Geoscience Reference
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increased bioavailability of iron, an important
micronutrient for primary production, at lower sea-
water pH. This is supported by some (Breitbarth et
al. 2010) but not all (Shi et al. 2010 ) experimental
data. Another example of a possible indirect effect
is the tight link that may exist between processes
such as photosynthesis and calcii cation. If photo-
synthesis stimulates calcii cation, a stimulation of
photosynthesis (which removes CO 2 and so tends to
increase CO 3 2- ) by ocean acidii cation could benei t
calcii cation by mitigating the limited supply of car-
bonate ions. Conversely, if calcii cation stimulates
photosynthesis, a decrease in calcii cation gener-
ated by ocean acidii cation could have a negative
effect on photosynthesis. Such cascading, indirect
effects could occur at both the organism and com-
munity levels.
Gail ( 1919 ) reported results from a study which
looked at the combined effect of changes in pH and
temperature on survival, reproduction, and growth
of a macroalga ( Fucus ; Fig. 1.1 ). Observations were
made over a few weeks, which enabled an assess-
ment of acclimation. Germination was more suc-
cessful at pH values above 7.4 and below 8.6 at all
temperatures considered. The maximum germina-
tion occurred in seawater at pH values between 8.0
and 8.2 and decreased on either side of these. The
growth of spores as well as larger plants of Fucus
was inhibited when the pH value was below 7.2.
Powers ( 1920 ) suggested that the abundance of
fauna at certain localities in the Puget Sound region
and the average size of species such as barnacles
collected at different localities were dependent on
pH. Two years later, he proposed that the 'ability
of marine i shes to absorb oxygen at low tension
from the sea water is more or less dependent upon
the hydrogen ion concentration of the water'
( Powers 1922 ). Bouxin ( 1926a ) found that the lar-
val development of a sea urchin was unaffected by
changes in pH within the range of 7.3 to 8.1, was
slower below this threshold and came to a halt at a
pH of 6.4. Skeletal growth was slower below 7.3,
and dissolution occurred below 6.4 (Bouxin 1926a,
1926b ).
Prytherch (1929) showed that pH in Milford
Harbor (CT, USA) was lowest at low tide and high-
est close to high tide (7.2 vs 8.2). He noted that the
failure of oysters to spawn at low tide was corre-
lated to relatively high temperature (above 20°C)
and low pH. Spawning occurred near the times of
high tide at a similar temperature but much higher
pH value (7.8 or above). He concluded that the most
important factors controlling oyster spawning are
'the temperature of the water, the range of tide, and
the hydrogen-ion concentration'. Rubey (1951) sum-
marized a large part of the earlier studies and
concluded:
1.4 A short history of ocean
acidii cation research
1.4.1
The early days
The distribution of pH in the oceans, its changes
with depth, tide, and other physical and biological
processes, and the impact of the changes on organ-
isms were studied early in the 20th century. Some
studies even pre-date the dei nition of pH (techni-
cally, p[H] as the initial dei nition was based on
concentration rather than activity as used today) by
Sørensen ( 1909 ). For example, Moore et al. ( 1906 )
investigated the effect of 'alkalies [ sic .] and acids' on
growth and cell division in the fertilized eggs of a
sea urchin.
A few key early studies can be mentioned, some of
which were remarkably innovative even by today's
standards. McClendon (1917) showed that the oxy-
gen consumption of certain marine invertebrates
varies with pH. He subsequently reported that the
pH range compatible with the life of seaweed is
rather broad, may be different for different species,
that little was known about the effect on different life
stages, and that there may be interaction with other
environmental factors (McClendon 1918). He also
found that corals from deep waters are smaller, more
fragile, and deposit less CaCO 3 than those of shallow
waters, and proposed that this was related to the
decline of pH with depth (McClendon 1918).
If only one-one hundredth of all this buried
carbon dioxide [fossil carbon] were suddenly
added to today's atmosphere and ocean (that
is, if the amount in the present atmosphere
and ocean were suddenly increased . . . seven-
fold, from 1.3 × 10 20 to 9.1 × 10 20 g), it would
have profound effects on the chemistry of sea
 
 
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