NCAR: Global Temperature Increase To Lower Oxygen Content of Most Ocean Zones by the 2030s

A reduction in the amount of oxygen dissolved in the oceans due to climate change is already discernible in some parts of the world and should be evident across large regions of the oceans between 2030 and 2040. — The National Center for Atmospheric Research in a press release on April 27th.


Loss of oxygen in the world’s oceans. It’s one of those really, really bad effects of a human-forced warming of our Earth. One of the those climate monsters in the closet that Steve Pacala talks about. The kind of thing we really don’t want to set loose.

Deoxygenated Oceans as Major Killing Mechanism During Hothouse Extinctions

The damage caused by ocean oxygen loss is multi-variant and wide-ranging. The most obvious harm comes in the form of generating environments in which oxygen-dependent life in the oceans can no longer breathe. Any living creature that filters oxygen out of the water for respiration falls under threat due to lowered ocean oxygen levels. A group that includes pretty much all the advanced, multi-cellular life in the seas.

A press statement from the new NCAR study notes:

Scientists know that a warming climate can be expected to gradually sap the ocean of oxygen, leaving fish, crabs, squid, sea stars, and other marine life struggling to breathe.


(Hydrogen sulfide producing bacteria blooms off the coast of Namibia during 2007. Hydrogen sulfide is a highly toxic gas. One that is produced by microbes that live in waters containing little or no oxygen. Image source: Earth Observatory.)

But a second, less immediately obvious hit comes in the form of generating expanding anoxic environments that favor the proliferation of toxin-producing microbes. Called dead zones, these oxygen-poor regions not only provide a suffocation threat to sea life, but they also form areas of water in which environmental toxins can build up. The result is a long-lasting negative impact to the health of life in the ocean and, in the most extreme cases, on land and in the airs as well.

The worst of these toxin-generating microbes are the hydrogen-sulfide producing bacteria. An ancient organism that is incompatible with oxygen-dependent life. A horror out of deep time that has tended to crop up again and again on the list of usual suspects of major hothouse extinction killers. A likely perpetrator of the big ocean and land die offs during pretty much all global warming based extinctions. An organism that dominated the world’s seas and likely vented its deadly gasses into the airs of the world of the Permian — during the worst die-off Earth has ever seen.

In short, hydrogen sulfide is deadly to almost all forms of life that currently dominate the world’s oceans, lands, and airs. And the bacteria that produces hydrogen sulfide requires oxygen-poor environments in which to grow and thrive. A world ocean high in oxygen keeps these little killers hidden away in the deep, dark corners of our Earth. But heat the world ocean up. Deprive it of oxygen. And they start to come out and become a threat (see more in Awakening the Horrors of the Ancient Hothouse).

Oxygen Loss to Become Widespread by the 2030s

Already today we see regions of the world ocean that are experiencing oxygen loss. Some of this oxygen loss is due to a process called eutrophication. In eutrophication, nutrients overload the ecosystems of water-based environments. As nutrient content rises, large bacterial blooms emerge. Eventually, these blooms overpopulate the waters and devour all the food sources. When the microbes then die en masse, their decay robs the surrounding waters of oxygen — generating a dead zone.

Eutrophication has been sapping the world’s oceans of oxygen over wider and wider regions due to both agricultural run-off (fertilizers and top soils flushed into rivers, lakes and oceans that feed large microbial blooms and related dead zones) and due to nitrogen fall out from fossil fuel burning. But human forced global warming also plays a key roll in the loss of oxygen to the world ocean system.

Ocean Deoxygenation Map

(According to a new study from NCAR, ocean oxygen levels are already starting to fall in some regions due to global warming. If warming continues, NCAR finds that most of the world’s oceans will experience some level of oxygen loss due to this warming and due to a related increased stratification of surface waters. Image source: NCAR.)

The new NCAR study provides an excellent description of how warming the world’s surface waters can reduce ocean oxygen levels:

The entire ocean—from the depths to the shallows—gets its oxygen supply from the surface, either directly from the atmosphere or from phytoplankton, which release oxygen into the water through photosynthesis. Warming surface waters, however, absorb less oxygen. And in a double whammy, the oxygen that is absorbed has a more difficult time traveling deeper into the ocean. That’s because as water heats up, it expands, becoming lighter than the water below it and less likely to sink.

