Ocean salt level may affect climate on Earth-like planets

 Salt levels of oceans on distant Earth-like planets affect their climates, according to a new study which found that extremely salty or fresh water seas may make a planet more habitable for alien life.

Computer simulations of habitable climates on Earth-like planets have mainly focused on their atmospheres. However, studying their oceans is vital for understanding climate stability and habitability - as on our own Earth.

Until now, researchers had not considered that the seas on Earth-like planets might not be quite like ours - they might be significantly more or less salty than the oceans on Earth.

"The number of planets being discovered outside our solar system is rapidly increasing. Our research helps to answer whether or not these planets could sustain alien life," said David Stevens, from University of East Anglia (UEA) in UK.

"We think that many planets may be uninhabitable because they are either too close or too far from their sun," said Stevens.

"A planet's habitable zone is based on its distance from the sun and temperatures at which it is possible for the planet to have liquid water," he said.

"We wanted to find out what might be happening on other planets which might appear superficially similar to Earth, but where conditions such as salinity are radically different to our own planet," said Stevens.

The research team used computer models of ocean circulation on exoplanets to see what would happen when their oceans had different salinity levels to Earth.

They considered oceans with very low salinity (similar to freshwater), salinity similar to the average value of Earth's oceans, and high salinity (similar levels to the Dead Sea).

"On Earth, we have a circulation where warm water moves towards the poles at the surface, before being cooled, then sinking at high latitudes and travelling towards the equator at depth," said Manoj Joshi from UEA.

"Our research shows that oceans on other planets with a much higher salinity could circulate in the opposite direction – with polar water flowing towards the equator at the surface, sinking in the tropics and travelling back towards the poles at depth," Joshi said.

"We also found a similar pattern emerging for freshwater oceans. Such a circulation scenario might extend the planet's range of habitability," he said.
The study was published in the journal PNAS.