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on parameters of the carbonate system other than
pH. However, important results were found (and
subsequently forgotten). For example, Swift and
Taylor (1966) reported that the growth of a cocco-
lithophore followed a bell-shaped response as a
function of pH. Such a bell-shaped response was
subsequently found to describe the effect of ocean
acidii cation on the calcii cation rate of a coccolitho-
phore (Langer
et al.
2006 ). The i rst purposeful ocean
acidii cation experiment was performed by Agegian
(1985) who showed a negative impact of ocean acid-
ii cation on the growth of coralline algae. A rela-
tively large number of manipulative experiments
have been carried out on zooxanthellate scleractin-
ian corals. The i rst one, published in 1998, related
the decline of calcii cation to the decrease of the
saturation state of calcium carbonate manipulated
through changes in the calcium concentration
( Gattuso
et al.
1998). Subsequent studies altered the
saturation state through changes in the concentra-
tion of carbonate which better mimic ocean acidii -
cation. Riebesell
et al.
( 2000 ) were the i rst to report
on the effect of ocean acidii cation on photosynthe-
sis and calcii cation in two phytoplanktonic species
(coccolithophores). Nitrogen i xation is also a key
process which has been shown to respond to ocean
acidii cation (Levitan
et al.
2007 ; see also Chapter 6 ).
A relatively large number of perturbation experi-
ments have been reported in recent years, but results
have not always been consistent. For example, some
calcii ers do not seem to be affected by ocean acidi-
i cation (e.g. Langer
et al.
2006 ; Iglesias-Rodriguez
et al.
2008 ; Ries
et al.
2009 ; Rodolfo-Metalpa
et al.
2010). Several hypotheses have been proposed to
explain these discrepancies: species differences
which could be related to different calcii cation
mechanisms, methodological differences, and mis-
interpretation of the data (see Chapters 6 and 7).
In addition to reconstructing past changes in the
carbonate system, modelling tools are critical for pro-
jecting future changes in the carbonate system and
the biogeochemical impacts of ocean acidii cation.
Caldeira and Wickett (2003) published a seminal
paper in which they compared the timing and mag-
nitude of past and future changes in ocean pH and
popularized the term 'ocean acidii cation', which
had originally been introduced by Broecker and
Clark (2001). Ocean carbon cycle models were used
to estimate changes in the carbonate system in the
recent past and the 21st century (e.g. Orr
et al.
2005 ),
identify the geographical areas which are most at
risk (Steinacher
et al.
2009), and project future changes
in calcii cation (Kleypas
et al.
1999 ) and feedbacks on
the global carbon cycle (e.g. Heinze 2004).
1.4.3 Bibliometric analysis
The recent attention paid to ocean acidii cation by
the scientii c community, policymakers, and the
media, as well as increased funding and the launch
of several national and international research pro-
jects, have spurred a steep increase in research
efforts, starting from around 1990 and accelerating
during the last few years. For the purpose of this
chapter, a bibliographic database including scien-
tii c articles, books, and book chapters on ocean
acidii cation was compiled in order to illustrate
trends in the publication effort. Dissertations,
reports, abstracts of presentations at meetings, and
popular articles were excluded. The complete list of
references is available in Appendix 1.1 at
http://
A total of 846 articles (from 1906 to 2010) were
included in this study. A series of keywords describ-
ing the content of each article, for example the type of
organism or process studied, was used to categorize
articles and extract statistical information from the
database. The primary categories used to classify
papers are shown in Fig. 1.2A. The main ones are:
'biological response', 'biogeochemistry', 'paleo'
(papers using a palaeo-oceanographic approach;
mainly reconstruction of past carbonate chemistry),
'modelling', 'chemistry' (including, for example,
time-series and cruise data), and 'review' (articles
that discuss and synthesize results from other papers).
Obviously, cataloguing an article into one of these
specii c categories can sometimes be difi cult and arti-
cles frequently required the allocation of several of
the above keywords to fully describe their content.
The 'biological response' category was further
divided into subcategories of taxonomic groups, and
processes and parameters studied (Fig. 1.2B to D).
Keywords indicating the type of study (laboratory or
i eld, mesocosms, and gene expression/genetic
diversity) were added to articles when appropriate
(mostly for 'biological response' and 'chemistry'
