Ocean Acidification
Harold F. Upton
Analyst in Natural Resources Policy
Peter Folger
Specialist in Energy and Natural Resources Policy
July 30, 2013
Congressional Research Service
7-5700
www.crs.gov
R40143
CRS Report for Congress
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epared for Members and Committees of Congress

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Ocean Acidification

Summary
With increasing concentrations of carbon dioxide (CO2) in the atmosphere, the extent of effects
on the ocean and marine resources is an increasing concern. One aspect of this issue is the
ongoing process (known as ocean acidification) whereby seawater becomes less alkaline as more
CO2 dissolves in it, causing hydrogen ion concentration in seawater to increase. Scientists are
concerned that increasing hydrogen ion concentration could reduce growth or even cause death of
shell-forming animals (e.g., corals, mollusks, and certain planktonic organisms) as well as disrupt
marine food webs and the reproductive physiology of certain species. While not yet fully
understood, the ecological and economic consequences of ocean acidification could be
substantial.
Scientists are concerned that increasing hydrogen ion concentration in seawater could alter
biogeochemical cycles, disrupt physiological processes of marine organisms, and damage marine
ecosystems. This report does not discuss the effects of increasing thermal stress to marine
organisms and ecosystems (e.g., coral bleaching) related to climate change. However, marine
ecosystems are likely to be affected by the synergistic effects of factors involved in both thermal
and chemical processes.
Congress is beginning to focus attention on better understanding ocean acidification and
determining how this concern might be addressed. In the 111th Congress, the Federal Ocean
Acidification Research and Monitoring Act of 2009 (Title XII, Subtitle D, of P.L. 111-11) directed
the Secretary of Commerce to establish an ocean acidification program within NOAA,
established an interagency committee to develop an ocean acidification research and monitoring
plan, and authorized appropriations through FY2012 for NOAA and the National Science
Foundation. The only bill related to ocean acidification that has been introduced during the 113th
Congress is the Coral Reef Conservation Act Amendments of 2013 (S. 839). S. 839 would
include ocean acidification in the criteria used to evaluate project proposals for studying threats to
coral reefs and developing responses to coral reef losses. No further action has been taken on this
bill.



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Contents
Introduction ...................................................................................................................................... 1
What Is Ocean Acidification? .......................................................................................................... 1
At What Rate Is Ocean Acidification Occurring, and What Factors Affect This Rate? .................. 2
What Are Some of the Potential Effects of Ocean Acidification? ................................................... 3
Effects of Changing Ocean Chemistry ...................................................................................... 3
Response of Marine Life to Changing Ocean Chemistry .......................................................... 5
Corals .................................................................................................................................. 5
Other Invertebrates .............................................................................................................. 6
Vertebrates ........................................................................................................................... 8
Physical Effects of Changing Ocean Chemistry ........................................................................ 9
Worst-Case Scenarios ................................................................................................................ 9
What Are the Natural and Human Responses That Might Limit or Reduce Ocean
Acidification? ............................................................................................................................. 10
What Is the Federal Government Doing About Ocean Acidification? ........................................... 11
What Is the Congressional Interest in Ocean Acidification? ......................................................... 13
Additional Selected References ..................................................................................................... 13

Contacts
Author Contact Information........................................................................................................... 14

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Ocean Acidification

Introduction
On January 30, 2009, a Monaco Declaration was signed by more than 150 marine scientists from
26 countries, calling for immediate action by policymakers to reduce carbon dioxide emissions so
as to avoid widespread and severe damage to marine ecosystems from ocean acidification.1 The
Monaco Declaration is based on the Research Priorities Report developed by participants in an
October 2008 international symposium on “The Ocean in a High-CO2 World,”2 organized by
UNESCO’s Intergovernmental Oceanographic Commission, the Scientific Committee on Oceanic
Research, the International Atomic Energy Agency, and the International Geosphere Biosphere
Programme. In December 2010, the United Nations Environment Programme highlighted the
emerging concerns over the relationship between ocean acidification and food security.3 While
not yet fully understood, the ecological and economic consequences of ocean acidification could
be substantial. Legislative attention by Congress on ocean acidification currently is focused on
authorizing, funding, and coordinating research to increase knowledge about ocean acidification
and its potential effects on marine ecosystems.
What Is Ocean Acidification?
The complex interplay between rising carbon dioxide (CO2) levels in the atmosphere and the
ocean’s chemistry is a process that scientists have recognized for more than a century. As
increasing CO2 from the atmosphere dissolves in seawater, seawater chemistry is altered. The
prevailing pH (a measure of hydrogen ion concentration) of water near the ocean surface is
around 8.1, or slightly alkaline.4 Ocean acidification is the name given to the ongoing process
whereby pH decreases as seawater becomes less alkaline when increasing amounts of
anthropogenic CO2 from the atmosphere dissolve in seawater. When atmospheric CO2 dissolves
into the ocean, it forms carbonic acid (H2CO3). Some of the carbonic acid dissociates in ocean
waters, producing hydrogen ions (H+). As the number of hydrogen ions increases, the pH of the
ocean decreases, and the water becomes less alkaline.
Scientists are concerned that this change in seawater pH could alter biogeochemical cycles,
disrupt physiological processes of marine organisms, and damage marine ecosystems. This report
does not discuss the effects of increasing thermal stress to marine organisms and ecosystems (e.g.,
coral bleaching) related to climate change. However, marine ecosystems are likely to be affected
by the synergistic effects of factors involved in both thermal and chemical processes.

