Available online at www.sciencedirect.com
Earth and Planetary Science Letters 265 (2008) 33 – 48
www.elsevier.com/locate/epsl
Indications for control of the Iceland plume on the Eocene–Oligocene
“greenhouse–icehouse” climate transition
Meir Abelson a,⁎, Amotz Agnon b , Ahuva Almogi-Labin a
b
a
Geological Survey of Israel, 30 Malkhey Israel St. Jerusalem 95501, Israel
Institute of Earth Sciences, Hebrew University,Givat Ram, Jerusalem 91904, Israel
Received 31 January 2007; received in revised form 19 September 2007; accepted 21 September 2007
Available online 29 September 2007
Editor: C.P. Jaupart
Abstract
The Eocene/Oligocene boundary, at about 33.5 Myr ago, marks the transition from ‘greenhouse-’ to ‘icehouse-world’,
accompanied by a sudden cooling of ocean bottom-water. We show that this global event is simultaneous with a deep rooted mantle
process: an abrupt suppression of the Iceland plume triggered rapid deepening of the Greenland–Scotland Ridge (GSR) — the sill
moderating deep circulation between the Nordic seas and North Atlantic. Striking coincidence of several sets of events reflects the
abrupt suppression of the Iceland plume and a rapid removal of its influence on the nearby Reykjanes Ridge (RR): 1) A sudden
segmentation of the paleo-RR seen on seafloor magnetic anomalies, 2) a drop in spreading rate of the North Atlantic, 3) a transition
from thick to normal oceanic crust, and 4) a rapid deepening and accelerated subsidence of the GSR, inferred from the sedimentary
record of DSDP site 336. The plume suppression and the concomitant GSR deepening coincide with the initiation of North Atlantic
Deep Water (NADW) at the Eocene/Oligocene (E/O) transition, attested by onset of drift sedimentation in the Faroe–Shetland
Channel (FSC), the deepest spill-point on the GSR, and in the North Atlantic, the Feni Drift. These processes have influenced
global deepwater composition and temperature as indicated by the striking correlation with the jump in global δ18O (N 1‰)
measured on benthic foraminifers that reflects the E/O global cooling, and with enrichment of unradiogenic Nd isotopes in the
southeastern Atlantic and Southern Ocean. The initiation of Atlantic thermohaline circulation at that time is inferred from the
abrupt split between planktonic and benthic δ18O, indicating the building of ocean-water stratification. This scenario is further
corroborated by a reversal in benthic δ18O at the late Oligocene, coincident with the renewal of vigorous Iceland plume some
25 Myr ago, causing a considerable retardation in NADW fluxes. The plume renewal is inferred from the emergence of the Iceland
plateau, the transition to oblique-unsegmented RR axis, the cessation in deepening of the GSR, and rapid increase in spreading rate
of the North Atlantic. These events coincide with decreasing difference in planktonic–benthic in global δ18O by the late Oligocene.
All these inferences suggest the role of the NADW sourced at the Nordic seas to form background cooler conditions in the long
time scale since the early Oligocene, or to form permanent conditions of invigorated thermohaline circulation that forces CO2 trap
in the oceans.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Iceland plume; North Atlantic magnetic anomalies; Reykjanes Ridge; Greenland–Scotland Ridge; North Atlantic Deep Water;
thermohaline circulation; Eocene–Oligocene cooling
⁎ Corresponding author.
E-mail address: [email protected] (M. Abelson).
0012-821X/$ - see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.epsl.2007.09.021
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M. Abelson et al. / Earth and Planetary Science Letters 265 (2008) 33–48
1. Introduction
The rifting and the spreading of the North Atlantic
have been influenced by the presence of the Iceland
mantle plume which has generated an oceanic crust
much thicker than the normal oceanic crust (Holbrook
et al., 2001; White, 1997). The presence of the Iceland
mantle plume is traced by an aseismic ridge, the
Greenland–Scotland Ridge (GSR) (Fig. 1), with a
crustal thickness of ∼ 30 km (Holbrook et al., 2001;
Smallwood et al., 1999). In addition, the Iceland plume
has influenced the nearby spreading centers, causing the
formation of thick oceanic crust, the Reykjanes Ridge
(RR) reaching 10–11 km thick and the Kolbeinsey
Ridge with 9–12 km (Hooft et al., 2006; White, 1997),
compared to 6–7 km for normal oceanic crust. Several
studies have stressed the fluctuations in the plume
activity and its impact on variations in crustal thickness
and the surrounding bathymetry (Abelson and Agnon,
2001; Ito, 2001; Jones et al., 2002; White, 1997; Wright
and Miller, 1996). The first goal of this study is to
constrain the role of the Iceland mantle plume in the
dynamics of spreading of the North Atlantic. Therefore,
we link patterns of magnetic anomalies off the RR,
variations in crustal thickness, subsidence history of the
GSR, appearance of drift sediments, and variations in
spreading rates of the North Atlantic.
The aseismic GSR is a submerged sill that restricts
free flow of deep ocean water from the Nordic seas and
Arctic Ocean towards the North Atlantic. Deepwater
overflowing across the GSR from the Nordic seas is the
principal source for North Atlantic Deep Water
(NADW) (Dickson and Brown, 1994; Hansen et al.,
2001), one of the major engines to global thermohaline
circulation (Dickson and Brown, 1994). It has been
previously hypothesized that deep and dense water
flowing from the Nordic seas influences world climate
through deep ocean circulation (Schnitker, 1980; Vogt,
1972). However, these studies assumed initiation of
overflow from the Nordic seas only in the Miocene. A
recent study which has identified sedimentary drift
deposits in the Faroe–Shetland channel (FSC), has
dated the initiation of deepwater overflowing the GSR
to the early Oligocene, ∼ 35 Ma (Davies et al., 2001).
This sedimentary record indicates deepwater flow
southward from the Nordic seas into the North Atlantic.
