How NOAA and Bad Modeling Invented an “Ocean Acidification” Icon: Part 2 - Bad Models

 Are the Oceans’ Upper Layers Really Acidifying?

Bad models, not measurements, have suggested ocean acidification in the upper layers of the oceans. As detailed in Part 1, NOAA’s Bednarsek, incorrectly attributed the dissolution of sea butterfly shells to anthropogenic CO2 although the evidence clearly showed the natural upwelling of deeper low pH waters were to blame. Based on models employed by NOAA’s Feely and Sabine, Bednarsek claimed the upper ocean layers are becoming more acidic and less hospitable to sea butterflies relative to pre-industrial times. However detecting the location and the depth at which anthropogenic CO2 now resides is a very, very difficult task. Because the ocean contains a large reservoir of inorganic carbon, 50 times greater than the atmospheric reservoir, the anthropogenic contribution is relatively small. Furthermore anthropogenic carbon comprises less that 2% of the combined CO2 entering and leaving the ocean surface each year. Thus there is a very small signal to noise ratio prohibiting accurate detection of anthropogenic CO2. Despite admittedly large uncertainties, modelers boldly attempt to infer which layers of the ocean are acidifying. 

Sea Butterfly  Limacina helicina

(To clarifying terminology, an organic carbon molecule is a molecule that is joined to one or more other carbons, such as carbohydrates and hydrocarbons. CO₂ with a lone carbon is considered inorganic, and when dissolved can take 3 forms (or “species”) collectively referred to as Dissolved Inorganic Carbon (henceforth DIC): 1) Carbonic acid (H₂CO₃),  2) Bicarbonate ion (HCO₃^-) after losing one H+ 3) Carbonate ion (CO₃^-2) after losing a second H+ )

However model results are based on three very dubious assumptions:

1) Models assume surface layers absorb anthropogenic CO2 by reaching equilibrium with atmospheric concentrations. With minor adjustments, models simply calculate how much dissolved inorganic carbon (DIC) will be added to the ocean based on increased atmospheric CO2 since pre-industrial times.

2) Models assume CO2 will diffuse into the upper ocean layers and be transported throughout the ocean in a similar fashion to tracers, like CFCs. Because CFCs accumulate disproportionately near the surface, models assume DIC does as well.

3) Models assume biosphere is in a steady state. Thus they do not take into account increased primary production and the rapid export of carbon to depth.

Although there is no doubt anthropogenic CO2 is taken up by the oceans, assertions that ocean surface layers are acidifying are the results of faulty model assumptions.

What Equilibrium?

CO2 equilibrium is rarely achieved between ocean and atmosphere. Ocean surface pH and thus calcium carbonate saturation levels are determined by the efficiency of the biological pump. In other words, when, where, and how much CO2 enters the ocean surface, requires surface CO2 concentrations to be lower than atmospheric concentrations. That difference depends on how much CO2 is fixed into organic carbon by photosynthesis and subsequently exported it to depth, or how much CO2 is upwelling. Photosynthesis indiscriminately draws down all CO2 molecules that have invaded surface waters either via upwelling from depth or by diffusion from the atmosphere. Despite opposing effects of mixing and diffusion, the biological pump maintains a strong vertical gradient of high surface water pH and low DIC, with decreasing pH and increasing DIC at greater depths. In regions where strong upwelling of DIC from the deeper ocean overwhelms the ability of photosynthesizing organisms to sequester carbon, surface pH drops and CO2 is outgassed to the atmosphere. Several models estimate that without the biological pump, atmospheric CO2 would increase by 200 to 300 ppm above current levels.

The efficiency of the biological pump determines to what depths anthropogenic carbon will be transported. However NOAA’s Sabine does not model the effects of the biological pump, oddly stating “although ocean biology plays an integral role in the natural distribution of carbon in the ocean, there is no conclusive evidence that the ocean uptake and storage of anthropogenic carbon, thus far, involve anything other than a chemical and physical response to rising atmospheric CO2.”

Does Sabine truly believe the undeniable biological pump discriminates between anthropogenic and natural carbon? Or does he believe that there have been no changes in primary production and carbon export?  As primary production increases, so does the carbon export to depth. Annual primary production in the Arctic has increased by 30% since 1998. We can infer primary production increased in the Sargasso Sea based on a 61% increase in mesoplankton between 1994 and 2006. North Atlantic coccolithophores have increased by 37%  between 1990 and 2012. And primary production and carbon export in the Peru Current has dramatically increased since the end of the Little Ice Age. The increasing trend in primary production and accompanying carbon export is potent evidence supporting an alternative hypothesis that the biological pump has sequestered increased invasions of anthropogenic CO2.

An examination of seasonal changes in surface CO2 concentration, illustrates how the biological pump determines when and how much CO2 enters the ocean, and how much DIC accumulates near the surface. As exemplified by the graph below from 2008 buoy data off the coast of Newport, Oregon (Evans 2011), each spring photosynthesis lowers ocean surface CO2 to 200 ppm, far below current atmospheric concentrations and much lower than what would be expected from equilibrium with a pre-industrial atmosphere. Spring surface waters are supersaturated, and any downwelling or mixing of these supersaturated waters cannot acidify upwelled water or subsurface layers. Furthermore the springtime draw down conclusively removes any anthropogenic CO2 residing in sunlit waters. Furthermore experiments show CO2 is often a limiting nutrient and added atmospheric CO2 stimulates photosynthesis. Microcosm experiments found that when atmospheric CO2 was increased, the plankton community consumed 39% more DIC.

Daily CO2 concentrations in surface waters off Newport Oregon from Evans 2011

Upwelling season begins in summer extending through fall. As illustrated above, upwelling events rapidly raise surface concentrations of CO2, reaching 1000 ppm. Physics dictates there can be no net diffusion from the atmosphere into the ocean when the oceanic concentration is higher than atmospheric, and thus there are virtually no anthropogenic additions during upwelling season. Here any lowering of surface pH or calcium carbonate saturation must be due to upwelling.

Finally during the winter, (not illustrated) surface waters exhibited a steady CO2 concentration of 340 ppm. Although photosynthesis is reduced, and winter mixing brings more subsurface carbon and nutrients to the surface, the surface remains below equilibrium with the atmosphere. Although surface concentrations are low enough to permit the invasion of atmospheric CO2, the biological pump continues to export that carbon to depth so that surface layers remain supersaturated all winter.

Diffusion of CO2 into the ocean is a slow process. It is believed that it requires about 1 year for the oceans to equilibrate with an atmospheric disturbance. But as spring arrives, increasing sunlight again enhances photosynthesis, so whatever anthropogenic CO2 that may have invaded the surface over the course of the year, is once again fully sequestered and pumped to depth, lowering surface CO2 concentrations to 200 ppm. Bednarsek’s claim that anthropogenic CO2 is acidifying the upwelled water along the Oregon California Coast is once again not supported.

Tracers Do Not Correctly Simulate Transport of Anthropogenic Carbon

Tracers like chlorofluorocarbons (CFCs) are synthetic gases that are biologically inert. They were introduced to the world during the 1920s primarily as a refrigerant. Climate scientists have assumed the physical transport and accumulation of CFCs and increasing anthropogenic carbon will be similar. Below in Figure 1, the red area just south of Greenland designates an area that has accumulated the most CFCs. This local concentration happens when high salinity Atlantic waters cool and carry surface water and its dissolved gasses downward to the abyss forming North Atlantic Deep Water. It is estimated that this downwelling has exported 18% of all CFCs below 1000 meters; implying dissolved anthropogenic carbon has been similarly exported and sequestered. However elsewhere CFCs accumulate disproportionally in upper surface layers, so models assume dissolved anthropogenic CO2 is likewise accumulating nearer the surface.