1 A copy of this declaration is available at http://scrippsnews.ucsd.edu/Releases/doc/MonacoDeclaration.pdf.
2 The full report is available at http://ioc3.unesco.org/oanet/Symposium2008/
ResearchPrioritiesReport_OceanHighCO2WorldII.pdf.
3 UNEP Emerging Issues: Environmental Consequences of Ocean Acidification: A Threat to Food Security, available at
http://www.grid.unep.ch/product/publication/download/Environmental_Consequences_of_Ocean_Acidification.pdf.
4 The pH scale is an inverse logarithmic representation of hydrogen proton (H+) concentration, indicating the activity
of hydrogen ions (or their equivalent) in the solution. A pH of less than 7.0 is considered acidic, while a pH greater
than 7.0 is considered basic (alkaline); a pH level of 7.0 is defined as “neutral.”
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At What Rate Is Ocean Acidification Occurring, and
What Factors Affect This Rate?
Over the past several decades, the oceans annually have absorbed about 2 billion metric tons of
the approximately 7 billion metric tons of carbon that all the countries in the world release as CO2
into the atmosphere each year.5 It has been estimated that a total of more than 530 billion tons of
CO2 have been absorbed by the ocean between 1800 and 1994,6 with the average pH of water
near the ocean surface decreasing by almost 0.1 pH unit.7 That decrease sounds small, but it
represents a 26% increase in the concentration of hydrogen ions, because the pH scale is
logarithmic (i.e., water with a pH of 6 is 10 times less acidic than water with a pH of 5, and 100
times less acidic than water with a pH of 4). Open ocean observational records of declining pH
are available from the Hawaiian Ocean Time-Series Station in the Pacific and the Bermuda
Atlantic Time-Series Station in the Atlantic.8 Up to a point, as atmospheric CO2 continues to
increase, ocean pH will continue to decrease; one estimate suggests that the rate of CO2 uptake by
the oceans could stabilize at around 5 billion metric tons per year by 2100.9 One prediction
suggests that continued burning of fossil fuels and future uptake of CO2 by the ocean could reduce
ocean pH by 0.3-0.5 units.10
All gases, such as CO2, are less soluble in water as temperature increases. Thus, marine waters
near the poles have a much greater capacity for dissolving CO2 than do ocean waters in the
tropics. In addition, dissolved CO2 is transported into ocean depths at these high latitudes (i.e.,
deep water formation mechanism) since the lower-temperature waters are of higher density,
causing greater convection to occur than happens in the more stratified tropical oceans. If
temperature were the only factor affecting the rate of ocean acidification and its impacts on
physical and biological features, these impacts might be more likely to occur in marine waters
nearer the poles. However, in addition to temperature, other factors modulate the impact of CO2
on marine waters. Cellular respiration and organic decomposition add CO2 to seawater, and
photosynthesis removes it. Deep oceanic water is enriched in CO2 due to respiration in the
absence of photosynthesis and, when brought to the surface by equatorial currents (i.e.,
upwelling), can place CO2-enriched seawater in contact with the atmosphere where it can absorb
even more CO2. Hence, the tropics, and most notably tropical coral reefs, are also vulnerable to
near-term effects. An additional factor is the potential increase in storm activity at higher
latitudes, as some climate models suggest.11 CO2 and other acidic gasses such as nitrogen dioxide

5 Richard A. Feely, Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, U.S.
Department of Commerce, World Ocean Forum, November 13-14, 2006, at http://www.thew2o.net/events/oceans/
oa_q_and_a.php; and Richard A. Feely et al., “Impact of Anthropogenic CO2 on the CaCO3 System in the Oceans,”
Science (2004), vol. 305, pp. 362-366.
6 C. L. Sabine, “The Oceanic Sink for Anthropogenic CO2,” Science, v. 305 (2004): 367-371.
7 James C. Orr et al., “Anthropogenic Ocean Acidification over the Twenty-First Century and Its Impact on Calcifying
Organisms,” Nature, vol. 437 (2005): 681-686.
8 See http://hahana.soest.hawaii.edu/hot/hot_jgofs.html and http://www.bios.edu/research/bats.html.
9 David Archer, “Fate of Fossil Fuel CO2 in Geologic Time,” Journal of Geophysical Research, v. 110 (2005): C09S05,
doi:10.1029/2004JC002625.
10 A. J. Andersson et al., “Coastal Ocean and Carbonate Systems in the High CO2 World of the Anthropocene,”
American Journal of Science, v. 305 (2005): 875–918.
11 See the Intergovernmental Panel on Climate Change’s Technical Paper on Climate Change and Water, available at
http://www.ipcc.ch/meetings/session28/executive_summary.pdf.
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are also dissolved in rainwater.12 An increase in North Atlantic or western North Pacific storms
could significantly accelerate the pH decrease of surface ocean waters in these regions.
Key scientific questions concern which factors may affect the future rate at which seawater pH
might decrease, especially whether the rate of decrease will remain constant in direct relationship
to the amount of CO2 in the atmosphere or whether other factors, such as rising ocean
temperatures diminishing CO2 absorption,13 will decelerate the rate that pH changes. There is also
the question of equilibrium—that is, how long might it take the process whereby the pH of
warming ocean waters is decreasing to come into equilibrium with the concentration of
atmospheric CO2, should the currently increasing atmospheric emission rate of CO2 eventually
stabilize or diminish? An adjunct to this question is how long might it take the rate of ocean
acidification to slow (or even reverse) in response to increasing water temperatures and any
measures that might be taken to slow, halt, or even reverse the increasing concentration of CO2 in
the atmosphere?14 Additional questions relate to how ocean circulation, which partially controls
the CO2 uptake rate, might change in response to changes in the overlying climate as a result of
greenhouse gas emissions.
What Are Some of the Potential Effects of Ocean
Acidification?
Since the marine environment is complex and some of the likely changes may be years in the
future, the potential effects identified in this section, although many are supported by laboratory
experimentation, are primarily conjecture and/or forecasts. However, field studies are beginning
to provide a more direct view of potential ocean acidification problems.15
Effects of Changing Ocean Chemistry
A lower pH affects marine life in the oceans and is related to other changes in ocean chemistry. In
addition to the lower pH, another consequence of the increased amount of dissolved CO2 in the
ocean is the production of more bicarbonate ions (HCO 1-
3 ). As more CO2 dissolves into the ocean,
bicarbonate ions form at the expense of carbonate ions (CO 2-
3 ), which scientists often describe by
the following reaction:
CO
2-
1-
2 + CO3 + H2O = 2HCO3

