Answer
Water gives off and absorbs large amounts of energy for small drops and rises in its temperature.
Work Step by Step
Ocean water moderates the temperature of nearby landmasses, acting as a heat reservoir. Water has a high specific heat capacity as compared to other common materials, meaning it is slow to warm up and slow to cool down.
In the winter, when the air is colder than the water, the air is warmed by the water resulting in a milder winter for the city by the water. In the summer, the reverse happens and the water cools off the air, resulting in a milder summer for the coastal city.