Claim: Acidification impedes shell development of plankton off the US West Coast


Research News


Shelled pteropods, microscopic free-swimming sea snails, are widely regarded as indicators for ocean acidification because research has shown that their fragile shells are vulnerable to increasing ocean acidity. 

A new study, published in the journal Scientific Reports, shows that pteropods sampled off the coasts of Washington and Oregon made thinner shells than those in offshore waters. Along the coast, upwelling from deeper water layers brings cold, carbon dioxide-rich waters of relatively low pH to the surface. The research, by a team of Dutch and American scientists, found that the shells of pteropods collected in this upwelling region were 37 percent thinner than ones collected offshore.

Sometimes called sea butterflies because of how they appear to flap their “wings” as they swim through the water column, fat-rich pteropods are an important food source for organisms ranging from other plankton to juvenile salmon to whales. They make shells by fixing calcium carbonate in ocean water to form an exoskeleton. 

 “It appears that pteropods make thinner shells where upwelling brings water that is colder and lower in pH to the surface, ” said lead author Lisette Mekkes of Naturalis Biodiversity Centers and the University of Amsterdam in the Netherlands. Mekkes added that while some shells also showed signs of dissolution, the change in shell thickness was particularly pronounced, demonstrating that acidified water interfered with pteropods’ ability to build their shells. 

The scientists examined shells of pteropods collected during the 2016 NOAA Ocean Acidification Program research cruise in the northern California Current Ecosystem onboard the NOAA Ship Ronald H. Brown. Shell thicknesses of 80 of the tiny creatures – no larger than the head of a pin – were analyzed using 3D scans provided by micron-scale computer tomography, a high-resolution X-ray technique. The scientists also examined the shells with a scanning electron microscope to assess if thinner shells were a result of dissolution. They also used DNA analysis to make sure the examined specimens belonged to a single population.  

 “Pteropod shells protect against predation and infection, but making thinner shells could also be an adaptive or acclimation strategy,” said  Katja Peijnenburg,  group leader at Naturalis Biodiversity Center. “However, an important question is  how long can pteropods continue making thinner shells in rapidly acidifying waters?”

The California Current Ecosystem along the West Coast is especially vulnerable to ocean acidification because it not only absorbs carbon dioxide from the atmosphere, but is also bathed by seasonal upwelling of carbon-dioxide rich waters from the deep ocean. In recent years these waters have grown increasingly corrosive as a result of the increasing amounts of atmospheric carbon dioxide absorbed into the ocean. 

“Our research shows that within two to three months, pteropods transported by currents from the open-ocean to more corrosive nearshore waters have difficulty building their shells,” said Nina Bednarsek, a research scientist from the Southern California Coastal Water Research Project in Costa Mesa, California, a coauthor of the study. 

Over the last two-and-a-half centuries, scientists say, the global ocean has absorbed approximately 620 billion tons of carbon dioxide from emissions released into the atmosphere by burning fossil fuels, changes in land-use, and cement production, resulting in a process called ocean acidification.

“The new research provides the foundation for understanding how pteropods and other microscopic organisms are actively affected by progressing ocean acidification and how these changes can impact the global carbon cycle and ecological communities,” said Richard Feely, NOAA Pacific Marine Environmental Laboratory and chief scientist for the cruise.


This research was supported by NOAA’s Ocean Acidification Program. 

From EurekAlert!

Addendum Charles: Perhaps pteropods in upwelling environments have had a different growth profile than those offshore for millions of years. Perhaps they grow faster in nutrient rich environments. I’m uncertain if their screening for “age” comparison takes this into account.

Here is the paper:

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January 20, 2021 2:02 pm

Utter, utter bilge.

Reply to  Chaswarnertoo
January 20, 2021 4:34 pm

..and it seems that every few years….someone does this exact same “study” again…over and over
..and none of them can explain what the white cliffs of Dover are made of?…when did they form…and what CO2 levels were then
according do their “theory”…it would have all been impossible

Last edited 2 years ago by Latitude
Reply to  Chaswarnertoo
January 20, 2021 6:22 pm

Yes, absolutely! See everything below

January 20, 2021 2:04 pm

So, hot water causes acidification and cold water causes acidification. Gotcha.

