Warming Oceans Less Hospitable for Plant Life

DEBORAH AMOS, host:

The ocean has been getting bluer, according to a study published today in the journal Nature. But that's not really good news for the planet. It means that the plants that tinge the ocean green aren't doing so well. Scientists say that's because the ocean has been getting warmer.

NPR's Richard Harris reports.

RICHARD HARRIS: When you picture green plants in your head, Michael Behrenfeld at Oregon State University says chances are you're thinking of grasses, trees, and shrubs.

Professor MICHAEL BEHRENFELD (Botany, Oregon State University): When you stand on the beach and look at the ocean, I mean the first thought that usually doesn't come to mind is plants. But in fact that surface layer that you look at is just loaded with, you know, trillions upon trillions of plants.

HARRIS: Those plants play a critical role in how the earth breathes. These ocean plants, phytoplankton, suck up carbon dioxide and release oxygen into the atmosphere. In order to see how this important plant life is doing, scientists have been spying on it by satellite. Gene Feldman at NASA says it's really quite straightforward. All they need to do is to measure the color of the water precisely.

Mr. GENE FELDMAN (Oceanographer, NASA): The less phytoplankton in the water, the bluer it is. The more phytoplankton in the water, the greener it is. And you can actually detect this greenness from space.

HARRIS: Feldman, Behrenfeld and colleagues, now report that the earth's hues have been changing over the past 10 years. For a few years in the late 1990s, the ocean got dramatically greener. But since then it's been gradually turning a deeper shade of blue. Behrenfeld says that the color change has coincided with the significant warming of ocean water. Warmer oceans are hard on phytoplankton.

Prof. BEHRENFELD: When I first started looking at the data, I was really surprised at just how strong these relationships were. I expected to see a relationship, but I was amazed that nearly all of the variability we saw could be attributed to changes in climates.

HARRIS: Just why this happens makes sense to Behrenfeld.

Prof. BEHRENFELD: So essentially what happens is that as water warms, it becomes lighter or less dense, and it floats essentially above the deep, cold, dense water.

HARRIS: Unfortunately for the phytoplankton, that deeper water contains minerals and nutrients they need to grow. So warm surface waters deprive phytoplankton of vital nourishment. Paul Falkowski at Rutgers University says that's bad news for the entire food chain, which depends on phytoplankton, the grass of the sea.

Mr. PAUL FALKOWSKI (Marine Sciences, Rutgers University): Well, the long term implications are that there will be a reduction in fisheries, for example, and resources that humans use from the ocean.

HARRIS: Falkowski is also concerned what this means for ocean chemistry. These phytoplankton help produce the amount of carbonic acid in the ocean.

Mr. FALKOWSKI: This type of chemical will erode calcium carbonate, the stuff that corals and many, many of the other shells of marine organisms are made out of.

HARRIS: Scientists say the ocean is already getting more acidic. Falkowski says if the ocean warming continues as many climate scientists predict, that will mean less phytoplankton and more rapid acidification of the seas.

Richard Harris, NPR News. Transcript provided by NPR, Copyright NPR.