of 10
ARTICLE
A deep Tasman out
fl
ow of Paci
fi
c waters during
the last glacial period
Torben Struve
1,2,3
, David J. Wilson
1,4
, Sophia K. V. Hines
5,6,7
, Jess F. Adkins
5
&
Tina van de Flierdt
1
The interoceanic exchange of water masses is modulated by
fl
ow through key oceanic choke
points in the Drake Passage, the Indonesian Seas, south of Africa, and south of Tasmania.
Here, we use the neodymium isotope signature (
ε
Nd
) of cold-water coral skeletons from
intermediate depths (1460
1689 m) to trace circulation changes south of Tasmania during
the last glacial period. The key feature of our dataset is a long-term trend towards radiogenic
ε
Nd
values of ~
4.6 during the Last Glacial Maximum and Heinrich Stadial 1, which are clearly
distinct from contemporaneous Southern Ocean
ε
Nd
of ~
7. When combined with previously
published radiocarbon data from the same corals, our results indicate that a unique radio-
genic and young water mass was present during this time. This scenario can be explained by
a more vigorous Paci
fi
c overturning circulation that supported a deeper out
fl
ow of Paci
fi
c
waters, including North Paci
fi
c Intermediate Water, through the Tasman Sea.
https://doi.org/10.1038/s41467-022-31116-7
OPEN
1
Department of Earth Science and Engineering, Imperial College London, SW7 2AZ London, UK.
2
The Grantham Institute for Climate Change and the
Environment, Imperial College London, SW7 2AZ London, UK.
3
Institute for Chemistry and Biology of the Marine Environment (ICBM), University of
Oldenburg, 26129 Oldenburg, Germany.
4
Institute of Earth and Planetary Sciences, University College London and Birkbeck, University of London, WC1E 6BT
London, UK.
5
Department of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA.
6
Lamont-Doherty Earth Observatory,
Columbia University, Palisades, NY, USA.
7
Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA,
USA.
email:
t.struve@icbm.de
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1
1234567890():,;
T
he exchange of water masses between ocean basins plays a
key role in the volume transport and heat budgets of the
global overturning circulation. The modern overturning
circulation is characterized by strong southward export of deep
waters from the North Atlantic into the Southern Ocean, as well
as deep water formation in the high-latitude Southern Ocean
1
.
Eventually, these deep waters reach the North Paci
fi
c, which hosts
the oldest waters in the open ocean
2
due to the absence of local
deep convection
3
. The return of such deep waters to the surface
results from diapycnal upwelling (across density surfaces) in the
Paci
fi
c, which feeds upper ocean return
fl
ows to the North
Atlantic Ocean
1
,
4
. Both diapycnal
fl
uxes directly into the Paci
fi
c
thermocline and isopycnal upwelling (along density surfaces) in
the Southern Ocean contribute to that transport
1
,
5
. The Southern
Ocean route is also important for returning old respired carbon to
the surface ocean
2
,
5
. Together, these upwelling and return path-
ways balance the deep export of water from the Atlantic basin
within the global overturning circulation system
1
,
4
,
5
. The return
fl
ows to the Atlantic Ocean typically follow two routes: the cold
water route through the Drake Passage
6
and the warm water
route via the Indonesian Through
fl
ow and the Agulhas Leakage
south of Africa
4
.
More recently, a third route has been recognized south of
Tasmania, which is known as the Tasman Leakage and originates
from the poleward transport of predominantly subsurface Paci
fi
c
waters along the East Australian margin
7
12
(Fig.
1
a). The
southward-
fl
owing subsurface waters contain a local variant of
Antarctic Intermediate Water (AAIW)
9
,
10
,
12
that crossed the
South Paci
fi
c Gyre after formation in the Southeast Paci
fi
c
13
.
Most of the southward-
fl
owing waters turn eastwards at the
Tasman Front near ~35°S, but a proportion
fl
ows west around the
Tasman margin towards the Indian Ocean
10
,
11
(Fig.
1
a). This
out
fl
ow at intermediate depths is more saline than AAIW in the
Southern Ocean
10
and comprises both eddy transport and a non-
eddy component
11
. The westward-
fl
owing Tasman Leakage
waters are bound to a narrow corridor due to bathymetric
constraints and the frontal system of the Antarctic Circumpolar
Current (ACC), which dictates predominantly eastward transport
of water masses to the south of Tasmania
7
,
10
,
14
(Fig.
1
a). From
the Indian Ocean, the Tasman Leakage waters follow the warm
water route via the Agulhas Leakage
4
,
15
,
16
and may represent up
to ~50 % of the upper ocean return
fl
ow to the North Atlantic
17
.
Unlike the Indonesian Through
fl
ow and Drake Passage routes,
the intermediate waters of the Tasman Leakage can preserve their
hydrographic properties during transit
9
,
10
, thus providing a dis-
tinct pathway for the transfer of climatic signals from the Paci
fi
c
to the Indian and Atlantic oceans
10
.
On daily to decadal timescales, the modern Tasman Leakage
shows highly variable transport, which has been related to
changes in wind forcing
7
,
11
,
12
,
16
. As such, the out
fl
ow can
respond sensitively to short-term changes in external forcing,
similar to other bottlenecks in the global overturning circulation
system
7
,
11
,
15
,
18
. On multi-decadal to orbital timescales, changes in
water
fl
ow through these various gateways have been proposed to
play an important role in modulating the distribution of heat and
salt between the ocean basins
19
22
. Moreover, the intensity of the
shallow Paci
fi
c out
fl
ow via the Indonesian Seas has been directly
linked to the overturning circulation strength in the Atlantic
23
and to deep water in
fl
ow and upwelling rates in the Paci
fi
c
basin
24
. These studies, therefore, indicate a potential mechanistic
connection between the upper-ocean Paci
fi
c out
fl
ow dynamics
and the deep branch of the global overturning circulation. Con-
sidering the role of Tasman Leakage waters in re-supplying the
Atlantic overturning circulation today
17
, circulation changes at
the Tasman margin may represent a critical component in the
global overturning circulation system over glacial-interglacial
timescales.
Previous research has focused on reconstructing Pleistocene
changes in hydrography and transport through the Indonesian
Seas
25
27
, the Agulhas Leakage
19
,
28
,
29
, and the Drake
Passage
22
,
30
34
. The combined evidence from these studies sug-
gests that the interoceanic exchange of water masses through the
Fig. 1 Coral sample locations and regional hydrography. a
Map showing the coral sample locations south of Tasmania (red diamond) and locations of
seawater Nd isotope pro
fi
les from stations SR3-60 (light gray triangle), TAN0803-41 (light gray circle), GeoB17019-1 (dark gray triangle), and GeoB17018-
1 (dark gray circle)
38
,
40
. Solid white arrows indicate simpli
fi
ed
fl
ow paths of intermediate waters, while the dashed arrow indicates the Tasman Leakage,
and dark blue arrows represent deep water
fl
ow
11
,
13
,
76
,
94
. The mean positions of the Subtropical Front (STF), Subantarctic Front (SAF), Antarctic Polar
Front (APF), and Southern ACC front (SACC) are indicated by gray lines
14
. Colored squares indicate locations of important paleoceanographic records
from sediment cores MD06-2986 (dark blue, 1477 m water depth), SO136-003GC (green, 944 m water depth)
66
, and MD97-2120 (black, 1210 m water
depth)
65
. The white diamond indicates the location of core FR1/97 GC-12 (990 m water depth)
85
.
b
Oxygen concentration section
95
(along the black line
in
a
), highlighting the major subsurface water masses in the study area: Subantarctic Mode Water (SAMW), Antarctic Intermediate Water (AAIW), Upper
Circumpolar Deep Water (UCDW), Lower Circumpolar Deep Water (LCDW), Paci
fi
c Deep Water (PDW), and Equatorial Paci
fi
c Intermediate Water
(EqPIW) representing a mixture of AAIW originating from the Southeast Paci
fi
c and upwelled PDW
13
,
38
. Thin black lines indicate surfaces of neutral
density anomalies
γ
n
(in kg/m
3
)
96
. Yellow triangles and red diamonds depict sampling depths of modern and fossil corals, respectively. Ocean fronts and
locations of water column pro
fi
les (gray circles and triangles) as in
a
. Base map in
a
and oxygen section in
b
generated with ODV software
97
.
