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PALEOCEANOGRAPHY, VOL. 24, PA4206, doi:10.1029/2008PA001725, 2009
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Article
North Atlantic Current variability through marine isotope stage M2
(circa 3.3 Ma) during the mid-Pliocene
Stijn De Schepper,1 Martin J. Head,2 and Jeroen Groeneveld3,4
Received 16 December 2008; revised 9 June 2009; accepted 25 June 2009; published 29 October 2009.
[1] The mid-Pliocene was an episode of prolonged global warmth and strong North Atlantic thermohaline
circulation, interrupted briefly at circa 3.30 Ma by a global cooling event corresponding to marine isotope stage
(MIS) M2. Paleoceanographic changes in the eastern North Atlantic have been reconstructed between circa 3.35
and 3.24 Ma at Deep Sea Drilling Project Site 610 and Integrated Ocean Drilling Program Site 1308. Mg/Ca
ratios and d 18O from Globigerina bulloides are used to reconstruct the temperature and relative salinity of
surface waters, and dinoflagellate cyst assemblages are used to assess variability in the North Atlantic Current
(NAC). Our sea surface temperature data indicate warm waters at both sites before and after MIS M2 but a
cooling of 2–3°C during MIS M2. A dinoflagellate cyst assemblage overturn marked by a decline in
Operculodinium centrocarpum reflects a southward shift or slowdown of the NAC between circa 3.330 and
3.283 Ma, reducing northward heat transport 23–35 ka before the global ice volume maximum of MIS M2. This
will have established conditions that ultimately allowed the Greenland ice sheet to expand, leading to the global
cooling event at MIS M2. Comparison with an ice-rafted debris record excludes fresh water input via icebergs in
the northeast Atlantic as a cause of NAC decline. The mechanism causing the temporary disruption of the NAC
may be related to a brief reopening of the Panamanian Gateway at about this time.
Citation: De Schepper, S., M. J. Head, and J. Groeneveld (2009), North Atlantic Current variability through marine isotope stage M2
(circa 3.3 Ma) during the mid-Pliocene, Paleoceanography, 24, PA4206, doi:10.1029/2008PA001725.
1. Introduction
[2] Our present knowledge of mid-Pliocene ocean circulation relies mainly on studies of the mid-Pliocene Warm
Period by the Pliocene Research, Interpretation and Synoptic Mapping (PRISM) project. The overall configuration
of North Atlantic surface currents was largely comparable
to the present day [e.g., Dowsett et al., 2009], but extensive
warming occurred in the North Atlantic and global temperatures reached higher values than today [e.g., Dowsett et
al., 1996; Haywood et al., 2002; Dowsett et al., 2005;
Dowsett, 2007]. This warming has been related to increased
meridional overturning and a more vigorous thermohaline
circulation (THC) [Raymo et al., 1996; Ravelo and
Andreasen, 2000], possibly driven by the progressive
closure of the Panamanian Gateway [Haug and Tiedemann, 1998; Bartoli et al., 2005].
[3] A major cooling event is observed at around 3.30 Ma
in the mid-Pliocene marine isotope stage (MIS) M2 [Prell,
1984; Keigwin, 1987; Shackleton et al., 1995; Jansen et
al., 2000; Lisiecki and Raymo, 2005; Tiedemann et al.,
1
Fachbereich Geowissenschaften, Universität Bremen, Bremen,
Germany.
2
Department of Earth Sciences, Brock University, St. Catharines,
Ontario, Canada.
3
MARUM, Universität Bremen, Bremen, Germany.
4
Now at MARUM Excellence Cluster, Alfred Wegener Institute,
Bremerhaven, Germany.
Copyright 2009 by the American Geophysical Union.
0883-8305/09/2008PA001725$12.00
2006; Head et al., 2008]. Also known as the Mammoth
cooling event after the Mammoth Subchron in which it
occurs, MIS M2 may represent a failed attempt of the
climate system to reach a full glacial state [Haug and
Tiedemann, 1998]. The large amplitude of the d18O shift
and inferred major sea level fall across MIS M2 [Lisiecki
and Raymo, 2005] compare with those of the early
Quaternary, suggesting a significant buildup of continental
ice in the Northern Hemisphere [Dwyer and Chandler,
2009]. Indeed, ice-rafted detritus (IRD) first appears as far
south as 53°N (DSDP Site 610) during MIS M2 [Kleiven
et al., 2002]. Oceanographic conditions in the North
Atlantic during MIS M2 may therefore have been comparable to those during Quaternary glacial episodes, involving reduced meridional overturning. However, the effect of
global cooling during MIS M2 [e.g., Backman and
Shackleton, 1983; Suc, 1984; Ehrmann and Keigwin,
1987] on North Atlantic surface ocean circulation or vice
versa remains elusive. Furthermore, even though a
strengthened North Atlantic Current (NAC) seems to have
played a major role in the intensification of the Northern
Hemisphere glaciation [e.g., Bartoli et al., 2005], its
variability during MIS M2 is unknown.
[4] Our investigation aims to understand the variability of
the NAC and the timing of its changes relative to the global
cooling event MIS M2 (circa 3.30 Ma, mid-Pliocene). Deep
Sea Drilling Project (DSDP) Hole 610A and Integrated
Ocean Drilling Program (IODP) Hole 1308C (Figure 1)
are located favorably to monitor the history of the NAC.
Geochemical signals (d18O and Mg/Ca) from the planktonic
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1 of 17
PA4206
DE SCHEPPER ET AL.: MID-PLIOCENE NAC VARIABILITY
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Figure 1. Location of DSDP Hole 610A and IODP Hole 1308C in the eastern North Atlantic, where
modern anually averaged sea surface (0 m) temperatures [Locarnini et al., 2006] are shown. The light
gray line is the 500 m isobath. Arrows show the warm surface water currents: North Atlantic Current
(NAC) and European Shelf Edge Current/Continental Slope Current (CSC). Simplified after Hansen and
Østerhus [2000]. Dashed line represents the modern Arctic Front (AF) [after Swift, 1986].
foraminifer Globigerina bulloides are applied as proxies for
sea surface temperature (SST) and salinity. Additionally,
dinoflagellate cyst assemblages are used as indicators of
surface water mass changes across MIS M2. Dinoflagellate
cysts have well known distributions in the North Atlantic
today [e.g., de Vernal et al., 2001], and have been used
successfully to reconstruct paleoceanographic conditions
not only in the later Quaternary [e.g., Matthiessen, 1995;
de Vernal et al., 2005] but also in the Pliocene [e.g.,
Versteegh, 1997]. The advantage of combining these proxies is that changes in surface water masses or ocean currents
such as the NAC (dinoflagellate cyst assemblages) are
linked directly to independent temperature and relative
salinity variations (geochemistry).
2. Background
2.1. Regional Setting and Oceanography
[5] In the modern North Atlantic Ocean, transport of
warm and saline waters to northern latitudes occurs via
the NAC and a Continental Slope Current [e.g., Hansen and
Østerhus, 2000] (Figure 1). The latter current is apparently
not linked directly to the NAC, although the boundary
between these two flows is not always clear, with NAC
waters entering the Rockall Trough at times from the south.
2 of 17
PA4206
DE SCHEPPER ET AL.: MID-PLIOCENE NAC VARIABILITY
The surface water mass in the Rockall Trough bears
properties of NAC waters as well as Eastern North Atlantic
Water (ENAW) that itself originates in the Bay of Biscay
region [Hansen and Østerhus, 2000; Holliday et al., 2000].
In the Nordic seas, the Arctic Front marks the boundary
between warm Atlantic waters in the east and those of the
arctic domain in the west [Swift, 1986].
[6] The arctic domain is the main region where deep
water is formed today. During the Last Glacial Maximum
(LGM), deep water formation occurred in the subpolar
North Atlantic, south of its present-day area of formation
in the Nordic seas [e.g., Labeyrie et al., 1992; Alley and
Clark, 1999; Sarnthein et al., 2000; Clark et al., 2002]. The
Arctic Front was then located at 37 – 45°N (Figure 1),
suggesting an eastward directed NAC [Pflaumann et al.,
2003]. The Nordic seas remained largely ice-free during
summer but ice covered to 60°N during winter [Kucera et
al., 2005]. The midlatitude North Atlantic was further
characterized by an anticyclonic gyre that transported warm
water up to 60°N in the western North Atlantic and cool
waters south along the western margin of the British Isles
[Pflaumann et al., 2003].
2.2. DSDP Hole 610A and IODP Hole 1308C
[7] DSDP Hole 610A (53°130N, 18°530N; 2417 m water
depth) is located approximately 700 km west of Ireland at
the southwestern edge of the Rockall Trough. The hole was
drilled on Feni Drift, a large and elongated sediment drift
that had been forming along the northwestern flank of the
Rockall Trough since the Oligocene –Miocene [McCave and
Tucholke, 1986; Stoker, 1997; Stoker et al., 1998; McDonnel
and Shannon, 2001; Stoker et al., 2005]. The sampled
interval consists of uniform calcareous nannofossil ooze
[Shipboard Scientific Party, 1987] and the sedimentation rate
is 5 cm/ka [De Schepper and Head, 2008a].
[8] The more southerly IODP Hole 1308C (49°530N,
24°140W; 3900 m water depth), a reoccupation of DSDP
Site 609, was drilled on the eastern flank of the MidAtlantic Ridge, about 400 km southwest of Site 610. The
section studied consists of nannofossil ooze with or without
silty clay, and has a sedimentation rate of about 8 cm/ka
[Expedition 303 Scientists, 2006].
[9] Both sites are located along the present-day trajectory
of the NAC (Figure 1) and provide a northeast – southwest
transect through the cool to mild temperate climate zones of
the eastern North Atlantic. Present-day annual average
temperatures at 0 –50 m depth for Sites 610 and 1308 are
11.7 and 13.1°C, respectively [Locarnini et al., 2006].
2.3. Existing Age Models for the Sites
[10] An age model for Hole 610A was published by
Baldauf et al. [1987], but inconsistencies in the magnetostratigraphy and biostratigraphy prompted revisions [De
Schepper and Head, 2008a]. The new model combined
the benthic isotope stratigraphy of Kleiven et al. [2002] for
the interval 3.6– 2.4 Ma with new, reinterpreted, and existing biostratigraphic and magnetostratigraphic data. The data
of Kleiven et al. [2002] were recalibrated to the LR04 global
stack of Lisiecki and Raymo [2005] to provide the most upto-date chronology possible for Hole 610A [De Schepper
and Head, 2008a].
PA4206
[11] For Hole 1308C, only the magnetostratigraphic
reversals identified by Expedition 303 Scientists [2006]
are available to establish an age model for the mid-Pliocene.