In addition, the record of drift sediments in the North
Atlantic starts at the same time, i.e., the Feni drift at the
Rockall trough (Miller and Tucholke, 1983; Tucholke
and Mountain, 1986; Wold, 1994), suggesting the
initiation of deep ocean circulation at the E/O boundary
(Miller and Tucholke, 1983; Tucholke and Mountain,
1986). Furthermore, studies of Nd isotopes from the
Southern Ocean and the southeast Atlantic indicated an
initiation of influence on the composition of the
deepwater of the NADW at the E/O boundary (Scher
and Martin, 2004; Via and Thomas, 2006). In this paper
we will show that mantle processes triggered the initiation
of the NADW, which in turn, has driven thermohaline
circulation with its global influence on climate.
2. Timing of long-time-scale plume pulsation inferred
from magnetic anomalies and sedimentary records
Plan-view geometry of a spreading axis may reflect
strong influence of a nearby hotspot (Abelson and
Agnon, 2001; Vogt and Johnson, 1975; White, 1997).
The absence of second-order discontinuities along the
Reykjanes Ridge (RR), south of Iceland (Fig. 1), and/or
its obliquity indicates strong plume influence (Abelson
and Agnon, 2001; White, 1997). Accordingly, White
(1997) and Smallwood and White (2002) have shown
from planforms of magnetic anomalies that the Iceland
plume had two main periods of intensive influence on
the RR; the enhanced plume influence is expressed by
unsegmented RR axis, accompanied by anomalously
thick oceanic crust. White (1997) explained the absence
of segmentation as an expression of elevated mantle
temperature induced by the Iceland mantle plume; the
elevated temperature mechanically weakens the ridge
axis and oppresses segmentation. We use interpretation
of the North Atlantic magnetic anomalies (Jones et al.,
2002), together with other geological inferences, to
determine the precise timing of this long-term plume
pulsation. In order to describe the temporal variations in
segmentation of the RR, we define the angle β which
measures the deviation of second-order segments from
the general trend of the ridge (Fig. 1) (Abelson and
Fig. 1. Prominent bathymetric features around Iceland and maps of magnetic anomalies (Jones et al., 2002) illustrating the spreading history of the
Reykjanes Ridge (RR) on both sides, east and west (insets). The submerged Greenland–Scotland Ridge (GSR) is a sill that moderates deep
undercurrents from the Nordic seas to the North Atlantic, namely the North Atlantic Deep Water (NADW). The two major overflows are across the
∼ 600 m deep Denmark Strait (DS) and the 800–900 m deep Faroe–Shetland channel (FSC) (Dickson and Brown, 1994; Hansen et al., 2001). Also
shown the location of site 336 of the Deep Sea Drilling Project (DSDP) on the GSR where data of paleo-water depth since the Eocene were obtained
(Clift et al., 1995; Talwani et al., 1976). The angle β describes the deviation of second-order segments from the general trend of the ridge, β = 0° for
unsegmented RR axis and β N 0° for segmented RR. A, B, and C arrows mark profiles of temporal variations in β shown in Figs. 2–4. Note that the
general trend of the RR has preserved its original orientation during the entire opening of the North Atlantic.
M. Abelson et al. / Earth and Planetary Science Letters 265 (2008) 33–48
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M. Abelson et al. / Earth and Planetary Science Letters 265 (2008) 33–48
Agnon, 1997; Abelson and Agnon, 2001). For periods
of absence of segmentation, β = 0°, i.e., the RR axis is
continuous, whereas during the period of segmented RR
axis the segments deviate from the general trend and
β N 0° (Fig. 1). It is noteworthy that despite the temporal
variations between segmented and unsegmented RR
axis, the general trend of the RR has been preserved
during the entire opening of the North Atlantic (Fig. 1).
Therefore, the observable that best describes the history
of the RR planform geometry is the angle β. The
temporal stability of the general trend of the RR implies
also a stable orientation of the mantle upwelling feeding
the axis since continental breakup (Abelson and Agnon,
1997), despite the discerned change in spreading
direction around the E/O transition (Smallwood and
White, 2002).
2.1. Suppression of the Iceland plume at the Eocene/
Oligocene (E/O) boundary
In this study we infer the history of plume influence
on the paleo-RR from spreading planforms as deduced
from magnetic anomalies and variations in crustal
thickness. We further corroborate this history by data
from deep sea drilling, at site DSDP 336 recording the
subsidence of the GSR, and appearance of drift
sediments in the FSC and North Atlantic.
2.1.1. History of the Reykjanes Ridge planform from
magnetic anomalies & variations in crustal thickness
According to the interpretation of Jones et al. (2002)
(Fig. 1) to magnetic maps of the North Atlantic (Macnab
et al., 1995), between anomaly 24 (54 Ma) and anomaly
17 (38–36.6 Ma (Cande and Kent, 1995)) the paleo-RR
axis was orthogonal to spreading direction with no
indications for segmentation (Fig. 1). The first clear
segmented RR occurred at chron 13 (33.5–33 Ma (all
ages of magnetic anomalies in this paper are according
to Cande and Kent, 1995)). This means that since the
formation of oceanic crust in the North Atlantic until
∼ 37 Ma, end of chron 17, the RR was strongly
influenced by the Iceland plume. This notion is
corroborated by a thick oceanic crust inferred from
seismic profiles between Greenland and magnetic
anomaly 19 (∼ 41 Ma) (Holbrook et al., 2001). The
inferred crustal thickness ranges between 30 km and 8–
9 km, larger than the 6–7 km of normal oceanic crust
free of plume influence. The gradual decrease in crustal
thickness indicates a decline in the plume influence on
the paleo-RR. Still, 8–9 km thick oceanic crust around
chron 19 indicates plume influence (Abelson and
Agnon, 2001; Detrick et al., 1995) on the thermal
structure of the paleo-RR axis. Therefore, the decrease
in plume influence on the RR was not sufficient to
trigger ridge segmentation until 36 Ma.
A transition from unsegmented to orthogonal and
segmented paleo-RR appeared subsequent to chron 17, a
continuous RR axis (Jones et al., 2002), and prior to
chron 13, i.e., between 36 Ma and 33.5 Ma, around the
E/O transition (Figs. 1 and 2). This transition was
accompanied by a sharp decrease in plume activity
indicated by a transition to a province of deeper
bathymetry with normal oceanic crust (White, 1997).