12 Rainwater is naturally acidic at a pH of around 5.6, and downwind of pollution sources has been measured as low as
pH 3.0.
13 Galen A. McKinley et al., “Convergence of Atmospheric and North Atlantic Carbon Dioxide Trends on Multidecadal
Timescales,” Nature Geoscience, v. 4, no. 9 (September 2011): 606-610.
14 The CO2 equilibration time between the surface mixed-layer of the ocean and the atmosphere is relatively fast—i.e.,
less than a year. Thus, the surface waters are anticipated to respond quickly to reductions in atmospheric CO2.
However, equilibration of CO2 for the entire ocean is more complex as mixing between the surface layer and the deep
ocean will take centuries to millennia.
15 See, for example, K. K. Yates and R. B. Halley, “Diurnal Variations in Rates of Calcification and Carbonate
Sediment Dissolution in Florida Bay,” Estuaries and Coasts, v. 29 (2006): 24-39; and K. K. Yates and R. B. Halley,
CO 2-
3 Concentration and pCO2 Thresholds for Calcification and Dissolution on the Molokai Reef Flat, Hawaii,”
Biogeosciences, v. 3 (2006): 357-369.
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The abundance and availability of carbonate ions are critical to many shell-forming marine
organisms. At current average ocean pH levels (about 8 or above), ocean waters near the surface
have ample carbonate ions to support shell formation and coral growth. However, as increased
amounts of carbonic acid form in the ocean as a result of higher atmospheric CO2 levels, pH
decreases and the amount of carbonate ions in the oceans declines, resulting in fewer carbonate
ions available for making shells.
Organisms make biogenic calcium carbonate for their shells and skeletons by combining calcium
ions (Ca2+)—which are abundant in the oceans—with carbonate ions to form solid calcium
carbonate (CaCO3). Certain marine organisms (e.g., corals and pteropods) precipitate one mineral
type of calcium carbonate called aragonite, and other marine organisms (e.g., foraminifera and
coccolithophorids) use another type called calcite. A third type of calcium carbonate—high
magnesium calcite—is precipitated by echinoderms (sea urchins and starfish) and some coralline
algae (an encrusting form of red algae that forms calcareous crusts like coral). Under present
conditions of ocean chemistry, these forms of calcium carbonate are relatively stable in waters
near the ocean surface, except for certain areas of high upwelling activity.16
Water near the ocean surface currently is supersaturated (i.e., more concentrated than normally
possible and therefore not in equilibrium) with calcite, high magnesium calcite, and aragonite,
meaning that organisms easily can form shells from all of these mineral types. However, as more
carbonic acid is formed in water near the ocean surface from higher levels of CO2 in the
atmosphere, the level of saturation decreases. If the ocean waters become undersaturated, then
shells made from all of these minerals would tend to dissolve. Shells made from high magnesium
calcite would tend to dissolve first, at lower concentrations of carbonic acid (and thus at higher
pH values) than would shells made from aragonite. Shells made from calcite would dissolve at
higher concentrations of carbonic acid than those made from aragonite.17 Thus, organisms that
incorporate high magnesium calcite (i.e., echinoderms and some coralline algae) are likely to be
the “first responders” to ocean acidification.18
Ocean waters at depths of thousands of feet are undersaturated with respect to all forms of
biogenic calcite, which is why most of the shells from dead organisms that “rain” down from the
ocean surface dissolve before reaching the ocean floor.19 Because of the combined effects of
increased CO2 and calcium carbonate solubility in cold water, some suggest that marine surface
waters closer to the poles may become undersaturated within the next 50 years.20 Researchers at
the Antarctic Climate and Ecosystems Cooperative Research Centre have demonstrated

16 Results from a 2007 National Oceanic and Atmospheric Administration survey along the U.S. West Coast
documented the first undersaturated waters at the ocean surface along the California coast, brought to the surface by
seasonal upwelling. See Richard A. Feely et al., “Evidence for Upwelling of Corrosive “Acidified” Water onto the
Continental Shelf,” Science, v. 320, no. 5882 (June 13, 2008): 1490-1492.
17 See Railsback, Some Fundamentals of Mineralogy and Geochemistry, at http://www.gly.uga.edu/railsback/
Fundamentals/820HMC-LMCSolubilities05LS.pdf.
18 Andreas J. Andersson, Fred T. Mackenzie, and Nicholas R. Bates, “Life on the Margin: Implications of Ocean
Acidification on Mg-Calcite, High Latitude and Cold-Water Marine Calcifiers,” Marine Ecology Progress Series, v.
373 (2008): 265-273.
19 Recent research suggests that no more than about 30% of the calcium carbonate produced in the surface ocean each
year is buried in shallow or deep sea sediments; the rest dissolves on its way down the water column. See Feely et al.
(2004), p. 365.
20 Orr et al. (2005).
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significant reductions in shell mass and thickness of several Southern Ocean marine algae and
animals that appear consistent with the projected effects of recent decreases in seawater pH.21
Response of Marine Life to Changing Ocean Chemistry
Although there has been a great deal of work growing organisms under different pHs, most
species have biochemical mechanisms to regulate internal pH and are able, within limits, to grow
skeletons even when the external medium is less alkaline. A lower pH environment may cause
these organisms to expend more energy, but overall they may be able to adapt in complex and
species-specific ways. Understanding how marine life might respond to less alkaline conditions is
more complicated than the simple claims that all will dissolve, which may ignore the actual
physiology of these organisms.
Corals
Some have raised questions downplaying the potential harm to coral reefs from ocean
acidification. Differences of opinion exist on the relative effects of climate change as expressed in
increased CO2 when compared to increased ocean temperature. Opinion has been expressed that,
in marine systems, increased temperature may have detrimental effects comparable to or larger
than those seen from increased CO2 concentration, for corals and for phytoplankton.22 Although
calcification rates in massive Porites coral were reported to have declined over a 16-year study
period by approximately 21% in two regions on Australia’s Great Barrier Reef, these findings
were consistent with other studies of the synergistic effect of elevated seawater temperatures and
CO2 concentrations on coral calcification.23 Concerns have also been expressed for coral reefs in
the eastern tropical Pacific.24 While ocean acidification may not appear currently to be killing
corals, decreasing seawater pH is slowing development of coral larvae into juvenile colonies.25
Some project that, in coral reef ecosystems, coral calcification will be reduced by 30% on average
by the end of the century.26 Calcareous algae, another contributor to building the reef frame, will
recruit, grow, and calcify under lower pH.27 However, the dissolution of reef carbonate by boring