Both CFCs and CO2 are gases, and their solubility is similarly modulated by temperature. Warm waters of the tropics absorb the least amount of CFCs and CO2, as illustrated by the dark blue regions in Figure 1 from Willey 2004. Thus equatorial waters feeding the California Undercurrent that upwell along the west coast have likewise absorbed the least amounts of anthropogenic carbon, if any. (The extremely low level of CO2 diffusion into the tropical ocean plus the super saturation of tropical waters, casts great misgivings on any claim that coral reefs have been significantly affected by anthropogenic acidification.)

However, unlike inert CFCs, any CO2 entering sunlit waters is quickly converted to heavy organic matter by photosynthesis. Although dissolved CFCs and dissolved carbon are passively transported in the same manner, particulate organic carbon (alive or dead) behaves very differently. Particulate carbon rapidly sinks, removing carbon from the surface to depth in ways CFC tracers fail to simulate. Examination of the literature suggests “various methods and measurements have produced estimates of sinking velocities for organic particles that span a huge range of 5 to 2700 meters per day, but that commonly lie between tens to a few hundred of meters per day”. Low estimates are biased by suspended particles that are averaged with sinking particles. Faster sinking rates are observed for pteropod shells, foraminifera, diatoms, coccolithophorids, zooplankton carapaces and feces aggregations, etc that are all capable of sinking 500 to 1000 meters per day. These sinking rates are much too rapid to allow respired CO2 from their decomposition to acidify either the source waters of upwelling such as along the Oregon and California coast, or the surface waters

Earlier experiments had suggested single cells sank very slowly at rates of only 1 meter per day and thus grossly underestimated carbon export. However single-cell organisms will aggregate into clusters that increase their sinking rates. Recent studies revealed the “ubiquitous presence of healthy photosynthetic cells, dominated by diatoms, down to 4,000 m.” Based on the length of time healthy photosynthesizing cells remain viable in the dark, sinking rates are calculated to vary from 124 to 732 meters per day, consistent with a highly efficient biological pump. Although NOAA's scientists have expressed concern that global warming will reduce the efficiency of the biological pump by shifting the constituents of phytoplankton communities to small, slow-sinking bacteria, new research determined that bacteria also aggregate into clusters with rapid sinking rates ranging from 440 to 660 meter per day.

Sequestration of carbon depends on sinking velocities and how rapidly organic matter is decomposed. Sequestration varies in part due to variations in the phytoplankton communities. Depths of 1000 meter are considered to sequester carbon relatively permanently, as waters at those depths do not recycle to the surface for 1000 years. Weber 2016 suggests 25% of the particulate organic matter sinks to 1000 meter depths in high latitudes while only 5% reaches those depths at low latitudes. But long-term sequestration does not require sinking to 1000 meter depths. Long-term sequestration requires sinking below the pycnocline, a region where the density changes rapidly. Dense waters are not easily raised above the pycnocline, so vertical transport of nutrients and carbon is inhibited creating long-term sequestration. Because the pycnocline varies across the globe, so do sequestration depths.

Below on the left is a map (a) from Weber 2016, estimating to what depths particles must sink in order to be sequestered for 100 years. Throughout most of the Pacific particles need only sink to depths ranging from 200 to 500 meters. In contrast the golden regions around the Gulf Stream, New Zealand and southern Africa must sink to 900 meters.

The map on the right (b), estimates what proportion of organic matter leaving the sunlit waters will be sequestered. The gold in the Indian Ocean estimates 80% will reach the 100-year sequestration depth, while 60% will reach sequestration depths along the Oregon California Coast. Again casting doubt on Bednarsek’s claims of more recently acidified upwelled waters acidifying sea butterfly shells. Elsewhere in map “b”, 20% or less of the exported carbon reaches sequestration depths.

Estimation of sequestration depths and proportion of carbon reaching sequestraton

The combination of sinking velocities and sequestration depths suggests significant proportions of primary production will be sequestered in a matter of days to weeks. This is consistent with the maintenance of the vertical DIC and pH gradients detected throughout our oceans. However it conflicts with claims by NOAA’s scientists.

Biased by CFC observations Sabine wrote, “Because anthropogenic CO2 invades the ocean by gas exchange across the air-sea interface, the highest concentrations of anthropogenic CO2 are found in near-surface waters. Away from deep water formation regions, the time scales for mixing of near-surface waters downward into the deep ocean can be centuries, and as of the mid-1990s, the anthropogenic CO2 concentration in most of the deep ocean remained below the detection limit for the delta C* technique.”

That NOAA scientists fail to incorporate the fact that particulate carbon can be sequestered to harmless depths in a matter of days to weeks instead of “centuries” appears to be the cause of their catastrophic beliefs about ocean acidification. Furthermore because CFCs have accumulated near the surface with only miniscule amounts in the deeper ocean, the tracer provides absolutely no indication of how upwelling brings ancient DIC to the surface. So by relying on a CFC tracer, their models will mistakenly assume that increased concentrations of DIC near the surface must be due to accumulating anthropogenic carbon, and not upwelled ancient carbon.

The Ocean’s Biosphere Steady State?

Given a steady export percentage of primary productivity, increasing amounts carbon will be exported in proportion to increasing productivity. Thus it is reasonable to hypothesize that if marine productivity has increased since the end of the Little Ice Age (LIA) aka pre-industrial times, that increased production will have sequestered the increasing amounts of anthropogenic carbon. Although there are only a few anoxic (depleted oxygen) ocean basins, where organic sediments can be well preserved, those basins all reveal that since the Little Ice Age, marine productivity and carbon export has indeed increased as the oceans warmed.

Research from Chavez 2011 is illustrated below and demonstrates that during the LIA, marine primary productivity (d) was low, but has increased by 2 to 3 fold over the recent 150 years. Sediments reveal that fast sinking diatoms increased 10 fold at the end of the LIA, but likely due to silica limitations, since 1920 diatom flux to ocean sediments has been reduced to about a 2-fold increase over the LIA. Nonetheless numerous studies find estimates of sedimentary diatom abundance is representative of carbon export production in coastal upwelling regions.

The increased primary production coincides with over a hundred-fold increase in fish scales and bones (f). And consistent with the need for increased nutrients to support increased primary production, proxy evidence suggests a 2-fold increase in nutrients in the water column (c). Such evidence is why researchers have suggested their observed decadal increases in upwelled DIC and nutrients might be part of a much longer trend. Finally in contrast to the global warming explanation for depleted ocean oxygen, the decomposition of increased organic carbon provides a more likely explanation for observations of decreased oxygen concentrations in the water column (a) and sediments (b). Because primary production had doubled by 1900, long before global warming or before anthropogenic CO2 had reach significant concentrations, it is unlikely anthropogenic CO2 contributed to increased upwelling, increased primary production or any other trends in this region

However increased primary production alone does not guarantee that sinking particulate carbon is removing enough carbon to counteract anthropogenic additions. However there are dynamics that suggest this must be the case. First consider that an examination of the elements constituting a phytoplankton community, there is a common ratio of 106 carbon atoms detected for every 16 nitrogen atoms (aka a Redfield ratio). Given that nitrogen typically limits photosynthetic production, if carbon and nitrogen are upwelled in the same Redfield proportion, unless other dynamics cause an excess of nitrogen, photosynthesis might only assimilate upwelled carbon but not enough to account for all the additional anthropogenic carbon.

