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Deep-Sea Research II 54 (2007) 2308–2324

Cenozoic Antarctic cryosphere evolution: Tales from deep-sea

sedimentary records

Amelia E. Shevenella,, James P. Kennettb

aSchool of Oceanography, University of Washington, Seattle, WA 98195, USAbDepartment of Earth Science, University of California Santa Barbara, Santa Barbara, CA 93106, USA

Accepted 24 July 2007

Available online 29 October 2007

Abstract

Antarctica and the Southern Ocean system evolved in the Cenozoic, but the details of this complex evolution are just

beginning to emerge via high-resolution investigations of globally distributed marine sedimentary sequences. Here we

review the recent progress in defining the orbital-scale evolution of the Antarctic/Southern Ocean system, with particular

attention paid to new high-resolution multi-proxy records generated across intervals of abrupt Antarctic ice growth in the

Paleogene and early Neogene. This more detailed perspective has allowed researchers to assess the processes and feedbacks

involved in the Cenozoic evolution of the Antarctic cryosphere, absent potential complication of the paleoceanographic

record by a substantial Northern Hemisphere ice volume signal. In this paper, we review the new tools being used to

examine these high-resolution records, assess lead–lag relationships between ice volume, temperature, and carbon cycling

during intervals of abrupt Antarctic ice growth, and consider the resulting implications for the global climate system.

r 2007 Elsevier Ltd. All rights reserved.

Keywords: Antarctica; Cenozoic; Paleoceanography

1. Introduction

Antarctica and the surrounding Southern Ocean

are presently integral components of Earth’s climate

system, exerting influence on the global climate:

Antarctic ice sheets regulate global sea level, large-

scale physical processes occurring in the SouthernOcean catalyze global thermohaline circulation and

carbon cycle dynamics, and as the main global heat

sink, Antarctica drives the southward flux of heat

and hence atmospheric circulation. The Cenozoic

evolution of these conditions that define the

contemporary Antarctic cryosphere was one of the

fundamental reorganizations of the global climate

system. Over the past several decades, substantial

research efforts have been undertaken to improve

our understanding of the Cenozoic evolution of the

Antarctic/Southern Ocean system and the processes

and feedbacks involved in this evolution.The Antarctic continent has been situated in

approximately its current location over the South

Pole since the mid-Cretaceous (Lawver et al., 1992),

but remained predominantly ice-free until the

middle to late Eocene (35 Ma; see Zachos et al.,

2001a for a review). Thus, Antarctica’s geographic

location has never been a sufficient explanation for

widely recognized Cenozoic global cooling and ice

growth trends (Fig. 1). Considerable progress has

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doi:10.1016/j.dsr2.2007.07.018

Corresponding author.

E-mail address: [email protected]

(A.E. Shevenell).

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been made toward developing a detailed record of

Cenozoic Antarctic ice-sheet evolution, much of

which is owed to technological advances, including

the improved quality of acquisition and recovery of

marine sedimentary sequences and the development

of powerful geochemical techniques and paleocli-mate proxies (e.g., Mg/Ca, alkenone, and TEX86paleothermometry).

Over the past several decades, two general groups

of hypotheses have emerged to explain the Cenozoic

evolution of global temperatures and ice volume: (1)

those positing changes in global carbon cycling and

atmospheric pCO2 (Raymo, 1994; Vincent and

Berger, 1985), and (2) those requiring a redistribu-

tion of heat over the Earth’s surface (Kennett, 1975;

Schnitker, 1980; Woodruff and Savin, 1989; De-

Conto and Pollard, 2003). Ultimately, long-term

Cenozoic cooling is likely a function of Earth’sboundary conditions (e.g., plate tectonics and/or

atmospheric greenhouse gas concentrations), while

short-term climate oscillations appear to be paced

by the sensitivity of the Earth’s climate system to

orbital forcing (Zachos et al., 2001a; Pa ¨ like et al.,

2006).

This review provides a summary of the current

understanding of both the long- and short-term

Cenozoic evolution of the Antarctic/Southern

Ocean system, as gleaned from geochemical records

of deep-sea sediments. Emphasis is placed on the

late Paleogene and early Neogene (late Eocene to

late Miocene) record, during which period geo-

chemical signals are not substantially complicated

by Northern Hemisphere ice volume (Zachos et al.,2001a). The processes and feedbacks involved in

early Antarctic ice-sheet development and later ice-

sheet expansions are investigated, with attention to

the role of atmospheric pCO2 in Antarctic glacial

advances.

1.1. New paleoclimate proxies

1.1.1. Foraminifer Mg/Ca

The benthic foraminifer d18O proxy, though it

reliably documents shifts in climate, is complicated

because it includes the influence of both global icevolume and deep-ocean temperatures. These two

variables may have distinct and autonomous effects

on climate; extracting ice volume from the aggregate

d18O record provides a clearer picture of continental

ice-volume variability on both long and short

timescales and also has the potential to constrain

the phasing of ice growth and temperature change.

Recent research efforts have focused on developing

a temperature proxy, independent of salinity that

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Fig. 1. Composite benthic foraminifer d18O and d13C records compiled by Zachos et al. (2001). The three abrupt expansions of the

Antarctic cryosphere discussed in the text are indicated by arrows (modified from Zachos et al., 2001).

A.E. Shevenell, J.P. Kennett / Deep-Sea Research II 54 (2007) 2308–2324 2309


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may be paired with benthic foraminifer d18O records

to isolate the global ice-volume signal. Of the

recently developed paleotemperature proxies, in-

cluding alkenone unsaturation, TEX86, and benthic

foraminifer Mg/Ca, the benthic foraminifer Mg/Ca

proxy is the most appealing because it can bemeasured on the same foraminiferal calcite as d18O.

Mg/Ca paleothermometry relies on laboratory

observations, indicating that the partition coeffi-

cient of Mg2þ into inorganic calcite is temperature

dependent. Culture and in situ studies of marine

biogenic calcites reveal a similar temperature

dependency, albeit with species-specific vital effects

(Hastings et al., 1998; Rosenthal et al., 1997;

Mashiotta et al., 1999 and others). Thus, the most

reliable foraminifer Mg/Ca records derive from

species for which an empirical Mg/Ca-temperature

calibration exists (Martin et al., 2002; Lear et al.,2000, 2002; Marchitto et al., 2007). However, these

calibrations are limited by our present inability to

successfully culture benthic foraminifers and the

lack of a robust temperature calibration at lower

temperatures ðo5 CÞ. Many researchers are pre-

sently working to improve existing calibrations and

culture benthic foraminifers in a variety of condi-

tions.

