The DOE Report on Ocean Acidification
The DOE report, authored by the Climate Working Group (CWG) only has a little to say about ocean acidification, but what it does say is somewhat bizarre, biased, and extremely problematic; it reveals what I consider irresponsible and short-sighted thinking on the part of CWG. Here's perhaps the most significant paragraph on p. 7.
While this process is often called “ocean acidification”, that is a misnomer because the oceans are not expected to become acidic; “ocean neutralization” would be more accurate. Even if the water were to turn acidic, it is believed that life in the oceans evolved when the oceans were mildly acidic with pH 6.5 to 7.0 (Krissansen-Totton et al., 2018). On the time scale of thousands of years, boron isotope proxy measurements show that ocean pH was around 7.4 or 7.5 during the last glaciation (up to about 20,000 years ago) increasing to present-day values as the world warmed during deglaciation (Rae et al., 2018).Thus, ocean biota appear to be resilient to natural long-term changes in ocean pH since marine organisms were exposed to wide ranges in pH.
There's a lot to unpack here. First, we should evaluate whether the term "ocean acidification" is an appropriate term to use. Second, we'll consider whether the DOE report has made its case that ocean biota are resilient to large swings in pH. And third, we'll evaluate why scientists expect ocean acidification to be harmful to marine organisms.
The Term "Ocean Acidification"
"Ocean acidification" is the term scientists use for the fact that the pH of the oceans is decreasing. It has decreased from about 8.2 to 8.05, decreasing at a rate of about -0.017/decade. Since this is a logarithmic scale, that also means there has been about a 30% increase in H+ ions in the upper oceans. Since acidity is a measure of H+ ions in a solution, a 30% increase in H+ ions is a 30% increase in ocean acidity, and that's why scientists have used the term "ocean acidification" since it was discovered that the oceans are acidifying. But since a neutral pH is 7, the oceans are still basic, and scientists do not expect the pH of the oceans to decrease below 7 because of AGW.
For some reason, contrarians seem to have trouble with the term "ocean acidification," since they believe that there's something "alarming" about that term. We're told it's a term that's designed to scare people. This report prefers to use "ocean neutralization" instead. In the grand scheme of things, the term we use to describe observations doesn't matter, as long as it is well-defined. Whether scientists decided to use "ocean acidification" or "ocean neutralization" to refer to the 30% increase in ocean acidity makes no difference whatsoever to what's happening in the oceans, and so I really don't care what we call it. But let me offer an analogy that I think illustrates why the scientists that coined "ocean acidification" were well within their rights to do so.
Imagine that you are in Tierra del Fuego near the southern tip of South America, and you want to travel to Bueno Aires in Argentina. Both locations are in the Southern Hemisphere, but if you travel from Tierra del Fuego to Buenos Aires you're traveling towards the Northern Hemisphere. In your travels, you will not reach the Northern Hemisphere or even the "neutral" Equator, but most people are still very comfortable saying that you're traveling northward. We recognize that it's possible to move northward without getting to "the North," and we don't need to use terms like "equatorization" to account for the fact that we didn't cross the Equator. Likewise, ocean waters are moving in the direction of becoming acidic, and even though they will not become either neutral or acidic, "ocean acidification" is the term scientists decided to use. If scientists decided to call ocean acidification by "lowerpHification" or "dealkalinization" I would have no real issue with the terminology. All that matters is the term is well-defined to communicate. Here are a few scientific organizations that use the term "ocean acidification:" British Royal Society, National Academy of Sciences, National Geographic, NOAA, American Chemical Society, Smithsonian Institution, Scripps Institution of Oceanography, Cambridge University, Roger Williams University, and Nature Knowledge Project. I know of no scientific organizations that refer to it by some other term.
The DOE Argument
The CWG claims that we don't need to be concerned about ocean acidification because "ocean biota appear to be resilient to natural long-term changes in ocean pH since marine organisms were exposed to wide ranges in pH." The evidence for this comes exclusively from two studies, neither of which have anything to do with whether ocean acidification is harmful to ocean biota. Let's look at each of the two studies.
