Earth and Planetary Science Letters 206 (2003) 253^271
www.elsevier.com/locate/epsl
Rapid sea-level fall and deep-ocean temperature change since
the last interglacial period
K.B. Cutler a , R.L. Edwards a; , F.W. Taylor b , H. Cheng a , J. Adkins c ,
C.D. Gallup d , P.M. Cutler a , G.S. Burr e , A.L. Bloom f
a
Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455, USA
Institute for Geophysics, University of Texas, 4412 Spicewood Springs Road, Austin, TX 78759-8500, USA
Division of Geological and Planetary Sciences, California Institute of Technology, MC 100-23, Pasadena, CA 91125, USA
d
Department of Geological Sciences, University of Minnesota Duluth, Duluth, MN 55812, USA
e
Department of Physcis, University of Arizona, Tucson, AZ 85721, USA
f
Department of Earth and Atmospheric Sciences, Snee Hall, Cornell University, Ithaca, NY 14853, USA
b
c
Received 4 June 2002; received in revised form 12 November 2002; accepted 27 November 2002
Abstract
We have dated Huon Peninsula, Papua New Guinea and Barbados corals that formed at times since the Last
Interglacial Period, applying both 230 Th and 231 Pa dating techniques as a test of age accuracy. We show that Marine
Isotope Stage (MIS) 5e ended prior to 113.1 8 0.7 kyr, when sea level was 319 m. During MIS 5b sea level was 357 m
at 92.6 8 0.5 kyr, having dropped about 40 m in approximately 10 kyr during the MIS 5c^5b transition. Sea level then
rose more than 40 m during the MIS 5b^5a transition, also in about 10 kyr. MIS 5a lasted until at least 76.2 8 0.4 kyr,
at a level of 324 m at that time. Combined with earlier data that places MIS 4 sea level at 381 m at 70.8 kyr, our late
MIS 5a data indicate that sea level fell almost 60 m in less than 6 kyr (10.6 m/kyr) during the MIS 5^4 transition. The
magnitude of the drop is half that of the glacial^interglacial amplitude and approximately equivalent to the volume of
the present-day Antarctic Ice Sheet. During this interval the minimum average rate of net continental ice
accumulation was 18 cm/yr, likely facilitated by efficient moisture transport from lower latitudes. At three specific
times (60.6 8 0.3, 50.8 8 0.3, and 36.8+0.2 kyr) during MIS 3, sea level was between 385 and 374 m. Sea level then
dropped to 3107 m at 23.7 8 0.1 kyr early in MIS 2, before dropping further to Last Glacial Maximum (LGM) values
and then rising to present values during the last deglaciation. Times of rapid sea-level drop correspond to times of
high winter insolation at low northern latitudes and high winter latitudinal gradients in northern hemisphere
insolation, supporting the idea that these factors may have resulted in high water-vapor pressure in moisture sources
and efficient moisture transport to high-latitude glaciers, thereby contributing to glacial buildup. We combined our
sea-level results with deep-sea N18 O records as a means of estimating the temperature and ice-volume components in
the marine N18 O record. This analysis confirms large deep-ocean temperature shifts following MIS 5e and during
Termination I. Deep-ocean temperatures changed by much smaller amounts between MIS 5c and 2. Maximum
temperature shift in the deep Pacific is about 2‡, whereas the shift at a site in the Atlantic is 4‡. Under glacial
conditions temperatures at both sites are near the freezing point. The shift in the Atlantic is likely caused by a
combination of changing proportions of northern and southern source waters as well as changing temperature at the
sites where these deep waters form.
* Corresponding author. Tel.: +1-612-626-0207; Fax: +1-612-625-3819.
E-mail address: edwar001@umn.edu (R.L. Edwards).
0012-821X / 02 / $ ^ see front matter F 2002 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0012-821X(02)01107-X
EPSL 6514 22-1-03 Cyaan Magenta Geel Zwart
254
K.B. Cutler et al. / Earth and Planetary Science Letters 206 (2003) 253^271
F 2002 Elsevier Science B.V. All rights reserved.
1. Introduction
Quaternary sea-level history provides a globally
averaged record of the glacial^interglacial cycles
and is important for establishing the timing and
extent of continental glaciation, £uctuations in
ocean temperatures, and the relationship between
orbital forcing and global climate. Because sealevel history is a key reference for other climate
records, an accurate history of these changes is
also essential for establishing an order of events
and causal relationships in climate history.
Since the 1960s [1,2] fossil corals collected from
tectonically uplifting coastlines have been used to
reconstruct late-Quaternary sea-level history. Because some species of reef corals grow near the
sea surface, they are useful for tracking sea-level
changes. In the late 1980s, the precision of these
reconstructions, largely based on the precision of
the coral ages, was signi¢cantly improved with the
development of high-precision mass spectrometric
230
Th dating methods [3^5]. Despite this advance
two problems have hindered this approach. First,
the timing of sea-level changes has remained
somewhat controversial due to the possibility of
diagenesis and alteration of coral aragonite. Such
alteration could shift parent^daughter ratios and
result in inaccurate 230 Th ages. Second, collection
of corals that grew during glacial times has proven di⁄cult as such corals are either below present
sea level or, in tectonically uplifted areas, may be
covered by corals that grew subsequently, during
times of higher sea level.
In this study we address aspects of these problems. In addition to traditional tests for diagenesis, we have tested 230 Th ages for concordancy
using high-precision techniques for 231 Pa dating
[6,7] of corals. We have also collected corals
that grew during lower sea-level stands through
drilling (e.g. [8^10]) as well as surface collection.
Included in our data set are the youngest corals
yet recovered from MIS 5 (collected from the surface at Barbados), early MIS 2 corals (collected
by drilling through the deglacial sequence and
LGM unconformity on the Huon Peninsula),
and MIS 5b corals (collected on the surface on
the Huon Peninsula). We assessed age accuracy
by testing for age concordance and by testing
whether initial uranium isotopic compositions
matched the marine value. We then applied the
same criteria to existing coral sea-level data. We
used the collective data set to establish our best
estimate of sea-level history since MIS 5e.
We will show that a relatively small fraction of
our initially large number of samples shows no
evidence for diagenetic alteration. Similarly, our
analysis of existing data indicates that only a
small fraction of published data satis¢es our criteria. We view our results as an initial step in
establishing a higher-resolution sea-level curve.
In addition to providing some tight constraints
on sea-level history, our data delineate speci¢c
portions of the sea-level curve for which we currently have few robust data.
2. Field collection
Drill-core and surface corals were collected on
the Huon Peninsula, Papua New Guinea and
southwestern Barbados between 1988 and 2001.
These locations are ideal [1,2,11,12] because their
tectonically uplifting coastlines raise and expose
coral reefs through time. The uplift rate at our
most important Barbados site (the FA site on
the ‘F’ transect of [13]) in southwestern Barbados
is 0.33 m/kyr ([14], see below) while on the Huon
Peninsula it is more rapid, increasing along the
coastline from about 1 m/kyr in the northwestern
portion to more than 2.5 m/kyr in the southeastern portion [2]. The samples were examined in the
¢eld for macroscopic evidence of alteration and in
the laboratory for secondary calcite growth by Xray di¡raction. In all, we further analyzed 32 samples (Table 1), which appeared unaltered on the
basis of these initial tests.
