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PALEOCEANOGRAPHY, VOL. 22, PA4203, doi:10.1029/2007PA001457, 2007
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The last five glacial-interglacial transitions: A high-resolution
450,000-year record from the subantarctic Atlantic
G. Cortese,1 A. Abelmann,1 and R. Gersonde1
Received 23 March 2007; revised 26 June 2007; accepted 12 July 2007; published 19 October 2007.
[1] A submillennial resolution, radiolarian-based record of summer sea surface temperature (SST) documents
the last five glacial to interglacial transitions at the subtropical front, southern Atlantic Ocean. Rapid fluctuations
occur both during glacial and interglacial intervals, and sudden cooling episodes at glacial terminations are
recurrent. Surface hydrography and global ice volume proxies from the same core suggest that summer SST
increases prior to terminations lead global ice-volume decreases by 4.7 ± 3.7 ka (in the eccentricity band), 6.9 ±
2.5 ka (obliquity), and 2.7 ± 0.9 ka (precession). A comparison between SST and benthic d 13C suggests a
decoupling in the response of northern subantarctic surface, intermediate, and deep water masses to cold events
in the North Atlantic. The matching features between our SST record and the one from core MD97-2120
(southwest Pacific) suggests that the super-regional expression of climatic events is substantially affected by a
single climatic agent: the Subtropical Front, amplifier and vehicle for the transfer of climatic change. The direct
correlation between warmer DTsite at Vostok and warmer SST at ODP Site 1089 suggests that warmer oceanic/
atmospheric conditions imply a more southward placed frontal system, weaker gradients, and therefore stronger
Agulhas input to the Atlantic Ocean.
Citation: Cortese, G., A. Abelmann, and R. Gersonde (2007), The last five glacial-interglacial transitions: A high-resolution
450,000-year record from the subantarctic Atlantic, Paleoceanography, 22, PA4203, doi:10.1029/2007PA001457.
1. Introduction
[2] While periodic changes in the Earth’s orbital parameters pace the glacial ages [Hays et al., 1976], many other
factors influence the detailed climatic evolution at a specific
location at suborbital (centennial to millennial) timescales.
The change in oceanic thermohaline circulation (THC)
intensity is probably one of the most important of these
factors. The evaporative balance of the different oceans
plays an important role for the THC: as the Atlantic Ocean
loses more moisture (0.32 Sv to the Pacific [Broecker,
1997]) than it produces, water must be drawn from other
oceans to balance this loss. The two main return water inlets
into the Atlantic are the Drake Passage (‘‘cold-water route,’’
CWR: South Atlantic Current brings cold water from the
Pacific Ocean), and the area south of the Cape of Good
Hope (‘‘warm-water route,’’ WWR: Agulhas Current brings
warm water from the Indian Ocean) (Figure 1). These two
water masses mix in the South Atlantic, and the Benguela
Current carries this water across the equator, and back to the
North Atlantic. A WWR reduction is capable of destabilizing the THC, as it decreases the amount of warm water
entering the Atlantic. This affects deep water formation in
the North Atlantic, as small changes in temperature, or
freshwater input, can tip the balance from conditions in
which North Atlantic Deep Water (NADW) forms, to
conditions in which it does not [Pierrehumbert, 2000].
1
Alfred Wegener Institute for Polar and Marine Research (AWI),
Bremerhaven, Germany.
Copyright 2007 by the American Geophysical Union.
0883-8305/07/2007PA001457$12.00
[3] As THC changes have a direct influence on Pleistocene climate, it is important to understand the role that the
Agulhas Current plays in conveying the Indo-Pacific warm
water pool toward higher latitudes. Monitoring studies of
Agulhas Current flow intensity into the South Atlantic point
to an association between increased flux and warmer than
usual SSTs [Agenbag and Shannon, 1987]. This area is also
particularly sensitive to temperature changes, as the southernmost Agulhas Current penetration is associated with the
STF position, separating warm, saline subtropical water
from cool, low-salinity subpolar water [Lutjeharms, 1981].
Currently at about 40°S, the STF location is linked to
southern Indian Ocean circulation patterns, and a STF
equatorward shift by 4° latitude would altogether prevent
Agulhas Current spillage into the Atlantic Ocean, and thus
alter the interocean heat budget. There is however debate
regarding the intensity of the Agulhas Current during the
Last Glacial, as some authors [Prell et al., 1980; Winter and
Martin, 1990; Flores et al., 1999; Rau et al., 2002;
Gersonde et al., 2003a; Esper et al., 2004] support either
uninterrupted or seasonally modulated heat transfer from
low to high latitudes, while others [Berger and Vincent,
1986; McIntyre et al., 1989] suggest it did not retroflect
during glacial times. Peeters et al. [2004] show how the
Agulhas spillage shifts from a strong reduction during midglacial times to a vigorous flow during late glacials. Over
glacial-interglacial cycles, STF position shifts and wind
system rearrangements both directly affect the intensity of
the Agulhas spillage, which in turn leaves an imprint on the
ODP Site 1089 SST record presented in this paper.
[4] Transfer functions applied to microfossil assemblages
have been successfully used to reconstruct past sea surface
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CORTESE ET AL.: ODP SITE 1089 SST RECORD OVER LAST 450 ka
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Figure 1. Location of the cores mentioned in the text: ODP Sites 980, 1089, and 1125, PS2821, MD962080, MD97-2120, DSDP Site 594, Vostok. The Subtropical Front position (dashed black line, modified
after Belkin and Gordon [1996]) and the general surface (red), intermediate (green) and deep (cyan)
oceanic circulation (adapted from Schmitz [1995]) are also shown. The two larger red arrows indicate the
inflow of warm surface waters into the Agulhas Retroflection area, and the eastward return flow of
surface water south of the Subtropical Front.
temperatures (SST) [CLIMAP Project Members, 1981;
Pisias et al., 1997; Zielinski et al., 1998; Abelmann et al.,
1999; Cortese and Abelmann, 2002; Niebler et al., 2003].
Radiolarians are particularly promising in this respect for
the study area, as they are highly diversified and well
preserved in Southern Ocean sediments [Brathauer and
Abelmann, 1999; Cortese and Abelmann, 2002].
[5] In the latter paper we developed a transfer function to
estimate paleoSSTs in the Southern Ocean from radiolarian
census data, and applied it to a splice of two cores (ODP Site
1089 and core PS2821-1) recovered from the Subtropical
Front (STF) in the South Atlantic. The resulting sub-millennial resolution SST record covered last 160 ka and documented the presence of strong, Dansgaard-Oeschger type
climatic instability during MIS 3 –4. Rapid cooling episodes
(‘‘Younger Dryas-type’’ and ‘‘Antarctic Cold Reversaltype’’) have been recognized for both Termination I and II.
