20 Facts About Ocean Acidification

Abstract

T his document presents the highlights of the Frequently Asked Questions about Ocean Acidification (2010, 2012; www.whoi.edu/OCB-OA/FAQs), a detailed summary of the state of ocean acidification research and understanding. The FAQs and this fact sheet are intended to aid scientists, science communicators, and science policy advisors asked to comment on details about ocean acidification. In all, 63 scientists from 47 institutions and 12 countries participated in writing the FAQ, which was produced by the Ocean Carbon and Biogeochemistry Project (www.us-ocb.org), the United Kingdom Ocean Acidification Programme (www.oceanacidification.org.uk), and the European Project on Ocean Acidification (EPOCA). More information and contacts can be found at any of these websites or at the Ocean Acidification International Coordination Centre's website (www.iaea.org/ocean-acidification). The Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report findings on ocean acidification can be viewed at www.ipcc.ch. 20 FACTS about 1 Ocean acidification (OA) is a progressive increase in the acidity of the ocean over an extended period, typically decades or longer, which is caused primarily by uptake of car-bon dioxide (CO 2)from the atmosphere. It can also be caused or enhanced by other chemical additions or subtractions from the ocean. Acidification can be more severe in areas where human activities and impacts, such as acid rain and nutrient runoff, further increase acidity.

Full text

This document presents the highlights of the Frequently Asked Questions about Ocean
Acidication (2010, 2012; www.whoi.edu/OCB-OA/FAQs), a detailed summary of the state of
ocean acidication research and understanding. e FAQs and this fact sheet are intended to
aid scientists, science communicators, and science policy advisors asked to comment on details about
ocean acidication. In all, 63 scientists from 47 institutions and 12 countries participated in writing
the FAQ, which was produced by the Ocean Carbon and Biogeochemistry Project (www.us-ocb.org),
the United Kingdom Ocean Acidication Programme (www.oceanacidication.org.uk), and the
European Project on Ocean Acidication (EPOCA). More information and contacts can be found at
any of these websites or at the Ocean Acidication International Coordination Centre’s website
(www.iaea.org/ocean-acidication). e Intergovernmental Panel on Climate Change (IPCC) Fih
Assessment Report ndings on ocean acidication can be viewed at www.ipcc.ch.
20 FACTS
about
1Ocean acidication (OA) is a progressive increase in the
acidity of the ocean over an extended period, typically
decades or longer, which is caused primarily by uptake of car-
bon dioxide (CO2)from the atmosphere. It can also be caused
or enhanced by other chemical additions
or subtractions from the ocean.
Acidication can be more severe
in areas where human activities
and impacts, such as acid rain and
nutrient runo, further increase
acidity.
2OA has been well
documented with
global observations
conducted over sev-
eral decades by hun-
dreds of researchers.
It has been denitively
attributed to human-generat-
ed CO2 in the atmosphere that has been released primarily
by fossil fuel combustion and land use changes.
3Acidity may be thought of as simply the hydrogen
ion concentration (H+) in a liquid, and pH is the loga-
rithmic scale on which this concentration is measured. It is
important to note that acidity increases as the pH decreases.
4Average global surface ocean pH has already fallen from
a pre-industrial value of 8.2 to 8.1, corresponding to an in-
crease in acidity of about 30%. Values of 7.8–7.9 are expected
by 2100, representing a doubling of acidity.
5e pH of the open-ocean surface layer is unlikely to
ever become acidic (i.e. drop below pH 7.0), because
seawater is buered by dissolved salts. e term “acidication”
refers to a pH shi towards the acidic
end of the pH scale, similar to the
way we describe an increase
in temperature from -20°C
to 0°C (-4°F to 32°F): it’s
still cold, but we say
it’s “warming.”
6OA is also
changing
seawater carbon-
ate chemistry.
e concentra-
tions of dissolved
CO2, hydrogen ions,
and bicarbonate ions
are increasing, and the
concentration of carbonate
ions is decreasing.
7Changes in pH and carbonate chemistry force marine
organisms to spend more energy regulating chemistry
in their cells. For some organisms, this may leave less energy
for other biological processes like growing, reproducing or
responding to other stresses.
Pteropods, also called sea butteries, are one type of shelled organism at risk from ocean
acidication. Photo by Nina Bednarsek (NOAA/PMEL).
T
Ocean Acidication
November 2013

