Caspian Sea

Rivers bring water into the Caspian Sea. No river takes water out.

The sun warms the water and some of it goes up into the air. The north part is very shallow. The south part is very deep.

The Caspian Sea sits in a big hollow in the land with no outlet. River water flows in, and the main way out is evaporation. The Volga River brings by far the most water, about 80 to 90 percent of all the river water that arrives.

The sea floor has three parts. The northern part is shallow, only 5 to 10 meters deep. The middle part reaches 788 meters, and the southern part is deepest, at 1,052 meters.

Samant and Prange (2023) describe the Caspian as an endorheic basin whose water budget is set by precipitation, evaporation, groundwater exchange and inflow from about 130 rivers. The Volga, which enters on the northern shelf, contributes about 80-90 percent of the total runoff.

The bathymetry divides the sea into three sub-basins: a shallow northern basin (5-10 m deep), separated by the Mangyshlak sill from a middle basin with a maximum depth of 788 m, which the Apsheron sill separates from the southern basin, 1,052 m deep. NASA notes that the north holds only about 1 percent of the water and averages 5-6 m deep.

The Caspian Sea gets higher and lower over the years.

Right now it is getting lower. In the north, new dry land is showing where water used to be.

Because no river flows out, the Caspian's level goes up and down. In the 1930s it dropped by 1.8 meters, and by 1977 it had fallen about 3 meters in all. Then it rose again until 1995.

Satellites show that it has been dropping since the mid-1990s. NASA pictures from 2006 and 2022 show new dry land along the shallow northern shore, with pale crusts that are likely salt. Research suggests the drop could continue as warmer air makes more water evaporate.

The record has swung both ways: a sharp 1.8 m drop in the 1930s continued slowly until 1977 (about 3 m in total), partly linked to less precipitation over the Volga catchment and to reservoir building on the Volga; the level then rose until 1995. Radar altimetry compiled by NASA's Global Water Monitor shows a decline since the mid-1990s, at about 6-7 cm per year according to Prange and colleagues (2020); Samant and Prange (2023) cite nearly 7 cm a year for 1996-2015 and about 10 cm a year for 2006-2021.

Projections differ. Prange and colleagues report projections of 9-18 m by the end of the century under medium to high emissions, enough to dry out the Kara-Bogaz-Gol Bay; Samant and Prange (2023) give about 8 m (model range 2-15 m) and 14 m (11-21 m) for two emission scenarios and say declines of these sizes would dry out the northern basin completely.

Caspian seals live only in this sea. Mother seals have their pups on the ice in winter.

Fish called sturgeon live here too, and birds live in the shallow north.

The Caspian seal lives nowhere else on Earth, and it is endangered. In winter, ice forms on the shallow northern part of the sea, and that is where the seals raise their pups.

The Caspian is also home to an estimated 90 percent of the world's last remaining sturgeon, NASA says. The shallow north is full of mollusks, crustaceans, fish and birds.

Prange, Wilke and Wesselingh (2020) describe the Caspian seal as an endangered species found only in the Caspian; at least 99 percent of its pupping grounds lie on the northern shelf, where winter sea ice forms (covering 20,000-95,000 km², according to Samant and Prange). The shallow shelf is also a spawning ground for native and endemic fish, including the endangered sturgeons.

NASA notes the northern shallows teem with mollusks, crustaceans, fish and birds. Ramsar sites, wetlands of international importance, are named after Ramsar, a city on the Caspian coast of Iran; the Caspian's protected areas include wetlands such as the Volga Delta.

Caspian beaches can be fun in summer.

Swim only where lifeguards watch, with a grown-up. If the water pulls you, swim along the beach, not against it.

General beach advice from the US National Weather Service is to check the local beach forecast, talk to the lifeguards and swim only where lifeguards are on duty.

Rip currents can form even on calm, sunny days, and NOAA notes they happen on the shores of the Great Lakes as well as on ocean coasts. If one pulls you, don't swim straight back against it. Swim parallel to the shore, then head back to land at an angle.

The US National Weather Service's advice applies to any beach: check the local beach forecast before you go, talk to the lifeguards and swim only at guarded beaches, because rip currents often form on calm, sunny days.

NOAA's National Ocean Service notes that rip currents occur along the shores of the Great Lakes as well as ocean coasts, can move at up to 8 feet (about 2.4 m) per second, faster than an Olympic swimmer, and that swimmers who fight them tire. The advice is to swim parallel to the shore and return at an angle.