[6] Planktonic and benthic stable isotopic records (G.
bulloides and Cibicidoides d13C and d18O) are available
for ODP Site 1089 [Hodell et al., 2003a], and their
paleoceanographic interpretation has been discussed in a
series of closely related papers. Ninnemann and Charles
[2002] analyzed benthic foraminiferal oxygen and carbon
isotopic records in cores close to Site 1089. They concluded
that the substantially lower values of d 13C Cibicidoides in
the glacial Southern Ocean indicate not only a reduced
NADW input to this area during glacial periods, but also a
different mode of Southern Ocean deep water formation.
Hodell et al. [2003b] further suggested, on the basis of
benthic d 13C records from Sites 1088, 1089 and 1090, that
during glacial times, a chemical divide existed in the
Southern Ocean, separating well-ventilated water above
2500 m from poorly ventilated water below. Mortyn et al.
[2002] discussed, by means of d 18O and d 13C measured on
different species of planktonic foraminifera, the surface
water structure over two glacial terminations in the Atlantic
close to Site 1089. They concluded that the glacial subantarctic was less thermally stratified than it is today.
[7] In this paper, we extend down to 430 ka the
previously published radiolarian-based SST estimates for
the spliced Site 1089 and PS2821-1 cores, covering last
160 ka [Cortese and Abelmann, 2002]. The time series
produced represents a high-resolution climatic record of last
five glacial-interglacial cycles located at the boundary
between two oceanic regions: the subtropical Indian Ocean
and the subantarctic Atlantic Ocean (Figure 1). The analysis
of the SST record at this site thus provides clues both about
local climatic changes, and those occurring in other regions
(Agulhas Retroflection, subantarctic SW Pacific, North
Atlantic). The sensitivity of this location to various climate
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change mechanisms is due to its proximity to the Subtropical Front, where strong atmosphere/ocean interactions take
place, and to the marked influence of the Atlantic/Indian
Ocean water exchange through the Agulhas spillage.
[8] We will first discuss the SST record at Site 1089 in
terms of its general pattern, the main events recognized, and
the structure of Terminations, and then compare it to other
climatic proxies from both other oceanic cores and from
Antarctic ice cores. The comparison between oceanic,
transfer function-derived paleoSST from a Subantarctic site
and the deuterium excess record from the Vostok ice core
allows us to investigate the controls on the Subantarctic SST
history, and recognize possible shifts in the moisture source
locations for East Antarctica.
[9] We revise the age models for Sites 1089 and 980, as
well as for core MD97-2120, and will then compare our
SST reconstruction to similar climatic records from the
Agulhas region (core MD96-2080), the southwest Pacific
(core MD97-2120, DSDP Site 594 and ODP Site 1125),
Antarctica (EPICA Dome C ice core), and the North
Atlantic (Site 980) (Figure 1).
2. Material and Methods
[10] Site 1089 (ODP Leg 177) and piston core PS2821-1
(RV Polarstern cruise ANT XIV/3) are located beneath the
South Atlantic Subtropical Front (40°560S; 9°540E, 4620 m
water depth and 40°570S; 9°530E, 4575 m water depth,
respectively, Figure 1). In order to avoid core sections
possibly affected by drilling disturbances, the topmost
8.5 meters of piston core PS2821-1 were used instead of
the corresponding portion of Site 1089 [Cortese and
Abelmann, 2002]. We also discuss results from three
additional sites for which a detailed reconstruction of the
palaeoclimate evolution over several glacial-interglacial
cycles is available. Site 980 [McManus et al., 1999] is
located in the North Atlantic, core MD96-2080 [Rau et al.,
2002] in the southeast Atlantic and core MD97-2120
[Pahnke and Zahn, 2005] in the southwest Pacific.
[11] Radiolarian-based SST estimates at Site 1089 were
previously presented by Cortese and Abelmann [2002] for
the topmost 24.49 mcd (meters composite depth), covering
last 160 ka. In this paper, we extend that record to 67.57 mcd,
corresponding to an age of 430 ka. A total of 484 levels in
the cores, at an average spacing of 14 cm, were sampled. The
average time resolution is 900 years, decreasing to a few
hundred years close to Terminations I and II.
[12] Radiolarian slides were prepared according to standard laboratory techniques [Abelmann et al., 1999]. A Zeiss
Axioskop microscope, at 160 magnification, was used to
determine the relative abundance of radiolarian species, by
counting an average of 470 specimens for each slide. The
software packages PaleoToolBox and MacTransfer [Sieger
et al., 1999] were used to run Q-mode Factor Analysis
[Imbrie and Kipp, 1971] on radiolarian census data. Details
on oceanographic data, statistical properties of the reference
data set, and regression equation have been presented
elsewhere [Cortese and Abelmann, 2002].
[13] Improved age models have been developed only for
those sites having a benthic d18O record. The age model for
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Site 1089 (Figure 2) was obtained by correlating the
Cibicidoides d 18O signal from this Site [Hodell et al.,
2003a] to the stack of benthic d18O records of Lisiecki
and Raymo [2005]. The correlation coefficient between the
stack and the Site 1089 Cibicidoides d18O record was 0.94.
The age model for the other core we used for comparison
(Site 980), has also been developed by correlation to the
Lisiecki and Raymo [2005] stack. We decided not to tune
the age model of core MD97-2120, a Pacific Sector core
used for SST comparisons, to our Site 1089 record by peak
to peak correlation between the two SST curves (if this were
done, the correlation coefficient would be 0.75). Instead,
in order to minimize artificial phase shifts, we used the fixed
age points used by Pahnke et al. [2003] as a starting point
for correlation, and added a few additional tie-points,
resulting in a maximum shift between the two records of
less than 3 ka over the last 350 ka.
[14] In order to improve the quality of correlation between
marine and ice core records, we plotted all data (dD,
DTsource, DTsite) from the Vostok ice core on the EPICA
Dome C (EDC II) age model [EPICA Community Members,
2004], which is quite comparable to the Lisiecki and Raymo
[2005] stack, at least during the past four climate cycles. By
doing so, we avoided the occurrence of artificial phase shifts
between ice and sediment cores arising from different
chronologies. As an example, when comparing the GT4
[Petit et al., 1999] and EDC age models for the Vostok ice
core by correlation of the dD record of this core plotted on
the two age scales (r = 0.98), the age assignment of a given
depth in the Vostok core can shift by as much as 15 kyrs
over last 450 ka. Further information on the development of
both the marine and ice core age models used in this paper
can be found in auxiliary material Figures S1– S31.
