Prehistoric marine life extinction may happen again

The possibility of mass mortality in the oceans that happened when the earth experienced a greenhouse effect during Late Cretaceous Period could happen again, researchers warned.

Studying 85 million-year-old layers of ocean bed sediment drilled off the coast of western Africa, professors Martin Kennedy from the University of Adelaide and Thomas Wagner from Newcastle University discovered a significant amount of organic material from marine life buried within deoxygenated layers of the sediment.

According to the geologists, high amounts of carbon dioxide in the atmosphere together with increasing temperature caused hypoxia – or severe lack of oxygen – in the oceans, eventually leading to mass extinction of some life forms.

In the past, according to Professor Kennedy in a press release, "hypoxia in the deep ocean … occurred relatively rapidly – in periods of hundreds of years, or possibly even less – not gradually over longer, geological time scales, suggesting that the Earth's oceans are in a much more delicate balance during greenhouse conditions than originally thought, and may respond in a more abrupt fashion to even subtle changes in temperature and CO₂ levels."

Considering that the amount of carbon dioxide in our atmosphere has doubled in the past 50 years, Kennedy said it is "like hitting our ecosystem with a sledge-hammer' compared to the very small changes in incoming solar energy (radiation) which was capable of triggering these events in the past.”

Thus, he said, "This could have a catastrophic, profound impact on the sustainability of life in our oceans, which in turn is likely to impact on the sustainability of life for many land-based species, including humankind."

"We know that 'dead zones' are rapidly growing in size and number in seas and oceans across the globe," Professor Wagner added. “These are areas of water that are lacking in oxygen and are suffering from increases of CO₂, rising temperatures, nutrient run-off from agriculture and other factors."

On the upside, the geological record studied also showed that a hypoxic phase is naturally followed by improved oxygen concentration in the oceans and the return of marine life. Specifically, the natural processes of carbon burial occur, and soil-formed minerals collect and bury the organic matter dissolved in seawater. This burial of excess carbon ultimately results in the removal of CO₂ from the atmosphere, which results in the cooling of the ocean and the planet.

Professor Wagner explained, "This is nature's solution to the greenhouse effect and it could offer a possible solution for us. If we are able to learn more about this effect and its feedbacks, we may be able to manage it, and reduce the present rate of warming threatening our oceans."

The study, Clay mineral continental amplifier for marine carbon sequestration in a greenhouse ocean by Martin J. Kennedy and Thomas Wagner was published in the May 17, 2011 issue of the Proceedings of the National Academy of Sciences.