Gary Lagerloef Profile

Variations in water density help drive ocean circulation. For example, the Gulf Stream carries warm salty water from the tropics to the far north Atlantic. These warm waters modify the climate of northern Europe, making Great Britain and Scandinavia more habitable. As these salty waters reach the far northern Atlantic, they cool and sink due to their increased density. Deep-water currents carry these cold waters throughout the abyss where they gradually warm and return to the surface. Scientists speculate that if the sub-polar waters of the North Atlantic warm due to human-induced climate change, melting ice caps could dilute the water by 0.5 to 1.0  parts per thousand. The water might no longer be dense enough to sink, and the ocean circulation responsible for driving the Gulf Stream could grind to a halt.

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• Movie description (mouse over / select) Ocean Circulation Conveyor Belt Helps Balance Climate
  As part of the ocean conveyor belt, warm water from the tropical Atlantic moves poleward near the surface where it gives up some of its heat to the atmosphere. This process partially moderates the cold temperatures at higher latitudes. As the warm water gives up its heat it becomes more dense and sinks. This circulation loop is closed as the cooled water makes its way slowly back toward the tropics at lower depths in the ocean. If the poles warm, it is possible that melt water from glaciers and the polar ice cap can shut off this circulation and interrupt this circulation system. The melt water is fresher and hence less dense than the ocean water it melts into, and thus the melt water will tend to accumulate near the surface. This layer of fresh water acts as an insulating barrier between the atmosphere and the normal ocean water. The water from the tropics can not release its heat to the atmosphere, and the circulation loop is interrupted. The mechanism has a positive feedback potential in that if the ocean circulation slows, then even less heat will make it to the higher latitudes re-enforcing an effect that will cool the climate at these higher latitudes.
  
  Courtesy NASA/Goddard Space Flight Center Conceptual Image Lab

Although salinity measurements date back over 125 years, the data currently available are spotty, coming mostly over the summer months from ships and buoys. Seventy-three percent of the ocean has been sampled fewer than ten times or has never been sampled at all. The Aquarius satellite will measure the salinity of the top centimeter of all oceans every seven days. It will do so by sensing low-frequency microwaves that respond to the ocean’s electrical conductivity. This conductivity is a function of salinity and water temperature. Scientists will be able to correct for water temperature based on temperature readings other satellites provide. A radar instrument on the Aquarius/SAC-D satellite will correct for wind-caused disturbances along the ocean surface. A separate higher frequency microwave sensor will provide data on rainfall, wind, and sea ice.

As the principal investigator, Gary is working with the engineers at NASA to make sure that the satellite is designed to meet the scientific objectives of the mission. He also must make sure that the project remains on budget and on time. 

Gary says that data the Aquarius satellite provides will help ocean and climate scientists on a number of fronts. For the first time, scientists will be able measure how sea-surface salinity patterns vary from season to season and from year to year. They can observe how salt is transported across the ocean and gain insights into why, for example, the Atlantic Basin is saltier than other ocean basins. Scientists will be able to refine their measurements of rainfall, runoff, and evaporation by observing changes in sea-surface salinity. These improved measurements will strengthen the models linking the ocean and atmosphere.

Scientists also hope to learn the role salinity plays in climate events such as El Nino. El Nino occurs when unusually warm water pools in the eastern Pacific Ocean off the coast of Peru and Ecuador due to the disruption of the normal east to west current. The climatic consequences are far-reaching, ranging from severe droughts in the western Pacific and eastern Africa to unusually heavy rainfall in Peru, Ecuador, and the southern United States. A 2003 study concluded that changes in salinity preceded past El Nino events, and that by measuring salinity, scientists can improve their forecasts of future El Nino events by six to 12 months. 

(latest realtime OSCAR data courtesy NOAA: source)

Gary is also a principal investigator of OSCAR (Ocean Surface Currents Analysis Real-time). He and Fabrice Bonjean of Earth Space Research have developed equations to map ocean currents based on satellite measurements of sea surface elevation and wind speed and direction. The goal of OSCAR is to compile and analyze these data then post real-time information on ocean currents on a web site. Gary says that ocean scientists log onto the site most often, including those who are studying El Nino.  But they are also trying to attract other users, including ship operators and fishery researchers studying how changes in ocean circulation affects the distribution of commercially important fish.

Both Aquarius/SAC-D and OSCAR will provide scientists with more complete information on which to build their models of sea-surface currents and ocean circulation. These models will in turn provide scientists with better insights into the interplay between atmosphere and ocean and how these interactions shape our climate.