Waters that are less likely to sink are less likely to mix. And waters that are less likely to mix transfer less of the atmosphere’s oxygen to the global ocean. It’s a process called ocean stratification. A set of circumstances triggered by warming that can sap the world’s waters of their ability to support life even as it enhances their ability to generate environments favorable to toxin-producing microbes. And in the absolute worst cases, a stratified, oxygen-deprived ocean can transition into a dead, life-on-Earth-threatening Canfield Ocean.

Mobile Ocean Dead Zone

(Mobile ocean dead zones, like this one seen off the West African Coast during 2015, may grow more widespread as the world’s surface waters are depleted of oxygen due to a fossil fuel emission based warming. A new study from NCAR both explains how warming waters can hold less oxygen and notes that loss of oxygen to ocean surface waters becomes very widespread by the 2030s. Image source: Biogeosciences.)

In the NCAR study, which is well worth reading in full, scientists used model runs to determine when and where climate change would start to deprive the world ocean system of oxygen. The study found that regions off the coast of West Africa, regions west of South America, an area to the west of Australia, and a section of the Beaufort Sea were already experiencing lower levels of ocean oxygen due to global warming. West African seas were the first and hardest hit by warming in the models. This is interesting due to the fact that Namibia on the West Coast of Africa is one of the only regions of the world now observed to experience blooms of hydrogen sulfide producing bacteria that extend into the surface waters. West African waters have also generated a number of mobile, low-oxygen dead zones that have spiraled on off into the North Atlantic.

The fact that the NCAR study indicates that global warming has already reduced ocean oxygen levels in a region that is producing both dead zones and, in the case of Nambia, periods during which hydrogen sulfide producing bacteria appear at the surface, is cause for some concern. For by the 2030s, the NCAR model study indicates that global warming will be actively reducing ocean oxygen levels across the vast majority of the North Pacific, a majority of the South Pacific, most of the South Atlantic, and pretty much all of the Indian Ocean region covered in the new research. This raises the risk that open water dead zones like the ones seen off Africa and even hydrogen sulfide producing hot spots like Nambia may begin to creep into other regions of the world ocean — generating further threats to sea life, to fishing industry, and to human beings who depend on healthy oceans for livelihood and for life.


Widespread Loss of Ocean Oxygen (due to Climate Change) to Become Noticeable by the 2030s

Steve Pacala

Earth Observatory

Awakening the Horrors of the Ancient Hothouse


Mobile Ocean Dead Zones


Ocean Stratification

Canfield Ocean

Hat Tip to Colorado Bob

Hat Tip to June


Did The Human-Warmed Ocean Just Kill 8,000 Murres?

Around the world, mass sea creature die-offs have been occurring at an alarming rate. Off the US West Coast alone, the past three years have seen severe losses along almost ever link of the marine food chain from sea stars, to salps, to crabs, to sea lions. Many of these deaths have been linked directly or indirectly to impacts caused by a chronic warming of the region’s ocean surface dubbed ‘the hot blob.’

Now, a tragic and heart-wrenching new die-off has been recorded in the region of Prince William Sound. There, according to recent reports in the Washington Post, more than 8,000 murres — a kind of deep-swimming sea bird — were found dead. Washed up on shore, the mures bodies were shrunken and emaciated. Their stomachs completely empty of food.

Researchers noted that the mass death was likely due to starvation. But the potential cause given for the starvation was rather more ominous.

The Link to Human Warming of the World Ocean

Mures feed on small fish that swim within the top 300 feet of the ocean surface. The graceful murres ride the airs above the water until they catch sight of a school of these fish. Swooping in from above, the mures plunge toward their prey, snaring them with rapier-quick thrusts of their beaks.

Such fish usually swim close to the coast — thriving in the cold, nutrient-rich waters off Prince William Sound. But warm the waters up by just a little and the fish may leave — following their own food supply into colder regions.

sea surface temperature anomaly map

(The hot blob still holds sway over the Northeastern Pacific. This despite a series of strong El Nino storms and a somewhat flattening of the Jet Stream. It’s an extreme ocean warming that has been ongoing for more than two years. One that’s been linked to the mass deaths of numerous marine creatures. Image source: The National Weather Service.)