Study 1 - Krissansen-Totton et al 2018[1]
"Even if the water were to turn acidic, it is believed that life in the oceans evolved when the oceans were mildly acidic with pH 6.5 to 7.0 (Krissansen-Totton et al., 2018)."
Krissansen-Totton do indicate that Ocean pH was lower during the Archean and Proterozoic. The abstract is clear:
We find that the Archean climate was likely temperate (0–50 °C) due to the combined negative feedbacks of continental and seafloor weathering. Ocean pH evolves monotonically from 6.6 -0.4 +0.6 (2σ) at 4.0 Ga to 7.0 -0.5 +0.7 (2σ) at the Archean–Proterozoic boundary, and to 7.9 -0.2 +0.1 (2σ) at the Proterozoic–Phanerozoic boundary. This evolution is driven by the secular decline of pCO2, which in turn is a consequence of increasing solar luminosity, but is moderated by carbonate alkalinity delivered from continental and seafloor weathering.
But CWG doesn't seem to be aware that during the Archean, when the pH of the oceans was increasing from 6.6 to 7.0, there was virtually no oxygen in the atmosphere. It wasn't until the beginning of the Great Oxygenation Event (GOE) shortly after the beginning of the Proterozoic that the our atmosphere contained a substantial amount of O2. Virtually no animals or plants alive today could survive without oxygen in the atmosphere, since virtually all require aerobic respiration (and the few that don't mostly depend on life that does). It's absolutely ludicrous to suggest that because the oceans were acidic during the Archean, when the atmosphere contained no O2, ocean biota would be fine if the oceans became acidic again; a return to Archean oceans would kill off virtually all marine life. This is an obvious non sequitur, and it flies in the face of common sense.
Rae et al 2018[2]
"On the time scale of thousands of years, boron isotope proxy measurements show that ocean pH was around 7.4 or 7.5 during the last glaciation (up to about 20,000 years ago) increasing to present-day values as the world warmed during deglaciation (Rae et al., 2018)."
Rae et al 2018 does contain a graph showing lower pH values during the Last Glacial Maximum. Here's the graph from the paper.
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Deep Southern Ocean CO2 chemistry and atmospheric CO2 over the last 40,000 years from Rae et al 2018 |
During the Last Glacial Maximum (LGM), the pH of the whole ocean is thought to have been significantly more basic, as inferred from the isotopic composition of boron incorporated into calcium carbonate shells, which would partially explain the lower atmospheric CO2 concentration at that time.In fact, at least since the Mid-Pleistocene Transition ocean pH has ranged between 8.2 during interglacial periods and 8.3 during glacial periods. The European Environment Agency summarizes, "Over the last million years, mean surface seawater pH has been relatively stable. Oscillating between 8.3, during cold periods (e.g. during the last glacial maximum 20,000 years ago), and 8.2, during warm periods (e.g. just prior to the industrial revolution)."
The deep ocean is under high pressure, and as ocean depth increases, pressure significantly affects the dissociation of carbonic acid, and a decrease in pH with depth is expected. Biological process in the ocean interior can also drive changes in deep ocean pH. Lauvset et al 2020[4] has observed in situ pH measurements ranging between "7.52 ± 0.05 and 8.33 ± 0.10 in the interior ocean" currently. It would seem that the CWG didn't do their homework on ocean pH at all. There is no evidence ocean biota near the surface were exposed to "wide ranges in pH" during the last million years, at least near the surface where most marine organisms live.
Why Ocean Acidification is Harmful
As CO2 is added to the atmosphere, some of it dissolves into ocean water, and this begins the process of ocean acidification. The ocean system is a little complicated because it constitutes a a buffered system, but we can summarize the reactions as follows:
- Step 1: CO2 dissolves in the oceans produce Carbonic Acid:
CO2(aq) + H2O <-> H2CO3 - Step 2: The carbonic acid dissociates to produce bicarbonate ions and protons:
H2CO3 <-> HCO3- + H+ - Step 3: Bicarbonate ions dissociate into carbonate ions and protons:
HCO3- <-> CO3^2- + H+ - Step 4: Both of these last two steps produce protons. However, sea water buffers against changes in pH. The buffering capacity can be expressed as follows:
CO2(aq) + CO3^2- + H2O -> 2HCO3- - Step 5: HCO3- partly dissociates (see step 3) producing more H+.
