns along the ocean bottom to the equator may be altered if water densities change:7
The Younger Dryas cold period, between 14,500-11,500 years ago, may have reflected an interruption in the Atlantic Meridional Overturning Circulation when meltwater from the North American ice sheet was redirected. Instead of flowing down the Mississippi River into the Gulf of Mexico, cold water runoff escaped through the St. Lawrence River and altered the temperature and salinity gradients which power the ocean currents. Meltwater from Greenland could create a similar impact, acting like a climate switch.8
Close scientific monitoring of the Atlantic Meridional Overturning Circulation pattern dates back only to 2004, but examination of ocean sediments allows an assessment of changes over time dating back far longer.
red shows near-surface transport and blue shows return flow at depth of the Atlantic Meridional Overturning Circulation
Source: Met Office, Risk management of climate thresholds and feedbacks: Atlantic Meridional Overturning Circulation (AMOC) (May 2, 2001)
It appears the ocean current began weakening in the mid-1800's, and in 2018 a scientific report concluded it was at a low point 15% slower than 1,600 years ago. The impact is that waters off the Virginia coast are warmer, species of fish are changing, and sea level alongside the Virginia coastline is higher.
More ominously, one researcher suggested the ocean circulation pattern could change quickly, and:9
If a warmer climate disrupts the Atlantic Meridional Overturning Circulation, warm and cold waters with different levels of salinity will find a new equilibrium. New currents could replace the Gulf Stream.
If aggressive human action reduced carbon dioxide to 400 parts per million or lower, the climate will not revert to "normal" quickly. The existing Atlantic Meridional Overturning Circulation would not be automatically be re-established. Instead, a new equilibrium could develop to redistribute waters of different densities.10
Atlantic Meridional Overturning Circulation (AOMC) with the warm Gulf Stream, the North Atlantic Current (NAC), and Labrador Current in red, and the cold deep western boundary current (DWBC) in blue
Source: American Geophysical Union, Observations, inferences, and mechanisms of the Atlantic Meridional Overturning Circulation: A review (by Martha W. Buckley and John Marshall)
ocean colors reveal how the Gulf Stream veers away from the continent at Cape Hatteras
Source: National Aeronautics and Space Administration (NASA) Visible Earth, Gulf Stream