2.1. New Guinea surface samples
We analyzed 14 samples (Table 1) collected
EPSL 6514 22-1-03 Cyaan Magenta Geel Zwart
Table 1
Coral ages, isotopic composition, and elevation data
Samplea
Spc
Evd
(m)
Evg e
(m)
238
U
(ppb)
A
A
A
A
333 8 0.5
335 8 0.5
341 8 0.5
345 8 0.5
358 8 1
361 8 1
379 8 2
3107 8 2
3355 8 3
2390 8 3
2840 8 3
3475 8 4
3275 8 3
3278 8 3
2424 8 3
2219 8 3
3462 8 4
3146 8 4
3479 8 6
P
353 8 0.5
3119 8 2
P
358 8 0.5
3111 8 1
II
P
22 8 2
374 8 3
II
P
982
377 8 2
II
P
982
385 8 2
IIIa
IIIa
IIIb
IIIb
G
P
F
P
35 8 2
75 8 2
45 8 2
30 8 2
377 8 4
362 8 5
391 8 5
360 8 2
IV
V
M
P
75 8 2
113 8 2
351 8 4
358 8 5
V
P
117 8 2
354 8 4
VI
VI
VIIb
P
P
G
169 8 2
177 8 2
195 8 2
352 8 7
349 8 7
317 8 4
VIIb
P
Ap
195 8 2
321 8 7
181
324 8 3
Ap
P
181
28 8 2
324 8 3
314 8 4
Ap
Ap
31 8 1
20 8
315 8 3
328 8 4
P
Ap
29 8 2
31 8 1
317 8 4
319 8 3
20 8 2
42 8 2
331 8 4
39 8 3
[230 Th/238 U]
(activity)
N234 Um f
(x)
286 8 9
9292 8 143
249 8 5
856 8 8
1058 8 11
1000 8 7
112 8 7
69 8 5
4117 8 35
3907 8 94
4197 8 52
0.1233(6)
0.1251(7)
0.1431(5)
0.2206(8)
0.2212(8)
0.2212(7)
0.2346(7)
0.2367(8)
0.2598(15)
0.2619(13)
0.2629(14)
141.3 8 1.2
141.8 8 1.2
139.8 8 1.2
131.0 8 1.2
130.8 8 1.2
132.2 8 1.3
136.2 8 1.1
132.7 8 1.3
131.5 8 1.2
128.7 8 1.2
135.8 8 1.3
12.45 8 0.06
12.54 8 0.13
14.61 8 0.05
23.58 8 0.10
23.66 8 0.10
23.63 8 0.09
25.13 8 0.09
25.48 8 0.10
28.30 8 0.19
28.65 8 0.17
28.56 8 0.18
146.4 8 1.2
146.9 8 1.3
145.7 8 1.2
140.1 8 1.3
139.8 8 1.2
141.4 8 1.3
146.3 8 1.2
142.6 8 1.3
142.4 8 1.3
139.5 8 1.3
147.2 8 1.4
2527 8 3
2990 8 3
2902 8 3
2943 8 4
2700 8 3
2744 8 4
3078 8 4
3823 8 4
2321 8 3
3355 8 4
3623 8 4
3232 8 4
2605 8 3
2704 8 3
2499 8 3
2710 8 4
2389 8 3
2928 8 3
2824 8 4
2850 8 3
2873 8 3
2869 8 3
2611 8 3
1936 8 16
2301 8 28
61 8 8
160 8 24
38 8 5
62 8 9
36 8 6
41 8 8
497 8 19
51 8 5
173 8 5
71 8 12
59 8 6
108 8 10
158 8 13
153 8 13
341 8 13
26 8 6
38 8 5
35 8 6
52 8 7
40 8 7
342 8 5
0.3240(14)
0.3242(31)
0.3921(30)
0.3902(13)
0.4173(26)
0.4202(17)
0.4801(15)
0.4096(24)
0.4054(21)
0.4128(13)
0.3945(13)
0.5207(16)
0.6455(19)
0.6442(21)
0.6443(84)
0.6364(22)
0.7489(25)
0.7711(26)
0.7442(23)
0.7298(22)
0.7381(64)
0.7352(22)
0.7351(40)
125.7 8 1.2
127.2 8 1.1
120.1 8 1.3
119.4 8 1.2
123.2 8 1.1
121.1 8 1.2
118.1 8 1.1
128.7 8 1.2
121.1 8 1.1
119.0 8 1.2
116.9 8 1.1
112.3 8 1.2
115.3 8 1.0
112.9 8 1.3
109.9 8 1.3
107.7 8 1.3
109.7 8 1.1
126.9 8 1.1
110.8 8 1.2
110.5 8 1.3
110.6 8 1.2
110.6 8 1.2
103.4 8 1.1
36.80 8 0.20
36.76 8 0.42
46.64 8 0.45
46.41 8 0.20
50.23 8 0.40
50.80 8 0.26
60.57 8 0.26
48.76 8 0.36
48.56 8 0.32
49.81 8 0.20
47.18 8 0.20
68.07 8 0.31
92.57 8 0.45
92.60 8 0.51
93.06 8 1.89
91.61 8 0.52
119.34 8 0.76
121.87 8 0.78
117.77 8 0.69
113.90 8 0.65
116.16 8 1.80
115.36 8 0.66
116.80 8 1.15
139.5 8 1.4
141.1 8 1.3
137.0 8 1.4
136.2 8 1.3
142.0 8 1.2
139.8 8 1.4
140.1 8 1.3
147.7 8 1.4
138.9 8 1.2
137.0 8 1.3
133.5 8 1.2
136.1 8 1.4
149.7 8 1.3
146.7 8 1.7
143.0 8 1.8
139.5 8 1.6
153.7 8 1.6
179.1 8 1.6
154.6 8 1.7
152.5 8 1.8
153.5 8 1.9
153.2 8 1.7
143.8 8 1.6
3258 8 5
3107 8 3
2746 8 4
3004 8 4
3652 8 4
3623 8 4
3310 8 4
3155 8 4
3722 8 4
3446 8 4
3379 8 4
3438 8 4
3241 8 4
3071 8 4
65 8 8
355 8 13
189 8 12
322 8 10
468 8 13
214 8 13
589 8 10
48 8 16
107 8 14
1416 8 11
151 8 14
430 8 13
143 8 12
44 8 7
0.5676(15)
0.5658(17)
0.5670(16)
0.6709(16)
0.6798(21)
0.7013(21)
0.7193(17)
0.7150(22)
0.7169(22)
0.7278(18)
0.7284(22)
0.7256(23)
0.7539(24)
0.7351(26)
115.3 8 1.6
114.7 8 1.3
117.0 8 1.7
112.1 8 1.2
110.1 8 1.1
117.1 8 1.2
118.6 8 1.1
123.9 8 1.2
110.3 8 1.3
110.0 8 1.2
106.7 8 1.2
108.8 8 1.3
129.0 8 1.5
103.6 8 1.1
76.49 8 0.34
76.20 8 0.35
76.17 8 0.35
98.84 8 0.43
101.20 8 0.50
105.30 8 0.60
109.60 8 0.50
107.50 8 0.60
110.50 8 0.60
113.50 8 0.60
114.30 8 0.70
113.10 8 0.70
116.70 8 0.70
116.80 8 0.80
143.1 8 2.0
142.2 8 1.6
145.1 8 2.1
148.2 8 1.6
146.6 8 1.5
157.7 8 1.6
161.7 8 1.5
167.9 8 1.6
150.8 8 1.8
151.5 8 1.7
147.4 8 1.7
149.8 8 1.8
179.4 8 2.0
144.1 8 1.6
230
Th age
(ka)
N234 Ui f
(x)
[231 Pa/235 U]
(activity)
231
Pa age
(ka)
0.238(5)
12.8 8 0.3
0.401(3)
0.407(5)
0.426(9)
0.413(5)
24.2 8 0.2
24.7 8 0.4
26.2 8 0.8
25.2 8 1.2
0.475(8)
0.433(6)
30.5 8 0.7
26.8 8 0.5
0.536(15)
0.525 (9)
0.615(8)
0.612(5)
0.645(7)
0.659(8)
0.724(4)
0.625(10)
0.485(9)
0.605(12)
0.552(9)
36.3 8 1.6
35.2 8 0.9
45.1 8 0.9
44.7 8 0.6
49.0 8 1.0
50.8 8 1.2
60.8 8 0.8
46.3 8 1.3
31.3 8 0.9
43.9 8 1.5
37.9 8 0.9
0.859(16)
0.864(7)
0.833(17)
92.7 8 5.2
94.4 8 2.3
84.6 8 4.9
0.917(12)
0.932(12)
117.6 8 6.7
126.7 8 8.1
0.902(6)
109.8 8 2.8
0.876(14)
98.7 8 5.5
0.800(4)
0.799(7)
76.1 8 1.1
75.8 8 1.6
0.837(4)
0.889(6)
85.8 8 1.3
103.9 8 2.6
0.912(6)
0.884(6)
114.6 8 3.0
102.0 8 2.6
0.903(13)
0.902(6)
0.934(7)
0.875(8)
110.2 8 6.3
109.7 8 3.0
128.7 8 5.0
98.1 8 3.0
231
Pc g
N234 Uc g
^
Y
^
^
Y
Y
Y
Y
^
Y
Y
Y*
Y*
Y*
Y*
Y*
Y*
Y*
Y*
Y*
Y*
Y*
Y
Y
Y
Y
Y
Y
Y
N
N
N
N
^
N
Y
N
^
N
N
^
^
N
^
N
Y*
Y*
N
N
Y*
Y*
Y*
Y
Y
N
N
N
Y
Y*
Y
Y
Y
N
N
Y
Y
Y
Y
^
Y
Y
^
N
Y
^
N
N
^
N
Y
N
N
Y
Y*
Y*
Y
Y
N
N
N
Y
Y
Y
Y*
N
Y
255
Ap
S
232
Th
(pg/g)
K.B. Cutler et al. / Earth and Planetary Science Letters 206 (2003) 253^271
EPSL 6514 22-1-03 Cyaan Magenta Geel Zwart
New Guinea drill core
GP 38.0
GP 40.95
KNM 46.7
KNM 50.0 (A)
(B)
(C)
KNM 58.7 (A)
(B)
KWA 64.3 (A)
(B)
(C)
New Guinea surface
KNM-T-2 (a)
(b)
KWA-I-1 (A)
(B)
KWA-N-1 (A)
