Unexplored dephts

Climate change will have massive impacts on the ocean, as marine researchers agree. But even scientists have no clear idea what form such changes will take. “The ocean ecosystem is too complex to be simulated in a model,” says Michael Türkay, head of the marine zoology department of the Senckenberg Research Institute. “Many impacts in biology can only be assessed in retrospect.”

Some changes, however, can already be observed today. Because the temperature of the North Sea has risen, many commercial fish species are moving north. But there is a limit to how far north they can go. Their migratory options are confined to where they find food. “Fish populations are being crowded together,” Türkay says. Because there is no longer enough space for all, fish stocks are dwindling.

“On the whole,” the marine biologist says, “we anticipate a globalisation of fauna. Migration will lead to interbreeding, which will reduce the diversity of species and make the system more susceptible to disruption.” In general terms, biodiversity allows an ecological system to better adapt to change. Türkay admits that he does not know what will happen precisely. “We are groping in the dark.” It is plainly unknown how individual species will react to the changes ahead.

Carbon dioxide (CO2) is a crucial factor in climate-ocean interaction. So far, the oceans have absorbed around a third of the CO2 released by human activity, though their absorption capacity seems to be dwindling (note interview on page 260). Today, single-celled marine algae produce as much oxygen as all of the world’s rainforests together.

Algae require more than just water and CO2 to produce oxygen; they also need nutrients such as nitrate or phosphate. Given an adequate supply of such nutrients, algae become assiduous CO2 consumers, so attempts are being made to store CO2 in the oceans and inject nutrients to stimulate algal growth. It is a clever idea but it has yet to work in practice.

Natural nutrients exist in the oceans’ depths. Currents carry them from the deep sea to the surface. However, such currents will be affected by climate change.

No one can forecast what will happen if major ecosystem parameters change, for instance if the average temperature rises or a link in the food chain disappears. Marine biological models can only depict theoretical ecosystem interactions, because so little is known about the oceans. Although they cover twice as much of the earth as all the continents put together, they are still largely unexplored, especially where the sea bed drops below 1,000 metres. “The only detailed knowledge we have of this huge area is confined to around five square kilometres,” Türkay points out. Which is why, he adds, the German research ministry has now stepped up marine research.

To lend more weight to these issues, government representatives from 80 countries met in May for the first World Ocean Conference. Although its final communiqué contained no concrete resolutions, the six members of a new Coral Triangle Initiative – Indonesia, the Philippines, Malaysia, Timor Leste, the Solomon Islands and Papua New Guinea – at least agreed to protect their coral reefs better and curb overfishing.

Claudia Isabel Rittel