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Big Storms Roil Even the Deep Ocean
1 February 2012 10:17 am
Sebastian the crab may have been wrong about the deep sea. In Disney's The Little Mermaid, the orange crustacean famously touted the tranquility of life well below the waves, singing "it's better down where it's wetter." But the ocean's depths can get stormy, too, researchers say. New observations taken from a canyon in the Mediterranean Sea during an epic storm reveal that surface weather can shake up even the bottom-most ocean habitats.
Of course, it was one big storm. The gale pounded the coast of northeast Spain on 26 December 2008, with winds hitting speeds of more than 70 kilometers per hour, while waves topped off over 10 meters high. In all, residents hadn't seen a tempest that fierce in at least 25 years.
And marine habitats took a beating, too. The storm, for instance, whipped up sand and silt along shallow waters, burying many sea grass beds that are home to a range of fish, invertebrates, and other organisms, and scouring countless others.
Still, whether such a squall could shake up marine communities in deeper water—such as in Blanes Canyon, which juts from the Spanish coast and plumbs depths of up to 1500 meters—hadn't been clear. This time, however, environmental scientist Anna Sanchez-Vidal of the University of Barcelona in Spain and colleagues had a way to find out. The month before the storm, the researchers had lowered equipment for measuring current speeds and traps for collecting debris into the canyon. What they got there was "explosive," Sanchez-Vidal says.
Water rushing along the coast dove into Blanes Canyon at speeds of at least 2.5 kilometers per hour, she says (see video). Under those conditions, Sebastian, or his Mediterranean cousins the red shrimp (Aristeus antennatus), would have suffocated or feasted. The team collected coarse sand--typical of shallower habitats—at the canyon's mid-water mouth, a definite burying hazard. But minute detritus plunged even deeper into the canyon, carrying nutrients such as organic carbon, food for a normally starving ecosystem. The researchers spotted this nutrient in a trap 1200 meters below the sea surface, they report online this month in PLoS ONE. According to their calculations, the storm-borne currents flushed roughly 5500 metric tons of organic carbon into the canyon. In comparison, flooding from the rain-choked Tordera River during the same storm dumped only 40 metric tons of organic carbon into the sea.
It's a classic case of robbing the rich—in this case, the normally nutrient-rich sea-grass beds--to feed the poor, Sanchez-Vidal notes. When a storm hits, these "negative impacts in the shallow water can be positive in the deep sea." Next, she and her colleagues will explore how commonly-fished animals, such as the hand-sized red shrimp, fare following such once-in-a-lifetime jolts of energy.
"It's a really cool paper," says Steve Elgar, an oceanographer at the Woods Hole Oceanographic Institution in Massachusetts. Scientists have tracked currents and even silt into submarine canyons after big storms, but few have followed the carbon, arguably a much more important commodity. Sanchez-Vidal's team put all the pieces together, he says.