NASA's Operational Land Imager aboard Landsat 8 recently captured an image of a gigantic swirling phytoplankton bloom in the Baltic Sea's Gulf of Finland. The massive 'whirlpool' of algae is larger than Manhattan Island (a ship is visible for scale). There is no explanation for what's causing the strange pattern. According to NASA, an ocean eddy may be pumping nutrients up from the depths. In recent years, "dead zones" have also accompanied the spread of such algae blooms in the Baltic Sea.