THINGS YOU NEED TO KNOW ABOUT OCEAN ACIDIFICATION
Article – Super Greenhouse Events
Dr Matt Edmunds, Australian Marine Ecology.
In the ancient past, back when dinosoars roamed the land and the continents had just started to drift apart, there were ‘super’ green house events. These were runaway events causing extreme changes to the shallow seas. The warmer conditions stimulated blooms of microscopic algae, enriched by nutrients from land runoff and higher concentrations of carbon dioxide dissolving into the seas from the atmosphere, turning waters into a pea-green soup. These blooms produced a rain of organic material into deeper waters. On the way down, bacteria would start decomposition of the organic matter, using up much of the oxygen in the process. Deeper down, where there was very little oxygen, especially adapted bacteria continued the decomposition process, but produced toxic hydrogen sulphide as a by-product of surviving with little oxygen. This was toxic to most animals. Below this toxic zone, there was no oxygen and very little that lived – a dead zone where organic material fell to the seabed stayed there, undisturbed. Normally, our deep seas are irrigated by oxygenated water through sinking of near-freezing, salty water at the poles of the Earth, flowing along the ocean floor all the way to the equator. During a super greenhouse event, the ice at the poles has melted and there is no longer any sinking of oxygenated water into the deep seabed habitats – the ocean seabed stagnates.
Millions of species go extinct during these events – known as mass extinction events. A phenominal amount of organic matter – dead plants and animals – accumulated on the stagnant seabed. Heavy rains and monsoons during these events also washed silts and muds into the seas, settling with and over the organic sludge on the seabed. In time, the algal blooms had absorbed carbon dioxide back out of the atmosphere, reducing the greenhouse effect and the earth cooled. The rains decreased and reduced land runoff and the fertilisation of algae in the oceans. At the same time, the cold, deep currents kick-started up again, bringing life-giving oxygen to the seabed again. Over hundreds of millions of years, the organic layer in the seabed is compressed by overlying sediments, forming shale rock. In some places, this rock was driven deeper into the earths crust and cooked by the underlying magma, producing oil. The oil then seeps back up through the earths crust and, in places, is trapped just beneath the surface by capping rocks.
This is the very oil we drill, extract and refine to put in our car, releasing the energy harnessed by the algal blooms back in the dinosaur age. In using this ancient energy – we also release the carbon dioxide that was trapped during the super greenhous events. We are now driving our way into the next super greenhouse event and the next mass extinction event. We know what happened before. We know what will happen next.
Episode 2, Coming Soon, 9 December. Send us your questions: twitter.com/wildiaries #LIHOU