According to White (1997), in contrast to the unsegmented paleo-RR, the province of the segmented paleoRR with its deeper bathymetry shows some seismic
indications for oceanic crust with normal thickness. A
thin Oligocene oceanic crust (4–7 km) was also
identified by a recent study from the Aegir Ridge
north of the GSR in the Norwegian Basin (Greenhalgh
and Kusznir, 2007). As notified by these authors
(Greenhalgh and Kusznir, 2007), this situation possibly
indicates normal asthenosphere temperature, in contrast
to elevated asthenosphere temperatures during the
Paleocene and Miocene–recent.
The transition from unsegmented to segmented RR
has been explained as resulting from a change in
spreading direction (e.g., Jones, 2003; Smallwood and
White, 2002). This means that a large change in
spreading direction, ∼ 30° the angle between the
unsegmented axis and the 2nd-order segments, should
occur abruptly between chrons 17 and 13. However, it
seems that a change in spreading direction solely is not
sufficient to generate ridge segmentation. This notion is
attested by the reverse transition to unsegmented and
oblique RR axis in later stage (∼ 25 Ma; see Section
2.2), when spreading direction has remained constant
during the disappearance of 2nd-order segmentation.
This reverse transition was accompanied by indications
of increase in plume influence. Therefore, beside a
change in spreading direction, the absence or presence
of plume influence was crucial for appearance or
disappearance of the RR segmentation, respectively
(Abelson and Agnon, 2001; White, 1997). Regardless
whether or not the transition to unsegmented RR at the
E/O boundary was due to change in spreading direction
solely, it appears that this transition was associated with
a sharp decrease in the plume influence on the RR
(Smallwood and White, 2002; White, 1997), as further
confirmed in this section.
According to the considerations mentioned above,
the variations in β demonstrate that the two major longterm pulses of intensified plume activity have lasted
more than 20 Myr each, being separated by a period of
M. Abelson et al. / Earth and Planetary Science Letters 265 (2008) 33–48
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Fig. 2. History of variations of the angle β measured along A, B, and C, profiles (Fig. 1) on each side of the Reykjanes Ridge (RR). The zones of β = 0
mark periods of strong influence of the Iceland plume on the RR spreading. The high β reflects a period of absence of plume influence. An abrupt
increase in β occurred between anomalies #17 and #13 around the E/O boundary. This transition in axis planform correlates with the initiation of
NADW, dated from drift sediments in FSC (Davies et al., 2001). A reverse transition, from high β to continuous axis (β = 0), occurred at the late
Oligocene with the emergence of the Iceland plateau, dated to ∼ 25 Ma (Saemundsson, 1986; Vogt et al., 1980). The two periods of long-term plume
pulsation are accompanied by indications of shorter time scale of plume pulsation, 3–6 Myr: diachronous V-shaped ridges (Wright and Miller, 1996)
(gray bars) and dating of seamounts in the Northeast Atlantic (O'Connor et al., 2000) (black bars).
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M. Abelson et al. / Earth and Planetary Science Letters 265 (2008) 33–48
M. Abelson et al. / Earth and Planetary Science Letters 265 (2008) 33–48
plume quiescence during the Oligocene that lasted
nearly 10 Myr (Figs. 2 and 3). The two major pulses of
elevated plume influence were superposed by shorttime-scale pulsation, about 5 Myr time scale, expressed
by the formation of seamounts (O'Connor et al., 2000)
during the first period, and V-shaped diachronous ridges
(Wright and Miller, 1996) during the second long-pulse
period (Fig. 2). The long-time-scale pulsation shows
larger fluctuations in the plume activity, as expressed by
the RR segmentation (significant removal of plume
influence on the RR), and as pertinent to our case, by the
strong influence on the GSR bathymetry.
2.1.2. Subsidence history of the Greenland–Scotland
Ridge from DSDP 336
A pronounced observation supporting the abrupt
decrease in plume activity at the E/O transition is the
GSR deepening found in a sedimentary record from a
borehole at site DSDP 336 located on the GSR, northwest
of Faroe Islands (Talwani et al., 1976) (Fig. 1). The paleowater depth inferred from microfaunal record at this site
indicates rapid seafloor deepening at the Iceland–Faroe
Ridge between 36 Ma to 32 Ma, around the time of E/O
transition (Fig. 2). This rapid deepening clearly correlates
with the transition from unsegmented to segmented RR
(Figs. 3 and 4). Until that time the depth of this site was
shallow, ∼10–20 m, for ∼7 Myr. Around the E/O
boundary, the GSR at this site deepened to 50–100 m
(Fig. 2). A tectonic subsidence pattern back-stripped from
the paleo-water depth (Clift et al., 1995) indicates
modulation of spreading-induced GSR subsidence by
the plume activity. Instead of monotonous deceleration in
subsidence expected for spreading-induced thermal
subsidence (e.g., Parsons and Sclater, 1977), we see a
period of significant acceleration, from 20 m/Myr to 40 m/
Myr, started around the E/O transition (∼35 Ma). During
that time, subsidence rate shows a two-fold increase and a
subsequent acceleration to 120 m/Myr at 32 Ma (Figs. 3
and 4). It appears that a rapid decline in plume activity at
the E/O transition caused rapid deepening of the GSR to a
critical depth that enabled overflow of deep Nordic
39
waters. This overflow initiation, namely the NADW (or
northern component water — the proto-NADW (Oppo
and Fairbanks, 1987; Wright and Miller, 1996), occurred
in the GSR's deepest part, i.e., the Faroe–Shetland
channel, attested by the Southeast Faroe drift (Davies
et al., 2001) and beginning of drift sedimentation, the Feni
drift, in the North Atlantic (Tucholke and Mountain,
1986).
The spill-point of the FSC is at a distance of
∼ 750 km from the nowadays plume center (Fig. 1). The
site of DSDP 336 is around 400 km from the present
plume center. In order to estimate a lower boundary for
the plume influence by dynamic support on the uplift/
subsidence at the FSC we used the present distances.
According to the data from DSDP 336 the tectonic
subsidence between 36 Ma and 32 Ma was 120–150 m,
and proceeded its subsidence to 240–320 m until 31 Ma
(Fig. 3). Nadin et al. (1995) have modeled the regional
vertical displacements induced by a mantle plume. From
a 2D model considering viscosity contrast between
mantle lithosphere and asthenosphere, they showed that
a plume-driven uplift of 150 m at a distance of 400 km,
such as the location of site 336, corresponds to uplift of
50 to 100 m, 750 km away from the plume center.