To ensure accurate paleotemperature estimates,

the Mg/Ca signal preserved in the foraminifers must

be primary and not altered. As with all paleoclimateproxies, the benthic foraminifer Mg/Ca proxy is not

foolproof. Caveats include the influence of diagen-

esis/dissolution and carbonate saturation (Lear

et al., 2000; Lea et al., 2000). Perhaps the most

difficult issue to overcome when applying the

Mg/Ca paleotemperature proxy on longer Cenozoic

timescales relates to temporal variations in seawater

Mg/Ca (Lear et al., 2000; Billups and Schrag,

2002; Shevenell et al., 2004). Several geochemical

models of seawater predict significant background

variability in Mg/Ca during the Cenozoic (Wilk-

inson and Algeo, 1989; Stanley and Hardie, 1998;

Berner et al., 1983). However, it is important to note

that because the residence times of Mg and Ca in

the ocean are relatively long (13 and 1 My,

respectively), downcore variations in foraminifer

Mg/Ca that occur in o1 My should not be impacted

by a dynamic seawater Mg/Ca ratio (Lear et al.,

2000; Shevenell et al., 2004). To alleviate this

uncertainty, Lear et al. (2000) proposed that

existing foraminifer calibration equations may be

modified to reflect past seawater Mg/Ca (as

estimated by existing models) using the equation

of Lear et al. (2002):

BWT

¼ lnðMg/CaM=ð0:9nðMg/CaSWM=Mg/CaSWPÞÞÞ=0:11,

ð1Þ

where Mg/CaM refers to measured Mg/Ca,Mg/CaSWM to the modeled Mg/Ca of seawater,

and Mg/CaSWP to the Mg/Ca of present day

seawater. Researchers are actively attempting to

reconstruct the evolution of seawater Mg/Ca. Thus,

in the future, we may be able to reconstruct more

accurately the absolute temperatures of seawater

through the Cenozoic. It should be emphasized that

this weakness is essentially limited to the absolute

temperatures. Relative changes in temperatures are

robust and instructive. While there are many

caveats to the Mg/Ca paleotemperature proxy, itis important to recognize that this proxy is the best

available at present and significant advances in our

understanding of the global climate system have

been made using this approach (Lear et al., 2000;

Lea et al., 2000; Billups and Schrag, 2002; Shevenell

et al., 2004 and others).

1.1.2. pCO2 proxies

Several proxies, including boron isotopes ðd11BÞ

and the d13C of alkenones, have been developed so

that researchers may obtain an accurate estimate of atmospheric pCO2 through the Cenozoic. Although

these proxies must be interpreted with caution, the

new techniques have provided researchers with a

means by which to assess the influence of atmo-

spheric pCO2 changes on the evolution of the

Antarctic cryosphere and Earth’s climate system

(Pagani et al., 1999, 2005; Pearson and Palmer,

2000) The d11B proxy is based on the premise that

the pH of the surface ocean will change as atmo-

spheric pCO2 changes (Pearson and Palmer, 2000).

The d11B value of foraminiferal calcite is correlated

with surface ocean pH (Sanyal et al., 1995, 1996);

thus, the d11B of fossil foraminifers should indicate

changes in surface seawater pH through time. These

pH estimates can be used to calculate the aqueous

CO2 concentration and then estimate the atmo-

spheric pCO2 (see Pearson and Palmer, 2000, for

details of the method). The proxy may be compli-

cated by the fact that the pH and aqueous CO2concentrations of the surface ocean vary spatially as

a result of regional productivity, freshwater influx,

and upwelling (Sanyal et al., 1995; Pearson and

Palmer, 2000). Therefore, the best estimates of

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atmospheric pCO2 derived from foraminiferal d11B

come from sites in the low-latitude gyres (Pearson

and Palmer, 2000).

The d13C of sedimentary alkenones is another

proxy used to estimate past changes in atmospheric

pCO2 (Pagani et al., 1999, 2005). The proxy is basedon the observation that changes in atmospheric

pCO2 alter the relationship between d13CDIC and the

d13C of phytoplankton ðd13CorgÞ (see Pagani et al.,

1999, for a detailed discussion of the method). This

proxy is also not without complication, as there is

some indication that changes in cellular growth rate

and geometry may influence the intercellular CO2available for carbon fixation (see Pagani et al., 1999,

for a review). However, by analyzing the d13Corg of

one particular biomarker (in this case alkenones

from haptophyte algae), it is possible to limit

complications arising from different classes of organisms with different cell geometries (Pagani et

al., 1999, 2005). The alkenone d13C is then

converted to paleo [CO2ðaqÞ] and then to pCO2 via

Henry’s Law (see Pagani et al., 1999). Alkenones are

thought to be relatively stable within the sediments

and thus may be used to generate pCO2 records on

long geologic timescales.

1.2. Long-term Cenozoic climate trends

1.2.1. The benthic foraminifer d18O record

Geochemical records from marine sediments

reveal both the long- and short-term evolution of

high-latitude temperatures and global ice volume

during the Cenozoic and provide the framework for

our understanding of Antarctic cryospheric evolu-

tion. Traditionally, the oxygen isotopic ðd18OÞ

composition of benthic foraminifer calcite

ðCaCO3Þ has been used to reconstruct past changes

in ice volume and temperature (Shackleton and

Kennett, 1975; Miller et al., 1987; Zachos et al.,

2001a). The most recent global compilation of Cenozoic benthic foraminifer d18O records from

marine sediments (Zachos et al., 2001a) exhibits a

long-term 4% increase in d18O between 50 and 0 Ma

that reflects both high-latitude cooling and ice

growth (Fig. 1). Significantly, d18O values do not

increase steadily over the 50 Ma interval; abrupt

step-like increases ð1%Þ occur at the Eocene/

Oligocene boundary ð35MaÞ, in the middle

Miocene ð14MaÞ, and in the middle Pliocene

ð3 MaÞ (Fig. 1; Zachos et al., 2001a). These abrupt

d18

O increases are typically inferred to reflect rapidaccumulations of ice on Antarctica in the Eocene/

Oligocene (Zachos et al., 1993; Exon et al., 2001)

and middle Miocene (Shackleton and Kennett,

1975; Flower and Kennett, 1994; Shevenell and

Kennett, 2004) and the onset of Northern Hemi-

sphere glaciation in the Pliocene (Zachos et al.,

2001a).

