Scanning Electron Microscope (SEM) images of fossilized diatom phytoplankton specimens. The specimens are sampled from salt marsh sediments and help scientists by providing clues to present and past environmental and hydrodynamic characteristics.
Scanning Electron Microscope (SEM) images of fossilized diatom specimens (microfossils). Diatoms are microscopic phytoplankton (algae) that are found in aquatic environments all over the world. Plankton species have preferences for different water and environmental conditions, such as salt or fresh water, attaching to sand or vegetation, or river versus estuary. Therefore, the species of plankton present in a sample provide scientists with information on the present and past environmental and hydrodynamic characteristics of the location where the sample was obtained. Diatoms have a silica "skeleton" called a frustule that preserves in the sediment forming the microfossil seen in these images. Microfossil specimens found on the sediment surface are usually recently deposited, whereas samples found deeper in the sediment represent our Earth's past. The diatoms in this image were sampled from salt marsh sediments. USGS scientists can make comparisons between diatom species found in surface sediments versus those found deep in the salt marsh to understand the impacts of sea level rise and tropical storms on salt marsh ecology.