A gyre (pronounced jai-uh) is a natural phenomenon consisting of a large circular system of ocean currents. They are formed from the Earth’s rotation, prevailing winds, and ocean currents.
The Earth’s rotation is a huge influence on gyre formation due to the process of geostrophic flow, a type of movement that occurs when the forces acting on a surface are so weak (relative to the influence from the rotation of the Earth) that Coriolis deflection becomes the key factor influencing the direction of motion.
A gyre is essentially like a vortex which swirls and rotates. Gyres have increasingly been reported internationally by scientists and journalists because they often lead to a concentration of plastic waste, described as natural nets out at sea. An example of this is the Great Pacific Garbage Patch.
There are five major ocean gyres around the world and multiple small-scale regional gyres. The giant global gyres help to circulate ocean water around the world, moving it in a huge ocean conveyor belt. This global conveyor belt transfers ocean water through the gyres and in doing so spreads cold saline water away from the poles and heat away from the tropics. More saline water is found in areas like the Weddell Sea gyre because sea ice has a lower salinity therefore when the ice forms it ejects salt, which concentrates, becomes denser and then sinks called Antarctic Bottom Water.
Gyres are grouped into three classifications: subpolar, tropical and subtropical. The Weddell Sea is a subpolar gyre which circulates under low atmospheric pressure in the high latitudes of the southern hemisphere.
The Weddell Sea gyre is one of only two gyres around Antarctica (the other being the Ross Sea gyre). It moves in a clockwise direction. These Antarctic gyres are essential cogs in the global ocean conveyor belt. The Weddell Sea gyre plays an incredibly important role in regulating air‐sea exchanges because as sea ice grows, it insulates the Weddell Sea from the atmosphere and inhibits the transfer of heat from the relatively warm subsurface waters up into the cold atmosphere.
You can learn more about the Weddell Sea gyre from this open access review article "The Weddell gyre, Southern Ocean: present knowledge and future challenges".
The rotation of the Weddell Sea gyre is clearly visible from satellite imagery. The gyre moves in a clockwise direction taking with it surface sea ice. A way to visualise this movement is to chart the journey of Sir Ernest Shackleton’s ship The Endurance from the point where it entered the Weddell Sea ice pack in December 1914. Ice closed in around the ship on 18 January 1915, and from then on The Endurance was held captive in the pack ice, with temperature regularly dropping below -20°C. The ship moved clockwise around the Weddell Sea before being crushed on 21 November 1915, 15 months and 13 days after it set sail. It had drifted 1186 miles under the influence of the gyre and moving ice. Remarkably all 28 men famously survived the disaster. The wreck remains on the bottom of the Weddell Sea.