[15] The Arand software package (P. Howell, Arand software, 1995, freely available from http://pixie.geo.brown.edu/
esh/paleo/arand/arand.html) was used to perform Cross
Spectral Analysis and to calculate covariance/phases of the
time series, while the program AnalySeries [Paillard et al.,
1996] was used to correlate between cores. For cross-spectral
analysis (80% confidence interval error bar), time series were
normalized to unit variance and equally resampled (1 ka
sampling interval). The analysis (Figure 3 and Tables 1a and
1b) covered the last 436 ka, and used 131 lags (corresponding
to 30% of the series length) and a Bartlett window. A
maximum entropy analysis (30% lags) was also applied to
the same time series in order to better identify the position
of spectral peaks along the frequency scale.
3. Results
3.1. Palaeo-SST Reconstruction
[16] Today’s summer SST above Site 1089 (Figure 2)
averages 15.7°C, as interpolated from World Ocean Atlas
data [Conkright et al., 2002] for the months of December –
March. The radiolarian-based SST estimates, having a
standard error of estimate of 1.2°C [Cortese and Abelmann,
2002], match this value very well, as they predict 15.1°C at
1.8 ka (our youngest sample).
1
Auxiliary materials are available in the HTML. doi:10.1029/
2007PA001457.
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Figure 2. Radiolarian IKM SST, d18O G. bulloides, d 18O and d13C Cibicidoides (in % deviation from
the Pee Dee Belemnite standard), summer solstice insolation at 30°S (in Watt m2). The climatic optima
for each glacial cycle are boxed. Today’s SST (15.7°C) at Site 1089 location is marked as a dashed line.
Marine Isotopic Stages (MIS) are shown on top, boundary ages according to Lisiecki and Raymo [2005].
The numbers at the bottom represent the approximate length (in ka) of interglacial optima. Blue arrows
indicate d13C Cibicidoides minima right after climatic optimum conditions during interglacials. Important
climatic events recognized at core site MD96-2080 [Rau et al., 2002] are also shown: Globorotalia
menardii accumulation rate peaks at 22, 139, and 258 ka (red arrows), and relative abundances of
Neogloboquadrina pachyderma (dextral) higher than 20% (blue horizontal bars), see text for discussion.
The North Atlantic cooling event C21, at 82– 85 ka (terminology after Chapman and Shackleton [1999])
is also highlighted.
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CORTESE ET AL.: ODP SITE 1089 SST RECORD OVER LAST 450 ka
Figure 3. Blackman-Tukey cross spectra (power, coherency, and phase) for Site 1089 SST and d 18O Cibicidoides.
The input options were as follows: 437 samples, 131 lags
(30% of series length), Bartlett Window filtering, 80%
confidence interval, series normalized to unit variance and
equally resampled at 1 ka interval. The periods of the main
peaks (vertical dashed lines) are shown on top. The 80%
confidence interval error bars are plotted on the Coherence
and Phase diagrams. The two bottom plots are power
density spectra for a maximum entropy analysis (30% lags)
carried out on the same time series, in order to better
identify the position of spectral peaks along the frequency
scale, as this technique has better resolution (but lower
confidence) compared to the Blackman-Tukey technique.
Pie diagrams show the phase relationship, in the eccentricity, obliquity, and precession band, between SST, d 18O
and d 13C G. bulloides, d 18O and d13C Cibicidoides, and
CaCO3%. The data used to construct these diagrams are
also shown in Tables 1a and 1b.
[17] The palaeo-SST record displays the last five glacial
to interglacial terminations, each having a magnitude of 6°–
7°C. We also observe during intervals between 20– 70 ka
(MIS 2 – 4) and 140 – 190 ka (MIS 6) rapid warming
episodes (3° – 5°C in amplitude) similar to the DansgaardOeschger events (D/O), recognized in Greenland ice cores
and in North Atlantic oceanic records [Martrat et al., 2007].
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A similar high temperature variability during glacial intervals has also been recently documented for the EPICA
Dronning Maud Land ice core [EPICA Community Members, 2006], with warm episodes during MIS 3
corresponding to cold events in Greenland.
[18] At Site 1089 (Figure 4), climatic optima generally
take place during the initial part of each interglacial interval.
However, the past five interglacials display a wide range of
duration and amplitude: the climatic optima of MIS 1 and 7
are similar, both 2°C warmer than present and 5 to 7 ka
long, while MIS 9 and 11 are 3.5°C warmer and 9 to 22 ka
long. The MIS 5 optimum is intermediate both in temperature (3°C warmer) and duration (6 ka).
[19] Another characteristic feature of our paleoclimatic
record is the occurrence of cooling rebounds at glacial
terminations. These events are present at all last five
Terminations, indicating how their occurrence is not limited
either spatially (to the North Atlantic), or temporally (to last
Termination: MIS 2 to MIS 1).
[20] Our record starts at the transition between MIS 12
and 11, and the first two glacial periods (MIS 10 and 8)
display relatively warm and stable conditions, compared to
the highly variable MIS 2 – 4 and 6. The latter two glacial
intervals, in fact, have colder average temperatures compared to MIS 8 and 10, but display a marked short-term
climatic variability, with sudden, bundled oscillations in
temperature. Anomalously high temperatures for a glacial
interval characterize MIS 10, as they fall in the range of the
highest temperatures reached during two later interglacials
(MIS 1 and 7). Termination III (at 240 ka), although
similar to the two previous ones in its duration, the presence
of a cooling event, and the attainment of a climatic optimum
during its earliest part, introduces a very short-lived optimum, as temperatures quickly drop to values 3°C colder
than today. MIS 2, the last glacial interval, exhibits the
coldest temperatures of our record (11°C). Another noticeable and recurrent feature of the climatic evolution at
Site 1089 is the regular occurrence of sharp d13C Cibicidoides decreases directly after the attainment of highest SST
at the beginning of interglacial periods (Figure 2).
3.2. Early SST Response at Terminations
[21] Cross-spectral analysis between SST and ocean circulation, global ice volume and surface hydrography proxies
(d13C, d 18O Cibicidoides and d18O/d13C G. bulloides,
respectively) from Site 1089, allows us to recognize a lead
of the surface hydrography signal compared to the global ice
volume signal: the first major increase in SST at Terminations
at this Southern Ocean location leads (Figures 3 and 4 and
Tables 1a and 1b) global ice volume decrease (as recorded by
d18O Cibicidoides peaks measured from the same core) by
1 – 9 ka [Ninnemann and Charles, 1997; Hodell et al.,
2001].