Early lower-resolution d18O records revealed a

unidirectional d18O increase, suggesting the possi-

bility that one mechanism may account for Cen-

ozoic cooling and ice growth (e.g., opening and or

closing of tectonic gateways) and that positivefeedbacks reinforced the initial forcing (Shackleton

and Kennett, 1975; Miller et al., 1987). However,

the most recent global Cenozoic d18O compilation

does not exhibit a unidirectional increase since the

late Eocene (Fig. 1; Zachos et al., 2001a). Global

benthic foraminifer d18O values decrease abruptly

ð0:521%Þ at the end of the Oligocene (26–27 Ma)and remain relatively low until the middle Miocene

ð14MaÞ, suggesting an interval of reduced Ant-

arctic ice volume and/or warmer temperatures

following the rapid warming and/or expansion of Antarctic ice at 3 4 M a (Zachos et al., 2001a).

There is some debate as to the global relevance of

this warming, as composite records may be biased

toward particular regions or ocean basins (Lear

et al., 2004). Nonetheless, researchers have begun to

focus on identifying alternate and multiple mechan-

isms and/or feedbacks to explain the abrupt climate

events of the Cenozoic.

1.2.2. The benthic foraminifer Mg/Ca record

In 2000, Lear et al. published the first low-resolution Cenozoic Mg/Ca paleotemperature re-

cord generated using the benthic species Cibicidoides

floridanus and the Mg–temperature relationship of

Hastings et al. (1998) (Fig. 2A). This record reveals

a 12 C cooling of deep-ocean temperatures

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Fig. 2. (A) Composite benthic foraminifer d18O record complied by Miller et al. (1987) (center). A benthic foraminifer Mg/Ca temperature

record generated by Lear et al. (2000) indicating a 12 C cooling over the Cenozoic (left). Estimates of Cenozoic seawater d18O change, a

proxy for global ice volume, extracted from the d18O and Mg-temperature records using the d18O-based paleotemperature equation of

Shackleton (1974) (right) (modified from Lear et al., 2000). (B) A more detailed benthic foraminifer d18O and seawater d18O record

(calculated from Mg/Ca paleotemperatures) from Southern Ocean Site 747 (Kerguelen Plateau) spanning the late Oligocene to Present

with the Haq et al. (1987) sea-level curve plotted for reference (modified from Billups and Schrag, 2002).



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between 50 and 0 Ma that followed a similar pattern

to the global Cenozoic d18O curve (Fig. 2A; Lear

et al., 2000). However, abrupt cooling steps similar

to the abrupt d18O steps are not recognized in the

record, suggesting that the d18O steps predomi-

nantly reflect changes in global ice volume(Fig. 2A).

This low-resolution Mg/Ca paleotemperature

record was paired with the benthic d18O a n d a

record of seawater d18O (d18Osw, a proxy for ice

volume) was extracted using the d18O paleotem-

perature equation of Shackleton (1974). The results

revealed major increases in global ice volume

associated with each of the previously recognized

abrupt d18O increases at the Eocene/Oligocene

boundary and in the middle Miocene and confirmed

that the first significant glaciation of Antarctica

occurred at the Eocene/Oligocene boundary(Fig. 2A). The record also identified decreases in

Antarctic ice volume during the Oligocene and early

to middle Miocene. Billups and Schrag (2002)

produced a higher-resolution benthic Mg/Ca record

between 27 and 0 Ma that was consistent with Lear

et al.’s (2000) findings regarding the middle Miocene

d18O increase (Fig. 2B).

A difficulty with the paired d18O and Mg/Ca

approach is that the isotopic composition of past

Antarctic ice sheets remains unknown. Juxtaposing

calculated d18

Osw records with independent recordsof sea-level change of similar resolution may

buttress Mg/Ca-derived d18Osw records and illumi-

nate the past d18O composition of Antarctic ice

sheets (Billups and Schrag, 2002; Lear et al., 2004;

Fig. 2B). Efforts are underway to increase the

resolution of the global sea-level curve, particularly

in the middle Miocene (K. Miller, pers. comm.).

1.2.3. The Cenozoic pCO2 record

Recently, million-year to orbital scale records of

Cenozoic atmospheric pCO2

have been generated

using the d11B and alkenone d13C techniques. In

general, these records (Fig. 3) exhibit elevated

atmospheric pCO2 levels in the Paleocene and

Eocene (d11B: 1000–4000 ppmv; Pearson and Pal-

mer, 2000; alkenone d13C: 500–2000 ppmv) and

atmospheric pCO2 levels approaching present day

values after the Oligocene (150–300 ppmv for both

d11B and alkenone d13C, Pearson and Palmer, 2000;

Pagani et al., 1999, 2005). Atmospheric pCO2estimates from alkenone d13C reveal a trend toward

lower concentrations during the Eocene (as does the

d11B record) and an abrupt decline to levels

conducive to ice-sheet growth at the Eocene/

Oligocene boundary (Fig. 3A; Pagani et al., 2005).

This relationship suggests linkages between the

global carbon cycle and climate existed at least

through the Oligocene. Both the d11B and alkenone

d13

C records indicate a shift to modern pCO2 levelsoccurred in the Neogene, just following the Oligo-

cene/Miocene boundary (Fig. 3A). High-resolution

pCO2 proxy records from the early to middle

Miocene suggest orbitally forced (400 kyr) changes

in pCO2 that coincide with episodes of Antarctic

glaciation inferred from the Cenozoic d18O record

(Miller et al., 1991; Zachos et al., 2001a; Figs. 1 and

4). However, these records are presently of too low a

resolution to determine the phasing of pCO2changes and ice growth (Pagani et al., 1999; Pearson

and Palmer, 2000).

2. Major ice expansion events in the Cenozoic

evolution of the Antarctic cryosphere

The pairing of benthic foraminifer d18O and

foraminiferal trace-metal records has revolutionized

understanding of the long-term evolution of the

Antarctic cryosphere, particularly in the Paleogene

and early Neogene. Armed with this knowledge,

recent research efforts have focused on reconstruct-

ing high-resolution paleoclimate records across the

intervals of rapid cryosphere expansion to deter-mine both the structure of the transitions and the

lead–lag relationships between orbital forcing,

temperature, ice volume, and carbon cycling.

