The mass extinction of marine life during the Late Cretaceous Period offers a present day warning of what we could experience in the future, if we’re willing to listen.
Using core samples drilled from the ocean bed off the coast of Western Africa, researchers found large amounts of dead marine life buried within deoxygenated layers of sediment.
“Our research points to a mass mortality in the oceans at a time when the Earth was going through a greenhouse effect, with high levels of carbon dioxide in the atmosphere, and rising temperatures, leading to a severe lack of oxygen (hypoxia) in the water that marine animals are dependent on,” said Professor Martin Kennedy from the University of Adelaide’s School of Earth & Environmental Sciences, who along with Professor Thomas Wagner from Newcastle University have been studying oceans that have been depleted of oxygen and suffered from increases in carbon dioxide levels and temperature.
“What’s alarming to us as scientists is that there were only very slight natural changes that resulted in the onset of hypoxia in the deep ocean. This occurred relatively rapidly – in periods of hundreds of years, or possibly even less – not gradually over longer, geological time scales, which suggests 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 than previously thought.”
As is often the case, studies of our planets ancient history has direct relevance for us today. “We know that ‘dead zones’ are rapidly growing in size and number in seas and oceans across the globe,” said Professor Wagner. “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.”
“If you consider that the amount of carbon dioxide in our atmosphere could double over the next 50 years, this will be 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,” Kennedy added. “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.”
Thankfully, there is a glimmer of hope within the geological record, thanks to a natural response to greenhouse conditions.
“After a hypoxic phase, oxygen concentration in the ocean seems to improve, and marine life returns,” said Professor Kennedy. “Our results show that natural processes of carbon burial kick in. Importantly, this rescue comes from the land, with soil-formed minerals acting to collect and bury excess dissolved organic matter in seawater. Burial of that excess carbon ultimately contributes to CO2 removal from the atmosphere, cooling the planet and the ocean.”
“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.”