Ocean acidification is the process by which oceanic waters progressively become more and more acidic, mostly as a result of absorption of atmospheric carbon dioxide. To put that another way, as atmospheric carbon dioxide levels increase, the process of ocean acidification will increase as well. To a point anyways.
Acidic in this case is actually something of a slight misnomer, though, as the “acidification” is actually more of a move to pH-neutral conditions, from the generally slightly basic (pH >7) condition’s of the earth’s oceans.
This move to pH-neutral conditions will have a profound impact on the myriad lifeforms found within the oceans though, as witnessed during previous ocean acidification events such as “The Great Dying” (~252 million years ago), rather than being a trivial process.
Impacts that can be reliably expected are: major changes to plankton distribution, types, and numbers; increasingly common mass coral bleaching events; associated extinctions; depressed metabolic rates and immunity in some types of marine animals, as well as behavioral changes; fishery collapses; and increasingly common red tide events.
To go back over that earlier point a bit more — seawater is generally slightly basic (pH>7), as it absorbs carbon dioxide (CO2) from the atmosphere, or from elsewhere (carbon seeps, etc), some of the absorbed CO2 reacts to form carbonic acid (H2CO3), and leads as well to carbonate (HCO3−) and bicarbonate (CO32−) formation. The carbonate and bicarbonate formation results in increased hydrogen ion (H+) concentrations in the ocean water (acidity) — as they are the “leftovers” of the formation process.
To put at another way — each molecule of carbonic acid that is formed in the ocean as the result of atmospheric carbon dioxide absorption eventually results in the transformation of 2 carbonate ions into bicarbonate ions. Overall, there’s a net-decrease in the quantity of carbonate ions available for the formation of biogenic calcium carbonate by organisms such as: corals, and some types of plankton.
Without the waters that these organisms live in being saturated with concentrations of carbonate ions, they are prone to dissolution and disappearance. (“Saturation” concentrations are tied to temperature, pressure, and depth — as well as to relevant ion concentrations and pH.)
When exposed to elevated CO2 levels, corals, shellfish, coccolithophore algae, coralline algae, pteropods, and foraminifera, all are known to experience reduced calcification and/or enhanced dissolution.
So how much have the waters of the world’s oceans “acidified” since the industrial period began (since significant levels of anthropogenic carbon dioxide emissions began)? How much has ocean acidification progressed since then?
Roughly in step with the progress seen with regard to deforestation, desertification, and extinction rates, apparently.
Conservative estimates are that between 1751 and 1996 surface ocean pH decreased from approximately around 8.25 to 8.14 — representing a roughly 35% increase in oceanic H+ ion concentrations during that time period.
Since the late 1990s the rate of acidification seems to have increased notably — with a 2012 research paper on the matter published in the journal Science stating that there are apparently no historical analogs with regard to the speed of ocean acidification, not anytime in the last 300 million years anyways. The closest analog with regard to speed of acidification would very likely be The Great Dying (discussed in depth in its own section).
Amazingly, during just the 15-year time period between 1995 and 2010 the acidity of the top 100 meters of ocean water in the Northern Pacific (Hawaii to Alaska) increased by 6%, research has shown. This is a much more rapid rise than was predicted previous to that time period.
Another study, dating to 2013, found that current ocean acidification was occurring at a rate roughly 10 times faster than during any previous known event in the earth’s history — including during any of the mass extinction events of the last half-billion years.
A separate synthesis report published in 2015 in the journal Science stated that ocean chemistry was now changing more rapidly than at any time since the Permian-Triassic Extinction Event (The Great Dying). That study noted that “dramatic impacts” are in store without fundamental changes to current carbon dioxide emissions trends.
That’s in reference to the fact that current estimates are that if there are no fundamental cultural changes resulting in vastly reduced carbon dioxide emissions that ongoing ocean acidification will lower average ocean water pH by a further 0.3 to 0.5 pH units by 2100. These figures may represent underestimations, though, as the rate of observed change over the last few decades has been greater than expected.
The former chief biodiversity advisor to the World Bank, Thomas Lovejoy, was publicly quoted awhile back as stating that “the acidity of the oceans will more than double in the next 40 years. This rate is 100 times faster than any changes in ocean acidity in the last 20 million years, making it unlikely that marine life can somehow adapt to the changes.”