Considering that the top of cold and dense Nordic
deepwater is ∼ 150 m above the present sill floor
(Hansen et al., 2001; Poore et al., 2006), such a
subsidence of 50–100 m is critical for regulation of
deepwater overflow across the GSR. Therefore, the
GSR rapid subsidence at the E/O boundary has reached
a critical depth that has enabled the onset of the NADW,
expressed by the Southeast Faroe drift.
2.2. Renewal of intensive plume activity by the end of
the Oligocene (∼ 25 Ma)
The coincidence of transitions in magnetic patterns off
RR and vertical motions around the Iceland plume repeats
once again toward the end of the Oligocene, this time in a
reversal mode. Here we present geological inferences for
the renewal of a strong plume influence on its surrounding.
Fig. 3. Temporal correlations between (a) geometrical variations in North Atlantic magnetic anomalies, (b) paleo-water depth and tectonic subsidence of
the GSR, and (c) variations in spreading rates. (a) Temporal variations of the angle β measured from the magnetic anomalies along A, B, and C profiles
shown in Fig. 1, west of the RR. The northernmost profile – A – reflects the history of plume influence nearest to GSR. Periods of plume influence on the
paleo-RR are expressed by β = 0°. Gray and black bars mark shorter term of pulsation, as in Fig. 2. (b) Temporal profile of maximum and minimum estimate
of paleo-water depth from site 336 (solid line) and calculated tectonic/thermal subsidence (Clift et al., 1995) (dashed lines). (c) Variations of average
spreading rates of the North Atlantic calculated from several spreading systems north (Mohns and Aegir ridges) and south (RR) of Iceland (Mosar et al.,
2002). A decrease in spreading rate is observed during the first long-term pulse of Iceland in agreement with the decrease in thickness (thick grey arrow) of
oceanic crust to 8–9 km thick, still with presence of plume influence seen also by RR planform, β = 0°. A drop in spreading rate occurred at the E/O
transition with drop in dynamic support on the GSR (see b), transition to normal oceanic crust at the RR, and orthogonal and segmented RR (a). A sudden
increase in spreading rate occurred by the late Oligocene with the emergence of Iceland plateau, transition to oblique and unsegmented RR (a), and
significant retardation in thermal subsidence at the GSR (b), due to renewal of vigorous Iceland plume.
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M. Abelson et al. / Earth and Planetary Science Letters 265 (2008) 33–48
2.2.1. Magnetic anomalies
By the end of the Oligocene the Icelandic plume reintensified its activity, as expressed by the gradual
transition from orthogonal and segmented to oblique
and unsegmented RR (Figs. 1 and 2). The northernmost
segmented paleo-RR is found ∼ 400 km away from
Iceland (location of cross-section A in Fig. 1). This area
represents the period of minimum influence of the
Iceland plume on the RR. In the Iceland basin (RR east
in Figs. 1 and 2), we see segmented axis during
magnetic anomalies 12–8 (Fig. 1), i.e., between 33.5
and 25.8 Ma. At this latitude anomaly 6B (23–22.5 Ma)
is continuous and oblique (Fig. 1). The edges of the
oblique and unsegmented axes crosscutting the segmented paleo-RR, mark a front of a gradual transition
from segmented and orthogonal to continuous and
oblique RR (Jones et al., 2002) (Fig. 1). This front
mimics the initiation (or renewal) of along-axis lateral
flow of plume material manifested by the diachronous
V-shaped ridges which are located off RR axis (e.g., Ito,
2001; Jones et al., 2002; Vogt and Johnson, 1975).
Accordingly, the oblique and unsegmented axis indicates a strong plume influence (Abelson and Agnon,
1997; Abelson and Agnon, 2001; Vogt and Johnson,
1975; White, 1997) delivered by along-axis lateral flow
of plume material. Therefore, according to the geometry
of the magnetic anomalies in Iceland basin this
transition has started some 25 Myr ago. At the Irminger
basin (RR west in Figs. 1 and 2), this gradual transition
has started with anomaly 8 (26.5–25.8 Ma).
2.2.2. Emergence of the Iceland plateau
The renewal in intensive activity of the Iceland
plume can be deduced also from the volcanic history on
Iceland at this time span. Saemundsson (1986) suggested a broad definition for the renewal of excessive
volcanism in Iceland block sometime between 35.5 Ma
and 19.5 Ma. Within this time range, a more accurate
estimation for the emergence of Iceland plateau and
Fig. 4. Temporal correlations between variations of spreading planform
of the RR, subsidence history and water depth on the GSR, global
benthic δ18O, and Nd isotope record from the southeastern Atlantic
(ODPs 1262–1264). (a) As in Fig. 3. (b) Subsidence and deepening
rates of the GSR calculated from the data presented in Fig. 3b.
(c) Cenozoic global compilation of δ18O measured from benthic
foraminifers (Zachos et al., 2001). (d) Nd isotope data from Walvis
Ridge, ODP sites 1262–1264 (Via and Thomas, 2006). Decreasing
values of ɛNd reflect significant contribution of NADW (Scher and
Martin, 2004). Note the significant coincidence of abrupt RR
segmentation (a), significant increase in GSR deepening/subsidence
rates (b), step increase of benthic δ18O (c), start of decreasing ɛNd (d),
and initiation of NADW around the E/O boundary. The renewal of
intensive Iceland plume some 25 Myr ago coincides with transition to
unsegmented RR (a), cessation of deepening and subsidence of the
GSR (b), emergence of Iceland plateau, step decrease in δ18O (c), and
initiation of decreasing trend in ɛNd in southeastern Atlantic (d).
M. Abelson et al. / Earth and Planetary Science Letters 265 (2008) 33–48
invigoration of volcanic activity in Iceland was made by
Vogt et al. (1980) and Sigurdsson and Loebner (1981).
On the basis of magnetic anomalies, Vogt et al. (1980)
suggested that the emergence of the Iceland plateau
occurred around 25 Ma, whilst a similar estimation was
made according to increased explosive volcanism found
in deep sea sediments (Sigurdsson and Loebner, 1981).
