Awakening the Horrors of the Ancient Hothouse — Hydrogen Sulfide in the World’s Warming Oceans

“Dead Cthulu waits dreaming…” H.P. Lovecraft

In the 1930s, pulp horror writer H.P. Lovecraft penned tales of ancient monsters called Old Ones that, if awakened, would emerge to devour the world. One of these horrors, Cthulu, lay in death’s sleep in his house called R’lyeh at the bottom of the Baltic Sea (Charles Stross) awaiting some impetus to disturb him from necrotic slumber (ironically, the Baltic sea bed contains one of the world’s highest concentrations of the deadly hydrogen-sulfide producing bacteria that are a focus of this article).

Namibia Hydrogen Sulfide Emission 2007

(2007 Hydrogen Sulfide emission off the coast of Namibia. Such emissions tend to color the surface water green and, in extreme cases, black. Image source: Earth Observatory)

In the imaginary world of H.P. Lovecraft, terrible lore of these horrific Old Ones, among which, Cthulu was the worst, lay stored in ancient tomes. To learn of these mysteries was to risk madness. For the Old Ones were too awful for the human mind to conceive without succumbing to a hopeless darkness.

In researching the terrors that could emerge in a world destabilized by human warming, I am often reminded that human imagination is not without a sense of dramatic irony. But in this case, the irony invoked is that human imagining, in fiction, seems to sometimes possess a broader perception of potential real world risks and their implications for human thought, than the far more defined warning signal coming from the sciences.

Cthulu, in this case, may as well be a metaphor for one of the worst of the world’s ancient climate horrors — the oceanic production of hydrogen sulfide gas that occurred from time to time, during various hothouse events. A production implicated in many of the worst mass extinction events ever to mar the history of life on Earth.

Hydrogen Sulfide — Bi-product of Bacterial Metabolism in the Ancient Oceans

In understanding this ancient horror, we must first take a look at some of the world’s oldest and smallest creatures. Primordial bacteria.

About 3.5 billion years ago, the Earth was a hot, toxic place, bombarded by solar radiation. It was still cooling down after its initial formation. The oceans had spilled out over its surface, but the continents had yet to emerge. Atmospheric levels of CO2 were high and oxygen was virtually nonexistent.

676px-Dvulgaris_micrograph

(Desulfovibrio vulgaris, one of the most well-researched hydrogen sulfide producing bacteria. Image source: Commons)

But, in this world, small microbial organisms thrived. Deprived of oxygen, which is the now typical means of respiration for non plant organisms, the microbes required other sources for their simple cellular metabolism. Sulphate was common in the world’s emerging oceans and reacted well with hydrogen, which was also very common. The result was the emergence of some of the oldest known living organisms — the sulphate reducing bacteria.

Suphate reducing bacteria combined sulphate and hydrogen to produce hydrogen sulfide gas or H2S.

As a result, ancient oceans were cauldrons bubbling over with hydrogen sulfide which was the biproduct of these primordial organisms’ respiration in much the same way that oxygen is a biproduct of plant respiration and CO2 is a biproduct of animal respiration. Such an ocean state, called a Canfield Ocean by today’s scientists, was the common state for the world’s oceans until the emergence of more complex life around 2.5 billion years ago. By about 600 million years ago, the Canfield Ocean state only very rarely came into being and when it did, mass death tended to rapidly follow.

Changes Came With the Emergence of Oxygen

As the Earth system matured and new organisms came into being, CO2 reducing photosynthetic life emerged and began to produce an abundance of oxygen. Toxic to the ancient organisms, the abundance of oxygen pushed the sulphate reducing bacteria into the world’s low-oxygen corners. The deep ocean, or anaerobic mud became a haven for these tiny primordial monsters. Never again would they dominate as they once did. But, from time to time, when priomordial ocean states would infrequently emerge during various hot-house phases in Earth’s climate progression, these life forms would explode, producing prodigious volumes of what, to more complex life, was the very toxic hydrogen sulfide gas.