And the waters near and around Prince William Sound have been much warmer than normal during recent years. As of January 14th, 2016, sea surface temperatures in the region have ranged from 1 to 4 degrees Celsius above average. Extremely high differentials for an ocean surface that, during the Holocene, rarely varied by more than 1 or 2 degrees from typical ranges.

This extreme Northeastern Pacific warming is but an aspect of a larger heating trend ongoing in the global ocean system due to a rampant human emission of greenhouse gasses. This massive burning of fossil fuel has dumped hundreds of billions of tons of carbon into the world’s atmospheres and oceans — setting off a raging greenhouse effect and causing the Earth surface to warm by more than 1 degree Celsius above 1880s levels. It may not sound like much, but 1 C is just 1/4 the difference between now and the last ice age — but on the side of hot. And this 1 C warming happened in just 130 years where at the end of the last ice age the same amount of warming would have taken 25 centuries.

A Hothouse Dead Zone For Prince William Sound?

To the oceans and to the innocent creatures that live within, upon and above it, such a rapid accumulation of heat is a brutal insult. It removes whole habitats. It forces sea creatures to change their patterns of migration. It makes the surface waters more suitable for the kinds of dangerous algae blooms that produce ocean dead zones. Zones of low or zero oxygen in which very few forms of life can survive.

Prince William Sound Dead Zone

(Prince William Sound dead zone visible in this December 6, 2015 satellite shot? Tell-tale greens and blues hint that a large algae bloom may be robbing the waters around the sound of much needed nutrients and oxygen. A kind of new deadly ocean environment that is proliferating as sea surface temperatures warm into ranges in which dead zone producing microbes can thrive. Image source: LANCE MODIS.)

And it’s this kind of generation of an ocean killing field that is perhaps the most brutal and terrifying aspect of what we’ve already done to our planet. What the legacy of our fossil fuel carbon emissions will continue to do for decades to centuries to, perhaps, millennia.

And sadly, looking at the NASA MODIS satellite data, we do see an indication of the kind of algae bloom that may be depleting the waters near Prince William Sound of that life-giving oxygen. We see the tell-tale greens and blues of a large bloom of the kind that can rob waters both of nutrients to support fish life and of oxygen itself. Visual analysis alone cannot positively identify this kind of bloom with 100 percent certainty. Water samples must be taken in the area and analyzed. But scientists asking the very pertinent question — did global warming cause this? — may only need to take a look at the composition of this bloom to get their answer.

An answer that won’t save the thousands of already dead murres, but that might help us build the resolve to prevent more catastrophes like this one. To stop burning fossil fuels and halt the accumulation of a terrible build-up of heat forcing that is ripping the very underpinnings of life in the oceans asunder.

UPDATE — MODIS Chlorophyll Sensor Yet Another Indicator of Dangerous Algae Bloom in the Region of Prince William Sound

Further analysis of NASA satellite data provides yet more evidence that a dangerous algae bloom began showing up in the waters near Prince William Sound at the start of December.

December 6 MODIS Shot of Prince William Sound With Chlorophyll Layer

(December 6, 2015 NASA MODIS satellite shot of Prince William Sound with chlorophyll production overlay. Chlorophyll production in all ocean regions near the sound show up as elevated with some areas hitting the top of the graph at 20 mg per cubic meter [indicated in red]. Link: LANCE MODIS.)

High levels of chlorophyll in the waters near Prince William Sound provide yet one more instrumental indication of a large algae bloom in the region. As noted above, major algae blooms can rapidly remove nutrients from the water, creating a population crash as the algae starve themselves off. In the mass die-off of algae that follows, microbial decomposition can rob large areas of surface waters of oxygen — killing fish and other sea life or driving it away.

Warm waters provide an environment that tends to support these kinds of large algae blooms and is a primary reason why human heating of the world ocean is dangerous to ocean health. In addition, warmer waters hold less oxygen in suspension even as changes to ocean currents tend to generate more stratified oceans — preventing the kind of mixing that keeps oceans both oxygen and life-rich.

In any case, the added chlorophyll signal coming from Prince William Sound and the nearby ocean region are yet one more indicator that initial suspicions among ocean researchers may well be correct — abnormally warm waters related to human-forced climate change was probably a key trigger involved in the mass death of sea birds there.