3. Material and Methods
3.1. Samples
[12] Twenty-one samples from Hole 610A were analyzed
for dinoflagellate cysts and tests of the planktonic foraminifer Globigerina bulloides. Samples were selected between
163.02 and 159.60 m below seafloor (mbsf) from sections
610A-18-1, 610A-17-6, and 610A-17-5 (Tables 1a and 1b).
The distance between samples varies from 6 to 23 (average
14) cm, corresponding to 1.3– 16.7 (average 4.7) ka, except
that between section 610A-18-1 and 610A-17-6, a gap of
about 77 cm results from poor sediment recovery.
[13] From Hole 1308C, seventeen samples were analyzed
for dinoflagellate cysts and G. bulloides between 260.61 and
266.49 meters composite depth (mcd) (235.19–240.49 mbsf).
Benthic foraminifers were recorded only sporadically, and
hence not analyzed. The distance between samples varies
from 22 to 61 (average 39) cm, representing 2.8–10.4 (average
5.5) ka. Stable isotopes and Mg/Ca ratios were measured
between 253.47 and 268.59 mcd (228.74–242.39 mbsf).
[14] Dinoflagellate cysts and tests of G. bulloides were
extracted from the same sample to facilitate direct comparison. Samples of about 10 cm3 were wet sieved at 125 mm
to retain the foraminifers and ensure that all dinoflagellate
cysts (size range 15– 100 mm) passed through the sieve. The
sediment filtrate (<125 mm) was dried, weighed and prepared for dinoflagellate cyst analysis using standard techniques [De Schepper and Head, 2008b]: Lycopodium
clavatum tablets were added, followed by digestion in cold
HCl and HF. No oxidation, alkali or ultrasonic treatments
were applied. Organic residues were sieved through a
10-mm nylon mesh and strew mounted onto microscope
slides using glycerine jelly. The >125 mm fraction was
subsequently dry sieved to obtain a 250– 315 mm fraction.
Globigerina bulloides tests were picked from this fraction
for d 18O and Mg/Ca analyses.
3.2. Planktonic Foraminiferal Geochemical Analysis
[15] From the Hole 610A samples, at least 25 tests per
sample of Globigerina bulloides were measured for stable
isotopes at the Godwin Laboratory (University of Cambridge).
Samples were first treated with a 3% solution of hydrogen
peroxide to remove organic contaminants. Tests were then
crushed, cleaned using an ultrasonic bath, and rinsed with
acetone. The samples were reacted with 100% orthophosphoric
acid at 90°C using a Micromass Multicarb Sample Preparation
System. The carbon dioxide produced was dried and transferred cryogenically into a VG Isotech SIRA–Series II mass
spectrometer for isotopic analysis. The results were reported
with reference to the international standard VPDB (Vienna
Peedee belemnite) calibrated through the NBS19 standard
[Coplen, 1995], and the analytical precision was better than ±
0.08% for 18O/16O.
[16] A Finnigan MAT 251 mass spectrometer was used to
measure the d18O composition of G. bulloides (5 tests
from the 250– 315 mm fraction) from Hole 1308C. The
isotopic composition of the carbonate sample was measured
3 of 17
1308C-26-2
1308C-26-3
1308C-26-3
1308C-26-3
1308C-26-3
1308C-26-3
1308C-26-4
1308C-26-4
1308C-26-4
1308C-26-4
1308C-26-4
1308C-26-5
1308C-26-5
1308C-26-5
1308C-26-5
1308C-26-6
1308C-26-6
Aco
0.00
0.00
0.00
0.01
0.00
0.00
0.02
0.03
0.03
0.01
0.03
0.02
0.03
0.00
0.01
0.00
0.00
26-2a
26-3e
26-3d
26-3c
26-3b
26-3a
26-4e
26-4d
26-4c
26-4b
26-4a
26-5d
26-5c
26-5b
26-5a
26-6b
26-6a
Sample
Code
26-2a
26-3e
26-3d
26-3c
26-3b
26-3a
26-4e
26-4d
26-4c
26-4b
26-4a
26-5d
26-5c
26-5b
26-5a
26-6b
26-6a
0.01
0.01
0.01
0.02
0.01
0.00
0.01
0.05
0.05
0.01
0.03
0.03
0.01
0.00
0.00
0.01
0.00
Clab
129 – 131
20 – 22
51 – 53
76 – 78
107 – 109
139 – 141
14 – 16
44 – 46
69 – 71
105 – 107
144 – 146
14 – 16
44 – 46
79 – 81
109 – 111
14 – 16
59 – 61
SI (cm)
0.01
0.06
0.05
0.08
0.03
0.00
0.10
0.30
0.35
0.14
0.22
0.18
0.10
0.00
0.11
0.05
0.03
Iacu
235.19
235.60
235.91
236.16
236.47
236.79
237.04
237.34
237.59
237.95
238.34
238.54
238.84
239.19
239.49
240.04
240.49
Depth
(mbsf)
0.00
0.02
0.00
0.02
0.01
0.00
0.02
0.01
0.02
0.05
0.04
0.05
0.03
0.00
0.07
0.00
0.01
Ipal
260.61
261.07
261.41
261.69
262.03
262.39
262.66
263.00
263.27
263.67
264.11
264.33
264.66
265.05
265.38
265.99
266.49
Depth
(mcd)
0.00
0.01
0.03
0.10
0.05
0.00
0.07
0.13
0.16
0.08
0.17
0.10
0.13
0.01
0.12
0.02
0.02
Ipar
3253
3260
3266
3270
3274
3280
3285
3291
3300
3309
3320
3325
3328
3332
3334
3340
3346
Age
(ka)
0.01
0.01
0.03
0.01
0.00
0.00
0.01
0.01
0.01
0.02
0.05
0.03
0.02
0.00
0.00
0.00
0.00
Ipat
1.18
1.05
1.34
1.03
1.31
1.24
1.44
2.12
2.03
1.64
1.06
1.26
1.18
1.07
1.08
1.18
1.10
d18O
(%)
0.01
0.01
0.00
0.00
0.04
0.02
0.07
0.03
0.02
0.04
0.05
0.09
0.02
0.00
0.03
0.01
0.11
0.00
0.06
0.02
0.03
0.05
0.00
0.05
0.02
0.00
0.00
0.01
0.01
0.00
0.00
0.02
0.01
0.00
Itab
2.66
2.55
3.26
3.41
3.61
3.31
2.35
2.05
1.84
2.02
2.43
2.44
2.45
2.62
2.72
2.39
2.39
0.05
0.10
0.37
0.13
0.07
0.19
0.27
0.11
0.23
0.18
0.31
0.27
0.44
0.16
0.39
0.08
0.37
Ilac
Mg/Ca
(mmol/mol)
d13C
(%)
0.07
0.14
0.10
0.02
0.30
0.07
0.24
0.14
0.16
0.46
0.21
0.15
0.33
0.12
0.19
0.15
0.07
Nlab
15.6
15.2
17.6
18.1
18.6
17.8
14.4
13.0
11.9
12.8
14.7
14.7
14.8
15.4
15.8
14.5
14.5
SSTMg/Ca
(deg C)
0.86
0.60
0.70
0.62
0.44
0.90
0.20
0.06
0.02
0.03
0.03
0.21
0.22
0.82
0.29
0.74
0.73
Ocen
1.14
0.92
1.77
1.57
1.96
1.71
1.12
1.47
1.12
0.96
0.82
1.03
0.96
1.00
1.10
0.90
0.82
d 18Osw
(%)
0.02
0.02
0.00
0.00
0.00
0.00
0.01
0.00
0.00
0.00
0.00
0.02
0.03
0.03
0.04
0.00
0.02
Smir
1.28
1.02
1.71
1.55
1.89
1.71
0.98
1.06
0.67
0.84
0.97
1.08
1.01
1.03
1.11
0.76
0.80
d 18Osw-ice
(%)
0.03
0.13
0.09
0.14
0.13
0.02
0.26
0.26
0.20
0.18
0.25
0.18
0.12
0.03
0.26
0.03
0.02
Other
1449
1134
1117
259
277
3597
317
267
263
254
96
249
144
1053
133
444
359
DC
(cyst/g)
9
8
7
2
2
20
2
1
1
1
0
1
2
10
1
3
3
DAR
(cysts/cm2/a)
18
11
26
11
1
12
26
68
56
29
12
21
14
0
0
0
2
BPC
(cyst/g)
0.99
0.99
0.98
0.96
1.00
1.00
0.92
0.80
0.83
0.90
0.88
0.92
0.91
1.00
1.00
1.00
0.99
D/(D + P)b
0.62
1.50
1.26
1.65
1.67
0.50
2.27
2.39
2.18
1.99
2.30
2.39
2.08
0.73
2.34
0.99
1.09
S-W
0.23
0.51
0.43
0.54
0.56
0.23
0.78
0.73
0.72
0.66
0.78
0.77
0.71
0.30
0.79
0.40
0.40
Evenness
DE SCHEPPER ET AL.: MID-PLIOCENE NAC VARIABILITY
4 of 17
a
Sea surface temperatures calculated using formula of Elderfield and Ganssen [2000]. Lower boundary of the Mammoth Subchron (3.330 Ma) is between samples 26-5b and 26-5c at 239.03 mbsf (see Figure 2).
Sample 26-6b is from marine isotope stage MG2, and samples 26-4d, 26-4c, and 26-4b belong to marine isotope stage M2. SI, sample interval; Aco, Ataxiodinium confusum; Clab, Corrudinium? labradori; Iacu,
Impagidinium aculeatum; Ipal, Impagidinium pallidum; Ipar, Impagidinium paradoxum; Ipat, Impagidinium patulum; Ilac, Invertocysta lacrymosa; Itab, Invertocysta tabulata; Nlab, Nematosphaeropsis
labyrinthus; Ocen, Operculodinium centrocarpum sensu Wall and Dale [1966]; Smir, Spiniferites mirabilis; Other, other species; DC, dinocyst concentration; DAR, dinocyst accumulation rate; BPC, bisaccate
pollen concentration; S-W, Shannon-Wiener index.
b
P is bisaccate only.
