stratification是什麼意思

　　Stratification in polar water normally is weak and transient.

　　極地水域的成層性是微弱而暫時的`。

　　Stratification in polar waters normally is weak and transient.

　　極地水域的成層性是微弱而暫時的。

　　The stratification of beach deposits has been studied particularly.

　　對海灘沉積物的層理進行了著重研究。