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oceanic choke points was reduced during the Last Glacial Max-
imum (LGM: 18
24 ka BP), yet the overturning circulation was
more active in the Paci
fi
c Ocean at the LGM
35
. One possibility is
that changes in the out
fl
ow south of Tasmania could have com-
pensated for reductions in the strength of the Indonesian
Through
fl
ow, as suggested for centennial to millennial
timescales
12
. However, it has proven challenging to test this idea
for the glacial ocean, because tracing changes in the provenance
of intermediate and deep water masses is dif
fi
cult with traditional
paleoceanographic tools in this highly dynamic region.
Here we use the neodymium (Nd) isotope composition of the
aragonitic skeletons of cold-water corals collected from intermediate
water depths south of Tasmania (Fig.
1
) to test the idea that cir-
culation changes in this region played a role in the interoceanic
exchange of water masses during the last glacial period between ~68
and12.7kaBP.Atabroadscale,themoderndistributionofNd
isotopes in the deep ocean is dominated by mixing between unra-
diogenic North Atlantic Deep Water (NADW) (
ε
Nd
~
13)
36
and
radiogenic Paci
fi
c-derived water masses (
ε
Nd
~
3to
4)
37
,
38
.
Mixing between these water masses in the ACC forms Circumpolar
Deep Water (CDW), which has intermediate Nd isotope compo-
sitions (
ε
Nd
~
8)
39
,
40
. The Nd isotope composition of upwelling
Upper CDW (UCDW) is largely preserved during the transfor-
mation to AAIW, and is similar in composition to Lower CDW
(LCDW), which results in a relatively uniform vertical distribution
of Nd isotopes in the modern Southern Ocean water column
39
42
(Fig.
2
a). However, this Southern Ocean Nd isotope homogeneity
did not persist back in time
33
,
34
, indicating the potential of using
this tracer to explore past changes in ocean circulation and struc-
ture. Speci
fi
cally, a glacial Nd isotope record from south of Tas-
mania could reveal variability in Paci
fi
c water contributions to this
region, subject to constraints on past Nd cycling and Nd isotope
compositions in the Paci
fi
c Ocean. In turn, such evidence would
enable a unique assessment of links between the out
fl
ow of Paci
fi
c
waters via the Tasman Sea and large-scale glacial-interglacial ocean
circulation changes.
Results and discussion
Sample locations
. For this study, we selected 62 fossils and three
late Holocene (referred to as modern) cold-water coral specimens
of
Desmophyllum dianthus
that were collected from south of
Tasmania (~44°S and ~147°E) (Fig.
1
a) using the remotely
operated submergence vehicle JASON during cruise TN-228. The
three modern corals
43
provide a vertical transect from 951 to
2170 m water depth (Supplementary Data 1), sampling both
AAIW and UCDW, which are approximately separated by the
neutral density surface
γ
n
of 27.55 kg/m³ at ~1200 m water
depth
13
(Fig.
1
b). The AAIW layer in the study area is occupied
by different variants of AAIW, including northward-
fl
owing
Southern Ocean AAIW and southward-
fl
owing Paci
fi
c AAIW,
which is further modi
fi
ed along the East Australian margin by the
incorporation of Tasman Sea thermocline waters to form Tasman
Sea AAIW
13
(Fig.
1
). The fossil coral specimens were collected
from a narrow range of 1460 to 1689 m water depth
43
,
44
, which in
the modern ocean is occupied by UCDW and corresponds to a
neutral density
γ
n
of 27.75
27.85 kg/m³ (refs.
7
,
40
,.) (Fig.
1
b).
We recognize that the water mass structure and properties may
have changed in the past, but use the nomenclature of the modern
water masses to describe past oceanographic changes at the depth
levels presently occupied by these water masses.
Signi
fi
cance of the Tasman coral Nd isotope signal
. The
modern corals range from relatively radiogenic
ε
Nd
values of
6.6 ± 0.4 at 951 m water depth to less radiogenic
ε
Nd
values of
8.3 and
8.7 ± 0.2 at ~1900 and ~2170 m depth, respectively
(Fig.
2
a and Supplementary Data 1). The fossil corals were col-
lected from the narrow depth range of 1460 to 1689 m and
covered the later part of the last glacial period from 67.5 to
12.7 ka BP
44
, revealing
ε
Nd
variability between
4.6 ± 0.2 and
7.7 ± 0.2 (Fig.
2
; Supplementary Data 1). The record is char-
acterized by a long-term trend from
ε
Nd
values of
7.5 ± 0.2
during early Marine Isotope Stage (MIS) 3 towards maximum
ε
Nd
values of
4.6 ± 0.2 during late MIS 2. Superimposed on the long-
Fig. 2 Modern and fossil Tasman cold-water coral data. a
Coral Nd isotope data (symbols and error bars as in
b
) compared to modern seawater Nd
isotope pro
fi
les from the Southern Ocean
40
and West Paci
fi
c
38
(symbols as in Fig.
1
). Light and dark gray bars indicate the range of Nd isotope signatures
(
ε
Nd
) of water masses between 400 and 3000 m water depth in the Southern Ocean
40
and in the West Paci
fi
c
38
, respectively. Also shown is a pro
fi
le from
North Paci
fi
c station BO-1 (gray squares; 40°N, 160°E)
98
. Error bars for seawater Nd isotope data represent the 2 s uncertainties reported in the original
publications
38
,
40
,
98
. SAMW Subantarctic Mode Water, AAIW Antarctic Intermediate Water, UCDW Upper Circumpolar Deep water, LCDW Lower
Circumpolar Deep Water, PDW Paci
fi
c Deep Water.
b
Time series of fossil coral
ε
Nd
compared to Pb isotope (
206
Pb/
204
Pb) data from the same
specimens
50
. Error bars represent the analytical uncertainties of coral Nd (Methods) and Pb isotope data
50
. A light gray bar outlines the 2 SD of Nd isotope
compositions of CDW from the Indian Ocean and the Drake Passage between 10 and 70 ka BP
34
,
57
,
59
(see Fig.
3
b for more details). The dark gray bar
represents the 2 SD of past seawater Nd isotope compositions from north of the Tasman Sea for the time interval between 10 and 30 ka BP
71
,
72
. The
numbers and boundaries of Marine Isotope Stages (MIS) are shown along the top axis. Dotted lines and numbers indicate Heinrich Stadials. ACR Antarcti
c
Cold Reversal, LGM Last Glacial Maximum. Ages are reported in thousand years before the present (ka BP, present
=
1950). Modern coral data include one
replicate (see Supplementary Data 1).
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3
term evolution, the corals indicate abrupt centennial to
millennial-scale Nd isotope shifts, with deviations of up to ~1.5
ε
Nd
units from the overall trend line (Fig.
2
b). During the
deglaciation, we observe a large shift from
ε
Nd
=
4.9 ± 0.2 at
16.7 ka BP, within early Heinrich Stadial 1 (HS 1), to
ε
Nd
=
7.3 ± 0.2 at 14.8 ka BP, around the end of HS 1. Those less
radiogenic values characterize the Antarctic Cold Reversal (ACR)
up to the youngest analyzed sample at 12.7 ka BP (Fig.
2
b).
Rigorously cleaned skeletons of cold-water coral
D. dianthus
have been shown to reliably record ambient seawater Nd isotope
signatures
45
,
46
. Here we add three modern corals from the
Tasman continental margin to the existing calibration datasets.
The Nd isotope compositions of the corals at ~1900 and ~2170 m
water depth are in excellent agreement with the mean Southern
Ocean seawater
ε
Nd
value of
8.2 ± 0.9 for UCDW (2 SD,
n
=
41)
40
, and with the most proximal seawater data
40
(Fig.
2
a).
