Thermohaline circulation

  • Thermohaline Circulation
  • Circulation driven by the unequal heating of earth by the sun, together with surface patterns of evaporation and precipitation. 
Abstract from DBPedia
    Thermohaline circulation (THC) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. The adjective thermohaline derives from thermo- referring to temperature and -haline referring to salt content, factors which together determine the density of sea water. Wind-driven surface currents (such as the Gulf Stream) travel polewards from the equatorial Atlantic Ocean, cooling en route, and eventually sinking at high latitudes (forming North Atlantic Deep Water). This dense water then flows into the ocean basins. While the bulk of it upwells in the Southern Ocean, the oldest waters (with a transit time of around 1000 years) upwell in the North Pacific. Extensive mixing therefore takes place between the ocean basins, reducing differences between them and making the Earth's oceans a global system. On their journey, the water masses transport both energy (in the form of heat) and matter (solids, dissolved substances and gases) around the globe. As such, the state of the circulation has a large impact on the climate of the Earth. The thermohaline circulation is sometimes called the ocean conveyor belt, the great ocean conveyor, or the global conveyor belt. On occasion, it is used to refer to the meridional overturning circulation (often abbreviated as MOC). The term MOC is more accurate and well defined, as it is difficult to separate the part of the circulation which is driven by temperature and salinity alone as opposed to other factors such as the wind and tidal forces. Moreover, temperature and salinity gradients can also lead to circulation effects that are not included in the MOC itself.

    熱塩循環(ねつえんじゅんかん、英: thermohaline circulation)は、おもに中深層(数百メートル以深)で起こる地球規模の海洋循環を指す言葉である(水深千数百メートル以下での海洋循環を指すという説もある。)。語源の thermo は熱、haline は塩分の意味で海水の密度はこの熱と塩分により決定される。メキシコ湾流のような表層海流が、赤道大西洋から極域に向かうにつれて冷却し、ついには高緯度で沈み込む(北大西洋深層水の形成)。この高密度の海水は深海底に沈み、1200年後に北東太平洋に達して再び表層に戻る。その間それぞれの海盆の間で広範囲に渡って混合が起こり均一化することで海洋の世界的なシステムを作っている。この過程で、水塊は(熱)エネルギーと物質(固体、溶解物質、ガス)を運んで地球上を移動する。このように、循環現象は地球の気候に大きな影響を与えている。 熱塩循環と表層で起こる風成循環とを合わせて、海洋大循環と呼ぶ。熱塩循環は大循環、深層大循環、グローバルコンベアーベルトとも呼ばれる。海水が南北に移動し表面近くと深層の間を行き来することにより特徴付けられるため、子午面循環(英語で meridional overturning circulation)と呼ばれることもある。


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