The National Weather Service

Mysterious Mass Death of Seabirds Baffles Scientists

Hat Tip to Colorado Bob

Hat Tip to Leland Palmer

Human CO2 Emissions to Drive Key Ocean Bacteria Haywire, Generate Dead Zones, Wreck Nitrogen Web

Trichodesmium. It’s the bacteria that’s solely responsible for the fixation of nearly 50 percent of nitrogen in the world’s oceans. A very important role for this microscopic critter. For without nitrogen fixation — or the process by which environmental nitrogen is converted to forms usable by organisms — most of life on Earth would not exist.

Now, a new study produced by USC and the Massachusetts-based Woods Hole Oceanographic Institution (WHOI), has found that human carbon emissions are set to drive this essential organism haywire. Forcing evolutionary changes in which the bacteria is unable to regulate its growth. Thus generating population explosions and die-offs that will be very disruptive to the fragile web of life in the world’s oceans.


(A Trichodesmium bloom off New Caledonia. Image source: Earth Observatory.)

Trichodesmium — A Mostly Helpful Bacteria Essential to Ocean Life

Trichodesmium is a form of cyanobacteria. It resides in the near surface zone composing the top 200 meters of the water column. Possessing gas vacuoles, the bacteria is able to float and sink through the water column in order to access the nutrients it needs for growth — nitrogen, iron, and phosphorus. A widespread bacteria, it is often found in warm (20 to 34 C), nutrient-poor waters in the Red Sea, the Indian Ocean, the North and South Atlantic, the Caribbean, near Australia, and in the Northeastern Pacific.

Trichodesmium congregates in blooms which are generally a straw-like color. For centuries, this coloration has generated its common name — sea straw. However, in higher concentrations it can turn waters red. The Red Sea, for example, owes its name to this prolific little bacteria. Trichodesmium blooms generate a strata that support mutualistic communities of sea creatures including bacteria, diatoms, dinoflagellates, protozoa, and copepods. These small organisms, in turn, are fed on by a variety of fish — notably herring and sardines.

But Trichodesmium’s chief role in supporting ocean health is through making nitrogen in the air and water available to living organisms. It does this by turning environmental nitrogen into ammonia as part of its cellular metabolism. This ammonia can then be used for growth by a wide variety of creatures on up the food chain. Trichodesmium is an amazing producer of this biologically available nitrogen — perhaps generating as much as 50 percent of organic nitrogen in the world’s oceans (70 to 80 million metric tons) each year.

Human Fossil Fuel Burning is Projected to Drive Trichodesmium Haywire

But now a new study by USC and WHOI shows that atmospheric CO2 concentrations projected to be reached by the end of the 21st Century in the range of 750 ppm CO2 could force Trichodesmium’s nitrogen fixation rate into overdrive and lock it there indefinitely.

Trichodesium Nitrogen Fixation before and after

(Rate of nitrogen fixation in Trichodesmium at 380 ppm CO2 [black and red], at 750 ppm CO2 [pink, yellow and light blue], and when CO2 levels are returned to 380 ppm after five years of exposure to 750 ppm levels [dark blue]. Image source: Nature.)

The study subjected Trichodesmium to atmospheric CO2 concentrations (750 ppm) projected under a somewhat moderate rate of continued fossil fuel burning scenario by 2100 for five years. After this five year period of exposure, Trichodesmium nitrogen fixation rates nearly doubled (see above graphic). But, even worse, after the Trichodesmium bacteria were returned to the more normal ocean and atmospheric conditions under 380 ppm CO2, the rate of nitrogen fixation remained elevated.

In essence, researchers found that Trichodesmium evolved to fix nitrogen more rapidly under higher ocean acidity and atmospheric CO2 states at 750 ppm levels. But when atmospheric levels returned to 380 ppm and when oceans became less acidic, Trichodesmium’s rate of nitrogen fixation remained locked in high gear. For an organism like Trichodesmium to get stuck in a broken rate of higher metabolism and growth is practically unheard of in evolutionary biology. Organisms typically evolve as a response to environmental stresses. Once those triggers are removed, organisms will typically revert to a near match of previous states. Strangely, this was not the case with Trichodesmium.

David Hutchins, professor at the USC Dornsife College of Letters, Arts and Sciences and author of the new study described this alteration to Trichodesium as ‘unprecedented’ stating that:

“Losing the ability to regulate your growth rate is not a healthy thing. The last thing you want is to be stuck with these high growth rates when there aren’t enough nutrients to go around. It’s a losing strategy in the struggle to survive.”