Further high-resolution work is required at globally

distributed sites

2.1. The Oi-1 glaciation (33.7 Ma)

After much debate, the paleoclimate community

has reached a consensus that the prominent abrupt

1% d18O increase at the Eocene/Oligocene (Oi-1,

Miller et al., 1991; 33.7 Ma) boundary reflects the

initiation of substantial and permanent ice sheets on

East Antarctica. Lear et al.’s (2000) pioneering work

with benthic foraminifer Mg/Ca across Oi-1 sug-

gests that the majority of the d18O signal relates to

Antarctic ice growth occurred with little or no

change in deep-ocean temperatures, and by exten-

sion, polar surface temperatures (Fig. 5A). In

addition to the geochemical evidence, direct evi-

dence of Antarctic ice growth comes from Southern

Ocean marine sediments, which reveal a shift in

the clay mineral assemblage toward assemblages

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associated with more physical weathering of the

Antarctic continent (Robert and Kennett, 1997) and

an increase in ice-rafted debris (Zachos et al., 1993)

coincident with the global d18O increase, as well as

an estimated 80 15m global sea-level drop

(Kominz and Pekar, 2001; Miller et al., 2005).

Thus, a preponderance of the geologic evidence

supports rapid Antarctic ice growth during Oi-1.

Recent research efforts have focused on develop-

ing globally distributed high-resolution geochemical

records and climate models necessary to identify the

elusive triggers and feedbacks involved in the Oi-1

climate reorganization. Presently, the highest-reso-

lution sedimentary record spanning Oi-1 comes

from the equatorial Pacific (ODP Leg 199, Site

1218; 3800 m paleodepth) (Lyle et al., 2002; Lear

et al., 2004; Coxall et al., 2005). Such records are

providing researchers with the ability to assess leads

and lags between temperature, ice volume, and

carbon cycle proxies at orbital time scales. The

benthic foraminifer d18O record from Site 1218

reveals that the Oi-1 glaciation occurred in two

distinct 40-kyr-long steps separated by 200 kyr at

a node of low eccentricity and obliquity (Coxall

et al., 2005). The 1:5% increase in d18O is coinci-

dent with a 1-km increase in the Pacific calcite

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Fig. 3. (A) Cenozoic pCO2 estimates derived from the carbon isotopic composition of sedimentary alkenones ðd13C37:2Þ (see Pagani et al.,

2005, for method details). The shaded region denotes the error estimates. Antarctic cryosphere expansions discussed in the text are

indicated by arrows (modified from Pagani et al., 2005). (B.I) Cenozoic pCO2 estimates derived from boron isotopes ðd11BÞ (see Pearson

and Palmer, 2000 for method details). (B.II) Close up of atmospheric pCO2 derived from d11B across the middle Miocene d 18O increase

(modified from Pearson and Palmer, 2000).



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compensation depth (CCD) inferred from the

CaCO3 mass accumulation rate (MAR) (Rea and

Lyle, 2005; Coxall et al., 2005).A paired benthic foraminifer d18O and Mg/Ca

record from Site 1218 (Lear et al., 2004) exhibits

similarities to initial Mg/Ca studies at DSDP Site

522 (Fig. 5B; Lear et al., 2000), which suggests no

permanent cooling of global deep waters across

Oi-1. At Site 1218, average deep-water temperatures

across Oi-1 are 3:7 1:5 C, with a 2 C coolingacross the first d18O step and a 2C warming

associated with the second phase of ice growth

(Lear et al., 2004). Seawater Mg/Ca changes would

affect the absolute value of the Mg/Ca by þ2 C

(Wilkinson and Algeo, 1989) but not any Mg/Ca

changes that occur in o1 M y (Lear et al., 2004;

Fig. 5B). Lear et al. (2004) cautiously suggest that

this pattern of temperature change may be asso-

ciated with the cause of glaciation as well as the

response of the global carbon cycle (e.g., a reduction

in silicate weathering on Antarctica) to glaciation,

respectively. Alternatively, Lear et al. (2004) suggest

that the warming observed in the benthic Mg/Ca

record at Site 1218 may reflect a carbonate

saturation effect on Mg partitioning in CaCO3

related to the deepening of the CCD in the Pacific

and a global sea-level fall. Further evidence to

suggest that the Mg/Ca temperature response across

Oi-1 may be damped by the carbonate saturationeffect comes from the Li/Ca record at Site 1218

(Lear and Rosenthal, 2006).

A record of seawater d18O (d18OswÞ was generated

using the equation of Bemis et al. (1998)) and

documents a 1:5% d18Osw increase across Oi-1 (Learet al., 2004). This d18Osw increase suggests an

apparent sea-level lowering of 90 m across Oi-1 that

is comparable with backstripping estimates from the

New Jersey Margin (Kominz and Pekar, 2001).

Following Oi-1, sea level rises between 33 and

31 Ma, suggesting a 50-m decline in Antarctic ice

volume. However, this decline might be too large if

Mg/Ca is influenced by a carbonate saturation effect

(Lear et al., 2004, 2006).

Several lines of evidence suggest changes in global

carbon cycling associated with Oi-1. It has long

been established that a dramatic increase in depth of

the CCD in the Pacific Ocean occurred at the

Eocene/Oligocene boundary (Van Andel, 1975;

Exon et al., 2000; Coxall et al., 2005). Site 1218 in

the Equatorial Pacific contains the most detailed

record of this increase, and the %CaCO3 at the site

increases abruptly at 34 Ma in two 40-kyr steps

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Fig. 4. Atmospheric pCO2 estimates from Southwest Pacific Site 588 based upon the d13C of alkenones (Pagani et al., 1999). CM events

represent carbon maxima events of Woodruff and Savin (1991) and Mi events are the inferred orbitally paced glacial maxima of Miller et

al. (1991) (modified from Pagani et al., 1999).



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separated by a 200-kyr plateau (Coxall et al.,

2005). This pattern of change is similar to that of the

benthic foraminifer d18O record. Although the Site

1218 benthic foraminifer d13C record reveals a

similar pattern of change exhibited in the d18O

and %CaCO3 records, a slight (o10 kyr) lag of

d18O in the 40-kyr band with respect to d13C

suggests that changes in the global carbon cycle

related to Earth’s obliquity (damped seasonality)

may have forced the Oi-1 event (Coxall et al., 2005).