21 Bruce Mapstone, “Acid Oceans in the Spotlight,” Antarctic Climate and Ecosystem News, edition 4 (August 2008):
1.
22 Clinton E. Hare et al., “Consequences of Increased Temperature and CO2 for Phytoplankton Community Structure in
the Bering Sea,” Marine Ecology Progress Series, v. 352 (2007), p. 14.
23 T. F. Cooper et al., “Declining Coral Calcification in Massive Porites in Two Nearshore Regions of the Northern
Great Barrier Reef,” Global Change Biology, v. 14 (2008): 529-538.
24 D. P. Manzello et al., “Poorly Cemented Coral Reefs of the Eastern Tropical Pacific: Possible Insights into Reef
Developments in a High-CO2 World,” Second Symposium on the Ocean in a High-CO2 World, Monaco, October 6-9,
2008.
25 R. Albright et al., “Effect of Aragonite Saturation State on Settlement and Post-Settlement Growth of Porites
astreoides Larvae,” Coral Reefs, v. 27, no. 3 (2008): 485-490.
26 Joan A. Kleypas et al., “Geochemical Consequences of Increased Atmospheric Carbon Dioxide on Coral Reefs, “
Science, v. 284, no. 5411 (April 2, 1999): 118-120; C. Langdon and M.J. Atkinson, “Effect of Elevated pCO2 on
Photosynthesis and Calcification of Corals and Interactions with Seasonal Change in Temperature/Irradiance and
Nutrient Enrichment,” Journal of Geophysical Research, v. 110 (2005): C09S07. doi:10.1029/2004JC002576.
27 I. B. Kuffner et al., “Decreased Abundance of Crustose Coralline Algae due to Ocean Acidification,” Nature
Geoscience, v. 1, no. 2 (2008): 114-117.
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microflora could increase by 50% under less alkaline conditions by the end of the century.28 The
decrease in coral and crustose coralline algae combined with the increase of carbonate dissolution
under less alkaline conditions has the potential to jeopardize the maintenance and resilience of
coral reefs and their services to human populations (in terms of food and economic resources).
Emerging evidence for the variability in coral response to acidification as well as response to past
climate change suggest greater heterogeneity in the pace and degree of reef degradation.29 In
addition, shallow-water coral reefs with long water residence times may be able to mask the
effects of ocean acidification in some downstream habitats.30 In support of the ability of certain
corals to survive decreasing pH, stony and soft corals have been grown successfully in open
systems with water from a saltwater well at a pH between 7.5 and 7.8 since the 1970s.31 However,
given the high level of adaptation in corals to facilitate calcification via complex processes, at
least some corals may be sensitive to changes in pH because of adaptation to invariant pH, with
evidence coming primarily from the discovery that periods of high CO2 in the geological past
were often also periods of low aragonite-coral abundances and diversity.32 Others have found that
certain species of coral survive in the laboratory at a pH of 7.3 to 7.6 after their calcified structure
dissolves by functioning similar to sea anemones, and retaining the ability to recalcify when pH is
increased.33 However, in the natural marine environment, predation could be a significant factor
in limiting the viability of such “naked” corals, and it is unlikely that such organisms could form
reefs and attract the diverse community that constitutes a coral reef.
Other Invertebrates
Increasing acidification may alter marine microbial activity, resulting in fundamental changes to
how nitrogen is cycled in the ocean. Ocean acidification appears to decrease nitrification, which
could reduce emissions of the greenhouse gas nitrous oxide to the atmosphere. In addition, an
unknown but potentially significant proportion of the ocean’s primary productivity could shift
from nitrate- to ammonium-supported, possibly resulting in cascading effects in marine food
webs.34
In the open ocean, some species of phytoplankton (i.e., microscopic floating plant life) may
respond positively (increasing their primary production rate) to rising CO2 concentrations in the
ocean, while others, such as the calcifying coccolithophores, could be negatively affected
(decreasing their calcification rate) by lower pH.35 Regarding the latter, however, some have