Uncontrolled Blooms, Population Crashes, Biotoxin Production, Dead Zones

Nitrogen is a key component of cellar growth. So Trichodesmium nearly doubling its rate of nitrogen fixation means that the bacteria’s rate of production will greatly increase as atmospheric CO2 levels and ocean acidification continue to rise. Under heightened CO2, the bacteria essentially loses its ability to restrain its population.


(Large algae/bacterial blooms like this red tide off La Jolla, San Diego are causing the expansion of hypoxic and anoxic dead zones throughout the world’s oceans. A new study has found that one of the ocean’s key microbes goes into growth overdrive as atmospheric and ocean CO2 concentrations rise — which would greatly enhance an already dangerous rate of dead zone expansion in the world ocean system. Image source: Commons.)

As a result, researchers warn that Trichodesmium blooms may run out of control under heightening levels of CO2. Such out of control blooms would rapidly remove scarcer nutrients like phosphorous and iron from the water column. Once these resources are exhausted, Trichodesmium would begin to die off en-masse. As with other large scale bacterial die-offs in the ocean, the decaying dead cellular bodies of Trichodesmium would then rob the nearby waters of oxygen — greatly enhancing an already much amplified rate of anoxic dead zone formation. And we know that anoxic waters can rapidly become home to other, far more dangerous, forms of bacterial life. In addition, large concentrations of Trichodesmium are known to produce biotoxins deadly to copepods, fish, and oysters. Humans are also rarely impacted suffering from an often fatal toxicity response called clupeotoxism when the Trichodesmium produced toxins biomagnify in fish that humans eat. Sadly, more large Trichodesium blooms will enhance opportunities for clupeotoxism to appear in human beings.

Exacerbating this problem of heightened Trichodesmium blooms and potential related dead zone formation is the fact that ocean waters are expected to become more stratified as human-forced warming continues. As a result, more of the nutrients that Trichodesmium relies upon will be forced into a thinner layer near the surface — thus heightening the process of bloom, die-off, and dead zone formation.

Final impacts to ocean health come in the form of either widely available nitrogen, (during Trichodesmium bloom periods) which would tend to enhance the proliferation of other microbial life, or regions of nitrogen desertification (during Trichodesmium die-offs). It’s a kind of ocean nitrogen whip-lash that can be very harmful to the health of life in the seas. One that could easily ripple over to land life as well.

No Return to Normal

But perhaps the most shocking finding of the new research was that alterations in Trichodesmium’s rate of growth and nitrogen fixation may well be permanent after the stress of high CO2 and ocean acidification are removed. Hinting that impacts to ocean health from a rapid CO2 spike would be long-lasting and irreparable over anything but very long time-scales. Yet more evidence that the best thing to do is to avoid a major CO2 spike altogether by cutting human carbon emissions to zero as swiftly as possible.


Irreversibly Increased Nitrogen Fixation in Trichodesmium in Response to High CO2 Concentrations

Climate Change Will Irreversibly Force Key Ocean Bacteria into Overdrive


Earth Observatory

Red Tide Algae Bloom off San Diego

Awakening the Horrors of the Ancient Hothouse

Trichodesmium: A Widespread Marine Cyanobacteria with Unusual Nitrogen Fixation Properties

Nitrogen Fixation

Hat Tip to Colorado Bob

The Hothouse Breeds More Toxic Waters — Lake Erie ‘Painted Green’ By Enormous Algae Bloom

Enormous blooms of algae painting the waters green, sickly blue, or blood-red. Algae producing toxins making water unsafe to drink or swim in. Making fish, shellfish and crabs unsafe to eat. Generating life-snuffing dead zones of low oxygen and, potentially, producing deadly hydrogen sulfide gas ranging our lakes, seas, and oceans.

This is what happens when the world is forced to warm, when run-off due to climate change induced extreme rainfall events increases, when the land that run-off comes from is loaded with fossil fuel based fertilizers, and when fossil fuel burning itself generates a constant fall-out of nitrogen from the skies. In ancient hothouse events, similar forces generated mass extinctions in the world’s waters. And through fossil fuel burning we’re setting off a related hothouse type stress to the life-giving liquid we all rely upon. A stress that is yet worsened due to the efficiency with which we are able to load the air, land, and seas with environmental toxins that aid in the generation of algae blooms of an intensity nature alone would have never kicked off.

