The last time Earth experienced a Great Dying was during a dangerous transition from glaciation and to hothouse. We’re doing the same thing by burning fossil fuels today. And if we are sensitive to the lessons of our geological past, we’ll put a stop to it soon. Or else doesn’t even begin to characterize this necessary, moral choice.
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The Great Dying of 252 million years ago began, as it does today, with a great burning and release of ancient carbon. The Siberian flood basalts erupted. Spilling lava over ancient coal beds, they dumped carbon into the air at a rate of around 1-2 billion tons per year. Greenhouse gasses built in the atmosphere and the world warmed. Glacier melt and episodes of increasingly violent rainfall over the single land mass — Pangaea — generated an ocean in which large volumes of fresh water pooled at the top. Because fresh water is less dense than salt water, it floats at the surface — creating a layer that is resistant to mixing with water at other levels.
Algae Blooms and Red Tides in the Stratified Ocean
This stratified ocean state began to cut the life-giving thread of the world’s great waters. Reduced mixing meant the great ocean currents slowed. Oxygen transport into the depths declined. Moreover, a constant rain of debris in the form of particulate matter from burning forests and nitrogen oxides from the smoldering coal beds fertilized the ocean surface. Food for algae also came from increasing continental run-off. And a spike in iron loading due to glacial melt added yet more fertilizer. Great microbial blooms covered the world ocean, painting its face neon green, blue, or blood red.
(Stratified Ocean waters hosting massive algae blooms. It’s a combination that can quickly rob ocean waters of oxygen. During the Permian, a transition to stratified and then Canfield Ocean conditions led to the worst mass extinction event in the history of life on Earth. Today, the Southern Ocean’s waters are increasingly stratified due to glacial melt run-off of fresh water. In addition, these waters also host very large algae blooms like the ones seen above in a NASA satellite shot from 2012. Image source: NASA and Live Science.)
Rising CO2 levels increased ocean acidification even as the blooms spread toxins through the waters. When the blooms finally exhausted all the available food in their given region, they died off en masse. And by decay they further robbed the waters of life-giving oxygen. At this point the strains to ocean life became extreme and the first mass deaths began to occur. The stress opened pathways for disease. And the warming, de-oxygenating waters forced migrations to different Latitudinal zones and ocean depths. What life there was that couldn’t move, or couldn’t move fast enough died in place.
Transitioning to a Canfield Ocean
At first, ocean deaths appeared prominently in the bottom regions that saw the most rapid declines in oxygen levels and the swiftest increases in temperatures. For not only did the fresh water at the surface of the world’s oceans prevent mixing — it also prevented the oceans from ventilating heat into the air. Instead, the ocean heat was increasingly trapped at depth. Aiding this process of heat transport into the world’s deeps was a bottom water formation that issued from the hot Equator. There, evaporation at the surface increased saltiness. The heavier, hotter, saltier waters sank — carrying with them the Equatorial surface heat which they then delivered to the ocean bottom.
The hot, low oxygen bottom water became increasingly loaded with methane as the heat activated frozen stores. It created an environment where a nasty little set of primordial, hydrogen sulfide producing, creatures could thrive. These little microbes cannot live in oxygen rich environments. But warm, anoxic bottom waters are more like the ancient environments from which they emerged. Times long past when the world was ruled by microbes in conditions that were simply deadly to the more complex and cold-loving life forms of later times. To most life, the hydrogen sulfide gas produced by these little monsters is a deadly toxin.
(Oxygen, iron and hydrogen sulfide content of the world’s oceans over the past 4 billion years. Ancient oceans were hotter than today. They were rich in iron and densely populated with hydrogen sulfide producing bacteria. They were also anoxic. During hothouse events, oceans can again lapse into these ancient ocean states. Called Canfield Ocean environments and named after Dr. Donald Canfield who discovered them, these states are extremely deadly to ocean life. If they become too deeply entrenched, Canfield Oceans can also transform the global atmosphere, resulting in extinctions of land animals as well. Such an event was thought to be the primary killing mechanism during the Permian Extinction. Image source: Nature.)
The rotten-eggs stinking, hydrogen sulfide filled waters at first did their dirty work in silence at the bottom of the warming world ocean. But, steadily, anoxia progressed upward, providing pathways for the hydrogen sulfide producing bacteria to fill up the oceans. Death expanded from the bottom toward the surface.
