For the past 20 years, NASA satellites have captured stunning white specks on the surface of the Atlantic Ocean. These limestone deposits appear and disappear without any scientist being able to explain why.
The first sightings of white patches amid the deep blue ocean date back to the 1930s. These streaks appear regularly around the Bahamas Banks, limestone platforms that form small islands.
Grains of calcium that come and go without explanation
The composition of these spots was quickly studied: they are tiny grains of carbonate calciumcalcium that float on the surface of the water. However, scientists have never really understood why these calcium deposits surface in abundance at certain times, before disappearing. Many scientists have looked into the question since the first satellite images, which date back to 2003.
A few years ago, some believed that ocean currents were responsible for these deposits, others believed rather that the blooming of phytoplankton triggered their appearance. Despite all the satellite photos, debates about their origin are still ongoing. Because these spots appear and disappear in a mysterious way: if some last only a few days, others resist up to 3 months.
White spots vary unrelated to climate
To try to understand what triggers them, and makes them disappear, the University of Florida studied all the satellite images between 2003 and 2020. They discovered that the majority of the spots appear during the spring and winter. Their size varies from 100 meters to 226 km2with an average size of 2.4 km2the equivalent of 450 football pitches.
In their study published in Remote Sensing of Environmentthe team announces that the total surface of the water on which these spots are distributed has largely increased in 12 years: from 25 km2 in 2003 to 300, even 350 km2 in 2015. Surprisingly, after 2015, this surface regressed, falling again to 25 km2 in 2020. Scientists admit that they have no idea so far what causes the sudden increase and decrease of these spots and the extent over which they are found.
The hypothesis of ocean warming is no longer relevant: because the temperature of the oceans continues to increase with the climate changeclimate changeand yet, the white spots have clearly decreased after 2015. The University of Florida leans rather for a cause mixing water pH, level of salinitysalinity, winds and currents. It is also not impossible that there is a link with living organisms or chemical products, but for now, scientists have still not found the answer to the mystery of the white spots.
