Why are oceans at risk from global warming?

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Why are oceans at risk from global warming?
mongabay.com
February 17, 2008

Climate change is putting the world's oceans at risk by increasing the temperature and acidity of seawater, and altering atmospheric and oceanic circulation, warned a panel of scientists this week at the American Association for the Advancement of Science (AAAS) annual meeting in Boston.

The vastness of our oceans may have engendered a sense of complacency about potential impacts from global climate change, said Jane Lubchenco, a marine biologist at Oregon State University and moderator of the panel. The worlds oceans are undergoing profound physical, chemical and biological changes whose impacts are just beginning to be felt.

Ocean ecosystems are facing new stresses and new combinations of stress, said Gretchen Hofmann, a molecular physiologist at the University of California, Santa Barbara. The water is warmer, circulation patterns are changing in unpredictable ways, and oceans are becoming acidic.

Particularly at risk are coral reefs. Rising temperatures increase the risk of coral bleaching, while elevated carbon dioxide concentrations increase ocean acidity, making it more difficult for corals to form their calcium carbonate structural basis. Coral bleaching occurs when symbiotic algae that provide corals with sustenance are expelled, leaving corals more susceptible to disease and death.

Research published over the past year indicates that PETM climate change helped drive the evolution of modern primates by causing the dispersal of tarsier-like primates across the globe.

Carbon dioxide levels threaten oceans regardless of global warming
Rising levels of carbon dioxide will have wide-ranging impacts on the world's oceans regardless of climate change, reports a study published in the March 9, 2007, issue of the journal Geophysical Research Letters The study, authored by Ken Caldeira from the Department of Global Ecology at the Carnegie Institution at Stanford University and Long Cao and Atul Jain of the University of Illinois, shows the increasing absorption of carbon dioxide is acidifying global oceans, putting sea life at risk.

Coral reefs decimated by 2050, Great Barrier Reef's coral 95% dead
Australia's Great Barrier Reef could lose 95 percent of its living coral by 2050 should ocean temperatures increase by the 1.5 degrees Celsius projected by climate scientists. The startling and controversial prediction, made last year in a report commissioned by the World Worldwide Fund for Nature (WWF) and the Queensland government, is just one of the dire scenarios forecast for reefs in the near future. The degradation and possible disappearance of these ecosystems would have profound socioeconomic ramifications as well as ecological impacts says Ove Hoegh-Guldberg, head of the University of Queensland's Centre for Marine Studies.

We have already lost some 80 percent of the reef corals in the Caribbean over the last three decades, and losses in the Pacific Ocean also are widespread and severe, said Nancy Knowlton, a marine biologist with the Smithsonian Institution. Reefs are like cities, with some parts growing and some parts being destroyed, and only when net growth is positive can reefs persist. These reefs already are under threat to overfishing and local pollution and unless drastic action to reduce greenhouse gas emissions is taken soon, these reefs will cease to exist as we know them.

Increasing ocean acidity is also threatening other organisms, including the base of the ocean foot chain: plankton.

Ocean acidification harms plants and animals that form shells from calcium carbonate, said Scott Doney of the Woods Hole Oceanographic Institution. Calcifying organisms include not just corals, but many plankton, pteropods (marine snails), clams and oysters, and lobsters. Many of these organisms provide critical food sources or habitats for other organisms and the impact of acidification on food webs and higher trophic levels is not well understood."

Newly emerging evidence suggests that larval and juvenile fish may also be susceptible to changes in ocean pH levels. Ocean acidification is rapidly becoming a real problem.

The panelists said that changes in ocean circulation are also having an impact. Jack Barth, an oceanographer at Oregon State University, spoke about hypoxia events that have killed marine life in the Pacific Northwest since 2000.

One of the things we've observed is how wind patterns have changed and greatly affected upwelling, Barth said. Two decades ago, the winds would last for three or four days, and then subside. Now they persist for 20 to 40 days before settling down. This creates significant impacts on upwelling and biological productivity, but these impacts can swing wildly from one extreme to another and have been difficult to predict.

This article is based on a news release from Oregon State University

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