Peter W
Reply to  shrnfr
January 20, 2021 4:09 pm

The cold water from the depths picked up it’s CO2 from the atmosphere? Apparently the authors have not heard about undersea volcanic activity which emits CO2, and is caused by plate tectonics. As any consumer of soda water knows, as liquid warms, it loses the CO2. Therefore, what is needed to solve this problem is obviously more global warming!

January 20, 2021 2:05 pm

Is this that produce acid rain too? I heard this type of rain is pretty bad, that’s why we should remove all statues from the open.

Reply to  Pauleta
January 21, 2021 4:58 am

“mr youse needn’t be so spryconcernin questions arty
each has his tastes but as for ii likes a certain party
gimme the he-man’s solid blissfor youse ideas i’ll match youse
a pretty girl who naked isis worth a million statues”
― E.E. Cummings

Gordon A. Dressler
January 20, 2021 2:10 pm

From the above article: “. . . deeper water layers brings cold, carbon dioxide-rich waters of relatively low pH to the surface.”

Uhhhh, is there any reason— any reason at all—that the pH of the “deeper water layers” was NOT given a numerical pH value or ranges of pH values?

It would make a big difference if, say, those deeper water layers were at a pH level around 7 versus a pH level around 8.1, which is close to the average of today’s global oceans.

I am sure that the lack of specificity of pH value(s) was intentional. However, not all people are so gullible as to fall for such a trick.

Reply to  Gordon A. Dressler
January 20, 2021 2:30 pm

“In recent years these waters have grown increasingly corrosive as a result of the increasing amounts of atmospheric carbon dioxide absorbed into the ocean.”
Not only did they leave off the pH data they think reduced alkilinity is a move toward caustic. I was taught it was the other way round.

Reply to  Gordon A. Dressler
January 20, 2021 2:32 pm

People just need to quit belching when they go to the deep ocean.

Rud Istvan
Reply to  Gordon A. Dressler
January 20, 2021 2:40 pm

Uh, in the body of the paper they did. Offshore surface pH8.1 (pretty standard). Onshore upwelling surface pH ~7.7-7.8. Also pretty standard. See essay Shell Games in ebook Blowing Smoke for actual depth profiles taken along the Cal/Oregon coastline. Because the pteropods fabricate ‘nanorods’ of arogonite to incorporate in their exoskeleton shell, they-like corals-use their metabolism to micromanage the synthesis pH in their bodies. Like corals, they handle this small range easily.
The real culprit is upwelling cold temperature. See comment below.

Gordon A. Dressler
Reply to  Rud Istvan
January 20, 2021 6:08 pm

Rud, thank you for this clarification . . . I did not bother to read the full paper.

I will just note two things in follow up (not directed to you but to the author(s) of the above article):

1) It is scientifically incorrect to state that mixing pH 7.7-7.8 sea water with pH 8.1 seawater is a process of “acidification” (this is elementary chemistry)

2) It is absolutely incorrect to refer to seawater having a pH in the range of 7.7-7.8 as “carbon dioxide rich” (claimed in second and seventh paragraphs of above article), no matter how cold that water. Just consult the Zeebe and Wolf-Gladrow paper and its included Bjerrum plot (Figure 1) at From that plot, one can see that available CO2 (in chemical equilibrium as a dissolved gas) in sea water at pH 7.7-7.8 is only about 14% (on a mole/kg basis) of that that would be present in pH 7.0 seawater at the same temperature.

Reply to  Rud Istvan
January 21, 2021 4:49 am

“In recent years these waters have grown increasingly corrosive as a result of the increasing amounts of atmospheric carbon dioxide absorbed into the ocean.”

Also, how do they know that the CO2 dissolved into the upper layer of the oceans has any effect on the CO2 in upwelling water coming from depth. The “fingerprint” of man-made atmospheric CO2 is the C13/C12 ratio. What’s the ratio in the cold upwelling ocean waters?

Joel O'Bryan
January 20, 2021 2:13 pm

Sort of like the Antarctic ozone hole appearing every September, it was automatically a “crisis” the first time it was actually measured and the assumption made in the leap to causality of man-made freon.