A Toxic, Volatile Gas

Hydrogen sulfide is directly toxic to most plant and animal based life. Its effects in animals are similar to that of hydrogen cyanide in that it eventually results in cardio-pulminary shock and then death. Lower levels of hydrogen sulfide are associated with loss of smell, blindness, respiratory infections, and loss of neurological and nervous system function. At very low levels, hydrogen sulfide is non toxic and is even produced in cells to perform various functions. Human lethality begins at around 600 parts per million. Smaller mammals with higher respiration rates begin to show lethality at around 450 ppm. Doses in the range of 10-20 parts per million have been known to cause eye irritation and damage over long periods of exposure. Levels over 50 ppm are generally considered harmful if exposure occurs for long durations. Doses between the irritation dose (10 ppm) and the lethality dose (600 ppm) over extended periods are shown to cause the eye damage and degenerative nerve and lung changes listed above.

In the environment, hydrogen sulfide causes numerous other damaging impacts. The gas reacts with hydroxyl and oxygen over the course of about 1 to 3 days to produce sulfur dioxide. Aside from providing a mechanism to draw down local oxygen levels, the sulfur dioxide product can end in the stratosphere where it substantially degrades the protective ozone layer.

Though hydrogen sulfide is slightly heavier than air, tending to pool at lower elevations, it is light enough to be born aloft by winds to various layers of the atmosphere and its even lighter sulfur dioxide products are quite a bit more mobile. At high enough atmospheric concentrations, both it and its sulfur products could begin to seriously degrade the Earth’s protective ozone layer. And evidence exists in the geological record of such events occurring on at least a couple of occasions during the last 250 million years. Notably, during the Permian extinction event, large numbers of fossils have been found with the characteristic UV damage that would occur in a world in which the ozone layer had been greatly degraded.

At high enough concentrations, hydrogen sulfide is volatile enough to burn. A 4.3 percent concentration is immediately combustible, producing a bluish flame. This extraordinarily high concentration would be almost immediately lethal to humans if inhaled and usually only presents a fire risk at highly concentrated sources.

In the current day, high concentrations of hydrogen sulfide gas are often associated with natural gas extraction. Natural gas, by volume, can contain as much as 90 percent hydrogen sulfide. The hydrogen sulfide, in this case, occurs due to catalytic reaction of the hydrocarbon with certain minerals present in the Earth. Though not produced by the same mechanisms as oceanic hydrogen sulfide, the gas in this form is just as dangerous and is a constant concern to workers of the oil and gas industry. Notably, risks of hydrogen sulfide exposure, leaks, and release into the environment have greatly increased with the widespread adoption of hydro-fracking practices that use high pressure liquids to rupture tight gas deposits and chaotically release the substance for its collection at one of the US’s 1 million well sites.

In general, the volatility, danger, and toxicity of the gas is difficult to overestimate. Notably, its lethality resulted in its use as a chemical weapon during World War I.

Culprit of Past Mass Extinctions

High concentrations of hydrogen sulfide, resulting both from its production in a Canfield type ocean state and, possibly, through its release in large methane pulses from the sea bed during catastrophic warming events, has been implicated in numerous mass extinction events both on land and in the ocean. Notably, the Permian-Triassic extinction, the Triassic-Jurassic extinction, and the PETM extinction in the deep oceans all show signs related to ocean anoxia and varying levels of hydrogen sulfide gas production. Earlier mass extinctions such as the Devonian and Ordovician extinctions were also likely caused by anoxia and related hydrogen sulfide production. Lesser extinctions in which ocean anoxia also probably played a part include  the Ireviken, Mulde, Lau, Toarcian and Cenomanian-Turonian events.