Hole-CoreSection
Sample
Code
Table 1a. Summarized Isotope and Mg/Ca Data for Globigerina bulloides, Including the Calculated Sea Surface Temperatures, and Dinoflagellate Cyst Relative Abundance Data From
IODP Hole 1308Ca
PA4206
PA4206
0.00
0.00
0.01
0.07
0.10
0.02
0.03
0.00
0.04
0.04
0.01
0.01
0.03
0.11
0.16
0.08
0.05
NA
0.04
0.01
0.00
17-5a
17-5b
17-5c
17-5d
17-5e
17-5f
17-5g
17-6a
17-6b
17-6c
17-6d
17-6e
17-6f
17-6g
17-6h
17-6i
17-6j
17-6CC
18-1a
18-1b
18-1c
0.03
0.00
0.01
0.01
0.04
0.01
0.02
0.00
0.01
0.00
0.00
0.02
0.04
0.08
0.06
0.08
0.04
NA
0.01
0.11
0.06
Ffil
60 – 62
79 – 81
90 – 92
98 – 100
114 – 116
130 – 132
136 – 138
9 – 11
22 – 24
30 – 32
44 – 46
61 – 63
76 – 78
94 – 96
105 – 107
117 – 119
132 – 134
8 – 10
11 – 13
29 – 31
42 – 44
SI (cm)
0.05
0.02
0.03
0.01
0.03
0.04
0.04
0.02
0.05
0.03
0.02
0.00
0.03
0.03
0.02
0.02
0.02
NA
0.02
0.16
0.07
Iacu
159.60
159.79
159.90
159.98
160.14
160.30
160.36
160.59
160.72
160.80
160.94
161.11
161.26
161.44
161.55
161.67
161.82
161.94
162.71
162.89
163.02
Depth
(mbsf)
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.00
0.01
0.02
0.01
0.01
0.02
0.05
0.02
0.02
0.02
NA
0.03
0.03
0.03
Ipal
3235
3246
3254
3257
3262
3266
3270
3274
3276
3278
3281
3285
3289
3293
3296
3299
3302
3304
3316
3319
3336
Age
(ka)
0.01
0.01
0.01
0.02
0.01
0.00
0.00
0.00
0.04
0.03
0.02
0.01
0.08
0.05
0.03
0.02
0.03
NA
0.03
0.02
0.02
Ipar
1.17
1.44
1.54
1.62
1.59
1.79
1.73
1.50
1.72
1.75
1.90
1.92
2.13
2.23
2.10
1.96
2.23
1.91
2.15
1.80
1.50
d 18O
(%)
0.07
0.02
0.05
0.02
0.01
0.00
0.00
0.00
0.04
0.01
0.00
0.00
0.00
0.01
0.00
0.00
0.00
NA
0.00
0.00
0.02
Ipat
0.18
0.20
0.31
0.31
0.28
0.38
0.33
0.41
0.17
0.34
0.38
0.03
0.17
0.28
0.25
0.28
0.32
0.15
0.22
0.05
0.22
d 13C
(%)
0.01
0.01
0.01
0.00
0.01
0.00
0.01
0.00
0.00
0.00
0.01
0.01
0.05
0.04
0.01
0.01
0.01
NA
0.01
0.02
0.05
Ilac
2.67
2.40
2.77
2.55
2.32
2.33
2.46
2.25
2.55
2.16
2.48
2.28
2.18
1.98
1.80
1.90
2.08
2.13
1.97
2.43
2.54
Mg/Ca
(mmol/mol)
0.05
0.06
0.04
0.06
0.21
0.32
0.23
0.10
0.13
0.10
0.35
0.17
0.29
0.26
0.33
0.35
0.31
NA
0.40
0.11
0.16
Nlab
15.6
14.6
16.0
15.2
14.2
14.3
14.8
13.9
15.2
13.5
14.9
14.0
13.6
12.6
11.7
12.2
13.1
13.4
12.6
14.7
15.1
SSTMg/Ca
(deg C)
0.36
0.47
0.51
0.39
0.26
0.35
0.43
0.74
0.55
0.62
0.44
0.72
0.18
0.04
0.07
0.08
0.03
NA
0.02
0.42
0.32
Ocen
1.15
1.16
1.60
1.49
1.23
1.45
1.52
1.07
1.59
1.23
1.71
1.52
1.63
1.50
1.14
1.13
1.62
1.35
1.41
1.56
1.35
d18Osw
(%)
0.02
0.00
0.00
0.00
0.11
0.06
0.11
0.03
0.04
0.02
0.03
0.01
0.09
0.09
0.12
0.18
0.39
NA
0.37
0.04
0.07
Pdal
1.23
1.36
1.70
1.56
1.25
1.37
1.47
0.97
1.53
1.20
1.63
1.39
1.31
1.00
0.64
0.65
1.23
1.03
1.31
1.52
1.35
d 18Osw-ice
(%)
0.06
0.07
0.07
0.07
0.02
0.03
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
NA
0.00
0.00
0.05
Smir
0.16
0.14
0.14
0.14
0.08
0.12
0.05
0.04
0.11
0.08
0.08
0.04
0.14
0.12
0.08
0.08
0.06
NA
0.05
0.05
0.09
Other
9,968
3,569
2,676
2,532
2,572
3,343
5,172
6,190
6,514
7,927
9,812
25,741
10,408
10,037
17,262
11,537
14,136
NA
24,068
5,637
9,321
DC
(cyst/g)
8
2
2
4
6
2
17
17
18
23
15
40
23
17
50
26
43
NA
113
26
2
DAR
(cysts/cm2/a)
0
39
8
8
78
41
87
19
325
214
78
289
629
905
884
352
243
NA
261
43
169
BPC
(cyst/g)
1.00
0.99
1.00
1.00
0.97
0.99
0.98
1.00
0.95
0.97
0.99
0.99
0.94
0.92
0.95
0.97
0.98
NA
0.99
0.99
0.98
D/(D+P)b
2.08
1.81
1.87
2.01
2.18
1.86
1.80
1.08
1.76
1.55
1.60
1.08
2.34
2.53
2.21
2.18
1.85
NA
1.69
1.97
2.29
S-W
0.67
0.59
0.60
0.65
0.73
0.63
0.58
0.38
0.59
0.53
0.53
0.39
0.73
0.77
0.70
0.66
0.60
NA
0.53
0.64
0.75
Evenness
DE SCHEPPER ET AL.: MID-PLIOCENE NAC VARIABILITY
5 of 17
a
Sea surface temperatures calculated using formula of Elderfield and Ganssen [2000]. Lower boundary of the Mammoth Subchron (3.330 Ma) is between samples 18-1c and 18-1b at 162.95 mbsf (see Figure 2).
Sample 18-1c is from marine isotope stage MG2; samples 17-6f, 17-6g, 17-6h, 17-6i, 17-6j, and 17-6CC belong to marine isotope stage M2; sample 17-5a is from marine isotope stage KM6. SI, sample interval;
Btep, Bitectatodinium tepikiense; Ffil, Filisphaera filifera; Iacu, Impagidinium aculeatum; Ipal, Impagidinium pallidum; Ipar, Impagidinium paradoxum; Ipat, Impagidinium patulum; Ilac, Invertocysta lacrymosa;
Nlab, Nematosphaeropsis labyrinthus; Ocen, Operculodinium centrocarpum sensu Wall and Dale [1966]; Pdal, cyst of Pentapharsodinium dalei; Smir, Spiniferites mirabilis/hyperacanthus; Other, other species;
DC, dinocyst concentration; DAR, dinocyst accumulation rate; BPC, bisaccate pollen concentration; S-W, Shannon-Wiener index; NA, not analyzed.
b
P is bisaccate only.
Btep
610A-17-5
610A-17-5
610A-17-5
610A-17-5
610A-17-5
610A-17-5
610A-17-5
610A-17-6
610A-17-6
610A-17-6
610A-17-6
610A-17-6
610A-17-6
610A-17-6
610A-17-6
610A-17-6
610A-17-6
610A-17-CC
610A-18-1
610A-18-1
610A-18-1
17-5a
17-5b
17-5c
17-5d
17-5e
17-5f
17-5g
17-6a
17-6b
17-6c
17-6d
17-6e
17-6f
17-6g
17-6h
17-6i
17-6j
17-6CC
18-1a
18-1b
18-1c
Sample
Code
Hole-CoreSection
Sample
Code
Table 1b. Summarized Isotope and Mg/Ca Data for Globigerina bulloides, Including the Calculated Sea Surface Temperatures, and Dinoflagellate Cyst Relative Abundance Data From
DSDP Hole 610Aa
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DE SCHEPPER ET AL.: MID-PLIOCENE NAC VARIABILITY
on the CO2 gas evolved by treatment with phosphoric acid
at a constant temperature of 75°C. For all stable isotope
measurements a working standard (Burgbrohl CO2 gas) was
used, which has been calibrated against VPDB by using the
NBS 18, 19 and 20 standards. The analytical standard
deviation was about ± 0.07% (Isotope Laboratory, Faculty
of Geosciences, University of Bremen).
[17] For the Mg/Ca measurements, about 40 tests of
G. bulloides from each sample of both holes were picked
and cleaned according to the procedure of Barker et al.
[2003]. After dissolution, the samples were centrifuged for
10 min at 6000 rpm and diluted for analysis on an ICPOES (Perkin Elmer Optima 3300R, Department of Geosciences, University of Bremen). The analytical precision of
the Mg/Ca analyses for G. bulloides was 0.23%, while
reproducibility based on replicate samples was ± 0.12
mmol/mol (3.5%). The validity of analyses was checked
by analyzing the Mg/Ca standard ECRM752-1 [Greaves et
al., 2008]. We used the algorithm of Elderfield and Ganssen
[2000], established from core top sediment samples in the
North Atlantic, to transform the foraminiferal Mg/Ca ratios
of G. bulloides into SSTMg/Ca: Mg/Ca = 0.52 exp 0.10 T.
The total error on the reconstruction of paleotemperature by
Mg/Ca is estimated to be 1.0– 1.5°C.
[ 18 ] The oxygen isotope composition of seawater
(d 18Osw) was calculated via the formula of Shackleton
[1974]. Since Mg/Ca and d18Obull are measured on the
same species, the possible effects of seasonality and habitat
differences are excluded. We used the global benthic d 18O
stack of Lisiecki and Raymo [2005] as an approximation for
changes in ice volume. After normalizing this record, we
subtracted it from d18Osw, resulting in a d 18Osw-ice record,
which indicates local variations in salinity alone. Because
the salinity-d 18Osw relationship for the Pliocene is not
known, changes can only be represented as relative changes
in salinity [Rohling, 2007].
3.3. Dinoflagellate Cyst Analysis
[19] All palynomorph groups (including pollen, acritarchs
and reworked dinoflagellate cysts) were counted at 40
magnification until at least 200 (and often 300) dinoflagellate cysts had been enumerated from each sample (auxiliary
material).1 Records outside of the counts were excluded
from calculations of relative abundances and paleoenvironmental indices. Dinoflagellate cyst concentrations (cysts/g
dry weight of the sample fraction <125 mm) and their
associated errors were calculated following Stockmarr
[1971]. The Shannon-Wiener diversity index [Krebs,
1998] for the dinoflagellate cysts, and the dinoflagellate
cyst/bisaccate pollen ratio (D/P = D/(D + P)), have been
calculated to aid interpretation [e.g., Versteegh and
Zonneveld, 1994; De Schepper et al., 2009].
4. Results
4.1. Age Models
[20] For Hole 610A, De Schepper and Head [2008a]
recalibrated the entire 3.6– 2.4 Ma benthic isotope data set
1
Auxiliary materials are available at ftp://ftp.agu.org/apend/pa/
2008pa001725.
