15 December 2025 news

Akvaplan-niva led an international project that gathered a unique and likely last-of-its-kind multi-year dataset from Lake Urmia, the Middle East’s largest hypersaline lake—now on the brink of disappearing. These measurements, the first and possibly the last detailed instrumental observations of a centuries-old lake, provide rare insight into how an extreme saline system behaves in its final stages.

Dr. Peygham Ghaffari, senior scientist and project manager at Akvaplan-niva, explains:

“Our data show that Lake Urmia operates under a dual mixing regime driven almost entirely by salinity. In warm months, the lake becomes polymictic, repeatedly mixing throughout its depth, while in colder months it shifts into inverse meromixis, forming stable layers that resist circulation. This layering is reinforced by remarkably sharp vertical gradients, including a thermocline only a few centimetres thick, where temperature and salinity change abruptly and lock the water column into place.”

The research team also discovered that extreme hypersalinity produces effects strikingly similar to ice cover in Arctic lakes. Just as ice suppresses vertical exchange, Urmia’s salinity effectively “freezes” circulation, isolating stratified layers even without actual ice. To capture this distinct behavior, the authors introduce a new classification—hyperhalimictic lakes—describing systems where salinity, rather than temperature, governs mixing and stability.

As Lake Urmia edges toward possible disappearance, these observations preserve a rare scientific record of how a major hypersaline lake functioned under extreme stress—a snapshot future generations may never be able to observe directly.More details in the published article:

https://www.sciencedirect.com/science/article/pii/S2214581825005269