[22] Cross-spectral analysis of the SST and d 18O Cibicidoides signals over the last 436 ka at Site 1089 indicates a
lead of SST by 4.7 ± 3.7 ka (in the eccentricity frequency
band), 6.9 ± 2.5 ka (obliquity), and 2.7 ± 0.9 ka (precession). Similar values for the lead of SST over d 18O Cibicidoides (4.9 ± 1.9 ka, 1.6 ± 1.6 ka, 3.0 ± 1.1 ka for the
eccentricity, obliquity, and precession band, respectively)
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Table 1a. Summary of the Blackman-Tukey Cross-Spectral Analysis Applied to SST and d 18O Cibicidoides: Cross-Spectral Significant
Peaks (80% Confidence Level)a
Frequency
Period, ka
Power SST
Power Cibs
Coherence
Phase, rad
Phase, deg
Phase, ka
0.0090
0.0230
0.0335
0.0445
0.0655
111.1
43.5
29.9
22.5
15.3
62.96
23.22
25.92
9.44
7.36
14.69
6.75
2.27
1.77
0.26
0.85
0.69
0.81
0.84
0.68
0.27
1.03
0.80
0.73
1.60
15.3
59.1
45.9
41.9
91.8
4.7
7.1
3.8
2.6
3.9
a
See methods paragraph in section 2 and Figure 3 caption for input options. The first five significant peaks (80% confidence level) are reported, along
with their frequency, period, power, and phase (in radians, degrees, and ka). The bottom half of the table shows the coherency (k), phase, and error (in
degrees (phi) and ka) for SST and d18O Cibicidoides for the three main orbital frequencies.
were obtained by Becquey and Gersonde [2003] for core
PS2489, from the Subantarctic. The shorter lead recognized
by these authors in the obliquity band (0 – 3 ka compared to
5 – 9 ka in our study) might be related to a more ‘‘polar,’’ and
therefore more affected by obliquity, character of the PS2489
record as this core is located in the southern Subantarctic,
compared to the almost subtropical location of Site 1089,
where the fastest response is in the precession band.
[23] During terminations, ocean circulation, surface hydrography, and global ice volume proxies from Site 1089
suggest that the SST increase is roughly synchronous to
increases in the benthic d13C signal and both lead the global
ice-volume signal by 1 – 9 ka.
4. Discussion
4.1. Surface Hydrography Changes Prior to
Glacial Terminations
[24] At the past five terminations (Figures 3 and 4), Site
1089 SST leads d 18O Cibicidoides (global ice volume
proxy) by 4.7 ± 3.7 ka in the eccentricity frequency band,
6.9 ± 2.5 ka (obliquity), and 2.7 ± 0.9 ka (precession). This
is an indication of early warming of the surface ocean prior
to glacial terminations at this subantarctic South Atlantic
location, as SST rose substantially at subantarctic latitudes
before any considerable continental ice volume change was
recorded. The importance of the lead, and freshwater fluxes
into the Southern Ocean, has already been stressed [Seidov
et al., 2001], and a similar early response at terminations
occurs in the California Current (East Pacific), at subtropical/subboreal latitudes [Herbert et al., 2001], at subantarctic latitudes [Charles et al., 1996; Labeyrie et al., 1996;
Brathauer and Abelmann, 1999], in the eastern tropical
Atlantic Ocean [Schneider et al., 1995], in the SW Africa
upwelling system [Kim et al., 2002], and in the Polar and
Antarctic Zone as well [Kunz-Pirrung et al., 2002; Bianchi
and Gersonde, 2002, 2004]. In the California Current region
SST increases several kyrs in advance of deglaciation at past
glacial maxima [Herbert et al., 2001], suggesting that the
surface ocean responded faster than continental ice sheets to
an external climatic agent, for example, solar activity
changes, sea-ice retreat, atmospheric CO 2 decrease
[Shackleton, 2000].
[25] The early warming of the surface subantarctic Atlantic
waters [Charles et al., 1996], deep Pacific, and surface eastern
tropical Pacific, was synchronous with early warming over
Antarctica and the Southern Ocean [Spero and Lea, 2002]. The
connection between North Pacific and subantarctic Southern
Ocean is also confirmed by modeling studies indicating a
stronger AAIW ventilating the North Pacific during glacial
times [Campin et al., 1999] and by the observation that deep
Pacific Ocean warming, possibly linked to early warming in
Antarctica, preceded major deglaciation, ice sheet melting, and
sea level rise [Mix et al., 1999].
[26] The similar early warming response at terminations
at subtropical/subantarctic latitudes (California Current and
Site 1089) might represent a quick response of intermediate
water formation to atmospheric processes. This sensitivity
could derive from strong interactions between atmosphere
cells and oceanic fronts at these latitudes, acting as powerful
climatic feedback mechanisms.
[27] The transfer mechanism of rapid climate change
would be mixed, both atmospheric and oceanic: the climate
signal (e.g., the temperature rise during a termination) may
originate, by direct radiation forcing, in the tropics, an area
particularly prone to strong circulation reorganizations
[Pierrehumbert, 2000], be transported via oceanic circulation or via the atmosphere to the Southern Ocean, and from
there, probably through the ventilation of intermediate
waters [Pahnke and Zahn, 2005], to the rest of the world
(e.g., North Atlantic). The surface hydrography lead in our
record probably documents one of the early stages of this
chain of events, as it integrates the oceanic transport out of
Table 1b. Summary of the Blackman-Tukey Cross-Spectral Analysis Applied to SST and d 18O Cibicidoides: Phase Between SST and
d 18O Cibicidoides at Orbital Frequenciesa
1/100 kyr1
1/41 kyr1
1/23 kyr1
SST Versus
k
phi
ka
k
phi
ka
k
phi
ka
d 18O Cibicidoides inv
d 18O G. bulloides inv
d 13C Cibicidoides
d 13C G. bulloides
CaCO3%
0.84
0.82
0.74
0.76
0.73
17,1 ± 13,2
19,6 ± 14,1
19,1 ± 18,7
35,7 ± 17,7
105,8 ± 19,2
4,7 ± 3,7
5,5 ± 3,9
5,3 ± 5,2
9,9 ± 4,9
29,4 ± 5,3
0.69
0.72
0.73
0.61
0.75
60,3 ± 21,7
48,4 ± 19,9
41,2 ± 18,9
70,4 ± 26,7
27,7 ± 17,9
6,9 ± 2,5
5,5 ± 2,3
4,7 ± 2,1
8,0 ± 3,0
3,2 ± 2,0
0.82
0.72
0.70
0.78
0.63
42,1 ± 14,1
23,6 ± 19,6
44,1 ± 20,8
83,6 ± 16,1
7,6 ± 25,5
2,7 ± 0,9
1,5 ± 1,3
2,8 ± 1,3
5,3 ± 1,0
0,5 ± 1,6
a
See footnote for Table 1a.