Similarly pteropods shells between these two areas are a crisis after the first time they are measured and compared. No historical baselines to compare those measurements to, just make the leap of causility based on “what else could it be?” pre-exisitng bias.

January 20, 2021 2:26 pm

Fanny Monteiro’s nice review of the history of coccolithophores, calcified plankton, shows that they reached their peak in abundance at the end of the Cretaceous 70-100 million years ago. This was when global temperatures were 7-10 C warmer than today, and atmospheric CO2 close to 1000 ppm.

Since the end-dinosaur event, the cooling and falling CO2 have been bad for the cocco’s. They have suffered reduction in diversity and abundance.

So to improve things for calcified plankton, the earth needs to warm up quite a few degrees C and at least double its CO2 level in air.

cocco historic abundance monteiro.PNG
Reply to  Phil Salmon
January 20, 2021 4:47 pm

abundance is putting it mildly… thick were the sediments that made the white cliffs of Dover

Reply to  Latitude
January 21, 2021 6:31 am

Yes the white cliffs of Dover stand as proof that calcified plankton like coccolithophores do just fine in warmer climate and much higher CO2. Their existence refutes the whole acidification myth.

Reply to  Phil Salmon
January 21, 2021 8:48 am

actually, it’s proof they do a whole lot better
…try culturing them without having to add CO2

Last edited 2 years ago by Latitude
Rud Istvan
January 20, 2021 2:30 pm

Read the paper. The key is Discussion section paragraph 4. It was known long before this paper, as noted in para 4, that temperature has a strong effect on rate of pteropod shell formation. Warmer means faster; just basic metabolism rate. So in the significantly colder and slightly lower pH upwelling water shell formation would be significantly slower for similarly aged individuals, resulting in thinner shells. Little to do with the speculated ‘acidification’.

Joel O'Bryan
Reply to  Rud Istvan
January 20, 2021 2:45 pm

Upwellings have long been associated with delivery of nutrient-rich deep waters and resulting fish population booms. Colder water upwellings are also higher in dissolved oxygen for fish. It is quite deceptive of the authors to concentrate on the pH in upwelling areas, areas that are going to be high in [CO2] regardless of mankind’s CO2 addition to the atmosphere.

H. D. Hoese
January 20, 2021 2:32 pm

“ pH fluctuations in coastal regions are larger than trends of ocean acidification. Metabolically intense habitats increase ΩAr by high productivity. Calcification is controlled by biological processes.” from Hendriks, I. E., et al. 2015. Biological mechanisms supporting adaptation to ocean acidification in coastal ecosystems. Estuarine Coastal Shelf Science.152(5): A1-A8.

 ΩAr like having to do with shells. From the paper–
“Because a recent study using particle tracking demonstrated sustained retention for 5–6 weeks in the coastal regions of the CCE during the upwelling season17, we considered the in situ oceanographic variables measured at the time and place of pteropod collection to be representative of the conditions they experienced during most of their lifetime……Although L. helicina pteropods produce thinner shells along the upwelling gradient in the CCE, we did not find increased dissolution of the shells along the upwelling gradient (Fig. 5)…….Little is known about the formation of pteropod shells, but it is likely under strong biological control, as found for other mollusks45,46.”

 of 59 citations most from the last 5 years.Need to study things like this, its only numbers..

“Already in the year 2050, more than half of the waters in the CCE [California Current Ecosystem] will be aragonite-undersaturated year-round28,48”

Clyde Spencer
Reply to  H. D. Hoese
January 20, 2021 7:00 pm

“under strong biological control”
Meaning that the organism can actually manipulate the pH at the shell growth-surface through the expenditure of energy. That is the implication of Rud’s comments, above. That will be impeded if the organism is experiencing colder than optimal temperatures, thus reducing the metabolic rate. These pteropods may be living in temperatures or pH fluctuations that are less than optimal; however, if the upwelling were to stop, the nutrients would disappear and so would the pteropods. Organisms often have to make compromises, but lack of food is one of the most severe restrictions on survival.

