© NASA
For almost a century, people have observed these so-called "whiting" events, which typically cover an area equivalent to a few hundred football fields, but nobody knows the exact cause of this phenomenon. Samples show that the discoloration is caused by fine-grained calcium carbonate that floats over the Bahama Banks, which are carbonate structures that surround the archipelago, but it's not clear why the grain clouds sporadically appear in the ocean.
To shed light on this enigma, researchers from the University of South Florida compiled the longest and most detailed space-down view of the Bahama Bank whiting events using observations captured by NASA's Aqua satellite between 2003 and 2020.
The team also trained a machine learning tool to analyze the images, an approach that revealed a "mysterious increase" in whiting events over the past decade, which peaked in 2015, as well as seasonal patterns in these discolorations, according to a recent study in the journal Remote Sensing of Environment.
"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 who co-authored the study, in an email to Motherboard.
"The former would lead to decreased events while the latter would lead to increased events, at least according to theory," he added. "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, an area roughly equivalent to the city of Detroit, Michigan.
Those huge white patches represented the zenith of an overall increase in the total area of the whiting events that occurred from 2003 to 2015. After 2015, the occurrence of such large patches gradually tapered off, reaching an average size of about 10 square miles by 2020.
The seasonal and decadal patterns revealed by the study are certainly tantalizing, but they haven't yet unlocked the origin of the events. Though scientists have speculated that the phenomenon could be related to sporadic flourishing of microorganisms in the ocean, or to currents that drag calcium carbonate particles to the surface, these milky splashes in the Bahamas are still an unsolved riddle, at least for now.
"More field work is required to continuously monitor the ocean properties and processes as well as whiting events in order to have a better understanding," Hu concluded.
