The chlorophyll maps show milligrams of chlorophyll per cubic meter of seawater each month. Places where chlorophyll amounts were very low, indicating very low numbers of phytoplankton are blue. Places where chlorophyll concentrations were high, meaning many phytoplankton were growing, are dark green. The observations come from the MODIS sensor on NASA's Aqua satellite. Land is dark gray, and places where MODIS could not collect data (reasons include sea ice, polar darkness, or clouds) are light gray.
The carbon monoxide maps show the monthly averages of carbon monoxide at an altitude of about 12,000 feet, based on data from the MOPITT sensor on NASA’s Terra satellite. Concentrations of carbon monoxide are expressed in parts per billion by volume (ppbv). A concentration of 1 ppbv means that for every billion molecules of gas in the measured volume, one of them is a carbon monoxide molecule. Yellow areas have little or no carbon monoxide, while progressively higher concentrations are shown in orange and red.