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Figure 4. Detail of the SST (in black, this paper) and d 18O Cibicidoides (in gray [Hodell et al., 2003a])
evolution at Site 1089 during last five terminations. Cooling events at terminations are highlighted (gray
boxes), while Marine Isotopic Stage numbers, according to the Lisiecki and Raymo [2005] chronology,
are indicated in bold.
the tropics (as the location is affected by the Agulhas
Spillage, having its sources at low latitudes in the Indian
Ocean) and the ensuing atmospheric transport to high
latitudes (regulated by changes in moisture sources to
Antarctica, following changes in the position of the STF).
4.2. Cooling Rebounds at Terminations
[28] Our Southern Ocean record shows coolings at each
of the last five glacial terminations (Figure 4). Their causes
reappear at each deglaciation event, and are not necessarily
linked to the occurrence of meltwater discharges in the
North Atlantic [Clark et al., 2001]. These cooling rebounds
are not present at all terminations in ice core dD-derived
temperature records from Antarctica (they appear only at
Terminations I and V, Figure 5: DTsite curve), but they are
present at each termination in deuterium excess records
from Vostok (Figure 5: DTsource curve). This is because this
signal also incorporates the oceanic signature of lower
latitudes, specifically from the source areas for the moisture
precipitating in Vostok. They have also been recently
documented for some of the last four terminations in a
record (MD97-2120) from the subantarctic zone of the
southwest Pacific [Pahnke and Zahn, 2005], they are also
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record has a slight trend toward decreasing average glacial
SSTs, with pre-Termination III (at 250 kyr) glacial baseline values in MIS 8 and 10 being higher compared to later
glacial intervals. Interestingly, the amplitude of the d13C
Cibicidoides signal also decreases sharply after Termination
III, and glacial baseline values are higher during later
glacials (Figure 2), an indication of stronger deep-water
ventilation in the Cape Basin during the older half of our
record, both during glacials (by CDW) and interglacials (by
NADW).
[32] Nannofossils also suggest very different oceanographic conditions at Site 1089 in the time interval older
than 250 ka [Flores et al., 2003]. The assemblage suddenly
becomes dominated by Gephyrocapsa caribbeanica, which
frequently reaches 75% of the nannofossil flora from its
Last Common Occurrence (249 ka) to its First Common
Occurrence (540 ka). As this species is strongly calcified
and represents a warm-water and oligotrophic indicator
Figure 5. Comparison between SST record of Site 1089
and DTsource, DTsite and their gradient from the Vostok ice
core, as derived [Vimeux et al., 2002] from deuterium and
oxygen isotopes. Vostok data are plotted on the EPICA
Dome C (EDC) timescale [EPICA Community Members,
2004]. Arrows mark the approximate position of cooling
rebounds at glacial terminations.
visible at Sites 1093 and 1094 located south of the APF in
the Atlantic Sector [Kunz-Pirrung et al., 2002; Bianchi and
Gersonde, 2002, 2004], and could therefore be a Southern
Ocean feature. The position of the STF (both our and the
MD97-2120 records are located just south of it), together
with the prevailing wind field and current systems (like the
Agulhas Spillage in the South Atlantic) and local meltwater
pulses [Weaver et al., 2003], could play a major role in the
expression of these cool events during terminations.
[29] Such perturbations of the wind system, and in particular the location of the westerlies belt, took place during
the last glacial (and presumably during earlier glacial times
as well), and were associated with a northward movement
of up to 5° latitude of the oceanographic fronts around
Antarctica [Gersonde et al., 2003a, 2003b, 2005].
[30] Additional perturbations of the oceanic circulation
occur a few kyr after terminations at Site 1089. These
manifest as sharp decreases in the d 13C of Cibicidoides
following the attainment of optimum temperatures at the
beginning of interglacial periods. These anomalies (arrows,
Figure 2) were also recognized in the southwest Pacific (core
MD97-2120: [Pahnke and Zahn, 2005]), and interpreted as
regionally (Southern Ocean-) forced ventilation minima.
4.3. Diverging Climatic Trends at 250 ka
[31] The duration of the climatic optimum at interglacials
shortens through time (Figure 6). At the same time, the SST
Figure 6. Comparison between the SST records of Sites
980 and 1089, MD97-2120 (see Figure 1 for core positions),
and the dD record for the Vostok ice core. Data sources are
as follows: Site 980 [McManus et al., 1999], MD97-2120
[Pahnke and Zahn, 2005], Vostok ice core [Petit et al.,
1999]. Age models for Sites 980 and 1089 have been
developed by correlation of their benthic d 18O signal to the
Lisiecki and Raymo [2005] stack, while the Vostok dD
record is plotted on the EPICA Dome C (EDC) timescale
[EPICA Community Members, 2004]. Core MD97-2120 has
been synchronized to Site 1089 by correlation of the two
SST records, starting from the tie-points published by
Pahnke et al. [2003]. See auxiliary material Figures S1 – S3
for further information on age models development. The
long-term glacial baseline trend in SSTs (dashed line) is
indicated for Site 1089.
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Figure 7. Cartoon of the main climatic mechanisms in the study area during normal interglacial and
glacial conditions, and during MIS 10 (warm water anomaly at Site 1089).
[Flores et al., 2003], their findings support our hypothesis
for a stronger influence of the Agulhas Current into the
Cape Basin earlier than 250 ka. A strong change in surface
water conditions in the southeast Atlantic (warmer waters
and more clearly defined glacial-interglacial cycles), based
on shifts in planktonic foraminiferal assemblages and sediment composition, has also been found at approximately
200 – 250 ka in core MD96-2080 [Rau et al., 2002], and
linked by these authors to a decreased intensity of Agulhas
ring shedding and associated subantarctic (cold) water
intrusions. The more sustained periods of high SSTs during
glacial times earlier than 250 ka at Site 1089 would thus
indicate a stronger Agulhas influence into the subantarctic
during this time compared to later glacials.