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of Kleiven et al. [2002] to the LR04 global stack of Lisiecki
and Raymo [2005]. In the present study, the same exercise
was performed in greater detail for the time interval 3.40–
3.20 Ma (Figures 2a and 2b). The benthic isotope record of
Cibicides spp. of Kleiven et al. [2002] was graphically
correlated to the LR04 global stack (r = 0.76; Figure 2a)
using Analyseries 2.0.4.2 software [Paillard et al., 1996].
Magnetic reversals at the base and top of the Mammoth and
Kaena subchrons [Clement and Robinson, 1987] were used
as guidelines (Figure 2c). Reversals are usually placed at the
midpoint between two samples of differing polarity, so that
each reversal actually falls within an interval of uncertainty.
Because our age model for this interval is based on a
combination of isotope stratigraphy and magnetostratigraphy, and since we treat reversals not as tie points but narrow
intervals of uncertainty that constrain the model, our estimated position of reversals may differ slightly from those
listed in the work by Clement and Robinson [1987].
[21] For Hole 1308C, benthic foraminifers were insufficiently numerous to establish a benthic isotope record.
Therefore, the planktonic isotope record of G. bulloides
(Figure 2a) was correlated graphically to the LR04 stack
(r = 0.81) using the lower and upper paleomagnetic
reversals of the Mammoth Subchron [Expedition 303
Scientists, 2006]. All tie points used for the age models
are listed in Figure 2d.
[22] For Hole 610A (circa 3.336 –3.235 Ma) and Hole
1308C (circa 3.346 – 3.253 Ma), the absolute age of each
sample is based on interpolation from the respective age
model (Tables 1a and 1b). The accuracy of these ages
relative to the astronomical timescale is defined ultimately
by (1) the graphic correlation of Holes 610A and 1308C to
the LR04 stack and (2) the tuning errors of the LR04 stack
itself, which are less than 10 –15 ka for the interval studied
[Lisiecki and Raymo, 2005]. While the absolute (i.e.,
astronomically calibrated) ages of samples in our study will
be affected by errors inherent within the LR04 stack, these
errors will not significantly affect the estimated duration of
time between samples. Such durations are based on interpolation between tie points, and assume uniform sedimentation rates between each tie point. Likewise, errors in
correlation between Holes 610A and 1308C are based only
on the graphic correlation of these holes to the LR04 stack.
4.2. The d18O Record
[23] The record for the interval studied is comparable at
both sites, and the subpolar species Globigerina bulloides
registers considerably heavier d 18O values during MIS M2
(610A: 1.95%; 1308C: 1.44%) than before or after. The
shift to heavier isotopic values for G. bulloides in Hole
610A appears to occur before the heaviest benthic values are
reached (Figures 2a, 3e, and 3f). This differs from the planktonic record based on the polar species Neogloboquadrina
pachyderma (s) of Kleiven et al. [2002] which gives heaviest
values when the heaviest benthic isotope values are also
recorded (Figure 3e).
4.3. Mg/Ca Record, Paleo-SST, and Calculated d18O
Seawater Composition
[24] At Site 610, SSTs of 11.7– 13.4°C (1.80– 2.13 mmol/
mol Mg/Ca) are recorded in MIS M2, but the SST drop
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occurs shortly before MIS M2 (Figure 3h and Tables 1a and
1b). SSTs before and after MIS M2 are generally higher at
around 14.0°C (one exception at 13.5°C) with a maximum
of 16.0°C. At the more southerly Site 1308, SSTs of 11.9–
13.0°C (1.84– 2.05 mmol/mol) are recorded in MIS M2,
these being considerably lower than the 14.4 – 18.6°C range
for those samples before and after MIS M2. Hence, a total
SST range of 11.9–18.6°C (1.84–3.90 mmol/mol; Figure 3h)
was recorded for the interval studied at Site 1308.
[25] The isotopic composition of the seawater corrected
for ice volume (d 18Osw-ice) at Site 610 records lowest values
in MIS M2, suggesting lowered salinity during this glacial
compared to the studied interval before and after (Figure 3g).
At Site 1308, d 18Osw-ice values are similarly lowest during
MIS M2, although the signal was already low before this
glacial.
4.4. Palynological Assemblages
[26] The palynological assemblages are typical of midPliocene deposits from the eastern North Atlantic [De
Schepper, 2006; De Schepper and Head, 2008a, 2008b].
About 60 and 40 dinoflagellate cyst taxa were identified in
Holes 610A and 1308C, respectively (auxiliary material).
The number of taxa per sample ranges between 9 and 26
(average 18) in Hole 1308C and 16 to 27 (average 21) in
Hole 610A. The highest number of taxa is recorded during
MIS M2 at both sites, which is also reflected in the
Shannon-Wiener diversity index (Figure 3k). Reworked
dinoflagellate cysts were identified in a few samples only.
[27] Assemblages consist mainly of Bitectatodinium tepikiense, Filisphaera filifera, cysts of Pentapharsodinium
dalei (predominantly Hole 610A), several species of the
genera Impagidinium and Invertocysta (predominantly Hole
1308C), Nematosphaeropsis labyrinthus and Operculodinium
centrocarpum sensu Wall and Dale [1966] (hereafter
O. centrocarpum) (both holes). These species together
always comprise 75% or more of the assemblage in each
sample (auxiliary material). O. centrocarpum is a prominent
component of both records, with abundances often exceeding 50%, but immediately before and during MIS M2 its
relative abundance drops below 10% at both sites (Figures 3i
and 3j). This drop in relative abundance is also expressed in
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the absolute abundance of this species (Figure 4). At the
more northerly Site 610, O. centrocarpum is replaced by
N. labyrinthus, P. dalei, F. filifera, B. tepikiense, and
I. pallidum. At Site 1308, N. labyrinthus, I. paradoxum
and I. aculeatum replace O. centrocarpum; while I. pallidum,
B. tepikiense and P. dalei show slightly elevated numbers.
Spiniferites mirabilis is sometimes present when
O. centrocarpum is abundant, but rare to absent from both
sites when it is not.
[28] Dinoflagellate cyst concentrations vary between
2532 and 25,741 cysts/g dry weight (average 9421; 9–
16% error, excluding sample 17-6e: 23.6% error) in Hole
610A, and 95– 3596 cysts/g dry weight (average 671; 11–
13.5% error) in Hole 1308C (Figure 4). In Hole 610A,
concentrations are generally higher during MIS M2. Terrestrial palynomorphs are very scarce at both sites, but an
increase in the concentration of bisaccate pollen is recorded
during MIS M2 (Figure 3l).
5. Discussion
5.1. Mg/Ca Sea Surface Temperature
[29] Globigerina bulloides is a spinose species lacking
symbionts. It lives primarily in temperate regions of the
open ocean [Hemleben et al., 1989; Pflaumann et al., 2003],
where it inhabits the surface layer of the water column
[Huang et al., 2000; Schiebel et al., 2001] and is possibly
restricted to 20– 40 m water depth [Schiebel et al., 1997;
Ganssen and Kroon, 2000; Peeters et al., 2002]. Its downcore Mg/Ca record is best interpreted as representing nearsurface annual average temperatures [Pak et al., 2004;
Dowsett, 2007; Robinson et al., 2008]. Our Mg/Ca-derived
temperatures therefore should be somewhat lower than
those estimated from dinoflagellate cysts, which are based
mostly on summer SST.
[30] The average SST measured from samples outside
MIS M2 ( = non –MIS M2 samples; Table 2) in Hole 610A
is 14.6°C, comparable to SSTMg/Ca from the nearby Rockall
Plateau DSDP Hole 552A during the PRISM time slab
[Dowsett, 2007, Figure 7, p. 473]. Direct comparison with
PRISM reconstructions [Dowsett et al., 2005, 2006;
Dowsett, 2007] shows slightly lower SSTs for Hole
Figure 2. (a) Age model for DSDP Hole 610A and IODP Hole 1308C based on correlation of oxygen isotope records (%)
from the studied intervals with the LR04 benthic oxygen isotope global stack [Lisiecki and Raymo, 2005]. (left) Hole 610A:
polarity chrons/subchrons shown against depth (mbsf) in Hole 610A, with uncertainty interval for the exact position of each
reversal [Clement and Robinson, 1987]. G/G, Gilbert/Gauss Chron boundary; KAE, Kaena Subchron; MAM, Mammoth
Subchron. Study interval in Hole 610A showing the analyzed core sections (note the coring gap between core sections 18-1
and 17-6), the magnetic reversals and their uncertainty intervals, and the isotope records of N. pachyderma (s) and
Cibicides spp. [Kleiven et al., 2002] and of G. bulloides (this study). Marine isotope stages in Hole 610A (approximate
position indicated by gray shading) were identified from the benthic isotope record. (middle) LR04 global stack of benthic
isotope records [Lisiecki and Raymo, 2005] plotted against time. (right) Hole 1308C: the G. bulloides oxygen isotope
record expresses MIS M2 in core section 26-4, above the base of the Mammoth Subchron. On the right of the image,
polarity subchrons shown against depth (mcd) in Hole 1308C, with uncertainty interval given for the position of each
reversal [Expedition 303 Scientists, 2006]. Thin lines between curves indicate tie points used to correlate graphically the
isotope records in both holes to the LR04 global stack of Lisiecki and Raymo [2005]. (b) Planktonic and benthic oxygen
isotope record between 150 and 170 mbsf in Hole 610A from Kleiven et al. [2002], with these authors’ approximate
positioning of marine isotope stages (gray shading). Thin lines indicate position of the tie points used for correlation with
LR04 (see above). Box indicates the interval studied. (c) Tie points used for the age model of Hole 610A. (d) Tie points
used for the age model of Hole 1308C.
8 of 17
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Figure 3
9 of 17
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DE SCHEPPER ET AL.: MID-PLIOCENE NAC VARIABILITY
610A, which is likely explained by the use of different
proxies. Such a discrepancy between proxies is also demonstrated in the work of Robinson et al. [2008] for Site 609/
1308 (see also Table 2). For Hole 1308C, the reconstructed
average SST of 15.8°C from non – MIS M2 samples is
slightly higher than for previous studies [Bartoli et al.,
2005; Robinson et al., 2008]. This could be caused by our
sampling interval that only encompasses the lower part of
the PRISM time slab, which is known to record high sea
surface temperatures at Site 609/1308 [Robinson et al.,
2008]. Comparing with the present day, the non – MIS M2
samples record an average SST that is almost 3°C higher at
both sites. This is consistent with increased meridional
ocean heat transport during the Pliocene [e.g., Dowsett et
al., 1992; Robinson et al., 2008].
[31] MIS M2 samples record an average SST of 12.8°C at
Site 610 and 12.6°C at Site 1308 (Table 2). The surface
waters cooled by 1.8°C at Site 610 and by 3.2°C at Site
1308. The northward transport of warmer surface waters
was therefore interrupted during MIS M2.
