Answer:
The ocean is constantly expanding due to a slow process called seafloor spreading, which occurs when tectonic plates move apart and magma seeps up to the surface of the ocean floor, solidifying as new ocean crust. There are two main causes of ocean expansion: thermal expansion, which occurs when water warms and expands, and increased melting of land-based ice. The Atlantic ocean, for example, expands at least 1.5 inches per year. Although this process is slow, over the past 20 years the Atlantic ocean has risen about 2 and a half feet, demonstrating the long-term effects of ocean expansion.