28 A. Tribollet et al., “Effects of Elevated pCO2 on Dissolution of Coral Carbonates by Microbial Euendoliths,” Global
Biogeochemical Cycles, doi:10.1029/2008GB003286, in press.
29 John M. Pandolfi et al., “Projecting Coral Reef Futures under Global Warming and Ocean Acidification,” Science, v.
333 (July 22, 2011): 418-422.
30 Kenneth R. N. Anthony et al., “Coral Reefs Modify Their Seawater Carbon Chemistry—Implications for Impacts of
Ocean Acidification,” Global Change Biology, v. 17, no. 12 (December 2011): 3655–3666.
31 M. J. Atkinson, B. Carlson, and G. L. Crow, “Coral Growth in High Nutrient, Low-pH Seawater: A Case Study of
Corals Cultured at the Waikiki Aquarium, Honolulu, Hawaii,” Coral Reefs, v. 14, no. 4 (1995): 215-223.
32 Personal communication, John W. McManus, Director, National Center for Coral Reef Research, Rosenstiel School
of Marine and Atmospheric Science, University of Miami, February 21, 2009.
33 Maoz Fine and Dan Tchernov, “Scleractinian Coral Species Survive and Recover from Decalcification,” Science, v.
315, no. 5820 (March 30, 2007): 1811.
34 J. Michael Beman et al., “Global Declines in Oceanic Nitrification Rates as a Consequence of Ocean Acidification,”
Proceedings of the National Academy of Sciences of the United States, v. 108, no. 1 (January 4, 2011): 208-213.
35 U. Riebesell et al., “Reduced Calcification in Marine Plankton in Response to Increased Atmospheric CO2,” Nature,
(continued...)
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suggested that several larger coccolithophore species may be able to increase their calcification in
response to anthropogenic CO2 release.36 Investigating 40,000 years of deposition in sediment
core samples, others find a marked pattern of decreasing calcification of coccolithophores with
increasing CO2 and decreasing bicarbonate.37
There is also the concern that decreasing seawater pH may dissolve marine calcium carbonate
sediments with potential harm to species and communities residing in and on these sediments.38
Since many of these organisms provide food or modify habitat for other organisms, the well-
being of these carbonate-dependent species will affect other species. Because of these
interrelationships, the potential indirect effects of decreased seawater pH on other marine
organisms is not well understood.
While some have raised concerns that ocean acidification, by harming calcifying plankton
species, could shift ecological balances so as to increase populations of some noncalcifying
species, there appears to be no significant relationship between jellyfish abundance and lower pH
conditions, and any role of pH in structuring zooplankton communities is believed to be
tenuous.39
There are also concerns that decreasing seawater pH could alter the ability of some invertebrate
organisms to conduct essential biochemical and physiological processes.40 For example, scientists
have found that, when exposed to water of pH 7.7, roughly equivalent to pH levels predicted for
the year 2100, sea urchin sperm swam much more slowly. Overall, fertilization fell by 25%, and
in almost 26% of cases where the eggs were fertilized, they did not survive long enough to
develop into larvae.41 While marine invertebrates in general, and their early developmental stages
in particular, are believed to be more sensitive to environmental disturbance, available data to
assess their vulnerability to ocean acidification is contradictory.42
In a controlled study at pH values anticipated in 2100, calcification was reduced 28% in the
pteropod Limacina helicina. These animals continued to grow and produce their shells even under

(...continued)
v. 407 (2000): 634-637; and W.M. Balch and V.J. Fabry, “Ocean Acidification: Documenting its Impact on Calcifying
Phytoplankton at Basin Scales,” Marine Ecology Progress Series, v. 373 (2008): 239-247.
36 P. R. Halloran et al., “Evidence for a Multi-Species Coccolith Volume Change over the Past Two Centuries:
Understanding a Potential Ocean Acidification Response,” Biogeosciences, v. 5 (2008): 1651-1655.
37 L. Beaufort et al., “Sensitivity of Coccolithophores to Carbonate Chemistry and Ocean Acidification,” Nature, v. 476
(August 4, 2011): 80-83.
38 M. Gehlen, L. Bopp, and O. Aumont, “Short-term Dissolution Response of Pelagic Carbonate Sediments to the
Invasion of Anthropogenic CO2: A Model Study,” Geochemistry, Geophysics, and Geosystems., v. 9 (February 16,
2008): Q02012.
39 A. J. Richardson and M. J. Gibbons, “Are Jellyfish Increasing in Response to Ocean Acidification?,” Limnology and
Oceanography, v. 53, no. 5 (2008):2040-2045.
40 Hans-O. Pörtner, “Ecosystem Effects of Ocean Acidification in Times of Ocean Warming: A Physiologist’s View,”
Marine Ecology Progress Series, v. 373 (2008): 203-217.
41 Jon N. Havenhand, Fenina-Raphaeia Buttler, Michael C. Thorndyke, and Jane E. Williamson, “Near-Future Levels
of Ocean Acidification Reduce Fertilization Success in a Sea Urchin,” Current Biology, v. 18, no. 15 (August 2008):
651-652.
42 S. Dupont and M. C. Thorndyke, “Impact of CO2-Driven Ocean Acidification on Invertebrates Early Life History—
What We Know, What We Need to Know and What We Can Do,” Biogeosciences Discussions, v. 6 (2009): 3109-
3131.
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high CO2, but at a slower rate.43 Many species, including Pacific salmon, mackerel, herring, cod,
and baleen whales, feed upon pteropods. Effects, if any, on the food web are unknown,
since pteropod growth is strongly influenced by food availability and temperature, among other
things. It is possible that higher temperatures could compensate for growth depression by CO2.
Coastal areas with upwelling of deeper waters may be at risk from detrimental effects of ocean
acidification much more quickly. Concerns have been expressed for benthic calcareous organisms
living in the nearshore shelf along the North American west coast.44 More specifically, scientists
in one of the Intergovernmental Panel on Climate Change (IPCC) scenarios have projected that
mussel and oyster calcification, and thus shell strength, could decrease significantly by the end of
the 21st century.45 Recently, oyster growers in the Pacific Northwest have experienced severe
larval mortalities resulting in multi-year reproductive failures which may be related to changing
ocean chemistry.46 In addition, laboratory experiments indicate that mussels may exhibit
significant signs of deterioration under acidified conditions predicted by the IPCC.47 Others have
attempted to project the timing and severity of the effects of ocean acidification on commercial
mollusc harvests.48
Vertebrates
Answering the question of how acidification may affect fisheries will likely require the
integration of knowledge across multiple disciplines.49 Although evidence suggests that larval and
juvenile fish are more susceptible to changes in ocean water pH than adults, larval and juvenile
fish exposed to exceedingly high CO2 concentrations (more than 100 times current levels)
suffered little apparent harm.50 Fish appear to be among the more tolerant marine animals. These
scientists believe that “the relative tolerance of fish may relate to high capacity for internal ion
and acid-base regulation via direct proton excretion, and an intracellular respiratory protein that
results in a high oxygen-carrying capacity and substantial venous oxygen reserve.” 51 Other
studies indicate that ocean acidification can impair olfactory discrimination and homing ability of
a marine fish such as the clown fish in coral reefs.52