Furthermore, the lag of the d18O and CCD records

with respect to the d13C record indicates that the

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Fig. 5. (A) Mg/Ca temperatures based upon three benthic foraminifer species (Lear et al., 2000) and d18O across the Oi-1 glaciation at

DSDP Site 522 (Zachos et al., 1993). There is no decrease in Mg-derived temperature across Oi-1 indicating that the majority of the d18O

increase must reflect an increase in global ice volume (modified from Lear et al., 2000). (B) Benthic foraminifer stable isotope and trace

metal data versus age across Oi-1 from DSDP Site 522 (triangles; Zachos et al., 1993; Lear et al., 2000) and Site 1218 (circles; Lear et al.,

2004) (modified from Lear et al., 2004).



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CCD increase was likely a result of Antarctic

cryosphere expansion and related to a shift in

global CaCO3 sedimentation from the continental

shelves to the deep ocean (Coxall et al., 2005).

2.2. The Mi-1 glaciation (23 Ma)

A transient (200 kyr) 1% benthic foraminifer

d18O increase is observed in globally distributed

deep-sea records at the Oligocene/Miocene bound-

ary (23.7 Ma; Mi-1; Fig. 6A). Although Mi-1 is one

in a series of orbital scale Antarctic glaciations that

occurred during the Oligocene and Miocene

(Zachos et al., 2001b; Pa ¨ like et al., 2006), the

amplitude of the isotopic signal associated with

Mi-1 suggests that this event represents a brief but

extensive expansion of the East Antarctic ice sheet

during a period of relative global warmth and

reduced global ice volumes (Zachos et al., 1997).

Support for this interpretation comes from a glacialmarine sediment sequence collected from the

Antarctic Margin, which suggests a period of ice

sheet expansion and contraction in the eastern Ross

Sea region associated with Mi-1 (Naish et al., 2001).

This observation indicates that the Antarctic ice

sheet reached the continental shelf in the region

during Mi-1 and is thought to have acted similarly

to the Northern Hemisphere ice sheets of the

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Fig. 6. (A) The d18O record of the Mi-1 event (bounded by the gray box) and orbital eccentricity and obliquity curves from 22 to 24 Ma.

Mi-1 corresponds with an interval of low eccentricity related to the 400-kyr cycle and an extended low-obliquity node (modified from

Zachos et al., 2001b). (B) Benthic foraminifer Cibicidoides spp. stable isotope and trace metal data versus age from Site 1218. Mg-derived

temperatures were obtained using the Lear et al. (2002) equation. Vertical shaded bars reflect intervals of bottom water cooling (modified

from Lear et al., 2004).



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Plio-Pleistocene (Naish et al., 2001). Thus, substan-

tial research effort has gone into trying to under-

stand the origin of this glacial expansion.

Detailed benthic foraminifer stable isotope re-

cords across Mi-1 from at Ceara Rise ODP Site 929

and at Equatorial Pacific Site 1218 exhibit a positive1:2% d18O excursion (23.3–23.0 Ma) coeval with a0:8% d13C increase centered at 23 Ma (Zachos et al.,2001b; Fig. 6A). Oxygen isotope records from both

sites exhibit strong obliquity (41 kyr) pacing be-

tween 23.3 and 23 Ma, suggesting a high latitude

climate control on the d18O signal prior to the Mi-1

event (Zachos et al., 2001b). A 3-kyr lag in the d18O

record from Ceara Rise with respect to obliquity

indicates that Antarctic ice growth and/or cooling

was paced by changes in Earth’s orbital parameters

during a period of reduced seasonality and cool

summers (Zachos et al., 2001b). d18O records acrossMi-1 also exhibit sensitivity to Earth’s eccentricity

pacing; power is observed in the 400-kyr band

between 24 and 23 Ma and then shifts to the 100-kyr

band at 23.0 Ma (Zachos et al., 2001b). A similar

shift in orbital sensitivity from the obliquity (41 kyr)

to the eccentricity (100 kyr) band is observed in the

Antarctic margin glacial marine sedimentary se-

quence (Naish et al., 2001).

The 400-kyr eccentricity period is rare in the

geologic record. However, power at this period is

enhanced between 24 and 23 Ma and most pro-nounced in the d13C record, which exhibits a mean

increase and enhanced 400-kyr variability 1 My

before the d18O increase of Mi-1 (Zachos et al.,

2001b). This pattern of change has been observed

elsewhere in the geologic record and has been

attributed to enhanced burial of organic carbon on

the margins and a drawdown of atmospheric pCO2(Vincent and Berger, 1985). However, there is little

evidence in the geologic record for organic-rich

sediments deposited at this time. Some researchers

have proposed that lower pCO2

levels may increase

the climate system’s sensitivity to eccentricity

forcing (Zachos et al., 2001b). This interpretation

is further supported by an increase in the sensitivity

of d18O to the 100-kyr eccentricity forcing at a time

when d13C values reach a maximum (Zachos et al.,

2001b). Interestingly, the d18O signal leads d13C in

this interval, suggesting that climate and ice volume

changes are feeding back into the carbon cycle.

Benthic foraminifer stable isotope records have

yielded important information regarding the phas-

ing of carbon cycling and ice-volume/temperature

changes on orbital timescales. However, little was

known about how deep-sea temperatures changed

across Mi-1 (Billups and Schrag, 2002). Lear et al.

(2004) generated a benthic Mg/Ca record across

Mi-1 at Site 1218 that exhibits a 2 C cooling

between 23.8 and 23.7 Ma, a 2 C warming between

23.7 and 23.3 Ma, and additional cooling from 23.3to 23.1Ma (Fig. 6B). This temperature record

suggests that cooling of deep-ocean waters may

have played a role in triggering Mi-1. Interestingly,

deep waters (and by inference polar surface waters)

appear to have warmed shortly after the advances of

the Antarctic ice sheet. Lear et al. (2004) propose a

negative feedback toward ice growth at this time

caused by the blanketing of Antarctica by ice and a

subsequent reduction in global chemical weathering.

This hypothesized increase in atmospheric pCO2may have led to the partial melting of the newly

formed Antarctic ice sheet, and deep-sea warming(Lear et al., 2004); an observation supported by the

alkenone d13C record of Pagani et al. (1999) (Fig. 4).

Finally, the Mi-1 event is unusual in that it

coincides with an interval of low eccentricity

associated with the 400-kyr cycle and an extended

period of low obliquity associated with the 1.25 My

cycle (Fig. 6A; Zachos et al., 2001b). It has been

proposed that the accumulation of ice on Antarctica

is limited by high seasonality (warm summers).

A protracted period of low amplitude obliquity

variations coupled with low eccentricity suggeststhat Mi-1 occurred at a time of low seasonality

when Antarctic summer temperatures were rela-

tively cool (Zachos et al., 2001b). The Mi-1

glaciation reversed itself as eccentricity increased.

