oceans in manmade peril

YahooLiveScience | One hundred days ago Thursday, the oil rig Deepwater Horizon began spewing oil into the Gulf of Mexico. As profoundly as the leak of millions of barrels of oil is injuring the Gulf ecosystem, it is only one of many threats to the Earth's oceans that, many experts say, could change the makeup of the oceans as we know them and wipe out a large portion of marine life.

The waters of the Gulf were already heavily fished, and the Gulf has been home to an oxygen-depleted dead zone generated by agricultural runoff rich in nutrients.

The Gulf and the rest of the world's waters also face the uncertain and potentially devastating effects of climate change. Warming ocean temperatures reduce the water's oxygen content, and rising atmospheric carbon dioxide is altering the basic chemistry of the ocean, making it more acidic. There is no shortage of evidence that both of these effects have begun to wreak havoc on certain important creatures.

Human beings created these problems, largely in the two centuries since the Industrial Revolution, but for some researchers, they bring to mind the ancient past. The Earth has seen several mass extinctions, including five that annihilated more than half the planet's species. Experts now believe Earth is in the midst of a sixth event, the first one caused by humans.

"Today the synergistic effects of human impacts are laying the groundwork for a comparably great Anthropocene mass extinction in the oceans, with unknown ecological and evolutionary consequences," Jeremy Jackson of the Scripps Institution of Oceanography at the University of California, San Diego, wrote in a 2008 article published in the journal Proceedings of the National Academy of Sciences.