However calcifying organisms like pteropods, coccolithophores and foraminifera export greater proportions of inorganic carbon because their sinking calcium carbonate shells lack nitrogen. This can create an excess of nitrogen relative to upwelled carbon in surface waters. Second diazotrophs are organisms that convert atmospheric nitrogen into biologically useful forms. Free-living diazotrophs like the cyanobacterium Trichodesmium, can be so abundant their blooms are readily observed. (The blooms of one species are primarily responsible for the coloration of the Red Sea.) Some diazotrophs form symbiotic relationships with diatoms and coral. So diazotrophs can cause an excess of nitrogen that allows photosynthesis to assimilate both upwelled carbon and anthropogenic carbon. Furthermore as discussed in Mackey 2015 (and references therein) “To date, almost all studies suggest that N₂ fixation will increase in response to enhanced CO2.”

With all things considered, the evidence suggests NOAA scientists have an upside down characterization of the ocean’s “steady state.” There is no rigid rate of primary production and export that prevents assimilating anthropogenic carbon and pumping it to depth. On the contrary the combined dynamics of nitrogen fixation and the biological pump, suggest the upper layers of the ocean have likely maintained a pH homeostasis, or a pH steady state, at least since pre-industrial times. Increases in atmospheric CO2, whether from natural upwelling or from anthropogenic sources, are most likely assimilated quickly and exported to ocean depths where they are safely sequestered for centuries and millennia. As also discussed in the article How Gaia and Coral Reefs Regulate Ocean pH, claims that the upper ocean has acidified since preindustrial times are not measurements, but merely results from modeling a “dead” ocean and ignoring critical biological processes.

How NOAA and Bad Modeling Invented an “Ocean Acidification” Icon: Part 1 - Sea Butterflies

If you google “ocean acidification,” the first 3 websites presented according to “Google’s truth rankings” are: 1) Wikipedia, 2) NOAA’s PMEL site featuring the graphic cartoon shown below with a dissolving pteropod shell (a sea butterfly) as the icon of ocean acidification, and 3) the Smithsonian’s Ocean Portal site similarly featuring a dissolving sea butterfly shell. However NOAA’s illustration incorrectly implies shells are dissolving near the surface due to invading anthropogenic atmospheric CO2. As will be shown, the depiction would be far more accurate if it was turned upside down, so that the downward arrows point upwards to illustrate shell dissolution happens when old carbon stored at depth is upwelled to the surface. Furthermore the horizontal depiction of extreme dissolution illustrated by their intact (green) sea butterfly shell dissolving into an extremely shriveled shell (red), rarely if ever happens in the ocean’s upper layers. Surface waters are supersaturated regards calcium carbonates. Although upwelling causes some near surface dissolution, dead sea-butterfly shells only experience such extreme dissolution when they sink to depths containing ancient corrosive waters.

NOAA's Upside Down Cartoon of Sea Butterfly SHell Dissolution

As for most organisms, pteropod populations fluctuate over the short term. But research finds no significant long-term trends in pteropod abundance. Nonetheless NOAA’s Nina Bednarsek has been preparing a preliminary report arguing sea butterflies should be listed as endangered and NOAA’s cartoon appears to be an attempt to gain support for her claims. To warrant endangered status, Bednarsek presents a hypothesis that increasing CO2 has reduced critical pteropod habitat by raising the depth of calcium carbonate saturation horizons.  The threshold above which high concentrations of carbonate ions (CO₃^2-) promote abiotic calcium carbonate precipitation but below which favors dissolution, is referred to as the saturation horizon. The horizon is quantified as 1, and higher numbers characterize supersaturated water that favor calcification. As seen below in Fig 10 from Jiang 2016, most of the globe’s surface oceans are supersaturated.

Global calicum carbonate supersaturation from Jiang 2016

Bednarsek assumes anthropogenic carbon is mostly accumulating near the surface based on modeling results. However as detailed in Part 2, all ocean acidification models are deeply flawed based on an incorrect assumption that CO2 enters the ocean and is then transported like an inert tracer. But CO2 is not inert! When CO2 first invades sunlit surface waters, it indeed dissolves into 3 forms of inorganic carbon (DIC) and lowers pH (DIC is discussed in How Gaia and Coral Reefs Regulate Ocean pH). But in contrast to those models, DIC is rapidly assimilated into particulate organic carbon via photosynthesis, which raises pH.  Particulate organic carbon (alive or dead) is heavy, and if not consumed and recycled, it sinks. For millions of years, this process created and maintained a DIC/pH gradient with high pH/low DIC near the surface and low pH/higher DIC at depth.

Gravity drives the biological pump and removes a significant proportion of organic carbon (assimilated from both natural and anthropogenic carbon). That carbon is transported to depths where it can be harmlessly sequestered for hundreds to thousands of years. However NOAA’s models fail to account for the biological pump, based on the narrow belief that carbon storage is strictly “a chemical and physical response to rising atmospheric CO2” (Sabine 2010). In contrast to Bednarsek’s anthropogenic hypothesis, an increase in the assimilation of CO2 and an efficient biological pump can prevent a decrease in surface pH and calcium carbonate saturation. In fact experiments show CO2 is often a limiting nutrient. Mesocosm experiments found that when atmospheric CO2 was increased, primary production by plankton community consumed 39% more DIC. When primary production increases, more carbon is shuttled to depth.

Meet the Sea Butterflies

 

 

Sea Butterfly  Limacina helicina

 

Sea butterflies are pteropods, a kind of snail exclusively living in the open ocean. A cubic meter of seawater may contain 50 to several thousand individuals. Unlike their terrestrial relatives that plod along on a slimy “foot”, pteropods transformed their foot into a pair of wings to “fly” through ocean waters.

Pteropods are divided into two main groups: sea butterflies with extremely thin, coiled or cone-shaped shells, and “naked” sea angels that evolved a way to shut off their shell-making genes completely when larvae. Sea butterflies feed by suspending themselves in the water column and extruding a web of mucus that passively catches sinking plankton and other organic particles. In contrast sea angels specialized to aggressively prey on sea butterflies. Abandoning their shell suggests whatever benefits a shell may have provided, those benefits were not critical, but losing the shell increased their maneuverability for the hunt. When encountering a sea butterfly, the bizarre sea angel shoots out tentacles from its head. The tentacles dig into the butterflies’ shells and if properly grasped, the tentacles give the angel leverage to extract the butterfly from its shell opening. Below is a 2-minute video below of a sea angel attacking a sea butterfly (not in English). Fish and whales also feed on sea butterflies, gulping mouthfuls at a time. So overall the butterfly’s shell offers precious little protection from their main predators.

https://www.youtube.com/watch?v=Phj5WS6czeA

While Bednarsek fears pteropods might not adapt quickly enough to rising atmospheric CO2, pteropod behavior argues they are already well adapted. Sea butterflies prefer to graze in highly productive regions generated by nutrient rich but corrosive upwelled waters. Accordingly upwelled regions are typically key reproductive habitat supporting an abundance of juveniles. Sea butterflies are most abundant in the upper 50 meters of the ocean, grazing on abundant phytoplankton. However depending on the species, the population, and location, most sea butterflies migrate daily to depths of 100 meters or more (sometimes below 500 meters) where pH can drop to around 7.6 and waters become corrosive. Similarly they will migrate to deeper more “acidic” depths to over-winter. And although tropical waters are the most supersaturated and the most unlikely to promote shell dissolution, pteropods are least abundant in those tropical waters. In contrast they are very abundant in marginally supersaturated waters around Antarctica.

