Climate Change, Collapse of Industrial Civilization, David Attenborough, Ecological Overshoot, Environmental Collapse, Extinction of Man, Interactive Map of Eutrophication & Hypoxia, Julian Cribb, Ocean Dead Zones, Sylvia Earle
Julian Cribb, the science writer who gained some notoriety with his letter to the journal Nature urging a rename of the not-so-wise Homo sapiens, has written a recent essay entitled ‘March of the Dead Zones‘. Are we quickly cooking the oceans into a state of mass extinction as has happened in Earth’s ancient past?
…The cause of Dead Zones is well understood: they are driven by the avalanche of nutrients which humanity dumps in the oceans – from agriculture, sewage, leaky landfills, urban stormwater, soil erosion, industrial and vehicle emissions. This rich nutrient soup provides the food source for vast blooms of algae – and as these die off they sink to the sea floor and decompose causing blooms of bacteria which strip the essential oxygen from the water column, often resulting in fish kills – their most visible impact. They are also hastened by global warming, which stratifies the water, trapping the stagnant water and preventing it from mixing with the oxygen-rich surface layer.
What many people do not realise is that some of the worst extinctions in the history of life on Earth occurred because of a process very similar to this. In the biggest of the lot, the Great Death of the Permian around 252m years ago, an estimated 95 per cent of marine species were wiped out – rugose corals, nautiloids, armoured fish, trilobites – never to be seen again.
What triggered it is still a scientific mystery – an outbreak of volcanism, striking asteroids, a giant solar storm, colossal seabed methane eruptions: who knows? – but the geological evidence points to a massive global spike in CO2 levels, accompanied by rapid planetary warming, huge outbreaks of anoxia (loss of oxygen from seawater) and the destruction of marine habitats. One thing is fairly clear – by the end of it all fungi and moulds were rulers of the Earth, feasting on the dead.
The multiplying Dead Zones in the world’s oceans today not only resemble the Permian event on a local scale in terms of what drove them – but have two additional drivers: overfishing and pollution from the 83,000 chemicals which humans manufacture on the land and then carelessly liberate into the global environment.
The biggest contributors of all are the 110 million tonnes of nitrogen, 9 million tonnes of phosphorus and other nutrients which we unleash into the planetary ecosystem every year as we try to feed ourselves. That is off-the-scale compared with what the pre-human Earth circulated naturally.
The really unsettling fact is that, if we continue to depend upon agriculture for our food supply, then humanity’s dependence on artificial fertilisers is likely to double by the 2060s – and so will our indiscriminate release of nutrients into the world’s rivers, lakes and oceans. That release, in turn, will spawn more and larger Dead Zones – like that affecting 22,000 square kilometres of sea at the mouth of America’s Mississippi river…
Below is a screen shot of a project called the Interactive Map of Eutrophication & Hypoxia (low-oxygen dead zones) which have spread to nearly 500 sites, all in places where there is significant human development along the oceans and seas of the world.
…Their study, published in Nature Geoscience, showed that the average global temperature rise of around at least two degrees Celsius between the peak and the end of the last Ice Age (between about 10,000-20,000 years ago) had a massive effect on the oxygen content of seawater.
“The warmer the global average temperature, the more extended the oxygen minimum zones are, so the volume of these oxygen-poor water bodies is more extended during warm periods than in cold periods,” Jaccard said.
What is worrying is that, currently, global average temperature is predicted to rise by at least two degrees in the coming century due to climate change. This is of a similar magnitude to the warming the planet has undergone since the last Ice Age 20,000 years ago.
“So we would assume that if, indeed, temperatures are increasing in the next 100 years, these oxygen minimum zones would also increase in volume and that the general oxygen concentration of the ocean will decrease,” Jaccard said.
And what is more: “our analysis has shown that not only was absolute temperature important, but also the rate of change, so the faster the warming, the more expanded these zones are…
The demise of the dinosaurs, thought to have been caused by an asteroid, wasn’t the only mass extinction around that time, according to new international research.
Evidence suggests that many species of ocean organisms were killed by volcanic eruptions before the asteroid impact. The eruptions took place in India, filling the atmosphere with greenhouse gases that warmed the globe and caused seafloor life to die.
“The eruptions started 300,000 to 200,000 years before the impact, and they may have lasted 100,000 years,” said study lead author Thomas Tobin at the University of Washington in a press release.
The scientists discovered this earlier extinction when they studied fossils from Seymour Island near Antarctica. The island has an unusually thick bed of sediment, where more sediment than normal accumulated in each time period.
This allowed the researchers to date fossils more precisely and create a detailed timeline. They used the prehistoric changes in Earth’s magnetic field to date each fossil sample.
“I think the evidence we have from this location is indicative of two separate events, and also indicates that warming took place,” said Tobin.
“It seems improbable to me that they are completely independent events.”
The first extinction event may have seriously affected some species, making them unable to survive the second extinction, although there’s no evidence for this yet….
“We are now appearing to wage war on life in the sea with sonars, spotter aircraft, advanced communications, factory trawlers, thousands of miles of long lines, and global marketing of creatures no one had heard of until recent years. Nothing has prepared sharks, squid, krill and other sea creatures for industrial-scale extraction that destroys entire ecosystems while targeting a few species…
The concern is not loss of fish for people to eat. Rather, the greatest concern about destructive fishing activities of the past century, especially the past several decades, is the dismemberment of the fine-tuned ocean ecosystems that are, in effect, our life-support system.
Photosynthetic organisms in the sea yield most of the oxygen in the atmosphere, take up and store vast amounts of carbon dioxide, shape planetary chemistry, and hold the planet steady.
The ocean is a living system that makes our lives possible. Even if you never see the ocean, your life depends on its existence. With every breath you take, every drop of water you drink, you are connected to the sea…” ~ Sylvia Earle