January 20, 2021 2:32 pm

From the study, “Temperature is known to have a strong influence on the shell-building capacity of calcifying organisms with several studies showing that increasing temperatures stimulate shell growth (reviewed by Gazeau et al.)….For example, in our study, depth-averaged water temperature over the upper 100 m ranged from 8.84 °C nearshore to 11.16 °C offshore”

It is therefore possible that warmer waters offshore enhanced calcification. Hence, both temperature and ocean carbonate chemistry may have contributed to the observed variation in shell thickness along the upwelling gradient of the CCE. Future studies will be needed to further disentangle the relative contribution of these important environmental variables.

Here is link to study:

January 20, 2021 2:38 pm

A couple of points:

1) Upwelling waters are colder and denser than regular ambient waters, therefore in order to maintain a positive buoyancy the planktonic Pteropods don’t require as much shell thickness to float. Upwelling brings phosphates from the deep ocean depths into the photic zone which fertilizes algae causing algal blooms.

2) It is to the benefit of these shelled Pteropods to maintain a positive buoyancy so they can be in the photic zone which is in the upper 100 m meters of the water column, so they can feast on the algae which are blooming and thriving in this fertilized upper ocean layer. Is it possible that there is an evolutionary adaptation which the Pteropods have undergone which allows them to harvest their main food supply?

The water is not acidic it is just lower alkalinity. It would be interesting to understand the evolutionary adaptation of the Pteropods to their ecosystem rather than jump conclusions.

michael hart
January 20, 2021 3:12 pm

They can’t even reconcile the contradictions in their own data.
They describe the conditions as being more corrosive, and then find no evidence of corrosion. Some scientists might then consider that CO2 is perhaps not the cause of the thinner shells they found.

January 20, 2021 3:44 pm

So their shells grow thinner in cold water on average for as long as they live….Doesn’t seem to be ground breaking….hmmm…

Brian Pratt
January 20, 2021 3:51 pm

In the introduction they state “While there is an indication that pteropods can counter dissolution due to the protection provided by an organic layer, the periostracum, and short-term repair capacity, the extent to which these mechanisms offset the sensitivity of pteropods to ocean acidification is currently unknown.” Then they ignore what the two cited Peck et al. papers have actually determined, which is that not all the pits and scrapes are truly due to dissolution. How something like this can get published is a disgrace. We’ve seen a number of these studies by the same group in recent years.

Mike Dubrasich
January 20, 2021 4:36 pm

As best as I can tell the researchers measured 6 variables (omega-Ar, pH, pCO2, temperature, oxygen, and depth) and used Principal Component Analysis, thereby mixing all 6 (or combinations) into a single “vector”. Their PCA could not (mathematically impossible) differentiate pH from any of the other variables. PCA is a bunk stat method for this reason. It’s kitchen sinking, everything measured into one stew pot and excluding everything we didn’t measure.

Cold water is usually deep and has a marginally different chemistry than warm water. The researchers note this:

Seasonal upwelling brings up cold and aragonite undersaturated waters (omega-Ar < 1) with high pCO2 and low pH from the offshore intermediate waters of the northern Pacific onto the continental shelf.

It’s normal and happens every year. Nothing new. Just what we’d expect. It’s not known which factors (measured or not) affect sea snail shell formation; PCA won’t tell you. Furthermore, it’s seasonal so during some times of the year (or multi-decadal oscillations) the water is warmer and the sea snails do fine. Important point: sea snails are not going extinct. Nobody claims that. The researchers do claim, however:

In addition, the exchange and downward mixing of anthropogenic CO2 from global and local atmospheric sources, and increased respiration at intermediate and bottom depths leads to further shoaling of these aragonite-undersaturated waters.

That’s a weasel claim about anthro-CO2, unproven, unmeasured, not in the study, and partially discounted by other claims about respiration and “shoaling”, which were also not measured and not in the study.

The entire harem-scarem conclusion about anthro-CO2 is from out of left field, not something measured, not in the study, which itself is based on clubfoot stat analysis of a common, seasonal, natural phenomenon that happens regardless of atmospheric CO2 levels and has been happening for 500 million years or more. And here’s the kicker: sea snails have thicker shells in WARM water. Warmer is better for pteropods!