As a closing note, to give a better idea of what’s in store for many species — the larvae of temperate sea stars (a close relative of the common sea star) when exposed to waters with the pH reduced by just 0.2 to 0.4 units, during a study on the subject, experienced mortality rates of 99.9% in just 8 days time.
Ocean Acidification Causes, Effects, & Examples: Top 10 List
Phytoplankton Die-Offs + Changes In Range & Distribution
Some of the most important impacts of ocean acidification, as it continues over the coming decades and centuries, will be those relating to marine phytoplankton.
Recent research published in the journal Nature Climate Change by a consortium of different research groups noted that increasing ocean acidification will drastically affect global populations of phytoplankton. Which are, it should be remembered, the absolute base of the marine food chain in the vast majority of environments.
Affects will vary by phytoplankton species type, environment, and niche. Some species will very likely die out completely, some will flourish and move into emptied spaces, and some may not be affected much. This change in the balance of plankton species around the world will have profound, but very unpredictable affects on the marine environments in question. Rapid boom and bust cycles, that larger animals will be very negatively affected by, seem very likely.
The principal researcher in MIT’s Center for Global Change Science that worked on the study, and also lead author, Stephanie Dutkiewicz, commented: “I’ve always been a total believer in climate change, and I try not to be an alarmist, because it’s not good for anyone. But I was actually quite shocked by the results. The fact that there are so many different possible changes, that different phytoplankton respond differently, means there might be some quite traumatic changes in the communities over the course of the 21st century. A whole rearrangement of the communities means something to both the food web further up, but also for things like cycling of carbon.”
The work was essentially a meta-analysis, relying on 49 different papers examine the effects of ocean acidification, and low pH levels, on various phytoplankton.
What the study predicts, is that whole food chains will collapse, and that many phytoplankton species will move towards the poles — resulting in the fundamental rearrangement (and likely collapse) of whole marine ecosystems.
It should probably be noted here that following The Great Dying there was a period of at least 5 million or so years when no new species seem to have emerged (a dead zone, as these time periods are known). During this time the oceans, shallow seas, and land masses, near the equator apparently didn’t support large animals — most animals larger than very small shellfish apparently were restricted to the polar regions.
Commenting on the recent research, Dutkiewicz stated: “If you went to Boston Harbor and pulled up a cup of water and looked under a microscope, you’d see very different species later on. By 2100, you’d see ones that were living maybe closer to North Carolina now, up near Boston.”
A separate study focused on the Indian Ocean found that over just the past 60 years there’s been a decline in total marine phytoplankton biomass of up to 20% (in the Indian Ocean) — as the result of a variety of factors, of which ocean acidification is one.
As an interesting ending note, some researchers have suggested that the expected decline in coccolithophores accompanying worsening ocean acidification will result in increased oceanic warming as a result of reduced albedo.
The Great Dying (Permian-Triassic Mass Extinction Event)
The Great Dying, alternately known as the Permian–Triassic extinction event, or the end-Permian extinction event, was a mass extinction event that serves as the boundary marker between the Permian and Triassic geologic periods (and the Paleozoic and Mesozoic eras).
It is the “worst” mass extinction event known to have ever taken place on the earth — with up to 96% of all marine species going extinct during the event; around 70% of terrestrial vertebrate species going extinct; 57% of all families going extinct; and 83% of all genera going extinct. Notably, this event is the only known mass extinction of insects (probably related to abrupt, extreme drying of many land areas).
As a result of how extensive it was, “recovery” from the mass extinction took up to 10 million years — or more.
The Great Dying occurred right around 252 million years ago, though there may have been more than 3 distinct pulses to the event. While the exact triggers aren’t known for sure, the mass extinction event seems to have coincided with a massive increase in atmospheric carbon dioxide levels, a massive rise in temperature (8° Celsius, or 14° Fahrenheit), and ocean acidification. Interestingly, there are also seems to have been an increase of ultraviolet light making to the surface of the earth (as evidenced by very commonly, notably mutated plant spores).
