Beyond the five major oceans, the planet is dotted with smaller seas — many of them partially enclosed by continents or chains of islands. The Philippine Sea is the largest by area, covering about 5.7 million km² in the western Pacific. The Mediterranean Sea lies between Europe to the north, Africa to the south, and Asia to the east, connecting to the Atlantic through the narrow Strait of Gibraltar. In the western Atlantic, the Caribbean Sea is bounded by Central America, South America, and the many islands of the region, while the Red Sea between Africa and the Arabian Peninsula is famously one of the saltiest seas in the world, with salinity exceeding 40 parts per thousand because high evaporation rates are not balanced by freshwater inflow.
Other seas play crucial roles in regional geography and trade. The Bering Sea lies between Alaska and Russia and links the Pacific to the Arctic through the Bering Strait. The South China Sea is one of the most geopolitically contested bodies of water on Earth, crossed by vital shipping lanes and claimed in overlapping fashion by several nations including China, Vietnam, and the Philippines. The Sea of Japan, sometimes called the East Sea by Korea, separates the Korean Peninsula from Japan, while the Arabian Sea occupies the northwestern part of the Indian Ocean between the Arabian Peninsula and the Indian subcontinent.
Several bodies of water are notable for being landlocked or nearly so. The Caspian Sea is the world's largest enclosed inland body of water, bordered by five countries: Russia, Kazakhstan, Turkmenistan, Iran, and Azerbaijan. The Black Sea connects to the Mediterranean through a chain of waterways — the Bosphorus Strait, the Sea of Marmara, and the Dardanelles — giving countries like Ukraine and Romania an indirect outlet to the open ocean. The Coral Triangle in the western Pacific, encompassing the waters of Indonesia, Malaysia, Papua New Guinea, the Philippines, the Solomon Islands, and Timor-Leste, represents the global epicenter of marine biodiversity.
Some unusual water bodies defy easy classification. The Sargasso Sea in the North Atlantic is the only sea without land boundaries, defined entirely by encircling ocean currents and named after the floating mats of Sargassum seaweed that drift within it. The Dead Sea, bordered by Jordan and Israel/Palestine, is a hypersaline lake with salinity around 34% — nearly ten times saltier than typical seawater — and its surface sits at the lowest land elevation on Earth, approximately 430 meters below sea level. The Aral Sea, once a vast lake in Central Asia, has shrunk dramatically since the 1960s because Soviet-era irrigation projects diverted water from the Amu Darya and Syr Darya rivers that fed it.