Prominent researchers such as Ward and Kump propose that hydrogen sulfide production by sulfate reducing bacteria is a primary extinction mechanism in stratified and anoxic oceans due to their inevitable multiplication in these environments which are, to them, far more favorable than oxygen-rich mixed oceans. In a Canfield Ocean world, large, episodic releases of hydrogen sulfide gas would cause local mass poisonings of land dwelling animals, especially of those living near large ocean-linked bodies of water. The ocean itself would be brimming full and spilling over with this nasty substance. This condition would be highly toxic to most life, requiring extreme adaptation to survive in naturally occurring havens.

Separate depletion of atmospheric oxygen through both the plant killing mechanism of hydrogen sulfide gas and its long-term reaction with oxygen would also make life far more difficult to terrestrial creatures. Finally, the massive amounts of sulfur dioxide produced in such a world would combine with the hydrogen sulfide pulsing into the atmosphere to create an ongoing, long-term degradation of the ozone layer, further harming surface dwelling plants and animals.

During the Permian Extinction, such conditions, together with other impacts of a global hothouse featuring a massive flood basalt, are thought to have wiped out more than 70% of terrestrial organisms and a total of more than 95% of all life on Earth.

Occurrence in Current Seas

Expanding Ocean Anoxia Hydrogen Sulfide in the Baltic Sea

(Expanding bottom anoxia, hypoxia and hydrogen sulfide production since 1960 in the bottom zone of the Baltic Sea. Red indicates region experiencing low or no oxygen content. Black indicates areas where H2S gas is detected. Image source: Baltic Sea Trends)

The world’s oceans, according to recent research, are rapidly becoming more stratified and less oxygen-rich. The result is that mixing between various layers of the ocean is beginning to shut down reducing oxygen content in the deep ocean and spurring the expansion of numerous oceanic dead zones.

Over the past 150 years, the Pacific Ocean was observed to become more stratified at a pace ten times that seen during the end of the last ice age about 12,000 years ago. Such a rapid pace of stratification is putting severe stress on the world’s oceans with numerous regions showing the effects of low oxygen (hypoxia) and some regions succumbing to increasingly anoxic states.

These low oxygen events have been associated with multiplying oceanic dead zones. Very large dead zones have been observed in the Pacific, specifically off the coast of Oregon. Other major dead zones continue to be observed at the mouth of major river systems, such as within the Gulf of Mexico, where the appearance of massive related toxic algae blooms is now an almost annual event. In general, almost all ocean dead zones are expanding leading to the dramatic reduction in habitat size of numerous fish species. And even the most cursory research provides ample evidence that ocean hypoxia is expanding concurrently with a rapidly expanding ocean stratification.

When combined with the jarring effects of rapid ocean warming and expanding acidification, it becomes plainly obvious to almost any ocean ecologist that the world’s ocean system is suffering the heavy bombardment of a new mass extinction event.

It is this kind of low or no oxygen environment that is a prime breeding ground for hydrogen sulfide producing bacteria. In numerous places around the world, such as off the coast of Namibia, in the Black Sea, in the Baltic Sea, in the Gulf of Mexico, in the Chesapeake Bay, and off the coast of Oregon, large and expanding zones of hydrogen sulfide have been observed in deep water environments. In some regions, this hydrogen sulfide occasionally penetrates to the surface layer resulting in major fish kills and a concordant rotten egg smell.

Off the Oregon coast, in perhaps one of the most extreme examples of ongoing ocean hypoxia, one of the world’s largest and most oxygen-starved dead zones continues to expand. The oxygen levels in this region are so low that local fisherman often bring back horrific tales of baby bottom dwelling creatures such as crabs and octopus climbing anchor ropes to escape the dangers of their oxygen-starved environment. In another, possibly related event, masses of starfish perished during 2013 and 2014 as they, over the course of a few weeks, turned to goo. The fact that this sci-fi esque mass death of starfish occurred near one of the world’s largest dead zones should not be lost on those concerned for world ocean health.

But perhaps even more concerning is the fact that this region off the Oregon coast is producing substantial volumes of hydrogen sulfide gas. Volumes high enough in concentration to occasionally cross the ocean-air boundary.