Whether CaCO3 crystals form or dissolve is largely dependent on the concentration of CO3^2-, and in particular, the saturation state, or ratio of concentration of CO3^2- in seawater over the concentration at saturation, which we can call Ω. If Ω > 1, then CaCO3 crystals tend to form. If Ω <1, they tend to dissolve. And Ω decreases with depth, so CaCO3 is more likely to dissolve in deeper waters. So as CO3^2- decreases with ocean acidification, Ω can become < 1 in shallower waters. In some places it can reach the surface. When Ω is undersaturated, CaCO3 will dissolve from chalk, limestone, bivalve shells, corals and other life forms that make use of CaCO3. Aragonite is more soluble than calcite, so this is a bigger problem for animals that produce aragonite cells than calcite shells. CO2 is more soluble in colder waters, so high latitude surface waters are more likely to become undersaturated than tropical waters. This suggests that there clearly are threats to marine biota from ocean acidification, and there are dozens of studies available to evaluate those threats.
CWG does not consider any threats to marine life save for a superficial treatment of concerns that ocean acidification will "reduce the calcification rate of coral reefs" on pp. 7-8. The discussion that follows deals exclusively with the Australia's Great Barrier Reef (GBR) and the effect of ocean acidification on the behavior of reef fishes. CWG's treatment of the GBR is dismissive of published scientific studies[5] and is heavily biased towards the claims of Peter Ridd, whose views are not representative of the vast majority of scholarship on the GBR. CWG focuses on the supposed "recovery" in the GBR following 2009. In fact, the "recovery" of the GBR coral cover has occurred at the expense of biodiversity. AIMS has consistently pointed out that increase of coral cover has been dominated by Acropora species of corals. This is the genus of coral that is the fastest growing but also are susceptible to heat stress and tropical cyclones. The scientists that are studying the GBR do not share Ridd's optimism, and the GBR has taken a hit in 2024 as a result of the global-scale mass bleaching event.
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| AIMS Graph of GBR Coral Cover |
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| From Eddy et al 2021[6] |
The CWG also discusses a meta-analysis by Clements et al 2022[7] (cited incorrectly "Clements et al, 2021") on the effects of CO2 on reef fishes. This is true. Replication studies such as those by Clark et al 2020[8] have been unable to replicate studies that had previously concluded that ocean acidification had negative impacts on fish behavior. But there are many other ocean acidification threats to marine life that are not related to fish behavior, and the DOE report discusses none of these. In the references below I list many studies evaluating risks associated with ocean acidification and its impact on marine heatwaves [9][10], general marine life [11][12][13][14], coral reef health[15-28], and shellfish[29][30][31]. Aside from a superficial and biased take on the GBR, none of this is discussed in the report.
Conclusion
You would think that a report advertised as "evaluating existing peer-reviewed literature and government data on climate impacts of Greenhouse Gas (GHG) Emissions and providing a critical assessment of the conventional narrative on climate change" might want to evaluate the extensive peer-reviewed literature in existence on ocean acidification and provide a critical assessment of it. The threats to marine biota is extensively documented in the literature, but the CWG is essentially asking us to ignore all these threats because "ocean life is complex and much of it evolved when the oceans were acidic" and the deep Southern Ocean had a lower pH during the LGM.
On a more positive note, a couple years ago I found an interesting paper by Ziveri et al 2023[32] that looks like it may lead to significant improvements in our understanding of how much AGW will continue acidify the oceans. Ziveri et al found that marine calcifying phytoplankton produces CaCO3 more quickly than it can be exported to deeper waters, below the photic zone. By keeping more CaCO3 closer to the surface of the oceans, the oceans can absorb more CO2 with less acidification. If this increases with AGW, then that could be a negative feedback that may decrease projected rates of ocean acidification. The authors write,
if the dissolution of coccolithophore CaCO3 within the photic zone is in part related to the degree of calcification and/or the remineralisation of organic carbon contained within the soft tissue of the calcifying organisms, this decrease in the PIC/POC of coccolithophores may lead to a negative feedback with CO2, with increased dissolution (and thus reduced export of alkalinity) out of the surface ocean acting to buffer rising atmospheric CO2. Given the potential importance of CaCO3 export in driving changes in alkalinity and atmospheric CO2, and the large uncertainties in our current understanding, future work should focus on understanding the processes by which CaCO3 is either dissolved within the photic zone or exported to depth.