All calcifying organisms have a protective organic layer that minimizes sensitivity to any changes in seawater pH and all isolate their calcifying chambers from ambient water conditions. Mollusks like clams, oysters and snails have a protective outer layer of organic tissue called the periostracum. The mollusk periostracum has allowed them to colonize the acidic depths of ocean floors, colonize freshwater lakes and streams where pH falls to truly acidic levels below 6.0, and to colonize the flanks of submerged volcanoes where escaping CO2 naturally lowers the pH between 7.3 and 5.39.

Single cell foraminifera and coccolithophorids have some of the thinnest organic layers that effectively prevent dissolution, and the petite sea butterfly has one of the thinnest mollusk periostraca. How well it protects the sea butterfly has created a debate between Bednarsek and other pteropod researchers. Bednarsek argues the sea butterfly’s thin periostracum, especially in juveniles, offers very little to no protection from low pH water suggesting they are very susceptible to life threatening shell dissolution. In contrast other researchers argue shell dissolution occurs when the periostracum is damaged. During the sea butterflies’ short life, which can be less than a year, they are under constant attacks from predators like sea angels that can damage their periostracum. There also exists a whole range of shell-inhabiting/shell-digesting organisms from bacteria to sponges and worms (aka the epibiont) that drill through a mollusk’s periostracum. Thus researchers argue when the periostracum remains intact, “the shell appears pristine with no sign of dissolution”, even when exposed to undersaturated waters. Only the damaged shells showed dissolution when exposed to undersaturated water. Based on observations, they concluded sea butterflies “are perhaps not as vulnerable to ocean acidification as previously claimed, at least not from direct shell dissolution.”

Dissolution of Sea Butterfly Shell from Bednarsek 2014

Furthermore to counteract shell dissolution in damaged areas, sea butterflies rapidly repair their shells by adding more calcium carbonate to the inside of the shell. Biogenic calcification happens at much greater rates than dissolution, and such rapid repair mechanisms would be expected for an animal seeking low pH upwelled waters to graze.

Ironically Bednarsek’s electron microscope images of corroded sea butterfly shells, provide evidence that supports her detractors. The shell (Figure 2 above) from Bednarsek’s 2014 paper, shows severe dissolution (labeled “b”) on the innermost whorls, similar to her other images (not shown here) showing widespread dissolution on juvenile shells. However despite dissolution during its juvenile stage, the snail clearly survived and continued to grow. The subsequent growth shows very little dissolution (labeled “a”). That suggests two possible scenarios that are not mutually exclusive. The snail’s exposure to corrosive waters was limited to short-term episodic upwelling during its earliest years, and was an insignificant cost of grazing in highly productive waters. Or if corrosive conditions continued, then the more developed periostracum protected the shell from further dissolution. The small area of severe dissolution within the section of unharmed shell (the patch to the right of region b) further supports the argument that dissolution only happens where there is damage. Otherwise, if the periostracum provided little protection, then the whole region would have suffered dissolution not just the isolated patch. Thus life-threatening dissolution is just conjecture, and as Bednarsek later admits, “dissolution-driven mortality in pteropods has not been directly confirmed.”

Catastrophic Dissolution?

Long before the politics of climate wars emerged, Mark Twain quipped, “There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.”  Indeed the oft-cited Orr 2005 “ocean acidification” paper is an iconic example illustrating Twain’s observation. Orr et al examined just 14 living sea butterflies (Clio pyramidata, see photograph below), captured in the subarctic Pacific. Orr exposed them for 48 hours to experimentally induced under-saturated water that he predicted would occur in the future around Antarctica due to rising atmospheric CO2. All specimens survived. However scanning electron microscopy revealed etching on their shells.

Although it is highly unlikely such minor etching would be of any consequence, Orr 2005 jumped to hypothesizing that pteropod species “will not be able to adapt quickly enough to live in the undersaturated conditions”. Orr 2005 lamented rising atmospheric CO2 would reduce pteropod habitat and survival, leading to ecosystem collapse in polar regions. He speculated arctic pteropods could be forced southward to warmer waters that were more saturated. Due to the butterfly’s imagined extirpation via dissolution, he predicted sea butterfly predators such as sea angels, fish and whales would all suffer. Such was their wholesale catastrophic conjecture, published in a top journal, based on etching in 14 specimens. 

Observed Dissolution due to Ancient CO2 Enriched Waters

Nina Bednarsek followed with a 2012 paper in which she too attributed shell dissolution of a sea butterfly (Limacina helicina) to increasing anthropogenic CO2. Media outlets promoted her conclusions in articles like Science Daily’s “First Evidence Of Ocean Acidification Affecting Live Marine Creatures In The Southern Ocean.”  Unfortunately the term “ocean acidification” is indiscriminately used to describe any reduction of pH even if naturally induced by upwelling.

On her cruise through the Scotia Sea (just north of the Antarctic peninsula), Bednarsek collected snails at depths of 200 meters from 6 different stations. Snails at five stations showed no evidence of shell dissolution. All stations exhibited supersaturated surface waters. Her shell dissolution was limited to just one station.

All stations experienced upwelling and Bednarsek acknowledged, “these upwelled waters are approximately 1000 years old”. Thousand-year old water means it had not contacted the surface for 1000 years, and those deep waters had not absorbed any anthropogenic CO2. The water’s corrosiveness was due to a millennium of decomposing sunken organic matter that increasingly released CO2 and lowered pH. Still she conjectured the observed dissolution was due to anthropogenic CO2.

Because winds will mix supersaturated surface waters with corrosive upwelled waters in the upper 200 meters, mixing can neutralize any corrosive effects of upwelled waters. To attribute her observed dissolution to anthropogenic CO2, Bednarsek argued recent invasions of anthropogenic CO2 into the surface water had lowered its surface pH to such an extent, mixing no longer counteracted the low pH of upwelled water. It was a reasonable hypothesis, however there was no evidence to support it.

At the one and only station where snails had experienced dissolution, surface waters were far more supersaturated than at any other station. In contrast to Bednarsek’s narrative, that station’s supersaturated waters should have had the most neutralizing effect. Her anthropogenic attribution was simply not consistent with observations. More parsimoniously either that one station experienced greater upwelling, or there was less wind mixing to deepen the neutralizing effect. It is puzzling why peer-review or the editors at Nature allowed her unsupported anthropogenic conclusion to be published.

In 2014, NOAA News promoted another paper by Bednarsek about dissolving sea butterfly shells with the headlines, “NOAA-Led Researchers Discover Ocean Acidity Is Dissolving Shells Of Tiny Snails Off The U.S. West Coast.”  NOAA’s press release explicitly stated the term “ocean acidification” described the process of ocean water becoming corrosive as a result of absorbing nearly a third of the carbon dioxide released into the atmosphere from human sources.” In contrast, her observed shell dissolution only happened where upwelling was the greatest, along Oregon and northern California.  Along southern California where upwelling was minimal, Bednarsek found no dissolution. If acidification was due to atmospheric CO2, we would expect a more uniform pattern of dissolution. But again Bednarsek set forth a scenario to blame anthropogenic CO2, arguing upwelled waters had been directly “acidified” by anthropogenic CO2.

