Rise in temperature linked to wane of ocean food base

ASSOCIATED PRESS

The critical base of the ocean food web is shrinking as the world’s seas warm, NASA satellite data show. The discovery has scientists worried about how much food will grow in the future for the world’s marine life.

The data show a significant link between warmer water — either from the El Nino weather phenomenon or global warming — and reduced production of phytoplankton of the world’s oceans, according to a study in today’s journal Nature.

Phytoplankton are the microscopic plant life that zooplankton and other marine animals eat, essentially the grain crop of the world’s oceans.

“Everything else up the food web is going to be impacted,” said oceanographer Scott Doney of the Woods Hole Oceanographic Institute. “What’s worrisome is that small changes that happen in the bottom of food web can have dramatic changes to certain species at higher spots on the food chain.”

This study and others with real-time data show harmful effects of global warming that can be tallied scientifically, researchers said.

A satellite commissioned by NASA tracked water temperature and the production of phytoplankton from 1997 to 2006. For most of the world’s oceans, when water temperature rose, phytoplankton production decreased and vice versa, said study lead author Michael Behrenfeld, a biological oceanographer at Oregon State University.

As water temperatures increased from 1999 to 2004, the crop of phytoplankton dropped significantly, about 200 million tons a year. An average of about 50 billion tons of phytoplankton are produced yearly, Mr. Behrenfeld said.

Some ocean regions, especially around the equator in the Pacific, experienced as much as a 50 percent drop in phytoplankton production during that period, he said.

However, the satellite first started taking measurements in 1997 when water temperatures were at their warmest because of El Nino, the regular cyclical warming of part of the Pacific Ocean that affects climate worldwide.

After that year, the ocean cooled significantly until 1999 and the phytoplankton crop soared by 2 billion tons during those two years.

“The results are showing this very tight coupling between production and climate,” Mr. Behrenfeld said.

Phytoplankton, which turn sunlight into food, need nutrients such as nitrogen, phosphates and iron from colder water below, Mr. Behrenfeld said. Warmer water at the surface makes it harder for the phytoplankton to absorb those nutrients.

Mr. Behrenfeld said the link between the El Nino changes and phytoplankton production is clear. Scientists warning about climate change have said warmer waters will reduce phytoplankton production and this shows it’s happening, he said.

Other oceanographers agree with the El Nino link but said it is harder to make global warming connections with only a decade of data.

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