So there are some studies that could be positively seen as "good news" regarding ocean acidification that CWG could have addressed, but even these types of studies were ignored by the DOE report. Instead, CWG gave us a superficial, biased, and extremely selective treatment of a complex topic. They misrepresented scientific studies that simply did not support their claims, ignored studies evaluating actual threats facing marine life, and instead complained about the terminology scientists use to describe the lowering of ocean pH. The CWG could do better.
References:
[1] J. Krissansen-Totton, G.N. Arney, & D.C. Catling, Constraining the climate and ocean pH of the early Earth with a geological carbon cycle model, Proc. Natl. Acad. Sci. U.S.A. 115 (16) 4105-4110, https://doi.org/10.1073/pnas.1721296115 (2018).[2] Rae, J.W.B., Burke, A., Robinson, L.F. et al. CO2 storage and release in the deep Southern Ocean on millennial to centennial timescales. Nature 562, 569–573 (2018). https://doi.org/10.1038/s41586-018-0614-0
https://scispace.com/pdf/co2-storage-and-release-in-the-deep-southern-ocean-on-1i880hd90a.pdf[6] Tyler D. Eddy, Vicky W.Y. Lam, Gabriel Reygondeau, Andrés M. Cisneros-Montemayor, Krista Greer, Maria Lourdes D. Palomares, John F. Bruno, Yoshitaka Ota, William W.L. Cheung, Global decline in capacity of coral reefs to provide ecosystem services, One Earth, Volume 4, Issue 9, 2021, Pages 1278-1285, ISSN 2590-3322, https://doi.org/10.1016/j.oneear.2021.08.016.
(https://www.sciencedirect.com/science/article/pii/S2590332221004747)
(https://www.sciencedirect.com/science/article/pii/S2590332221004747)
[7] Clements JC, Sundin J, Clark TD, Jutfelt F (2022) Meta-analysis reveals an extreme “decline effect” in the impacts of ocean acidification on fish behavior. PLoS Biol 20(2): e3001511. https://doi.org/10.1371/journal.pbio.3001511
[9] Burger, F.A., Terhaar, J. & Frölicher, T.L. Compound marine heatwaves and ocean acidity extremes. Nat Commun 13, 4722 (2022). https://doi.org/10.1038/s41467-022-32120-7
[10] Capotondi, A., Rodrigues, R.R., Sen Gupta, A. et al. A global overview of marine heatwaves in a changing climate. Commun Earth Environ 5, 701 (2024). https://doi.org/10.1038/s43247-024-01806-9
[11] Kroeker, K.J., Kordas, R.L., Crim, R., Hendriks, I.E., Ramajo, L., Singh, G.S., Duarte, C.M. and Gattuso, J.-P. (2013), Impacts of ocean acidification on marine organisms: quantifying sensitivities and interaction with warming. Glob Change Biol, 19: 1884-1896. https://doi.org/10.1111/gcb.12179
[12] Hu, N., Bourdeau, P.E. & Hollander, J. Responses of marine trophic levels to the combined effects of ocean acidification and warming. Nat Commun 15, 3400 (2024). https://doi.org/10.1038/s41467-024-47563-3
[13] Zhang, F., Wen, Z., Wang, S. et al. Phosphate limitation intensifies negative effects of ocean acidification on globally important nitrogen fixing cyanobacterium. Nat Commun 13, 6730 (2022). https://doi.org/10.1038/s41467-022-34586-x
[14] Wang, S., Foster, A., Lenz, E. A., Kessler, J. D., Stroeve, J. C., Anderson, L. O., et al. (2023). Mechanisms and impacts of Earth system tipping elements. Reviews of Geophysics, 61, e2021RG000757. https://doi.org/10.1029/2021RG000757
[15] N.R. Mollica, W. Guo, A.L. Cohen, K. Huang, G.L. Foster, H.K. Donald, & A.R. Solow, Ocean acidification affects coral growth by reducing skeletal density, Proc. Natl. Acad. Sci. U.S.A. 115 (8) 1754-1759, https://doi.org/10.1073/pnas.1712806115 (2018).
