High carbon dioxide levels turning oceans more acidic

Posted: 23 July 2004

By the middle of this century, the amount of carbon dioxide entering the world's oceans will lead to increasing acidity of the upper layers that may harm marine life and disrupt the food chains, scientists at a UN sponsored intergovernmental symposium have concluded.

Such dramatic changes in the carbon dioxide (CO2) system in open-ocean surface waters have not been observed for more than 20 million years of Earth's history, according to scientists from the world's leading oceanographic institutions.

The accumulations of CO2 will be three times greater in magnitude and 100 times faster than those experienced between ice ages, the marine scientists predict.

Tuna fishing, Favignana, Sicily. Photo: DaniloCedrone/FAO/NOAA
Tuna fishing, Favignana, Sicily. Photo: DaniloCedrone/FAO/NOAA
Tuna fishing, Favignana, Sicily. Increased carbon dioxide in the world's oceans could disrupt marine food chains.© DaniloCedrone/FAO/NOAA
This increase in acidity could disrupt marine food chains and alter ocean biogeochemistry in ways that are not yet understood or predictable, according to research presented at the symposium, which was organized by UNESCO's Intergovernmental Oceanographic Commission (IOC) and the International Council for Science's Committee on Oceanic Research.

The symposium took place in Paris from May 10 to 12. The deliberations of the group and supporting studies were released on Friday.

Carbon build-up

According to research led by Christopher Sabine of the National Oceanographic and Atmospheric Administration (NOAA) in the United States the ocean has taken up approximately 120 billion metric tons of carbon generated by human activities since 1800. His research was published in the July 15 issue of the journal Science.

Carbon dioxide in the Earth's atmosphere is building up as fossil fuels such as coal, oil and gas are burned for power and transportation. The IOC reports that some 20 to 25 million tons of CO2 are being are being added to the oceans each day.

The scientists begin their report on priorities for future research by warning, "The atmospheric concentration of carbon dioxide is now higher than experienced on Earth for at least the last 400,000 years, if not the last several million years, and is expected to continue to rise, leading to significant global temperature increases by the end of this century."

Some governments such as the United States and Australia have been working towards sequestration of some of the atmospheric carbon dioxide in the ocean.

Red Sea Anemonefish. Photo: Thomas Jundt/ICRIN
Red Sea Anemonefish. Photo: Thomas Jundt/ICRIN
Red Sea Anemonefish. Marine life, large and small, could be affected by more acidity in the oceans© Thomas Jundt/ICRIN
All marine life from whales to microscopic organisms may be affected as the oceans become more acidic.

Carbon sequestration

Ocean strategies for sequestering atmospheric CO2 involve enhancing the ocean's natural capacity to absorb and store atmospheric CO2, either by inducing and enhancing the growth of carbon-fixing plants in the surface ocean, or by bypassing the slow, surface-to-deep water transfer of dissolved CO2 by directly injecting it into the deep ocean, the scientists explain. The absorption of carbon dioxide by the oceans is considered a beneficial process that reduces the concentration of CO2 in the atmosphere and mitigates its impact on global temperatures. But there is growing concern over the price of this service.

They caution that the effectiveness and risks of such sequestration have not been thoroughly assessed.

"Even relatively small changes in CO2 concentrations may have large, as yet not completely understood, impacts on marine life and natural biogeochemical cycles of the ocean," they warn.

Symposium participants did not address whether it would be a good policy choice to sequester carbon dioxide in the ocean, but did identify what scientific information is available, and what is still needed, to make informed policy decisions.

Threatened reefs

After hearing presentations on ocean physics, chemistry and biology related to increasing atmospheric and oceanic CO2 levels, and group discussions, the scientists concluded that by 2050 the ocean would be more acidic globally, and would also be more stratified in the high latitudes.

Nutrient concentrations in surface waters of high-latitude regions would be lower, subsurface waters would be less oxygenated, and phytoplankton would experience increased exposure to sunlight, they predict.

They expect many species and biological communities to be affected by these changes.

Rising temperatures - combined with elevated CO2 and increasing acidity - pose a serious threat to coral reefs, possibly leading to the elimination of some reefs by the end of this century, the scientists said.

Gorgonian soft coral on sea fan, Red Sea.
Gorgonian soft coral on sea fan, Red Sea.
Gorgonian soft corals on sea fan, Brothers Islands, Red Sea, Egypt.© Mary Lou Frost/ICRIN
Participants at the symposium stressed that although the impact of climate change on the ocean has been much debated, the direct chemical and biological impact of CO2 itself has largely been neglected.

But changes are "clearly underway and their effects may be large and may seriously destabilise marine ecosystems," the participants concluded.

Their report signals the need for more research and identifies research priorities, in a bid to increase understanding of the changes taking place and their consequences, and to allow for more informed policy decisions in this area.

Source: © Environment News Service (ENS) 2004. All Rights Reserved.

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