density gradient

Ocean currents are driven partly by density gradients caused by differences in temperature and salinity.洋流部分由温度和盐度差异引起的密度梯度驱动。

The density gradient within the Earth's interior determines the behaviour of seismic waves as they travel through different layers.地球内部的密度梯度决定了地震波穿过不同层时的行为。