It’s agenda-driven pseudo science at best, hugely political, with a minutia of actual (though crappy) science, and bleeding-heart hair-on-fire alarmist emotional sobbing. Greta should love it, when (if) she learns how to read.

Last edited 2 years ago by forestermike
Mike Dubrasich
Reply to  Mike Dubrasich
January 20, 2021 5:48 pm

While I’m ranting, let me add this:

Sea snail shell thickness is being used as an “indicator” of allegedly anthropogenic CO2 in the oceans. Any (and every) time you see the word “indicator” you can be sure the science behind it is pathetic or completely bogus. Other popular “indicators” include lichens for air pollution, mayflies for water pollution, and ectomycorrhizas for soil pollution.

None of those are substitutes for actual measurements of chemical constituents of air, water, or soil. Their presence, absence, increase, or decrease do not “indicate” anything. They are also not “canaries in the coal mine”. Coal mines don’t use canaries anymore. That practice ceased when CO detectors were invented. Science marches on, or at least it used to.

Mr. Lee
January 20, 2021 4:42 pm

How long before the ocean turns into that stuff that turned the Joker into the Joker?

January 20, 2021 4:55 pm

“Over the last two-and-a-half centuries, scientists say, the global ocean has absorbed approximately 620 billion tons of carbon dioxide from emissions released into the atmosphere by burning fossil fuels, changes in land-use, and cement production, resulting in a process called ocean acidification.” I thought it was 1940 or so that man’s massive CO2 emissions started, not in 1770.

Reply to  TomH
January 21, 2021 1:11 pm

Over the last two-and-a-half centuries, scientists say, the global ocean has absorbed approximately 620 billion tons of carbon dioxide from emissions released into the atmosphere by burning fossil fuels, changes in land-use, and cement production, resulting in a process called ocean acidification.”
Yeah, I noticed that, too.

Do these folk have any idea how big the oceans are?
I wonder if they do.
620 billion tonnes in two and a half centuries. About 2.5 billion tonnes a year.
Oceans, seas, etc [I assume they are forbidden from discriminating] have an area of – roughly – 120 million square miles.
So, rate per square mile, per year is about 21 tonnes absorbed [their numbers].
About 1.75 tonnes per square mile, per month.
A Square mile is close to 2.25 million square metres.
So a bit less than one gram per month per square meter.

The oceans are big.


Dan Mullock
January 20, 2021 5:07 pm

by my calculation, those 640 billion tons of CO2 divided into the many trillions of tons of ocean water indicates a %.0000004 increase in CO2 content. So they think that a 4 parts per billion increase (assuming it is all dissolved and remains there and that there are no offsetting deposits of alkaline material) in CO2 makes the ocean significantly more corrosive (less alkaline). Now that would be remarkable.

Alan M
January 20, 2021 7:09 pm

“This research was supported by NOAA’s Ocean Acidification Program”
WTF- NOAA has an Ocean Acidification Program?

Reply to  Alan M
January 21, 2021 1:14 pm

Alan M
Aren’t you getting a fat grant from the Woods Hole Jovian Alkalization Scheme?
Some folk are, I assume.


January 21, 2021 12:19 am

Interestingly it doesn’t mention the ammount of plankton found in cold upwelling waters versus hot waters.

Johann Wundersamer
February 1, 2021 4:57 am

Charles Rotter will never stop science fantasy about “ocean acidification”

Marine biology: Acidified oceans may corrode shark scales

Charles Rotter / ~cr comment

Prolonged exposure to high carbon dioxide (acidified) seawater may corrode tooth-like scales (denticles) covering the skin of puffadder shysharks, a study in Scientific Reports suggests. As ocean CO2 concentrations increase due to human activity, oceans are becoming more acidic, with potential implications for marine wildlife. Although the effects of acidified water have been studied in several species, this is the first observed instance of denticle corrosion as a result of long-term exposure.

Lutz Auerswald and colleagues investigated the effects of exposure to acidified seawater in puffadder shysharks. The authors found that in three sharks housed in acidified seawater for nine weeks, 25% of denticles on average were damaged, compared to 9.2% of denticles in a control group of three sharks that had been housed in non-acidic water.