She speculated the upwelled waters had been near the surface 50 years ago, during which time it equilibrated with the 1960s atmosphere. Those waters then sank to depths of 80 to 200 meters, and were now upwelled to the surface. However the problem with this scenario is the source of upwelled waters along the California Oregon coast can be traced back to the California Undercurrent. The California Undercurrent originates in equatorial regions primarily at depths 100 to 200 meters and flows poleward beneath the equatorward flowing California Current. The undercurrent is supplied with low pH, low oxygen, and high inorganic carbon waters from the eastern tropical Pacific. Due to the accumulation of ancient carbon, the eastern tropical Pacific contains some of the oldest waters on earth and more than any other region on earth ventilates tremendous amounts of CO2 from the ocean into the air.

Studies of the changing characteristics of the California Undercurrent conclude all its “changes are consistent with an increasing influence of Pacific equatorial waters” over the past decades. During a negative Pacific Decadal Oscillation (PDO) or a La Nina, research shows the California Undercurrent acquires increased amounts of those ancient waters and upwelling is stronger. Although those studies did not consider possible anthropogenic contributions, the trends in lower oxygen and lower pH were explained by natural increased mixing of older water masses. That mixing trend could represent decadal variability or the centuries long increasing upwelling trend documented under the Peru Current (detailed in Part 2).

The same corrosive upwelling associated with Bednarsek’s sea butterfly dissolution was also responsible for the corrosive waters that oyster fisherman unwittingly pumped into larval-rearing tanks in 2008-9. (To make matters worse, oyster fishermen pumped water in the early morning when nighttime respiration further acidified the water). And consistent with multidecadal variability, during the previous negative PDO from 1940 to the late 70s, corrosive upwelled waters had similarly reduced survival of larval oysters in those bays. Clearly natural oscillations episodically upwell more nutrient-rich, oxygen-poor corrosive waters. And because oceans contain the greatest concentration of inorganic carbon by far, the question remains has anthropogenic CO2 significantly exacerbated the corrosiveness of natural upwelling? In contrast, NOAA’s Richard Feely believes anthropogenic CO2 is the primary factor. Thus he answers that question with an upside down perspective, stating upwelling “exacerbates [anthropogenic] ocean acidification”. And as detailed in part 2, NOAA's models have an upside down representation of carbon distribution.

The sea butterfly joins the parade of icons like polar bears, penguins, pika, mangroves and Parmesan’s butterflies where the effects of natural climate variability or direct human interference are obscured and falsely promoted as catastrophic climate change.

How Gaia and Coral Reefs Regulate Ocean pH

Although some researchers have raised concerns about possible negative effects of rising CO2 on ocean surface pH, there are several lines of evidence demonstrating marine ecosystems are far more sensitive to fluxes of carbon dioxide from ocean depths and the biosphere’s response than from invasions of atmospheric CO2. There is also ample evidence that lower pH does not inhibit photosynthesis or lower ocean productivity (Mackey 2015). On the contrary, rising CO2 makes photosynthesis less costly. Furthermore in contrast to researchers arguing rising atmospheric CO2 will inhibit calcification, increased photosynthesis not only increases calcification, paradoxically the process of calcification produces CO2 and drops pH to levels lower than predicted by climate change models. A combination of warmer tropical waters and coral reef biology results in out-gassing of CO2 from the ocean to the atmosphere, making coral reefs relatively insensitive to the effects of atmospheric CO2 on ocean pH.

Sixty million years ago proxy evidence indicates ocean surface pH hovered around 7.4. If surface pH was in equilibrium with the atmosphere, then CO2 concentrations would have hovered around 2000 ppm, but there is no consensus that CO2 reached those levels. However as will be discussed, there are biological processes that do lower surface pH to that extent, despite much lower atmospheric CO2 concentrations.

Over the next 40 million years corresponding with the rearrangement of the continents and ocean currents, the formation of the Antarctic Circumpolar Current and initiation of Antarctic glaciers, the evolutionary expansion of diatoms and their increasing abundance (diatoms are the most efficient algae for exporting carbon to ocean depths), ocean carbonate chemistry was greatly altered. As a result ocean surface pH gradually rose above pH 8. Then for our last 20 million years, ocean surface pH has fluctuated within this new equilibrium between 8.4 and 8.1, as seen in Figure 1 below (Pearson and Palmer 2000). For the past 400,000 years, pH rose to about 8.35 during the depths of each ice age. Then during each warm interglacial period, when both land and marine productivity increased, pH fell to ~8.1 (Honisch 2005).

60 million years of ocean pH

Although it is commonly assumed atmospheric CO2 and ocean surface pH are in equilibrium, studies examining various time frames from daily and seasonal pH fluctuations (Kline 2015) to the millennial scale transitions from the last ice age to our warm interglacial (Martinez-Boti 2015), demonstrate surface ocean pH has rarely been in chemical equilibrium with atmospheric CO2. Because oceans contain over 50 times as much CO2 as the atmosphere, surface pH is more sensitive to changes in the rates of upwelling of low-pH, carbon-rich deep waters. It is the response of photosynthesizing organisms and the food webs they support that largely determines how much carbon is sequestered in the surface layers and then sent to deeper waters (the biological pump).

As discussed in an earlier essay, the “biological pump” modulates how much CO2 is sequestered and how much CO2 will out-gas to the atmosphere. It has been estimated that without the biological pump, pre-industrial atmospheric CO2 would have out gassed and raised atmospheric CO2 to 500 ppm, instead of the observed 280 ppm. Ironically the processes that build coral reefs also increase surface CO2 concentrations and lower regional pH to levels lower than expected by equilibrium with atmospheric CO2. This biological control of the earth’s chemistry is the essence of Gaia theory.

Gaia theory stimulated great scientific interest (as well as controversy) since the 1970s, and stimulated more extensive investigations into how the biosphere affects the earth’s chemistry. Gaia’s founding scientist James Lovelock formulated Gaia theory while working for NASA seeking chemical signatures of life on other planets. For example, due to living organisms our atmosphere maintains about a 21% concentration of oxygen. Without photosynthesizing organisms, the atmosphere would contain extremely low amounts of oxygen. Thus Lovelock argued, “if life has merely a passive role in cycling the gases of the air, then the concentrations will be set by equilibrium chemistry; in fact they most certainly are not.” Shedding the mystical connotations that many “New Age” adherents attributed to Gaia, several universities have now created departments studying Gaia’s effects, but under less anthropomorphic titles such as Earth System Sciences or Biogeochemistry.

Unfortunately Gaia is often misrepresented as a conscious super-being deserving of religious devotion, with some adherents even advocating Gaia should replace the earth’s major religions. Gaia’s deification was resented both in established religious circles, and by Gaia’s scientific proponents like Dr. Lynn Margulis. She stressed Gaia is simply “an emergent property of interactions among organisms". Or as one of her graduate students suggested, Gaia is simply “symbiosis as seen from space”.