[33] We moreover report elsewhere [Cortese et al., 2004]
the presence of an episode of warmer than expected SSTs at
Site 1089 during the MIS 10 glacial stage. During this
interval, glacial boundary conditions (stronger trade winds
and upwelling, driven by intensified atmospheric and oceanic gradients) correspond to a stronger than usual Agulhas
Current and a more southern position of the STC (Figure 7).
This episode is already ‘‘forecast’’ by the particularly high
DTsource values during MIS 10 at Vostok, which indicate
that the moisture source region was also experiencing a
strong warming (or migrated to lower latitudes), thus
feeding the Agulhas Current with warmer than usual waters
for a glacial interval. In particular, MIS 10 (anomalously
warm for a full glacial) would be an example of a strong,
prolonged Agulhas spillage event, overriding the normal
glacial-interglacial cycle.
4.4. Teleconnections and Changes in the Agulhas
Retroflection
[34] Our SST record displays strong similarities, both on
orbital and millennial scale, with a Mg/Ca-derived SST
record (core MD97-2120) from the Pacific Sector, just south
of the Subtropical Front [Pahnke et al., 2003] (Figure 6).
These similarities concern the large amplitude (up to 8°–
9°C) of Terminations, the length and relative intensity of the
last four interglacial optima, the occurrence of cooling
events during the last portion of each termination, and the
very strong variability and marked warmings occurring
during the ‘‘glacial half’’ of each climatic cycle. The
detailed evolution of each climatic cycle (i.e., the relative
magnitude and timing of rapid warmings occurring over the
general cooling trend of each cycle) also matches very well
between these two widely separated records. Another common trait between Site 1089 and core MD97-2120 is the inphase behavior of SST and d 13C Cibicidoides (Figure 2):
most positive SST excursions tend to coincide with higher
d13C values. The reason is that at orbital and millennial
scale the SST record of core MD97-2120 is strongly
influenced by the intensity of Antarctic Intermediate Water
ventilation, and higher SST values generally coincide with
heavier benthic d 13C [Pahnke and Zahn, 2005].
[35] However, the benthic d13C record of core MD972120 is affected by AAIW, while Site 1089 reflects changes
in the properties of Circumpolar Deep Water (CDW)
[Hodell et al., 2003a]. Interestingly, in both cores SST
and benthic d13C are covarying at an orbital scale, but there
are many exceptions to this coupling at a millennial scale,
particularly during glacial intervals. This could represent a
decoupling between the reaction of intermediate (AAIW)
and deep (CDW) water masses at mid-Southern Hemisphere
latitudes to a cooling in the North Atlantic. The interpretation of the benthic d 13C record in terms of intermediate/deep
water mass ventilation and the exact synchronization of
chronologies for different oceanic cores is problematic.
However, it can be interesting to analyze what happens in
different areas during a prolonged cold episode in the North
Atlantic. In order to do so, we synchronized the two SST
curves from core MD97-2120 and Site 1089 (two sites with
good SST and benthic d 13C records, indicative of intermediate and deep water conditions in the Southern Ocean,
respectively) to within 3 ka over the last 350 ka.
[36] We then chose a particularly long-lasting cooling
event occurring during last glacial cycle in the North
Atlantic (C21, at 82– 85 ka, terminology after Chapman
and Shackleton [1999]), in order to minimize the possibility
for real or artificial (due to dating uncertainties) phase shifts
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between the different proxies. The C21 event corresponds to
a peak in ice-rafted debris (IRD) abundance and a major
drop in benthic d 13C in the North Atlantic (core NEAP18K,
Chapman and Shackleton [1999]), and correlates well with
higher SST and higher benthic d13C in core MD97-2120
[Pahnke and Zahn, 2005, Figure 2]: a perfect example of
the bipolar seesaw [Stocker and Johnsen, 2003], with
meltwater presence in the North Atlantic, sluggish NADW,
and lower SST in the North Atlantic corresponding to
increased AAIW production and higher SST in the southwest Pacific. The same time interval corresponds, at Site
1089 (Figure 2), to a strong SST peak (indicative of a
regional, Southern Ocean response in surface waters), but
with a marked minimum in benthic d13C (weaker CDW in
the Atlantic, contrasting with a stronger AAIW in the
Pacific, and therefore decoupling between intermediate
and deep water masses responses to this cooling event in
the North Atlantic). Another line of evidence confirming
linkage between bottom water (AABW) overturn and glacial-interglacial climate in the Southern Ocean, at least at an
orbital scale, comes from the study of the silt/clay ratio and
sortable silt content of Site 1089 [Kuhn and Diekmann,
2002]: higher values of these two variables, both indicative
of stronger deep water activity, are generally associated with
interglacial, warm SSTs. No millennial-scale variability was
however detected by these authors in their sortable silt
record.
[37] The amplitudes of SST changes at terminations at
Site 1089 (6°– 7°C for last five terminations) are very
similar to what was found by Schäfer et al. [2005] at the
Subtropical Front, in the southwest Pacific: the amplitudes
throughout the last 1 Myr were always greater south (5°–
14°C) of the STF than north (2°– 7°C) of it, with a trend
toward increased amplitudes south of the STF from the
early to late Pleistocene. Very similar results were obtained
for the warm peaks during the last five interglacials: 2°–
3.5°C warmer than present at Site 1089, and 2°– 4°C
warmer than present at DSDP Site 594. Schäfer et al.
[2005] also suggest that the STF did not migrate north of
its present location during glacials, owing to the frontal
system being locked to a submarine high: the Chatham Rise.
Instead, they argue for an intensification of the temperature
gradient across the front. A similar mechanism can also be
assumed for the Cape Basin, where the Agulhas Plateau
bounds the position of the STF.
