Thinking beyond the data: When the sea went dark

What is it about?

Water, whether in seas or lakes, absorbs light strongly in the red end of the visible spectrum, with very little penetrating more than the top few metres. Blue light is absorbed much less, and so drives photosynthetic productivity in these water masses. In contrast, aerosol in the atmosphere preferentially scatters or absorbs blue light compared to red, producing the familiar red skies seen under smoke hazes. This makes the seas especially sensitive to any aerosol loading in the atmosphere, with a much greater reduction in light occurring in them compared to that seen on the land under the same conditions. Using a simple model it was shown that even moderate aerosol loadings could reduce the amount of light in the sea by 48-99% with many affects for life in the sea.

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Photo by Lionello DelPiccolo on Unsplash

Photo by Lionello DelPiccolo on Unsplash

Why is it important?

This is important for three key reasons. Firstly in adds to our understanding of the processes involved during mass extinction events, all of which had very large rates of extinction among marine species. Secondly, given current geo-engineering proposals to inject aerosol in the stratosphere to reduce the effect of global warming, it is critical that we understand the way this might alter the spectrum of light reaching the surface. These geo-engineering approaches may well reduce the productivity of the high latitude oceans, which are critical in the removal of carbon dioxide from the air, as well as being key global ecosystems. Thirdly, industrialization has produced extensive smoke hazes over coastal oceans, which may well be reducing their productivity now.