During periods of the Great Dying ocean surface temperatures seem to have gotten as hot as 40° Celsius (104° Fahrenheit) — presumably those near the equator. Such high temperatures of course don’t offer much opportunity for survival to large animals, or even the vast majority of smaller ones.
Recent research has found that different groups of animals and plants became extinct at different times — implying cascading collapse, and booms and busts, rather than a single asteroid or comet impact event as a sole cause. For instance, ostracod and brachiopod extinctions seem to have been separated by a period of some 670 to 1170 thousand years. There’s a very clear sequence observed in a very comprehensive fossil record in eastern Greenland — one where a great many various animal species are seen to go extinct within a period only 10,000 to 60,000 years long, and are then followed into extinction by numerous plant species several hundred thousand years later.
To expand on that — research dating to 2011 led by Stephen Grasby of the Geological Survey of Canada – Calgary argued that evidence had been found that volcanism had caused massive coal beds to ignite. This, according to the researchers, seems to have led to the release of over 3 trillion tons of carbon into the atmosphere.
The researchers involved in the work apparently found vast coal ash deposits within deep rock layers found near what’s now Buchanan Lake. Their paper on the matter noted that “coal ash dispersed by the explosive Siberian Trap eruption would be expected to have an associated release of toxic elements in impacted water bodies where fly ash slurries developed…. Mafic megascale eruptions are long-lived events that would allow significant build-up of global ash clouds.”
Grasby himself noted in a public statement on the work: “In addition to these volcanoes causing fires through coal, the ash it spewed was highly toxic and was released in the land and water, potentially contributing to the worst extinction event in earth history.”
After the extinction event was “concluded” there wasn’t any observed speciation for quite some time, but rather various “disaster taxa” (opportunists) experienced periods of recurrent boom and bust for quite some time. The generalist Lystrosaurus being an example.
(You could effectively argue that humans fall into this category — opportunists taking advantage of climatic changes and the extinction of numerous megafauna competitors to experience a relatively rapid boom period, before an inevitable bust.)
Recent research shows that specialists, and lifeform types involved in complex ecosystems and/or food webs, took a particularly long time to recover. Rapidly changing circumstances, and just general prolonged environmental difficulties are thought to have been the primary cause of this. In other words, nothing settled down enough for complex exchanges and interactions to reemerge, for some time — outside of various refugia anyways.
To get back to the subject of ocean acidification, most of the marine extinctions seem to have been the result of acidified waters (from high atmospheric carbon dioxide levels), whether directly or indirectly. The very fast rise in temperatures that seems to have occurred very likely played a part in numerous extinctions as well. This may well had led to large oceanic dead zones (anoxic zones, where there’s very limited oxygen).
Notably, one of the primary theories concerning the cause of the mass extinction event supposes massive coal and/or gas fires, explosions from the Siberian Traps, and/or mass methane release from the sea floor.
It’s interesting to note that some groups of animals that nearly went extinct during the event later became widespread and diverged greatly — the sea lilies (crinoids) being an example.
Those marine organisms that did survive the mass extinction event seem to have preferentially been those that possessed active control of their circulatory processes, that possessed elaborate gas exchange abilities, and that were relatively lightly calcified. Those depending upon heavy calcification seem to have been much more likely to go extinct, as well as those with relatively simple gas exchange (breathing) processes.
So, likely those that were more effective at extracting oxygen from their environment, and able to remove unwanted gases from their bodies, as well as those not particularly reliant upon dissolved minerals. In other words, those similar to modern animals that can make a living in anoxic zones, such as the vampire squid.
Interestingly, sea anemones, for instance, experienced only very limited losses — and then later diverged to give rise to most modern corals. There were corals of a sort around at the time, though, rugose and tabulate corals, that experienced very heavy losses during the mass extinction event.
As a bit of a further comment on why high carbon dioxide levels pose such a problem for most marine organisms, it should be recalled that carbon dioxide is roughly 28 times more soluble in water than oxygen is. And also that most marine organisms are used to functioning with very lower body concentrations of the gas (much lower than land animals, which mostly have to remove the gas from their bodies through breathing). As a result, with an extreme increase in oceanic carbon dioxide levels, many organisms have a very hard time functioning — with particularly notable effects being: impaired synthesis of proteins, reduced fertilization rates, and growth deformities.
