Caspian Sea Salinity

The Caspian Sea exhibits significant salinity variations across its vast basin, with current average levels around 12.8 parts per thousand (ppt) but showing concerning increases in recent years due to accelerating water loss.britannica​

Current Salinity Levels and Spatial Distribution

The Caspian's salinity demonstrates marked spatial heterogeneity:

Average Conditions: The open sea maintains an average salinity of approximately 12.8 ppt (12.8‰ or 12.8 g/L), roughly one-third the salinity of typical ocean water (35 ppt). This relatively low salinity reflects the sea's status as an endorheic basin receiving substantial freshwater inflow.wikipedia+1​

Regional Variations:

• Northern Basin: Salinity averages 9.28 ppt, dropping to less than 1 ppt near the Volga River outlet where freshwater influx is greatestiranicaonline​

• Central Basin: Approximately 13 ppt throughout the water columniranicaonline​

• Southern Basin: Slightly higher at 13.1 ppt, increasing marginally with depthiranicaonline​

• Eastern Coastal Areas: Particularly saline due to high evaporation rates and limited freshwater inputiranicaonline​

Extreme Salinity Zones

The Kara-Bogaz-Gol lagoon on the eastern coast represents one of Earth's largest hypersaline reservoirs, with salinity ranging from 270-300 g/L (270-300 ppt)—approximately 10 times oceanic salinity. This extreme concentration results from restricted water exchange with the main Caspian basin and intense evaporation in the arid coastal environment.savethecaspiansea+1​

Recent Salinity Increases

The ongoing water level crisis is driving significant salinity escalation:

• Current Trend: Salinity has increased from the historical average of 12.8 ppt to 14-15 ppt in many areaswanaen​

• Primary Driver: The 15-20% reduction in Volga River inflow combined with accelerated evaporation concentrates dissolved salts in the shrinking water volumewanaen​

• Projection: Continued water level decline will further concentrate salts, threatening sturgeon populations and broader aquatic biodiversitywanaen​

Vertical Stratification

In deep water areas, salinity shows minimal vertical variation, increasing only 0.1-0.2 ppt from surface to bottom. The density stratification depends more on temperature changes than salinity gradients in the open sea. However, near river mouths, sharp salinity gradients occur horizontally rather than vertically.copernicus​

Seasonal Variations

Salinity fluctuates seasonally, particularly in the northern basin:

• Summer: Heavy spring freshwater influx from tributary rivers significantly reduces salinityiranicaonline​

• Winter: Salinity rises again as river flow decreases and ice formation concentrates remaining saltsiranicaonline​

• Central and Southern Basins: Experience only slight seasonal variations due to more stable conditionsiranicaonline​

Ecological Implications

The increasing salinity threatens the Caspian's unique ecosystem:

• Sturgeon Populations: Particularly vulnerable to salinity increases beyond their tolerance rangeswanaen​

• Coastal Economies: In northern Iran, retreating shorelines (300-500 meters) combined with salinity changes are projected to reduce the southern Caspian coastal economy by 25-35%wanaen​

• Drinking Water Quality: Saltwater intrusion into freshwater aquifers is degrading drinking water quality in coastal citieswanaen​

The salinity changes represent a critical component of the broader environmental transformation affecting the world's largest inland sea, with implications extending far beyond simple water chemistry to regional economies, food security, and biodiversity conservation.

1. https://www.britannica.com/place/Caspian-Sea
2. https://en.wikipedia.org/wiki/Caspian_Sea
3. https://www.iranicaonline.org/articles/caspian-sea-i/
4. http://savethecaspiansea.com/tpost/aayryngfa1-advances-in-environmental-monitoring-of
5. https://wanaen.com/caspian-sea-on-the-brink-of-an-irreversible-crisis/
6. https://os.copernicus.org/articles/6/311/2010/os-6-311-2010.pdf
7. https://pmc.ncbi.nlm.nih.gov/articles/PMC6202737/
8. https://www.naturalhistorymag.com/features/112161/fate-of-the-caspian-sea
9. https://www.reuters.com/sustainability/climate-energy/azerbaijan-sounds-alarm-over-shallowing-caspian-sea-2025-08-21/
10. https://www.sciencedirect.com/science/article/pii/S0277379107002624