(B)
KWA-Q-1
KAN-D-4
KAN-C-2
KWA-K-1 (A)
(B)
SIAL-E-1
KWA-S-1 (A)
(B)
KWA-U-1 (A)
(B)
SIAL-Q-1
SIAL-O-2
KIL-3 (a)
(b)
(C)
(D)
KIL-5
Barbados surface
FA-3 (A)
(B)
FA-00-1
GQ-3 (A)
(B)
OC-2
OC-5 (A)
(B)
GQ-4
OC-1 (A)
(B)
(C)
OC-4
UWI-17
Trcb
320 8 4
319 8 4
29 8 2
33 8 2
P
Ap
Parentheses show 2c errors in the last signi¢cant ¢gures.
a
KNM = Kanomi, KWA = Kwambu, GP = Gagidu Point, KIL = Kilasairo, KAN = Kanzarua, SIAL = Sialum, FA = Holders Hill, GQ = Grazettes Quarry, OC from
[19], SSS = St. Stephens School, and UWI = University of West Indies Hill; Replicates (A), (B),T are fragments of the same coral and (a), (b),T are aliquots of the
same sample; sub-samples in bold type were found to be unaltered.
b
Terrace number [2].
c
Species: A = Acropora sp., Ap = Acropora palmata, F = Favia laxa, G = Gardineroseris planulata, M = Montipora sp., P = Porites sp., and S = Siderastria sp.
d
Present elevation.
e
Growth elevation (see text).
f
N234 Um is measured and N234 Ui is initial value.
g 231
Pac indicates whether concordancy criteria are satis¢ed; N234 Uc indicates whether N234 Ui criteria are satis¢ed (see text).
N
N
N
^
80.3 8 1.6
88.3 8 1.1
112.9 8 5.3
0.817(63)
0.845(34)
0.908(10)
134.6 8 1.6
133.6 8 1.6
171.3 8 1.6
162.2 8 2.2
109.70 8 0.70
109.70 8 0.60
117.70 8 0.70
118.40 8 1.00
98.7 8 1.2
98.0 8 1.2
122.8 8 1.1
115.9 8 1.5
0.7054(24)
0.7046(21)
0.7530(22)
0.7521(32)
307 8 10
338 8 10
87 8 14
117 8 15
3654 8 4
3763 8 3
3228 8 3
3160 8 4
35 8 4
43 8 3
Ap
UWI-19 (A)
(B)
GQ-1
SSS-93
Trcb
Samplea
Table 1 (Continued).
Spc
Evd
(m)
Evg e
(m)
238
U
(ppb)
232
Th
(pg/g)
[230 Th/238 U]
(activity)
N234 Um f
(x)
230
Th age
(ka)
N234 Ui f
(x)
[231 Pa/235 U]
(activity)
231
Pa age
(ka)
231
Pc g
N
N
N
N
K.B. Cutler et al. / Earth and Planetary Science Letters 206 (2003) 253^271
N234 Uc g
256
from surface exposures on the Huon Peninsula
(Fig. 1). The samples were obtained from exposed
coral reef Terraces II^VII (de¢ned in [2,11]) on
transects perpendicular to the coastline. SIAL-E1, Q-1 and O-2 were collected near Sialum [15];
KWA-I-1, N-1, Q-1, K-1, S-1, and U-1 were collected near Kwambu [2]; KIL-3 and 5 were collected near Kilasairo [15]; and KAN-D-4 and C-2
were collected near Kanzarua [2] in 1988 [16].
KNM-T-2 was collected near Kanomi [17] in
1996. Samples were primarily Porites sp., but
also included Favia laxa, Gardineroseris planulata
and Montipora sp. (Table 1). To establish present
elevations, we subtracted sample height relative to
the terrace crest from the known height of the
terrace crest. For Sialum, Kwambu, and Kilasairo
samples we used a single set of terrace crest elevations [15] because of the close proximity of
these sites. For Kanzarua we used terrace elevations from [16,18] and for Kanomi we interpolated the elevations between nearby sites Blutcher
[2] and Kanzarua.
To establish uplift rate at each locality we subtracted 5 m (last interglacial sea level) from the
present elevation of the last interglacial terrace,
Terrace VIIb, and divided by 120 ka. Calculated
uplift rates were 1.85 m/kyr for Sialum, Kwambu,
and Kilasairo, 2.6 m/kyr for Kanomi, and 2.8 m/
kyr for Kanzarua and are generally consistent
with those calculated for the Holocene [16]. Key
New Guinea surface samples include KWA-S-1,
which establishes the timing and height of sea
level during MIS 5b, and KNM-T-2, KWA-N-1,
and KWA-Q-1, which constrain sea level during
portions of MIS 3, including the end, immediately
prior to the MIS 3^2 transition.
2.2. New Guinea drill-core samples
We analyzed six drill-core samples (Table 1)
collected during three drilling operations at sites
just above sea level near Kwambu in 1996, and
Kanomi and Gagidu Point in 1997 (Fig. 1). The
Kwambu and Kanomi cores both penetrated the
unconformity at the base of the deglacial sequence
into early MIS 2 corals. The Kwambu core penetrated deeper than the 1988 core (of Chappell and
Polach [9] and Edwards et al. [10]) and includes
EPSL 6514 22-1-03 Cyaan Magenta Geel Zwart
K.B. Cutler et al. / Earth and Planetary Science Letters 206 (2003) 253^271
257
50.0 and KNM 58.7 from the Kanomi core and
KWA 64.3 from the Kwambu core. These samples place constraints on sea level early in MIS 2
and during the transition between MIS 3 and 2.
In particular, we will show that KNM 50.0 is
about 13 kyr younger than KNM-T-2 (collected
on the surface immediately inland from the drill
site) and is at present 67 m lower in elevation than
KNM-T-2. This pair constrains the rate of sealevel fall during the MIS 3^2 transition.
2.3. Barbados surface samples
Fig. 1. Map of Papua New Guinea including the Huon Peninsula ¢eld area, showing locations of samples in Table 1.
Coral ages generally increase landward from the coastline
and uplift rates increase along the coastline from the northwest to the southeast [2].
all of the late Pleistocene, early Holocene sequence that is preserved at the site. Ground level
is 5.9 m above sea level, core depth is 68.6 m, and
the sample is from a depth of 64.3 m (relative to
ground level). The Kanomi site is 6.3 m above sea
level, core depth is 63.0 m, and samples are from
depths of 46.7, 50.0 and 58.7 m. The Gagidu
Point site, located less than 0.5 km north of
Finschhafen, is 5.8 m above sea level, core depth
is 59.0 m, and sample depths are 38.0 and 40.9 m.
