Plants Dance to the Rhythms of the Ocean


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If you watched a movie of the Earth’s climate history, you would see the ocean frequently plays the role of leading actor. If you observed sea surface temperature across the entire globe, over a span of years you would begin to detect patterns. Of course, since you cannot see heat, you would have to assign colors to represent temperature. What would become immediately obvious to your eye is that the temperature anomalies of El Niño and La Niña occur roughly every 3 to 7 years. These would appear as vast red and blue spikes, respectively, appearing off the west coast of South America and extending westward along the equator across most of the Pacific Ocean.

Watching the movie a little longer, your eye might pick up the fact that there is a long-distance relationship between the equatorial Pacific and the equatorial Atlantic Oceans. Interestingly, and for reasons scientists don’t fully understand, when the southern Pacific is warmer than average the southern Atlantic is cooler than average, and vice versa. These temperature patterns swing back and forth between the two oceans like a pendulum. You might also notice that there is an oscillation in the Northern and Southern Atlantic Ocean, on either side of the equator. One side is cooler than average for a year or two while the other side is warmer than average, then they flip-flop and this pattern continues.

If you watched for a decade or longer, many more recurring patterns would begin to reveal themselves. For instance, you would see that the body of water that extends from the western equatorial Pacific into the eastern Indian Ocean, called the Indo-Pacific warm pool, seems to pulsate. That is, the warm pool expands and contracts in size while its average annual temperatures rise and fall over cycles of about two decades.

The movie has a surprise ending. Perhaps you didn’t notice, but there was another actor onscreen—on the land. Turn your attention to the continents and you will see green waves of vigorous plant growth and creeping brown hues of drought wax and wane across the landscapes as if the world’s vegetation dances in response to the rhythms of the ocean. How can this be? Is there a connection?

Yes, say a team of scientists at NASA’s Goddard Space Flight Center. Led by Sietse Los, terrestrial biologist, the team recently assembled the first long-term global data set that demonstrates there is a connection between changing patterns of sea surface temperature and patterns of plant growth across the Earth’s landscapes. The results of their new study appeared in the April 2001 issue of the Journal of Climate (Los et al. 2001).

next A New Look at an Old Data Set

  images of January SST and NDVI

The above series of images shows changes in sea surface temperature and land plant growth in every January from 1983 to 1989. In the ocean, blue indicates where temperatures are cooler than normal and red is warmer than normal; on land, yellow indicates less vigorous than normal vegetation growth and green shows more vigorous growth than normal. As sea surface temperatures rise and fall, the vegetation in adjacent areas responds. In general, cool ocean water upwind leads to drought and reduced vegetation growth, while warm ocean waters produce excess rainfall and vigorous plant growth. Notice how the vegetation in northern South America responds to water temperatures in the Atlantic Ocean. The corresponding animation shows the effect dramatically.

Images courtesy Marit Jentoft-Nilsen, NASA GSFC Visualization and Analysis Lab, based on data from Sietse Los, University of Wales.