Link found between rapid Antarctic ice sheet formation and ocean acidity

6 January 2005

An international team of researchers, led by scientists from the Southampton Oceanography Centre and Cardiff University, have shed new light on the nature and speed of ice sheet formation on the Antarctic continent around 34 million years ago.

The largest single glaciation event in Antarctica occurred in two rapid steps, and coincided exactly with an extreme decrease in indicators of ocean acidity, according to the research published today in the journal 'Nature'.

Geologists analysed tiny fossil carbonate shells of foraminifera, animals the size of pinheads living on the sea floor, that record past ocean water temperatures, and the total amount of ice present in the polar ice caps. They say that the speed of glaciation during that period was much faster than previously estimated, and happened at exactly the same time as a big increase in the depth of the so-called submarine carbonate 'snow-line' that marks out the area of sea-floor over which calcium carbonate is deposited, showing that the oceans became less acidic as the world developed a polar icecap.

Lead author, Dr Helen Coxall, said, "Our data show that an increase in carbonate deposition took place an order of magnitude faster in the Pacific than previously published, in the twinkling of a geological eye, and not as a single event but in two 40,000 year steps, separated by an intermediate plateau of 200,000 years."

The work, partly funded by the Natural Environment Research Council, shows how rapidly, in geological terms, major changes in Earth's system can occur.

While ice at the poles may seem natural to us, the presence of large continental ice sheets on our planet is atypical geologically speaking. Earth is widely thought to have been largely ice free for most of the last 150 million years (until the 34 million year event). Large ice-sheets play a major role in controlling global albedo, sea level, ocean chemistry and the movement of gases between air and sea.

Dr Paul Wilson, one of the two co-chief scientists during the expedition, said, "This research is not only concerned with the climate many million years ago. Researching and understanding 'extreme' climate events from the geological past allows us to better tune climate models, to understand present and future events, and the response to perturbations."

The scientists used a correspondence between the measurements from microfossil shells and periodically re-occurring changes of the Earth's orbit around the sun to establish the relative duration of events, stressing the importance of obtaining undisturbed and high-quality sediments from the deep oceans.

All of the authors participated in an international Ocean Drilling Program expedition to the equatorial Pacific in 2001 in order to recover the sediments from close to 5 km below the sea surface, and several hundred meters below the ocean floor.

Research is underway to figure out what links Antarctic glaciation to ocean acidity and to provide additional high-resolution studies of the climate system over more extended periods of time.

Further information

Kim Marshall-Brown
Press Officer
National Oceanography Centre, Southampton
Tel: 023 8059 6170

Dr. Paul Wilson
Corresponding author
Tel: 023 8059 6164

NERC Press Office
Natural Environment Research Council
Polaris House, North Star Avenue
Swindon, SN2 1EU
Tel: 01793 411561
Mob: 07917 557215

Notes

1. The article "Rapid stepwise onset of Antarctic glaciation and deeper calcite compensation in the Pacific", by Helen K Coxall, Paul A Wilson, Heiko Pälike, Caroline H Lear and Jan Backman is published in Nature on 6 January 2005 . Scientists from the University of Rhode Island in the USA and the University of Stockholm in Sweden also worked on this project.

2. The Ocean Drilling Program (ODP), and its successor the Integrated Ocean Drilling Program (IODP) is an international scientific endeavour that supports basic research into the history of the ocean basins, the nature of climate change, the composition and structure of ocean crust and sediments and life that exists beneath the seafloor. IODP conducts technologically advanced ocean drilling expeditions which investigate regions beneath the seafloor that are inaccessible by any other technology.

3. NERC is one of the UK's research councils. It uses a budget of about £300m a year to fund and carry out impartial scientific research in the sciences of the environment. NERC trains the next generation of independent environmental scientists. It is addressing some of the key questions facing mankind such as global warming, renewable energy and sustainable economic development.

Press release: 04/05

Link found between rapid Antarctic ice sheet formation and ocean acidity

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