Ocean Ecology and Biodiversity Viewed from Space

Climate models are not the only type of research tool that we use. We also analyze observational data, which help us improve our understanding of the natural world and evaluate the model data. We are particularly interested in the observations of marine phytoplankton, microscopic algae that float freely in the sunlit surface layer of the ocean, because they form the basis of most oceanic food chains and play a very important role in the global carbon cycle, as they absorb CO2 and turn it into organic matter in the process of photosynthesis. A fascinating way to observe phytoplankton is ocean color remote sensing from artificial satellites that orbit the Earth. This is also the only way to get regularly repeated observations of phytoplankton across vast ocean expanses. Phytoplankton pigments (such as the green pigment chlorophyll) and cellular structures interact with sunlight that enters seawater, absorbing some wavelengths of light while scattering other wavelengths. The light that is deflected into space after being in contact with phytoplankton has characteristic properties. When this light meets a sensing device onboard a satellite, its properties are measured and recorded, and can in turn be used to determine various phytoplankton variables, including chlorophyll concentration and biomass.

Most recently, our collaborator Tihomir Kostadinov (University of Richmond) developed a method - based on backscattering of satellite signals - to quantify the biomass of specific groups of phytoplankton that differ in the size of their cells. Low nutrient environments favor smaller phytoplankton, while in high nutrient environments larger phytoplankton dominate, and this affects the organization and functioning of entire regional ecosystems, as well as biogeochemistry.

We are now using the observations of phytoplankton size groups to learn how they vary in response to physical and climate-driven factors.


Percentage contributions of (a) picophytoplankton, (b) nanophytoplankton and (c) microphytoplankton to average total phytoplankton carbon biomass in the surface layer of the ocean over the period September 1997 – December 2010, based on observations from the SeaWiFS satellite. The size ranges in brackets refer to the diameter of phytoplankton cells belonging to a given group, expressed in micrometers (a [µm] is a millionth part of a meter).

Satellite Observations research team:

  • Irina Marinov
  • Postdoc: Anna Cabré
  • Grad student: Priya Sharma
  • Penn undergraduate students: Danica Fine, David Shields, Harry Smith
  • Collaborator: Dr. Tihomir Kostadinov, Univ. of Richmond
  • alumni: Svetlana Milutinović
  • Representative publication:
    Kostadinov, T. S., Milutinović, S., Marinov, I., and Cabré, A.: Carbon-based phytoplankton size classes retrieved via ocean color estimates of the particle size distribution, Ocean Sci. Discuss., 12, 573-644, doi:10.5194/osd-12-573-2015, 2015.