Land cools quicker than the sea/ocean waters in the night.
As the land cools faster than the sea, air above the sea will be warmer than the air above land. Thus, air above the sea will expand greater than the air above land, and rise since the density is lower.
The air above land then rushes in to fill the empty space above the sea, and the air that previously rose above will become cooler and denser at higher altitudes, and sink back down to fill the space above land.
This creates a cycle of air flow with air blowing from the shores out to the waters at night.
Hope this helps! :)
