Scientists have finally put a name to an ocean phenomenon wreaking havoc on marine life for decades. Marine biologists have witnessed the aftermath of blackout events for years, puzzled over the devastation left behind. With no reliable method of detection, these menacing events slipped through the nets of science, remaining under the radar and masking themselves as various other ocean-climate issues.

Many coastal habitats and regions have experienced episodes of total darkness, in which sunlight availability plummets by at least 50% below normal level so that ocean ecosystems are plunged into near-complete darkness. This dramatic loss of light intensity can be accredited to factors such as precipitation and human impacts. Research has shown a strong correlation between this darkness and large-scale storms and weather events, such as cyclone Gabrielle in February of 2023. Storms cause increased sedimentation, and the over-saturation of nutrients in the water led to an algal bloom, otherwise known as eutrophication . Together, they severely reduced water clarity, welcoming darkness in affected areas.

This phenomenon poses extreme threats to marine life in these habitats — most critically to photosynthetic organisms like algae, sea grasses, and coral who depend on light to function, and to visual predators who depend on light to identify and catch their prey. These dark spells can completely disrupt marine ecosystems, altering behavior, patterns, reproductive cycles, and survival of animals as well as possibly causing mass mortalities, population collapses, and entire ecosystem transformations. They impact a diverse array of ecosystems, including macroalgal forests, tropical coral reefs, seagrass meadows, and kelp forests.

Research biologist Bob Miller and his team of scientists at UC Santa Barbara's Marine Science Institute named these events “darkwaves.” Darkwaves are described by Francois Thoral — post-doc fellow at the University of Waikato and Earth Sciences New Zealand and lead author of the team's research — as “episodic reduction in underwater light.” Darkwave events can last anywhere from a few days to two months. The research team identified between 25 to 85 historically significant darkwave events within a 21-year period. One of the most intense marine darkwaves on record occurred between Dec. 23, 2006 and Jan. 13, 2007, resulting in an 82.15% loss of light in the area compared to baseline conditions. Another case highlights the longest marine darkwave event, lasting from July 26 to Sept. 27, 2007 — a whole 64 days.

Despite the intensity and frequency of these events, Miller’s team realized oceanographic research lacked a universal method to measure and document them. The associated phenotypes of marine darkwaves closely resemble those produced by other more readily measurable environmental conditions such as fluctuations in oxygen levels, temperature, and water pH, allowing them to go wrongly classified for years. Using their accumulated data, the team formulated a quantitative framework to enable proper classification of any future marine darkwave events. This scientific tool is a significant advancement, helping to differentiate between multiple climate conditions.