Oregon possesses numerous features that would aid in the transport of this gas to the surface. Primarily, the near Oregon ocean system frequently features strong up-welling currents. These currents can push bottom waters through stratified layers and cause them to contact the surface. If these oxygen starved bottom waters contain hydrogen sulfide gas, as they increasingly do, this harmful gas can be transported into the local atmosphere through mixing.

Such events, thus far, have been limited. However, since the Oregon dead zone’s discovery in 2001, its expansion has been both deeply concerning and well documented, showing a rapid and dangerous growth over the 13 years since its emergence. Despite the documented expansion of deep water hydrogen sulfide in numerous oceanic regions, the only other ocean zone on Earth observed to emit hydrogen sulfide gas to the atmosphere is in the region of coastal Namibia.

In Namibia, huge volumes of organic compounds fall into the sea after being flushed down ocean terminating streams and rivers. These organic compounds rain down into the deep ocean directly off Nambia’s coasts. There, the ocean bottom hosts both an anoxic environment and masses of hydrogen sulfide producing bacteria. As a result, toxic hydrogen sulfide gas periodically erupts from the ocean and into the atmosphere there.

The Very Real Threat That is Oceanic Hydrogen Sulfide Gas Production

There are few limiters to oceanic hydrogen sulfide production in the world’s increasingly stratified and oxygen starved oceans. Sulphate, which the bacteria require for respiration, is one of the most common ocean elements. In the current ocean, it is present in volumes greater than those seen during the Permian Extinction when these tiny monsters are thought to have done their worst.

Iron and manganese in the world ocean system aids in the development of less permeable boundary layers that help keep a lid on deep ocean concentrations of hydrogen sulfide. However, even in the anemic circulation of stratified and Canfield oceans, upwelling will bring the gas to the surface in certain regions. In addition, as the oceans contain greater and greater volumes of the toxic gas, it will push closer and closer to the surface, rendering metals that help reinforce the boundary layer a practically useless prophylactic (such high metal concentrations currently prevent hydrogen sulfide from penetrating the surface layer in the Black and Baltic Seas as well as in the Chesapeake Bay).

In addition, modern industrial farming practices provide extra nutrients upon which these dangerous microbes can feed. High levels of hydrogen sulfide in the deeper regions of the Chesapeake Bay, for example, owes its existence, in part, to massive farm run-off into the Bay and the dumping of mass volumes of nutrients upon which the sulphate reducing bacteria can feed.

It is important to note that we observe heightened levels of hydrogen sulfide gas in the world ocean system now. As hypoxia and anoxia progress with the human-caused warming of the oceans, and as glacial melt interrupts and alters the now strong ocean currents and related mixing, it is certain that hydrogen sulfide production in the deep ocean will continue to increase resulting in elevating levels of harm to ocean dwelling animals and ever more numerous instances of hydrogen sulfide gas contact with coastal and surface waters.

Dead Cthulu Rises

In the context of increasing ocean hypoxia and stratification, we might do well to remember that we are tiny, weak beings at the mercy of great natural forces which we can barely conceive or understand. Forces that we have unwittingly, callously and ignorantly set into motion.

*   *   *   *   *

Long ago, when I was a ten year old child, I was fortunate enough to meet an amazingly kind, adventurous and inquisitive man. The man, whom I will call Rick to keep safe his identity, was a bit of a local paramour in ocean and bay research. He was constantly in contact with both the ocean and adjacent Chesapeake bays, ever venturing out to explore and to conduct research on marine life. In later years, he would be the impetus behind annual summer marine science camps hosted by the Virginia Institutes of Marine Science, Norfolk Academy, and Old Dominion University. But this was later. Now, Rick was helping an elementary school student present on the issue of our then expanding understanding of marine science.