[16] Henley, B.J., McGregor, H.V., King, A.D. et al. Highest ocean heat in four centuries places Great Barrier Reef in danger. Nature 632, 320–326 (2024). https://doi.org/10.1038/s41586-024-07672-x
[17] Great Barrier Reef Marine Park Authority. Great Barrier Reef Outlook Report. 2024. https://outlookreport.gbrmpa.gov.au/
[18] The Great Barrier Reef Marine Park Authority, and The Great Barrier Reef Marine Park Authority. Reef 2050 Plan Annual Report , Australian Government, July 2019. https://www.dcceew.gov.au/sites/default/files/documents/reef-2050-long-term-sustainability-plan-2021-2025.pdf.
[19] Benjamin Petrick et al.,High sea surface temperatures were a prerequisite for the development and expansion of the Great Barrier Reef.Sci. Adv.10,eado2058(2024).DOI:10.1126/sciadv.ado2058
[20] McHugh, L.H., Lemos, M.C., Margules, C. et al. Divergence over solutions to adapt or transform Australia’s Great Barrier Reef. npj Clim. Action 3, 115 (2024). https://doi.org/10.1038/s44168-024-00180-8
[21] Pendleton, L., Hoegh-Guldberg, O., Albright, R., Kaup, A., Marshall, P., Marshall, N., … Hansson, L. (2019). The Great Barrier Reef: Vulnerabilities and solutions in the face of ocean acidification. Regional Studies in Marine Science, 100729. doi:10.1016/j.rsma.2019.100729
[22] GCRMN. Status of Coral Reefs of the World: 2020. https://gcrmn.net/2020-report-v1-2023/
[23] Emslie, Michael J., Annual Summary Report of Coral Reef Condition 2021/2022, Australian Institute Of Marine Science, 1 Aug. 2022. https://www.aims.gov.au/sites/default/files/2022-08/AIMS_LTMP_Report_on%20GBR_coral_status_2021_2022_040822F3.pdf.
[24] Emslie, Michael J., et al. “Decades of Monitoring Have Informed the Stewardship and Ecological Understanding of Australia's Great Barrier Reef.” Biological Conservation, vol. 252, 2020, p. 108854., https://doi.org/10.1016/j.biocon.2020.108854.
[25] Graham, N., Jennings, S., MacNeil, M. et al. Predicting climate-driven regime shifts versus rebound potential in coral reefs. Nature 518, 94–97 (2015). https://doi.org/10.1038/nature14140
[26] Dietzel Andreas, Bode Michael, Connolly Sean R. and Hughes Terry P. 2020Long-term shifts in the colony size structure of coral populations along the Great Barrier ReefProc. R. Soc. B.2872020143220201432 http://doi.org/10.1098/rspb.2020.1432
[27] Mellin, Camille, et al. “Spatial Resilience of the Great Barrier Reef under Cumulative Disturbance Impacts.” Global Change Biology, vol. 25, no. 7, 2019, pp. 2431–2445., https://doi.org/10.1111/gcb.14625.
[28] Stuart-Smith, R.D., Brown, C.J., Ceccarelli, D.M. et al. Ecosystem restructuring along the Great Barrier Reef following mass coral bleaching. Nature 560, 92–96 (2018). https://doi.org/10.1038/s41586-018-0359-9
[31] Talmage SC, Gobler CJ (2011) Effects of Elevated Temperature and Carbon Dioxide on the Growth and Survival of Larvae and Juveniles of Three Species of Northwest Atlantic Bivalves. PLoS ONE 6(10): e26941. https://doi.org/10.1371/journal.pone.0026941
[17] Great Barrier Reef Marine Park Authority. Great Barrier Reef Outlook Report. 2024. https://outlookreport.gbrmpa.gov.au/
[18] The Great Barrier Reef Marine Park Authority, and The Great Barrier Reef Marine Park Authority. Reef 2050 Plan Annual Report , Australian Government, July 2019. https://www.dcceew.gov.au/sites/default/files/documents/reef-2050-long-term-sustainability-plan-2021-2025.pdf.
