Geoscience Reference
In-Depth Information
CHAPTER 8
on nektonic organisms
Hans-O. Pörtner, Magda Gutowska, Atsushi Ishimatsu,
Magnus Lucassen, Frank Melzner, and Brad Seibel
8.1 Integrative concepts relevant
in ocean acidii cation research
nic conditions (i.e. elevated
p
CO
2
levels), that reach
beyond those projected in the offshore surface
ocean. These organisms might, therefore, be pre-
adapted to relatively high ambient
p
CO
2
levels. The
anthropogenic signal will nonetheless be superim-
posed on the pre-existing natural variability.
These phenomena lead to the question of whether
future changes in the ocean's carbonate chemistry
pose a serious problem for marine organisms. Those
with calcareous skeletons or shells, such as corals
and some plankton, have been at the centre of scien-
tii c interest. However, elevated CO
2
levels may also
have detrimental effects on the survival, growth,
and physiology of marine animals more generally
(Pörtner and Reipschläger 1996; Seibel and Fabry
2003 ; Fabry
et al
. 2008 ; Pörtner 2008 ; Melzner
et al.
2009a). Global warming and expanding hypoxia
( Stramma
et al.
2008 ; Bograd
et al.
2009 ) pose addi-
tional physiological challenges that may act syner-
gistically with ocean acidii cation to impair various
aspects of performance, including muscular exer-
cise (Pörtner
et al.
2005a , b ; Pörtner and Farrell 2008 ;
Rosa and Seibel 2008 ; Munday
et al
. 2009a ; Pörtner
2010). The elevation in oxygen demand caused by
warming is limited by the availability of ambient
oxygen, which is reduced in warm compared
with cold waters and even more so during environ-
mental hypoxia. Additionally, CO
2
may impair
oxygen transport by lowering blood pH, thereby
The average surface-ocean pH is reported to have
declined by more than 0.1 units from the pre-indus-
trial level (Orr
et al.
2005), and is projected to
decrease by another 0.14 to 0.35 units by the end of
this century, due to anthropogenic CO
2
emissions
(Caldeira and Wickett 2005; see also Chapters 3 and
14). These global-scale predictions deal with aver-
age surface-ocean values, but coastal regions are
not well represented because of a lack of data, com-
plexities of nearshore circulation processes, and
spatially coarse model resolution (Fabry
et al.
2008 ;
Chapter 3). The carbonate chemistry of coastal
waters and of deeper water layers can be substan-
tially different from that in surface water of offshore
regions. For instance, Frankignoulle
et al.
( 1998 )
reported
p
CO
2
(note 1) levels ranging from 500 to
9400 μatm in estuarine embayments (inner estuar-
ies) and up to 1330 μatm in river plumes at sea
(outer estuaries) in Europe.
1
Zhai
et al.
( 2005 )
reported
p
CO
2
values of > 4000 μatm in the Pearl
River Estuary, which drains into the South China
Sea. Similarly, oxygen minimum layers show ele-
vated
p
CO
2
levels, associated with the degree of
hypoxia ( Millero 1996 ). These i ndings suggest that
some coastal and mid-water animals, both pelagic
and benthic, are regularly experiencing hypercap-
1
For consistency within this volume, we use the lower case italic
p
as a symbol for partial pressure of CO
2
in seawater
(
p
CO
2
) and the capital italic
P
as in
P
CO
2
for body l uids. We thereby acknowledge that the use of symbols for partial
pressure differs between disciplines. According to conventions in physics and physiology, the symbol of pressure is a
capital italic
P
that also applies to the partial pressure of gases. In ocean chemistry a lower case italic
p
is used instead
(1000 μatm = 101.3 Pa).
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