Similar nodes exist in the climate record though not

all are associated with transient glaciations of the

magnitude of the Mi-1 event (Zachos et al., 2001b).

It appears that changes in global carbon cycling that

began 1 My prior to Mi-1 may have primed to

system to react sensitively to this astronomical event

(Zachos et al., 2001b).

2.3. The middle Miocene climate transition

(16– 13 Ma)

A significant reorganization of Earth’s climate

system occurred in the middle Miocene, as evi-

denced by the abrupt 1% increase in global

benthic foraminifer d18O at 14Ma (Fig. 1;

Shackleton and Kennett, 1975; Miller et al., 1987;

Flower and Kennett, 1994; Zachos et al., 2001).

This step-like d18O increase is one of three major

events that punctuate the long-term Cenozoic d18O

ARTICLE IN PRESS



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record and reflects some combination of Antarctic

ice growth and global cooling (Shackleton and

Kennett, 1975; Matthews and Poore, 1980; Miller

et al., 1987; Prentice and Matthews, 1991; Flower

and Kennett, 1994). Evidences for both ice growth

and global cooling are found throughout thegeologic record of the middle Miocene: Southern

Ocean ice-rafted debris is more abundant after

14 M a (Margolis, 1975; Kennett and Barker,

1990), large fluctuations in global sea level are

inferred (Haq et al., 1987; John et al., 2004),

paleobotanical and faunal change occurred (Flower

and Kennett, 1994 and references therein), and the

East Antarctic Ice Sheet expanded across the

Antarctic continental margin (Ross Sea sector;

Anderson, 1999; Cape Roberts Science Team,

2000).

The magnitudes of middle Miocene Antarctic icegrowth and temperature change (17–13 Ma) have

been estimated using indirect methods, including

meridional stable isotope gradients (Shackleton and

Opdyke, 1973; Miller et al., 1991; Wright et al.,

1992) and sequence stratigraphy (Haq et al., 1987;

Miller et al., 1987; John et al., 2004). Results from

these studies suggest that 70% of the global 1%

benthic d18O increase at 14 Ma relates to Antarctic

ice volume. Thus, global deep waters are inferred to

have cooled 1.8–2:5 C between 14.2 and 13.8 Ma

(Miller et al., 1991; Wright et al., 1992; Flower andKennett, 1994; John et al., 2004). While indirect

methods provide useful approximations of the

relative contributions of ice volume and tempera-

ture to the middle Miocene d18O signal, none

involves a truly independent measure of either

deep-water temperature or ice volume.

Benthic foraminifer (Cibicidoides mundulus)

Mg/Ca data from the Southern Ocean reveal a 2

1:5 C cooling of regional bottom waters during themiddle Miocene climate transition (14.2–13:8 Ma),which indicates that the globally recognized d18O

increase (14 Ma) describes a major expansion of

the Antarctic cryosphere and that 80% of the

d18O signal relates to ice volume (Shevenell et al., in

review; Fig. 6). Interestingly, this cooling is not

significant or permanent, and temperatures warm

following the d18O increase, much like the Mg/Ca

records across Oi-1 and Mi-1 (Lear et al., 2004;

Figs. 4 – 6). A record of seawater d18O, calculated

using paired C. mundulus Mg/Ca and d18O records

and the paleotemperature relationship of Lynch-

Stieglitz et al. (1999), suggests that Antarctic ice

sheets entered an interval of eccentricity-modulated

glacial advance and retreat at 15Ma, 1 My

before the 1% middle Miocene d18O increase at

a time when Mg/Ca-derived surface and deep-water

temperatures were relatively warm (Fig. 7; Shevenell

et al., 2004, in review). Glacial episodes increased in

intensity between 15 and 13.8 Ma, revealing acentral role for internal climate feedbacks (e.g., ice

albedo feedbacks) in this major Cenozoic climate

transition (Shevenell et al., in review).

The positive d13C excursion of the middle

Miocene suggests a major reorganization of the

global carbon cycle and has been studied extensively

as it is the largest and longest d13C increase of the

Cenozoic (Fig. 1; 16:5–13.5 Ma). Several hypoth-eses have been put forth to account for this d13C

increase including the silicate weathering hypothesis

of Raymo (1994) and the Monterey hypothesis of

Vincent and Berger (1985). Substantial organic-richdeposits surrounding the Pacific Rim have been

dated to this time and suggest that large amounts of

organic carbon were sequestered in continental

margin basins as a result of invigorated ocean

circulation, upwelling of nutrients, and an expan-

sion of oxygen minimum zones (Vincent and Berger,

1985). One problem with hypotheses that relates

changes in carbon cycling with Antarctic ice growth

during the middle Miocene is the 2:5-My offsetbetween the changes in global carbon cycling (the

initial increase in d13

C at 16.5 Ma) and the d18

O stepat 14 Ma. However, the Mg/Ca-derived d18Oswrecord of Shevenell et al. (in review) seems to

indicate that ice growth began 1Ma before the

major d18 O step, suggesting only a 1.5 My lead of

the carbon cycle. This lead, coupled with the strong

400-kyr cycle observed in both the d13C and d18O

records prior to the middle Miocene d18O increase,

is similar to that observed before Mi-1 (Zachos

et al., 2001b). This similarity and the initiation of ice

growth at 15 Ma during the Miocene Climatic

Optimum provides new support for a substantial

role of the global carbon cycle in the middle

Miocene climate transition (Shevenell et al., in

review). Furthermore, comparison of ice volume,

paleotemperature, and paleo- pCO2 records indicate

that middle Miocene expansion of the Antarctic

cryosphere coincided with an interval of relatively

warm Southern Ocean surface and deep-ocean

waters and inferred low atmospheric pCO2 (Fig. 7;

Shevenell et al., in review). This relationship

suggests that changes in heat and moisture trans-

port were important in the development of the

Antarctic cryosphere and that atmospheric pCO2

ARTICLE IN PRESS



13/17

concentrations may dictate the sensitivity of the

Antarctic system to low-latitude-derived heat and

moisture.

3. The role of the global carbon cycle in Cenozoic

Antarctic cryosphere evolution

The Cenozoic evolution of the Antarctic Cryo-

sphere and Southern Ocean system has been linked

to the progressive tectonic, oceanographic, and

thermal isolation of Antarctica. Substantial geologic

evidence exists for the opening of the Tasman

Gateway between Australia and Antarctica at the

Eocene/Oligocene boundary (Kennett, 1977; Exon

et al., 2000), but the precise timing of the opening of

the Drake Passage and the initiation of the

Antarctic Circumpolar Current remains unresolved.

