Jakarta, Indonesia Sentinel — The waters of the Mulut Kumbang Strait in Alor Kecil, East Nusa Tenggara, are home to one of the rarest oceanographic phenomena on Earth, a sudden drop in sea temperature from 28°C (82°F) to just 12°C (53°F) that causes fish to “faint.” The extreme event, known as an Extreme Upwelling Event (EUE), has never been reported anywhere else in the tropics.
According to Achmad Sahri, a senior researcher at Indonesia’s National Research and Innovation Agency (BRIN), the phenomenon occurs when an unusually cold mass of deep-sea water suddenly rises to the surface.
“Normally, temperature drops caused by upwelling in tropical regions are only around two degrees Celsius. But in Alor, we recorded a 10-degree drop within just an hour,” Sahri said on Friday (October 30).
Professor Anindya Wirasatriya, an oceanographer at Diponegoro University, explained that the event coincides with a full-moon spring tide, which triggers rapid vertical water movement.
“This event happens during the spring tide, when vertical currents move at about 0.012 meters per second,” Anindya said. “In addition to the sharp temperature decline, seawater salinity increases from 30 PSU to 36 PSU, indicating that the upwelled water originates from deeper, saltier layers of the ocean.”
He noted that EUEs typically last between one and four days and can occur twice daily, following semi-diurnal tidal cycles. While rare, such events have significant implications for local marine ecosystems.
A unique oceanographic signature
Researchers say the phenomenon in the Mulut Kumbang Strait is globally unique, driven by a combination of local oceanography and underwater topography found nowhere else in tropical waters.
“This EUE is unlike anything seen in other tropical regions,” Anindya said. “It’s triggered by the interaction of tidal currents, deep-sea flow, and the strait’s steep, narrow seafloor topography.”
During high tide, cold deep-sea water flows northward through a narrow underwater channel, while warm Indonesian Throughflow currents move southward. The collision of these opposing flows generates powerful turbulence that pushes frigid water to the surface.
The event typically occurs between August and November, influenced by monsoonal patterns that affect regional currents and sea temperatures. The combination of tides, deep-sea circulation, and unique seabed structure makes the Mulut Kumbang Strait an ideal setting for this extraordinary ocean process.
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Ecological and tourism potential
The extreme cooling has immediate effects on marine life. Tropical fish exposed to the sudden temperature drop experience thermal shock and become temporarily immobile, a moment often seized by local fishermen.
“The event also attracts dolphins and other marine mammals that take advantage of the stunned fish,” Sahri added.
Beyond its scientific and ecological importance, researchers say the phenomenon holds strong potential for eco-tourism and educational travel. Visitors could witness the rare natural event while promoting sustainable conservation.
“People can observe dolphins and marine life safely from the shore without using boats that might disturb their natural behavior,” Sahri said.