[38] The strong glacial to interglacial SST shifts at terminations we document for the last 450 ka at Site 1089 have
also been recognized, on the basis of foraminiferal assemblages, at core site MD96-2080, located leeward of Agulhas
Bank [Rau et al., 2002]. The establishment of warmer
conditions in the SE Atlantic and southward movement of
the STF, clearly seen in the rapid SST increase at terminations at the Site 1089 location, is occurring at times of
maximum surface water leakage from the Indian Ocean at
the last three glacial terminations, as demonstrated by the
occurrence of Globorotalia menardii accumulation rate
peaks at 22, 139, and 258 ka (Figure 2, red arrows) at core
site MD96-2080 [Rau et al., 2002]. At the latter location,
higher relative abundances of Neogloboquadrina pachyderma (dextral), indicative of peaks in the subantarctic
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assemblage, represent instead cold water incursions (abundances higher than 20% are reported as blue horizontal bars
in Figure 2) over the Agulhas Bank during glacials. The
most marked event recorded by Rau et al. [2002] in this area
is a shift at 200– 250 kyr: a mixed northern subantarctic/
transitional surface water mass with limited variability
on glacial-interglacial cycles during the MIS 12-7 interval
is replaced by warmer conditions and more pronounced
glacial-interglacial fluctuations. While this change (see
section 4.3) and the more pronounced cyclicity starting at
250 kyr are also noticeable at Site 1089 (glacial SSTs are
much higher earlier than this turning point compared to
later, see Figure 2), the climatic evolution of our record is
opposite to the one of core MD96-2080, as glacial intervals
at Site 1089 become colder (rather than warmer) and less
variable later than 250 kyr. This different climatic evolution
indicates a change in the functioning of the Agulhas
Retroflection, affecting the northern and southern sides of
the STF in opposite ways, and stronger ring shedding
intensity during glacials earlier than 250 kyr. This would
cause colder conditions north of the STF (cold-core Agulhas
rings from the south, core MD96-2080), and warmer conditions south of it (warm-core Agulhas rings from the north,
Site 1089).
4.5. Climate Mechanisms
[39] In summary, the available records of climatic evolution over the last four to five climatic cycles at several
locations in the ocean (north and south of the STF, both in
the Atlantic and Pacific Sectors of the Southern Ocean)
display strong similarities both at the orbital scale, and in
the detailed variability during glacial intervals, deglaciations, and interglacial climatic optima. These similarities
can be explained by the strong influence of the STF at all
these locations, while the remaining differences are due to a
variety of climatic mechanisms having local importance for
some of them (see above and also detailed discussions by
both Schäfer et al. [2005] and Rau et al. [2002]): Agulhas
warm-core (Site 1089) and cold-core (MD96-2080) eddy
shedding, bottom-topography bounding of the STF
position (Site 1125, MD96-2080), incursions of CDW
(DSDP Site 594) and SAW (Site 1125), waning of the
warm East Cape Current (Site 1125).
[40] The SST record [McManus et al., 1999] from Site
980 (North Atlantic, Feni Drift) also displays several
features in common with the SST record of Site 1089. This
concerns, in particular, the presence of very warm events
(higher than half full interglacial SST values) and sustained
intervals of warm temperatures during full glacial periods,
as well as an interval of extremely high SSTs centered
around 350 ka, comparable to the Site 1089 MIS 10 warm
anomaly [Cortese et al., 2004].
[41] The similarities between some of Vostok climatic
indicators (DTsource and DTsite) and Site 1089 SSTs would
suggest a connection between the subantarctic ocean and
Antarctic continent, in the form of moisture exchange, as
indicated by models [Delaygue et al., 2000]. The similarities to the southwestern Pacific (MD97-2120), and North
Atlantic Ocean (Site 980) records imply further oceanic
connection mechanisms. This suggests how the climatic
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variability of these widely separated areas can be coupled
and covarying at millennial timescales (a few to 10 ka
periods), and changes in the intensity of some processes
(THC, modulation of Agulhas Current intensity and ring
shedding, changes in STF position and strength, wind fields
reorganizations during glacials and terminations) have the
potential to link the climate response at these locations.
[42] The matching features between our SST record from
Site 1089 and the one from core MD97-2120 (its counterpart in the southwest Pacific, as it is also located just south
of the STF) provide indication that the super-regional
expression of the observed climatic events (terminations,
coolings at terminations, warmings during glacial cycles,
etc.) should be substantially affected by a single climatic
agent. The most likely candidate for such a role, as both
core locations lie just to the south of its modern average
position, is the Subtropical Front, a very marked boundary
in the ocean and also of strong significance for atmospheric
circulation, which may act as both an amplifier and a
vehicle for the transfer of climatic change between different
regions (e.g., Atlantic, Indian, Pacific Sectors of the Southern Ocean, and teleconnections to both Antarctic and
Greenland ice sheets). This extraregional connection between mid- and high-southern latitudes has been already
proposed on the basis of oceanic records [Pahnke et al.,
2003], and is also becoming established thanks to deuterium
excess studies, both for the northern and southern hemisphere [Johnsen et al., 1995; Masson-Delmotte et al., 2005;
Vimeux et al., 1999, 2001a, 2001b].
4.6. Deuterium-Excess Link: Ice and Marine
Records Come Together
[43] The EPICA Dronning Maud Land (EDML) ice core
d 18O record [EPICA Community Members, 2006] is a proxy
for local temperature on the Antarctic ice sheet. Its overall
pattern closely resembles that recorded in most Antarctic ice
cores covering the same time period (e.g., r2 = 0,94 for the
correlation between EDML d18O and the EPICA Dome C,
EDC hereafter, dD records over the last 150,000 years).
Owing to this excellent correlation, and as deuterium excess
measurements are not yet available for the last 450 ka from
EDML, we will in the following center our discussion on
the results from the EDC and Vostok ice cores.
[44] Delaygue et al. [2000] demonstrated by GCMs that
the moisture source for coastal sites is mostly located in the
high-latitude belt of the Southern Ocean, while plateau
locations (EDC, Vostok, Dome Fuji) would receive moisture from more distant sources, mostly at subtropical
latitudes, in the Indian Ocean. Additionally, moisture source
areas change over climatic cycles and affect the deuterium
excess signal: the source of moisture for precipitation in
Antarctica is located at lower, warmer latitudes during
glacial intervals, when the expanded sea-ice cover around
Antarctica limits the moisture contribution from high, cold
southern latitudes, and the opposite is true during interglacials [Masson-Delmotte et al., 2005].
[45] However, it is still possible to compare the Vostok
source temperature signal with oceanic SSTs over a short
time interval, assuming that during that period sources
remained fixed at a given latitude. Traces of shifts in
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moisture sources and rearrangements of large-scale atmospheric systems are found in our oceanic paleotemperature
record. In fact, DTsite and Site 1089 SST are positively
correlated (Figure 5), probably since warmer conditions
imply a more southward placed frontal system, weaker
gradients, and therefore stronger Agulhas input to the
Atlantic (which is recorded at Site 1089). This condition
is typical for interglacial periods, while glacials display the
opposite pattern.
[46] At orbital timescale, Site 1089 SST closely follows
(Figure 5) the DTsite record of Vostok, as one can easily
correlate most of the features between these two records.