As a side note, the Permian–Triassic geologic boundary is often host to extremely high levels of marine and terrestrial fungi — apparently as a result of all of the dead things lying around, and the relative lack of living scavengers. This would probably match well with periodic booms and busts following the extinction pulses, as various opportunists worked to expand and grow until collapse occurred.
While there has been some criticism of this idea in the past, with some claiming that much of what was interpreted as being fungi was in fact alga, recent chemical evidence and analysis seems to definitively support the idea that the finds are in fact fungi remains/spores.
Carbon Dioxide Emissions
Ocean acidification is directly caused by rising levels of atmospheric carbon dioxide. Which is itself a direct effect of anthropogenic carbon dioxide emissions, and the feedback loops have now been set into motion (increasing forest fires, drying of rain forests, methane release from permafrost and the sea floor, etc).
As well as from various other human activities, such as deforestation and agriculture — and their associated offspring: soil erosion and desertification.
Anthropogenic carbon dioxide emissions are related to practically every aspect of the modern, industrial world — from industry and the power sector, to agriculture, to transportation and shipping, to heating and climate control. (That last bit has some rather dry humor to it I guess.)
While most carbon dioxide emissions remain in the atmosphere, some end up absorbed and dissolved into the world’s oceans, lakes, and rivers. To date, an estimated 30-40% of anthropogenic carbon dioxide emissions have been absorbed this way — hence ocean acidification. How long the world’s oceans will work so effectively as a carbon sink remains to be seen, as they may well stop absorbing as much carbon dioxide as they now do as ocean chemistry continues changing with acidification.
Notably, atmospheric carbon dioxide levels have been continuing to rise at an ever faster rate every year, seemingly — with the 400 ppm (arbitrary) threshold having been passed “permanently” now.
Coral Reef Bleaching
A very obvious effect of ocean acidification is with regard to mass coral bleaching events, whereby large expanses of coral are killed during relatively short periods of time. While ocean acidification is only one factor amongst a great many in coral bleaching, it is a notable one.
Primary contributors to coral bleaching, other than ocean acidification, are: rising water temperatures (seemingly the main cause); associated rises in pathogenic bacteria and organisms; agricultural runoff; and general environmental stress. Cyanide fishing seems to also have played a part in some events.
As sea temperatures continue to rise, and as ocean acidification continues, coral bleaching events are seemingly becoming more common and severe — with the longest coral bleaching event ever recorded occurring just this year (2016).
Something that’s probably obvious, but that should be stated anyways, is that lower pH levels in ocean water make the building of the calcareous skeletons that coral animals live in much more energy intensive.
“The fluid in the internal compartments where corals grow their exoskeleton is also extremely important for calcification growth. When the saturation rate of aragonite in the external seawater is at ambient levels, the corals will grow their aragonite crystals rapidly in their internal compartments, hence their exoskeleton grows rapidly. If the level of aragonite in the external seawater is lower than the ambient level, the corals have to work harder to maintain the right balance in the internal compartment. When that happens, the process of growing the crystals slows down, and this slows down the rate of how much their exoskeleton is growing. Depending on how much aragonite is in the surrounding water, the corals may even stop growing because the levels of aragonite are too low to pump in to the internal compartment. They could even dissolve faster than they can make the crystals to their skeleton, depending on the aragonite levels in the surrounding water.”
On that subject, there are actually some places where this process can be observed — near carbon seeps on the sea floor. Previous research has shown that the lower pH levels near carbon dioxide seeps are associated with lower overall coral species diversity, and also that coral bio-erosion are much higher than elsewhere. Interestingly, there are spots near Palau though where carbon seeps aren’t associated with lower coral species diversity — though high rates of bio-erosion are still observed.
A final note — a recent study from the Atkinson Center for a Sustainable Future found that rising temperatures and increasing ocean acidification could result in oceanic conditions in which the vast majority of corals won’t survive within only 50 years, going on current projections.
(This article had to be split into 2 to avoid crashing, to see items 5 through 10 of the Top 10 list see: Ocean Acidification Effects, Causes, & Examples List Part 2).