They suggest that such corrosion may impair the sharks’ skin protection and open-water sharks’ ability to swim, as denticle surface affects their swimming speed. They also speculate that similar corrosion may occur in sharks’ teeth (which have the same structure and composition as denticles), which may negatively impact their feeding.

However, the authors also found that although exposure was linked with increased carbon dioxide concentrations in blood taken from a total of 36 sharks housed in acidified seawater for different periods of time, concentrations of carbonate also increased. This prevented the blood from becoming more acidic, suggesting that these sharks may be able to adjust to high CO2 conditions during periods of exposure.


Article and author details

Acid-base adjustments and first evidence of denticle corrosion caused by ocean acidification conditions in a demersal shark species

Corresponding author:

Lutz Auerswald
Department of Environment, Forestry and Fisheries and Stellenbosch University, Stellenbosch, South Africa



Online paper

From EurekAlert!

~cr comment.  PH of 7.3 expected in the year 2300, probably under RCP 8.5


What real science says about “ocean acidification” –

Geophysical Research LettersVolume 47, Issue 3

Research Letter

The Potential Impact of Nuclear Conflict on Ocean Acidification

Nicole S. Lovenduski Cheryl S. Harrison Holly Olivarez … See all authors

First published:21 January 2020


We demonstrate that the global cooling resulting from a range of nuclear conflict scenarios would temporarily increase the pH in the surface ocean by up to 0.06 units over a 5‐year period, briefly alleviating the decline in pH associated with ocean acidification.

Conversely, the global cooling dissolves atmospheric carbon into the upper ocean, driving a 0.1 to 0.3 unit decrease in the aragonite saturation state ( Ωₐᵣₐ𝓰 ) that persists for 10 years. The peak anomaly in pH occurs 2 years post conflict, while the Ωₐᵣₐ𝓰 anomaly peaks 4‐ to 5‐years post conflict.

The decrease in Ωₐᵣₐ𝓰 would exacerbate a primary threat of ocean acidification: the inability of marine calcifying organisms to maintain their shells/skeletons in a corrosive environment.

Our results are based on sensitivity simulations conducted with a state‐of‐the‐art Earth system model integrated under various black carbon (soot) external forcings. Our findings suggest that regional nuclear conflict may have ramifications for global ocean acidification.


© 2020 American Geophysical Union

The Wiley Network Wiley Press Room

Copyright © 1999-2019 John Wiley & Sons, Inc. All rights reserved

Microbial corrosion, also called bacterial corrosion, bio-corrosion, microbiologically influenced corrosion, or microbially induced corrosion (MIC), is corrosion caused or promoted by microorganisms, usually chemoautotrophs. It can apply to both metals and non-metallic materials. › wiki

Microbial corrosion – Wikipedia

– The decrease in Ωₐᵣₐ𝓰 would exacerbate a primary threat of ocean acidification: the inability of marine calcifying organisms to maintain their shells/skeletons in a corrosive environment. –> The decrease in Ωₐᵣₐ𝓰 as any ocean pH neutralisation wouldn’t noticeably affect marine organisms.

[ Our results are based on sensitivity simulations conducted with a state‐of‐the‐art Earth system model integrated under various black carbon (soot) external forcings. Our findings suggest that regional nuclear conflict may have ramifications for global ocean acidification. ]

– [ ] under various black carbon (soot) external forcings. Our findings suggest that regional nuclear conflict may have ramifications for global ocean acidification. –> various black carbon (soot) external forcings are business as usual at Earth’s conditions, terms since ~4.8 billion years with vulcanoe activities, continental movements, subduction / pressure zones.


– “ocean acidification” is in fact a decrease in Ωₐᵣₐ𝓰 and leads to ocean pH neutralisation.

– black carbon (soot) external forcings aren’t new “ramifications” in the planets history.

– Studies based on ocean acidification and atmospheric deposits try to associate corrosion with hazards, although corrosion is simply an important nutritional basis for all organisms.

– atmospheric deposits are business as usual in Earth’s history.

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