require records to be spliced together from several
species.
Low-latitude planktonic foraminiferal d
18
O records are good proxies for tropical sea surface temperatures. Tropical temperatures are an important
component of the climate system because they influence evaporation, and hence, total moisture in the
atmosphere. Planktonic and benthic foraminiferal
d
18 O comparison allows one to assess equator-topole as well as vertical temperature gradients during
the Cenozoic, and thus, to determine planetary
temperature changes. Finally, much of the climatic
change in the last 65 million years has been ascribed
to poleward heat transport or greenhouse gas fluctuations. General circulation models indicate that
each mechanism should produce different temperature patterns that can be approximated with the
planktonic and benthic d
18 O records.
The first benthic d
18 O syntheses generated, as well
as more recent compilations, show the same longterm patterns. After the Cretaceous–Tertiary (K/T)
boundary events, deep-water d
18 O values remained
relatively constant for the first 7 million years of the
Paleocene (Figure 7A). At 58 Ma, benthic foraminiferal d
18
O values began a decrease over the
next 6 My that culminated during the early Eocene
Planktonic foraminifera
Benthic foraminifera
2
3
4
5
0
0.5
1.0
1.5
Age (Ma)
_ 2
_ 1
0
18
O%
benthic foraminifera
˚
18
O% planktonic foraminifera
˚
Holocene
Pleistocene
123 4 5 6
7
9
1 1
13
15
17 19 21 23 25 27 29 31 33 35 37 39 4143 45 4749
Planktonic foraminifera
Benthic foraminifera
2
3
4
5
1.5
2.0
2.5
3.0
Age (Ma)
_ 2
_ 1
0
18
O%
benthic foraminifera
˚
18
O% planktonic foraminifera
˚
Pleistocene
51 5355 57 59 61 63 65 67 69 71 7375 77 79 8183 85 87 89 919395
96 98 100
Pliocene
(A)
(B)
Figure 6 Planktonic and benthic foraminiferal d
18 O records for the last 3 million years. Note the high frequency signals in the
records. For the interval between 3 and 1 Ma, a 40 000 year cycle dominates the records. After 1 Ma, the beat changes to a 100 000
year cycle and the amplitudes increase (relative to PDB).
416 CENOZOIC CLIMATE – OXYGEN ISOTOPE EVIDENCE
species.
Low-latitude planktonic foraminiferal d
18
O records are good proxies for tropical sea surface temperatures. Tropical temperatures are an important
component of the climate system because they influence evaporation, and hence, total moisture in the
atmosphere. Planktonic and benthic foraminiferal
d
18 O comparison allows one to assess equator-topole as well as vertical temperature gradients during
the Cenozoic, and thus, to determine planetary
temperature changes. Finally, much of the climatic
change in the last 65 million years has been ascribed
to poleward heat transport or greenhouse gas fluctuations. General circulation models indicate that
each mechanism should produce different temperature patterns that can be approximated with the
planktonic and benthic d
18 O records.
The first benthic d
18 O syntheses generated, as well
as more recent compilations, show the same longterm patterns. After the Cretaceous–Tertiary (K/T)
boundary events, deep-water d
18 O values remained
relatively constant for the first 7 million years of the
Paleocene (Figure 7A). At 58 Ma, benthic foraminiferal d
18
O values began a decrease over the
next 6 My that culminated during the early Eocene
Planktonic foraminifera
Benthic foraminifera
2
3
4
5
0
0.5
1.0
1.5
Age (Ma)
_ 2
_ 1
0
18
O%
benthic foraminifera
˚
18
O% planktonic foraminifera
˚
Holocene
Pleistocene
123 4 5 6
7
9
1 1
13
15
17 19 21 23 25 27 29 31 33 35 37 39 4143 45 4749
Planktonic foraminifera
Benthic foraminifera
2
3
4
5
1.5
2.0
2.5
3.0
Age (Ma)
_ 2
_ 1
0
18
O%
benthic foraminifera
˚
18
O% planktonic foraminifera
˚
Pleistocene
51 5355 57 59 61 63 65 67 69 71 7375 77 79 8183 85 87 89 919395
96 98 100
Pliocene
(A)
(B)
Figure 6 Planktonic and benthic foraminiferal d
18 O records for the last 3 million years. Note the high frequency signals in the
records. For the interval between 3 and 1 Ma, a 40 000 year cycle dominates the records. After 1 Ma, the beat changes to a 100 000
year cycle and the amplitudes increase (relative to PDB).
416 CENOZOIC CLIMATE – OXYGEN ISOTOPE EVIDENCE