The Sea of Marmara, also known as the Sea of Marmora, is an inland sea located in Turkey, which connects the Aegean Sea with the Black Sea. As Turkey is a transcontinental country, the sea separates European Turkey from Asian Turkey. The Bosphorus Strait links the Sea of Marmara to the Black Sea, while the Dardanelles Strait links it to the Aegean Sea. The sea is named after Marmara Island, which is a rich source of marble, and is derived from the Greek word marmaron, which means "marble." The ancient Greeks, who sailed through it to reach the Black Sea, named the Sea of Marmara Propontis, which is derived from the words pro, meaning "before," and pontos, meaning "sea."
The Sea of Marmara is a relatively small sea, covering an area of approximately 4,380 square miles. Additionally, the sea is 174 miles long, 50 miles wide, and has a maximum depth of 4,490 feet. According to the International Hydrographic Organization (IHO), the sea's western limit is defined by the Dardanelles limit of the Aegean Sea, while its northeast limit is defined by a line joining Cape Anatoli with Cape Rumili. The Sea of Marmara's average surface salinity is 22 parts/1,000, which is slightly higher than that of the Black Sea. Water at the sea's bottom is more saline, averaging 38 parts/1,000, which is almost the same as the Mediterranean Sea. The sea's salinity level is constantly reduced by the inflow of water from several rivers, including the Biga, Susurluk, and Gonen. The sea contains a number of islands, such as Marmara Island, Paşalimanı Island, and Avşa Island. The North Anatolian Fault runs under the sea and has caused several earthquakes including the 1999 earthquakes in the Turkish cities of Izmit (August) and Düzce (November).
The catchment basin surrounding the Sea of Marmara is an important economic area, as economic activity within the region accounts for approximately 40% of Turkey’s gross domestic product (GDP). It is considered the country’s most developed and populated socio-economic region, and is characterized by a wide range economic activity, including agriculture and heavy industry. The Turkish Strait System is one of the busiest maritime passages in the world, serving more than 50,000 vessels each year, of which 20% are oil tankers. Additionally, ports on the Sea of Marmara register about 18% of all Turkish fishing fleets, which includes 14,500 vessels.
The Sea of Marmara features a unique ecosystem, as it is a transitional medium between the Black Sea and the Mediterranean Sea. Although the Sea of Marmara is relatively small in terms of area, its depth allows water from the two seas to create oppositely flowing double layers of water with different densities. As a result, the biodiversity in the Sea of Marmara depends on the ecological conditions dictated by the water influx from the two basins. About 507 of Turkey’s 795 marine flora are distributed mainly in the southern coast of the sea. The sea contains an estimated 200 species of fish, although the exact number may be lower due to overfishing. Additionally, 115 phytoplankton species have been reported in the northeastern parts of the sea.