The Atlantic meridional overturning circulation (AMOC) is the "main current system in the South and North Atlantic Oceans". As such, it is a component of Earth's oceanic circulation system and plays an important role in the climate system. The AMOC includes currents at the surface as well as at great depths in the Atlantic Ocean. These currents are driven by changes in the atmospheric weather as well as by changes in temperature and salinity. They collectively make up one half of the global thermohaline circulation that encompasses the flow of major ocean currents. The other half is the Southern Ocean overturning circulation.
In one paper, AMOC collapse only occurs in a full general circulation model after it ran for nearly 2000 years, and freshwater quantities (in Sv) increased to extreme values. While the conditions are unrealistic, the model may also be unrealistically stable, and the full implications are not clear without more real-world observations
1992-2002 altimeter data from NASA Pathfinder indicated a slowing (red) in the subpolar gyre region. This was used as a proxy for AMOC before the initiation of RAPID, and before subsequent research demonstrated that the subpolar gyre often behaves separately from the larger circulation
RAPID tracks both the AMOC itself (third line from the top, labelled MOC) as well as its separate components (three lower lines) and the AMOC flow combined with the subpolar gyre and/or the western boundary current flow (upper two lines) AMOC flow during 2004-2008 appears stronger than afterwards
AMOC is considered to be one of the several major parts of the climate system which could pass tipping point around a certain level of warming and eventually transition to a different state as a result. The graphic shows the levels of warming where this tipping is most likely to occur for a given element
Gulf Stream
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The Gulf Stream is a warm and swift Atlantic ocean current that originates in the Gulf of Mexico and flows through the Straits of Florida and up the eastern coastline of the United States, then veers east near 36°N latitude and moves toward Northwest Europe as the North Atlantic Current. The process of western intensification causes the Gulf Stream to be a northward-accelerating current off the east coast of North America. Around 40°0′N 30°0′W, it splits in two, with the northern stream, the North Atlantic Drift, crossing to Northern Europe and the southern stream, the Canary Current, recirculating off West Africa.
Surface temperatures in the western North Atlantic: Most of the North American landmass is black and dark blue (cold), while the Gulf Stream is red (warm). Source: NASA
Benjamin Franklin's chart of the Gulf Stream printed in London in 1769
Evolution of the Gulf Stream to the west of Ireland continuing as the North Atlantic Current
Hurricane Sandy intensified as it tracked northward along the axis of the Gulf Stream in 2012