Emiliania huxleyi, often abbreviated "EHUX", is a species of
coccolithophore with a global distribution from the tropics to subarctic waters. It is one of thousands of different
photosynthetic plankton that freely drift in the euphotic zone of the ocean, forming the basis of virtually all marine
food webs. It is studied for the extensive
blooms it forms in nutrient-depleted waters after the reformation of the summer
thermocline. Like other coccolithophores,
E. huxleyi is a single-celled
phytoplankton covered with uniquely ornamented
calcite disks called
coccoliths (also informally known as liths or scales). Individual coccoliths are abundant in marine sediments although complete coccospheres are more unusual. In the case of
E. huxleyi, not only the shell, but also the soft part of the organism may be recorded in sediments. It produces a group of chemical compounds that are very resistant to decomposition. These chemical compounds, known as
alkenones, can be found in marine sediments long after other soft parts of the organisms have decomposed. Alkenones are most commonly used by
earth scientists as a means to estimate past
sea surface temperatures.