The modern coral from intermediate water depths has an
ε
Nd
value of
6.6 ± 0.4, which is more radiogenic than the nearby
Southern Ocean AAIW
ε
Nd
values of
8.1 ± 0.3 (2 SD,
n
=
3)
measured on modern seawater
40
. This difference can be
attributed to the mixing between northward-
fl
owing AAIW
derived from the Southern Ocean and southward-
fl
owing
intermediate waters, which deliver more radiogenic Nd from
the West Paci
fi
c region (
ε
Nd
~
5)
38
to the Tasman margin
10
13
(Figs.
1
,
2
a). Overall, our data con
fi
rm that the skeletons of
D.
dianthus
record ambient seawater Nd isotope compositions and
indicate the value of Nd isotopes for tracing the presence of
Paci
fi
c versus Southern Ocean water masses in the study area.
The Nd isotope composition of local seawater in the past could
potentially have been modi
fi
ed by changes in particulate and/or
solute
fl
uxes from nearby land masses. While terrestrial input
fl
uxes from the South Island of New Zealand into the eastern
Tasman Sea were largely invariable during the last glacial-
interglacial cycle
47
, changes in
fl
uvial activity and dust emissions
in Australia have been documented and represent a possible
source of radiogenic Nd (
ε
Nd
>~
5) to the study area
48
,
49
.To
evaluate possible changes in local Nd inputs in the past, it is
informative to look at lead (Pb) isotopes in the same Tasman
corals
50
. Due to its higher particle reactivity, dissolved Pb has a
shorter residence time than Nd in seawater
51
, such that changes
in local input
fl
uxes and sediment-seawater interaction are
expected to be more readily re
fl
ected in the authigenic seawater-
derived Pb isotope composition of the Tasman corals
50
. Past
seawater Pb isotope reconstructions from a subset of the corals
spanning ~40 to 12 ka BP show no correspondence with our Nd
isotope data (
R
²
=
0.03; Fig.
2
b)
50
, which argues against local
processes as a major control on the reconstructed Nd isotope
changes. Moreover, the modern seawater and coral Nd isotope
datasets do not indicate a signi
fi
cant in
fl
uence of boundary
exchange in the study area
40
. This assertion is consistent with
observations from other highly dynamic regions of the Southern
Ocean, including the Drake Passage where UCDW is forced
through a narrow channel of rocks and sediments with relatively
radiogenic Nd isotope compositions
46
. The Drake Passage
experienced pronounced glacial-interglacial changes in both
ocean circulation and the local input of reactive lithogenic
material, with no indication that boundary exchange controlled
the Nd isotope composition of past seawater
33
,
34
. Consequently,
there is no reason to expect that boundary exchange was more
pronounced in the study area during the last glacial period, so our
data are best explained by a primary control from changes in
water mass sourcing on a regional to basin-scale (Fig.
2
a).
Origin of the radiogenic Nd isotope signal
. Neodymium isotope
signatures of ~
5 during the late glacial interval (25.3
16.7 ka
BP) are approximately three
ε
Nd
units higher than modern sea-
water values at the coral sampling locations (Fig.
2
b) and mark
the culmination of a long-term evolution during MIS 3 and MIS 2
that corresponds to a global cooling trend (Fig.
3
a, b). Building on
our arguments above, we consider four possible scenarios to
explain the highly radiogenic Nd isotope composition of
late glacial seawater south of Tasmania: (i) changes in the com-
position of UCDW in the Southern Ocean, (ii) enhanced
admixture of water masses from below, (iii) local deepening of a
more radiogenic glacial version of AAIW, and (iv) enhanced
advection of intermediate water masses from the West Paci
fi
c.
In the modern ocean, the dominant water mass at the fossil
coral sampling locations is UCDW (Figs.
1
b,
2
a), and a
northward shift of the ACC frontal system in the Indo-Paci
fi
c
sector of the Southern Ocean
21
,
52
(Fig.
3
c) could be expected to
have reinforced the presence of UCDW at the sampling
locations during the late glacial interval. While Nd isotope
reconstructions for glacial UCDW have been attempted using
foraminifera in sediment cores east of New Zealand
53
,
54
,the
records from this area are compromised by an offset of ~1
2
ε
Nd
units between the measured Holocene signal
53
,
54
and nearby
modern seawater values
42
, which precludes a direct comparison
to our coral-based record. In contrast, reconstructions from
UCDW depths in the Atlantic sector of the Southern Ocean
show good agreement between late Holocene foraminifera
values and modern seawater, and indicate late glacial
ε
Nd
values
of ~
7.5 for UCDW
55
. A more representative Southern Ocean
UCDW signal is provided by Drake Passage cold-water corals,
with a single specimen from UCDW depths recording an
ε
Nd
value of
6.4 during HS 1
30
. This UCDW value integrates the
circumpolar
fl
ow after interaction with the radiogenic water
masses of the Paci
fi
c, at a time when unradiogenic water masses
from the North Atlantic exerted a reduced in
fl
uence in the
Southern Ocean
30
. However, a Nd isotope composition of ~
6.4
for UCDW in the Southern Ocean is not suf
fi
ciently radiogenic
to explain late glacial
ε
Nd
values of ~
5 recorded at the Tasman
margin (Fig.
3
b).
The late glacial Nd isotope composition of LCDW was more
radiogenic than in the modern ocean, which could re
fl
ect a
reduced presence of unradiogenic NADW in the glacial deep
ocean
34
,
56
60
, changes in the composition of NADW
61
,
62
and/or
changes in the interaction with Paci
fi
c waters
54
,
63
. Upwelling
along sloping isopycnals provides an ef
fi
cient and direct route for
LCDW to reach the upper water column of the Southern Ocean
1
,
5
(Fig.
1
b). Therefore, a northward shift of the ACC frontal
system
21
,
52
(Fig.
3
c) could potentially have increased the exposure
of the Tasman corals to LCDW during the late glacial interval
(Fig.
1
b). However, glacial LCDW was characterized by relatively
unradiogenic
ε
Nd
values of ~
6to
8, as evidenced by
reconstructions from the South Paci
fi
c
60
, the Drake Passage
34
,
and the deep Indian Ocean
57
,
59
(Fig.
3
b). These values are too
unradiogenic to drive concurrent
ε
Nd
values south of Tasmania to
~
5. Importantly, an increased presence of LCDW at the coral
sampling locations would require a northward shift of the ACC
frontal system and the associated isopycnals by more than 10°
latitude, which would push both the Subantarctic Front and the
Antarctic Polar Front against the Tasman margin (Fig.
1
b). Such
a scenario is dif
fi
cult to reconcile with the modern observation
that the South Tasman Rise and Campbell Plateau force the deep-
reaching fronts of the ACC into a circumpolar trajectory to the
south of the coral sampling locations
14
(Fig.
1
a). Moreover,
LCDW was characterized by a low radiocarbon content at the
LGM, with a B-atm offset (i.e. the offset between marine benthic
and atmospheric
14
C ages
64
) of ~3000 years, whereas concurrent
B-atm values at the Tasman margin
fl
uctuated around ~1200
years
44
(Fig.
3
d). Thus, we exclude the exposure to LCDW as a
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primary control on the Nd isotope evolution recorded by the
cold-water corals.
If glacial AAIW in the Southern Ocean had a signi
fi
cantly more
radiogenic Nd isotope composition than today, local deepening of
the AAIW layer could provide a possible explanation for the
radiogenic Nd isotope signatures at the coral sampling locations
(Fig.
1
b). A deepening of Southern Ocean AAIW to reach the
coral sampling depths would be consistent with the relatively well-
ventilated signal reconstructed from radiocarbon
44
(Fig.
3
d).
However, AAIW is formed from UCDW, which was signi
fi
cantly
less radiogenic (
ε
Nd
~
7)
30
,
55
than our coral data (
ε
Nd
~
5)
during the late glacial interval (Fig.
