stratification是什么意思

　　Stratification in polar water normally is weak and transient.

　　极地水域的成层性是微弱而暂时的。

　　Stratification in polar waters normally is weak and transient.

　　极地水域的成层性是微弱而暂时的。

　　The stratification of beach deposits has been studied particularly.

　　对海滩沉积物的层理进行了着重研究。