Gaia theory also weighed in on climate change debates and was advocated by Al Gore and climate scientists such as Stephen Schneider. While basic Gaia theory simply argues a variety of biological interactions provide negative feedbacks from which a degree of self-regulating homeostasis emerges, those with a more alarmist view of the earth’s changing climate argued those self regulating processes had been pushed to a disastrous tipping point by rising CO2.  In contrast climate skeptics like world-renowned physicist Freeman Dyson also embraced the concepts of Gaia as a “great force for good” uniting people to save natural habitat and endangered species. But Dyson also bemoaned, “I am horrified to see the environmental movement hijacked by a bunch of climate fanatics, who have captured the attention of the public with scare stories.”

Despite Lovelock’s belief that life regulates earth’s chemistry via a variety of negative feedbacks, his logic was at first swayed by those CO2 scare stories. In a more fearful state of mind Lovelock published books like “The Revenge of Gaia” and in newspaper interviews predicted fast-approaching, global-warming doom stating, “Billions of us will die” and only the “few breeding pairs of people that survive will be in the Arctic”.

More recently however Lovelock recanted stating, “I was 'alarmist' about climate change & so was Gore!” 'The problem is we don't know what the climate is doing. We thought we knew 20 years ago”.

Putting politics and religion aside, the Gaia perspective provides a valuable framework that incorporates the biosphere as a critical active player in global climate and chemical cycles. And only from that framework can we fully account for oscillations in the oceans’ pH on daily, annual, decadal and millennial timeframes.

pH in a Lifeless World

Global climate models, such as used by Caldeira and Wickett 2005, estimated that ocean pH has dropped by (0.09 pH) from 8.2 to ~ 8.1 since preindustrial times due to rising anthropogenic carbon dioxide emissions. They then predicted a further pH drop of 0.3 to 0.4 by 2100 as emissions increase. This claim has been cut and pasted into nearly every journal article that hypothesizes an impending catastrophe driven by “ocean acidification”. However an average pH of 8.1 is typical for interglacial periods such as the one we are now experiencing.  But more importantly Caldeira and Wickett’s modeling experiments only examined geochemical processes and erroneously assumed 1) ocean surface CO2 is in equilibrium with the atmosphere; and 2) the biosphere was a neutral participant.  Caldeira’s model was based on their non-Gaia assumption that ocean surface pH is “affected only by air-sea fluxes and directly injected carbon.”  Indeed, if sequestration of CO2 by photosynthesis is immediately offset by the release of CO2 in the surface layers via respiration, then such an assumption may hold some validity. However that is never the case. And according to the IPCC if there were no biological pump transporting carbon to the ocean depths, oceans would now be experiencing an 8.0 pH.

Relationship between Atmospheric CO2 and Ocean pH

As seen in the graph above from Cohen and Happer models that suggest ocean pH should have declined over the past 150 years as atmospheric CO2 concentrations rose are supported by an abiotic chemical analysis. Modulated by ocean alkalinity, at 400 ppm atmospheric CO2, surface seawater declines to pH 8.2 or 8.1 (blue curve).  For un-buffered rainwater (or river outflows without buffering) pH drops to 5.5 (red dashed curve). However even without any modulating biological effects, the graph suggests a degree of chemical homeostasis where increasing CO2 concentrations have an increasingly smaller effect on ocean pH. For example when CO2 concentrations increase from 0 to 100 ppm, pH rapidly drops from over 11.0 to 8.7. In contrast a quadrupling of atmospheric CO2 since pre-industrial times (~250 to 1000 ppm) would only lower ocean surface pH from 8.3 to 7.9 (blue curve). Counter-intuitively the different dissolved CO2 species exert strong buffering effects. Furthermore far from being catastrophic, not only is a pH range between 8.4 and 7.7 experienced daily in thriving coral reefs, that range appears to be an optimal balance that supports both photosynthesis and calcification!

Extreme views by researchers like Hoegh-Guldberg (2014) have speculated 95% of the coral will be lost by 2050, and he argues our current high levels of CO2 are creating conditions coral have not experienced for millions of years. Yet in terms of pH (and temperature) such “scientific” claims are pure nonsense. First a modeled average surface pH tells us very little about the pH that directly affects marine organisms locally. Due to the counteracting effects of photosynthesis, respiration and calcification, coral reefs can experience a pH hovering around 8.5 or higher during the day followed by a low pH of 7.8 or lower at night. Kline 2015 acknowledged, “As with many other reefs, the nighttime pH minima on the reef flat were far lower than pH values predicted for the open ocean by 2100.” Elsewhere researchers concluded that in addition to atmospheric pH, the complex interactions controlling pH especially in coastal zones, make detection of any trends towards acidification “not trivial and the attribution of these changes to anthropogenic CO2 emissions is even more problematic.” (Duarte 2013)

Why More Acidic Conditions Benefit Photosynthesis

Shallow-water reef-building corals are able to thrive in low-nutrient tropical waters via their symbiosis with a genus of photosynthesizing algae (discussed here.) In order to sustain photosynthesis, corals actively pump hydrogen ions (H+) into the vesicles encapsulating their algal symbionts. This lowers its internal pH to truly acidic levels between pH 4 and 5  (Barott 2015). This increases H+ concentrations up to 10,000 times greater than any theoretical contributions to surface waters by atmospheric CO2. If coral do not acidify their symbionts’ surroundings, the limiting supply of CO2 would dramatically decrease the rate of photosynthesis.

Why does an acidic environment benefit photosynthesis?

To understand the benefits of corals’ purposeful acidification, we must first review how CO2 reacts when dissolved in water. Dissolved CO2 can take 3 forms (or “species”) collectively referred to as Dissolved Inorganic Carbon (henceforth DIC):

1) Carbonic acid (H₂CO₃),

2) Bicarbonate ion (HCO₃^-) after losing one H+

3) Carbonate ion (CO₃^-2) after losing a second H+ .

When CO2 first dissolves, a small proportion bonds to water molecules and forms a weak carbonic acid (H₂CO₃). But the bond is weak causing carbonic acid to convert back and forth with its CO2 form so rapidly, most researchers treat these two forms as the same chemical species.  Carbonic acid is a weak acid, and weak acids are critical buffering agents for most living organisms precisely because its species can rapidly and reversibly change form. Carbonic acid and phosphoric acid are the 2 most critical buffering agents for maintaining a narrow pH range in humans and other animals. In the form of carbonic acid, water’s 2 H+ ions can more easily detach to form bicarbonate and carbonate ions when pH rises. Buffering happens because those added H+ ions counteract a rising pH. (Higher pH means lower H+ concentrations.) Conversely when pH falls (Lower pH means higher H+ concentrations), the excess H+ ions recombine with and are sequestered by any existing carbonate and bicarbonate ions to counteract the falling pH.

Figure 2 illustrates how changes in pH alter the species composition of DIC. For example during photosynthesis CO2 is consumed causing pH to rise. Between pH 7.0 and 8.6, over 90% of the dissolved CO2 naturally converts to bicarbonate ions (HCO₃^-). But bicarbonate ions cannot be directly used in photosynthesis. Photosynthesizing organisms can only use CO2. Thus if photosynthesis drives pH to 8.2 or higher, the requisite CO2 species approach zero. In addition to competing for a dwindling supply of CO2, photosynthesis consumes the limited supplies of nutrients. Thus photosynthesis creates negative feedbacks that inhibit additional photosynthesis.

