Ocean depth and ice no longer a barrier to climate science

GREENHOUSE 2011 - A climate science research program generating unprecedented volumes of data is about to venture deeper and into previously hidden corners of the world’s oceans to confirm rising ocean temperatures.

Most excess heat being absorbed by the Earth is stored in the oceans, and half of this excess heat has gone into warming the southern hemisphere oceans.

“Within a decade, scientists will begin receiving a three dimensional view of the ocean from the surface to the seafloor, and beneath expanding and retreating sea ice from a new generation of sensor-equipped robots,” says visiting US oceanographer Dr Dean Roemmich.

“In the past 10 years scientists have constructed a 30-nation comprehensive observing system that has altered what we know of the oceans from the surface layer down to 2000 m and the major influences they exert on the global climate system.

"Below those surface layers the scientific ‘dots’ have been sparse but we are now looking at the opportunity to join them together and expand our knowledge of all the ocean processes ­– their deepwater circulation patterns, temperatures and salinity, and the manner in which they can store away carbon and other greenhouse gases.

"Because 90% of the excess heat being absorbed by our planet is stored in the oceans, with comprehensive measurements of ocean temperature we are now able to describe the global pattern of climate warming. Moreover, a finding from our data is that over half of this excess heat has gone into warming the southern hemisphere oceans between about 30S and 60S,” Dr Roemmich said.

Dr Roemmich, from the Scripps Institution of Oceanography was speaking at the national climate change conference, Greenhouse 2011. He jointly leads the ocean robotic research program, called Argo, with an oceanographer from CSIRO’s Wealth from Oceans Research Flagship, Dr Susan Wijffels.

Of interest to Australians, who felt the influence of La Nina through flooding and cyclones earlier this year, Argo measurements are revealing global patterns of temperature and rainfall (from ocean salinity) variability during El Nino/La Nina episodes. Argo data are now being used by operational modelling centres in many nations to improve the prediction of seasonal to inter-annual climate variations including El Nino/La Nina.

Australian science organisations, including: the Integrated Marine Observing System, CSIRO’s Wealth from Oceans Flagship, and the Antarctic Climate & Ecosystem Cooperative Research Centre, have deployed more than 400 Argo profilers since 1999, and are the third largest contributors to the International Argo program.

Dr Roemmich said that with each robotic profiler reporting every 10 days, and some having done so for the past seven or more years, scientists now have access to an unprecedented bank of ocean data that will expand as new sensors are tested and installed in new deployments of profilers. For example, additional oxygen sensors will indicate sub-surface change that has implications for ocean productivity and the security of the food supplied by the oceans.

“We now have a 140-year historical record of ocean temperatures, from the first purely oceanographic voyage by the Challenger in the 1870s through to today with ocean profilers below the surface, and satellites generating constant surface information.

"It is beneath the ice and in those deeper corners of the ocean where we need to be now focussing our attention as engineers and oceanographers,” Dr Roemmich said.

Background information

· The ocean comprises 70 per cent of the world’s surface area.

· Its average depth, calculated by the Woods Hole Oceanographic Institution, is about 3,600 metres.

· 90% of the excess heat being absorbed by our planet is stored in the oceans

· A finding from Argo data is that over half of this excess heat has gone into warming the southern hemisphere oceans between about 30S and 60S

· The ocean is generally layered and includes several water masses, from the surface layer that interacts directly with the atmosphere, to the thermocline where the ocean temperature drops rapidly, to intermediate water masses that are storing significant amounts of carbon, to Antarctic Bottom Water, formed at the edge of the Antarctic continent.

· The flywheel of global climate is found in the series of deep and mid-water ocean currents known as the ocean conveyor belt. The largest of these currents is the Antarctic Circumpolar Current at around 150 times the volume of the Amazon River.

· The composition of gases in the ocean provides a timeframe for scientists to identify when they entered the ocean, and the degree of interchange between water masses.

· Scientists have observed measurable warming of deep ocean temperatures over the last few decades around much of the globe, even into the far reaches of the north Pacific Ocean.

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