Corals collected from drill cores were Acropora
and Porites species.
Uplift rates for Kanomi and Kwambu are calculated as described above. The uplift rate at Gagidu Point is not critical for the sea-level record
presented here; however, we have calculated its
value. Because the VIIb terrace elevation was
not available, we established the uplift rate based
on the elevation di¡erence between Gagidu Point
deglacial corals and known deglacial sea level. We
subtracted the Gagidu Point growth elevations
(GP 38.0 or GP 40.95, Table 1) from known sea
level [10] and divided by age, determining an uplift rate of 2.1 m/kyr.
With regard to sea-level history, the most important New Guinea core samples are from below
the unconformity between early MIS 2 and the
deglacial sequence. The key samples are KNM
We analyzed 12 Barbados samples (Table 1)
collected from surface exposures in 1991, 1993,
and 2000 (Fig. 2). FA-3 and FA-00-1 were collected near sea level west of Holders Hill at the
FSL site [14] and along the ‘F’ transect [13] ; GQ1, 3, and 4 were collected from Grazettes Quarry;
OC-1, 2, 4, and 5 were collected from the OC site
[13,19]; UWI 17 and 19 were collected from the
western £ank of the University of the West Indies
hill; and SSS-93 was collected from the construction site for St. Stephen’s School. The majority
were Acropora palmata, which tracks sea level
Fig. 2. Map of Barbados showing First High Cli¡ (dashed
line), Second High Cli¡ (dotted line), major roads (gray
lines), and locations of samples in Table 1. First High Cli¡
is immediately seaward of the Rendezvous Hill (Last Interglacial) Terrace crest. Coral ages generally increase landward
[12,19].
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K.B. Cutler et al. / Earth and Planetary Science Letters 206 (2003) 253^271
particularly closely, growing within a few meters
of sea level [20]. In addition, we collected Porites
and Siderastrea species.
To establish present elevations, we measured
the elevation di¡erence between the sample location and the nearest topographic contour. Barbados uplift rates were calculated in a similar fashion to uplift rates for New Guinea surface sites ;
here the last interglacial terrace is the Rendezvous
Hill Terrace. The uplift rates were found to be
0.33 m/kyr for FA, 0.30 m/kyr for GQ, and 0.44
m/kyr for OC, UWI and SSS. As shown below,
Barbados corals constrain rates of sea-level fall
during the glacial buildup following MIS 5a
(FA-3, FA-00-1) and rates of sea-level fall immediately after MIS 5e (OC-1).
aments. The Th and Pa fractions were loaded
with graphite and run using the single-¢lament
technique [21] and the U fraction was run using
the double-¢lament technique [22]. Single ¢laments were run at temperatures between 1600
and 1900‡C. For double ¢laments, the evaporation ¢lament was run at currents between 0.5 and
1.0 A and the ionization ¢lament between 4.2 and
5.0 A. Filaments were run on a Finnigan MAT
262 RPQ mass spectrometer with a secondary
electron multiplier operated in pulse-counting
mode at the Minnesota Isotope Laboratory. Using the age equation of [23] for 230 Th and of [24]
for 231 Pa and the half-lives of [25] for 238 U, of [22]
for 234 U and 230 Th, of [25] for 235 U, and of [26]
for 231 Pa, we established the isotopic ratios and
ages shown in Figs. 3 and 4 and in Table 1.
3. Analytical methods and results
3.2. Results
3.1. Methods
The New Guinea drill-core samples have 230 Th
ages between 12 and 29 kyr and surface samples
have ages between 36 and 117 kyr. The 230 Th ages
of Barbados surface samples ranged between 76
and 118 kyr. Although the majority show evidence for diagenetic alteration through non-marine initial N234 U and/or discordant 231 Pa and
230
Th ages, a substantial number record marine
initial N234 U and concordant ages, exhibiting no
signs of alteration.
Figs. 3 and 4 reveal that, in general, surface
samples are more likely to record non-marine
N234 U and lie o¡ of concordia than the younger
drill-core samples. Most, but not all samples that
lie o¡ of concordia, lie below concordia (231 Pa age
less than 230 Th age). This sense of o¡set is consistent with U gain or daughter loss, if the lost
component does not have a signi¢cantly higher
230
Th/231 Pa ratio than the sample [27]. 230 Th
ages are as much as 12 kyr older and as much
as 30 kyr younger than 231 Pa ages, illustrating
the importance of the concordia test. The samples
with non-marine uranium isotopic composition
have N234 U values both above (as high as 35x
higher) and below (as much as 12x lower) the
modern marine value, indicating the need to test
samples by uranium isotopic composition as well.
Discordance and the shifts in uranium isotopic
32 samples showed no macroscopic signs of alteration, contained no calcite detectible by X-ray
di¡raction techniques, and were selected for further analysis. We removed a 1 g sub-sample, or in
some cases multiple sub-samples for replicate
analyses, and ultrasonicated each piece. For corals that had previously been dated by 230 Th methods, we analyzed a new sub-sample for both 230 Th
and 231 Pa ages so that we could assess the accuracy of the 230 Th age for that particular sub-sample.
We dissolved each sub-sample and aliquoted
the solution into two portions. We spiked those
portions destined for 230 Th age analyses with
229
Th and a 233 U^236 U double spike. Those portions intended for 231 Pa age analysis were spiked
with 233 Pa. We then dried down the solutions with
HClO4 to ensure sample^spike equilibration, redissolved them in 2 N HCl, added iron, and
co-precipitated the U, Th, and Pa by adding
NH4 OH. We centrifuged the samples to separate
the precipitate, dissolved it in HNO3 , and ran
each solution through an anion exchange column
to separate the elements.
We then loaded and dried down the puri¢ed U,
Th and Pa fractions on zone-re¢ned rhenium ¢l-
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259
Fig. 3. New Guinea and Barbados isotopic data. Solid green bars are New Guinea drill-core samples, red ellipses are New Guinea surface samples, and blue ellipses are Barbados surface samples. Dimensions of the symbols correspond to 2c errors. (a)
[231 Pa/235 U]^[230 Th/234 U] concordia diagram. Tick marks indicate age in kyr. Samples that plot on the curve (concordia) have
identical 231 Pa and 230 Th ages. (inset) Enlargement for samples with ages between 20 and 60 kyr. (b) Measured N234 U versus
[230 Th/238 U]. Numbers next to vertical lines are 230 Th ages in kyr and those on sub-horizontal curves are N234 Ui values in x.
The shaded envelope shows the 146x modern marine value and error limits used when screening samples by N234 Ui value.
composition are likely associated with a complex
set of processes involving adsorption of nuclides
from groundwater, dissolution/precipitation reactions with groundwater, and leaching into
groundwater of nuclides from recoil-damaged
sites. The common factor is groundwater. In
Fig. 4, the di¡erence between initial and marine
N234 U is plotted versus the di¡erence between
231
Pa and 230 Th age, showing a weak correlation
2
(R = 0.21). The fact that there is some coupling
suggests that both measures of diagenesis respond, in part, to the same processes. The fact
that the coupling is weak indicates that diagenetic
processes do not a¡ect the two variables in the
same way. The weakness of the coupling indicates
that both tests are needed to screen for diagenesis.
Support for the dual screen also comes from the
fact that some samples record marine uranium
isotopic composition, but have discordant ages,
whereas others have concordant ages, but nonmarine uranium isotopic composition (Fig. 4).
To the extent that the variables are coupled, we
can investigate relationships among initial N234 U,
230
Th age, and 231 Pa age. Gallup et al. [14]
showed that isotopic data for Barbados samples
with elevated N234 U could be explained, broadly,
through addition of both 234 U and 230 Th from
groundwater, while keeping U concentration constant. Their model used a molar ratio of 1.41 for
234
U/230 Th addition to reproduce the data to ¢rst
order. This addition ratio yields a shift of about
0.25 kyr in 230 Th age per N-unit shift in 234 U/238 U.
