Climate Influenced by Deep Ocean Currents and Worsening Acidity

A deep ocean current with a volume equivalent to 40 Amazon Rivers has been discovered by Japanese and Australian scientists in the Indian Ocean sector of the Southern Ocean. This will influence climate, now and in the future. While carbon dioxide emissions that contribute to global warming are also turning the oceans more acidic at the fastest pace in hundreds of thousands of years, the National Research Council reported.

CSIRO Reports (26 April 2010):

In a paper published today in Nature Geoscience, the researchers described the current –more than three kilometres below the Ocean’s surface – as an important pathway in a global network of ocean currents that influence climate patterns.

“The current carries dense, oxygen-rich water that sinks near Antarctica to the deep ocean basins further north,” says co-author Dr Steve Rintoul from the Antarctic Climate and Ecosystems CRC and CSIRO’s Wealth from Oceans Flagship.

“Without this supply of Antarctic water, the deepest levels of the ocean would have little oxygen.

“Mapping the deep current systems is an important step in understanding the global network of ocean currents that influence climate, now and in the future.”

 “The ocean influences climate by storing and transporting heat and carbon dioxide – the more the ocean stores, the slower the rate of climate change. The deep current along the Kerguelen Plateau is part of a global system of ocean currents called the overturning circulation, which determines how much heat and carbon the ocean can soak up.”

While earlier expeditions had detected evidence of the current system, they were not able to determine how much water the current carried. The joint Japanese-Australian experiment deployed current-meter moorings anchored to the sea floor at depths of up to 4500m. Each mooring reached from the sea floor to a depth of 1000m and measured current speed, temperature and salinity for a two-year period. 

“The continuous measurements provided by the moorings allow us, for the first time, to determine how much water the deep current carries to the north,” Dr Rintoul said. The current was found to carry more than 12 million cubic metres per second of Antarctic water colder than 0 °C (because of the salt dissolved in sea water, the ocean does not freeze until the temperature gets close to -2 °C).

“It was a real surprise to see how strong the flow was at this location. With two-year average speeds of more than 20cm per second, these are the strongest mean currents ever measured at depths three kilometres below the sea surface.

“Mapping the deep current systems is an important step in understanding the global network of ocean currents that influence climate, now and in the future.  Our results show that the deep currents near the Kerguelen Plateau make a large contribution to this global ocean circulation,” Dr Rintoul said.

Antarctic waters carried northward by the deep currents eventually fill the deep layers of eastern Indian and Pacific Oceans.

The research team included scientists from the Institute of Low Temperature Science (ILTS) at Hokkaido University in Japan, the Centre for Australian Weather and Climate Research, the Antarctic Climate and Ecosystems Cooperative Research Centre and the Wealth from Oceans National Research Flagship. Funding support was provided by the Australian Climate Change Science Program, the Cooperative Research Centre Program and logistics support from the Australian Antarctic Division.The lead author of the paper is Dr Yasushi Fukamachi, from the ILTS.

CSIRO initiated the National Research Flagships to provide science-based solutions to Australia’s major research challenges and opportunities. The 10 Flagships form multidisciplinary teams with industry and the research community.

Source: www.csiro.au

By Deborah Zabarenko, Environment Correspondent, Reuters (22 April 2010):

WASHINGTON – Carbon dioxide emissions that contribute to global warming are also turning the oceans more acidic at the fastest pace in hundreds of thousands of years, the National Research Council reported on Thursday.

“The chemistry of the ocean is changing at an unprecedented rate and magnitude due to anthropogenic carbon dioxide emissions,” the council said. “The rate of change exceeds any known to have occurred for at least the past hundreds of thousands of years.”

Ocean acidification eats away at coral reefs, interferes with some fish species’ ability to find their homes and can hurt commercial shellfish like mussels and oysters and keep them from forming their protective shells.

Corrosion happens when carbon dioxide is stored in the oceans and reacts with sea water to form carbonic acid. Unless carbon dioxide emissions are curbed, oceans will grow more acidic, the report said.

Oceans absorb about one-third of all human-generated carbon dioxide emissions, including those from burning fossil fuels, cement production and deforestation, the report said.

The increase in acidity is 0.1 points on the 14-point pH scale, which means this indicator has changed more since the start of the Industrial Revolution than at any time in the last 800,000 years, according to the report.

The council’s report recommended setting up an observing network to monitor the oceans over the long term.

“A global network of robust and sustained chemical and biological observations will be necessary to establish a baseline and to detect and predict changes attributable to acidification,” the report said.

ACID OCEANS AND ‘AVATAR’

Scientists have been studying this growing phenomenon for years, but ocean acidification is generally a low priority at international and U.S. discussions of climate change.

A new compromise U.S. Senate bill targeting carbon dioxide emissions is expected to be unveiled on April 26.

Ocean acidification was center stage at a congressional hearing on Thursday, the 40th anniversary of Earth Day in the United States.

“This increase in (ocean) acidity threatens to decimate entire species, including those that are at the foundation of the marine food chain,” Democratic Senator Frank Lautenberg of New Jersey told a Commerce Committee panel. “If that occurs, the consequences are devastating.”

Lautenberg said that in New Jersey, Atlantic coast businesses generate $50 billion a year and account for one of every six jobs in the state.

Sigourney Weaver, a star of the environmental-themed film “Avatar” and narrator of the documentary “Acid Test” about ocean acidification, testified about its dangers. She said people seem more aware of the problem now than they did six months ago.

“I think that the science is so indisputable and easy to understand and … we’ve already run out of time to discuss this,” Weaver said by telephone after her testimony. “Now we have to take action.”

Source: www.alertnet.org