Climate Change is Affecting the Color of the Ocean

Climate change has an impact on phytoplankton.  These microscopic marine algae are sensitive to changes in ocean temperature and salinity.   The appearance of color in the ocean is affected by what’s in or not in the water.  Ocean water molecules absorbs all portions of light except for blue which is reflected back.  Areas of barren deep ocean appear dark blue from space.  Phytoplankton contain chlorophyll, which is a pigment that absorbs predominately in the blue portions of sunlight in order to produce carbon for photosynthesis.  In the sunlit layer of the ocean with a high density of phytoplankton, more green light is reflected back, giving the water a dark-green hue.  Green-blue reflectance has been measured by satellites since the late 1990s.

This underwater photo shows how arctic water (left) can be turned green by a bloom of phytoplankton.  Photo: Karen Frey (Clark University) via NASA, 2012.

This underwater photo shows how arctic water (left) can be turned green by a bloom of phytoplankton. Photo: Karen Frey (Clark University) via NASA, 2012.

Researchers from MIT and the University of Southampton recently sought to look at how satellite measurements of reflected light could be used to predict the affect of climate change on phytoplankton.  Using an ocean physics, biogeochemistry and ecosystem model tweaked to incorporate reflected light measurements, the researchers modeled a  global temperature increase of 3 degrees Celsius by 2100 to predict the impact on phytoplankton.  The model predicted that 50 percent of the world’s oceans will shift in color with subtropical regions becoming more blue (and devoid of phytoplankton) while polar regions will become more greener as warmer waters become more hospitable to phytoplankton.


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The Study

Dutkiewicz, S., Hickman, A. E., Jahn, O., Henson, S., Beaulieu, C., & Monier, E. (2019). Ocean colour signature of climate change. Nature Communications, 10(1), 578. https://doi.org/10.1038/s41467-019-08457-x
Dutkiewicz et al.(2019) used the hue angle to quantify true color using values between value between 0° and 360°. From the researchers: "Open ocean values range between green (~100°) where there is high productivity to blue (~230°) in the oligotrophic subtropical gyres. We find a change in the hue angle by up to 10° in some locations and a decrease of up to 5° in others (map b). Map a shows Mean for 1998–2015, and map b visualizes the difference in model 2085–2100 mean and the current day (1998–2015)."

Dutkiewicz et al.(2019) used the hue angle to quantify true color using values between value between 0° and 360°. From the researchers: “Open ocean values range between green (~100°) where there is high productivity to blue (~230°) in the oligotrophic subtropical gyres. We find a change in the hue angle by up to 10° in some locations and a decrease of up to 5° in others (map b). Map a shows Mean for 1998–2015, and map b visualizes the difference in model 2085–2100 mean and the current day (1998–2015).”

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