Consider the following statements:

1. Surface currents account for about 10 per cent of ocean water and occupy roughly the upper 400 metres.
2. Deep-water currents account for the remaining 90 per cent.
3. Deep water sinks into ocean basins at high latitudes where low temperature increases density.
4. Currents are normally weakest at the surface and exceed five knots in deep water.

Which of the statements given above are correct?