4
). Recent work from the
Drake Passage shows that the Nd isotope signal of UCDW is
generally preserved during water mass transformation in the
Southern Ocean upper overturning cell
33
. Moreover, based on
modern seawater data it can be expected that any local in
fl
uences
would drive the surface waters between Australia and Antarctica
to even less radiogenic values than the upwelling UCDW
ε
Nd
signal
40
. Therefore, a deep variant of AAIW forming in the
Southern Ocean south of Australia would be unable to explain the
shift to such radiogenic Nd isotope signatures at the coral
sampling locations during the last glacial period. In addition,
rather than a glacial deepening, independent evidence from stable
oxygen and carbon isotopes and from redox-sensitive proxies
(rhenium and uranium) suggests a glacial shoaling of Southern
Ocean AAIW in the study area
65
67
(Fig.
3
e).
A more radiogenic variant of AAIW is present in the modern
West Paci
fi
c
38
(Fig.
2
a). This variant is mainly supplied by AAIW
formation in the Southeast Paci
fi
c and modi
fi
ed to Tasman
AAIW upon entering the Tasman Sea from the north
13
,
67
(Fig.
1
a). A recent study proposed an increased presence of
Tasman AAIW over the Challenger Plateau in the eastern
Tasman Sea (west of New Zealand) during the LGM
67
. Never-
theless, previous work from the main AAIW formation region
in the Southeast Paci
fi
c
68
,
69
, as well as in areas in
fl
uenced
by Tasman AAIW (i.e., eastern Tasman Sea and Bay of
Plenty)
66
,
67
,
70
(Fig.
1
a), are inconsistent with a deepening of
Tasman AAIW to reach water depths of ~1500
1700 m during
the LGM.
Consequently, the highly radiogenic Nd isotope signatures
observed in late glacial corals from south of Tasmania were
probably not the result of changes in the composition and/or
depth ranges occupied by LCDW, UCDW, or AAIW. Instead, we
consider the advection of radiogenic water masses from the
Paci
fi
c Ocean north of the Tasman Sea to provide the most likely
explanation (Fig.
1
b). Importantly, this scenario requires a shift in
the glacial circulation compared to the modern-day.
North Paci
fi
c water mass signals at the Tasman margin during
the last glacial period
. The circulation between the Tasman Sea
and the West Paci
fi
c is restricted by complex bathymetric features
(Fig.
1
a), which con
fi
ne the exchange of waters below ~1500 m
water depth to narrow deep channels. The density range of the
waters bathing our fossil coral sampling locations is currently
Fig. 3 Mid-depth Nd isotope evolution south of Tasmania in
paleoceanographic context. a
WAIS Divide ice core oxygen isotope (
δ
18
O)
data (thin gray line) with a
fi
ve-point running mean (thick black line)
99
.
b
Mid-depth cold-water coral Nd isotope (
ε
Nd
) data from south of
Tasmania (this study) compared to Drake passage Lower Circumpolar
Deep Water (LCDW)
34
and Upper Circumpolar Deep Water (UCDW)
30
and Indian Ocean LCDW from core SK129-CR2 (light blue)
57
,
59
. Error bars
and light blue shading represent the respective 2 SD uncertainties.
c
Abundance of subpolar species (light gray;
fi
ve-point running mean in
black) from core MD03-2611 as an indicator of changes in Southern Ocean
front positions south of Australia
21
.
d
Tasmanian cold-water coral benthic-
atmosphere (B-atm) radiocarbon age offsets and their propagated
uncertainties (see also caption of Fig.
4
) for fossil corals (black
diamonds)
44
and for the modern UCDW (black triangles) and AAIW corals
(inverted black triangle)
43
included in this study (Figs.
1
b,
2
a, b).
e
Benthic
carbon isotope (
δ
13
C) data from eastern Tasman Sea cores MD06-2986
(UCDW, 11-point running mean in dark blue) and SO136-003GC (AAIW:
Antarctic intermediate water; 11-point running mean in green)
66
, compared
to Southwest Paci
fi
c core MD97-2120 (light gray; 11-point running mean in
black)
65
. Arrow indicates trends in AAIW depth, which is shallower than
1210 m when the MD97-2120 record converges with UCDW compositions.
f
Benthic
δ
13
C data from northern Tasman Sea core FR1/97 GC-12
85
(radiocarbon dates re-calibrated using CALIB 8.1 software
100
and Marine20
calibration curve
101
) compared to a spliced record of North Paci
fi
c cores
SO201-2-101KL and SO201-2-85KL
84
,
86
(light gray;
fi
ve-point running
mean in purple), representing a North Paci
fi
c Intermediate Water (NPIW)
source signal, and
δ
13
C from sub-thermocline-dwelling foraminifera
G.
hexagonus
in ODP 1240 (light gray;
fi
ve-point running mean in brown),
recording the composition of Equatorial Paci
fi
c Intermediate Water
(EqPIW). The convergence of the latter two records has been interpreted
as NPIW expansion into the Equatorial Paci
fi
c
84
. Heinrich Stadials are
numbered and highlighted with gray bars along the top axis. LGM Last
Glacial Maximum. ACR Antarctic Cold Reversal. The numbers and
boundaries of Marine Isotope Stages 1
4 (MIS) are shown along the lower
axis according to Fig.
2
b.
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5
occupied by UCDW and PDW, which share similar
ε
Nd
values of
~
3to
4 in the modern West Paci
fi
c
38
(Figs.
1
,
2
a). Recon-
structed glacial
ε
Nd
values of ~
2.5 to
4 for mid-depth waters
(~2
2.6 km water depth) in the West Paci
fi
c from north of the
Tasman Sea
71
,
72
are indistinguishable from those modern values
(Fig.
2
b). However, while the radiogenic Nd isotope compositions
of the Tasman corals approached PDW values during the
late glacial interval (
ε
Nd
=
2to
4)
54
,
71
, they were associated
with much younger ventilation ages (Fig.
4
). At the LGM, PDW
was characterized by a pronounced radiocarbon depletion (B-atm
~3000 years)
64
, while the coral data from the Tasman margin
show B-atm values of ~1200 years
44
(Fig.
3
d). Therefore, an
increased presence of PDW is unsuitable to explain the trend
towards more radiogenic Nd isotope compositions at the Tasman
margin during the last glacial period (Fig.
4
). The combined
radiocarbon and Nd isotope evidence suggest that our LGM and
early deglacial coral data lie on a mixing trend between an
unradiogenic and poorly-ventilated source represented by glacial
Southern Ocean UCDW and relatively well-ventilated and
radiogenic Paci
fi
c-derived waters (Fig.
4
). We hypothesize that
this Paci
fi
c-derived out
fl
ow signal was driven by an expansion of
North Paci
fi
c Intermediate Water (NPIW) during the last glacial
period.
In the modern ocean, NPIW is characterized by
ε
Nd
values of ~
3
37
,
38
, but is con
fi
ned to the North Paci
fi
c
73
,
74
(Fig.
5
a) as it
leaves the Paci
fi
c through the Indonesian Seas
74
above the sill
depth of ~1300 m
18
,
75
,
76
. Its incorporation into the deep Tasman
out
fl
ow during the last glacial period would thus require a
mechanism that enables the cross-equatorial
fl
ow of NPIW
(Fig.
5
c). Modeling studies indicate that the formation of
intermediate water masses in the North Paci
fi
c and/or their
expansion across the Paci
fi
c basin may be sensitive to the strength
of the Indonesian Through
fl
ow
77
,
78
. Glacio-eustatic sea-level fall,
the associated shelf exposure in the Indonesian Seas, and changes
in the coupled ocean-atmosphere system of the tropical Indo-
Paci
fi
c probably led to a reduction in the Indonesian Through-
fl
ow during glacial periods
25
,
27
(Fig.
5
c). An additional reduction
of the Indonesian Through
fl
ow may have arisen from a possible
link with the weakened overturning circulation in the Atlantic
Ocean under glacial boundary conditions
23
.
