Geoscience Reference
In-Depth Information
CHAPTER 1
and history
Jean-Pierre Gattuso and Lina Hansson
1.1 Introduction
the oceanic and terrestrial sinks mitigate climatic
changes. Should their efi ciency decrease, more CO
2
would remain in the atmosphere, generating larger
climate perturbations.
This topic has four main groups of chapters. The
i rst group reviews the past (Zeebe and Ridgwell,
Chapter 2 ), recent, and future (Orr, Chapter 3 )
changes in seawater carbonate chemistry. The sec-
ond group of chapters reviews the biological and
ecological consequences of ocean acidii cation,
looking at the response of calcii ers to past ocean
acidii cation events (Knoll and Fischer, Chapter 4),
the response of heterotrophic microorganisms
(Weinbauer
et al.
, Chapter 5) as well as pelagic
(Riebesell and Tortell, Chapter 6), benthic
(Andersson
et al.
, Chapter 7 ), nektonic (Pörtner
et al.
, Chapter 8 ), and sedimentary (Widdicombe
et al.
, Chapter 9) organisms and ecosystems, and the
effects on biodiversity and ecosystem function
(Barry
et al.
, Chapter 10). The chapters of the third
group summarize the biogeochemical consequences
of ocean acidii cation, both on the production of
climate-relevant trace gases (Hopkins
et al.
, Chapter
11) and overall biogeochemical cycles (Gehlen
et al.
,
Chapter 12 ). Chapters of the fourth group address
the societal consequences of ocean acidii cation
(Turley and Boot, Chapter 13) and the impact of cli-
mate change mitigation on future projections (Joos
et al.
, Chapter 14 ). The i nal chapter summarizes
what is known and what is unknown, and provides
recommendations for future research (Gattuso
et al.
,
Chapter 15 ).
The aim of the present chapter is to introduce
ocean acidii cation in a broad context, starting with
the chemical background (Section 1.2 and Box 1.1)
and its effects on biological and biogeochemical
The ocean and the atmosphere exchange massive
amounts of carbon dioxide (CO
2
). The pre-industrial
inl ux from the ocean to the atmosphere was 70.6
Gt C yr
-1
, while the l ux in the opposite direction
was 70 Gt C yr
-1
( IPCC 2007 ). Since the Industrial
Revolution an anthropogenic l ux has been super-
imposed on the natural l ux.
The concentration of CO
2
in the atmosphere,
which remained in the range of 172-300 parts per
million by volume (ppmv) over the past 800 000
years (Lüthi
et al.
2008), has increased during the
industrial era to reach 387 ppmv in 2009. The rate of
increase was about 1.0% yr
-1
in the 1990s and
reached 3.4% yr
-1
between 2000 and 2008 (Le Quéré
et al.
2009). Future levels of atmospheric CO
2
mostly
depend on socio-economic parameters, and may
reach 1071 ppmv in the year 2100 (Plattner
et al.
2001), corresponding to a fourfold increase since
1750. As pointed out over 50 years ago, 'human
beings are now carrying out a large scale geophysi-
cal experiment of a kind that could not have hap-
pened in the past nor be reproduced in the future'
( Revelle and Suess 1957 ).
Anthropogenic CO
2
has three fates. In the years
2000 to 2008, about 29% was absorbed by the ter-
restrial biosphere and 26% by the ocean, while the
remaining 45% remained in the atmosphere (Le
Quéré
et al.
2009). The accumulation of CO
2
in the
atmosphere increases the natural greenhouse effect
and generates climate changes (IPCC 2007). It is
estimated that the surface waters of the oceans have
taken up 118 Pg C, or about 25% of the carbon gen-
erated by human activities since 1800 (Sabine
et al.
2004 ). By taking CO
2
away from the atmosphere,
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