Question

(a) Stations A and B are at the same sea surface elevation level and have a bottom depth of 2000 m. Both stations have seawater with a uniform density with respect to depth; however the seawater density at A and B are different (sA = 24.7 kg/m3 ; sB = 25.4 kg/m3 ). [A = 40o 45' N, 25o 45' W; B = 41o 5' N, 24o 45' W]

(b) Does this current vary with respect to depth ? If so, explain how it varies and why

Answer 1

We know that the density can be understood as mass per unit volume. The density of station B is more so the waves crossing in unit volume will be more at station B. Since both the stations are at same bottom depth but located at different latitudes so the current will definetely vary with respect to depth.

We know that the ocean currents are driven by two forces the Sun and the rotation of earth.The effect of the Sun is to alter the density of the ocean surface water directly by changing its temperature. If water is cooled or becomes saltier through evaporation, it becomes denser. This can result in the water column becoming unstable, setting up density-dependent currents, also known as the thermohaline circulation.
The rotation of the Earth also affects the currents through the Coriolis force. This force causes water to move to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. In the present case, the variation with respect to depth can be explained as follows:

The pressure P equation can be given as

g is the gravity, rho is the density and z represents the depth. As the dept varies the pressure will also vary and will result in a pressurre gradient. The pressure varies in both manners horizontal and vertical. Horizontal differences in density (due to variations of temperature and salinity) measured along a specific depth cause the hydrostatic pressure to vary along a horizontal plane or geopotential surface, a surface perpendicular to the direction of the gravity acceleration. Horizontal gradients of pressure, though much smaller than vertical changes in pressure, give rise to ocean currents.Clearly, the equation of hydrodynamics (given by (1)) states the current will vary with height.