Researchers study currents for clues to ocean ‘weather’
The weather is a little different underwater.
Some things are similar: When scientists study the interaction of currents known as the “internal weather” of the Atlantic Ocean, they find updrafts, downward flows and even cyclones.
But the currents are made of water, not air, so things are different. When was the last time a TV meteorologist talked about a cyclone sucking up plankton?
One group trying to unlock the secrets of ocean “weather” is based at the Virginia Institute of Marine Science in Gloucester Point, Va., near Williamsburg. As part of a larger project run by the Woods Hole Oceanographic Institution in Massachusetts, the researchers are studying how complex water currents affect the smallest aquatic creatures.
The research has implications for fisheries because those animals are at the bottom of the food chain that supports commercially important species. “They are such an integral part of the ocean food web,” said Deborah Steinberg, a professor at the Virginia institute. “We need to understand why they’re distributed the way they are.”
In particular, the scientists are studying formations called “eddies,” which might sound like riffles in a trout stream but are actually the oceanic equivalent of swirling storm cells – cores of cold or warm water, sometimes dozens of miles wide. Just as variations in air pressure cause storm systems in the atmosphere, differences in water temperature and salinity, which alter density, drive such systems underwater.
The researchers work from boats in the Sargasso Sea, an area of the Atlantic near Bermuda. Their first order of business is to find an eddy, which can be a difficult task because they can’t be seen from the surface.
The way to find them is to use satellites that map altimetry – the height of the ocean’s surface at various points. The currents inside an eddy are strong enough that they can actually force the water at its center to move slightly above or below the rest of the ocean.
“It’s weird to think that the ocean is like that,” Steinberg said.
Once an eddy is located, researchers crisscross it in a boat, towing a string of very fine-mesh nets. At specified depths, the nets open and close, capturing a sample of the animals there.
The theory is that eddies – which bring up a kind of dissolved fertilizer from the deep sea – are a great home for algae and attract tiny animals that feed on the algae.
To check the theory, the researchers need to look for a pigment left by the algae in the plankton’s guts. And they can’t very well autopsy an animal the size of a grain of rice.
More brutal methods are needed.
“We freeze them, we mush ‘em up, and then we extract the pigment with a solvent,” Steinberg said.
Beyond learning about the basics of the aquatic food web, the researchers say there could be implications for studying ocean’s role in global warming.
It turns out that, as they eat and excrete, plankton can capture carbon from the carbon dioxide in the air and send it to the bottom of the ocean in tiny fecal pellets.
Steinberg compared this to a “biological pump,” taking a greenhouse gas out of circulation one tiny bit at a time. The hope is that the animals in eddies will provide a window into how the process works.