[19] Benjamin Petrick et al.,High sea surface temperatures were a prerequisite for the development and expansion of the Great Barrier Reef.Sci. Adv.10,eado2058(2024).DOI:10.1126/sciadv.ado2058
[20] McHugh, L.H., Lemos, M.C., Margules, C. et al. Divergence over solutions to adapt or transform Australia’s Great Barrier Reef. npj Clim. Action 3, 115 (2024). https://doi.org/10.1038/s44168-024-00180-8
[21] Pendleton, L., Hoegh-Guldberg, O., Albright, R., Kaup, A., Marshall, P., Marshall, N., … Hansson, L. (2019). The Great Barrier Reef: Vulnerabilities and solutions in the face of ocean acidification. Regional Studies in Marine Science, 100729. doi:10.1016/j.rsma.2019.100729
[22] GCRMN. Status of Coral Reefs of the World: 2020. https://gcrmn.net/2020-report-v1-2023/
[23] Emslie, Michael J., Annual Summary Report of Coral Reef Condition 2021/2022, Australian Institute Of Marine Science, 1 Aug. 2022. https://www.aims.gov.au/sites/default/files/2022-08/AIMS_LTMP_Report_on%20GBR_coral_status_2021_2022_040822F3.pdf.
[24] Emslie, Michael J., et al. “Decades of Monitoring Have Informed the Stewardship and Ecological Understanding of Australia's Great Barrier Reef.” Biological Conservation, vol. 252, 2020, p. 108854., https://doi.org/10.1016/j.biocon.2020.108854.
[25] Graham, N., Jennings, S., MacNeil, M. et al. Predicting climate-driven regime shifts versus rebound potential in coral reefs. Nature 518, 94–97 (2015). https://doi.org/10.1038/nature14140
[26] Dietzel Andreas, Bode Michael, Connolly Sean R. and Hughes Terry P. 2020Long-term shifts in the colony size structure of coral populations along the Great Barrier ReefProc. R. Soc. B.2872020143220201432 http://doi.org/10.1098/rspb.2020.1432
[27] Mellin, Camille, et al. “Spatial Resilience of the Great Barrier Reef under Cumulative Disturbance Impacts.” Global Change Biology, vol. 25, no. 7, 2019, pp. 2431–2445., https://doi.org/10.1111/gcb.14625.
[28] Stuart-Smith, R.D., Brown, C.J., Ceccarelli, D.M. et al. Ecosystem restructuring along the Great Barrier Reef following mass coral bleaching. Nature 560, 92–96 (2018). https://doi.org/10.1038/s41586-018-0359-9
[29] Nina Bednaršek, Richard A. Feely, Marcus W. Beck, Simone R. Alin, Samantha A. Siedlecki, Piero Calosi, Emily L. Norton, Casey Saenger, Jasna Štrus, Dana Greeley, Nikolay P. Nezlin, Miranda Roethler, John I. Spicer, Exoskeleton dissolution with mechanoreceptor damage in larval Dungeness crab related to severity of present-day ocean acidification vertical gradients, Science of The Total Environment, Volume 716, 2020, 136610, ISSN 0048-9697, https://doi.org/10.1016/j.scitotenv.2020.136610.
[30] Siegel, K. R., Kaur, M., Grigal, A. C., Metzler, R. A., & Dickinson, G. H. (2022). Meta-analysis suggests negative, but pCO2-specific, effects of ocean acidification on the structural and functional properties of crustacean biomaterials. Ecology and Evolution, 12, e8922. https://doi.org/10.1002/ece3.8922
[32] Ziveri, P., Gray, W.R., Anglada-Ortiz, G. et al. Pelagic calcium carbonate production and shallow dissolution in the North Pacific Ocean. Nat Commun 14, 805 (2023). https://doi.org/10.1038/s41467-023-36177-w
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