The oceans, as the picture above illustrates, are far from being a uniform blue! The reason is that dissolved substances, chlorophyll from plankton, small grains of rock washed or blown into the ocean, and "yellow material" ( gelbstoffe in German if you want to sound like a Scientist) absorbs and scatters sunlight.
A long-standing interest of mine has been to understand how this fact affects climate and ecosystems. While at the Geophysical Fluid Dynamics Lab, I worked with Whit Anderson to make the absorption of sunlight depend on chlorophyll, observed from NASA satellites. After he had done that, I made him turn the oceans properly blue- the kind of "what if" scenarios one can do with a model.
The results were pretty startling. We found that a perfectly blue ocean would experience what amounts to a permanent El Nino (Anderson et al., 2007). Not only do oceanic phytoplankton produce about half of the oxygen we breathe, they also fundamentally change the distribution of weather around the planet- even influencing the distribution of hurricanes and typhoons (Gnanadesikan et al., 2010).
Recently, my graduate student Grace Kim developed (with very little help from me) a new parameterization of the absorption of sunlight that includes colored dissolved materials. We've found that including this additional source of absorption in our coupled climate model has a significant impact on ocean ecosystems. By making them more light limited-the effect of including absorption is to shift the whole ecosystem closer to the surface, increasing surface biomass and chlorophyll, but also nutrients. Over the water column as a whole, however, biomass decreases, particularly in coastal regions. This work appeared in Biogeosciences (Kim, Pradal and Gnanadesikan, 2015).
A follow-up to this work, published in 2016 (Kim et al. 2016) shows that the additional trapping of sunlight actually leads to more sea ice formation in the Arctic, a highly nonintuitive result! A third paper, (currently in the second round of revisions at Geophysical Research Letters) demonstrates that the presence of colored dissolved organic matter can produce significant shifts in ocean heat ccontent, so that ocean "yellowing" needs to be considered in parallel with changes in greenhouse gasses.
Anderson, W., A. Gnanadesikan, R.W. Hallberg, J.P. Dunne and B.L. Samuels 2007: Impact of ocean color on the maintenance of the Pacific Cold Tongue, Geophys. Res. Lett., 34, L11609, doi:10.1029/2007GL030100.
Gnanadesikan A., K. Emanuel, G.A. Vecchi, W.G. Anderson and R. Hallberg 2010: How ocean color steers Pacific tropical cyclones, Geophys. Res. Lett. 37, L18802, doi:10.1029/2010GL044514.
Kim, G., M.-A. Pradal and A Gnanadesikan, 2015: Quantifying the biological impact of surface ocean light attenuation by colored detrital matter in an ESM using a new optical parameterization, Biogeosciences., 12, 5119-5132.
Kim, G., A. Gnanadesikan and M.A. Pradal, 2016: Increased surface ocean heating by colored detrital matter (CDM) linked to greater Northern Hemisphere sea ice formation in the GFDL CM2Mc ESM, J. Climate, 29, 9063-9076.
Kim, G., A. Gnanadesikan, C.E. del Castillo and M.A. Pradal, Upper ocean cooling in a coupled climate model due to light attenuation by yellowing materials, rev. for Geophys. Res. Lett.