The Sea of Marmara, also called the Sea of Marmora, the Marmara Sea, or Propontis (pronounced /prəˈpɒntɪs/; ancient Greek: Προποντίς /pro.ponˈdis/), is a small inland sea completely inside Turkey. It connects the Black Sea and the Aegean Sea through the Bosporus and Dardanelles straits, separating Turkey’s European and Asian sides. It covers an area of 11,350 square kilometers (4,380 square miles) and measures 280 kilometers by 80 kilometers (174 miles by 50 miles), making it the smallest sea in the world. Its deepest point is 1,370 meters (4,490 feet).
Name
The Sea of Marmara is named after the largest island on its southern side, called Marmara Island. This name comes from the island's abundance of marble, a type of rock (Greek: μάρμᾰρον, mármaron).
In ancient times, the sea was called the Propontis. This name comes from the Greek words pro meaning "in front of" and pontos meaning "sea," specifically referring to the Black Sea. The Ancient Greeks used this sea as a route to reach the Black Sea.
Mythology
In Greek mythology, a storm on the Propontis forced the Argonauts to return to an island they had already left. This event caused a battle, during which either Jason or Heracles killed King Cyzicus, who thought they were enemies from the Pelasgian people.
Geography and hydrology
The International Hydrographic Organization describes the boundaries of the Sea of Marmara as follows:
On the west, the boundary follows the Dardanelles limit of the Aegean Sea, defined by a line connecting Kum Kale (26°11′E) and Cape Helles.
On the northeast, the boundary is a line connecting Cape Rumili with Cape Anatoli (41°13′N). The southern coast of the sea has many deep inlets, including the Gulf of İzmit (Turkish: İzmit Körfezi), the Gulf of Gemlik (Turkish: Gemlik Körfezi), the Gulf of Bandırma (Turkish: Bandırma Körfezi), and the Gulf of Erdek (Turkish: Erdek Körfezi).
The average surface salinity of the Marmara Sea is about 22 parts per thousand, which is slightly higher than that of the Black Sea but only about two-thirds of the salinity found in most oceans. The water at the bottom of the sea is much saltier, averaging around 38 parts per thousand, similar to the salinity of the Mediterranean Sea. This dense, salty water remains at the bottom and does not rise to the surface, unlike the water in the Black Sea. Rivers such as the Susurluk, Biga (Granicus), and Gönen also lower the sea’s salinity, though their effect is less significant than on the Black Sea. Most of these rivers flow from Anatolia, as there is little land in Thrace that drains southward.
The Sea of Marmara contains two main groups of islands. To the north are the Princes' Islands, an archipelago that includes the inhabited islands of Kınaliada, Burgazada, Heybeliada, Büyükada, and Sedef Adası, as well as uninhabited islands like Sivriada, Yassıada, Kaşıkadası, and Tavşanadası. These islands are easily reached by ferry from both the European and Asian sides of İstanbul, and the entire group is part of the connected area around İstanbul.
To the south are the Marmara Islands, an archipelago that includes the island of Marmara and three other inhabited islands—Avşa, Paşalimanı, and Ekinlik—as well as seventeen mostly uninhabited islands. One of these is Imralı, a prison island that has held the PKK leader Abdullah Öcalan since 1999. These islands are located within Balıkesir province and are most easily accessed from Tekirdağ in Thrace or Erdek on the southern shore of the Sea of Marmara. During the summer, additional ferries operate from İstanbul to Avşa and the Marmara Islands to support tourism.
Other individual islands exist in the Sea of Marmara, such as Koç Adası, located near Tuzla. This island is privately owned by the Koç family, a group of industrialists.
Environmental challenges
The North Anatolian Fault lies beneath the ocean and has caused several major earthquakes, including the Izmit earthquake in August 1999 and the Düzce earthquake in November 1999. The August 1999 earthquake is often called the Marmara Earthquake because its center was under the sea, and many areas most severely damaged by the earthquake and the following tsunami were located along the coast.
On December 29, 1999, a storm caused the Russian oil tanker Volgoneft-248 to split in two in the Marmara Sea, releasing over 1,500 tonnes of oil into the water.
The Marmara Sea is a small inland sea surrounded by major cities in Turkey, including Istanbul, the country’s largest city. Although the sea is small, the area around it is home to about one-third of Turkey’s population. Rapid population growth and uncontrolled building in this region have placed great pressure on the sea. For many years, waste was dumped into the Marmara Sea with little or no treatment, exceeding the sea’s ability to manage it. This led to the disappearance of many sea species, and fishing was banned in the "East Bay" of the Marmara Sea for years because of severe pollution. A major environmental issue in recent years has been mucilage, a thick, sticky substance that appeared for up to six months. The mucilage outbreak began in January 2021 and ended in June 2021. It caused habitat loss, economic problems, and disrupted important ecosystem services, such as fishing.