Consistent with those modelling predictions
77
,
78
, proxy
evidence points to the existence of a chemical divide at about
2000 m water depth in the Paci
fi
c Ocean at the LGM, with the
upper part of the water column dominated by relatively well-
ventilated waters
35
,
79
,
80
. This ventilated state has been attributed
to a deepening and intensi
fi
cation of NPIW formation
35
,
79
81
,
which was presumably related to subpolar gyre dynamics and
reduced freshwater
fl
uxes to the North Paci
fi
c
35
,
82
. The expanded
glacial NPIW signal was detected in reconstructions from the
equatorial Paci
fi
c
83
,
84
(Fig.
3
f) and has been proposed to have
spread towards the Southern Ocean predominantly along the
western boundary of the Paci
fi
c
35
. A record of benthic carbon
isotopes from 990 m water depth on the east Australian margin
(northern Tasman Sea) (Fig.
1
a) reveals values that were
originally interpreted to result from changes in mixing between
AAIW and UCDW
85
. However, glacial NPIW and glacial UCDW
are characterized by rather similar
δ
13
C
66
,
84
(Fig.
3
e, f). Thus, the
northern Tasman Sea record may also be explained by an
increased in
fl
uence of southward-
fl
owing glacial NPIW (low
δ
13
C)
84
,
86
alternating with shallower AAIW (higher
δ
13
C)
66
,
70
,
85
at these depths during the last glacial period (Fig.
3
f). Notably, the
peak in NPIW formation during HS 1
20
,
86
,
87
coincides with the
most radiogenic Nd isotope compositions and improved ventila-
tion recorded south of Tasmania (Fig.
3
b, d). Hence, we propose
that the long-term glacial trend towards more radiogenic Nd
isotope compositions south of Tasmania was linked to the
expansion of glacial NPIW and its incorporation into an out
fl
ow
through the Tasman Sea below the depth range of modern
Tasman Leakage waters. If this interpretation is correct, our data
provide evidence that glacial NPIW reached the extratropical
South Paci
fi
c.
Glacial reorganization of Paci
fi
c Ocean circulation and inter-
ocean exchange
. It has previously been speculated that a reduc-
tion in the Indonesian Through
fl
ow could be compensated, on
centennial to millennial timescales, by enhanced export of Paci
fi
c
water masses via the Tasman Sea
12
. Our coral data corroborate
Fig. 4 Tasman cold-water coral data in radiocarbon
Nd isotope (
ε
Nd
)
space.
The benthic-atmosphere radiocarbon (
14
C) age offsets (B-atm) were
calculated using an atmospheric
14
C age of 0 years (1950 AD) for the
modern seawater values
2
,
102
. For past B-atm, we used coral
14
C ages
44
and
IntCal20 atmospheric
14
Cages
102
.Atmospheric
14
C values were calculated
as averages of the reported 1 s coral calendar age uncertainty range
44
.Error
bars represent 1 s propagated uncertainties for B-atm age offsets and 2 SD
uncertainties for
ε
Nd
. Modern water column data comprise regional Antarctic
Intermediate Water (AAIW), Upper Circumpolar Deep Water (UCDW), and
Lower Circumpolar Deep Water (LCDW) properties
2
,
40
. Hypothetical
mixing calculations (dotted lines) use the following endmembers: modern
North Atlantic Deep Water (NADW,
ε
Nd
=
13.2, [Nd]
=
17.6 pmol/kg, B-
atm
=
500 years, DIC [dissolved inorganic carbon]
=
2160
μ
mol/kg)
2
,
36
;
modern Paci
fi
c Deep Water (PDW,
ε
Nd
=
3.5, [Nd]
=
44.4 pmol/kg, B-
atm
=
2100 years, DIC
=
2350
μ
mol/kg)
2
,
37
. Note that these hypothetical
mixing lines do not account for non-conservative processes along the water
mass
fl
ow paths. Glacial PDW was de
fi
ned using an LGM B-atm age offset of
3000 years
64
and otherwise modern PDW parameters due to the similarity
of glacial and modern PDW Nd isotope compositions
54
,
71
,
72
. Glacial UCDW
was estimated based on the Drake Passage coral Nd isotope
30
,
34
and
radiocarbon data
31
,
69
,
103
. Glacial North Paci
fi
c Intermediate Water (NPIW)
properties at its source are estimated based on modern Nd isotope
compositions
37
,
38
and LGM radiocarbon ages
35
. A dashed gray arrow
indicates mixing between glacial UCDW and glacial NPIW. Local ventilation
(e.g., via deepening of Southern Ocean AAIW) would lead to lower
B-atm and relatively invariant
ε
Nd
values (black arrow). Where paired
radiocarbon
Nd isotope data were not available from the same coral
specimen, we matched the Nd isotope data with radiocarbon data from
nearby corals of the same age (i.e., within age uncertainty and with <100 m
depth difference).
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this idea and provide evidence that a glacial reorganization of
ocean circulation in the Paci
fi
c could have involved the export of
NPIW via the Tasman Sea (Fig.
5
c, d). Such export would have
been particularly ef
fi
cient during times when NPIW deepened
below the Indonesian Through
fl
ow sill depth of ~1300 m
75
(Fig.
5
c). A reduced in
fl
ow of Southern Ocean AAIW into the
intermediate depths of the Paci
fi
c Ocean (Fig.
5
c, d), linked to a
shoaling
66
and/or weakening
65
of Southern Ocean AAIW for-
mation during the LGM, could have further supported the
southwards expansion of NPIW within the Paci
fi
c basin
77
.We
emphasize that the glacial out
fl
ow described here was found at
depths signi
fi
cantly below the modern Tasman Leakage waters
(Fig.
5
a, c). Taken in combination with the possible lower
boundary of Tasman AAIW near ~1000 m water depth
67
,
85
, our
coral dataset suggests that the deep out
fl
ow extended from ~1000
to at least ~1700 m water depth during the last glacial interval. At
these depths, the southwards expanding glacial NPIW was
probably subject to an admixture of other water masses in the
West Paci
fi
c, potentially including glacial PDW, UCDW, and
different variants of AAIW (Figs.
1
b,
5
c, d). It is dif
fi
cult to
diagnose their individual contributions to the deep out
fl
ow signal
at the Tasman margin from our dataset because these water
masses have similar Nd isotope compositions in the modern
Paci
fi
c Ocean, re
fl
ecting the non-conservative effects of local Nd
inputs on the Nd isotope composition of seawater
38
. However,
relatively invariant glacial-interglacial
ε
Nd
values of ~
2.5 to
4
reconstructed from sites north of the Tasman Sea
54
,
71
,
72
(Fig.
2
b)
suggest that any changes in advection, boundary exchange,
benthic
fl
ux, weathering inputs, or open ocean particle-seawater
interactions appear to have had a minimal effect on mid-depth
West Paci
fi
c Nd isotope signatures across this interval
38
,
47
,
63
,
71
,
72
.
Accordingly, a glacial intermediate water mass entering the
Tasman Sea from the north would probably have been char-
acterized by
ε
Nd
values near or above ~
4, making it suitable to
drive the trend towards more radiogenic glacial
ε
Nd
values at the
Tasman margin.
The key
fi
nding from our work is that these radiogenic Paci
fi
c-
derived water masses contributed substantially to an out
fl
ow from
the Tasman Sea at water depths of ~1500
1700 m during the last
glacial period. This scenario is different from the modern
situation, in which the out
fl
ow is concentrated in the Tasman
Leakage at depths shallower than ~1200 m
10
,
12
,
16
. We ascribe this
deep Tasman out
fl
ow to a glacial mode of more active NPIW
formation
35
,
81
,
84
(Fig.
5
c, d), which has been proposed to have
promoted the carbon storage in the deep ocean thus contributing
to the glacial reduction of atmospheric CO
2
35
.
The deep Tasman out
fl
ow waters could have taken two
possible routes after passing the coral sampling locations, with
Fig. 5 Schematic of inferred circulation changes between the modern-day and the Last Glacial Maximum (LGM).
Cross-sections show the Paci
fi
c Ocean
circulation for
a
the modern-day and
c
the LGM. Maps focus on the intermediate-depth circulation in the study area near Tasmania for
b
the present-day
(see also Fig.
