In late October 2011, the North Sea sported multiple shades of green. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this natural-color image of the region on October 23, 2011.
The varied shades are likely due to a combination of factors. Near coastal estuaries, sediments probably lend significant color to the water, notes Norman Kuring of the Ocean Color Team at NASA’s Goddard Space Flight Center. “The North Sea is relatively shallow and can be subject to heavy seas and strong tidal currents, so re-suspension of bottom sediments in probably not uncommon, especially after storms.”
Kuring adds that another factor near the coast may be dissolved organic matter, sometimes called gelbstoff. Resulting from decaying bits of once-living organisms, dissolved organic matter can color ocean waters over a wide enough area to appear in satellite imagery.
Farther out to sea, the blue-green shades may result from a mixture of re-suspended sediment and phytoplankton—microscopic marine plants that thrive along coastlines and continental shelves.