An alteration of seawater chemistry caused by a continental collision 50 million years ago has been linked with past climate changes, researchers say.

"Seawater chemistry is characterized by long phases of stability, which are interrupted by short intervals of rapid change," geoscientist Ulrich Wortmann of the University of Toronto said.

Wortmann and co-author Adina Paytan of the University of California Santa Cruz cite the collision between India and Eurasia about 50 million years ago as one example of an interval of rapid change caused by a change in ocean chemistry.

The collision sped up the dissolution of the most extensive belt of water-soluble gypsum on Earth, stretching from Oman to Pakistan and well into western India, they said.

The dissolving of massive gypsum deposits changed the sulfate content of the ocean, the researchers said, affecting the amount of sulfate aerosols in the atmosphere and thus climate.

"We propose that times of high sulfate concentrations in ocean water correlate with global cooling, just as times of low concentrations correspond with greenhouse [warmer] periods," Paytan said

"Abrupt changes in seawater composition are a new twist in our understanding of the links among ocean chemistry, plate tectonics, climate and evolution," said Candace Major, program director in the Division of Ocean Sciences of the National Science Foundation, which supported the research.