Living so close to the bay and ocean, I was intimately in contact with the living boundary of land and sea. In the more demanding and less stimulating forum that was public education, I seldom had the opportunity to indulge my passion for the oceans. But at age 10 I was given the opportunity to give a broad marine science presentation for my classmates. As part of my project, I constructed posters and models depicting the current state of world ocean research. I graphically illustrated the various known zones of the bathysphere, the light and life filled ones and the more mysterious and far less well understood depths. But Rick was the centerpiece of my presentation. He was my keynote. And he energetically answered all my own and fellow students’ questions, speaking in the kind and intriguing manner that would later draw so many into his charismatic orbit.

In later years, I would attend Rick’s summer marine science camps on two different occasions. In both cases, I observed what appeared to be an increasing concern about both the health of the Chesapeake Bay and the neighboring oceans. In later years, Rick’s attitude, once so full of optimism, bordered on cynicism. The world he loved so deeply was experiencing death on a scale that horrified him. And he harbored a deep sense of betrayal that we weren’t doing more to stop the senseless slaughter of so many of the living things he saw as both beautiful and wondrous.

In the mid 2000s, Rick committed suicide. To me, one of the great ocean pioneers of my developmental years had passed away by taking his own life. And I couldn’t help but wonder if the horrible ways in which the oceans that he so loved were changing was just too much for him. If the commercialization and cheapening of all the things he held most dear along with their subsequent damaging and putting at great risk of terrible harm had robbed his life of beauty and purpose.

Rick was, if anything, a very intelligent and sensitive man. He knew what was happening to the Bay and ocean on a personal level. When the Bay was harmed it was as if it hurt Rick too.

Rick also knew how temperature changes affected the depths. For he was on the front line studying it. He was hauling up the fish and the water samples. He was doing the measuring with his own hands.

Was the awakening of terrible Cthulu, in the form of hypoxia, anoxia and deadly hydrogen sulfide producing bacteria, too much for Rick to continue bearing mute witness? Did his pleas to those working in the marine science community fall only on deaf ears? Was it just too much for this sensitive, feeling, and intelligent man to bear?

*   *   *   *   *

If Rick taught me anything it was that our lives and the life of the ocean are deeply connected. One cannot remain healthy without the other. In contrast to this basic understanding, the damage our continued industrial emission of greenhouse gasses is doing to the world ocean system is a horrific travesty. And the damage we have already caused, have already done to those most sensitive creatures among us, have already set in play for future decades and centuries, is tremendous.

The ocean suffocates, bleeding deadly hydrogen sulfide gas. Cthulu rises from his ancient house in the depths. And yet we still continue down the wretched path in pursuit of more terrible things to come.

Links:

The Earth Observatory

Baltic Sea Trends

Commons

Through the Looking Glass of the Great Dying

Sulphate Reducing Bacteria

Impact From the Deep

Toxicological Profile for Hydrogen Sulfide

Positive Reinforcement, H2S and the Permo-Triassic Extinction

Massive Release of Hydrogen Sulfide to the Surface Ocean and Atmosphere During Intervals of Ocean Anoxia

Expanding Ocean Dead Zones are Shrinking Marlin, Tuna, and Billfish Habitats

Dead Zone Causing Wave of Death off Oregon Coast

Information about Hydrogen Sulfide in the Baltic Sea

Residence time for Hydrogen Sulfide in the Atmosphere

Dramatic Expansion of Ocean Dead Zones

Under a Green Sky

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A Deadly Climb From Glaciation to Hothouse — Why the Permian-Triassic Extinction is Pertinent to Human Warming

In looking at the potential impacts of human caused climate change over the coming decades and centuries, scientists have often pointed toward more recent times such as the Eemian (the most recent warm interglacial in which global temperatures are similar to what they are now and where they are expected to be over the next 20 years), the Pliocene (2-3 million years ago and the most recent time in which CO2 levels were about equal to those of today), and the PETM (about 55 million years ago and the most recent period during which CO2 levels were above 600 ppm and in which there was very rapid warming, possibly due to methane hydrate release).

