The ocean turns sour

Greenhouse gases threaten marine ecosystems

By consuming fossil fuels, every person on our planet produces a daily average of eleven kilograms of carbon dioxide which enters the atmosphere. Four kilograms of this amount are absorbed by the world’s oceans, a process alleviating the green house effect. Unfortunately, the carbon dioxide reacts with sea water to produce acid capable of dissolving the calcareous shells of many marine organisms.

A new study, currently published in the scientific journal Nature by a group of 27 marine researchers from Europe, Japan, Australia and the USA and with participation of the Alfred-Wegener-Institute of Polar and Marine Research, demonstrates that the acidification of the oceans in polar regions could lead to the loss of marine organisms within the next fifty to one hundred years – much earlier than previously thought. Sea cucumbers, cold water corals and winged snails in the water column are especially threatened. Since these animals provide important food sources for other animals including crustaceans, salmon and whales, severe impacts on the whole ecosystems must be expected. It is clear that human activities have caused acidification of the ocean; the researchers demand a drastic reduction of green house gas emissions.

The study is based on worldwide measurements of carbon dioxide concentrations in the oceans. “In order to substantiate the predictions, we fed the data into 13 alternative computer models”, explains Prof Reiner Schlitzer of the Alfred-Wegener-Institute. “The results differed slightly among models, but the fundamental outcome was always the same: The oceans turn acid much faster than previously thought.” According to the scientists, this prediction is much more reliable than current climate forecasts, because the uptake of carbon dioxide by the oceans is governed by simple laws of physics, and comparatively few confounding factors need to be taken into consideration.

The computer models show that, with the current rate of increase of carbon dioxide concentration in the atmosphere, it will take only fifty years before the shells of winged snails (Pteropoda) occurring in enormous abundances in the polar oceans, will simply be dissolved. The warmer oceans would follow with some delay. The principle investigator of the study, Prof James Orr of the Laboratoire des Sciences du Climat et de l'Environnement, thinks that “many humans alive today will experience the polar oceans becoming uninhabitable for some of the currently existing key species.“

The shell of winged snails consists of aragonite, a common form of calcium carbonate. Only if sea water is sufficiently saturated with aragonite, the snails can grow their shells. Within the 21st century, according to the researchers’ calculations, aragonite concentrations across the world’s oceans will be sinking rapidly. Apart from the winged snails, sea cucumbers and cold water corals, found predominantly in the North Atlantic, will also be affected. Other than their better known tropical relatives, cold water corals grow very slowly and, at present, are already severely threatened by dragnet fisheries. Should the corals disappear, the whole associated reef community of deep sea fishes, eels, shrimp and other organisms would be lost as well. Other shell-bearing marine dwellers, e.g. the ecologically important calcareous algae which use calcite instead of aragonite for their protective structure, would not be affected at this stage. They would last another fifty to one hundred years until they, too, would meet the same destiny if carbon dioxide emissions continued to rise.


Bremerhaven, September 29th, 2005

Reference: Nature 437 (29th September 2005): 681-686

Contact: Prof. Reiner Schlitzer
Tel. 0471/4831-1559
E-Mail: rschlitzer@awi-bremerhaven.de