Ocean study alters view of global warming

By measuring nitrogen and phosphorus levels in a sediment core off western Mexico, an international research team led by Edinburgh University's Dr Raja Ganeshram, concludes that climatic change may be a more complex process than was previously thought.

The study is the first to suggest that the oceans are not only losing fixed nitrogen but also phosphorus and that could alter scientists' understanding of how oceanic fertility levels are changing.

Dr Ganeshram's team claims that between the last glacial maximum 22,000 years ago and the present inter-glacial period, the nitrate and phosphate content of the oceans fell by up to 50 per cent and 15 per cent, respectively.

Until now, it was thought that phosphorus levels had remained constant. Any fall in phosphorus or nitrogen levels is significant, because those elements - with carbon - are the basic nutrients required for plant growth.

The study contests the view that rising CO2 levels have been driven solely by the marine nitrogen cycle. It suggests that changes in marine nitrogen and phosphorus cycles produced an N-P ratio greater than that needed for photosynthesis. The changes would have suppressed nitrogen fixation and left the influence of photosynthesis on atmospheric CO2 to be driven by small, slow increases in phosphorus concentration.

Dr Ganeshram continued: ``By comparing data taken from Ice Age samples and those taken from, say 100 years ago, a picture of change begins to emerge. Studies such as ours suggest that global warming will not just affect temperatures, sea levels and the size of polar ice caps, but also the ocean's nutrient levels and ultimately the food chain.''

For further information please contact Dr Raja Ganeshram