The relationship between pH and proportion of CO2 species

To overcome the limiting supply of CO2, organisms like coral concentrate bicarbonate ions in compartments into which they pump H+ ions and lower the pH. As seen in Figure 2, at pH 5 or lower, 90% of the DIC converts to CO2. Once bicarbonate ions are imported and concentrated, the conversion to CO2 is also accelerated by the ubiquitous enzyme carbonic anhydrase. However bicarbonate ions cannot simply diffuse into a cell or pass through internal membranes. The ions must be pumped. However pumping and concentrating those ions requires transporters and an expenditure of energy. In contrast whenever surrounding waters experience a lower pH, it makes CO2 more available so that the energy expenditures drop because CO2 freely diffuses into cells and through membranes.

The same carbonate chemistry reactions that provide more CO2 for photosynthesis also explain how some pharmaceutical antacids work and how DIC buffers ocean pH. Bicarbonate is a common ingredient in antacids like Alka-seltzer. When H+ ions increase due to acid indigestion, ingested bicarbonate ions rapidly bond to H+ to form CO2 gas, which can then be carried away by the blood or by a good belch. Likewise when ocean concentrations of H+ ions increase, they more readily bond to the bicarbonate and carbonate ions to minimize the drop in pH and form more CO2, which can be quickly utilized during photosynthesis.

However below pH 7.0, nearly all carbonate ions  (CO₃^-2) will be converted to bicarbonate (HCO₃^-), so that carbonate ions no longer serve as buffering agents. (CO₃^-2  + H+ forms HCO₃^- ). However in coral reefs, that loss of buffering capacity at lower pH is counteracted to a degree by increased dissolution of calcium carbonate minerals. Dissolution of calcium carbonates counter-intuitively absorbs CO2 and releases carbonate ions to increase the water’s buffering capacity, thus exerting a negative feedback that tries to raise pH (Morse 2007). Nonetheless the concept that a lower pH reduces the concentration of carbonate ions evoked climate fears amongst some researchers who incorrectly believed calcifying organisms require carbonate ions.  But research shows no such requirement. All calcifiers use the more abundant bicarbonate ions and bicarbonate ions will be plentiful even if pH unrealistically fell to 6.0

Outside of coral reefs, other marine ecosystems also benefit from lower pH. For example diatoms now account for 40% of the world’s ocean primary productivity and flourish in upwelling waters that bring abundant CO2 and DIC from the ocean’s dark depths into sunlit surface regions. Although this upwelling deceases surface pH and provides more CO2, diatoms still rely on bicarbonate transporters and carbonic anhydrase to ensure an adequate supply of CO2 for photosynthesis. Hopkinson et al. (2011) calculated a doubling of ambient CO2 levels would save diatoms ~20% of the energy they expended on importing bicarbonates. Globally different photosynthesizing organisms have demonstrated a variety of responses to rising CO2 but altogether there appears to be few negative effects on photosynthesis due to elevated CO2 and depending on the species small to large benefits (Mackey 2015).

The Omega Myth

In a lifeless ocean when carbonate ions rise to a certain concentration, they react with ever-present calcium ions to form calcium carbonate minerals like aragonite and calcite. Those minerals are used to make shells, skeletons and reefs. If carbonate ion concentrations are lower, calcium carbonate minerals are more likely to dissolve. When there is a balance between formation and dissolution of those minerals, the water is said to be saturated with respect to that mineral, and saturation is represented by the omega symbol (W). The oceans are currently oversaturated with respect to calcium carbonate minerals, but some researchers became fearful that a falling pH could lower the supply of carbonate ions, and eventually drive the ocean’s saturation point so low that calcium carbonate minerals will dissolve faster than they form. However biologically controlled calcification reveals that simple metrics of chemical equilibriums and saturation points do not accurately demonstrate the biologically controlled calcification process. In that regard several researchers have now published evidence demonstrating the “Omega Myth”.

First biologically controlled calcification does NOT depend on, or directly utilize seawater carbonate ions. Nor does calcification depend on observed saturation states of the oceans (Maranon 2016). Transporters are required for carbonate ions to cross any membrane, but no carbonate transporters have ever been detected. Instead, as with photosynthesis, calcifiers actively uptake the more abundant bicarbonate ions and concentrate them in compartments. Most calcifying organisms have evolved mechanisms to “up-regulate” their internal pH by pumping H+ ions out of the compartment and raising internal pH. In addition pumping  H+ ions out of the calcifying compartments is beneficial because it maintains an electrical gradient that facilitates importing calcium ions (Ca++) into the calcifying compartment. With a higher internal pH, bicarbonate sheds an H+ and converts into carbonate ions and when concentrated in the presence of concentrated Ca++, calcium carbonate minerals readily form.

Although in some species photosynthesis and calcification compete for bicarbonate ions, photosynthesis generally benefits calcification by providing energy, and by raising external pH, which lowers the cost of pumping internal H+ ions to the surrounding waters. In addition on a per molecule basis, the cost of calcification requires less than 1% of the energy produced by photosynthesis (McCulloch 2012). Accordingly numerous studies have reported that greater rates of photosynthesis correlate with greater rates of calcification. The same holds true for other calcifying organisms. For example across the tropical ocean, the ratio of net calcification to net photosynthesis for coccolithophores remained constant despite regions of widely varying surface pH and calcite saturation levels (Maranon 2016).

Past hypotheses arguing calcification was dependent on carbonate ion concentration, or aragonite and calcite saturation levels, were most likely misled by the fact that higher carbonate ion concentrations are a daily “side effect” of photosynthesis. It is the rate of photosynthesis and the energy it provides that typically controls calcification rates. And as reported in the discussion on the coral adaptive bleaching hypothesis, coral are always shifting and shuffling their symbionts to maximize photosynthesis to best adapt to changing local microclimates. The bigger threat to coral photosynthesis is heavy sediment loads from disturbed landscapes that can block the sun and suffocate polyps. 

How Calcification Lowers pH more than Atmospheric CO2

Strangely enough, although some researchers fret higher CO2 concentrations will reduce calcification, it is the very process of calcification that results in the “alkalinity pump.” Calcification removes buffering bicarbonate and carbonate ions from the surface and pumps them to the deep. Calcification also releases CO2 in the surface waters and in combination with less buffering capacity, lowers pH to a much greater extent than possible by surface exchanges with rising atmospheric CO2.

Assuming the modeled background pH of 8.1, and if all else is equal, we would expect pH to rise during the day due to photosynthesis and then fall back to pH 8.1 at night due to respiration. As seen in the graph below for daily (diel) pH values on Heron Island in the Great Barrier Reef (from Kline 2015), coral reefs rarely spend any time at Caldeira’s modeled pH value of 8.1. When photosynthesis and carbonate dissolution outweigh respiration and calcification, surface pH can rise to 8.4 or higher as would be expected. Furthermore when surface pH is above 8.1, the concentration of surface CO2 is lower than atmospheric CO2, and this difference allows CO2 to diffuse into the ocean.  However any absorbed CO2 is quickly sequestered into organic molecules via photosynthesis during which surface pH remains high and never comes into equilibrium with atmospheric CO2 during the day.

