query: What is the Caspian Sea named for?
passage: Caspian Sea
Turkic languages refer to the lake as Khazar Sea. In Turkmen, the name is Hazar deňizi, in Azeri, it is Xəzər dənizi, and in modern Turkish, it is Hazar denizi. In all these cases, the second word simply means "sea", and the first word refers to the historical Khazars who had a large empire based to the north of the Caspian Sea between the 7th and 10th centuries. An exception is Kazakh, where it is called Каспий теңізі, Kaspiy teñizi (Caspian Sea).
passage: Dead Kultuk
It had a distinct coastline in former times, but since the 1990s, with higher Caspian Sea levels, the water penetrates inland through the neck of the bay producing waterlogged marshes. Located at the mainland end of the bay, the Kaydak Inlet cuts deep into the coast extending east and then southwards. Nowadays both the bay and the inlet are filled with Caspian Sea water. Currently there are oil fields in the area.
Owing to its special colour the Dead Kultuk is the bay which appears in early maps of the Caspian Sea as 'Blue Sea' ( in maps in that language). The area was mapped by Fedor Ivanovich Soimonov during the Caspian Expedition, which surveyed the Caspian Sea from 1719 to 1727, but was not accurately described until G. S. Karelin did so in 1832.