THE SARGASSO Sea, like other mid-ocean regions of the world, is warmer, saltier, bluer, and clearer than most other parts of the North Atlantic.
The prevailing oceanographic wisdom has suggested that such open waters were mostly desert-like, unproductive regions populated by a few smaller plant species।
The prevailing oceanographic wisdom has suggested that such open waters were mostly desert-like, unproductive regions populated by a few smaller plant species।
For two decades, scientists have puzzled over how vast blooms of microscopic plants can form in the middle of otherwise barren mid-ocean regions.
High activity
Now a research team led by the Woods Hole Oceanographic Institution (WHOI) has shown that episodic, swirling current systems known as eddies act to pump nutrients up from the deep ocean to fuel such phytoplankton blooms.
Dennis McGillicuddy, a WHOI oceanographer and leader of the Eddies Dynamics, Mixing, Export, and Species composition (EDDIES) project, found that biological activity was surprisingly high when the ocean was stirred by certain types of eddies.
Natural nutrient source
He and colleagues published their work in the May 18 issue of the journal Science. The team's observations showed oxygen and other biologically important elements being consumed at a higher rate than the theories and models could account for. There had to be some natural nutrient source.
Now, McGillicuddy and colleagues have found that eddy-driven nutrient transport actually primes the ocean's "biological pump," fertilizing the waters with nutrients from the deep, according to a WHOI press release.
Population explosion
Fed by this unusual upwelling, the phytoplankton population explodes and, in turn, attracts more zooplankton and other animals higher up the food chain.
The fate of all of that biomass is also important, as plankton blooms can remove substantial amounts of carbon dioxide from surface waters and sink it to the deep ocean.
The eddies (distinct parcels of water) are formed by differences in ocean temperature and salinity that give water different densities.
On a rotating planet, these different water masses tend to dance around one another rather than mix.
The density inside an eddy can be higher or lower than the surrounding water, like high and low-pressure systems in the atmosphere.
The balance between density and pressure differences, along with earth's rotation (the Coriolis force) gives eddy currents their distinctive clockwise or counterclockwise spin.
The direction of the spin depends on whether the eddy contains cooler "mode water" or a warmer core. In nearly six months of ship-based work in the summers of 2004 and 2005, the researchers employed a combination of remote sensing, video plankton recorders, electronic plankton nets, ocean drifters, tracers, and traditional measurements of water properties and current speeds.
Swirling currents
Working from a long-debated but mostly untested hypothesis, EDDIES investigators measured how these swirling currents can perturb the layers of the ocean and cause an upwelling of nutrient-rich water into the sunlit "euphotic" zone— the top 330 feet (100 metres) that light penetrates.
They started with NASA satellite measurements of sea surface height to locate eddies in the Sargasso Sea, south and east of the Gulf Stream in the North Atlantic.
The 18-member research team then sailed into those eddies with their research vessels.
High activity
Now a research team led by the Woods Hole Oceanographic Institution (WHOI) has shown that episodic, swirling current systems known as eddies act to pump nutrients up from the deep ocean to fuel such phytoplankton blooms.
Dennis McGillicuddy, a WHOI oceanographer and leader of the Eddies Dynamics, Mixing, Export, and Species composition (EDDIES) project, found that biological activity was surprisingly high when the ocean was stirred by certain types of eddies.
Natural nutrient source
He and colleagues published their work in the May 18 issue of the journal Science. The team's observations showed oxygen and other biologically important elements being consumed at a higher rate than the theories and models could account for. There had to be some natural nutrient source.
Now, McGillicuddy and colleagues have found that eddy-driven nutrient transport actually primes the ocean's "biological pump," fertilizing the waters with nutrients from the deep, according to a WHOI press release.
Population explosion
Fed by this unusual upwelling, the phytoplankton population explodes and, in turn, attracts more zooplankton and other animals higher up the food chain.
The fate of all of that biomass is also important, as plankton blooms can remove substantial amounts of carbon dioxide from surface waters and sink it to the deep ocean.
The eddies (distinct parcels of water) are formed by differences in ocean temperature and salinity that give water different densities.
On a rotating planet, these different water masses tend to dance around one another rather than mix.
The density inside an eddy can be higher or lower than the surrounding water, like high and low-pressure systems in the atmosphere.
The balance between density and pressure differences, along with earth's rotation (the Coriolis force) gives eddy currents their distinctive clockwise or counterclockwise spin.
The direction of the spin depends on whether the eddy contains cooler "mode water" or a warmer core. In nearly six months of ship-based work in the summers of 2004 and 2005, the researchers employed a combination of remote sensing, video plankton recorders, electronic plankton nets, ocean drifters, tracers, and traditional measurements of water properties and current speeds.
Swirling currents
Working from a long-debated but mostly untested hypothesis, EDDIES investigators measured how these swirling currents can perturb the layers of the ocean and cause an upwelling of nutrient-rich water into the sunlit "euphotic" zone— the top 330 feet (100 metres) that light penetrates.
They started with NASA satellite measurements of sea surface height to locate eddies in the Sargasso Sea, south and east of the Gulf Stream in the North Atlantic.
The 18-member research team then sailed into those eddies with their research vessels.
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