Toxic algae blooms become common for western Lake Eerie

(In a human-warmed world, toxic algae blooms that threaten Toledo, Cleveland and Akron water supplies are becoming all too common. Algae biomass graphic for the 2013 and 2014 Lake Erie algae blooms provided by NOAA.)

Lake Erie in the Firing Line

In the US, one of the most vulnerable bodies of fresh water to this kind of toxic algae growth is Lake Erie. Over recent decades as the local climate changed, the water warmed. Weather patterns resulted in increased heavy rainfall events. Increased farm industry and fertilizer use meant that much of the run-off was heavily laden with algae food. And the atmosphere itself became loaded up with nitrogen. In addition, the lake is more vulnerable to a life-snuffing stratified state in which the top and bottom layers fail to mix. A final blow came from an invasive species of mollusk — the zebra mussel — which changed the food web in such a way that it favored the growth of the toxic algae we see today. All these factors combined to make the surface waters more and more vulnerable to large, toxic algae blooms and the follow-on formation of dead zones.

Since the mid 1960s, late summer algae blooms have been a regular occurrence on the lake. But more and more now, the blooms are prolific enough to threaten city water draws.

In 2011, Lake Eerie suffered its worst algae bloom on record. At that time, fully 20 percent of the lake was covered in the toxic stuff. Then, both Ohio and Canadian cities along the lake had to shut off water intakes to prevent toxins entering the water system. During 2014 the blooms had again threatened water supplies forcing Toledo to shut its valves. Now, a new algae bloom is threatening Cleveland, Toledo and Canadian water supplies. And, according to NOAA officials, the current bloom may be nearly as intense and widespread as the 2011 event. NOAA notes:

The bloom will be expected to measure 8.7 on the severity index with a range from 8.1 to potentially as high as 9.5. This is more severe than the last year’s 6.5, and may equal or exceed 2013, which had the second worse bloom in this century. The severity index runs from a high of 10, which corresponds to the 2011 bloom, the worst ever observed, to zero.

Toxic Algae Visible From Satellite

As of yesterday, the widespread bloom of toxic algae was plainly visible in the LANCE MODIS satellite shot:

Lake Eerie Algae Bloom

(A large and growing toxic algae bloom in Lake Erie visible from satellite on August 5. It’s a bloom that may eventually prove to be the largest such event on record for the Lake. Image source: LANCE MODIS.)

A huge swath of the western end of the lake was covered with the stuff as of August 5, 2015. A clearly visible green blob blanketing much of Erie’s western surface. Researchers out on boats monitoring this year’s outbreak described the lake as being painted in a thick sheen of goop.

According to NASA, the particular kind of algae that now appears annually in Lake Eerie is called Microcystis. It produces a toxin that is highly dangerous to humans. If consumed, Microcystis may cause numbness, nausea, dizziness, vomiting, lead to liver damage and even result in death. One part per billion in water is all it takes to hit unsafe levels. And boiling toxin-laced water is no remedy — resulting in further concentration of the dangerous stuff.

During August of 2014, unsafe levels were reached at Toledo intakes causing water officials to shut down the lake water supply there. This year, officials are closely monitoring the water supply ready to hit the off switch if the water again hits a dangerous threshold.

Sadly, Lake Erie isn’t the only place on Earth suffering the impacts of hothouse-spurred toxic algae blooms. In the Pacific Ocean, a massive blob of hot water is hosting a red tide of record depth and extent. That particular bloom risks the expansion of an already large dead zone, the proliferation of anoxic and hypoxic waters, and the potential for bottom water production of toxic hydrogen sulfide producing bacteria. In the North Atlantic, swirls of algae blooms are generating mobile dead zones even as the far North Atlantic is witnessing a massive blue-green algae bloom (more on these dangerous human warming related events in upcoming posts).


NOAA Predicts Severe Algae Bloom

Earth Observatory: Lake Eerie Algae Bloom

Eerie’s Enormous Algae Bloom is Back


Hot Pacific Ocean Runs Bloody

Underwater Cyclones of Death

Hat Tip to Andy in San Diego

Hat Tip to Colorado Bob

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.


(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.


The Earth Observatory

Baltic Sea Trends


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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