Geoscience Reference
In-Depth Information
CHAPTER 15
Ocean acidii cation: knowns,
unknowns, and perspectives
Jean-Pierre Gattuso, Jelle Bijma, Marion Gehlen, Ulf Riebesell,
and Carol Turley
vious chapters with one minor exception. Early
work has shown that ocean acidii cation signii cantly
affects the propagation of sound in seawater and
suggested possible consequences for marine organ-
isms sensitive to sound (Hester
et al
. 2008 ). However,
subsequent studies have shown that the changes in
the upper-ocean sound absorption coefi cient at
future pH levels will have no or a small impact on
ocean acoustic noise (Joseph and Chiu 2010;
Udovydchenkov
et al
. 2010 ).
The goal of this section is to condense the current
knowledge about the consequences of ocean acidii -
cation in 15 key statements (Table 15.1). Each state-
ment is given levels of evidence and, when possible,
a level of coni dence as recommended by the
Intergovernmental Panel on Climate Change (IPCC)
for use in its 5th Assessment Report (Mastrandrea
et
al.
2010). For the sake of brevity, the sections below
do not provide the bibliographic citations which
have already been given in the other chapters of this
book. Readers are invited to refer to the relevant
chapters indicated in Table 15.1 for a complete list
of supporting references.
15.1 Introduction
Although the changes in the chemistry of seawater
driven by the uptake of CO
2
by the oceans have been
known for decades, research addressing the effects
of elevated CO
2
on marine organisms and ecosys-
tems has only started recently (see Chapter 1). The
i rst results of deliberate experiments on organisms
were published in the mid 1980s (Agegian 1985) and
those on communities in 2000 (Langdon e
t al.
2000 ;
Leclercq e
t al.
2000). In contrast, studies focusing on
the response of terrestrial plant communities began
much earlier, with the i rst results of free-air CO
2
enrichment experiments (FACE) being published in
the late 1960s (see Allen 1992). Not surprisingly,
knowledge about the effects of elevated CO
2
on the
marine realm lags behind that concerning the terres-
trial realm. Yet ocean acidii cation might have sig-
nii cant biological, ecological, biogeochemical, and
societal implications and decision-makers need to
know the extent and severity of these implications
in order to decide whether they should be consid-
ered, or not, when designing future policies.
The goals of this chapter are to summarize key
information provided in the preceding chapters by
highlighting what is known and what is unknown,
identify and discuss the ecosystems that are most at
risk, as well as discuss prospects and recommen-
dation for future research.
15.2.1 Chemical aspects
15.2.1.1 Ocean acidii cation occurred in the past
It is known with a very high level of coni dence that
ocean acidii cation occurred in the past. On geologi-
cal timescales, the CO
2
concentration in the atmos-
phere and the carbonate chemistry of the oceans are
constantly changing and adjusting to the forcings of
tectonics, volcanism, weathering, biology, and, cur-
rently, human activity. Note, however, that atmos-
pheric
p
CO
2
alone does not tell us much about the
15.2
The chemical, biological, ecological, biogeochemi-
cal, and societal implications of ocean acidii cation
have been comprehensively reviewed in the pre-
Knowns and unknowns
291
