What occurs when ice forms at the poles during ocean circulation?

When ice forms at the poles during ocean circulation, it leads to downwelling of high salinity water, primarily influenced by the process of brine rejection. As seawater freezes, the ice crystals exclude salt, making the surrounding water saltier. This increase in salinity causes the density of the water to increase, making it denser than the surrounding water. The denser water then sinks, contributing to the downwelling process.

This downwelling is a crucial component of global ocean circulation, particularly in driving the thermohaline circulation, which plays a significant role in regulating climate by transporting heat around the planet. In contrast, the other choices do not accurately describe the processes occurring during ice formation at the poles; for example, lower salinity and density would not result from the formation of ice but rather from freshwater inputs or melting ice, and ice formation does not stop ocean currents or significantly raise sea levels.