The Labrador Sea, located in the northern North Atlantic Ocean, is a region where the ocean waters are consistently cooled by dry, cold winter winds coming from northern Canada. The cooled, and therefore dense "Labrador Sea Water" sinks and spreads widely throughout the North Atlantic and beyond, thereby "communicating" changes in the earth's climate to the deep ocean. A current carrying warmer waters flows into the Labrador Sea to balance this lost heat, the Irminger Current, but it is confined mainly to the periphery of the Labrador Sea. Occasionally, eddies containing a core of warm boundary current water, called Irminger Rings, break off and drift into the interior region of the Labrador Sea. Although the location of some of these eddies can be determined from satellite-borne instruments, there are very few actual in situ measurements of where and how they deposit their cargo of warm water into the open sea. Such information is needed to determine the impact of the rings on the heat balance of the Labrador Sea.
New in situ measurements of Irminger Rings will be made using a combination of established and innovative technology. A deep-sea mooring with temperature, salinity and current sensors will be deployed in the path of young Irminger Rings for two years beginning in 2007 to observe their initial vertical and horizontal structure. It is anticipated that ~12 newly formed Irminger Rings will pass over the mooring site based on a census of eddies from satellite observations. Attached to the same mooring will be 12 profiling floats: one float will be released each time an eddy passes the mooring. Trapped in the eddy cores by the ring's strong swirling velocity, the floats will measure changes in their water properties for up to two years. These observations will be combined with satellite data and other in situ measurements to estimate the flux of heat into the interior Labrador Sea, and to verify results from numerical models.
This research will contribute to the advancement of climate science as well as oceanography. The project involves collaboration with Canadian oceanographers and will contribute to international exchange of scientific ideas. Through a pilot program with the Perkins School for the Blind, we will provide an educational experience to a group of students typically underrepresented in the geosciences.
The northern North Atlantic Ocean is a region where the ocean gives up heat to the atmosphere. This warms the air and makes northern Europe and Scandinavia warmer than other land areas at similar latitudes. The heat that is lost from the ocean is replaced by warm currents that carry water northward from lower latitudes. These currents typically run around the perimeter of the northern North Atlantic, so one big unknown is how the warm water in these currents spreads out away from the perimeter and into the ocean interior. One mechanism that has been suggested to be important is the formation of warm-core eddies (large, swirling masses of seawater) along the path of the boundary currents. These eddies have been observed to carry their load of warm water away from the perimeter and into the ocean interior. But not much is understood about how many eddies form, where they go exactly and how they deposit their heat in the ocean interior. In this project, we put in place a deep-sea mooring in the Labrador Sea (between Greenland and Canada) to measure the properties of passing eddies. With its temperature, salinity and current sensors, it saw 12 eddies over a two year period. This is about the number we had predicted based on earlier studies, but we also found that some eddies were so small that they would be hard if not impossible to detect by any other method, such as from space. This means we need to revise our thinking about how many eddies form each year and how we will monitor them in the future. We also learned that the eddies do not have just one "flavor", but that their heat and salt content varies by season. This project also demonstrated the value of using an autonomous platform to release freely drifting buoys in remote areas, where research vessels cannot operate year-round because of severe weather. Twelve drifters were released from the launch platform over two years. We had hoped that these subsurface drifters would end up in the passing eddies, but this proved to be more challenging than expected. Nonetheless, the drifters are contributing to the thousands of similar instruments that are being deployed to monitor the temperature and salinity of the ocean over the entire globe. We will use the experience gained from this project to improve the performance of the launch platform in the future. Finally, this project included a significant outreach program with the Perkins School for the Blind in Watertown, Massachusetts. With funding provided by NSF, the principal investigator (Bower), who is herself legally blind, met frequently with Perkins students and teachers to describe her research and explain how science can be done by blind and visually impaired people. Highlights of the program were the development of an outreach website (www.whoi.edu/projects/OceanInsight) and the participation of a Perkins science teacher on a research expedition to the Labrador Sea.
