When you think of the ocean,
you may find yourself envisioning a big blue body of salty water. But the ocean
isn’t just uniformly blue, it’s a hypnotic spectrum of greens and blues, greys
and whites and sometimes even red. The color of the ocean is a function of
what’s is in it and how much – greener oceans are alive with little guys called
phytoplankton, bluer oceans are thought of as lifeless ocean deserts, white
oceans are indicative of coccolithophore blooms, grey oceans are born from extensive
cloud cover, etc. We are working on the ocean optics/ocean color team to
characterize the stuff that influences light propagation in the ocean.
On land, we use satellite
images to detect changes in ocean color, which is linked to changes in how ecosystems
work, and can be applied to a spectrum of questions concerning ocean health.
Satellites detect the reflectance of the oceans at different wavelengths (under
ideal circumstances, 60m deep in clear waters, whoa baby!) and can relate that
to things like chlorophyll concentration and particle size (from 5-50 microns
in diameter). Ground truthing is
critical. This necessitates worldwide cruises to validate the satellite
information and explore the optical properties in greater depth.
On this cruise, we collect
samples to understand the contribution of chlorophyll and other photosynthetic
pigments, colored dissolved organic matter (CDOM), and non-living particles to
light loss in the sun-lit layer of the ocean. In these waters, the top layer
that receives light is about 80m deep, but it will shoal as we move into higher
latitudes and into more productive waters because light is lost more when
there’s more plankton in the water. We also put a radiometer into the ocean
every day around solar noon to measure upwelling and downwelling light
irradiance within the euphotic zone. (top 100m). This is used to calibrate the satellite
measurements and also helps our understanding of how light interacts with
particles in the ocean.
Understanding the dynamics of
the electromagnetic spectrum from the ultraviolet to the infared ‘sheds light’
into the concentration and type of particles that are in our seas, which is
important for ecosystem characterization and understanding the ocean’s critical
role in stabilizing climate. Though it may be strange to think about studying
the ocean from outer space, satellites lend a unique perspective to study our
blue(ish) planet.
By Kelsey Bisson and Erik
Stassinos
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| Deploying the spectroradiometer |
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| Measuring irradiance in the water |
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| Recording the data |