5.2. Salinity
[32] Salinity (d 18Osw-ice) was lowered during MIS M2 at
Site 610 and, although less well expressed, also at Site 1308
(Figure 3g). Freshening of the surface waters may be
explained by a reduced northward flow of saline waters.
Other possible causes are local changes in precipitation and
evaporation during the glacial stage, or large-scale melting
of icebergs toward the end of the glacial. Indeed, during the
last glacial maximum (LGM), a freshening of areas with
marked extensive sea ice cover may have been related to
summer melting of sea ice [de Vernal et al., 2005]. Kleiven
et al. [2002] reported IRD in Hole 610A within the upper
part of MIS M2 (Figure 3e), and iceberg melting over the
site may have lowered the surface water salinity at that time.
5.3. Dinoflagellate Cysts
5.3.1. Background Mid-Pliocene Conditions:
Intense NAC
[33] At both sites, dinoflagellate cyst assemblages before
and after MIS M2 contain high abundances of O. centrocarpum as well as elevated numbers of I. patulum (in Hole
610A only) and S. mirabilis (Figures 3i, 3j, and 4 and
auxiliary material). This is similar to observations from
sediments deposited at present [e.g., Rochon et al., 1999]
and during the last interglacial [Eynaud et al., 2004] in parts
of the eastern North Atlantic influenced by the NAC.
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Similar assemblages in the Pliocene then likely indicate
relatively warm surface water, consistent with our geochemical results, and an intense NAC.
[34] The present distribution of O. centrocarpum shows it
to be a cosmopolitan species [e.g., Marret and Zonneveld,
2003] that appears well adapted to unstable conditions
where oceanic and neritic waters mix at continental margins
[Dale, 1996]. It can dominate in arctic [Matthiessen et al.,
2005] as well as tropical environments. Nonetheless, high
abundances in the North Atlantic region today are strongly
correlated with the NAC [Harland, 1983; Rochon et al.,
1999; Marret and Zonneveld, 2003]. Its abundant presence
in the Arctic Ocean [Knies et al., 2002] and NorwegianGreenland Sea [Matthiessen, 1995] and along the eastern
Canadian margin [Scott et al., 1984] is also associated with
the inflow of warmer North Atlantic waters. During the last
interglacial, O. centrocarpum was associated with the inflow of warm Atlantic water into the Norwegian Sea [Van
Nieuwenhove et al., 2008] and Arctic [Matthiessen and
Knies, 2001]. At our sites, O. centrocarpum concentrations
are also highest before and after MIS M2 (Figure 4),
independently corroborating the relative abundance data.
We therefore consider these intervals to have been strongly
influenced by the NAC.
[35] The modern distribution of S. mirabilis is broadly
tropical to temperate [Marret and Zonneveld, 2003] and it is
absent from waters with summer SSTs below 12°C. This
corresponds to its restriction to warmer parts of the record
at our sites. We consider the presence of S. mirabilis to
be a reflection of relatively local conditions, although
Spiniferites specimens in modern open ocean sediments
can be interpreted as a result of transport from the shelf
[e.g., Dale, 1996]. The limited presence of terrestrial
palynomorphs and the ecological coherence of the dinoflagellate cyst assemblages at both sites imply that local
conditions are well expressed.
[36] Although recorded in low abundance, the presence of
I. pallidum (Figures 3i, 3j, and 4) indicates summer SST not
exceeding 22.5°C and winter SST below 17°C [Marret and
Zonneveld, 2003].
5.3.2. Reduced NAC Influence Before and During
MIS M2
[37] The dinoflagellate cyst associations at both sites are
characterized by a sharp decrease in O. centrocarpum,
dropping to no more than 20% and often below 10% of
assemblages (Figures 3i and 3j). Its concentration declines
Figure 3. IODP Hole 1308C and DSDP Hole 610A (a) sedimentation rate; (b) paleomagnetic timescale; (c) LR04 global
stack of benthic d 18O records [Lisiecki and Raymo, 2005]; (d) obliquity and summer insolation at 65°N [Laskar et al.,
2004]; (e) planktonic (N. pachyderma (s), dashed line) and benthic d18O (Cibicides spp., solid line) records from Hole
610A [Kleiven et al., 2002] (recalibrated to LR04 global stack) (also shown is the approximate position of ice-rafted debris
(IRD) recorded by Kleiven et al. [2002, Figure 3]); (f) d 18O record of G. bulloides; (g) d18Osw-ice as a measure of change in
salinity; (h) SST based on Mg/Ca ratios of G. bulloides, with an estimated error of 1°C as indicated by shading; (i and j)
relative abundances of the most abundant dinoflagellate cyst taxa in Hole 1308C (Figure 3i) and Hole 610A (Figure 3j)
(bluish (reddish) colors reflect cooler (warmer) water species) (note the drop in abundance of O. centrocarpum (yellow)
well before MIS M2); (k) Shannon-Wiener diversity index for the dinoflagellate cysts; and (l) dinoflagellate cyst/bisaccate
pollen ratio and bisaccate pollen concentration (dry weight). Gray bars represent marine isotope stages KM6, M2, MG2,
and MG4; their boundaries are drawn approximately midway between maxima and minima in the benthic d 18O records of
the LR04 global stack.
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Figure 4. Relative abundance (shaded) and concentration (solid line) of selected dinoflagellate cyst
species at IODP Hole 1308C and DSDP Hole 610A. The major decline in both relative abundance and
concentration of the otherwise dominant O. centrocarpum before and during MIS M2 indicates
significantly reduced influence of the NAC at both sites. Within this interval, cool-water neritic taxa are
well represented in Hole 610A, whereas a more oceanic association characterizes Hole 1308C. Gray
horizontal bars indicate approximate positions of MIS KM6, M2, and MG2 (see Figure 2).
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Table 2. Comparison of Sea Surface Temperatures for DSDP Site 610 and IODP Site 1308 for Various Time Intervals Based on PresentDay Observations, Measured Values in This Study, Measurements of Bartoli et al. [2005] Recalculated Using the Elderfield and Ganssen
[2000] Equation, and PRISM Reconstructionsa
Present
Dayb
3.35 – 3.24
Mac
610A
11.7°C
MIS M2: 12.8°C;
non – MIS M2: 14.6°C
1308C
(*609B)
13.1°C
MIS M2: 12.6°C;
non – MIS M2: 15.8°C
3.35 – 3.24
Mad
3.29 – 2.97
Mae
16.0 – 16.7°C
*15.2°C
*18.6 – 19.3°C
3.29 – 2.97
Maf
13.2 – 22.0°C (MIN);
16.0 – 29.0°C (MAX);
DSDP 552A: 13 – 15°C
(Mg/Ca, G. bulloides)
*18.2 – 25.6°C (MIN);
*25.0 – 34.6°C (MAX)
3.29 – 2.97
Mag
*13.5°C (Mg/Ca,
G. bulloides);
*17.5°C (alkenones);
*18.2 – 26.4°C (faunal)
a
Samples belonging to MIS M2 in Hole 610A comprise 17-6CC, 17-6j, 17-6i, 17-6h, 17-6g, and 17-6f, and those in Hole 1308C comprise 26-4b, 26-4c,
and 26-4d. Samples outside MIS M2 (non – MIS M2 in the table) are the remainder. Asterisks indicate values were obtained from ODP Site 609.
b
Annual average temperature at 0 – 50 m water depth. World Ocean Atlas 2005 [Locarnini et al., 2006].
c
This study Mg/Ca (G. bulloides).
d
Bartoli et al. [2005] Mg/Ca (G. bulloides).
e
PRISM3 [Dowsett et al., 2006], 0 – 57 m water depth.
f
PRISM [Dowsett et al., 2005; Dowsett, 2007].
g
Robinson et al. [2008].
by a factor of 10 to 20 during this interval (Figure 4). This
species is replaced partly by N. labyrinthus (as much as
46% of assemblages at Site 1308), a subpolar-temperate
species [Rochon et al., 1999; Marret and Zonneveld, 2003]
that has been linked to past climatic transitions (e.g.,
glacial – interglacial [Baumann and Matthiessen, 1992]
and interglacial – glacial [Eynaud et al., 2004]).
[38] A suite of cool-water neritic species (B. tepikiense,
P. dalei, F. filifera) increases in abundance at Site 610. In
the later part of MIS M2, B. tepikiense becomes an
important constituent of assemblages (up to 16%;
Figures 3j and 4). Its distribution today is closely related
to the subpolar– temperate transition [Dale, 1996] and its
abundance exceeds 10% of assemblages only when summer
SSTs are less than 17°C [Edwards and Andrle, 1992;
Marret and Zonneveld, 2003]. B. tepikiense is also tolerant
of reduced salinities (Gundersen [1988] in contrast to
Marret and Zonneveld [2003]), and has been linked to
reduced surface salinities resulting from melting ice in the
late Quaternary [Bakken and Dale, 1986]. Increased abundances may also indicate a strong seasonal temperature
gradient [Marret and Zonneveld, 2003] with enhanced
surface water stratification [Rochon et al., 1999]. Such
stratified conditions also seem to favor cysts of P. dalei,
which reach up to 40% of assemblages at Site 610. This
species occurs in a wide range of temperature and salinity
conditions [de Vernal et al., 1997, 2001], with abundances
exceeding 30% mostly in regions where mean summer SSTs
are no greater than 16°C [Marret and Zonneveld, 2003].
Salinity and stratification of the surface waters may have
been influenced by the melting of icebergs, as inferred from
recorded IRD at Site 610 [Kleiven et al., 2002], although
IRD occurs after rather than during peak values of
B. tepikiense and P. dalei (Figures 3e, 3i, and 3j).
[39] An insignificant cool-water neritic component in the
dinoflagellate cyst assemblages at Site 1308 reflects its
greater distance from the shelf compared to the more
northern Site 610. O. centrocarpum is replaced here by
N. labyrinthus, I. aculeatum and I. paradoxum (Figures 3i
and 4). The last two species have somewhat similar ecological ranges in the temperate to tropical marine realm
[Marret and Zonneveld, 2003]. I. aculeatum is common in
the North Atlantic where winter and summer SSTs are >
12°C and 18°C, respectively [Rochon et al., 1999], and has
abundances of >20% only when mean summer SST exceeds
16°C [Marret and Zonneveld, 2003].
[40] High percentages of I. aculeatum at Site 1308 would
seem to indicate summer SSTs of at least 16°C and possibly
a higher seasonal contrast in SST, i.e., warmer summers,
than at Site 610. However, our geochemical evidence,
suggests an annual SSTMg/Ca of 11.9 –14.7°C. We therefore
prefer to explain the elevated percentages and concentrations of I. aculeatum and I. paradoxum as reflecting a shift
to more oligotrophic waters at Site 1308, which would have
favored oceanic species. This change was presumably
caused by a deflection or slowdown of the NAC. Both
species are also persistent at Site 610, implying that truly
cold conditions did not exist there, at least during summer.
