Science journal publishes ocean currents discovery

Feb 02, 2007

A research fellow in the University of Wollongong’s School of Earth and Environmental Sciences has headed an international research team that has uncovered major findings regarding the impact of global warming on marine processes.

The research, published today (2 February) in the renowned international journal Science, shows how human induced climate change is having a direct impact on a process known as ‘coastal upwelling’ in northwest Africa.

Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-deplete surface water.

Dr Helen McGregor and her research team from MARUM Research Center Ocean Margins at the University of Bremen in Germany have found that climate induced changes in the ocean have never been more dramatic than in the past three or so decades.

According to their analysis, sea surface temperatures in this part of the Atlantic Ocean in northwest Africa declined by 1.2 degrees Celsius during the 20th century.

Upwelling systems like that off northwestern Africa are of high economical importance. Although they cover less than 1% of the global sea surface, about 20% of global fishing takes place there and they are potentially important for drawing carbon dioxide.

“Our research suggests that upwelling will continue to intensify with future greenhouse warming, potentially impacting the sensitive ecosystems and fisheries in these regions,” said Dr McGregor.

The research team obtained their findings from analysing the ratio of organic compounds in two sediment cores extending back 2500 years, which they drilled off Morocco. The marine sediments archive the region’s climate history from 520 BC to the present day.

The results align with the evidence from upwelling systems in the Arabian Sea.

“The apparent paradox relationship between rising temperatures in the atmosphere and declining sea surface temperatures can be explained easily,” said Dr McGregor.

“Both the increasing wind and the rotation of the Earth cause coastal surface waters to be transported to the open ocean.

"These water masses are then replaced by considerably cooler water being upwelled from deeper oceanic levels. The stronger the greenhouse effect the stronger the cold water pump works – and the cooler the coastal waters off Morocco.”

Because of the importance of upwelling systems, Dr McGregor said is was essential that the sensitive ecosystems were adequately monitored in the future, and added that she and her team were anticipating increased upwelling processes in other areas of the world as global warming and atmospheric carbon dioxide levels increase.