The PETM has been a period of very intense study for leading climatologists such as James Hansen who has warned of the potential for a mini-runaway warming event of this kind should humans continue along a business as usual path of fossil fuel burning through the 21rst Century. In particular interest in the PETM corollary scenario is both the amazing velocity of the initial human warming, with CO2 and greenhouse gas releases occurring at rates that are five (CO2) to 27 (methane) times faster than the PETM (Hat tip to Timothy Chase, Source: Skeptical Science). So rapid and powerful a rate of forcing puts at risk of greater release a number of very large global carbon deposits including the massive CO2 and carbon stocks stored in the world’s melting permafrost as well as the even larger stores of carbon locked in methane hydrates scattered across the world’s oceans. Hansen and other scientists have noted a potential for a 4-7 degree Celsius or greater warming by 2100 (at between 700 and 1000 ppm CO2) through a combination of human greenhouse gas emissions and Earth systems carbon emissions. Overall warming by 2300 from Earth Systems feedbacks, even if human emissions were to stop by 2100, is likely to be twice this level.

That such a massive warming would be catastrophic is a given. There is no evidence in the geological record for such a stunning pace of warming over so short a period. And the potential climate change impacts from such high levels of heating, alone, would be extraordinarily difficult for human civilizations and the innocent inhabitants of our living world to manage.

Late Permian Just Prior to De-glaciation

Late Permian Just Prior to De-glaciation at approx 260 million years ago.

(Image source: Ron Blakey, NAU Geology)

But this scientific scenario is based, in part, on knowledge gleaned by studying past geological periods such as the Eemian, Pliocene, and the PETM hyperthermal (other information is derived from the still-developing climate models of terrestrial, ocean, and Earth systems). And, in looking at each of these paleoclimate periods, we find that a single key factor is missing: they all occurred during periods in which Earth was either ice-free, or in which Earth was settling into its current period of glaciation. In the case of human-caused warming, the exact opposite process is ongoing. As during the great Permian Extinction event of around 250 million years ago, the Earth is rising out of a period of glaciation and into a potential human-caused hot-house.

No More Ice Ages and a Start Down the Path Toward De-glaciation

In the current period of human-caused warming we encounter the novel and relatively uncharted territory of an Earth System that is being forced to arise out of a 40 million year long period of glaciation. This period has been characterized, first, by the freezing of the vast land mass of Antarctica, then by the freezing of Greenland and, later, by long ice ages in which glaciers expanded from the poles to cover large areas of land and water. This latter ice age-interglacial period began about 800,000 years ago and has dominated until today.

Glaciation since PETM

(Image source: James Hansen)

With atmospheric CO2 levels now at 400 ppm and with humans continuing to emit high volumes of CO2 for at least the next two decades, we can officially declare the period of ice ages and interglacials at an end (or at least put on extended hold). For retaining even a very small portion of our current greenhouse gas emitting infrastructure or agriculture would be enough to stave off another ice age. Hansen notes:

Forces instigating ice ages, as we shall see, are so small and slow that a single chlorofluorocarbon factory would be more than sufficient to overcome any natural tendency toward an ice age. Ice sheets will not descend over North America and Europe as long as we are around to stop them.

Ice ages are now stopped in their tracks and current human levels of CO2 at 400 ppm are now sufficient to begin melting Greenland and West Antarctica. We can see this melt in yearly losses exceeding 500 gigatons of melt water and ice from Greenland and from Antarctic melt losses in the range of 300 gigatons per year or more. And with the increasing human heat forcing, these melt rates are on a very rapid incline. Greenland is showing a doubling in its melt rate every 5 years.