Since neither species is reported north of the modern Arctic
Front [Marret and Zonneveld, 2003], this front would have
remained north of Site 610.
[41] The presence of warm temperate to tropical Tectatodinium pellitum [Head, 1994; Marret and Zonneveld, 2003]
and Melitasphaeridium choanophorum [Head, 1997] (auxiliary material) at Site 610 further support the interpretation
that extreme cooling did not take place. However, these are
neritic species and their occurrence is presumably the result
of long-distance transport to this oceanic site.
[42] An increase in species diversity and a slight drop in
the D/P ratio at both sites (Figures 3k and 3l), and an
increase in total dinoflagellate cyst concentration at Site 610
(Figure 4) all suggest a greater influx of palynomorphs from
nearby shelves, consistent with a changed surface current
setting.
[43] While assemblages at sites 610 and 1308 are similar
in their scarcity of O. centrocarpum, they are characterized
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by different ‘‘replacement’’ taxa that reveal the influence of
separate water masses, dominantly neritic and oceanic,
respectively, over these two sites during this time.
5.4. Timing of Dinoflagellate Cyst Overturn
[44] The drop in relative and absolute abundance of
O. centrocarpum and the lowering of d 18Obull and SSTMg/Ca
values at Site 610 took less than 3 ka (Figures 3 and 4 and
Tables 1a and 1b). At this site, O. centrocarpum almost
completely disappears from the record between 3.319 and
3.316 Ma. At Site 1308, the major decline in relative
abundance of O. centrocarpum occurs between 3.332 Ma
(82%) and 3.320 Ma (3%), representing an interval of 12 ka
(Figure 3 and Tables 1a and 1b). However, the concentration data (Figure 4) show an abrupt decline between
3.332 Ma and 3.328 Ma, i.e., within 4 ka. The return of
O. centrocarpum to dominance occurs near the end of
MIS M2 at both sites, within 4 ka at Site 610 and 5 ka at
Site 1308 (Figures 3i and 3j).
[ 45 ] The apparent asynchroneity in the decline of
O. centrocarpum between Site 1308 (circa 3.330 Ma) and
Site 610 (circa 3.318 Ma) may result from the sampling
resolution, the coring gap in Hole 610A, and errors in
correlating holes to the LR04 stack. Given these uncertainties, the dinoflagellate cyst overturn at both sites can be
considered broadly, if not precisely, contemporaneous. The
apparent difference in overturn timing at the two sites,
occurring during a decline (Site 610) and increase (Site
1308) in summer insolation (Figures 3d, 3i, and 3j) [Laskar
et al., 2004], may therefore be an artifact of the age models.
Given the limitations of our age models, we cannot conclusively relate shifts in the dinoflagellate cyst association
to variability in orbital parameters such as insolation,
although a relationship with decreasing obliquity seems
plausible.
[46] The decline of O. centrocarpum at both sites (circa
3.330 – 3.318 Ma) occurs well before the global ice volume
maximum at MIS M2 (3.295 Ma [Lisiecki and Raymo,
2005]), the lowest sea surface salinity (3.300 – 3.296 Ma)
and the coolest recorded SSTs within MIS M2 (3.300 –
3.296 Ma). The relative timing of our various proxies
implies that NAC decline led the maximum expansion of
global ice volume by 23– 35 ka (Figure 3c) and the minimum sea surface salinity by 22– 30 ka (Figure 3g). The
decline coincides with or may even precede the global ice
volume minimum at 3.320 Ma [Lisiecki and Raymo, 2005].
[47] The insolation minimum in the later part of MIS M2
corresponds to the coolest SSTs, lowest relative salinity at
Site 610 and the heaviest d18Obenthic values for the interval.
The Greenland ice sheet was then likely large enough to
have produced icebergs that brought IRD down to the site
(Figure 3e) [Kleiven et al., 2002] and allowed meltwater to
enter the system. Meltwater is a likely explanation for
lowering the surface water salinity at Site 610, causing
(summer) water column stratification and the increase in
B. tepikiense at circa 8 ka before the end of MIS M2.
[48] SSTs at both sites show a steady recovery beginning
before the end of MIS M2 (Figure 3h). The return of
O. centrocarpum to dominance followed shortly thereafter,
when SSTs again exceeded 14°C. The high abundance of
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this species is likely not related directly to SST, but rather to
the return of surface waters with NAC characteristics (this
occurring relatively rapidly against a background of increasing SSTs and insolation).
5.5. North Atlantic Paleoceanography During MIS
M2
[49] Faunal reconstructions using foraminifers and nannofossils from the Atlantic, Indian and Pacific oceans
[Backman and Shackleton, 1983; Backman and Pestiaux,
1987; Ehrmann and Keigwin, 1987], terrestrial palynomorphs from the Mediterranean [Suc, 1984], and oxygen
isotope records [e.g., Lisiecki and Raymo, 2005] all confirm
global cooling at MIS M2. Earlier intervals with d 18O
enrichment had been caused mainly by ice volume increases
in the Antarctic region, but at 3.30 Ma the Greenland ice
sheet showed a marked expansion [e.g., Jansen et al.,
2000]. The first main IRD peak at Site 610 (Figure 3e)
and ODP Site 907 is recorded at that time [Kleiven et al.,
2002] and provides evidence of strong participation of the
Greenland and Laurentide ice sheets in the first major global
ice volume increase of the past 4 Ma.
[50] Our results indicate that a southward shift or slowdown of the NAC preceded MIS M2 (Figure 5), causing a
reduction in northward heat transport well before ice sheets
had reached their maximum development in the Northern
Hemisphere. This oceanographic change may therefore
have led to cooling and ice sheet expansion on Greenland,
triggering a global cooling event. Such a scenario contrasts
with the hypothesis that an intense NAC, operating when
the Panamanian Gateway was closed, provided the moisture
necessary for ice sheet growth on Greenland [e.g., Haug
and Tiedemann, 1998; Bartoli et al., 2005]. Modeling
studies have demonstrated that under such conditions the
associated northward transport of heat would have prevented growth of significant ice sheets on Greenland
[Klocker et al., 2005; Lunt et al., 2008]. An intense NAC
therefore likely delayed the formation of ice sheet growth
[Berger and Wefer, 1996], and its interruption or weakening is
perhaps responsible for the cooling observed during MIS M2.
[51] The mechanism leading to a weakened northward
transport of heat may have been a brief opening of the
Panama Isthmus. The Pacific –Atlantic exchange had already decreased significantly by 4.6 –4.0 Ma [Haug et al.,
2001; Steph et al., 2006; Groeneveld et al., 2008], but the
Panamanian Gateway was probably not fully closed until
3 –2 Ma. At around 3.4– 3.3 Ma, the Isthmus of Panama
experienced a short-lived reopening suggested by reduced
ventilation [Haug and Tiedemann, 1998; Schmidt, 2007].
The consequent inflow of lower-salinity Pacific waters into
the Caribbean could have weakened northward heat transport
via the NAC, destabilizing the mid-Pliocene climate system
at around 3.30 Ma and allowing northern ice sheet expansion.
[52] The conspicuous fall and rise in O. centrocarpum at
both our sites marks an abrupt decline and recovery of the
NAC that lasted 31– 47 ka. At Site 610, which is closer to
the continental shelf than Site 1308, O. centrocarpum was
replaced by such cool-water neritic species as B. tepikiense
and P. dalei, which may also signify seasonal stratification
of the upper water column potentially related to a southward
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DE SCHEPPER ET AL.: MID-PLIOCENE NAC VARIABILITY
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Figure 5. Changes in influence of the North Atlantic Current (NAC) as inferred from dominant species
in the dinoflagellate cyst associations and SSTMg/Ca (average MIS M2 and non– MIS M2 are shown; see
also Table 2). (a) During normal mid-Pliocene conditions, an intense NAC (position shown is that of
present day) influences both sites, and O. centrocarpum dominates the association. High average SSTs at
both DSDP Site 610 and ODP Site 1308 are evidence of increased meridional heat transport. (b) Before
and during MIS M2, a reduced influence of the NAC is evidenced by lower SSTs and the decline of O.
centrocarpum at both sites. At IODP Site 1308, O. centrocarpum is replaced by the temperate – tropical
oceanic species I. aculeatum and I. paradoxum. At Site 610, elevated numbers of B. tepikiense, cysts of P.
dalei, and N. labyrinthus suggest stratification of the water column and cooling. The reduced influence of
the NAC is presumably caused by (1) weakened intensity or (2) a southward shift. Pictures: 1, O.
centrocarpum; 2, N. labyrinthus (SEM); 3, B. tepikiense; 4, cyst of P. dalei; 5, I. aculeatum (SEM); and 6,
I. paradoxum (SEM).
shift of the Arctic Front toward the northern North Atlantic.
At Site 1308, the warmer-water oceanic dinoflagellate cyst
taxa that replaced O. centrocarpum indicate that the Arctic
Front remained significantly north of this location.
[53] The alignment of our two sites with the predicted
mid-Pliocene (i.e., modern) path of the NAC prevents us
from determining whether this decline reflects an overall
weakening of the NAC or its deflection southward of our
two sites (Figure 5). Additional sites must be analyzed to
resolve this issue. Whatever scenario is correct, our observations show that northward heat transport was curtailed
significantly during the approximate interval 3.330 –
3.283 Ma.
6. Conclusions
[ 54 ] Our study documents oceanographic changes
through MIS M2 in the North Atlantic by combining the
dinoflagellate cyst record with sea surface temperature and
salinity estimates based on foraminiferal Mg/Ca and d18O.
This is the first study to combine these proxies from the
same samples, and demonstrates the considerable potential
of this method for documenting past ocean current variabil-
ity. The reconstructed SSTs fit well into the existing data set
of PRISM [Dowsett, 2007; Robinson et al., 2008] and are
largely corroborated by temperature estimates based on
extant dinoflagellate cyst indicator species (see section 5.3).
Our data further demonstrate that even during the globally
warmer and more equitable conditions of the mid-Pliocene,
the NAC was sensitive to disturbance. The NAC decline at
our sites occurred within a duration of <3– 4 ka and well
before the full glacial conditions of MIS M2. Arrival of IRD
at Site 610 occurred after the initial decline of NAC
influence, thus excluding a causal relationship between this
decline and fresh water input via icebergs in the eastern
North Atlantic. Modeling studies [e.g., Stouffer et al., 2006]
introduce fresh water perturbations into the North Atlantic
to alter the meridional overturning circulation. A different
mechanism seems to be required for events leading to MIS
M2. The slowdown we document in northward heat transport beginning at circa 3.330 – 3.318 Ma likely prepared
conditions for later ice growth on Greenland during MIS
M2 [Kleiven et al., 2002; Lisiecki and Raymo, 2005]. It is
proposed that the disturbance of the NAC may have been
related to a brief reopening of the Panama Isthmus at 3.4–
3.3 Ma.
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[55] Acknowledgments. This contribution is based partly on the
doctoral research of S.D.S., who is grateful to the Gates Cambridge Trust
for the award of a Gates Cambridge Scholarship (University of Cambridge)
and additional funding from the Dudley Stamp Memorial Trust (Royal
Society) and Philip Lake Fund (Department of Geography, University of
Cambridge). S.D.S. also appreciates funding from the Deutsche Forschungsgemeinschaft (International Graduate College ‘‘Proxies in Earth
History,’’ EUROPROX, University of Bremen) and MARUM (G. Wefer).