A best-¢t line through the data in Fig. 4 has a
slope that corresponds to a shift in di¡erence between 231 Pa and 230 Th age of 1.6 kyr per N-unit
shift in 234 U/238 U. The sum gives a shift in 231 Pa
age of 1.85 kyr per N-unit shift in 234 U/238 U. Thus,
on average, 231 Pa age increases with increase in
N234 U, and the slope of this increase is higher
than the increase in 230 Th age with increase in
N234 U. However, because the variables do not correlate exactly and the processes responsible for
shifts in their values are poorly known, we cannot
accurately correct ages on the basis of these correlations.
Although a number of samples show evidence
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4. Sea-level curve
Fig. 4. Di¡erence between initial N234 U and modern marine
value versus di¡erence between 231 Pa and 230 Th age, for all
analyses in this study. The length of the gray rectangle corresponds to the N234 U criterion (within 8x of modern marine
U isotopic composition); the width of the rectangle corresponds to one concordancy criterion (ages within 2 kyr of
each other). In addition to the points that plot above the
rectangle, one other datum (over small gray square) satis¢es
both criteria (the concordancy criterion on the basis of a
measured 231 Pa/235 U value within 1% of the value calculated
from the 230 Th age). The data have a weak positive correlation (R2 = 0.21), indicating that the variables respond to a
small degree to the same diagenetic processes. On average,
231
Pa age increases with increasing initial N234 U (see text).
The weakness of the correlation and the fact that speci¢c
samples satisfy one criterion but not the other indicate that
both concordancy and N234 U criteria are needed to screen for
diagenesis.
for diagenesis, several key samples show no evidence for diagenesis. These include corals that
grew during MIS 5b (KWA-S-1 at 92.6 ka) and
early MIS 2 (KNM 50.0 at 23.6 ka; KNM-T-2 at
36.8 ka), as well as corals that grew at the end of
MIS 5a (FA-3 and FA-00-1 at 76.2 ka) and subsequent to MIS 5e (OC-1 at 113.1 ka). Of particular note are two pairs of samples. The ¢rst pair,
KNM 50.0 and KNM-T-2, both from the same
transect on the Huon Peninsula, constrain sea-level drop between MIS 3 and 2. The second pair,
FA-3 and FA-00-1, from the same site in Barbados, give the same age for the end of MIS 5a. This
point, coupled with an existing MIS 4 datum [28]
from a coral drilled immediately o¡shore from the
FA site, constrain the sea-level drop during the
MIS 5^4 transition.
Using the coral ages, we established the elevation of each sample when it was alive. Coral
growth elevations were determined by subtracting
the product of the uplift rate and the 230 Th age
from the present elevation of the coral. Errors in
growth elevation (Fig. 5b) were propagated from
errors in present elevation, age, and uplift rate.
After establishing the growth elevation of each
sample, we added our age and elevation data to
the existing 230 Th-dated coral sea-level data [5,
7,10,14,15,28^42] and tested the entire data set
for correspondence between each sample’s initial
234
U/238 U (N234 Ui ) value and the modern marine
234
U/238 U value. This method has been used
widely as a test for diagenetic alteration in coral
samples. In addition, we tested all surface samples
and most drill-core samples with 231 Pa data for
230
Th^231 Pa age concordancy.
On the basis of uranium isotopic composition,
we considered a sample to be unaltered if the
initial N234 U value was within 8 8x of the modern marine value (see [14,38,43], Fig. 4) and the
2c analytical error in N234 U value was less than or
equal to 8x. For the modern marine value we
used the measured value from the original study,
if reported. Otherwise, we used 150x [10,14] if
N234 Ui values were calculated with a 234 U decay
constant of 2.835U1036 yr31 [44,45] and 146x if
N234 Ui values were calculated with the revised
234
U decay constant of [22].
On the basis of 230 Th^231 Pa concordancy, we
considered a sample to be unaltered if (1) the
231
Pa/235 U ratio was within 1% of the expected
231
Pa/235 U ratio as calculated from the 230 Th age
and the 2c analytical error in 231 Pa/235 U was 1%,
or (2) the 231 Pa and 230 Th ages were within 2 kyr
of each other (see Fig. 4) and the 2c analytical
error in 231 Pa age was 2 kyr or less. We have
chosen 2 kyr to correspond with the criteria
used in the N234 U analysis. Following the ¢ndings
of Gallup et al. [14] on Barbados samples, an 8x
shift in N234 Ui corresponds to an age o¡set of
2 kyr. Stirling and others have found a similar
covariation between N234 Ui values and 230 Th age
in corals from Australia [38] and Henderson Island [43], suggesting that applying the N234 Ui cri-
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261
Table 2
Samples bounding most rapid intervals of sea-level fall (shaded portions in Fig. 5) and rates of sea-level fall
MIS
230
Th age
(ka)
2
2
3
4
5a
5b
5c
5d
5e
19.0
23.7
30.0
70.82
76.19
92.60
100.50
113.10
119.90
Evg a
Reference
MIS
transitions
(m)
(0.1)
(0.1)
(0.2)
(0.60)
(0.35)
(0.34)
(1.10)
(0.70)
(1.40)
3120
3107
388
381
324
358
314
319
6
(1)
(2)
(1)
(1)
(3)
(5)
(3)
(3)
(3)
[30]
this
[30]
[28]
this
this
[28]
this
[39]
study
Age
di¡erence
Sea-level
di¡erence
Average rate of
sea-level fall
(m/ka)
Minimum
rate of ice
accumulation
(cm/yr)
(ka)
(m)
3^2
3^2
11.01 (0.23)
6.38 (0.23)
32 (3)
19 (3)
2.9 (0.1)
2.9 (0.1)
5
5
5a^4
5.37 (0.69)
57 (3)
10.6 (0.1)
18
study
study
5c^5b
7.90 (1.15)
44 (6)
5.6 (0.2)
10
study
5e^5d
6.80 (1.57)
25 (4)
3.7 (0.3)
6
2c errors in the last signi¢cant ¢gures are in parentheses.
a
Growth elevation of coral.
terion more broadly may be justi¢ed. The 1% criterion is based on analytical error. For older corals, with relatively high 231 Pa concentrations, analytical errors of 1% can be achieved routinely
with current TIMS techniques. Two concordancy
criteria are warranted because of the nature of Useries systematics and analytical methods : at low
age, the precision of a typical analysis in terms of
percentage error is large but the absolute error in
age is small, whereas at high age the precision of
an analysis in terms of percentage error is small,
but the absolute error in age is large. In practice,
the percentage criterion is the critical constraint
for older samples, whereas the 2 kyr criterion is
the critical constraint for younger samples. Both
constraints screen for samples that have unusually
high analytical error for their 231 Pa analyses.
13 samples (bold in Table 1) satis¢ed these criteria, exhibiting no sign of diagenesis. These results, along with earlier data which also satisfy the
same criteria, are depicted by yellow points in Fig.
5b. Of the points that do not satisfy our criteria,
those that are most likely to be accurate are depicted in black (main part of Fig. 5b). The most
important black points are between 72 and 16
kyr. These data all satisfy the N234 U criterion,
but do not have 231 Pa analyses. The corals in
question all grew during times of low sea level
at sites with low uplift rates. Consequently, these
corals have largely been below sea level and have
not interacted extensively with groundwater.
Therefore these corals are more likely to record
accurate ages than others with the same isotopic
characteristics and have been included in the main
portion of Fig. 5b. Besides the 72^16 kyr samples,
we have also included, for completeness, samples
younger than 16 kyr, which satisfy the N234 U requirement, but for which no 231 Pa data are available. We have also included two MIS 5c points
described below. Note that in some cases samples
are not depicted in Fig. 5b because analytical errors exceeded our criteria.