Therefore, the time of emergence of the Iceland plateau
and excessive volcanism is compatible with the
beginning of the gradual transition from segmented to
unsegmented RR around 26–25 Ma (Figs. 2–4).
2.2.3. Significant subsidence deceleration of the GSR
from DSDP 336
The impact of the re-intensified plume is also
observed by the subsidence pattern of the GSR from
the record of DSDP 336 (Fig. 3). A reversal in the
subsidence anomaly is observed around 25 Ma when the
GSR has ceased its deepening, and the subsidence rate
significantly decelerated to 4 m/Myr, much lower than
the average subsidence rate (∼ 25 m/Myr) (Figs. 3
and 4), suggesting the re-intensification of plume
dynamic support. It appears that the renewal of intensive
Iceland plume has retarded the thermal subsidence of
the GSR at the more remote location of site 336, while at
the vicinity of the plume center the GSR has probably
undergone uplift with the emergence of the Iceland
plateau. This renewal of intensive Iceland plume
possibly restrained the overflow from the Nordic seas,
as discussed in Section 4.
3. Linkage between the Iceland plume activity and
the opening of the North Atlantic
Additional features that may describe the timing of the
long-time-scale pulsation of the Iceland plume are the
variations in spreading rates of the North Atlantic.
Previous studies have detected the history of spreading
rates in the North Atlantic and Nordic seas from the width
and age of magnetic anomalies as well as calculations
from poles of rotation (Mosar et al., 2002; Smallwood and
White, 2002). We show that prominent variations in
spreading rates significantly correlate with the history of
activity of the Iceland plume. Two studies exploring the
history of the North Atlantic (Mosar et al., 2002;
Smallwood and White, 2002) show slightly different
absolute values in spreading rates, but with very similar
trends and timing in the variations of spreading rates.
Right after continental breakup, the spreading
velocity of the paleo-RR was around 1.4 cm/yr (Smallwood and White, 2002) to 2 cm/yr (Mosar et al., 2002).
With the progress of spreading the spreading rate has
41
decreased to values around 1 cm/yr until around the time
of E/O transition. The spreading rate decrease is
compatible with the reduction of thickness of the
oceanic crust seen by seismic reflection and refraction
between the 56 Ma and ∼41 Ma (magnetic chron#19)
(Holbrook et al., 2001), i.e., reduction in the plume
influence on the RR is linked with a decrease in
spreading rate. Still, the relatively thick igneous crust,
8–9 km in a distance of 200 km from the hotspot track
(Holbrook et al., 2001), attests the influence of the
plume on the RR. At the E/O transition, the spreading
rate has dropped below 1 cm/yr to ∼ 0.7 cm/yr.
According to Smallwood and White (2002) the drop
was from ∼ 1.2 to 0.7 cm/yr and occurred at ∼ 36 Ma,
according to Mosar et al. (2002) it was from 1.3 to
0.7 cm/yr at 33.5 Ma. Both dates are around the E/O
boundary, correlating with the removal of dynamic
support of the Iceland plume (Fig. 3) and shift to
segmented RR between 36 to 33 Ma. The lowest rates
of spreading during most of the Oligocene correlate with
the deep bathymetry, thin oceanic crust, and segmented
RR, i.e., with the removal of the plume influence from the
RR axis. By the late Oligocene, with the emergence of
Iceland plateau, the shift from segmented to unsegmented
and oblique RR, and cessation of subsidence on site 336,
we see an abrupt increase in spreading rate (Fig. 3). This
means that an increase in spreading rate correlates with the
renewal of vigorous Iceland plume.
The above temporal correlations indicate that the
history of the North Atlantic spreading rates mimics the
long-term pulsation of the Iceland plume. Furthermore,
the observations linking between the histories of the
Iceland plume activity and spreading rates may demonstrate the role of the Iceland plume as an engine in the
opening of the North Atlantic and Nordic seas. Considering that the upwelling beneath the RR and Iceland plume
is buoyancy-driven rather than a passive response to plate
separation (e.g., Gaherty, 2001; Wolfe et al., 1997) and
indications for ridge push forces in the passive margins
(Lundin and Dore, 2002; Mosar et al., 2002; White and
Lovell, 1997), the correlations between periods of higher
spreading rates and vigorous plume indicate that the
Iceland plume contributes to the pushing apart of the plates
through ridge push (gravitational or drag forces) along the
RR (Lundin and Dore, 2002; Mosar et al., 2002).
4. Control of the Iceland plume on the initiation of
global thermohaline circulation and
‘greenhouse’–‘icehouse’ climate transition
One of the most dramatic events in the Earth Cenozoic
history is the cooling event around the E/O boundary
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M. Abelson et al. / Earth and Planetary Science Letters 265 (2008) 33–48
(∼34 Ma) accompanied by a major extinction in marine
fauna (Ivany et al., 2000; Raup and Sepkoski, 1986). This
abrupt cooling marked by Antarctic glaciation and a rapid
increase in global δ18O (N 1.0‰) measured on benthic
foraminifera, is the largest step in the “greenhouse–
icehouse” climate transition (Zachos et al., 2001) (Figs. 4
and 5). The sharp increase in the benthic δ18O can mark
both, a cooling event (Coxall et al., 2005; Zachos et al.,
2001) and/or an onset of bipolar glaciation (Coxall et al.,
2005; Moran et al., 2006). A second prominent climatic
event occurred by the late Oligocene, designated by
Zachos et al. (2001) as the late Oligocene warming event.
According to their compilation, this event is marked by a
drop of N1‰ in the benthic δ18O (Fig. 4). However, this
value may be an overestimate as implied from records of
benthic δ18O from the Atlantic (Miller et al., 1987; Miller
et al., 2005) and the Pacific (Lear et al., 2004; Palike et al.,
2006). According to these records the drop in benthic
δ18O was ∼0.5‰ (Fig. 5). Still, all records demonstrate
the existence of a warming event by the late Oligocene.
