NSF Awards Grant to Measure Changes in Ocean Circulation

New $16 Million Project Will Measure Changes in Ocean Waters

Oceanographers from University of Miami, Duke University, and the Woods Hole Oceanographic Institution have received $16 million in grants from the National Science Foundation to deploy a new observing system in the subpolar region of the North Atlantic. The observing system will measure the ocean's overturning circulation, a key component of the global climate system.

Photo: OSNAP will span the Irminger Sea in the North Atlantic Ocean; the sea is known for rough weather. 
Credit: Dan Torres, WHOI

The five-year initiative is part of the $32 million, U.S.-led Overturning in the Subpolar North Atlantic Program (OSNAP). International collaborators include scientists from Canada, the United Kingdom, Germany, France and the Netherlands.

"The program is very exciting, because it provides us with a first opportunity to directly link changes in the intensity of the North Atlantic overturning circulation with the air-sea interaction processes that drive deep water formation," said William Johns, the lead project scientist from the University of Miami. "The program also successfully combines a number of existing national programs into a single observing system. It has taken a lot of work to put it all together, but it has the chance to transform the way we think about and understand the Atlantic overturning circulation."

The overall goal of the program is to simultaneously measure the surface ocean currents that carry heat northward toward the Arctic Ocean, and the deep ocean currents that carry cooler waters southward toward the equator. Together, these currents form the overturning circulation that plays a role in redistributing heat from the equator to the poles. Recent modeling studies have shown a change in strength in this circulation would have a critical impact on temperatures and precipitation in North America, Europe and Africa.

In addition, the OSNAP array affords the opportunity to study how overturning changes impact the environment. OSNAP measurements will facilitate the study of how changes in the northward flow of warm water affects the reduction of Arctic sea ice and the shrinking of the Greenland Ice Sheet.

Duke, Woods Hole and Miami oceanographers, along with their international partners, will deploy moored instruments and sub-surface floats across the subpolar North Atlantic during the summer of 2014. The measurement period will last until 2018.

The array of instruments will stretch along two lines, from Labrador to southern Greenland and from Greenland east to Scotland. The instruments will provide the scientists with continuous measurements of surface-to-bottom water temperature, salinity, and velocities in areas of the subpolar ocean that historically have been under-sampled. Trajectories of the subsurface floats will provide the first look at deep-water pathways in the North Atlantic.

The OSNAP measurement system complements a U.K.-U.S. program that has been measuring the overturning circulation in the subtropical North Atlantic since 2004. Differences and similarities in these measures will provide oceanographers insight into the working of the ocean's overturning.

Overturning measures are also critical for an understanding of the ocean's continued ability to act as one of Earth's most important carbon sinks.

Surface waters absorb heat-trapping carbon dioxide from Earth's atmosphere. When cold, dense south-flowing waters from subpolar regions sink, they carry the surface water – and much of the CO2 it contains – into the ocean's depths, where it is no longer available to heat Earth's climate.

"It is critical that we learn more now about how changes in the overturning circulation affect heat and carbon storage in the oceans, and how these changes might feed back on our future climate, especially in view of the expected decline of the overturning circulation with global warming," Johns said.

The OSNAP program was designed at an international workshop led by Lozier at Duke in April 2010.

Principal U.S. investigators of the new program are Amy Bower, Fiamma Straneo and Robert Pickart, senior scientists in physical oceanography at Woods Hole; William Johns, professor of meteorology and physical oceanography at the University of Miami; and Lozier.

OSNAP will be one of the first projects to make use of the new, NSF-funded Ocean Observatories Initiative's array of moored sensors located in the Irminger Sea, off the southern tip of Greenland.

The OSNAP project is funded by two NSF grants, OCE-1259102 and OCE-1259103.

Note: William Johns is available at (305) 421-4054 or bjohns@rsmas.miami.edu
Susan Lozier is available for additional comment at (919) 681-8199 or mslozier@duke.edu
Amy Bower is available at (508) 289-2781 or abower@whoi.edu