The seabed in the south reaches 1,023 m (3,356 ft) below sea level, which is the third-lowest natural non-oceanic depression on Earth after Baikal and Tanganyika lakes.

It is predicted that during the 21st century, the depth of the sea will decrease by 9–18 m (30–60 ft) due to global warming and the process of desertification, leading to an ecocide.

The Caspian Sea was a comparatively small endorheic lake during the Pliocene, but its surface area increased fivefold around the time of the Pliocene-Pleistocene transition.

The Garabogazköl lagoon, which dried up when water flow from the main body of the Caspian was blocked in the 1980s but has since been restored, routinely exceeds oceanic salinity by a factor of 10.

The Middle–Southern boundary is the Apsheron Threshold, a sill of tectonic origin between the Eurasian continent and an oceanic remnant,[26] that runs through Chilov Island and Cape Kuuli.

The Caspian has several small islands, primarily located in the north with a collective land area of roughly 2,000 km2 (770 sq mi).

In the North Caspian, the majority of the islands are small and uninhabited, like the Tyuleniy Archipelago, an Important Bird Area (IBA).

The island of Vulf off Baku, for example, has suffered ecological damage as a result of the petrochemical industry; this has significantly decreased the number of species of marine birds in the area.

[34] The high concentration of mud volcanoes under the Caspian Sea were thought to be the cause of a fire that broke out 75 kilometers from Baku on July 5, 2021.

The principal limiting factors to successful establishment of plant species are hydrological imbalances within the surrounding deltas, water pollution, and various land reclamation activities.

About 11 plant species are found in the Samur River delta, including the unique liana forests that date back to the Tertiary period.

[40] Since 2019 UNESCO has admitted the lush Hyrcanian forests of Mazandaran, Iran as World Heritage Site under category (ix).

[33] Archeological studies of Gobustan Rock Art have identified what may be oceanic species including cetaceans from baleen whales to dolphins,[43][44] and auks most likely Brunnich's Guillemot,[43][45] although the rock art on Kichikdash Mountain which is assumed to depict either a beaked whale or a dolphin,[43][45] it may represent the famous beluga sturgeon instead due to its size (430 cm in length).

This is supported by the existences of current endemic, oceanic species such as lagoon cockles which was genetically identified to originate in the Caspian and Black Seas regions.

[42] Other examples of endemics are four species of Clupeonella, Gobio volgensis, two Rutilus, three Sabanejewia, Stenodus leucichthys, two Salmo, two Mesogobius and three Neogobius.

The high price of sturgeon caviar—more than 1,500 Azerbaijani manats[33] (US$880 as of April 2019[update]) per kilo—allows fishermen to afford bribes to ensure the authorities look the other way, making regulations in many locations ineffective.

In the late Pontian stage, a mountain arch rose across the south basin and divided it into the Khachmaz and Lankaran Lakes (or early Balaxani).

English traders Thomas Bannister and Jeffrey Duckett described the area around Baku as "a strange thing to behold, for there issueth out of the ground a marvelous quantity of oil, which serveth all the country to burn in their houses.

The world energy markets were influenced by Azerbaijan and Kazakhstan, as they became strategically crucial in this sphere, thus attracting the largest share of foreign direct investment (FDI).

Iran has an estimated 988.4 trillion cubic feet of natural gas, around 16 percent of world reserves, thus key to current paradigms in global energy security.

[65] Russia's extensive mineral and energy resources are the largest such reserves in the world,[66] making it the second leading producer of oil and natural gas globally.

The first Caspian Economic Forum was convened on August 12, 2019, in Turkmenistan and brought together representatives of Kazakhstan, Russia, Azerbaijan, Iran and that state.

In 1873, exploration and development of oil began in some of the largest fields known to exist in the world at that time on the Absheron Peninsula near the villages of Balakhanli, Sabunchi, Ramana, and Bibi Heybat.

[73] Many of the islands along the Azerbaijani coast retain great geopolitical and economic importance for demarcation-line oil fields relying on their national status.

In 1998, Dick Cheney commented that "I can't think of a time when we've had a region emerge as suddenly to become as strategically significant as the Caspian.

These projects would allow Western markets easier access to Kazakh oil and, potentially, Uzbek and Turkmen gas as well.

[75] However, analysts note that the pipelines would bypass Russia completely, thereby denying the country valuable transit fees, as well as destroying its current monopoly on westward-bound hydrocarbon exports from the region.

Access to the Volga is key for market efficiency and economic diversity of the landlocked states of Azerbaijan, Kazakhstan, and Turkmenistan.

There are similar tensions between Azerbaijan and Turkmenistan (the latter claims that the former has pumped more oil than agreed from a field, recognized by both parties as shared).

The Caspian littoral states' meeting in 2007 signed an accord that only allows littoral-state flag-bearing ships to enter the sea.