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(A)
200
30
150
20
100
10
50
0
0
(B)
8.2
8
7.8
7.6
7.4
(C)
4
3
2
1
0
(D)
4
3
2
1
0
(E)
4000
3000
2000
1000
0
100
0
20 40
Time (millions of years before present)
60
80
Figure 2.3
Carbonate chemistry reconstruction of surface seawater over the Cenozoic based on two different parameter combinations: (1) [CO
3
2-
] and
p CO
2
(blue lines) and (2) [CO
3
2-
] and pH
T
(green lines); see Tyrrell and Zeebe 2004. (A) Surface-ocean concentrations of CO
3
2-
(solid line, derived from
saturation state indicators) and Ca
2+
(dotted line, from l uid inclusions). (B) pH
T
based on combination 1 (blue line) and from stable boron isotopes (green
diamonds, Pearson and Palmer 2000). (C) Total dissolved inorganic carbon. (D) Total alkalinity. (E) p CO
2
from GEOCARB-III (blue squares, Berner and
Kothavala 2001) and based on combination 2 (green line).
toward smaller cell sizes in the Oligocene (~34 to ~23
Myr) relative to the Eocene (~55 to ~34 Myr) has been
suggested based on deep-sea sediment records
(Henderiks and Pagani 2008). These authors specu-
lated that the size trend in the haptophyte algae may
rel ect a response to increased CO
2
limitation associ-
ated with the decline in atmospheric CO
2
across the
Eocene-Oligocene transition. If so, this would repre-
sent a CO
2
-related effect on photosynthesis and cell
growth rather than on calcii cation. Regarding plank-
tonic foraminifera, a trend toward larger test sizes in
low-latitude species has been reported, particularly
since the end of the Miocene (Schmidt
et al.
2004 ). The
authors suggested that the size increase was a
response to intensii ed surface-water stratii cation at
low latitudes. Changes in Cenozoic carbonate chem-
istry appear unlikely to have caused the increase in
shell size in foraminifera, emphasizing the impor-
tance of other functional correlations with shell size.
For example, surface-water changes in CO
2
at the end
of the Miocene (~23 to ~5 Myr) seem rather small
compared with those during the Palaeogene. Thus, if
dissolved CO
2
or pH would have been important fac-
tors in determining shell size in planktonic foraminif-
era, one would expect large changes during the
Palaeogene (~65 to ~23 Myr), but this is not the case.
