Chlorophyll and Currents in the Red Sea
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acquired March 16, 2000 download large image (253 KB, JPEG, 890x890)
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Long and narrow, the Red Sea slices between Africa and the Arabian Peninsula, filling part of the Great Rift Valley, where several tectonic plates are spreading away from one another. Political instability and geographic isolation have limited studies of the Red Sea for decades. Detailed information about annual and seasonal patterns of biological productivity is scarce, particularly in the northern Red Sea. As is often the case in isolated places, satellites can provide scientists with information that is difficult or impossible to acquire from the ground.

This image shows chlorophyll concentrations in the waters of the Red Sea observed by the Sea-viewing Wide Field-of-View Sensor (SeaWiFS) on March 16, 2000. The chlorophyll is present inside single-celled marine plants called phytoplankton, which use the pigment to harvest light for photosynthesis. Places where concentrations of phytoplankton were high are colored yellow. Like the arid terrain surrounding it, the Red Sea is not especially productive. A few patches of blooming plants (yellow swirls) are surrounding by large areas of relatively unproductive waters (blue).

The precise location of the bloom in the northern Red Sea is particularly interesting because it corroborates a model of the water circulation in that area—a model that was proposed a decade ago but not confirmed. According to the model, the circulation in the northern Red Sea includes a pair of northward-flowing currents along each coast. The eastern current (purple arrows) actually rounds the bend along the northern shore and flows southward for a stretch before colliding with the western current (blue arrows). What does that have to do with the phytoplankton bloom pictured in this image?

Because the Red Sea is nutrient poor, blooms of phytoplankton can only occur where the surface waters are infused with a source of nutrients. Nutrient infusions can come from rivers, dust storms, or from the upwelling of deep water in which nutrients accumulate over time. If two currents were colliding in the northern Red Sea, as the model predicted, the turbulence of that collision should create upwelling that would infuse surface waters with nutrients and promote phytoplankton blooms. The high chlorophyll concentrations in this image occur precisely where the model predicts the currents would converge.

A team of scientists at NASA’s Goddard Space Flight Center conducted this research on the Red Sea as a demonstration of Giovanni, a Web-based software tool for displaying and conducting research with satellite data.

    References
  • Acker, J., Leptoukh, G., Shen, S., Zhu, T., and Kempler, S. (2007). Remotely-sensed chlorophyll a observations of the northern Red Sea indicate seasonal variability and influence of coastal reefs. Journal of Marine Systems, [Published Online, March 12, 2007]. doi:10.1016/j.jmarsys.2005.12.006

NASA image created by Jesse Allen, using SeaWiFS data provided courtesy of Jim Acker.

Instrument(s): 
OrbView-2 - SeaWiFS

Chlorophyll and Currents in the Red Sea

September 13, 2007
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