However, at suborbital/millennial timescale, glacial intervals and the part of the record older than 350 kyr display a
different pattern, as SSTs correlate better to the Vostok
DTsource DTsite gradient during pre-full glacial times, and
to DTsource (particularly concerning the presence of warm
anomalies) during full glacials and the interval preceding
350 kyr. These intervals display, during glacial conditions,
warm SST maxima with amplitudes ranging from approximately one third to almost full interglacial values. The
presence and degree of expression of these warm SST
maxima during full glacial conditions at Site 1089 has
interesting climatic implications. In fact, this location should
also partly document changes in SST occurring in regions,
such as the midlatitude Indian Ocean, that represent both a
source of moisture for Vostok, as well as a source of surface
waters, advected through the Agulhas spillage, for the site
itself. However, particularly during full glacial stages 2 and 6,
the oceanic SST maxima, although still present, are relatively
minor compared to the reconstructed values for DTsource
[Vimeux et al., 2002]. There are several, some of them
concomitant, explanations possible for the lack of an even
better match between DTsource and Site 1089 SST.
[47] 1. The DTsource signal is of a composite nature,
representing the integration of several moisture sources,
themselves changing over climatic cycles. Part of this signal
is represented by a shift in the predominant moisture source
area, which is warmer during glacial times, due to the
extended winter sea-ice cover around Antarctica, effectively
blocking, at least during this season, moisture input to the
continent from higher latitudes. The DTsource values are
higher during full glacial conditions, and must be corrected
by taking into account the source shift (as done for Greenland by Masson-Delmotte et al. [2005]).
[48] 2. The warmer moisture source is an even more
relevant contributor to the precipitation on Antarctica during
glacial times, owing to more effective atmospheric transport
during glacials, deriving from higher meridional temperature gradients, as also seen in the coincident higher values
of the Vostok DTsource DTsite gradient.
[49] 3. The SSTs at Site 1089 are only indirectly influenced, via the mediation of the Agulhas Spillage, by
temperature changes occurring in the midlatitude Indian
Ocean. The very high and prolonged SST maxima during
glacial stages 8 and 10 may represent an indication of a
different functioning of the Agulhas spillage, with a more
direct connection between the prevalent moisture sources to
Antarctica (i.e., the midlatitude Indian Ocean) and the
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location of Site 1089 (as discussed for MIS 10 by Cortese et
al. [2004]).
[50] These observations would explain why our SST
record matches best the Vostok DTsource curve in the
interval older than 340 kyr, and suggest that the DTsource
‘‘glacial bump’’ is representative not only of a major shift
toward a warmer moisture source location for Antarctica,
but also of warmer than usual waters at low latitudes during
this time interval. The expression of this warm anomaly into
our Cape Basin oceanic record would be indicative of an
‘‘open’’ Agulhas Spillage, itself anomalous for a glacial
time (Figure 7). The general trend toward colder average
temperatures and increased climatic variability, with more
frequent, but subdued, interstadials during glacial intervals
going from MIS 10 to MIS 2 could then be interpreted as
the effect, in the study area, of a change in the Agulhas
Current regime, going from less to more restricted, with
more marked activity pulses during recent glacials.
5. Conclusions
[51] 1. The palaeo-SST record for the last 450,000 years
at Site 1089 records rapid temperature fluctuations during
both glacial and interglacial intervals.
[52] 2. Brief cooling episodes have been recognized for
all last five terminations, directly before the climatic optima
of the succeeding interglacials.
[53] 3. The interglacial climatic optima range from 2 to
3.5°C warmer than present, with a duration that can span
from as short as 5 ka (MIS 7) to as long as 22 ka (MIS 11).
[54] 4. The first major increase in SST at terminations
occurs 1 – 9 ka earlier than the decrease in global icevolume (4.7 ± 3.7 ka, 6.9 ± 2.5 ka, and 2.7 ± 0.9 ka in the
eccentricity, obliquity and precession bands, respectively),
and most likely corresponds to a stronger advection of
warmer waters from the subtropical Indian Ocean via the
Agulhas Current.
[55] 5. The SST record displays similarities to both
atmospheric (Vostok ice core) and oceanic records from
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the Southern Hemisphere (cores MD97-2120 and MD962080) and Northern Hemisphere (Site 980, Feni Drift),
indicating how climatic variability of widely separated areas
(the Antarctic continent, temperate North Atlantic and
subantarctic South Atlantic and South Pacific) can be
strongly coupled and covarying at millennial timescales.
[56] 6. Traces of processes (shifts of moisture sources,
rearrangements of large-scale atmospheric systems) affecting the deuterium excess signature of antarctic ice cores
have been found in our oceanic paleotemperature record.
The occurrence of warmer DTsite at Vostok in correspondence to warmer SST at Site 1089 suggests that warmer
oceanic/atmospheric conditions imply a more southward
placed frontal system, weaker gradients, and therefore
stronger Agulhas input to the Atlantic (which is recorded
at Site 1089).
[57] 7. A comparison between radiolarian- (Site 1089,
southeast Atlantic) and Mg/Ca-derived (core MD97-2120,
southwest Pacific) SSTs, the corresponding benthic d 13C
records, meltwater and NADW overturn proxies from the
North Atlantic supports the seesaw hypothesis: strong oceanic coolings in the North Atlantic correspond to warmings in
the surface waters of the northern subantarctic Southern
Ocean. However, while intermediate water (AAIW) ventilation seems to be anti-correlated with NADW intensity during
these events, the opposite seems true for deeper water masses
(CDW), suggesting a decoupled response between surface,
intermediate, and deep water masses.
[58] Acknowledgments. Core repository facilities (Geology Institute,
Bremen University for ODP cores and AWI, Bremerhaven for R/V ‘‘Polarstern’’ cores), are gratefully acknowledged. We would like to thank, for
their suggestions and comments, the editor (Gerald Dickens) and the final
reviewers: Øyvind Hammer and Chris Hollis, as well as Françoise Vimeux
for several interesting and helpful comments over a previous version of this
manuscript. Samples for this study were provided by the Ocean Drilling
Program (ODP), sponsored by the U.S. National Science Foundation (NSF)
and participating countries, under the management of the Joint Oceanographic Institutions (JOI). We thank Ute Bock, Ruth Cordelair, and Tanja
Pollak for providing laboratory assistance. This research was supported by
the DFG-Research Center ‘‘Ocean Margins’’ of the University of Bremen.
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A. Abelmann, G. Cortese, and R. Gersonde,
Alfred Wegener Institute for Polar and Marine
Research (AWI), Columbusstrasse, P.O. Box
120161, D-27515 Bremerhaven, Germany.
([email protected])
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