Sea of Marmara

The Sea of Marmara is an inland sea entirely within Turkish territory. It connects the Black Sea through the Bosphorus strait to the northwest, while the Dardanelles strait to the southwest connects it to the Aegean Sea and the Mediterranean. For this reason it forms an important part of the waterway separating Europe and Asia.

The sea is elongated, running roughly northeast to southwest; it measures approximately 280 kilometres long and up to 80 kilometres wide, with an area around 11,000 km². The northern coast is home to the city of Istanbul, while the southern and eastern coasts host the gulfs of Izmit and Gemlik near Bursa. Other coastal cities include Tekirdağ, Bandırma and Çanakkale.

Name and islands

The name "Marmara" derives from Marmara Island, from which marble is extracted; the Greek word 'marmaros' means shining stone. Within the Sea of Marmara lie a group of small islands known as the Prince Islands (Adalar), located close to Istanbul, as well as Avşa and Ekinlik islands. Some of these islands are holiday destinations and inhabited areas.

Water structure

The Sea of Marmara has two distinct water layers. The upper layer consists of fresher water flowing in from the Black Sea through the Bosphorus, while the lower layer comprises denser, more saline water originating from the Mediterranean and entering through the Dardanelles. The two layers are separated by a boundary zone (halocline) that prevents water mixing. Maximum depth exceeds 1,000 metres in the central basin.

Seismicity

The North Anatolian Fault runs beneath the sea, making the Sea of Marmara a zone of intense seismic activity. The 1999 Izmit earthquake, which affected the eastern part of the sea, was among the most severe in recorded history. Scientists monitor a section of the fault underlying the sea that has not released accumulated strain for an extended period; this forms the basis for assessing earthquake hazard to Istanbul.

Environment and economy

The sea receives discharge from major cities and factories, and has been degraded by industrial pollution and overharvesting of marine life. In 2021, large quantities of mucilage (organic slime resulting from algal blooms) appeared on the surface, affecting fisheries and tourism; the Turkish government subsequently launched cleanup and monitoring programmes. Economically, the sea is vital for merchant shipping serving the Black Sea, fishing, and passenger ferry services between Istanbul and the southern coast.