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Climate Change and the Coastal Oceans

The last 30 years has seen a revolution in Earth science. That revolution has been defined by the ability to map the planet from orbiting satellites. NASA satellites have enabled an unprecedented view of Earth’s ocean, mapping everything from sea level ocean surface winds, sea surface temperature, movements of mass associated with glacial ice sheets, and most recently, ocean water salinity. (Top image: Landsat scene of the Great Barrier Reef off the Australian Coast. Credit: NASA/USGS.) 

Scientists use these data to understand the changes taking place in the environment and the impacts of those changes. A major challenge to measuring these impacts has been the application of the technology to map the coastal oceans, where the most significant impacts of climate change are felt. Because of the dominant use of coastal areas for recreation, fisheries, local weather forecasts, and more, accurate maps in those areas are critical.

The Eastern Boundary of the Pacific Ocean is associated with some of the most productive fisheries in the world. One particularly rich fishery is found off the Peruvian Coast, where cold, nutrient-rich water at depth comes to the surface. This process, called upwelling, stimulates the growth of phytoplankton, which leads to a productive and healthy fishery. Climatic events such as El Niño and La Niña, however, can have large effects on the upwelling, thus impacting the fisheries.

During El Niño, warm waters from the western Pacific make their way toward the Peruvian/Chilean Coast, weakening or shutting down the upwelling. This can vastly reduce the quantities of fish and can have devastating consequences on the local economy. During La Niña, in turn, the upwelling may strengthen, bringing even colder water to the surface. These changes can be clearly seen in maps of sea surface temperature and sea level as developed with data from NASA’s TOPEX/Poseidon, Jason-1, and Jason-2 satellites. (Learn more about these and other missions studying the ocean at http://sealevel.jpl.nasa.gov.) 

Current research along the Peruvian Coast has indicated that changes in the strength of the upwelling may be related to long-term changes in climate associated with major shifts in Pacific Ocean temperatures. One way to map the strength of the upwelling is to compare ocean surface temperature changes from one place to another.  The faster the temperature of the ocean changes going away from the coast, the stronger the upwelling. In upwelling regions such as those found along the Peruvian Coast, the temperature of the ocean surface will get much colder as you approach the coast.

Satellites can map the temperature of the ocean in two ways; one is by measuring the amount of heat coming off the ocean surface. NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) instrument onboard NASA’s Terra and Aqua satellites creates maps from sea surface temperature readings taken at one kilometer intervals (although not under cloudy conditions). NASA’s Advanced Microwave Scanning Radiometer – Earth Observing System (AMSR-E) on NASA’s Aqua satellite, can take temperature measurements- regardless of cloud cover, but only every 25 kilometers. Combining information from both of these satellites gives scientists a more complete picture of sea surface temperature conditions.

The figure at left shows the temperature of the ocean surface off the Peruvian/Chilean Coast during the 1997-1998 El Niño. The image at right shows the same for November 2012, a year with normal conditions. Notice the differences. During normal conditions cold water (blue and purple) reaches the surface, indicating healthy upwelling conditions. During the 1997-1998 El Niño, however, warmer waters (in red, orange and yellow), created by the shift of warm water from the Western Pacific to the Eastern Pacific, are a lot more extensive.

The figure at left shows the temperature of the ocean surface off the Peruvian/Chilean Coast during the 1997-1998 El Niño. The image at right shows the same for November 2012, a year with normal conditions. Notice the differences. During normal conditions cold water (blue and purple) reaches the surface, indicating healthy upwelling conditions. During the 1997-1998 El Niño, however, warmer waters (in red, orange and yellow), created by the shift of warm water from the Western Pacific to the Eastern Pacific, are a lot more extensive.

Scientists can also determine sea surface temperature by studying satellite measurements of other characteristics of the ocean surface – such as sea surface height – that are impacted by temperature changes. The images below were developed with data from the OSTM/Jason-2 satellite that shows sea surface height anomalies for the Pacific Ocean, that is a comparison of sea surface height at a given time with average conditions. Since sea-surface height is related to sea surface temperatures, with greater heights indicating warmer temperatures, scientists can use sea surface height measurements to identify large-scale weather patterns, including El Niño. Simply put, warmer waters expand, increasing sea level.

The images above show sea surface height anomalies in for the Pacific Ocean in January and April 2012. Blue shows where the sea level is lower than average, reds show heights that are above average. Click here to learn more. Credit: NASA Earth Observatory.

The images above show sea surface height anomalies in for the Pacific Ocean in January and April 2012. Blue shows where the sea level is lower than average, reds show heights that are above average. Click here to learn more. Credit: NASA Earth Observatory.

One of the future challenges will be to use these types of maps to better understand the impact of climate change along these critical regions of the world’s oceans – a mystery that is yet to be solved.

Post by Jorge Vazquez, oceanographer with the NASA Jet Propulsion Laboratory. Learn more about  how ocean data collected from space helps scientists such as Jorge map land and ocean process on Earth by participating in next week’s Aquarius/SAC-D webinar (in Spanish). 

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