43 S. Comeau et al., “Key Arctic Pelagic Mollusc (Limacina helicina) Threatened by Ocean Acidification,”
Biogeosciences Discussions, v. 6 (2009): 2523-2537.
44 Richard A. Feely et al., “Evidence for Upwelling of Corrosive “Acidified” Water onto the Continental Shelf,”
Science, v. 320, no. 5882 (June 13, 2008): 1490-1492.
45 Frederic Gazeau et al., “Impact of Elevated CO2 on Shellfish Calcification,” Geophysical Research Letters, v. 34, no.
7 (April 16, 2007): L07603 (5 p.).
46 Eric Scigliano, “The Great Oyster Crash,” Onearth (August 17, 2011); available at http://www.onearth.org/article/
oyster-crash-ocean-acidification.
47 Brian Gaylord et al., “Functional Impacts of Ocean Acidification in an Ecologically Critical Foundation Species,”
Journal of Experimental Biology, v. 214 (August 1, 2011): 2586-2594.
48 Sarah R. Cooley et al., “Nutrition and Income from Molluscs Today Imply Vulnerability to Ocean Acidification
Tomorrow,” Fish and Fisheries (2011), doi: 10.1111/j.1467-2979.2011.00424.x.
49 W. J. F. Le Quesne and J. K. Pinnegar, “The Potential Impacts of Ocean Acidification: Scaling from Physiology to
Fisheries,” Fish and Fisheries (2011), doi: 10.1111/j.1467-2979.2011.00423.x.
50 A. Ishimatsu et al., “Effects of CO2 on Marine Fish: Larvae and Adults,” Journal of Oceanography, v. 60, no. 4
(2004): 731-741.
51 V. J. Fabry et al., “Impacts of Ocean Acidification on Marine Fauna and Ecosystem Processes,” ICES Journal of
Marine Science, v. 65 (2008): 414-432.
52 Philip L. Munday et al., “Ocean Acidification Impairs Olfactory Discrimination and Homing Ability of a Marine
Fish,” Proceedings of the National Academy of Sciences, v. 106, no. 6 (February 10, 2009): 1848-1852.
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Physical Effects of Changing Ocean Chemistry
Concern has also arisen that lower ocean water pH will diminish low-frequency (below 10 KHz)
sound absorption in the ocean, increasing noise levels within the auditory range critical for
environmental, military, and economic interests.53 Frequency-dependent decreases to sound
absorption related to the current decrease in pH of about 0.1 pH unit may exceed 12%, and an
anticipated pH decrease of 0.3 pH units by mid-century may result in an almost 40% decrease in
sound absorption. It is unknown how marine mammals might be affected by and adapt to an
ocean increasingly transparent to sound at low frequencies.
Worst-Case Scenarios
Worst-case scenarios can be particularly hard to characterize, due to unforeseen consequences
and possible tipping points, where environmental response may suddenly no longer be directly or
linearly related to the causative factors. Although the likelihood of a “worst-case scenario”
coming to pass is uncertain and probably low, these circumstances require attention because
ignoring them could be potentially disastrous.54
Mass extinction events of marine organisms have occurred in geologic history, and some of these
events may have had some relationship to significant changes in ocean pH. The fossil record
indicates that marine organisms may be quite sensitive to ocean acidification—about 55 million
years ago, a large injection of CO2 into the deep ocean, presumably resulting from a massive
methane release, was followed by the extinction of some species of benthic foraminifera.55 In
addition, the extensive loss of marine biodiversity in the Late Triassic, about 200 million years
ago, appears to coincide with increased atmospheric CO2 concentration.56 Mass extinctions in the
geological record correspond to gaps of millions of years in coral reef building, and were likely
caused by problems in the carbon cycle, among which acidification is a strong
possibility.57 Some, however, caution that paleo-events may be imperfect analogs to current
conditions.58
The Intergovernmental Panel on Climate Change has predicted that, under their worst-case
scenario of no reduction or control of CO2 emissions, ocean pH could decrease to 7.7 by 2100.
Worst-case scenarios for ocean acidification focus on the potential for disruption of marine
ecosystems to the extent that food production from the ocean—finfish, shellfish, and other
invertebrates—could be compromised. Physiological changes caused by ocean acidification and
affecting ocean primary productivity—phytoplankton—have the potential to alter marine

