This filmmaker went deep into the ocean and filmed what science still struggles to fully understand

The deep sea remains one of the most mysterious and least explored places on Earth. Home to countless unknown species and unexplained natural phenomena, it continues to fascinate scientists and explorers alike. One such mystery—an elusive bioluminescent display known as a “flashback”—has long evaded documentation. Now, filmmaker Jacob Harrell, along with a scientific team from OceanX, has managed to capture this rare light event deep in the Indian Ocean, offering a rare glimpse into a phenomenon that science still struggles to fully understand.

Harrell’s mission took him aboard a state-of-the-art exploration vessel outfitted with the latest oceanographic technology. His primary objective was to film the mysterious flashback phenomenon—an event so uncommon and difficult to record that it has evaded documentation for years. Alongside this task, the team also aimed to contribute to marine biodiversity reports to support the Indonesian government's conservation initiatives.

Flashbacks are a form of bioluminescence, a natural process where living organisms emit light through chemical reactions. According to Mattie, the science program director at OceanXplorer, “When we're talking about flashback, we're talking about bioluminescence in general which basically is animals or organisms that make their own light.”

Understanding Bioluminescence: A Deep-Sea Puzzle

Bioluminescence is relatively rare on land, but in the ocean—especially between depths of 200 to 1,000 meters—it is strikingly common. Harrell noted that approximately 80% of animals living within this range are bioluminescent. This includes various fish, squid, jellyfish, siphonophores, comb jellies, and other water-dominant species, many of which fall under the category of gelatinous zooplankton.

Despite being a well-documented biological capability, the reason behind this light production remains largely speculative. Mattie explained the scientific dilemma: “This one animal might use it for attracting prey, this other animal might use it for escaping or creating a diversion. These other animals might use it as a form of communication. Like, we really don't know because it's so difficult to access the depths of the ocean where bioluminescence occurs.”

The light emitted can vary in color—commonly blue, but also red, green, or violet depending on the species. The glow is produced by a chemical reaction involving an enzyme and a substrate, though the specific compounds may differ between organisms.

The Challenge of Capturing Flashbacks

Documenting flashbacks presented significant technical and environmental challenges. The process requires the activation of strong artificial light beams to provoke a reaction from bioluminescent organisms. However, this intense light can cause organisms to flee or disorient those that are sensitive to brightness, making sightings unpredictable.

Nevertheless, Harrell and his team managed to observe a subdued flashback while stationed at a depth of approximately 375 meters on the ocean floor. With large beams of light radiating through the darkness, they witnessed a fleeting yet visually stunning display of bioluminescence above them.

While the footage only captured a mild version of the phenomenon, it marks a significant step in bringing visibility to one of the ocean’s many unresolved mysteries.