Also depicted in Fig. 5b is a green curve connecting the data. The curve is intended as a visual
guide. The subtleties of the curve’s position are, in
part, determined by data other than the speci¢c
points in Fig. 5b. The portion between 140 and
128 ka is based on the results of Gallup et al. [46];
the age limits of peak 5e were ¢xed using the
N234 Ui -screened data set of Chen et al. [39]; the
timing and height of peak 5a sea level follow the
results of Ludwig et al. [29] and Toscano and
Lundberg [41] ; and the curve is discontinuous
during periods (MIS 3 and 5d) where other climate proxies suggest major £uctuations, which we
have insu⁄cient resolution to re£ect. Note that
we chose the more conservative data set for setting the age limits of MIS 5e (Chen et al. [39]).
Use of the Stirling et al. [37,38] data set would
result in calculation of an even more rapid rate of
sea-level fall for the MIS 5e^5d transition than
the value calculated below.
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For the MIS 3^2 transition, we have drawn the
curve through the Acropora sp. data points and
above three data points representing other genera.
In addition to the species data supporting this
placement, there are also stratigraphic data in
the case of the three Papua New Guinea points
(triangles ^ one on the curve, two below the
curve). All three are from corals recovered from
drill core, a pair of samples from the Kanomi core
(KNM 50.0 and KNM 58.7) and one from the
Kwambu core (KWA 64.3). All three date to early
MIS 2 and lie stratigraphically between the basement and the unconformity that represents the
LGM. At Kanomi, KNM 50.0 is stratigraphically
the youngest coral in this interval (immediately
below the LGM unconformity), whereas KNM
58.7 is stratigraphically the oldest coral in this
interval (immediately above the basement substrate). KWA 64.3 occupies a stratigraphic position analogous to KNM 58.7, but at Kwambu.
Following MIS 3, the substrate at each site was
likely at some depth below the photic zone. Because of uplift, likely coupled with sea-level drop,
the water depth eventually became shallow
enough so that the ¢rst reef-building corals could
grow, meters below actual sea level and directly
above the substrate. The ages and stratigraphic
positions of KWA-64.3 (28.6 kyr) and KNM
58.7 (25.3 kyr) suggest such an origin. As both
sites experienced further shoaling, corals growing
very close to sea level were deposited just prior to
emergence, represented by the LGM unconformity. At Kanomi, the age and position of KNM
50.0 (23.6 kyr) just below the unconformity follow
263
this scenario. Hence, the stratigraphic relationships suggest that KWA-64.3 (Porites sp.) and
KNM 58.7 (Porites sp.) grew at some signi¢cant
depth below sea level, as the ¢rst corals to grow at
their respective sites during an interval of relative
sea-level drop, and that KNM 50.0 (Acropora sp.)
grew very close to sea level, as the last coral to
grow at the Kanomi site prior to emergence. The
genera data support this interpretation; hence our
placement of the curve through KNM 50.0 but
above KNM 58.7 and KWA-64.3.
Surprisingly, given all the work on the sea-level
curve over the years, no MIS 5c samples satisfy
both the N234 Ui and concordancy criteria. We
have therefore depicted the two points that
come closest to matching our criteria to establish
MIS 5c sea level. These are Barbados surface
samples AFZ-2 (100.5 8 1.1 ka and 314 8 3 m
[28]), which records marine N234 U but has no
231
Pa analysis, and FT-1(I) (103.1 8 0.5 ka and
310 8 4 m [7]), which has concordant 231 Pa and
230
Th ages but slightly elevated N234 U. This is
clearly a portion of the sea-level curve that warrants further careful work.
We can compare our sea-level record (main
portion of Fig. 5b) to the 230 Th-dated, coral sealevel record screened solely with N234 U criteria
(Fig. 5b inset, solid symbols). The data in the
inset have some inconsistencies, particularly in
the older portion. However, the data in the
main part of Fig. 5b are self-consistent, indicating
that the concordancy test is important. It is also
clear from the main portion of Fig. 5b that, given
fairly strict diagenesis criteria, the resulting data
6
Fig. 5. Coral sea-level record compared to insolation [66] and benthic N18 O records. (a) 65‡N summer half-year insolation curve.
Gray bars delineate periods of rapid sea-level fall. (left inset) Winter half-year insolation gradients: top curve is 35^50‡N, middle
is 50^65‡N, and bottom is 20^35‡N. (right inset) 15‡N winter half-year insolation curve. (b) Coral sea-level record based on samples showing no evidence of diagenesis (see text). Circles are data from previous studies and triangles from this study: Papua
New Guinea samples are upright and Barbados samples inverted. Yellow symbols are data that satisfy both concordancy and
N234 U criteria. Black symbols are a subset of the data that satisfy one of the two criteria (see text). Replicate samples were combined using a weighted average and error bars are 2c (if not visible, they are smaller than the symbol). Red boxes enclose samples older than 15 kyr of the genus Acropora, known to track sea level closely. Black bars give the duration of MIS 5e sea-level
high according to the N234 Ui -screened, coral data sets of Stirling et al. [37,38] (upper) and Chen et al. [39] (lower). The green line
provides our best estimate of past sea-level change (see text). Numbers give average rates of sea-level fall for each drop (Table
2). (inset) All coral sea-level data presently available, including those from this study, measured with high-precision 230 Th dating
methods. Solid symbols represent samples having N234 Ui values that match the modern marine value, open symbols represent
samples that do not. (c) Benthic N18 O record for Carnegie Ridge core V19-30 [59]. Numbers are oxygen isotope stages. Dotted
tie lines match similar features in the coral and N18 O records and are used in Figs. 6 and 7.
EPSL 6514 22-1-03 Cyaan Magenta Geel Zwart
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K.B. Cutler et al. / Earth and Planetary Science Letters 206 (2003) 253^271
set is small. Thus, we view the main part of Fig.
5b as a ¢rst cut at a robust sea-level curve.
Nevertheless, the curve con¢rms a number of
well-established aspects of sea level and adds
new constraints. Our data place sea level at
358 m during MIS 5b, de¢ning a drop of about
44 m between MIS 5c and 5b, and a subsequent
rise of about 46 m between MIS 5b and 5a. The
MIS 5b coral comes from New Guinea Terrace V
[2] and raises questions about previous correlations between Terrace V and MIS 5a [2]. The
di¡erence between our and previous assignments
may be explained in part by di¡erences in assigned age and in part by di¡erences in assigned
terrace elevations (as a result of resurveying of the
terrace heights along this transect, reported in
Stein et al. [15]).
In addition, the results establish sea level near
3107 m at 23.7 kyr ago, before the LGM. Presuming sea level continued to drop subsequent to
23.7 kyr, New Guinea LGM sea level was likely
lower than the 3105 m value obtained from glacio-isostatic models [47]. Our ¢ndings place sea
level near 3111 m at 28.6 kyr, casting doubt on
early reports that sea level was about 340 m between 28 and 31 kyr [2]. Further, our MIS 3 elevation data (374 to 385 m) are consistent with
the lower end of the range of earlier work [32].
Because of the limited number of points, our data
do not directly address the possibility that sea
level may have reached higher values (e.g. 345 m
[32,42,48]) at times during MIS 3. However,
Chappell [48] has presented a high-resolution
MIS 4/3 sea-level record based on both 230 Th
ages and a model of terrace evolution. The lower
range of his MIS 3 sea-level values agrees broadly
with our three MIS 3 data. Thus, it is likely that
MIS 3 sea level had a range of about 40 m, between about 345 and 385 m [48].
One of our more important results (two concordant Barbados samples having identical ages and
sea levels) is the placement of sea level at 324 m,
76.2 kyr ago. This indicates that sea level was still
relatively high several thousand years after the
main peak of MIS 5a. The data constrain the
timing of the end of MIS 5a and provide the
starting point for calculation of the average rate
of sea-level fall during the MIS 5^4 transition.
Finally, the full data set allows us to calculate
average rates of sea-level fall over four intervals:
the transitions between MIS 5a and 4, 5e and 5d,
5c and 5b, and 3 and 2 (Fig. 5b, Table 2). The
most rapid drop took place during the 5a^4 transition, when sea level fell at a rate of 10.6 8 0.1 m/
kyr averaged over 5400 yr.
