Thursday, June 11, 2015

The color of the ocean

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

Deploying the spectroradiometer
Measuring irradiance in the water
Recording the data