What Turned Turkey's Bosphorus Fluorescent Turquoise?

Turks were concerned their strait had been polluted, but scientists have fingered a tiny culprit for the eye-catching phenomenon

People playing backgammon in a coffee shop by Istanbul's suddenly turquiose Bosporus River, June 14, 2017.
Lefteris Pitarakis/AP

Scientists have explained why Turkey’s Bosphorus Strait suddenly turned fluorescent turquoise this week: an invasion of plankton.

Turks originally feared the strait that flows through Istanbul had been polluted. But NASA tweeted an image on Monday, stating, “Turquoise swirls in the Black Sea. These eye-catching hues indicate the presence of organisms known as phytoplankton.”

On its website, the U.S. space agency wrote: “Phytoplankton are floating, microscopic organisms that make their own food from sunlight and dissolved nutrients. Here, ample water flow from rivers like the Danube and Dnieper carries nutrients to the Black Sea. In general, phytoplankton support fish, shellfish, and other marine organisms. But large, frequent blooms can lead to eutrophication – the loss of oxygen from the water – and end up suffocating marine life.”

At this stage, the presence of the phytoplankton is not seen as cause for concern. The change in color of the sea and river from its normal murky blue can apparently be attributed to a particular type of plankton, known as coccolithophores. NASA explains that these are “microscopic plankton that are plated with white calcium carbonate.” When they gather in large numbers, these microscopic creatures are “easily visible from space as bright, milky water,” adds NASA. Take that, Great Wall of China.

Norman Kuring, an ocean scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said this year’s phenomenon was one of the brightest he has seen in the past five years, although noted that “the May ramp-up in reflectivity in the Black Sea, with peak brightness in June, seems consistent with results from other years.”

People trying to catch fish on a bridge over Istanbul's Golden Horn that leads to the Bosporus, June 13, 2017.
Lefteris Pitarakis/AP
A boat approaching Istanbul's Golden Horn, which leads to the Bosporus Strait, June 13, 2017.
Lefteris Pitarakis/AP

Meanwhile, Ahmet Cemal Saydam – professor of environmental science at Hacettepe University, Ankara – was quoted in The Guardian as telling Turkey’s Dogan news agency that the cause was a surge in the microorganism Emiliania huxleyi (also known as Ehux) – which is a species of coccolithophore.

Saydam also reassured Turks that the event “has nothing to do with pollution,” calling it “a blessing for the Black Sea.”

He even went so far as to deem it worthy of celebration: The presence of the plankton will boost anchovy numbers in the strait, with The Guardian noting that anchovies are a popular supper in Istanbul.

Children jumping into Istanbul's Bosporus River on June 14, 2017.
Lefteris Pitarakis/AP