When you imagine life beneath the sea, you’re probably picturing a horizontally bisected image: dark waters on the bottom, clearer, crystal waters at the top, illuminated by the sun. That sunlight filtering down fuels everything from microscopic plankton to towering kelp forests, all of which are either food or shelter for the creatures living in the darker part.
But scientists now say parts of the ocean that should be light are going dark with unsettling frequency.
Researchers have introduced a new concept called “marine darkwaves,” a term for short-term but intense dips in underwater light that can last days to months. Ocean darkening was already known, but it usually occurs over decades. Darkwaves are sudden blackouts triggered by a variety of things — storms, sediment runoff, algal blooms, and human activity like dredging and coastal construction.
Just as you need light to make the packet of seeds you bought at Home Depot bloom into a fruitful tomato plant, the marine life in the ocean needs light to fuel its engines. Take away the light, and photosynthesis grinds to a halt. Ecosystems will start to wobble, and animals that feed and live off underwater plant life, which is pretty much all of them to varying degrees, start to suffer. Until now, researchers didn’t have a consistent way to measure or even identify these extreme events. They didn’t even have a name until recently.
To get the ball rolling so future scientists could have a baseline language and understanding to launch from, researchers analyzed decades of measurements from coastal California and New Zealand and tossed in some satellite data taken from New Zealand’s East Cape, publishing their findings in Communication to Earth & Environment.
They found that between 2002 and 2023, up to 80 marine darkwaves hit that region alone, most lasting about a week or two. They found evidence of one that lasted for more than two months.
A lot of the darkwaves were caused by big storms, like the one caused by Cyclone Gabrielle in 2023, which dumped sediment and pollution into coastal waters. Others were related to deforestation, wildfire debris, and plankton blooms. When the darkwaves were at their worst, they created some of the darkest conditions those marine environments had experienced all year.
The study didn’t directly measure the ecological damage caused by these darkwaves, but previous research shows that even brief light loss can stress out seafloor plant life like kelp and corals. Even a slight disruption in light can throw off the natural rhythms of fish, sharks, and marine mammals. Climate change is only going to, pardon the pun, further muddy both the literal and figurative waters, possibly becoming a regular stressor for coastal ecosystems.
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