In coastal areas, there is little temperature difference between day and night due to the high specific heat capacity of water, which is about 4,200 J/kg°C. This means water can absorb and store a large amount of heat without a rapid rise in temperature. 

During the day, the ocean absorbs heat from the sun, and at night, it slowly releases this stored heat. This gradual release warms the surrounding air, stabilizing temperatures and preventing extremes. 

Thus, the high specific heat capacity of water helps coastal areas maintain a mild climate with minimal temperature difference between day and night.