Explanations for the E/O jump in benthic δ18O leaning on
decreasing carbon dioxide (Pagani et al., 2005) and
changes in ocean circulation around Antarctica (Kennett,
1977; Scher and Martin, 2006), cannot fully explain the E/
O timing of the cooling event and/or the reversal to global
warming in the late Oligocene (Table 1).
4.1. Linkage between Iceland plume activity and
Oligocene major climate events
Previous works have associated the pulsation of the
Iceland plume with fluctuations in the supply of dense
deepwaters from the Nordic seas by controlling the
depth of the GSR sill (Jones et al., 2002; Poore et al.,
2006; Wright and Miller, 1996). However, the influence
on the ocean deepwater was tested since the Miocene
and through the shorter time cycles of plume pulsation
reflected by the V-shaped ridges around the RR. As
shown above, the fluctuations in the activity of the
Iceland plume are much larger in the long-time-scale
pulsation, where during the Oligocene the plume
influence had remarkably decreased along the RR axis
and the subsidence of the GSR sill accelerated.
Fig. 5. Correlation between subsidence history and water depth on the
GSR, and values of benthic δ18O from particular sites from the
Atlantic and the Pacific. (a) As in Fig. 4b. (b) Values of benthic δ18O
from six sites in the North, Central, and South Atlantic (sites 608, 563,
558, 529, 523, 522) (Miller et al., 1987; Miller et al., 2005). (c) Values
of benthic δ18O from ODP site 1218 (Lear et al., 2004; Palike et al.,
2006) in the equatorial Pacific. The influence of the proto-NADW at
the E/O transition was probably delivered to the Pacific through the
open seaway of the Panama Isthmus, which had deepwater connection
prior the Miocene (Duque-Caro, 1990). Note that the late Oligocene
drop in the δ18O is ∼ 0.5‰ in both oceans, more moderate than the
N1‰ seen in the global compilation of Zachos et al. (2001) (Fig. 4).
M. Abelson et al. / Earth and Planetary Science Letters 265 (2008) 33–48
43
Table 1
Summary of observations linking between long-term activity of the Iceland plume and its influence on global ocean circulation at the Oligocene
Iceland mantle plume event
Tectonic impact
Paleoceanographic impact
Paleoclimatic event
Plume suppression at the
E/O transition (36–33 Ma)
• Abrupt segmentation
(change of β from 0° to 20°–30°)
of the Reykjanes Ridge (RR)
(Figs. 1–3)
• Approaching normal oceanic
crust (White, 1997;
Greenhalgh and Kusznir, 2007)
• Accelerated subsidence of GSR
(removal of dynamic support)
(Figs. 3–5)
• Drop in spreading rate
(Fig. 3)
Onset of NADW:
Global cooling at the E/O
transition and transition
to “icehouse-world”
Renewal of vigorous Iceland plume
at the late Oligocene (∼25 Ma)
• Shift to unsegmented
and oblique RR (Figs. 1–3)
• Transition to plume-affected
thick oceanic crust
(Jones et al., 2002; White, 1997)
• Significant deceleration of
GSR subsidence (renewal of
dynamic support) (Figs. 3–5)
• Emergence of Iceland
plateau (Sigurdsson and
Loebner, 1981; Vogt et al., 1980)
• Increasing spreading rate
(Fig. 3)
The history of the plume activity, i.e., plume
suppression at the E/O boundary and late Oligocene
renewal, shows a striking correlation with the two major
Cenozoic global climatic events (Figs. 4 and 5), the E/O
global cooling and glaciation and the late Oligocene
δ18O drop. The long-term changes in the global δ18O is
believed to have a tectonic origin (Zachos et al., 2001)
and these variations around the Oligocene significantly
correlate with the long-term activity history of the
Iceland plume. The rapid deepening of the Greenland–
Scotland Ridge observed at DSDP 336, and the
transition to segmented RR during the E/O transition,
match the E/O sharp increase in δ18O (Figs. 4 and 5).
The sudden removal of plume influence from the RR
that correlates with the rapid subsidence and deepening
of the GSR sill, together with the occurrence of the
Southeast Faroe drift, indicates initiation of NADW
from the Nordic seas to the North Atlantic triggered by
plume suppression. Plume suppression and GSR
deepening have started around 36 Ma (after chron 17).
Until that time the dense deepwater of the Nordic seas
• Inception of Southeastern Faroe
Drift sediments (Davies et al., 2001)
• Initiation of drift sedimentation in
the North Atlantic — the Feni Drift
(Tucholke and Mountain, 1986)
• Establishment of an increasing
trend of unradiogenic Nd isotopes
in the South Atlantic and Southern Ocean
(Via and Thomas, 2006) (Fig. 4)
• Step increase in global benthic δ18O
(Figs. 4 and 5)
• Step increase in planktonic–benthic
difference δ18O — onset of ocean-water
stratification, i.e., thermohaline
circulation (Fig. 6)
Moderation of NADW:
Late Oligocene
warming event
• A decrease in unradiogenic Nd isotopes
in the South Atlantic
(Via and Thomas, 2006) (Fig. 4)
• Step decrease in global
benthic δ18O (Figs. 4 and 5)
• A decrease in planktonic–benthic
difference δ18O — moderation of
ocean-water stratification (Fig. 6)
has been accumulated behind the elevated GSR sill
(Kaminski and Austin, 1999). At some critical depth,
during the rapid GSR subsidence, the dense deepwater
of the Nordic seas could overflow the GSR sill (Fig. 7).
