Wednesday, February 15, 2012

Earth pictures from space

From ESA : a southern summer bloom

Microscopic algae create a bright blue in a new photo snapped by a European Earth-observing satellite.

Photosynthesizing micro-organisms called phytoplankton created the figure 8 in the south Atlantic Ocean, about 360 miles (600 kilometers) east of the Falkland Islands.
The European Space Agency's Envisat spacecraft acquired the image on Dec. 2, 2011.

Such oceanic algal blooms are common in the Southern Hemisphere's spring and summer, when upwelling brings minerals from deeper waters to the surface, researchers said.
Phytoplankton depend on these minerals, and the organisms proliferate as a result.

Different types and quantities of phytoplankton produce blooms of different colors, such as the blues and greens seen in the new image.
By analzying such satellite pictures, scientists can monitor blooms and get an idea of the species involved.

Some algal blooms can be toxic, poisoning fish and other marine animals on a large scale.
When they occur in coastal waters, such harmful blooms are often referred to as "red tides," and they can affect fisheries and human health.

Phytoplankton form the base of the marine food chain, and they play a huge role in the removal of carbon dioxide from the atmosphere and the production of oxygen in the world's oceans.
So scientists are keen to monitor these tiny organisms, to get a better idea of ecosystem health and to monitor possible impacts of climate change.

The 8.8-ton Envisat spacecraft, which launched in 2002, is the largest non-military Earth-observing satellite ever built.
The $2.3-billion craft carries a suite of 10 different instruments, with which it monitors the planet's land, oceans, atmosphere and ice caps continuously.

Envisat snapped the new photo with its Medium Resolution Imaging Spectrometer (MERIS), an instrument that measures the solar radiation reflected by Earth.
MERIS images have a resolution of 1,000 feet (300 meters).

From NASA : the Eddy and the plankton

The ocean has storms and weather that rival the size and scale of tropical cyclones.
But rather than destruction, these storms—better known as eddies—are more likely to bring life to the sea...and often in places that are otherwise barren.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured these natural-color images of a deep-ocean eddy on December 26, 2011.
The top close-up shows the vortex structure of the eddy, traced in light blue by plankton blooming in the 150-kilometer wide swirl.
The lower, wider view shows the bloom and eddy in context, about 800 kilometers south of South Africa.

“Eddies are the internal weather of the sea,” says Dennis McGillicuddy, an oceanographer at the Woods Hole Oceanographic Institution.
They are huge masses of water spinning in a whirlpool pattern—either clockwise or counterclockwise—and they can stretch for hundreds of kilometers.
Eddies often spin off from major ocean current systems and can last for months.

In the image above, the anti-cyclonic (counter-clockwise) eddy likely peeled off from the Agulhas Current, which flows along the southeastern coast of Africa and around the tip of South Africa.
Agulhas eddies, or “current rings,” tend to be among the largest in the world, transporting warm, salty water from the Indian Ocean to the South Atlantic.

Certain types of eddies can promote blooms of phytoplankton.
As these water masses stir the ocean, they draw nutrients up from the deep, fertilizing the surface waters to create blooms of microscopic, plant-like organisms in the open ocean, which is relatively barren compared to coastal waters.

In satellite observations of sea surface height and in computer models, eddies appear as bumps or depressions in the ocean, indicating the upwelling or downwelling of water.
They also can be distinguished by higher or lower surface temperatures.

Links :
  • WHOI : the oceans have their own weather systems
  • ScienceMag : Eddy/wind interactions stimulate extraordinary mid-ocean plankton blooms
However, such observations were not available for the eddy depicted above.

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