430
S. Wakeham
A
Permanent East Antarctica
On-Off East Antarctica
ice sheet
~
glaciations
-221lIic~ilftf;;f¥';kfrpfrr:u
l
-23
,
T
c:a -24
c
0.. -25
en
=
!11.3 12.6 I J . O
C 27 Sterane
Shallow photic zone
~ -26 t 25 Today ···j···········
4!)
•.•• .•••
m
i
=- -27 (140C) ·
e -28
...
4!)
.e: -29
(.)
~ -30
to
-31
-32
-33
B 2
1
Stratified --+-Photi c zone -+-Mi xed
E
0
... -1
II)
Q,
-2
en
:C -3
(.)
M
-4
~
<]
-5
-6
Low
........ [C0 2 {aq) ]
warmer
j
High
[C0 2 (aq)]
cooler
Warmer
1.0 :::E
1.5 ~
- c
2.070
2.5 Colder
-7
« , ! I , ! , , ! , , I j
!
I
!
,
! I I
, .3.0
6
8
Late
M
10
.1
I
o
12 14 16 18 20 22
Age (Ma)
Middle
C E
I
N
Early
E
Fig. 19.5. a C27 steranes and C35 hopanes 813C values for the Naples Beach section of the Monterey formation (Naples Beach, California), indicating changing water masses in the shallow and deep euphotic
zone. The scope of the Antarctic ice sheet represents relative climatic conditions; b Isotopic difference e:,.13CH_ S
between CZ7 steranes and C35 hopanes. The lower solid line is as measured; the upper solid line is e:,. I3CH_ S
corrected by 1.~o/oo for the difference (e:,.13 CDIcl in the photic zone of contemporary Santa Monica Bay. The
interpretation is that in the late Miocene, the water column was stratified but in the early Miocene it was
mixed. The wavy ribbon is the Miocene 8 18 0 record from benthic foraminifera. From Schoell et al. (1994)