1
a) and
d
the LGM. Base maps in
b
,
d
produced with ODV software
97
. Water mass pathways are indicated by arrows: Antarctic Intermediate
Water (AAIW, black) and North Paci
fi
c Intermediate Water (NPIW, purple). SO: Southern Ocean. Note that the eastward
fl
ow of the Antarctic
Circumpolar Current (ACC) (circled dots in
a
and
c
) comprises also Upper Circumpolar Deep Water (UCDW) and Lower Circumpolar Deep Water
(LCDW) (see also Fig.
1
b for more details). Note also that the two possible pathways of glacial Tasman out
fl
ow waters are indicated by stippled lines in
c
,
d
and that the purple arrows in
c
,
d
do not represent pure NPIW, since it is in
fl
uenced by the admixture of other ambient water masses during its
southwards transport (see main text). Gray arrows in
a
,
c
indicate the deep overturning, where upwelling of LCDW and Antarctic Bottom Water (AABW)
feeds into the southward return
fl
ow of Paci
fi
c Deep Water (PDW). Flow strengths are schematically represented by the thickness of arrows (meridional
fl
ows) or the size of the circled dots/crosses (zonal
fl
ows). The solid black line in
a
represents the intermediate water layer ventilated primarily by AAIW
and NPIW in the modern Paci
fi
c Ocean, while the stippled black line in
c
indicates the deepened LGM analogue. Dashed boxes indicate the locations and
approximate depth extents of Paci
fi
c out
fl
ow along the Tasman margin and through the Indonesian Seas. The position of the Southern Westerly Winds
(SWW) is also shown with circled dots.
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7
distinct implications for the glacial overturning circulation
system. If the out
fl
ow waters followed the trajectory of the
modern shallower Tasman Leakage waters into the Indian and
Atlantic Oceans
17
(Fig.
5
a
d), they would have helped to
maintain the interoceanic exchange of water masses and provided
an oceanic pathway for the westward export of Paci
fi
c climate
signals
10
,
16
. Conversely, parts of the deep Tasman out
fl
ow waters
may have joined the eastward
fl
ow of the ACC (Fig.
5
c, b, d), thus
propagating climate signals into the Southern Ocean and
in
fl
uencing the nutrient availability in the Southern Ocean upon
upwelling to the surface
35
. Considering the enhanced northwards
de
fl
ection of circumpolar water masses in the Southeast Paci
fi
c
during the late glacial interval
22
,
32
, such eastward-
fl
owing waters
would have contributed to a more isolated upper overturning cell
in the Paci
fi
c Ocean
78
,
80
rather than enhancing interoceanic
exchange at that time.
While our coral data are unable to provide constraints on the
relative importance of these two possible routes downstream of
Tasmania, the most radiogenic
ε
Nd
values in our record suggest
that the out
fl
ow of Paci
fi
c waters was most pronounced during
HS 1 (Fig.
3
b) when changes in atmospheric circulation and
salinity feedbacks promoted convective activity in the North
Paci
fi
c
20
,
78
,
87
, and when a poleward shift of Southern Ocean
winds and fronts
21
,
52
(Fig.
3
c) may have effectively widened the
westward passageway for out
fl
ow waters at the Tasman margin
7
.
Accordingly, such frontal shifts may also have been responsible
for the rapid Nd isotope changes on centennial to millennial
timescales during MIS 2. Albeit the most radiogenic Nd isotope
compositions recorded by the Tasman corals coincided with HS
1, radiogenic Nd isotope excursions could also be a sign of
enhanced Paci
fi
c out
fl
ow during previous Heinrich stadials
(Fig.
3
b). Furthermore, our coral data clearly indicate that the
structure of the Paci
fi
c Ocean was substantially reorganized at the
end of HS 1. At that time, convection in the North Paci
fi
c
decreased
20
,
86
and the expansion of NADW supported more
modern-like water column characteristics in the Southern
Ocean
34
,
56
,
60
, leading to Nd isotope compositions approaching
modern values south of Tasmania (Fig.
3
b).
Overall, our study provides evidence that a Paci
fi
c out
fl
ow
through the Tasman Sea played a dynamic role in the interoceanic
exchange of water masses within the global overturning circula-
tion system through glacial-interglacial cycles. We demonstrate a
close link between changes in the deep Tasman out
fl
ow, NPIW
formation, and circulation changes in the Paci
fi
c Ocean during the
last glacial period. Implementing these
fi
ndings into re
fi
ned ocean
models will improve our understanding of how the out
fl
ow of
Paci
fi
c waters via the Tasman Sea affects the interoceanic
exchange of climate signals, the global overturning circulation
strength, and the oceanic carbon storage, over a range of
timescales in the past and the future.
Methods
Sample preparation and analytical procedures
. Neodymium isotope analyses
were carried out in the MAGIC laboratories at Imperial College London following
established protocols
46
,
88
. In brief, physically and chemically cleaned cold-water
coral samples were subjected to iron co-precipitation to concentrate trace metals
before separating uranium (U) and thorium (Th) for U-series dating
44
. The Nd
fractions of the fossil corals were collected during U-Th separation, whereas the Nd
fractions of the three modern corals were collected from the wash fraction during
Pb separation
50
. All Nd fractions were puri
fi
ed using a two-step ion-exchange
chromatography protocol for analysis by thermal ionization mass spectrometry
(TIMS) as NdO
+
88
.
Long-term TIMS results of 5 and 15 ng loads of JNdi-1 yielded
143
Nd/
144
Nd
=
0.512105 ± 0.000009 (2 SD,
n
=
110). For each analytical session, the
instrumental offset was corrected by normalizing the mass-bias corrected
143
Nd/
144
Nd ratios of samples based on the JNdi-1 reference ratio of
143
Nd/
144
Nd
=
0.512115 ± 0.000007
46
,
89
. The mass-bias corrected
143
Nd/
144
Nd ratios from
one analytical session were subjected to a secondary correction using
142
Nd/
144
Nd
90
(see also Supplementary Data 1), yielding
143
Nd/
144
Nd
=
0.512117 ± 0.000012 (2 SD,
n
=
5) for JNdi-1. The long-term external reproducibility was monitored with repeat
analyses of USGS reference material BCR-2 and our in-house coral reference material
during all analytical sessions, yielding
143
Nd/
144
Nd of 0.512637 ± 0.000010 (2 SD,
n
=
34) and 0.512336 ± 0.000011 (2 SD,
n
=
25), respectively. These results are in
excellent agreement with published results for BCR-2 (0.512637 ± 0.000012)
91
and
our coral reference material (0.512338 ± 0.000008)
92
. We report the 2 SD of the coral
reference material as the analytical uncertainty for samples unless the internal 2SE is
larger in which case the propagated error is reported. Full procedural blanks for
combined U-Th/Pb and Nd separation from the aragonitic matrix ranged from 5 to
31 pg Nd, with a mean of 20 pg (
n
=
12). All Nd isotope results are reported as
ε
Nd
=
((
143
Nd/
144
Nd
sample
)/(
143
Nd/
144
Nd
CHUR
)
1) × 10,000, where CHUR is the
chondritic uniform reservoir
93
.
Data availability
The data generated in this study are provided in the Source Data
fi
le and available in the
fi
gshare database under
https://doi.org/10.6084/m9.
fi
gshare.19355633
.
Received: 29 May 2021; Accepted: 6 June 2022;
References
1. Talley, L. D. Closure of the global overturning circulation through the Indian,
Paci
fi
c, and Southern Oceans: Schematics and transports.
Oceanography
26
,
80
97 (2013).
2. Key, R. M. et al. A global ocean carbon climatology: results from global data
analysis project (GLODAP).
Glob. Biogeochem. Cycles
18
, GB4031 (2004).
3. Warren, B. A. Why is no deep water formed in the North Paci
fi
c?
J. Mar. Res.
41
, 327
347 (1983).
4. Gordon, A. L. Interocean exchange of thermocline water.
J. Geophys. Res.
Oceans
91
, 5037
5046 (1986).
5. Marshall, J. & Speer, K. Closure of the meridional overturning circulation
through Southern Ocean upwelling.
Nat. Geosci.