Daily Changes in pH on Heron Island Great Barrier Reef

Conversely without photosynthesis, nighttime respiration and calcification increase surface CO2 concentrations and lower pH. Reefs benefit because those processes replenish the depleted CO2 required for photosynthesis on the following day. Furthermore if more organic molecules are formed and sequestered than subsequently respired, we would expect surface pH to remain above 8.1. Indeed photosynthesis produces a large reservoir of dissolved and particulate organic molecules that may persist for decades, centuries, and millennia. When those stored molecules eventually return to the surface, pH can be lowered due to respiration of ancient carbon, independent of atmospheric CO2. Other organic molecules are also formed that resist decomposition for millions of years. And molecules like DMS are out-gassed to the atmosphere where they serve as cloud condensation nuclei and inhibit further warming of ocean surface temperatures.

Thus due to long-term sequestration of CO2 that exceeds respiration we would expect surface pH to remain above 8.1 for the short term. However due to the release of CO2 during calcification, reef pH drops far below 8.1. Calcification infuses the surface waters with an excess of CO2 largely driving the nighttime pH down as low as 7.7.  Furthermore at a pH below 8.1, CO2 concentrations in the ocean’s surface rise higher than the atmosphere’s, and this results in nighttime out-gassing of CO2. Instead of CO2 invading the ocean and affecting coral, overall measurements show coral reefs are net sources of CO2 from the ocean to the atmosphere. Similar dynamics from calcifying coccolithophores likewise promotes CO2 fluxes from the open ocean, and inhibits uptake from the atmosphere. Again as Gaia predicts, biological processes control carbonate chemistry and when or where atmospheric CO2 enters or leaves the ocean.

Although studies in the waters around Hawaii (Dore 2009) reported an increasing trend in DIC that was “indistinguishable” from what rising atmospheric CO2 predicts researchers observed, “Air-sea CO₂ fluxes, while variable, did not appear to exert an influence on surface pH variability. For example, low fluxes of CO₂ into the sea from 1998–2002 corresponded with low pH and relatively high fluxes during 2003–2005 were coincident with high pH; the opposite pattern would be expected if variability in the atmospheric CO₂ invasion was the primary driver of anomalous DIC accumulation.”  However that observed pattern is exactly what we would expect to arise from biological effects.

Furthermore oscillating decadal trends in wind strength can further magnify biological effects causing pH to trend independently of atmospheric CO2. CO2 generated by calcification does not completely outgas and thus changes in the rate at which reefs are flushed with open ocean water will modulate how calcification affects surface pH. In contrast to Caldeira’s “lifeless” pH models that suggest pH has dropped from 8.2 to 8.1 since preindustrial times, a study of pH since 1700 AD on Flinder’s Reef in the Great Barrier Reef concluded pH has oscillated between 8.15 and 7.9 every 50 years. During a positive Pacific Decadal Oscillation and El Nino years, trade winds slowed and reduced the flushing rate of the reef. As a result there was a build up of CO2 released from calcification and average pH dropped pH to 7.9. When winds increased during a negative PDO and more La Ninas, the reef was flushed and pH rose to 8.15. Several studies have linked changes in pH driven with multidecadal oscillations.

For example examining surface pH in the Sargasso Sea Goodkin 2015 reported, “from 1950 to 1996, when surface ocean pHs are predicted to decline more rapidly due to anthropogenic CO2 emissions, pH at Bermuda increases in response to a declining AMO.”  They concluded, “ocean pH does not simply reflect atmospheric CO₂ trends but rather that circulation/biogeochemical changes account for >90% of pH variability in the Sargasso Sea and more variability in the last century than would be predicted from anthropogenic uptake of CO₂ alone.”

Similarly Yeakel 2016 reported Bermuda reefs experienced a drop in pH in association with a negative NAO that caused westerly winds to move further south and generate a deeper winter mixed layer just to the north of the Bermuda reefs. Deeper mixing brought more DIC to the surface layers and promoted greater plankton blooms. The resulting organic particles and zooplankton that fed on the blooms, then circulated over the Bermuda reef. The resulting increase in respiration and calcification caused an  “acidification event”.

Thus to reliably distinguish multidecadal trends in pH driven by ocean oscillations, upwelling and deeper surface mixing versus trends due to rising atmospheric CO2, it will require 60 to 100 years of observation; far longer than any data series to date.

Ocean Surface pH is More Sensitive to Ventilated CO2 Stored at Ocean Depths

Published estimates of anthropogenic CO2 now stored in the upper ocean layers and affecting pH has been based on “the assumption that ocean circulation and the biological pump have operated in a steady state since preindustrial times” (Sabine 2010). The problem is such assumptions are faulty and misleading. The biological pump and ocean circulation are not in a steady state. Regional upwelling has increased since the Little Ice Age (Gutiérrez 2009) and during the past 3 decades (Varela 2015). Multidecadal changes in hurricane frequency and intensity affect upwelling. Changes in surface winds due to El Nino and La Nina, the North Atlantic Oscillation and Pacific Decadal Oscillation affect upwelling (Ishii 2002). Coastal and equatorial upwelling bring an enormous amount of DIC to the surface, with subsequent transport to the gyres of the open ocean, causing declines in open ocean surface pH at rates that are much faster than possibly attributed to atmospheric diffusion.

While 50% of the sequestered carbon formed during photosynthesis is respired before sinking into the dark depths, a tremendous pool of dissolved organic carbon has been created that may not be respired for decades, centuries or millennia and slowly contributes to the pool of DIC at various depths and locations (Giorgiou 2002). This further complicates any attribution of trends in surface pH. For example upwelling of stored CO2 is believed to have been the main driver of the rise in atmospheric CO2 and the fall in ocean surface pH during the transition from the glacial maximum to our interglacial.

As discussed in the article on natural cycles of ocean “acidification”, and illustrated in the graph below by Martinez-Boti, over the past 15,000 years proxy data (thick lines) has determined surface pH has rarely been in equilibrium with expectations (green line) based on models driven by atmospheric CO2. As illustrated, surface pH was more sensitive to the upwelling of subsurface DIC. The venting of stored carbon led to a drop in average regional pH from the 8.3 during glacial times to a pH fluctuating between 8.1 and 8.2 during our current interglacial.

Difference between ocean surface pH and modeled pH from atmospheric CO2

The mechanisms that lowered surface pH to 8.3-8.4 during the Last Ice Age is a matter of considerable debate, but clearly more carbon was being sequestered at depth and less carbon was being pumped to the surface. Several authors have reported less upwelling during the Ice Age. While colder temperatures and less upwelling would reduce rates of photosynthesis, colder temperatures also reduce rates of respiration and calcification. A lower rate of respiration would allow more organic carbon to sink to deeper depths before being completely consumed. Sinking to deeper depths prevents a quick return to the surface during winter mixing or mild upwelling.

It has also been speculated that the loss of coral reefs during the last Ice Age contributed to the higher pH. Research has estimated that during the cold nadir of each ice age, coral reef extent was reduced by 80% and carbonate production was reduced by 73% relative to today. Lower calcification rates would reduce the alkalinity pump, reduce surface CO2 and increase the buffering capacity of surface waters. Conversely the growth of coral reefs as the earth warmed and sea levels rose would contribute to rising CO2 concentrations and falling pH. Vecsei 2004 concluded, “The pattern of reef growth that emerges suggests that emission of CO2 resulting from carbonate production was important particularly during the late stages of deglaciation.”

Overall observations of the effects of photosynthesis and calcification reveal coral reefs are not victims of a fall of pH from 8.2 to 8.1 pH as suggested by Caldeira and Wickett 2005, Doney 2009 or Hoegh-Guldberg (2014). 

On the contrary as Gaia theory would suggest, coral reefs are actively regulating surface pH.