8Many shell-forming marine organisms are very sensi-
tive to changes in pH and carbonate chemistry. Corals,
bivalves (such as oysters, clams, and mussels), pteropods
(free-swimming snails) and certain phytoplankton species
fall into this group. But other marine organisms are also
stressed by the higher CO2 and lower pH and carbonate ion
levels associated with ocean acidication.
9e biological impacts of OA will vary, because
dierent groups of marine organisms have a wide range
of sensitivities to changing seawater chemistry.
10Impacts from OA at any life stage can reduce the
ability of a population to grow or to recover from
losses due to disturbance or stress, even though news reports
have oen focused on juvenile forms that are highly vulner-
able to acidication (e.g. Pacic oyster larvae).
11OA will not kill all ocean life. But many scientists
think we will see changes in the number and abun-
dance of marine organisms. Many marine ecosystems may be
populated by dierent, and potentially fewer, species in the
future. It is unclear whether these biological impacts will be
reversible.
12Areas that could be particularly vulnerable to OA
include regions where there is natural upwelling of
colder, low pH, deep water onto the continental shelves,
such as the west coast of North America; the oceans near the
poles, where lower temperatures allow seawater to absorb
more CO2; and coastal regions that receive freshwater dis-
charge.
13
Long-term pH decline could exceed the tolerance
limits of marine species that live in coastal waters,
even though they may haveevolved strategies to deal with
uctuating pH on short timescales typical of coastal environ-
ments (where thedaily and seasonal changes in seawaterpH
are much greaterthan in the open ocean).
14Evolutionary adaptation to reduced pH has been
observed to act quickly when populations are large
and robust. Marine populations reduced by other coastal
ocean problems have more limited ability to respond evolu-
tionarily to acidication.
15e current rate of acidication may be unprec-
edented in Earth’s history; it is estimated to be 10 to
100 times faster than any time in the past 50 million years.
During an acidication event that occurred 55 million years ago
(the Paleocene-Eocene ermal Maximum), there was a mass
extinction of some marine species, especially deep-sea shelled
invertebrates.
16Full recovery of the oceans will require tens to hun-
dreds of millennia. Over decades to centuries, neither
weathering of continental rocks, deep ocean mixing, or dissolu-
tion of calcium carbonate minerals in marine sediments can
occur fast enough to reverse OA over the next two centuries.
17Geo-engineering proposals that seek just to cool the
planet will not address OA, because they do not tackle
its cause: excess atmospheric CO2. Proposals that capture CO2
and store it away from seawater will mitigate the eects of
OA somewhat, but most such proposals are now only cost- or
energy-eective on very small scales.
18Blue carbon is under investigation as a way of locally
osetting CO2 levels. “Blue carbon” is CO2 captured
from the atmosphere or seawater by salt marshes, mangroves,
and seagrass meadows. ese environments store it as organic
material for decades.
19Reducing nutrient runo might oset some of the
local changes caused by OA, and could increase the
overall health of marine ecosystems. But this would buy only a
little time, because the root cause of OA is global atmospheric
CO2 emissions.
20Ocean acidication represents yet another stress on
marine environments that may endanger the ow
of goods and services to marine-dependent communities.
Humans around the world depend on the ocean for food, water
quality, storm buering, and many other important functions.
Disruptions to marine ecosystems can alter these relationships.
All suggestions or comments for improvements to these talking points should
be addressed to co-chairs of the U.S. Ocean Carbon and Biogeochemistry
Subcommittee on Ocean Acidication: S. Cooley (scooley@whoi.edu), J. Mathis
(jeremy.mathis@noaa.gov), and K. Yates (kyates@usgs.gov).
Ocean Carbon and
Biogeochemistry Project–
Ocean Acidication
whoi.edu/OCB-OA
NOAA, Ocean Acidication
Program
oceanacidication.noaa.gov
Washington Sea Grant
wsg.washington.edu
WSG AS-04 November 2013
Ocean Acidication International
Coordination Centre
iaea.org/ocean-acidication
Ocean Acidification
International
Coordination Centre
OA-ICC
UK Ocean Acidication Research
Programme
oceanacidication.org.uk