5
, 171
180 (2012).
6. Rintoul, S. R. South Atlantic interbasin exchange.
J. Geophys. Res. Oceans
96
,
2675
2692 (1991).
7. Rintoul, S. R. & Sokolov, S. Baroclinic transport variability of the Antarctic
Circumpolar Current south of Australia (WOCE repeat section SR3).
J.
Geophys. Res. Oceans
106
, 2815
2832 (2001).
8. Speich, S., Blanke, B. & Madec, G. Warm and cold water routes of an
O.G.C.M. thermohaline conveyor belt.
Geophys. Res. Lett.
28
, 311
314 (2001).
9. Speich, S. et al. Tasman leakage: a new route in the global ocean conveyor belt.
Geophys. Res. Lett
.
29
, 55-1
55
4 (2002).
10. Ridgway, K. R. & Dunn, J. R. Observational evidence for a Southern
Hemisphere oceanic supergyre.
Geophys. Res. Lett
.
34
, L13612 (2007).
11. van Sebille, E., England, M. H., Zika, J. D. & Sloyan, B. M. Tasman leakage in a
fi
ne-resolution ocean model.
Geophys. Res. Lett
.
39
, L06601 (2012).
12. van Sebille, E. et al. Paci
fi
c-to-Indian Ocean connectivity: Tasman leakage,
Indonesian through
fl
ow, and the role of ENSO.
J. Geophys. Res. Oceans
119
,
1365
1382 (2014).
13. Bostock, H. C., Sutton, P. J., Williams, M. J. M. & Opdyke, B. N. Reviewing the
circulation and mixing of Antarctic intermediate water in the South Paci
fi
c
using evidence from geochemical tracers and Argo
fl
oat trajectories.
Deep Sea
Res. Part I Oceanogr. Res. Pap.
73
,84
98 (2013).
14. Orsi, A. H., Whitworth, T. & Nowlin, W. D. On the meridional extent and
fronts of the Antarctic circumpolar current.
Deep Sea Res. Part I Oceanogr.
Res. Pap.
42
, 641
673 (1995).
15. Biastoch, A., Boning, C. W., Schwarzkopf, F. U. & Lutjeharms, J. R. E. Increase
in Agulhas leakage due to poleward shift of southern hemisphere westerlies.
Nature
462
, 495
498 (2009).
16. Qu, T., Fukumori, I. & Fine, R. A. Spin-up of the southern hemisphere super
gyre.
J. Geophys. Res. Oceans
124
, 154
170 (2019).
17. Rousselet, L., Cessi, P. & Forget, G. Routes of the upper branch of the Atlantic
meridional overturning circulation according to an Ocean state estimate.
Geophys. Res. Lett.
47
, e2020GL089137 (2020).
18. Sprintall, J. et al. The Indonesian seas and their role in the coupled
ocean
climate system.
Nat. Geosci.
7
, 487
492 (2014).
19. Bard, E. & Rickaby, R. E. M. Migration of the subtropical front as a modulator
of glacial climate.
Nature
460
, 380
383 (2009).
20. Okazaki, Y. et al. Deepwater formation in the North Paci
fi
c during the last
glacial termination.
Science
329
, 200
204 (2010).
21. De Deckker, P., Moros, M., Perner, K. & Jansen, E. In
fl
uence of the tropics and
southern westerlies on glacial interhemispheric asymmetry.
Nat. Geosci.
5
,
266
269 (2012).
ARTICLE
NATURE COMMUNICATIONS | https://doi.org/10.1038/s41467-022-31116-7
8
NATURE COMMUNICATIONS
| (2022) 13:3763 | https://doi.org/10.1038/s41467-022-31116-7 | www.nature.com/naturecommunications
22. Lamy, F. et al. Glacial reduction and millennial-scale variations in Drake
Passage through
fl
ow.
Proc. Natl Acad. Sci. USA
112
, 13496
13501 (2015).
23. Sun, S. & Thompson, A. F. Centennial changes in the Indonesian through
fl
ow
connected to the Atlantic meridional overturning circulation: the ocean
s
transient conveyor belt.
Geophys. Res. Lett.
47
, e2020GL090615 (2020).
24. Feng, M., Zhang, X., Sloyan, B. & Chamberlain, M. Contribution of the deep
ocean to the centennial changes of the Indonesian Through
fl
ow.
Geophys. Res.
Lett.
44
, 2859
2867 (2017).
25. Holbourn, A. et al. Orbitally paced paleoproductivity variations in the Timor
Sea and Indonesian Through
fl
ow variability during the last 460 kyr.
Paleoceanography
20
, PA3002 (2005).
26. Stumpf, R. et al. Persistently strong Indonesian Through
fl
ow during marine
isotope stage 3: evidence from radiogenic isotopes.
Quat. Sci. Rev.
112
,
197
206 (2015).
27. Petrick, B. et al. Glacial Indonesian Through
fl
ow weakening across the mid-
Pleistocene climatic transition.
Sci. Rep.
9
, 16995 (2019).
28. Franzese, A. M., Hemming, S. R., Goldstein, S. L. & Anderson, R. F. Reduced
Agulhas Leakage during the Last Glacial Maximum inferred from an
integrated provenance and
fl
ux study.
Earth Planet. Sci. Lett.
250
,72
88
(2006).
29. Martínez-Méndez, G. et al. Contrasting multiproxy reconstructions of surface
ocean hydrography in the Agulhas Corridor and implications for the Agulhas
Leakage during the last 345,000 years.
Paleoceanography
25
, PA4227 (2010).
30. Robinson, L. F. & van de Flierdt, T. Southern Ocean evidence for reduced
export of North Atlantic Deep Water during Heinrich event 1.
Geology
37
,
195
198 (2009).
31. Burke, A. & Robinson, L. F. The Southern Ocean
s role in carbon exchange
during the last deglaciation.
Science
335
, 557
561 (2012).
32. Roberts, J. et al. Deglacial changes in
fl
ow and frontal structure through the
Drake Passage.
Earth Planet. Sci. Lett.
474
, 397
408 (2017).
33. Struve, T., Wilson, D. J., Flierdt, T., van de, Pratt, N. & Crocket, K. C. Middle
Holocene expansion of Paci
fi
c Deep Water into the Southern Ocean.
Proc.
Natl Acad. Sci. USA
117
, 889
894 (2020).
34. Wilson, D. J. et al. Sea-ice control on deglacial lower cell circulation changes
recorded by Drake Passage deep-sea corals.
Earth Planet. Sci. Lett.
544
, 116405
(2020).
35. Rae, J. W. B. et al. Overturning circulation, nutrient limitation, and warming
in the Glacial North Paci
fi
c.
Sci. Adv.
6
, eabd1654 (2020).
36. Lambelet, M. et al. Neodymium isotopic composition and concentration in the
western North Atlantic Ocean: results from the GEOTRACES GA02 section.
Geochim. Cosmochim. Acta
177
,1
29 (2016).
37. Fröllje, H. et al. Hawaiian imprint on dissolved Nd and Ra isotopes and rare
earth elements in the central North Paci
fi
c: Local survey and seasonal
variability.
Geochim. Cosmochim. Acta
189
, 110
131 (2016).
38. Behrens, M. K., Pahnke, K., Schnetger, B. & Brumsack, H.-J. Sources and
processes affecting the distribution of dissolved Nd isotopes and
concentrations in the West Paci
fi
c.
Geochim. Cosmochim. Acta
222
, 508
534
(2018).
39. Stichel, T., Frank, M., Rickli, J. & Haley, B. A. The hafnium and neodymium
isotope composition of seawater in the Atlantic sector of the Southern Ocean.
Earth Planet. Sci. Lett.
317
318
, 282
294 (2012).
40. Lambelet, M. et al. The neodymium isotope
fi
ngerprint of Adélie Coast
bottom water.
Geophys. Res. Lett.
45
, 11,247
11,256 (2018).
41. Carter, P., Vance, D., Hillenbrand, C. D., Smith, J. A. & Shoosmith, D. R. The
neodymium isotopic composition of waters masses in the eastern Paci
fi
c
sector of the Southern Ocean.