Yet even this, rapidly expanding, melt pace may seem slow if humans continue along their current path of greenhouse gas emissions growth. Last year, over 32 gigatons of CO2 were emitted into the atmosphere and the net human greenhouse gas emission was equivalent to more than 45 gigatons of CO2. At the current rate of emissions and emissions growth, we are now on track to hit between 500 and 600 parts per million of CO2 by the middle of this century. And this range of CO2 is enough or nearly enough to melt all the world’s ice, setting us on a path toward a place not seen in at least 40 million years. A path toward long-term temperatures in the range of 6 degrees Celsius hotter than the 1880s. If emissions continue until the end of this Century, the path is almost certainly toward that of a hyperthermal and one with unique consequences given the speed at which we approach it and the fact that we will send massive volumes of fresh meltwater into the oceans as we approach it.

The PETM and the Great Dying

And this is where we encounter a bit of a problem. Because the world is rapidly rising up out of a 40 million year long glacial period, it is bound to encounter changes not visible 40 million years ago as the Earth was steadily cooling down toward glaciation or even during the PETM as the Earth emerged from a lesser cool period and entered a hothouse state. In the case of the Permian and the current day, Instigating the loss of glaciers presents its own, rather unique, set of problems and difficulties.

In looking at the geological record, we find that the last major cold period with temperatures close to those of the recent ice ages (aside from a somewhat cool period during the late Jurassic and early Cretaceous) occurred during the late Carboniferous and the early to mid Permian period.

Past Hot and Cold Periods

Hot and cold periods during the last 500 million years (best proxy data used).

(Image source: Commons)

During the late Permian and early Triassic, however, very rapid and intense warming roughly equivalent to that of the Eocene of 55 million years ago occurred. Both events resulted in extinctions in the oceans and on land. Both events showed major temperature spikes toward the end that are theorized to be linked with large methane pulses and amplifying Earth Systems feedbacks. And both are typical to a mini runaway hyperthermal of the kind James Hansen warns is possible under a regime of human warming.

The primary differences between these two events is that, first, the Permian Triassic extinction event occurred after a long period of glaciation and, second, that the Permian extinction was the greatest mass extinction ever recorded in the geological past. What resulted killed off a devastating 96% of the species in the oceans and 80% of all species on land. It is for this reason that the Permian-Triassic boundary layer extinction is known as the great dying.

By contrast, the PETM resulted in a similar, but far less, extreme event. About 35-50% of the benthic forminifera of the deep ocean went extinct. Many other ocean species, especially those of the deep ocean, exhibited stress and losses. Life on land, especially among mammals, was pushed toward dwarfism to deal with the extreme high temperatures. But, overall, stresses to land and ocean animals was far, far less than that of the Permian extinction.

Putting a Lid on the Ocean — Glacial Melt’s Role in Enhancing Anoxia

At issue here is the likely anoxic ocean states resulting from major warming events. As the oceans are heated, they are able to hold less oxygen in solution. This steady depletion results in growing regions of anoxia and related algae blooms that can be very dangerous to marine and, in extreme cases, terrestrial organisms. Warmer, anoxic oceans are more likely to host blooms of deadly green and purple algae.

Troubling Green Algae Bloom North of Scandinavia.

Troubling Green Algae Bloom North of Scandinavia.

(Image source: NASA/Lance-Modis)

These primordial creatures once ruled the seas during the days of ancient Earth, before higher levels of oxygen were present. Now, a mixed, oxygen rich ocean keeps their development in check. But the warmer ocean during the time of the PETM is thought to have brought anoxic states back to the world’s deep oceans.

In short, ocean circulation is thought to have reversed. Heating at the tropics resulted in seas becoming saltier as waters there evaporated. These saltier waters grew dense and sank toward the ocean bottom drawing fresher, cooler water in from the poles. This type of ocean circulation is thought to have dominated for about 40,000 years during the PETM and contributed greatly to anoxic ocean states by concentrating warmer, anoxic water at the bottom of the world’s oceans.

During the Permian, anoxic ocean states were thought to be far, far more intense. Paleontological research conducted by Peter Ward found a massive series of three extinction events ranging over the course of about 165,000 years in which death began at the bottom of the Permian ocean and climbed toward the atmosphere.

