Driving Deep Circulation and the Conveyor Belt Model."

Deep circulation (thermohaline circulation)

(1) The water in the ocean, which is a fluid, has light water floating on the surface and heavier water sinking in the deeper part of the ocean. Water on the surface becomes denser as it cools. Surface water at high latitudes in the North Atlantic is highly saline. When that high-salinity water cools at the surface and becomes dense, it sinks to the depth of that density.

１）軽い水：light water　　　重い水：heavy water　　高密度化：Higher density

　Densification can be continuous. Then there will be a continuous sinking to deeper depths. As the water is pushed down in this manner, deep water is formed and the oceanic general circulation begins. The density of seawater is determined by water temperature and salinity. In other words, the ocean circulation is driven by the transfer of heat to seawater and changes in salinity, which is also called the thermohaline circulation.

１）軽い水：light water　重い水：heavy water　　高密度化：Higher density

密度は水温と塩分で決まる：Density is determined by water temperature and salinity.

熱の移動と塩分変化で海洋循環が駆動される：Heat transfer and salinity changes drive ocean circulation

熱塩循環：thermohaline circulation

　Deep water submerged in the high latitudes of the North Atlantic moves southward, crosses the equator, and reaches the Southern Ocean.

１）北大西洋高緯度域：(1) North Atlantic high latitudes

赤道を超えて南下：Southward across the equator

南大洋：South Pacific

　Deep Atlantic Ocean water moving southward merges with the Antarctic Deep Reflow, which circles around the Antarctic Continent (see next figure). Even in Antarctica, the surface water is considerably cooled in winter, and is well mixed from the surface to the deeper layers. Furthermore, in the Antarctic Ocean, seawater freezes in the winter, forming ice. When seawater freezes, only the freshwater portion crystallizes. The salts it contains cannot enter the crystals and are ejected out of the ice. This cold, ultra-high-salinity water expelled from the ice is so heavy that it stoops down to the bottom of the Antarctic Ocean. It mixes with the water from the surrounding North Atlantic Ocean and falls to the bottom of the ocean. This is the Antarctic Bottom Water. The Antarctic Bottom Water crawls along the bottom of all the oceans as it moves northward.

太平洋へ：To the Pacific Ocean　南極低層水：Antarctic low water　

南極大陸：Antarctica　南極深層還流：Deep Antarctic Reflux

北大西洋深層水：North Atlantic Deep Water　インド洋：Indian Ocean

南極底層水：Antarctic Bottom Water　大西洋へ：To the Atlantic Ocean

太平洋の底層水と深層水：Bottom and deep waters of the Pacific Ocean

深層循環の終着は、北大平洋高緯度といわれています：The terminus of the deep circulation is said to be at high northern Pacific latitudes.

南極：Antarctica　冷却と結氷：Cooling and freezing　アリューシャン：Aleutian

列島：archipelago　水深：depth of water　北太平洋深層水：North Pacific Deep Water

周極底層水：circumpolar bottom water　海底：submarine

気候庁HPの図を引用：Adapted from a diagram on the Climate Agency's website

　It is believed that the North Pacific Deep Water is brought to the surface slowly as it moves south, exchanging water with the middle layer. The surface water then promptly returns to the Atlantic Ocean.

１）北大西洋高緯度域：1) North Atlantic High Latitude Domain

２）南極海：(2) Antarctic Ocean

３北太平洋亜寒帯：3 North Pacific subduction zone

conveyor belt model

　The conveyor belt model, which represents such an oceanic general circulation, was proposed based on the idea that deep water being swept away one after another can be likened to a conveyor belt.

Vertical distribution of salinity

The vertical distribution of salinity in the North Atlantic (subarctic and arctic regions) to the North Pacific subarctic zone.

• In the North Atlantic, high-salinity surface water is transported from the subtropical to the subarctic to the arctic regions.
  
• In the middle of the process (②→①), the surface water becomes slightly hypochloritic (arrow A in the figure).
  
• The high-salinity surface water transported to the arctic region of the North Atlantic (1) is rapidly cooled and densified in winter and transported to deeper layers (arrow B in the figure).
  
• The North Atlantic Deep Water becomes slightly hypochloric (35‰ to 34.7‰) on its way southward through the Atlantic Ocean.
  
• The salinity of deep water in the Southern Ocean (Antarctic Ocean) and the Pacific Ocean (③) is uniform (34.7‰).
  
• The Pacific Ocean surface layer has low salinity, so a pronounced salinity dynamic layer appears from the surface to the middle layer (③).

Keep in mind the salt distribution in each ocean as shown in the figure above.