Final answer:
Surface currents move water horizontally across the ocean's surface. Warm water flows from the equator towards the poles and cold water from the poles towards the equator. For the GRASP CHECK, the current must flow horizontally from left to right for a rearward-pointing force when a downward magnetic field is present.
Step-by-step explanation:
Surface currents in the oceans play a significant role in distributing heat and maintaining the Earth's climate. When we talk about surface currents carrying warm or cold water, this movement is horizontally across the ocean's surface. Warm water typically originates from equatorial regions and is carried towards the poles, while cold water from the poles is driven towards the equator. This happens due to the density differences caused by temperature changes: warm water is less dense and thus stays on top, moving with the prevailing winds, while cold water is denser and sinks, forming currents that travel deep beneath the surface before they are eventually brought back up in a process known as ocean upwelling.
As for the GRASP CHECK question, in a scenario where the magnetic field is downward, the right-hand rule applied to determine the direction of force due to the current would lead us to conclude that the current must flow horizontally from left to right when viewed from the rear of the boat to get a rearward-pointing force (option c).