5. Discussion
5.1. Implications for rates of ice-sheet growth
In less than 6 kyr, during the steepest portion of
the MIS 5a^4 transition, sea level dropped 57 m,
nearly half of the glacial-maximum ice volume,
broadly equivalent to the volume of today’s Antarctic ice sheet. This rate of sea-level fall equates
to at least 18 cm/yr net ice accumulation on the
continents, a minimum established by setting the
accumulation area equal to the area covered by
northern hemisphere ice sheets during the LGM
[49] and assuming that mass loss due to ablation
was negligible. By comparison, current gross accumulation rates average 30 cm/yr in Greenland
[50]. However, the mass balance of this ice sheet is
close to zero due to losses. Thus, to achieve a net
ice accumulation rate of at least 18 cm/yr would
require a dramatic increase in accumulation minus ablation rate, as compared to Greenland today.
A number of conditions may have allowed rapid rates of net ice accumulation in the northern
hemisphere. The terrain in North America and
northern Eurasia is generally £at, increasing
slightly in elevation from north to south at latitudes where ice-sheet genesis was likely. Low relief means a small drop in temperature would
cause a large southward shift of the equilibrium
line, allowing the area of accumulation to expand
considerably. Because of the elevation lapse rate,
the gradual southward rise in elevation would
also counter some of the e¡ects of southward
warming. Once snow accumulation began, its
high albedo may have caused regional temperature lowering [51], reduced melting, and increased
snow accumulation as warm, moist air masses [52]
met this cold region.
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In addition, concurrent solar insolation conditions may have facilitated rapid ice-sheet growth.
All four sea-level drops took place when northern-hemisphere summer insolation values were at
a minimum (Fig. 5a), favoring reduced melting.
The drops also took place when northern-hemisphere winter insolation gradients and insolation
values near the equator were at a maximum (Fig.
5a, insets). High insolation values favor greater
sea-water evaporation and would potentially create a larger tropical moisture source, while high
insolation gradients would promote e⁄cient
transport and deposition of this moisture towards
the north [52], promoting rapid ice-sheet growth.
Notably, these observations support the assertion
that long periods of time are required to reach
maximum glaciation during the V100 kyr glacial
cycles, not because ice-sheet growth is inherently
slow, but because the conditions amenable to rapid glacial growth, i.e. speci¢c insolation characteristics, occur for only short periods of time [53].
Further, they indicate that models at least as sophisticated as the coupled ice^atmosphere^ocean
models are needed to accurately simulate past icesheet dynamics. For example, 2-D ice-sheet models driven by high-resolution temperature reconstructions from 65 kyr to the LGM show relatively steady ice-sheet growth during this time
[54]. Our results suggest that ice-sheet expansion
is characterized by rapid intervals of growth and
that at least one such interval occurred during this
period.
5.2. Implications for deep-sea temperatures
One of the classic problems in isotope geology
and paleoclimatology has been the separation of
the temperature and seawater oxygen isotope
components of the marine oxygen isotope record.
Given certain assumptions, these components can
be resolved by analysis of sea-level and marine
oxygen isotope records. This general approach
has been applied by a number of researchers
over the years, e.g. [8,55]. Two factors have
changed since the earlier applications and lead
us to apply this methodology to our record. First,
our sea-level curve has certain advantages over
earlier records because of our concordancy tests
265
and because portions of our curve had not been
previously determined (e.g. early MIS 2 and late
MIS 5a). Second, the oxygen isotopic composition
of LGM seawater has been determined directly by
analysis of marine pore £uids [56], providing a
key constraint that was not previously available.
Plots of our sea-level values versus benthic N18 O
for Carnegie Ridge core V19-30 (3‡S, 83‡W, 3091
m) in the East Paci¢c [57] and for Ceara Rise core
EW9209-1 (5‡N, 43‡W, 4056 m) in the equatorial
Atlantic [58] are given in Fig. 6. The main data
are a series of (sea-level)^(oxygen isotopic composition of foraminiferal calcite) data points derived
from the (sea level)^(marine oxygen isotope) correlations in Fig. 5. The plots con¢rm signi¢cant
deep-ocean temperature shifts subsequent to MIS
5e and during Termination I [54,32,59]. We established the amplitude of these shifts using the porewater data [60] and by assuming that average icesheet N18 O has remained constant with time. In
addition, we established continuous temperature
records since the last interglacial period using
the relationships in Fig. 6.
We assume that the mean isotopic composition
of ice (N18 Oice ) was constant through time at
the MIS 2 value of 330x, calculated from
N18 Oice = 3vN18 Osw U(D3H)/H, where D is the
average-ocean depth of 3790 m, H is the LGM
to present sea-level change of 121 m [8], and
vN18 Osw is the analogous change in the global
average-seawater N18 O [56]. To test our constant
N18 Oice assumption, we calculated how our reference line of seawater N18 O (Fig. 6) would change
using extreme N18 Oice values of 320 and 340x.
Because there is little ice during times of high sea
level and because the average N18 O of ice during
the LGM is constrained by the pore-water data,
our reference line is best constrained during times
of relatively high and relatively low sea level and
not as well constrained during times of intermediate sea level. For MIS 5a and 5c, this range in
N18 Oice allows less than 8 0.04x change in seawater N18 O, con¢rming that a major portion of
the 5c^2 glacial residuals, at least 80% in V19-30
and 90% in EW9209-1, were due to temperature
changes. For MIS 3, 4 and 5b, it is more di⁄cult
to resolve temperature changes from N18 Oice
changes. Nonetheless, at the Atlantic site, even
EPSL 6514 22-1-03 Cyaan Magenta Geel Zwart
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K.B. Cutler et al. / Earth and Planetary Science Letters 206 (2003) 253^271
with the largest possible shift of 8 0.22x during
MIS 4, deep waters experienced at least a 1.0‡C
drop in temperature between MIS 5a and 4. Thus,
the constant N18 Oice assumption is generally viable.
The plots reveal that deep-sea temperatures at
the Paci¢c site fell about 2‡C between MIS 5e and
5c (Fig. 7) and rose about 2‡C between MIS 2
and 1. Temperatures at the Atlantic site fell about
2‡C between MIS 5e and 5c and rose 3‡C between
MIS 2 and 1. The deglacial temperature shifts are
consistent with earlier work [56]. Within the glacial interval (between 5c and 2, inclusive), deepsea temperature fell about 0.6‡C at Carnegie
Ridge and 2.5‡C at the Ceara Rise. The larger
temperature signal at the Atlantic site is likely
due to a combination of changes in the proportions of warmer northern and cooler southern
source waters at the Ceara Rise (a process not
expected at Carnegie Ridge), and to the cooling
of high-latitude source waters. We ¢nd a strong
linear relationship between sea level and the 5c^2
N18 O temperature residuals at both sites (Fig. 6);
this correlation is signi¢cant and explains why the
temperature curves maintain the structure of a
standard ocean climate record.
The sea-level component of the Carnegie Ridge
and Ceara Rise cores are similar (Fig. 7), attesting
to an e¡ective separation of deep-sea temperatures and ice volume. Small discrepancies may
be caused by resolution di¡erences, local salinity
changes, or inaccuracies in the relationships de¢ned in Fig. 6. Because Carnegie Ridge experienced smaller temperature changes and less
water-mass mixing, the sea-level component of
the Carnegie Ridge record likely re£ects sea-level
history more accurately than that of the Ceara
Rise record. The strength of our approach is the
fact that we have a direct sea-level record. Thus,
our calculated sea-level component for the oxygen
isotope record can be viewed as an interpolation
(given certain rules) between a relatively small
number of well-established points on the sea-level
curve.
Our temperature records are reasonable in that
they do not give temperatures below freezing and
have some correlation with ice volume. Deep-sea
records from the Atlantic and Paci¢c have been
presented by Martin and others [61] (Mg/Ca thermometry applied to benthic forams) and Labyrie
et al. [62] (separation of the temperature component of marine oxygen isotope records). Dwyer et
al. [63] have reconstructed Atlantic deep-sea temperatures using Mg/Ca thermometry applied to
ostracodes and Shackleton [64] has reconstructed
Paci¢c deep-sea temperatures from the same foram oxygen isotope record that we have used.