53 Keith C. Hester et al., “Unanticipated Consequences of Ocean Acidification: A Noisier Ocean at Lower pH,”
Geophysical Research Letters, v. 35 (2008): L19601, doe:10.1029/2008FL034913.
54 Stephen Schneider, “The Worst-Case Scenario,” Nature, v. 458 (April 30, 2009): 1104-1105.
55 J. C. Zachos et al., “Rapid Acidification of the Ocean During the Paleocene-Eocene Thermal Maximum,” Science, v.
308 (2005): 1611-1615.
56 Jennifer C. McElwain, Peter J. Wagner, and Stephen P. Hesselbo, “ Fossil Plant Relative Abundances Indicate
Sudden Loss of Late Triassic Biodiversity in East Greenland,” Science, v. 324 (June 19, 2009): 1554-1556.
57 J. E. N. Veron, “Mass Extinctions and Ocean Acidification: Biological Constraints on Geological Dilemmas,” Coral
Reefs, v. 27 (2008): 459-472, and J. E. N. Veron, A Reef in Time, the Great Barrier Reef from Beginning to
End, Harvard University Press (2008), 289 p.
58 Scott C. Doney et al., “Ocean Acidification: The Other CO2 Problem,” Annual Review of Marine Science, v. 1
(January 2009): 169-192.
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ecosystems significantly, because primary production is at the base of almost all marine food
chains.
According to the most recent report on the status of the world’s fisheries by the United Nations
Food and Agriculture Organization,59 fisheries supply at least 15% of the animal protein
consumed by humans, provide direct and indirect employment for nearly 200 million people
worldwide and generate $85 billion annually. Any significant disruption of this industry could
have broad dietary as well as economic consequences.
Other consequences of a worst-case scenario include the loss of coral reefs, which, in addition to
being unique ecosystems supporting extensive biodiversity, provide coastal protection to mediate
storm and wave action as well as the basic structure for many island nations. Reef fish provide
subsistence for hundreds of millions of coastal residents, particularly in Southeast Asia. In
addition, reef tourism contributes significantly to the economy in the tropics—accounting for
about $2 billion dollars of income to Queensland, Australia, about $6 billion dollars of income in
the Caribbean (where developing countries can ill afford the loss of it), and a significant portion
of the $6 billion that all tourism contributes in the Florida Keys.60
What Are the Natural and Human Responses That
Might Limit or Reduce Ocean Acidification?
Several natural feedback mechanisms can act to moderate the process of seawater pH change. The
less alkaline the ocean becomes, the less CO2 will be dissolved. In addition, the warmer the
seawater becomes, the less CO2 will dissolve. Speculative questions exist about what might occur
should the oceans reach a ceiling (i.e., equilibrium) in their ability to take up CO2, and
atmospheric CO2 levels continue to increase. Even with increasing concentrations of atmospheric
CO2, scientists predict that the oceans are not likely to reach pH values of less than 7 (neutral).
Our ability to reduce ocean acidification through artificial means is unproven. Proposals have
suggested the addition of chemicals to the ocean, such as (1) using iron compounds to stimulate
planktonic algae growth, whereby the increased photosynthesis might capture/remove dissolved
CO2;61 (2) using limestone to neutralize (i.e., buffer) the lower-pH streams and rivers near where
they enter oceans and close to sources of limestone, or adding limestone powder directly to the
ocean where deeper, lower-pH water upwells;62 or (3) pumping the calcium bicarbonate
byproduct from limestone scrubbers at natural gas power plants into the ocean.63 Other measures

59 United Nations Food and Agriculture Organization, The State of World Fisheries and Aquaculture, Rome, 2008;
available at http://www.fao.org/docrep/011/i0250e/i0250e00.htm.
60 J. P. G. Spurgeon, “The Economic Valuation of Coral Reefs,” Marine Pollution Bulletin, v. 24, no. 11 (1992): 529-
536, and C. R. Wilkinson, “Global Change and Coral Reefs: Impacts on Reefs, Economies and Human Cultures,”
Global Change Biology, v. 2, no. 6 (1996): 547-558.
61 Richard Blaustein, “Fertilizing the Seas with Iron,” BioScience, v. 61, no. 10 (October 2011): 840; See also NOAA,
Report to Congress: Ocean Fertilization: The Potential of Ocean Fertilization for Climate Change Mitigation,
available at http://www.gc.noaa.gov/documents/2010_climate_fert_rept_Congress_final.pdf.
62 L. D. D. Harvey, “Mitigating the Atmospheric CO2 Increase and Ocean Acidification by Adding Limestone Powder
to Upwelling Regions,” Journal of Geophysical Research, v. 103 (2008): C04028, 21 p.
63 Greg H. Rau, “CO2 Mitigation via Capture and Chemical Conversion in Seawater,” Environmental Science and
Technology, v. 45, no. 3 (2011): 1088–1092.
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might include habitat restoration/creation, such as planting seagrass. Unless a massive global
effort is mounted, these techniques will at best be effective only on a very local scale. In addition,
manipulation of ocean chemistry has the potential to damage or otherwise alter the marine
environment and ecosystems in unforeseen ways. Reducing CO2 emissions to the atmosphere
and/or removing CO2 from the atmosphere (i.e., carbon sequestration) currently appear to be the
only practical ways to minimize the risk of large-scale and long-term changes to the pH of marine
waters. Because of the continuing increase in CO2 levels in the atmosphere, and its resident time
there, decreasing pH of ocean waters will likely continue for decades. Even if atmospheric CO2
were to return to pre-industrial levels, it could possibly take tens of thousands of years for ocean
chemistry to return to a condition similar to that occurring at pre-industrial times more than 200
years ago.64
What Is the Federal Government Doing About
Ocean Acidification?
Much of the current federal attention to ocean acidification focuses on research to better
understand the chemical processes involved and to become better able to predict how ocean
ecosystems might respond to decreasing pH.65
The National Science Foundation (NSF) was the first federal agency to become involved in
research related to ocean acidification. The modern surveys of CO2 in the oceans can be traced to
the NSF-sponsored Joint Global Ocean Flux Study (JGOFS), which originated in
recommendations from a National Academies of Science workshop in 1984.66 The more modern
concerns over ocean acidification arose from a May 2004 Paris workshop chaired by the now-
president of the National Academy of Sciences, Ralph Cicerone.67 In April 2005, NSF, the
National Oceanic and Atmospheric Administration (NOAA), and the U.S. Geological Survey
sponsored a workshop on the impacts of ocean acidification on coral reefs and other marine
calcifiers.68 In Section 701 of P.L. 109-479, Congress called for an 18-month comprehensive
national study by the National Research Council of the National Academies of Science on how
CO2 emissions absorbed into the oceans may be altering fisheries, marine mammals, coral reefs,
and other natural resources.69 This study was commissioned by NOAA and NSF in October 2008,
and a summary of Ocean Acidification: A National Strategy to Meet the Challenges of a

