Geoscience Reference
In-Depth Information
parameters remaining the same, the oceans capture
less atmospheric CO
2
as ocean acidii cation pro-
ceeds. In their study of calcium carbonate precipita-
tion on the Bahama Banks, Broecker and Takahashi
( 1966 ) were the i rst to report that the concentration
of CO
3
2-
, which decreases at elevated
p
CO
2
(Table 1.1),
could control community calcii cation. This i nding
was subsequently coni rmed in coral reefs (e.g.
Smith and Pesret 1974) and reef mesocosms (e.g.
Langdon
et al.
2000 ; Leclercq
et al.
2000 ).
Brewer (1978) derived a method for estimating
the original atmospheric equilibration signal of
water masses using total alkalinity and the concen-
tration of dissolved inorganic carbon and correcting
for the perturbations of the CO
2
system due to res-
piration, carbonate dissolution, and nitrate addi-
tion. This method provided the i rst direct evidence
that the increase in atmospheric CO
2
leads to a
corresponding increase in the
p
CO
2
of Antarctic
intermediate water and revealed a propagation of
the atmospheric CO
2
signal northwards. Several
other approaches were subsequently designed (see
Álvarez
et al.
2009 ).
Recent changes in the carbonate chemistry of sea-
water have been documented using time-series data,
i rst from the western North Atlantic (Bates 2001)
and subsequently from the eastern North Atlantic
(Santana-Casiano
et al.
2007), northern Pacii c (Dore
et al.
2009), and the Icelandic Sea (Olafsson
et al.
2009). The instrumental record begun only recently,
but palaeo-oceanographic tracers have been used to
extend estimates back in time. The i rst key papers
are those of Spivack
et al.
(1993) who used the boron
isotopic composition, Barker and Elderi eld ( 2002 )
who used foraminiferal size-normalized shell weight,
and Yu
et al.
(2007) who proposed the use of the
boron:calcium ratio to assess changes in carbonate
chemistry. Modelling has also been used to re-
construct past changes in the carbonate system using
simple box models (Zeebe and Westbroek 2003) or
more sophisticated process-driven ecosystem models
(e.g. Andersson
et al.
2003 ).
Manipulative experiments have been performed
to assess the response of organisms to changes in
seawater carbonate chemistry. Many of the i rst
experiments carried out used
p
CO
2
levels that were
unrealistically high in the context of anthropogenic
ocean acidii cation and provided little information
. . . For many forms of life, the concentration
of bicarbonate and hydrogen ions and the car-
bon-dioxide tension are among the most critical
factors in their chemical environment. A number
of higher marine animals (the herring, for exam-
ple) are extremely sensitive to small changes in
the pH of their environment. A large proportion
of the eggs of some marine animals remains
unfertilized if the acidity of sea water departs
more than about 0.5 pH from normal. Lower
organisms are commonly less sensitive; but many
species of mollusks, sea urchins, Medusa, dia-
toms, bacteria, algae, and others seem unable
to tolerate a range of more than about 1 unit of
pH. Recent workers attribute a larger part of
these observed biologic effects to the carbon-
dioxide tension or to the concentration of bicar-
bonate ions than to hydrogen-ion concentration
directly.
This was the i rst time that the early literature had
been explored, even though briel y. Obviously, the
results collected in the early days are not of great
utility for assessing the effects of future ocean acidi-
i cation because of the relatively uncertain meas-
urements of the carbonate system and the large
pH changes that were investigated. Some obvious
errors were also made. For example, it is now
known that the decline in coral calcii cation with
increasing depth is mostly controlled by decreasing
irradiance rather than pH (Gattuso
et al.
1999 ). It is
nevertheless very interesting to note that many
research questions which are given top priority
today (e.g. multifactorial perturbation experiments,
acclimation, and adaptation) had already been con-
sidered and sometimes investigated decades ago.
1.4.2 Modern research
The goal of this subsection is to provide a brief over-
view of how recent research on ocean acidii cation
developed and to identify seminal publications.
Readers are invited to consult the subsequent chap-
ters for in-depth reviews. Modern research, arbi-
trarily set from the 1950s, began with the landmark
paper of Revelle and Suess (1957) which showed
that the uptake of anthropogenic CO
2
decreases the
oceans' buffering capacity. In other words, other