Three of the four Atlantic sites, including ours,
are in the tropics or sub-tropics; the Dwyer et al.
[63] site is north of the other sites (41‡N). Our
record and the Labeyrie et al.[62] record agree
very well. All four studies record similar glacial^
interglacial amplitudes of 3^4‡, all record large
shifts in temperature immediately before and after
interglacial periods, and all record smaller
changes in temperature among the non-interglacial stages and sub-stages. Second-order di¡erences from our record and the Labeyrie et al. record
include: (1) a lower MIS 4 temperature in the
Martin et al. [61] record; (2) higher MIS 5c, 5b,
and 5a temperatures in the Dwyer et al. [63] record; (3) generally larger amplitudes for high-frequency (corresponding to millennial-scale periods)
temperature shifts in the Martin et al. [61] record
and in the higher-resolution portions of the
Dwyer et al. [63] record; and (4) a larger temperature drop in the Holocene in the Dwyer et al.
[63] record.
The three Paci¢c sites are essentially the same,
with our analysis, the Labeyrie et al. [62] analysis,
and the Shackleton [64] analysis using the same
oxygen isotope data from the same core [57] and
the Martin et al. study using data from a nearby
core. Our record agrees in all major respects with
the Labeyrie et al. [62] record, including a glacial^
interglacial amplitude of about 2‡, the largest
temperature shifts before and after interglacial periods, and small temperature changes during the
glacial and interstadial stages. As compared to
our and Labeyrie et al.’s [62] records, the Martin
et al. [61] record has lower temperatures during
MIS 5d, 5b, and 4 and higher temperatures during the latter portion of MIS 6. The Shackleton
[64] record has a larger glacial^interglacial amplitude in temperature, as well as larger temperature
changes during the non-interglacial stages. Over-
EPSL 6514 22-1-03 Cyaan Magenta Geel Zwart
K.B. Cutler et al. / Earth and Planetary Science Letters 206 (2003) 253^271
267
Fig. 6. Sea level versus benthic N18 O for Carnegie Ridge core V19-30 [59] (closed triangles) and Ceara Rise core EW9209-1 [60]
(closed squares). Tie points (correlations) between isotope and sea-level records are from Fig. 5. Linear correlations are found
within glacial stages (solid lines; regression line for V19-30 is: Sea level (m) = 3102.7(N18 O)+393.6, R2 = 0.99 and for EW9209-1
is: Sea level (m) = 375.8(N18 O)+203.9, R2 = 0.99) and within the interglacial stages (dashed lines). Open symbols represent calcite
LGM N18 O values calculated presuming no LGM to modern temperature shift: for Carnegie Ridge, we used an LGM to presentday shift in seawater N18 O of 1.0x [60] and for the Ceara Rise, we used a shift of 0.9x (this is 0.1x higher than the measured value [56], adjusting for the 1000 m depth di¡erence between the pore £uid and EW9209-1 sites and the higher proportion
of southern source waters at the deeper EW9209-1 site). The heavy dotted lines between MIS 1 and the pore-water results are
reference sea-level^N18 O relationships at each site, assuming the mean isotopic composition of ice (N18 Oice ) has remained constant
through time at the MIS 2 value of 330x [56]. Double-headed arrows correspond to the error in the reference line induced by
a 320 to 340x range in N18 Oice at several isotopic stages. Parallel lightly dotted lines are 1‡C increments of deep-ocean cooling
relative to the reference lines, based on a N18 O^temperature relationship of 34.0‡C/x [67]. For individual data, the deep-sea
temperature shift relative to modern can be read directly by comparing a datum to the dotted temperature contours. When making this comparison, the main assumption is the constant average N18 O value of ice. Possible errors in this assumption (indicated
by the double-headed arrows) are small for high sea levels because additional ice (beyond the modern volume) is small. The error
at the LGM is also small because the value is ¢xed by the pore-£uid datum. The largest errors are for intermediate sea levels.
Even considering errors, none of the data (other than MIS 1) plot on the dotted lines, indicating signi¢cant deep-sea temperature
change at both localities. If we make a second assumption, that intermediate values between the actual data plot on the regression (solid and dashed) lines, we can calculate the temperature component for all of both time series from the di¡erence in N18 O
between the reference lines (heavy dotted) and regression lines (solid and dashed). This assumption appears to be robust on the
basis of high correlation coe⁄cients for the regressions; however, there may be speci¢c times when this relationship does not
hold (e.g. possible decoupling of temperature and sea level during Termination II [65]). Temperature history calculated from these
relationships is shown in Fig. 7, along with sea level calculated from the residual.
all, there are substantial areas of agreement, particularly for the Atlantic records. There are also
clear discrepancies, particularly for the Paci¢c.
Ultimately, the strength and weakness of our approach lie with the regression lines in Fig. 6.
There may be speci¢c times for which the regres-
sions do not hold. For example, there is some
indication that sea level and temperature were decoupled for an interval during Termination II,
with sea level lagging temperature rise [65]. On
the other hand, for times for which the regression
lines are valid or if the regression lines de¢ne gen-
EPSL 6514 22-1-03 Cyaan Magenta Geel Zwart
268
K.B. Cutler et al. / Earth and Planetary Science Letters 206 (2003) 253^271
Fig. 7. Benthic N18 O records for (a) Carnegie Ridge and (b) Ceara Rise separated into temperature and sea-level components.
Separation assumes all glacial and interglacial values follow the relationships given by solid and dashed lines in Fig. 6, sea water
N18 O follows the slope of the dotted lines in Fig. 6, and that correlations between the deep-sea oxygen isotope and sea-level records are accurate (Fig. 5). Ages for each record were adjusted to match the absolute chronology of the sea-level record, using
tie points at MIS 2, 3, 4, 5a, 5b, 5c, 5e and the 135 kyr peak (Fig. 5).
eral phenomena (as implied by the high R2 values), the approach is powerful.
6. Conclusion
We have used high-precision 231 Pa dating methods as an independent check on the accuracy of
coral 230 Th ages. We applied this test, along with
traditional methods for detecting diagenesis, to
new and existing coral data to establish a sea-level
curve for times since the last interglacial period.
This curve is characterized by a relatively small
number of robust points, particularly for MIS 3,
5c, and 5d, illustrating the need for continued
work in this ¢eld. Nevertheless, the curve in its
present form places important constraints on the
timing, rates, and causes of sea-level change over
speci¢c time intervals. We place constraints on the
rate and extent of continental glaciation during
the MIS 5a^4 transition, raising new questions
about climatic conditions during glacial advances.
In addition, our ¢ndings, combined with porewater data, provide estimates of the temperature
and the ice volume components of deep-sea N18 O
records. Continued careful consideration of coral
diagenesis and age accuracy will be an integral
part of future work aimed at increasing the resolution of the sea-level record.
Acknowledgements
We thank J. Chappell for scienti¢c discussions
around tropical camp¢res, helping initiate this
project, and facilitating the ¢eld work and drilling
on the Huon Peninsula; J. Ho¡ and D.A. Richards for laboratory assistance ; C.R. Bentley and
J.A. Dorale for informative discussions ; R.G.
Johnson, E. Wallensky, G.R. Min, J.W. Beck,
and the 1988 PNG ¢eld team for sample collection e¡orts; and D. Lea and two anonymous reviewers for constructive criticisms that improved
the manuscript considerably. Supported by NSF
Grants ESH-9809459, EAR-9712037, and ARI9512334 to R.L.E. K.B.C. was supported by
NSF-sponsored grants for Geo£uids Research
(to M. Person) and Research Training (to M. Da-
EPSL 6514 22-1-03 Cyaan Magenta Geel Zwart
K.B. Cutler et al. / Earth and Planetary Science Letters 206 (2003) 253^271
vis), and the Doctoral Dissertation Fellowship
(University of Minnesota).[BARD]
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