Geochim. Cosmochim. Acta
79
,41
59 (2012).
42. Basak, C., Pahnke, K., Frank, M., Lamy, F. & Gersonde, R. Neodymium
isotopic characterization of Ross Sea Bottom Water and its advection through
the southern South Paci
fi
c.
Earth Planet. Sci. Lett.
419
, 211
221 (2015).
43. Thiagarajan, N. et al. Movement of deep-sea coral populations on climatic
timescales.
Paleoceanography
28
, 227
236 (2013).
44. Hines, S. K. V., Southon, J. R. & Adkins, J. F. A high-resolution record of
Southern Ocean intermediate water radiocarbon over the past 30,000 years.
Earth Planet. Sci. Lett.
432
,46
58 (2015).
45. van de Flierdt, T., Robinson, L. F. & Adkins, J. F. Deep-sea coral aragonite as a
recorder for the neodymium isotopic composition of seawater.
Geochim.
Cosmochim. Acta
74
, 6014
6032 (2010).
46. Struve, T. et al. Neodymium isotopes and concentrations in aragonitic
scleractinian cold-water coral skeletons - Modern calibration and evaluation
of palaeo-applications.
Chem. Geol.
453
, 146
168 (2017).
47. Cogez, A. et al. Constraints on the role of tectonic and climate on erosion
revealed by two time series analysis of marine cores around New Zealand.
Earth Planet. Sci. Lett.
410
, 174
185 (2015).
48. Bayon, G. et al. Extensive wet episodes in Late Glacial Australia resulting from
high-latitude forcings.
Sci. Rep.
7
, 44054 (2017).
49. De Deckker, P. Airborne dust traf
fi
c from Australia in modern and Late
Quaternary times.
Glob. Planet. Change
184
, 103056 (2020).
50. Wilson, D. J., van de Flierdt, T. & Adkins, J. F. Lead isotopes in deep-sea coral
skeletons: Ground-truthing and a
fi
rst deglacial Southern Ocean record.
Geochim. Cosmochim. Acta
204
, 350
374 (2017).
51. Henderson, G. M. & Maier-Reimer, E. Advection and removal of 210Pb and
stable Pb isotopes in the oceans: a general circulation model study.
Geochim.
Cosmochim. Acta
66
, 257
272 (2002).
52. Anderson, R. F. et al. Wind-driven upwelling in the southern ocean and the
deglacial rise in atmospheric CO2.
Science
323
, 1443
1448 (2009).
53. Noble, T. L., Piotrowski, A. M. & McCave, I. N. Neodymium isotopic
composition of intermediate and deep waters in the glacial southwest Paci
fi
c.
Earth Planet. Sci. Lett.
384
,27
36 (2013).
54. Hu, R. & Piotrowski, A. M. Neodymium isotope evidence for glacial-
interglacial variability of deepwater transit time in the Paci
fi
c Ocean.
Nat.
Commun.
9
, 4709 (2018).
55. Hu, R. et al. Neodymium isotopic evidence for linked changes in Southeast
Atlantic and Southwest Paci
fi
c circulation over the last 200 kyr.
Earth Planet.
Sci. Lett.
455
, 106
114 (2016).
56. Piotrowski, A. M., Goldstein, S. L., Hemming, S. R. & Fairbanks, R. G.
Temporal relationships of carbon cycling and ocean circulation at glacial
boundaries.
Science
307
, 1933
1938 (2005).
57. Piotrowski, A. M. et al. Indian Ocean circulation and productivity during the
last glacial cycle.
Earth Planet. Sci. Lett.
285
, 179
189 (2009).
58. Skinner, L. C. et al. North Atlantic versus Southern Ocean contributions to a
deglacial surge in deep ocean ventilation.
Geology
41
, 667
670 (2013).
59. Wilson, D. J., Piotrowski, A. M., Galy, A. & Banakar, V. K. Interhemispheric
controls on deep ocean circulation and carbon chemistry during the last two
glacial cycles.
Paleoceanography
30
, 621
641 (2015).
60. Basak, C. et al. Breakup of last glacial deep strati
fi
cation in the South Paci
fi
c.
Science
359
, 900
904 (2018).
61. Howe, J. N. W. et al. North Atlantic deep water production during the Last
Glacial Maximum.
Nat. Commun.
7
, 11765 (2016).
62. Zhao, N. et al. Glacial
interglacial Nd isotope variability of North Atlantic
deep water modulated by North American ice sheet.
Nat. Commun.
10
, 5773
(2019).
63. Du, J., Haley, B. A., Mix, A. C., Walczak, M. H. & Praetorius, S. K. Flushing of
the deep Paci
fi
c Ocean and the deglacial rise of atmospheric CO2
concentrations.
Nat. Geosci.
11
, 749
755 (2018).
64. Skinner, L. C. et al. Radiocarbon constraints on the glacial ocean circulation
and its impact on atmospheric CO2.
Nat. Commun.
8
, 16010 (2017).
65. Pahnke, K. & Zahn, R. Southern hemisphere water mass conversion linked
with North Atlantic climate variability.
Science
307
, 1741
1746 (2005).
66. Ronge, T. A. et al. Pushing the boundaries: glacial/interglacial variability of
intermediate and deep waters in the southwest Paci
fi
c over the last 350,000
years.
Paleoceanography
30
, 2014PA002727 (2015).
67. Durand, A. et al. Reduced oxygenation at intermediate depths of the southwest
Paci
fi
c during the last glacial maximum.
Earth Planet. Sci. Lett.
491
,48
57
(2018).
68. Martínez Fontaine, C. et al. Ventilation of the deep ocean carbon reservoir
during the last deglaciation: results from the Southeast Paci
fi
c.
Paleoceanogr.
Paleoclimatol.
34
, 2080
2097 (2019).
69. Li, T. et al. Rapid shifts in circulation and biogeochemistry of the Southern
Ocean during deglacial carbon cycle events.
Sci. Adv
.
6
, eabb3807 (2020).
70. Sikes, E. L., Elmore, A. C., Allen, K. A., Cook, M. S. & Guilderson, T. P. Glacial
water mass structure and rapid
δ
18O and
δ
13C changes during the last glacial
termination in the Southwest Paci
fi
c.
Earth Planet. Sci. Lett.
456
,87
97
(2016).
71. Hu, R., Piotrowski, A. M., Bostock, H. C., Crowhurst, S. & Rennie, V.
Variability of neodymium isotopes associated with planktonic foraminifera in
the Paci
fi
c Ocean during the Holocene and Last Glacial Maximum.
Earth
Planet. Sci. Lett.
447
, 130
138 (2016).
72. Wu, Q. et al. Foraminiferal
ε
Nd in the deep north-western subtropical Paci
fi
c
Ocean: Tracing changes in weathering input over the last 30,000 years.
Chem.
Geol.
470
,55
66 (2017).
73. Talley, L. D. Distribution and formation of North Paci
fi
c intermediate water.
J.
Phys. Oceanogr.
23
, 517
537 (1993).
74. Bingham, F. M. & Lukas, R. The southward intrusion of North Paci
fi
c
intermediate water along the Mindanao Coast.
J. Phys. Oceanogr.
24
, 141
154
(1994).
75. Gordon, A. L., Giulivi, C. F. & Ilahude, A. G. Deep topographic barriers within
the Indonesian seas.
Deep Sea Res. Part II Top. Stud. Oceanogr.
50
, 2205
2228
(2003).
76. Sprintall, J., Wijffels, S. E., Molcard, R. & Jaya, I. Direct estimates of the
Indonesian Through
fl
ow entering the Indian Ocean: 2004
2006.
J. Geophys.
Res. Oceans
114
, (2009).
77. McCreary, J. P. & Lu, P. In
fl
uence of the Indonesian Through
fl
ow on the
circulation of Paci
fi
c intermediate water.
J. Phys. Oceanogr.
31
, 932
942
(2001).
NATURE COMMUNICATIONS | https://doi.org/10.1038/s41467-022-31116-7
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