It is thought by some scientists that rapid warming during the Permian enhanced both glacial melt even as it amped up the hydrological cycle to increase fresh water runoff from the continental land mass. The result was a much greater freshening of the ocean surface. Enhanced evaporation at the equator is thought to have driven a similar ocean circulation to that of the PETM in which hotter, saltier water sank to the ocean bottom. Glacial melt, in this case, greatly enhanced an ocean circulation change that was already leading to anoxic ocean states. The result was that ocean layers became even more stratified and less mobile further amplifying anoxia. In the case of the Permian, ocean anoxia eventually enveloped a majority of the worlds oceans, permeating all the way to the surface and eventually invading the atmosphere.

The Emergence of the Canfield Ocean

A stratified, anoxic ocean developed which started increasing mortality among deep water life forms first. As anoxia rose through the deep and mid levels of the ocean, death advanced up the water column as green and purple algae found sunlit regions and proliferated, adding hydrogen sulfide gas as a killing mechanism to ocean acidification and low ocean oxygen levels. Eventually, the hydrogen sulfide reached the surface waters at which point it began bubbling into the atmosphere. The anoxic ocean had fully transitioned to a primordial Canfield Ocean.

Hydrogen sulfide gas is directly toxic to both plants and animals alike and this great out-gassing likely resulted in the massive loss of land species. Ironically, high temperatures (on the order of 9-12 degrees C hotter than now) enhance the lethality of hydrogen sulfide gas. When the gas reaches the stratosphere, it depletes the ozone layer, causing even greater harm to land species. Fossil remains show evidence of genetic damage indicative of a depleted ozone layer and related Canfield Ocean state.

Human Warming is Much, Much Faster

It took about 20,000 years for the Earth to warm 6 degrees Celsius during the PETM. During the Permian, the final extinction and related warming events lasted about 165,000 years. In the case of the PETM, it is thought that volcanism in India stoked global warming until a rapid methane release over a 20,000 year spike period occurred. During the Permian, volcanism is thought to have burned through coal patches over a large region of Siberia, possibly eventually setting off similar very large methane pulses to those suspected to have occurred during the PETM.

In both cases, temperatures rose to between 9 and 12 degrees Celsius hotter than today. But, in the case of human warming, we have the potential to warm the Earth by as much as 7 degrees Celsius by the end of this century and, possibly, to Permian/PETM levels over the next 300 years. Such a rapid pace of warming holds no corollary in either the Permian, the PETM or during any other major warming event visible in the geological record of Earth’s past. So while we may look to the Permian for potential enhanced ocean circulation and anoxia impacts due to glacial melt and increasingly intense ocean stratification, we have no rational means by which to determine how far behind increasing temperatures and glacial melt such events may arise. In the case of the Permian, it took about 165,000 years for a Canfield Ocean to arise. But anoxic ocean states emerged and intensified as warming ramped up. So it is likely that ocean anoxia and stratification will become an increasing problem as the Earth rapidly warms due to human forcing. We can also expect glacial melt to amplify the problems caused by anoxia by increasing stratification and by pushing warm, oxygen-poor waters toward the ocean bottom where they have little opportunity to recharge oxygen stores. Lastly, in the worst case, we can look for Canfield Oceans as a potential tail-end risk for human warming, especially if global temperatures approach 9 to 12 degrees Celsius above the 1880s average and if very large fresh water pulses from glaciers shut down and reverse current ocean circulation.

Links:

Climate Model Links Past Extinction to Higher Global Temperatures

Changes in Permian Ocean Circulation, Anoxia in the Permian Ocean, and Changes in the Permian Carbon Cycle

Rapid and Synchronous Collapse of Marine Ecosystems During Permian Biotic Crisis

Carbon Isotope Anomaly in Conjunction with Biotic Crisis

Biogeochemical evidence for euxinic oceans and ecological disturbance presaging the end-Permian mass extinction event

Storms of My Grandchildren

Under a Green Sky

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