Earth & Sky

Warming ocean surface threatens marine food chain

Photo by rappensuncle

Researchers say warming ocean surface waters spell trouble for tiny phytoplankton that live at the surface.

In turn, that could mean trouble for all ocean life. Scientists have charted a gradual warming of the ocean surface throughout the world. David Siegel, a professor of marine science at the University of California, Santa Barbara, has found that warmer surface water limits the growth of phytoplankton.

Phytoplankton use carbon dioxide, light, and nutrients to reproduce. The nutrients they need are dredged up from the deeper ocean. But warmer surface water creates greater density in the deep ocean, so it’s harder for wind and currents to bring nutrients from the ocean depths to the surface.

Fewer nutrients mean shrinking phytoplankton populations. In turn, this affects other marine creatures, since these phytoplankton form the base of the marine food chain.

David Siegel: All the food webs, where it goes into the zooplankton that eat the phytoplankton, and the small fishes that eat the zooplankton, the big fishes that eat the small fishes . . . all that’s dependent on how much energy gets put into the food web.

Siegel speculates that as oceans continue to warm up, phytoplankton numbers will continue to drop. What the long–range consequences will be for all ocean life, said Siegel, is still poorly understood.

Thanks today to NASA: explore, discover, understand.

Written by Jeremy Shere

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5 Comments for Warming ocean surface threatens marine food chain

1. 1

   May 31, 06:31 AM #

   Kenneth Crook says:

   Last month a show talked about too much nutrients in the ocean causing algae blooms that are causing dead spots in the ocean. Now a show talks about not enough nutrients in the ocean.
   Maybe the authors should get together and get their scare stories straight.

2. May 31, 06:52 AM #

   Deborah Byrd says:

   Kenneth, does it seem illogical to you that there could be too much algae in some parts of the ocean and not enough in others?

   That doesn’t seem illogical to me.

   Deborah

3. 2

   May 31, 11:49 AM #

   patty g says:

   Plus algae is different from phytoplankton.

4. 3

   Jun 3, 12:23 PM #

   Peter says:

   I am puzzled how warmer surface water increases the density of deep ocean water. Unless between roughly zero and four degrees, doesn’t warming reduce density?

5. 4

   Jun 7, 08:49 AM #

   Han says:

   It meens compared with the surface water, the deeper water’s density is higher.