Other gateways, such as the Indonesian gateway,

may have played a major role in the middle Miocene

expansion of the East Antarctic Ice Sheet; however,

a definitive chronology of that closure continues to

be elusive.

Recent high-resolution records across the major

Antarctic ice advances of the Paleogene and early

Neogene (including Oi-1, Mi-1, and the middle

Miocene d18O step) suggest that climate feedbacks

beyond the opening of tectonic gateways and

thermal isolation of Antarctica must be considered

to explain the timing and evolution of the Antarctic

cryosphere. For example, benthic foraminifer

Mg/Ca records indicate little or no permanent

deep-ocean cooling after the major ice expansion

at Oi-1 and after the middle Miocene d18O step.

This observation suggests that meridional heat

transport related to the opening and closing of

tectonic gateways cannot have been the sole arbiter

of Antarctic cryosphere expansion through the

Cenozoic (Huber et al., 2004). Additional mechan-

isms must have been involved.

A model simulating ice growth during Oi-1

(DeConto and Pollard, 2003) gradually reduced

ARTICLE IN PRESS

Fig. 7. Southern Ocean paleoclimate records from South Tasman Rise (STR) ODP Site 1171 (48300S, 14906:690E; 2150 m) based on thebenthic foraminifer C. mundulus and planktonic foraminifer G. bulloides. Gaps in the record are due to coring gaps. The age scale is based

on magnetostratigraphic and stable isotopic datums (Exon et al., 2000; Shevenell et al., 2004). Bottom panel: seawater d18O (d18Ow;

SMOW; Standard Mean Ocean Water scale) calculated from C. mundulus d18O and BWT estimates using the paleotemperature equation

of Lynch-Stieglitz et al. (1999). More positive d18Ow intervals (marked by arrows) are interpreted as Antarctic glaciations. Middle panel:

Mg/Ca-derived bottom water temperature (BWT). The temperature scale is exponential and based on conversion of Mg/Ca using the

relationship of Lear et al. (2003): SST ¼ ln(Mg/Ca/0.9)/0.1. Top panel: Mg/Ca-based SST (Shevenell et al., 2004) record derived fromplanktonic foraminifer G. bulloides (modified from Shevenell et al., in review).



14/17

atmospheric pCO2 concentrations to observe the

response of the system. The results suggested that a

gradual lowering of snowline elevations with lower

atmospheric pCO2 concentrations initiated the

formation and gradual coalescence of small but

dynamic ice sheets under favorable orbital condi-tions (cool summers) (DeConto and Pollard, 2003).

These ice sheets continued to increase in size due to

ice albedo feedbacks. This scenario is further

supported by additional iterations of the model in

which pCO2 is lowered at different times prior to

Oi-1 (Pa ¨ like et al., 2006). Results suggest that the

timing of pCO2 change does not influence the timing

of ice growth; rather, ice growth is triggered by

astronomical forcing if atmospheric pCO2 levels are

near a threshold. To determine the influence of

tectonic gateways on the initiation of Antarctic ice

growth at Oi-1, DeConto and Pollard (2003)simulated the opening of the Drake Passage. They

found that this produced only an 20% change in

oceanic heat transport if the gateway was opened

within a narrow range of atmospheric pCO2. They

concluded that atmospheric pCO2 is likely a more

important boundary condition for Cenozoic climate

change than tectonic configuration of the Southern

Ocean (DeConto and Pollard, 2003). Because the

threshold remains unknown, we argue that the

opening of Southern Ocean gateways during a time

of low atmospheric pCO2 and favorable orbitalconditions may have been the trigger for the

initiation of the rapid expansion of the East

Antarctic Ice Sheet at Oi-1.

It is likely that atmospheric pCO2 is a funda-

mental boundary condition for other glacial ad-

vances such as Mi-1 and the middle Miocene d18O

increase at 14 Ma. Atmospheric pCO2 also may

play an important role as a negative feedback

toward continued ice expansion after a glaciation.

Both the Mi-1 and the middle Miocene glacial

events occurred 1–1.5 Ma after a major change in

the state of the global carbon cycle, as inferred from

foraminiferal d13C records. Models suggest that

during intervals of low pCO2, Antarctic glaciations

may be triggered by favorable astronomical condi-

tions; such a relationship has been observed for

Mi-1 but not during the middle Miocene. After Mi-

1, deep-ocean temperatures warm and atmospheric

pCO2 increases (Lear et al., 2004; Pagani et al.,

1999). Lear et al. (2004) propose a negative

feedback toward runaway ice growth driven by

global carbon cycling: that the expanding ice sheet

removed a substantial source of silicate rock

available for weathering from the global carbon

cycle. The removal of this sink for pCO2 enabled

atmospheric pCO2 to increase enough to halt

Antarctic ice growth.

A similar pattern of change is seen after the

middle Miocene d

18

O increase at the end of theMonterey d13C excursion (Shevenell et al., in

review). Alternatively, meridional heat and moisture

transport may play a significant role in the advance

and retreat of Antarctic ice sheets under low pCO2conditions of the Neogene. The advance of the East

Antarctic Ice Sheet in the middle Miocene (15 Ma)

appears to have taken place during an interval of

relatively warm climate conditions when atmo-

spheric pCO2 was paradoxically low (Figs. 4 and

7; Pagani et al., 1999; Shevenell et al., 2004). At this

time, moisture transport regimes were altered such

that moisture was being supplied to the AntarcticDry Valleys (Sugden and Denton, 2004). Shevenell

et al. (2004, in review) use the relationships between

warm planktonic and benthic foraminifer Mg/Ca-

derived ocean temperatures (Fig. 7) to suggest that

middle Miocene ice growth occurred at a time of

reduced latitudinal thermal gradients and increased

moisture supply to Antarctica.

An orbitally paced cooling of Southern Ocean

surface temperatures south of Tasmania suggests an

expansion of the Antarctic Circumpolar Current

related to ice albedo feedbacks isolated Antarcticafrom receiving additional low-latitude-derived

moisture and heat. This isolation coupled with the

silicate weathering feedback discussed below acted

in concert to halt continued expansion of the East

Antarctic Ice Sheet and the Monterey d13C excur-

sion. Further modeling studies are required to

determine if the low atmospheric pCO2 of the

Monterey interval was the primary boundary

condition that allowed for the growth of the East

Antarctic Ice Sheet during the middle Miocene. It is

likely that the expansion of the East Antarctic Ice

Sheet in the middle Miocene led to a reorganization

of the global carbon cycle and that this reorganiza-

tion resulted in the stabilization of the East

Antarctic Ice Sheet (Shevenell et al., in review).

