Ocean robots installed off the coast of Massachusetts have helped scientists understand a previously unknown process by which warm Gulf Stream water and colder waters of the continental shelf exchange.
(From Eurekalert.org) — The process occurs when offshore waters, originating in the tropics, intrude onto the Mid-Atlantic Bight shelf and meet the waters originating in regions near the Arctic. This process can greatly affect shelf circulation, biogeochemistry and fisheries.
In 2006, scientists using satellite imagery observed an elongated body of warm water from a Gulf Stream warm-core ring intruding along the shelf edge, extending hundreds of miles from Massachusetts towards Cape Hatteras, NC.
“A lot of people were surprised by this,” said Weifeng ‘Gordon’ Zhang, associate scientist at Woods Hole Oceanographic Institution (WHOI), and lead author of the study published today in Geophysical Research Letters. “Normally, the Gulf Stream water, which is very warm and buoyant, doesn’t come in direct contact with the water on the continental shelf, which is much colder. There is a cascade of potential implications that need further study.”
Until now, scientists had been unable to study the phenomenon because satellites can only sense the ocean surface, and no data about the structure of the intrusion water below the surface were available. However, in April 2014, water column data in this area became available from preliminary deployments from the National Science Foundation-funded Ocean Observatories Initiative (OOI). Specifically, autonomous vehicles called “gliders” that collect data along a pre-defined path in the ocean, were deployed at the OOI Pioneer Array site south of Cape Cod. Zhang and his colleagues used preliminary glider data, collected from April through June 2014 and publicly available on the OOI website, to generate the first profile of the complex, layered masses of water at this vital point in the ocean.
“The edge of the continental shelf is a key location where dense, nutrient rich water ‘upwells’ to the surface, stimulating growth at the base of the food web,” said co-author Glen Gawarkiewicz, a senior scientist at WHOI. “This water is normally sandwiched between colder, fresher water on the shelf and warmer Gulf Stream waters offshore. Understanding changes in this region has important societal and economic implications.”
Satellite imagery shows five similar-looking intrusion events have occurred between 2007-2014 in the winter and spring seasons. Zhang and Gawarkiewicz have dubbed the events “Pinocchio’s Nose Intrusions” (PNI) because the warm water intrudes onto the shelf and continues to “grow” for hundreds of miles, moving in the opposite direction from the northeastward movement of the Gulf Stream.
Read the full article here: http://www.eurekalert.org/pub_releases/2015-09/whoi-gsr092915.php