Globe, centred on the Pacific Ocean, showing the effects of an El Nino event on ocean chlorophyll levels, a measure of phytoplankton mass. Chlorophyll levels are measured in milligrams per metre cubed of water and range from 0.01 (dark blue), through light blue and light green to 20 (dark green). El Nino is a warming of surface waters in the tropical eastern Pacific Ocean. The increase in warm water curtails the movement of deepwater nutrients to the surface, and therefore decreases the growth of phytoplankton populations, which are at the bottom of the marine food chain. Data obtained between 1st and 20th October 2015 by the MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Aqua satellite.