Oxygen-isotope record of sea level and climatic
variations in the Sulu Sea over the past 150,000 years
Braddock K. Linsley, Department of Earth and Atmospheric Sciences, University at Albany, State University of New York
On time scales of around 10,000 years, the Sulu Sea oxygen
isotope record closely matches changes in sea level deduced
from coral terraces on the Huon peninsula [Chappell and
Shackleton; 1986], particularly during isotope stage 3 (see top
panel) where the Sulu Sea oxygen-isotope record deviates from
the SPECMAP deep-ocean oxygen isotope record and indicates
that sea level at this time was only 40-50 meters below present
levels. A recent revision of the Huon peninsula terrace record
[Chappell et al., 1996], indicates lower sea levels during stage 3
adding to the controversy around stage 3 sea levels. If the
conclusion of higher stage 3 sea levels can be substantiated it
implies that the subsequent rate of increase in continental ice
volume during the return to full glacial conditions was correspondingly faster than previously thought.
25,000
50,000
75,000
100,000
125,000
150,000
-20.0
-2.8
Huon Peninsula4
Barbados6,34
0.0
5a
5c
-2.4
2
1
20.0
5b
4
3
5e
6
-2.2
40.0
-2
60.0
-1.8
80.0
-1.6
100.0
-1.4
120.0
Sulu Sea Site 769 (G.ruber) this study
Specmap Scaled
-1.2
-30.0
B
H7
GRIP Ice Core Oxygen Isotopes
Younger Dryas
H1 H2 H3 H4
H5
H6
-35.0
-2.8
-40.0
-2.4
-45.0
1
-2
2
3
4
5a
5b
5c
-1.6
5e
5d
6
δ18O ( o/oo, SMOW)
140.0
GRIP Ice Core
Planktonic δ18O ( o/oo, PDB)
-2.6
Huon Peninsula estimate
of sea level (meters below present)
0
A
Planktonic δ 18O ( o/oo, PDB)
As knowledge of variations in the Earth’s climate has grown,
concern over the origin and distribution of past “abrupt”
climatic events and their potential future impact has also risen.
The oxygen isotope (δ18O) composition of planktonic foraminifera recovered from marine sediments cored at ODP Site 769 in
the shallowly silled Sulu Sea on the edge of the western Pacific
warm pool has yielded new clues to past millennial-scale
climatic variations and possibly longer term sea level changes in
this important region [Linsley and Thunell, 1990; Linsley, 1996].
The glacial-interglacial δ18O amplitude in this record is only
1.3 o/oo, almost equaling the 1.3 o/oo [Fairbanks, 1989] to
1.0 o/oo [Schrag et al., 1996] planetary glacial-interglacial ice
volume signal. This suggests that at most 0.3 o/oo of the longterm δ18O signal is attributed to temperature or salinity change.
Several abrupt climatic events usually associated with higher
latitudes are also recorded in the Sulu Sea at ~11,000 years B.P.
(Younger Dryas), ~75,000 years B.P., and ~120,000 years B.P
(lower panel). The Younger Dryas is now thought to be a global
deglacial event originating at higher latitudes. The origin of the
older events remains uncertain as is the absence of pronounced
millennial-scale Dansgaard-Oschger events in isotope stage 3
(an interglacial period 23,000 to 58,999 years ago). However,
the mid-Eemian abrupt event adds support for the presence of
last interglacial climatic instability as suggested by ice core
records.
Ash
Present
-1.2
Sulu Sea Site 769 (G. ruber)
Sulu Sea Site 768 (G. ruber)
-0.8
0
25,000
50,000
75,000
Years B.P.
100,000
125,000
150,000
Upper Panel: ODP site 769 planktonic δ18O results (thin solid black line with
open circles) compared to a scaled version of the SPECMAP deep ocean
δ18O record (bold solid blue line), and past sea level estimated from the
Huon Peninsula (large open red circles) and Barbados (solid red triangles).
Numbers indicate isotope stages. Note the close correspondence between
the Huon Peninsula sea level record and Site 769 δ18O, in particular during
stage 3 when the SPECMAP record is ~0.5o/oo less negative.
Lower Panel: Oxygen isotopic (δ18O) analyses from Sites 769 (open black
circles) and 768 (filled black circles). Large arrows mark locations of
“abrupt” climatic events discussed in the text. (Upper Curve); GRIP
Greenland summit ice core δ18O results spanning the last 150,000 years. The
temporal position of the Younger Dryas and Heinrich events H1 - H6 are
marked by small arrows.
References:
Chappell, J., and N.J. Shackleton, Oxygen isotopes and sea level, Nature, 324,
137-140, 1986.
Chappell, J., A. Omura, T. Esat, M. McCulloch, J. Pandolfi, Y. Ota, and B. Pillans,
Reconciliation of late Quaternary sea levels derived from coral terraces at Huon
Peninsula with deep sea oxygen isotope records, Earth and Planetary Science
Letters, 141, 227-236, 1996.
Fairbanks, R.G., A 17,000-year glacio-eustatic sea level record: Influence of glacial
melting rates on the Younger Dryas event and deep ocean circulation, Nature,
342, 637-642, 1989.
Linsley, B.K., Oxygen isotope evidence of sea level and climatic variations in the
Sulu Sea over the past 150,000 years, Nature, vol 380, p234-237, 1996.
Linsley, B.K., and Thunell, R.C., The record of deglaciation in the Sulu Sea:
Evidence for the Younger Dryas event in the tropical western Pacific. in J.P.
Kennett, ed., Paleoceanography, Special Issue on the Younger Dryas, 5, no. 6,
1025-1039, 1990.
Schrag, D.P., G. Hampt, and D.W. Murray; The temperature and oxygen isotopic
composition of the glacial ocean; Science, 272, 1930-1931, 1996.