Final answer:
The difference in average yearly water temperatures between San Diego and Charleston is primarily due to differing ocean currents, with the cold California Current affecting San Diego and the warm Gulf Stream influencing Charleston.
Step-by-step explanation:
The average yearly water temperature in the ocean off Charleston, South Carolina, is much higher than the water temperature off San Diego, California, despite both cities being at the same latitude mainly due to the differences in ocean currents.
Ocean currents act like conveyor belts of warm or cold water, sending heat from the equator towards the poles and bringing cold water back towards the equator. The current affecting San Diego is the California Current, which brings cold water from the north Pacific southward along the western coast of the United States. On the other side of the country, Charleston is influenced by the Gulf Stream, which carries warm water from the Gulf of Mexico up along the eastern coast. These currents have a significant impact on climate and water temperatures. Due to the California Current, San Diego experiences cooler water temperatures, while the Gulf Stream keeps the water temperatures warmer near Charleston.