Magazine article Oceanus


Magazine article Oceanus


Article excerpt

It took only a month for the new Ocean Observatories Initiative (OOI) to reveal insights about shifting ocean circulation patterns that could have major impacts on marine life and fisheries off New England.

Ocean gliders patrolling the OOI Pioneer Array (see Page 50) showed how large masses of warm, nutrient-poor Gulf Stream waters periodically intrude into cooler, shallow waters on the continental shelf. These intrusions disrupt conditions that usually support abundant fish, whales, and other marine life at the shelf break--the dynamic region where the shallow seafloor of the continental shelf begins to slope steeply into the deep ocean.

"The edge of the continental shelf is a key location where nutrient-rich water upwells to the surface, stimulating the growth of the tiny plants and animals that form the basis of the food web," said Glen Gawarkiewicz, a physical oceanographer at Woods Hole Oceanographic Institution. "This upwelling is normally sandwiched along the shelf break--between relatively fresh, cold water flowing south from the Canadian Arctic along the coast, and saltier, warmer waters from the Gulf Stream farther offshore."

But in 2006, scientists using satellite imagery observed an elongated body of warm Gulf Stream water pushing onto the edge of the continental shelf and intruding southwestward along the shelf break. The intrusion grew out of a phenomenon called a warm core ring: a rotating current that eventually pinched off from the Gulf Stream and headed onto the shallower continental slope.

"A lot of people were surprised by this elongated intrusion of warm water," said WHOI physical oceanographer Weifeng 'Gordon' Zhang.

Satellite imagery showed five similar-looking intrusions between 2007 and 2014, each of which lasted weeks to months. Zhang and Gawarkiewicz dubbed these events "Pinocchio's Nose Intrusions." Like that fictional character's elongating proboscis, the warm-water intrusions continued to grow--in their case, for hundreds of miles in a narrow strip from Massachusetts toward Cape Hatteras in North Carolina, moving in the opposite direction of the northeastward-flowing Gulf Stream.

Because satellites can image only the ocean's surface, scientists in 2006 couldn't tell what subsurface processes might be causing the warm-water intrusions, or how deep the warmer temperatures extended. …

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