In all the great mass extinction events but, possibly, one, this heat-driven filling up of the world ocean with deadly hydrogen sulfide gas during hothouse periods represents the major killing mechanism. The other impacts of hothouse waters — ocean acidification and habitat displacement — do provide killing stresses. But the combined zero oxygen environment filled with a deadly gas generates zones of near absolute death in which few things but microbes and jellyfish can live. In rock strata, the anoxic, zones are marked by regions of black as the hydrogen sulfide producing bacteria-filled waters eventually take on the color of tar. In the lesser extinctions, these black zones are confined to the lower ocean levels. In the greater ones, they rise higher and higher.
During the Great Dying, the oceans brimmed full of the stuff. Black, purple and neon green waters bubbled to the surface to belch their lethal loads of hydrogen sulfide gas into the airs. The gas was deadly toxic to land plants and animals alike. And it eventually wafted into the skies, turning it from blue to green and eating away at the protective ozone layer.
In this terrible way, more than 99 percent of all living things were killed off. Of species, about 95 percent of ocean forms were lost with around 80 percent of the land forms being wiped out.
Early Signs of a New Ocean Extinction
The Great Dying of the Permian Extinction 200 million years ago should be a warning to anyone still enamored with the notion that today’s terrifying fossil fuel burning results in any future that is not horrible, wretched, bleak. Today, we dump 11 billion tons of carbon into the air each year — at least six times faster than during the Great Dying. Today, the great melting glaciers are beginning the painful process of ocean death by spreading out their films of stratifying, iron-loaded fresh water. Today fossil fuel industry, industrial farming and warming all together are fertilizing the ocean surface with nitrous oxides, particulates, phosphates flushed down rivers, and an overall increased runoff due to a multiplication of extreme rainfall events.
(The hot blob in the Pacific Ocean is setting off the largest red tide on record. Just one of many dangerous impacts to sea life due to this large region of abnormally warm water.)
And the impacts are visible to anyone who cares to look. In the Pacific Ocean, a climate change related blob of hot water is resulting in mass ocean creature die offs. Low oxygen waters beneath the blob are wrecking large zones of ocean productivity and risking the proliferation of deadly hydrogen sulfide producing bacteria. The largest red tide on record has spun off the hot blob. Covering waters 40 miles wide and 600 feet deep, it has left piles and piles of dead shellfish rotting on beaches across the North American West Coast.
Across the Continent, the Chesapeake Bay suffers a proliferation of dead zones and greatly reduced productivity. There’s a rising risk that, during coming years, increased warming will deliver a heavy blow to life in the Bay and turn one of the world’s greatest estuaries into a large hydrogen sulfide production zone similar to the Baltic Sea. In the Gulf of Mexico, a similar dead zone emerges near the outlet of the Mississippi. And out in the Atlantic Ocean, mobile dead zones now swirl providing a roving surface hazard to both the deep open waters and to the coastal regions that now sit in the firing line.
In the Arctic, recently ice-freed waters are now the host of massive blue and green Algae blooms.
(Large blue and green algae bloom covering the southern Barents Sea during late July of 2015. Large algae blooms are now a frequent feature of previously ice covered waters in a warming Arctic. Image source: LANCE-MODIS.)
Ever since the mid 2000s a massive algae bloom like the one pictured above has dominated the Barents Sea during summer time. Often running as deep as 400 feet, this sprawling mat can rapidly deplete northern waters of vitalizing oxygen and result in mass fish kills. Waters around Greenland, in the East Siberian Sea, the Chukchi, and the Beaufort have also hosted large, and potentially ocean-health threatening algae blooms.
And, in the polynyas and open waters off a melting Antarctica, massive algae blooms are also starting to form. Some of the blooms are so dense they emit a nasty rotten-eggs smell — a sign that sulfide producing bacteria may already be active in some of these waters. Fed by iron from melting glaciers, these immense blooms represent rapid explosions of life that can equally rapidly deplete waters of nutrients and then oxygen as they die off.
The blooms and the related expanding, low oxygen dead zones now range the entire world ocean. And where we see the red, the neon green, the cloudy light blue what we see are the signs of another ocean extinction in the making. An extinction that is likely building faster than at any time in the geological past. But we may still be able to avoid another great dying. The amount of carbon we’ve emitted into the world’s airs is immense, but it is still but a fraction of the carbon explosion that resulted in the Permian die-off. It is still a tiny fraction of the carbon that remains in the ground. The carbon that could be burned but shouldn’t. And a rapid cessation of fossil fuel burning now should, hopefully, be enough to prevent another hothouse spurred great dying in the oceans and upon the lands.
As for continued burning of fossil fuels — that results in ever greater risk of unleashing the horrors of the ancient hothouse. A set of now stirring monsters that we should carefully allow to fall back into slumber — leaving them to rest in dreams of the great long ago where they belong.