The expected δ18O values of the Nordic seas were
probably high relatively to the rest of the world oceans,
from several reasons: First, the high-latitude waters are
usually colder. Second, there is evidence for some icesheets on Greenland started ∼ 38 Myr ago (Eldrett et al.,
2007). Third, the regional change in spreading direction
added an opening component to the shear along the
Fram strait around chron 13 (Myhre and Eldholm,
1988; Vogt, 1986), thus enabling some connection
between the Nordic and Arctic waters as indicated by
faunal assemblages (Kaminski and Austin, 1999),
where the latter have also witnessed glaciation at that
time (Moran et al., 2006). Therefore, sudden invasion
of NADW at that time might have an abrupt influence
on the composition and temperature of bottom-water,
expressed by the jump in the global δ18O values in
benthic foraminifers around the E/O boundary (Fig. 4),
44
M. Abelson et al. / Earth and Planetary Science Letters 265 (2008) 33–48
Fig. 6. Benthic versus planktonic values of δ18O from Eocene to Miocene sampled from various sites in the Atlantic [J. Wright, personal
communication; Wright and Cramer, in preparation]. (a) Values of δ18O measured on planktonic (upper curve) and benthic foraminifers (lower
curve). (b) The difference (or overlap) between the two curves in (a) indicating variations in stratification of ocean water, implying the presence (or
absence) of thermohaline circulation. The jump in benthic–planktonic difference at the E/O transition suggests the initiation of thermohaline
circulation in the Atlantic and its global strengthening, coinciding with the sudden suppression of the Iceland plume. On the other hand, a decrease in
this difference at the late Oligocene suggests a moderation in thermohaline circulation, coinciding with the emergence of Iceland Plateau which in turn
restrained the NADW. The advancement in the opening of the Nordic and Arctic seas with the deepening of the GSR could have contributed to the
significant increase in the plankton–benthos difference during the late Cenozoic.
triggering global cooling. The transition to oceans with
N1‰ higher δ18O occurred within tens of thousands
years (Coxall et al., 2005), probably after the GSR has
reached a critical depth through its rapid subsidence. This
process was superposed by the short-term orbital
influence expressed by two steps with cyclicity of
40,000 yr (Coxall et al., 2005).
Our explanation of the influence of the Iceland
plume on global climate reflected by the δ18O record is
further substantiated by the striking correlation between the abrupt drop in δ18O of the late Oligocene
warming event, and the renewal of vigorous Iceland
plume some 25 Myr ago; the emergence of the Iceland
Plateau and the GSR uplift restrained the Nordic
M. Abelson et al. / Earth and Planetary Science Letters 265 (2008) 33–48
45
overflow of cold and dense deepwater to the world
oceans (Figs. 4 and 5). The renewal of intensive
Iceland plume at ∼ 25 Ma is observed by the transition
to unsegmented RR, emergence of Iceland plateau,
acceleration of spreading rate (Fig. 3), significant
deceleration of subsidence on GSR deduced from
DSDP 336 (Figs. 4 and 5).
4.2. Influence of the Iceland plume on deepwater
circulation — initiation versus moderation of observed
stratification of ocean waters
The sudden suppression of the Iceland plume and
GSR deepening at the early Oligocene has probably
initiated thermohaline circulation in the Atlantic and
invigorated global circulation. The initiation of the
ocean circulation has formed stratification that decouples between bottom- and surface-water, heralding the
initiation of the psychrosphere (Kennett and Shackleton,
1976; Wright, 2001). This is attested by the distinctive
contrast between the abrupt increase in the benthic δ18O
at the E/O boundary versus δ18O values measured on
planktonic foraminifers which has remained more stable
during this transition (Wright, 2001) (Fig. 6). The
initiation of thermohaline circulation in the Atlantic
involved with the Nordic seas is strongly supported by
both, the drift sediments in FSC indicating outflow of
deepwaters, and on the other hand, diatom assemblages
in the Norwegian Sea indicating entrance of warmer
surface-water from the low-latitude Atlantic by the latest
Eocene to Oligocene (Kaminski and Austin, 1999). A
reasonable engine for the entrance of the surface-waters
to the Nordic seas was the initiation of the proto-NADW
triggered by the E/O rapid subsidence of the GSR; the
open Panamanian Isthmus (Duque-Caro, 1990) implies
absence of the major engine for poleward currents of
surface-water (Haug and Tiedemann, 1998). The
entrance of the warmer surface-water into the Norwegian Sea could also increase the salinity and temperature
of the proto-NADW (Lear et al., 2003). The decrease in
δ18O immediately after the E/O major jump (Figs. 4
and 5) may imply increase in temperature of the protoNADW.
By the end of the Oligocene the split between
planktonic and benthic δ18O is reduced with the sharp
decrease of benthic δ18O, during the late Oligocene
warming event (Fig. 6). This reduction in the planktonic–benthic difference is compatible with attenuation in
bottom-water currents that subdued the Atlantic stratification. The attenuation of ocean stratification coincides with emergence of Iceland plateau and cessation of
GSR deepening seen in the record of DSDP 336 (Fig. 6).
Fig. 7. A scheme describing the NADW invasion from the Nordic seas
to the North Atlantic due to removal of dynamic support of the Iceland
plume. Until the Eocene/Oligocene transition, these dense waters have
been accumulated behind the elevated GSR (a). A rapid deepening of
the GSR has started at ∼ 36 Ma until ∼ 32 Ma. At some critical depth
around the E/O boundary the dense deepwaters spilled over the GSR
(b).
It is noteworthy that our hypothesis of the Iceland
plume influence on global thermohaline circulation
around the Oligocene can be tested by a comparison
between the global profile of benthic δ18O and the Arctic/
Nordic profile north of the GSR. Where in the latter, we
anticipate a gradual increase in the benthic δ18O rather
than a step increase as found across the E/O transition in
the global profile due to the plume regulation.
4.3. Influence of the Iceland plume on deepwater
circulation — signals from Nd isotopes
The early Oligocene onset of NADW contribution to
the deepwater in the southeastern Atlantic and to the
intermediate water in the Southern Ocean is reflected by
an initiation of gradual increase in unradiogenic Nd
isotopes (Scher and Martin, 2004; Via and Thomas,
2006) (Fig. 4d). Via and Thomas (2006) suggest that the
divergence in trends of enrichment of unradiogenic Nd
between the Southern Ocean and the southeast Atlantic
marks gradual increase in the NADW contribution.
They speculated that this initiation was induced by
tectonic deepening of the GSR sill. As we show here this
initiation of the NADW contribution was caused due to
sudden suppression of the Iceland plume. Furthermore,
according to Via and Thomas, the unradiogenic Nd
increases gradually towards a modern structure of the
southeastern Atlantic water mass, suggesting a longterm increase in NADW component (Via and Thomas,
46
M. Abelson et al. / Earth and Planetary Science Letters 265 (2008) 33–48
2006). This gradual increase is interrupted by a reversal
decrease in the unradiogenic Nd, starting some 25 Myr
ago, and is accompanied by dispersion of ɛNd values
(Fig. 4d). This reversal is compatible with a reduction in
the contribution of the NADW to the deepwater of the
southeastern Atlantic. The initiation of this reversal
coincides with the emergence of Iceland plateau and
plume renewal (Fig. 4), and extends over ∼ 3 Myr,
suggesting plume-induced moderation of the NADW by
the late Oligocene.
