Scientists have noticed a mysterious surge in the appearance of unexplained patches of white water in shallow waters off the coast of the Bahamas, according to a new study based on satellite observations.

For nearly a century, people have been observing these so-called “whiting events,” which usually cover an area equivalent to several hundred football fields, but no one knows the exact cause of the phenomenon. The samples show that the discoloration is caused by fine-grained calcium carbonate.

To shed light on this mystery, researchers from the University of South Florida have compiled the most detailed images of the Bahamas’ whiting events from space, using observations made by NASA’s Aqua satellite between 2003 and 2020.

The team also trained a machine learning tool to analyze the images, which revealed a mysterious increase in whiting events over the past decade, which peaked in 2015, as well as seasonal patterns in these color changes, as reported by the Remote Sensing of Environment journal.

“In a changing climate with decreased pH (i.e., ocean acidification) and increased temperature, one would expect slow, continuous change in whiting events,” said Chuanmin Hu, an oceanographer at the University of South Florida. “The former would lead to decreased events while the latter would lead to increased events, at least according to theory. However, what we observed was truly a surprise with a 10-year episode of increased whiting events.”

In addition to spotting these long-term patterns, the team found a large range of sizes and timeframes for the whiting events. Some patches vanished after a few days, while others stuck around for as long as three months. And while the smallest events cover a mere fraction of a square mile, the white discoloration regularly extended across more than 150 square miles from 2014 to 2015.   

The seasonal and decadal patterns found in the study are certainly interesting, but the origin of these phenomena has not yet been revealed. Although scientists speculate that the phenomenon may be related to sporadic blooms of microorganisms in the ocean or to currents that pull calcium carbonate particles to the surface, these milky splashes in the Bahamas remain an unsolved mystery, at least for now.