M.J.H. acknowledges support from a Natural Sciences and Engineering
Research Council of Canada discovery grant. J.G. is grateful for a MARUM
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Fellowship, funded through the DFG Research Center/Excellence Cluster
program ‘‘The Ocean in the Earth System.’’ G. Bartoli and H. Kleiven
kindly shared their raw data. Thanks are extended to M. Hall, P. Ferretti, L.
de Abreu, and J. Rolfe (University of Cambridge), M. Segl (University of
Bremen), and S. Vancauwenberghe (Ghent University) for technical assistance. Comments by F. Eynaud and H. Dowsett on an earlier version of the
manuscript and by J. Matthiessen, an anonymous reviewer, and G. Dickens
on a more recent version are gratefully acknowledged. IODP is thanked for
providing the samples.
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J. Groeneveld, MARUM Excellence Cluster,
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M. J. Head, Department of Earth Sciences,
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AUXILIARY MATERIAL
The following two tables display the raw palynological data (dinoflagellate cysts, acritarchs, and terrestrial
palynomorphs) and calculated paleoenvironmental indices used in this paper. The tables are based on text
files “2008pa001725-ts01.txt” and “2008pa001725-ts02.txt” (IODP Hole 1308C and DSDP Hole 610A
respectively) which are available for download from the Paleoceanography website. The text files were in
fact generated from the following tables, which we believe will be more helpful to readers for most
purposes.
References for taxa in open nomenclature are as follows:
De Schepper, S. (2006), Plio-Pleistocene dinoflagellate cyst biostratigraphy and palaeoecology of the
eastern North Atlantic and southern North Sea Basin. PhD thesis, 327 pp., University of Cambridge,
Cambridge, UK.
De Schepper, S. and M. J. Head (2009), Pliocene and Pleistocene dinoflagellate cyst and acritarch zonation
of DSDP Hole 610A, eastern North Atlantic. Palynology 33.
Head, M. J. (1996), Late Cenozoic dinoflagellates from the Royal Society borehole at Ludham, Norfolk,
eastern England. J. Paleontol. 70, 543–570.
Head, M.J. and H. Westphal (1999), Palynology and paleoenvironments of a Pliocene carbonate platform:
The Clino core, Bahamas. J. Paleont. 73(1), 1–25.
Louwye, S., M. J. Head, and S. De Schepper (2004), Dinoflagellate cyst stratigraphy and palaeoecology of
the Pliocene in northern Belgium, southern North Sea Basin. Geol. Mag. 141, 353–378.
Vink, A., K. A. F. Zonneveld and H. Willems (2000), Organic-walled dinoflagellate cysts in western
equatorial Atlantic surface sediments: distributions and their relation to environment. Rev. Palaeobot.
Palynol. 112(4), 247–286.
Wall, D., and B. Dale (1966), Living fossils in western Atlantic plankton. Nature 211, 1025–1027.
Table 1: based on raw data published online as a supplement to De Schepper et al. (2009).
Cite as De Schepper et al. (2009, auxilliary material: 2008pa001725-ts01.txt).
IODP Hole 1308C
Core-section 26-6
26-6
26-5
26-5
26-5
26-5
26-4
26-4
26-4
26-4
26-4
26-3
26-3
26-3
26-3
26-4
26-2
Sample 26-6a 26-6b 26-5a 26-5b 26-5c 26-5d 26-4a 26-4b 26-4c 26-4d 26-4e 26-3a 26-3b 26-3c 26-3d 26-3e 26-2a
Depth (mbsf) 240.49 240.04 239.49 239.19 238.84 238.54 238.34 237.95 237.59 237.34 237.04 236.79 236.47 236.16 235.91 235.60 235.19
Dry weight (g) 6.92
9.79 10.51 11.12
7.72
6.84 10.72 11.18 10.94 10.76 9.59
9.81
8.62 10.93 9.62
7.78 10.00
Age (ka) 3346 3340 3334 3332 3328 3325 3320 3309 3300 3291
3285 3280 3274 3270 3266 3260 3253
Sedimentation rate (cm/a) 6.26
6.26
6.26 10.57 10.57 10.57 3.82
3.82
3.74
3.74
2.85
4.75
5.58
6.70
6.70
5.69
5.53
Lycopodium clavatum 2344 1282 3990
476
3354 2184 3628 1963 1613 1942 1834
158
2336 1967
519
632
418
Tablets added (batch number 483.216)
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Dinoflagellate cysts
Ataxiodinium choane
Ataxiodinium confusum
Barssidinium pliocenicum
Barssidinium graminosum
Bitectatodinium raedwaldii
Bitectatodinium tepikiense
Corrudinium harlandii
Corrudinium? labradori
Edwardsiella sexispinosa
Filisphaera filifera
Filisphaera microornata
Impagidinium aculeatum
Impagidinium sp. 2 De Schepper & Head (2009)
Impagidinium pallidum
Impagidinium paradoxum
Impagidinium cf. paradoxum
Impagidinium patulum
Impagidinium plicatum
Impagidinium solidum
Impagidinium strialatum
Impagidinium spp. indet.
Invertocysta lacrymosa
Invertocysta tabulata
Melitasphaeridium choanophorum
Nematosphaeropsis labyrinthus
Nematosphaeropsis lativittata
1
1
3
6
3
5
2
5
12
2
2
7
8
2
1
9
1
13
4
1
16
7
+
4
+
1
1
3
8
1
4
5
16
1
5
2
32
8
22
36
+
1
2
1
3
1
33
1
2
2
21
1
Operculodinium centrocarpum sensu Wall &
Dale (1966)
O. centrocarpum sensu Wall & Dale (1966)
short processes
Operculodinium centrocarpum s.s.
Operculodinium? eirikianum crebrum
Operculodinium janduchenei
cf. Operculodinium janduchenei
Operculodinium sp. A of Vink (2000)
Cysts of Pentapharsodinium dalei
Round brown cysts
Spiniferites mirabilis
Spiniferites/ Achomosphaera spp. indet.
Spiniferites sp. 1
Dinocyst spp. indet.
Sum
Number of taxa
Dinocyst concentration (cyst/g)
Error (cyst/g)
1
+
2
6
2
2
2
20
1
5
25
5
3
36
43
43
87
9
19
3
5
7
34
16
9
15
24
8
5
2
1
4
11
4
39
14
3
1
2
1
4
2
17
1
5
10
1
1
11
1
8
4
1
1
90
26
4
38
3
+
+
1
+
+
4
1
1
8
1
2
16
25
1
5
29
1
1
1
3
8
5
3
2
3
1
1
1
2
8
1
+
5
1
2
18
2
1
2
30
1
7
21
25
2
2
+
9
8
6
22
14
+
1
5
1
1
12
15
+
+
1
3
3
5
5
3
5
15
3
1
10
4
2
1
2
17
2
1
2
45
2
6
9
6
1
58
2
36
+
65
4
29
8
42
8
139
5
39
1
42
8
73
21
89
7
1
31
43
24
228
219
49
242
44
42
5
8
5
16
57
266
131
182
210
181
280
1
3
39
5
3
2
3
3
1
1
3
3
+
1
1
1
1
1
1
1
1
6
6
5
8
5
2
1
1
1
7
7
5
1
300
19
1134
131
3
326
14
1449
171
1
3
355
3
1
3
59
1
8
1
1
12
5
45
14
51
2
8
1
2
3
429
10
1621
180
5
81
8
360
55
7
3
4
3
1
13
48
14
4
1
1
6
313
15
359
39
1
1
300
12
444
50
13
8
1
3
300
19
133
15
9
1
1
300
11
1053
124
4
1
1
1
1
1
6
4
1
1
200
19
144
17
3
5
1
1
3
1
4
1
3
20
1
3
3
200
22
249
29
1
200
19
96
11
300
20
254
28
250
21
263
30
3
300
26
267
30
4
300
18
317
35
2
1
1
5
138
4
43
93
13
29
68
430
7
5
20
77
6
87
3
2
10
50
4
18
2
6
4
186
4
1
44
2
61
312
8
264
29
14
607
8
639
66
2
1
4
135
9
120
15
5
2
6
260
10
275
31
34
3
53
8
76
3
25
2
4
+
1
4
3
3
1
1
300
9
3597
484
3
300
20
277
31
300
21
259
29
300
19
1117
131
14
40
2
1
130
1
6
3
6
20
1
8
2
1
Acritarchs
Algal cyst type 1 of Head (1996)
Algal cyst type A of De Schepper (2006)
Cymatiosphaera invaginata
Cymatiosphaera latisepta
Cymatiosphaera spp. indet.
Lavradosphaera crista
Micrhystridium spp. indet.
Nannobarbophora walldalei
Acritarch sp. 1 of De Schepper & Head (2009)
Acritarch sp. 1
Small acritarch spp. indet.
Sum
Number of taxa
Acritarch concentration (cyst/g)
Error bar (cyst/g)
1
9
1
1
1
1
1
4
4
5
2
1
2
3
9
3
13
5
3
3
1
1
1
2
2
7
5
1
5
7
8
1
6
5
4
2
6
32
6
40
8
93
4
18
3
1
11
281
9
134
15
19
17
26
5
38
4
456
92
56
4
52
8
1
1
47
1
15
6
1
6
209
9
181
21
3
1
3
Pollen + spores
Bisaccate pollen
Sphagnum
Sciadopitys
Trilete spore
Sum
Pollen concentration (cyst/g)
Error bar (cyst/g)
2
22
25
6
1
15
22
6
1
27
12
3
7
25
10
50
36
6
1
30
37
8
3
40
19
4
48
41
7
5
74
78
12
6
120
107
14
8
37
39
7
1
12
12
11
10
3
Reworked palynomorph
13
2
3
32
28
6
11
42
13
5
22
10
1
Other
Microforaminiferal linings
Tasmanites
Invertebrate remains indet.