4.4. Implications for Cenozoic evolution of global
climate
So far, we have considered the initiation of NADW as
a triggering agent for global glaciation. On the other
hand, enhancement of NADW fluxes during the
Miocene and Pliocene was associated with events of
warmer conditions and deglaciation (e.g., Boyle and
Keigwin, 1987; Charles and Fairbanks, 1992; Raymo
et al., 1992; Wright and Miller, 1996). The reverse effect
of enhanced NADW on “icehouse” states on shorter
time scales stems from intensive poleward heat transport
from lower latitude oceans by amplification of poleward
currents of shallower water. According to the striking
correlations presented here, between Oligocene cooling/
warming events and the Iceland plume activity we
suggest that the long-term gradual increase in the
NADW flux through the Cenozoic has formed a
‘background’ or average cooler conditions, perhaps by
cooling the deep ocean waters, stabilizing the long-term
transition to ‘icehouse’-world. The gradual Cenozoic
increase in NADW flux has been developed by
advancement of North Atlantic spreading, causing the
enlargement of the Nordic–Arctic seawater reservoir
and thermal deepening of the GSR sill, modulated by the
Iceland plume. In this mechanism the short-term
episodes of enhanced NADW linked to warmer periods,
serve as negative feedback to the general trend of
Cenozoic cooling. The long-term production of NADW
may have a double effect on formation of cooler
conditions: (1) transport and distribution of high-latitude
cold water in the world oceans, and (2) invigoration of
global thermohaline circulation (Fig. 6) that may lower
CO2 in the atmosphere; acceleration of upwelling and
productivity and increase of burial rate of organic
carbon relative to carbonate carbon cause the lowering
of CO2 in the atmosphere (Zachos and Kump, 2005). A
partial clue for the latter mechanism could be find by the
Cenozoic record of pCO2 (Pagani et al., 2005), when the
major decrease in pCO2 occurred later (∼ 32 Ma) than
the δ18O jump at the E/O boundary.
5. Summary
The onset of NADW from the Nordic seas was
triggered by the sudden suppression of the Iceland
plume at the E/O transition which increased the depth of
the GSR sill. This enabled the initiation of deep ocean
undercurrents in the Atlantic ocean and invigoration of
global thermohaline circulation, which in turn caused
the colder conditions during the Oligocene and the high
value of benthic δ18O (Figs. 4 and 5). The suppression
of the Iceland plume is inferred from the sudden
removal of the plume influence on the RR seen by (1)
abrupt transition to segmented axis, (2) transition from
thick to normal oceanic crust, and (3) a minimum in
spreading rate of the nearby spreading axes (Fig. 3). The
accompanied rapid subsidence of the GSR is seen from
the sedimentary record from borehole in site DSDP 336
(Fig. 3). The abrupt plume suppression and the rapid
GSR subsidence coincide with the inception of the
Southeast Faroe drift sediments at the FSC, marking the
NADW initiation at the E/O transition, and with the
occurrence of the Feni drift in the Rockall Trough
(Figs. 3 and 4). The global influence of the NADW
invasion at the E/O transition is reflected by the increase
in unradiogenic Nd in the deep South Atlantic and
Southern Ocean, and by a step increase in the global
benthic δ18O (Figs. 4 and 5). The E/O initiation of ocean
stratification, that may mark the initiation of Atlantic
thermohaline circulation, is corroborated by the jump in
the difference between the planktonic and benthic δ18O
values (Fig. 6).
The scenario of the influence of Iceland on global
climate reflected by the δ 18 O record is further
substantiated by the striking correlation between the
drop in δ18O, i.e., the late Oligocene warming event,
and the renewal of vigorous Iceland plume some 25 Myr
ago; the emergence of the Iceland Plateau and the
cessation of GSR subsidence restrained the Nordic
overflow of cold and dense deepwater to the world
oceans. The renewal of intensive activity of the Iceland
plume some 25 Myr ago is attested by the coincidence of
(1) the emergence of the Iceland plateau, (2) the
transition to oblique, unsegmented RR axis, (3) the
cessation in deepening of the GSR seen in the record of
DSDP 336, and (4) increase in spreading rate in the
opening of the North Atlantic and Nordic seas (Fig. 3).
The renewal of intensive Iceland plume coincides with
global restraint in the NADW attested by the decrease in
the unradiogenic Nd in the South Atlantic (Figs. 4 and 5),
and by a decrease in global difference between planktonic
and benthic δ18O (Fig. 6). This implies the impediment of
deep undercurrents overflowing the GSR and moderation
M. Abelson et al. / Earth and Planetary Science Letters 265 (2008) 33–48
of global deep ocean circulation by the amplification in
plume activity, inducing the late Oligocene warming
event.
Beside the striking correlation between E/O cooling
and the GSR deepening driven by plume suppression, an
additional appeal of the present hypothesis is the ability
to explain also the late Oligocene warming event by the
renewal of vigorous Iceland plume. This is an advantage
over previous hypotheses explaining the causes for the
‘greenhouse’–‘icehouse’ climate transition. Finally, the
apparent influence of the Nordic and Arctic seas during
the Oligocene, regulated by the Iceland plume, suggests
a control on global Cenozoic cooling: the advancement
of opening of the Nordic and Arctic seas, with the
thermal subsidence of the GSR and widening of these
seas during the last 34 Myr has formed an average
cooler conditions, stabilizing the reign of “icehouse”world.
Acknowledgements
We benefited from discussions with Jonathan Erez,
Yair Rosenthal, Jim Kennett, and Moti Stein. We thank
Peter Clift for providing us data of paleo-water depth
and subsidence calculations from DSDP 336. We are
grateful to Jim Wright for providing us unpublished data
of δ18O measured from planktonic and benthic foraminifera (Fig. 6), and to Peter Vogt for comments on early
version of the manuscript.
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