64 The Royal Society, Ocean Acidification Due to Increasing Atmospheric Carbon Dioxide, Policy Document 12/05
(June 2005), 60 p.
65 See also Cheryl A. Logan, “A Review of Ocean Acidification and America’s Response,” BioScience, v. 60, no. 10
(November 2010): 819-828.
66 For additional background, see http://www1.whoi.edu/jgofMission.html.
67 Ralph Cicerone, “The Ocean in a High CO2 World,” Eos, v. 85, no. 37 (September 14, 2004): 351, 353.
68 J. A. Kleypas et al., Impacts of Ocean Acidification on Coral Reefs and Other Marine Calcifiers: A Guide for Future
Research, report of a workshop held April 18-20, 2005, St. Petersburg, FL, sponsored by NSF, NOAA, and the U.S.
Geological Survey (June 2006), 88 p.
69 This measure required the Secretary of Commerce to request that the National Research Council study acidification
of the oceans and how this process affects the United States. See http://www.noaanews.noaa.gov/stories2008/
20081020_oceanacid.html.
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Changing Ocean was released in late April 2010; the full report was published in September
2010.70
The Federal Ocean Acidification Research and Monitoring Act of 2009 (FOARAM; P.L. 111-11)
established the interagency working group on ocean acidification (IWGOA). The IWGOA is
chaired by a representative from the National Oceanic and Atmospheric Administration and
includes representatives from the National Science Foundation, Bureau of Ocean Energy
Management, U.S. Department of State, Environmental Protection Agency, National Aeronautics
and Space Administration, U.S. Geological Survey, U.S. Fish and Wildlife Service, and U.S.
Navy. The IWGOA was charged with developing a strategic research and monitoring plan to
guide federal research on ocean acidification. In 2012, a draft of the Strategic Plan for Federal
Research and Monitoring of Ocean Acidification was released and sent to the National Research
Council for review.71 The strategic research plan attempts to provide a common vision and
specific goals to coordinate activities of federal agencies. The plan is organized into the following
seven themes,
1. monitoring of ocean chemistry and biological impacts,
2. research to understand responses to ocean acidification,
3. modeling to predict changes in the ocean carbon cycle,
4. technology development and standardization of measurements,
5. assessment of socioeconomic impacts and development,
6. education, outreach, and engagement strategy, and
7. data management and integration.
FOARAM also directed the IWGOA to submit a report to Congress every two years that
summarizes federally funded ocean acidification activities. The most recent report for FY2010
and FY2011 identifies funding levels by agency and by the strategic themes used in the strategic
research plan. In FY2011, total funding for ocean acidification activities was approximately $29
million. Funding for activities with a primary focus on ocean acidification was approximately $21
million and funding for activities related to ocean acidification was approximately $8 million.72

70 Available at http://www.nap.edu/openbook.php?record_id=12904&page=R1. In May 2011, a booklet, Ocean
Acidification: Starting with the Science, based on the longer report was released, and is available at http://dels.nas.edu/
resources/static-assets/materials-based-on-reports/booklets/OA1.pdf.
71 Interagency Working Group on Ocean Acidification, Strategic Plan for Federal Research and Monitoring of Ocean
Acidification, March 2012, http://www.st.nmfs.noaa.gov/iwgoa/
DRAFT_Ocean_Acidification_Strategic_Research_Plan.pdf.
72 Interagency Working Group on Ocean Acidification et al., Second Report on Federally Funded Ocean Acidification
Research and Monitoring Activities and Progress on a Strategic Research Plan, http://www.st.nmfs.noaa.gov/iwgoa/
documents/IWG-OA_Budget_Report-Official_Final_Version.pdf.
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What Is the Congressional Interest in Ocean
Acidification?
In comparison to previous sessions of Congress, legislative interest in ocean acidification
expanded significantly in the 110th Congress.73 Congressional attention focused primarily on
addressing the cause of ocean acidification—increasing atmospheric CO2.74 To date, legislative
attention to ocean acidification has focused on authorizing, funding, and coordinating research to
increase knowledge about ocean acidification and its potential effects on marine ecosystems.
In the 111th Congress, FOARAM directed the Secretary of Commerce to establish an ocean
acidification program within NOAA, established an interagency committee to develop an ocean
acidification research and monitoring plan, and authorized appropriations through FY2012 for
NOAA and the National Science Foundation. On April 22, 2010, the Senate Commerce, Science,
and Transportation Subcommittee on Oceans, Atmosphere, Fisheries, and Coast Guard held a
hearing on the environmental and economic impacts of ocean acidification. Several additional
measures were introduced in the 111th Congress to address this issue.75
The only bill related to ocean acidification that has been introduced during the 113th Congress is
the Coral Reef Conservation Act Amendments of 2013 (S. 839). S. 839 would include ocean
acidification in the criteria used to evaluate project proposals for studying threats to coral reefs
and developing responses to coral reef losses. No further action has been taken on this bill.

Additional Selected References
R.P. Kelly, et al., “Mitigating Local Causes of Ocean Acidification with Existing Laws,” Science,
v. 332 (May 27, 2011): 1036-1037.
Quirin Schiermeier, “Earth’s Acid Test,” Nature, v. 471 (March 10, 2011): 154-156.


73 For more details on ocean acidification legislation in the 110th Congress, see the section “Climate Change” in CRS
Report RL33813, Fishery, Aquaculture, and Marine Mammal Legislation in the 110th Congress, by Eugene H. Buck.
74 See CRS Issue in Focus “Climate Change Science and Technology” available at http://www.crs.gov/pages/
subissue.aspx?cliid=3878&parentid=2522&preview=False.
75For more details on ocean acidification legislation in the 111th Congress, see the section “Climate Change and Ocean
Acidification” in CRS Report R40172, Fishery, Aquaculture, and Marine Mammal Issues in the 111th Congress, by
Eugene H. Buck and Harold F. Upton.
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Author Contact Information

Harold F. Upton
Peter Folger
Analyst in Natural Resources Policy
Specialist in Energy and Natural Resources Policy
hupton@crs.loc.gov, 7-2264
pfolger@crs.loc.gov, 7-1517


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