Answer is 2. Salinity and temperature.
The movement of water in the ocean is called thermohaline circulation. This circulation is depends on temperature and salinity. These two factors together affect the density of seawater. More dense seawater sinks below less dense seawater and thus the oceans circulate partially based upon their temperature and salinity. Heat from the Sun affects temperature of seawater. Surface seawater gets more heat near the equator than near the poles, and similarly more in the summer than in the winter. Salinity of seawater is affected by evaporation, precipitation, ice formation, and ice melting. Evaporation increases the salinity of seawater because when seawater evaporates, the salts are left behind, thus increasing their concentration. Precipitation and river input decrease salinity because the input of freshwater dilutes the salts in seawater, thus decreasing their concentration.
