The correct option is 2 only.
Explanation
Ocean currents are generally classified based on depth into surface currents and deep water currents. These two types of currents are driven by distinct physical forces and occupy different proportions of the total ocean volume.
Statement 1 is Incorrect: Surface currents constitute only about 10 % of all the water in the ocean, typically confined to the upper 400 meters. It is the deep water currents that make up the remaining 90 % of the ocean volume.
Statement 2 is Correct: Deep water currents move around ocean basins primarily due to variations in density and gravity. This process is driven by differences in temperature and salinity (thermohaline circulation). Denser water sinks and moves towards areas of lower density under the influence of gravity.
Statement 3 is Incorrect: At high latitudes, water temperatures are very low, and freezing often increases salinity. This makes the water cold and dense, causing it to sink to the ocean floor (downwelling) rather than rise. Deep waters typically rise to the surface (upwelling) in lower latitudes or regions where surface water is displaced by wind, not due to thermal expansion at high latitudes.
Key Takeaway: The ocean's circulation system is divided into wind-driven surface currents (approx. 10%) and density-driven deep water currents (approx. 90%), the latter forming the global thermohaline circulation.