The correct answer is option 4 - Rotation of the Earth.
The rotation of the Earth plays a significant role in the deflection of wind in the southern hemisphere towards the left. This phenomenon is known as the Coriolis effect. The Coriolis effect occurs due to the rotation of the Earth on its axis.
As the Earth rotates, the equator spins faster than areas closer to the poles. This difference in rotational speed causes the air moving from north to south or south to north to be deflected. In the southern hemisphere, the Coriolis effect causes the wind to be deflected to the left, or in a clockwise direction. This is in contrast to the northern hemisphere, where the deflection is towards the right, or in a counterclockwise direction.
It is important to note that the other options mentioned in the question are not the correct reasons for the deflection of wind in the southern hemisphere. Option 1, difference in water masses, does not directly impact the direction of wind. Option 2, temperature and pressure variations, may affect wind patterns but do not explain the deflection towards the left. Option 3, the inclined axis of the Earth, is not directly related to the deflection of wind in the southern hemisphere.