Hurricanes churn up life-nurturing brews

Images of the North Atlantic taken from orbit suggest that hurricanes churn the ocean’s surface enough to bring cool, nutrient-rich waters to the surface, thereby stimulating algal blooms that can last for weeks.

Some areas of the ocean don’t support much surface life because the water lacks one or more of the nutrients required by marine microorganisms called phytoplankton, which are at the base of the sea’s food chain. In many cases, however, those nutrients lie just a few dozen meters below the ocean surface. One such region with subsurface supplies of nutrients such as nitrates and phosphates is the Sargasso Sea, says Steven M. Babin of Johns Hopkins University’s Applied Physics Laboratory in Laurel, Md. This continent-size expanse of ocean lies east of Bermuda.

When Babin and his colleagues looked at orbital images of the Sargasso Sea taken from 1998 to 2001, they found increases in the average chlorophyll concentration at the ocean’s surface along the paths of all 13 hurricanes that had passed through the region. Chlorophyll is the chemical that phytoplankton use to capture energy from light, so concentrations are a measure of the organism’s abundance.

Peak chlorophyll concentrations in those blooms jumped between 5 and 90 percent after a hurricane’s pass and didn’t return to normal for up to 3 weeks, Babin and his team report in the March 15 Journal of Geophysical Research (Oceans).

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