Environmental indices
D/P = D/(D+P) (with P = bisaccate pollen only)
Shannon-Wiener diversity index
Evenness
Marine Isotope Stage
2
0.99
1.09
0.40
1.00
0.99
0.40
MG2
1.00
2.38
0.81
1.00
0.75
0.31
1
2
1
3
1
0.91
2.11
0.72
0.92
2.45
0.79
0.88
2.32
0.79
0.90
1.99
0.66
5
1
1
0.83
2.18
0.72
0.80
2.44
0.75
0.92
2.32
0.80
1.00
0.50
0.23
1.00
1.71
0.57
0.96
1.65
0.54
1
+
0.98
1.26
0.43
1
0.99
1.52
0.52
0.99
0.66
0.25
M2
IODP Hole 1308C palynomorph count data (raw data), concentration estimates and calculated paleoenvironmental indices for each studied sample. Samples were counted until
more than 200, and often more than 300, dinoflagellate cysts had been enumerated. A "+" in the table indicates presence outside regular counts.
Table 2: based on raw data published online as a supplement to De Schepper et al. (2009).
Cite as De Schepper et al. (2009, auxilliary material: 2008pa001725-ts02.txt).
DSDP Hole 610A
Core-section 18-1
18-1
18-1
17-6
17-6
17-6
17-6
17-6
17-6
17-6
17-6
17-6
17-6
17-5
17-5
17-5
17-5
17-5
17-5
17-5
Sample 18-1c 18-1b 18-1a 17-6j
17-6i 17-6h 17-6g 17-6f 17-6e 17-6d 17-6c 17-6b 17-6a 17-5g 17-5f 17-5e 17-5d 17-5c 17-5b 17-5a
Depth (mbsf) 163.02 162.89 162.71 161.82 161.67 161.55 161.44 161.26 161.11 160.94 160.8 160.72 160.59 160.36 160.30 160.14 159.98 159.90 159.79 159.60
Dry weight (g) 18.69 13.04 12.91 20.09 20.05 15.65 21.24 16.74 23.32 19.96 20.54 21.39 21.88 18.63 20.99 20.42 19.94 19.24 23.55 19.62
Age (ka) 3336
3319
3316
3302
3299
3296
3293
3289
3285
3281
3278
3276
3274
3270
3266
3262
3257
3254
3246
3235
Lycopodium clavatum
Tablets added (batch number 483.216)
Dinoflagellate cysts
Achomosphaera andalousiensis andalousiensis
Amiculosphaera umbraculum
Ataxiodinium confusum
Ataxiodinium choane
Ataxiodinium zevenboomii
Barssidinium graminosum
Barssidinium pliocenicum
Bitectatodinium raedwaldii
Bitectatodinium tepikiense
Bitectatodinium? serratum
Brigantedinium spp.
Corrudinium harlandii
Corrudinium? labradori
Dapsillidinium pseudocolligerum
Edwardsiella sexispinosa
Filisphaera filifera subsp. filifera
Filisphaera filifera subsp. pilosa
Filisphaera microornata
Habibacysta tectata
Impagidinium aculeatum
Impagidinium sp. 2 De Schepper & Head (2009)
Impagidinium pallidum
Impagidinium paradoxum
Impagidinium patulum
Impagidinium solidum
Impagidinium strialatum
Impagidinium sp. 1 De Schepper & Head (2009)
Impagidinium spp.
Invertocysta lacrymosa
Invertocysta tabulata
Kallosphaeridium sp. of Head & Westphal (1999)
Lejeunecysta catomus
Lingulodinium machaerophorum
Melitasphaeridium choanophorum
Nematosphaeropsis labyrinthus
Nematosphaeropsis lativittata
Nematosphaeropsis spp. indet.
Operculodinium centrocarpum s.s.
Operculodinium centrocarpum sensu Wall &
Dale (1966)
Operculodinium centrocarpum sensu Wall &
Dale (1966) short processes
Operculodinium? eirikianum var. eirikianum
Operculodinium? eirikianum var. crebrum
Operculodinium israelianum
Operculodinium janduchenei
Operculodinium sp. 1 of Louwye et al. (2004)
Operculodinium? sp. A
Cysts of Pentapharsidinium dalei
Round brown cysts
Selenopemphix dionaeacysta
Selenopemphix nephroides
Spiniferites sp. A of De Schepper & Head (2009)
Spiniferites falcipedius
Spiniferites hyperacanthus
Spiniferites mirabilis
Spiniferites membranaceus
Spiniferites/Achomosphaera spp. indet.
Tectatodinium pellitum
Trinovantedinium glorianum
Trinovantedinium sp.
Dinocyst sp. A
Dinocyst spp. indet.
Sum
Number of taxa
Dinocyst concentration (cyst/g)
Error (cyst/g)
71
3
1
6
2
1
170
3
57
3
59
3
68
3
+
+
+
+
+
+
3
+
+
+
+
1
2
+
1
+
23
+
2
5
27
2
39
44
3
1
1
+
1
+
55
3
73
3
19
3
62
3
1
2
+
73
3
83
3
79
3
139
3
184
3
222
3
+
1
+
+
+
1
+
+
+
8
37
+
26
1
12
9
6
21
1
1
+
4
59
+
41
11
+
1
2
7
4
4
1
+
38
3
1
4
3
22
+
37
+
19
3
63
2
13
8
1
10
3
14
14
+
1
+
1
8
3
9
15
+
1
9
4
9
9
+
+
3
6
+
3
7
1
1
1
+
3
15
16
12
1
+
1
1
1
+
2
1
1
219
+
5
+
1
+
+
+
1
4
3
6
4
174
2
6
4
7
10
+
27
4
12
+
19
19
2
+
3
+
1
16
6
6
122
+
3
95
1
13
1
+
11
1
8
31
1
8
11
17
2
4
+
+
5
7
1
3
9
10
4
2
4
13
13
1
1
+
+
6
+
+
20
7
1
5
2
3
12
1
116
59
133
+
+
3
+
+
1
7
+
1
1
1
+
2
1
3
13
22
2
+
2
1
1
14
3
2
1
4
+
1
+
17
11
4
3
+
1
3
4
2
2
2
8
6
2
1
+
6
1
2
1
3
1
11
1
10
1
5
4
18
2
6
1
3
2
6
1
18
3
2
6
3
7
14
5
21
2
1
16
2
5
23
1
2
1
1
4
+
95
+
1
128
+
77
4
1
4
8
3
141
93
126
172
174
125
13
1
17
16
4
13
11
1
+
4
1
7
1
1
5
3
10
27
6
1
4
2
1
13
17
37
25
16
72
255
165
230
198
247
178
1
1
+
1
1
1
+
1
8
+
3
+
+
4
4
+
3
+
2
5
7
2
4
2
9
12
1
8
+
1
+
+
1
1
1
3
1
12
46
25
27
3
16
163
1
203
3
1
122
1
14
7
+
1
2
1
1
7
3
+
+
2
163
+
1
1
1
3
1
1
43
3
57
3
1
3
1
61
1
+
141
3
+
2
5
6
211
3
1
+
22
205
3
2
1
+
+
203
1
86
1
1
44
+
33
1
1
+
34
38
6
+
46
+
15
1
32
11
18
2
2
+
39
1
1
+
+
+
1
1
45
1
42
1
+
41
2
23
1
2
491
27
11537
1516
4
371
24
17262
2781
7
366
27
10037
1470
1
397
25
10408
1347
8
+
2
+
1
1
1
1
18
1
+
1
35
18
+
19
5
386
21
9321
1223
1
390
22
5637
534
1
1
553
24
24068
3394
2
3
1
+
2
2
1
1
1
+
+
5
2
23
+
+
13
+
8
21
23
25
20
3
+
13
+
23
+
7
+
21
+
34
1
27
2
45
1
75
+
52
2
83
2
86
3
356
16
25741
6090
2
379
20
9812
1363
3
371
19
7927
1031
1
361
20
6514
807
2
334
17
6190
788
+
3
418
22
5172
520
4
403
19
3343
307
1
364
20
2572
227
5
323
22
2532
233
2
339
22
2676
243
4
370
22
3569
363
2
348
22
9968
1443
1
2
+
2
+
+
1
523
22
14136
1968
Acritarchs
Cymatiosphaera? invaginata
Cymatiosphaera latisepta
Algal cyst type 1 of Head (1996)
Algal cyst type A of De Schepper (2006)
Lavradosphaera crista
Nannobarbophora walldalei
Acritarch sp. 1 of De Schepper & Head (2009)
Small spiny acritarchs
Incertae sedis A
Tasmanites spp.
Sum
Number of taxa
Acritarch concentration (cyst/g)
Error (cyst/g)
+
10
9
241
82
1
1
2
4
29
21
7
1
3
11
169
55
3
4
+
7
43
17
3
4
+
17
7
740
205
3
+
5
6
4
+
1
2
10
+
2
1
2
4
1
1
1
5
4
4
1
+
19
7
514
136
2
8
7
188
70
1
27
9
1256
308
4
19
7
521
139
3
5
79
46
9
+
+
9
243
87
15
+
2
17
352
96
19
33
1
3
37
905
194
24
5
2
31
629
136
6
4
1
+
2
1
1
1
1
+
2
+
1
1
+
1
+
2
+
+
1
3
72
74
2
4
52
37
+
9
6
192
68
3
4
54
32
+
2
4
37
27
1
9
7
111
38
1
5
5
41
19
4
+
1
5
289
146
3
2
1
6
78
33
10
1
1
12
214
67
18
1
1
20
325
81
1
2
7
1
3
19
11
8
87
32
5
3
3
11
41
13
1
+
+
5
10
0
2
0
/
5
3
39
18
10
3
79
26
1
1
4
5
39
20
0
2
0
/
+
11
4
1
+
1
2
4
1
+
2
15
78
21
1
8
8
3
8
5
5
39
18
2
0
0
3
4
1
Pollen + spores
Bisaccate pollen
Non-bisaccate pollen spp.
Trilete spore
Sum
Bisaccate pollen concentration (cyst/g)
Error (cyst/g)
6
+
6
261
112
1
20
884
239
Reworked dinoflagellate cysts
1
1
Fresh water algae
Gelasinicysta vangeelii
Prasinophyceae
Micrhystridium spp.
Environmental indices
D/P = D/(D+P) (with P = bisaccate pollen only)
Shannon-Wiener diversity index
Evenness
Marine Isotope Stage
+
+
1
1
+
0.98
2.29
0.75
MG2
0.99
1.97
0.64
0.99
1.69
0.53
0.98
1.85
0.60
0.97
2.18
0.66
0.95
2.21
0.70
M2
0.92
2.53
0.77
0.94
2.34
0.73
0.99
1.08
0.39
0.99
1.60
0.53
0.97
1.55
0.53
0.95
1.76
0.59
1.00
1.08
0.38
0.98
1.80
0.58
0.99
1.86
0.63
0.97
2.18
0.73
1.00
2.01
0.65
1.00
1.87
0.60
0.99
1.81
0.59
1.00
2.08
0.67
KM6
DSDP Hole 610A palynomorph count data (raw data), concentration estimates and calculated paleoenvironmental indices for each studied sample. Samples were counted until
more than 200, and often more than 300, dinoflagellate cysts had been enumerated. A "+" in the table indicates presence outside regular counts.