4. Continuing challenges

In the past decade, technological advances have

improved our ability to recover and generate high-

resolution paleoclimate/paleoceanographic records.

Consequently a more detailed understanding of

Cenozoic climate change and Antarctic ice sheet

ARTICLE IN PRESS



15/17

evolution is emerging. For example, there is consensus

within the paleoclimate community regarding the

timing of major ice expansions during the early

Oligocene (Oi-1) and the middle Miocene as well as

the existence of a transient glaciation at the Oligocene/

Miocene boundary (Mi-1). Furthermore, a handful of detailed studies have provided important insights into

the orbital scale structure of ice growth events as well

as preliminary insights into lead–lag relationships

between ice growth, temperature change, and global

carbon cycling. These results highlight the importance

of generating additional globally distributed high-

resolution multi-proxy records across major Cenozoic

climate reorganizations, including those during which

Antarctic ice sheets were thought to have retreated

(e.g., the early Miocene).

Despite recent advances, understanding of the

Cenozoic evolution of the Antarctic/Southern oceansystem and its influence on global climate remains

rudimentary at best. To gain an improved under-

standing of this evolution, high-resolution multi-

proxy geochemical studies must be generated at a

network of high-resolution deep-sea sites (with an

emphasis on the high latitudes and the tropics) in

which the lead–lag relationships between orbital

forcing, ice volume, carbon cycling, and tempera-

ture may be assessed across known intervals of

Antarctic ice sheet expansion (e.g., orbital scale

glaciations in the Oligocene and Miocene). Inaddition to deep-sea sedimentary sequences, we

must focus on obtaining dateable high-resolution

sedimentary sequences from the Antarctic continen-

tal margin that may be integrated with deep-sea

records to provide a complete and more direct

perspective on Cenozoic Antarctic cryosphere ex-

pansion. As high-resolution proxy records are only

as useful as the current proxies are reliable, future

research is required to ensure the utility of the Mg/

Ca and pCO2 proxies on Paleogene and Neogene

timescales. Finally, geochemists and modelers must

work closely with one another to develop detailed

simulations of both Antarctic ice sheet advances

and periods of ice retreat through the Cenozoic.

Such studies will assist in improving understanding

of our present climate system.

Acknowledgments

We thank G. Filippelli, D. Warnke, J.A. Flores,

and T. Marchitto for organizing the JOI USSSP

sponsored ‘‘Paleoceanography and Paleoclimatol-

ogy of the Southern Ocean: A Synthesis of Three

Decades of Scientific Ocean Drilling’’ workshop in

Boulder, CO in 2005. This research used samples

provided by the Ocean Drilling Program (ODP).

ODP is sponsored by the US National Science

Foundation and participating countries under the

management of JOI. This research was supportedby NSF Grant OPP0229898 to J.P. Kennett and

JOI/USSSP postcruise funds to A.E. Shevenell, and

a University of Washington Program on Climate

Change Postdoctoral fellowship to A.E. Shevenell.

We thank Carrie Lear, Jim Zachos, and Katarina

Billups for discussions and reviewers for suggestions

and improvements.

References

Anderson, J.B., 1999. Antarctic Marine Geology. CambridgeUniversity Press, Cambridge, 289 pp.

Bemis, B.E., Spero, H.J., Bijma, J., Lea, D.W., 1998. Reevalua-

tion of the oxygen isotopic composition of planktonic

foraminifera: experimental results and revised paleotempera-

ture equations. Paleoceanography 13 (2), 150–160.

Berner, R.A., Lasaga, A.C., Garrels, R.M., 1983. The carbona-

te–silicate geochemical cycle and its effect on atmospheric

carbon dioxide over the past 100 million years. American

Journal of Science 283, 641–683.

Billups, K., Schrag, D.P., 2002. Paleotemperatures and ice

volume of the past 27 Myr revisited with paired Mg/Ca and18O/16O measurements on benthic foraminifera. Paleoceano-

graphy, 17 doi:10.1029/2000PA000567.

Cape Roberts Science Team, 2000, Summary of results. In:

Barrett, P.J., Sarti, M., Wise, S. (Eds.), Studies from Cape

Roberts Project: Initial Report on CRP-3, Ross Sea,

Antarctica. Terra Antarctica, 8, 185–203.

Coxall, H.K., Wilson, P.A., Pa ¨ like, H., Lear, C.H., Backman, J.,

2005. Rapid stepwise onset of Antarctic glaciation and deeper

calcite compensation in the Pacific Ocean. Nature 433, 53–57.

DeConto, R.M., Pollard, D., 2003. Rapid Cenozoic glaciation of

Antarctica induced by declining atmospheric CO2. Nature

421, 245–249.

Exon, N.F., Kennett, J.P., Malone, M.L., the Leg 189 Shipboard

Scientific Party, 2001. Proc. ODP, Initial Reports 189 (CD-

ROM): Ocean Drilling Program, College Station, TX 77845-

9547, USA.Flower, B.P., Kennett, J.P., 1994. The middle Miocene climate

transition: east Antarctic ice sheet development deep ocean

circulation and global carbon cycling. Palaeogeography

Palaeoclimatology Palaeoecology 108, 537–555.

Haq, B.U., Hardenbol, J., Vail, P., 1987. Chronology of fluctuating

sea levels since the Triassic. Science 235, 1156–1167.

Hastings, D.H., Russell, A.D., Emerson, S.R., 1998. Foraminif-

eral magnesium in Globigerinoides sacculifer as a paleotem-

perature proxy. Paleoceanography 13, 161–169.

Huber, M., Brinkhuis, H., Stickley, C.E., Doos, K., Sluijs, A.,

Warnaar, J., Williams, G.L., Schellenberg, S.A., 2004. Eocene

circulation of the Southern Ocean: was Antarctica kept warm

by subtropical waters? Paleoceanography, PA4026 doi:10.

1029/2004PA001014.

ARTICLE IN PRESS


http://dx.doi.org/10.1029/2000PA000567http://dx.doi.org/10.1029/2004PA001014http://dx.doi.org/10.1029/2004PA001014http://dx.doi.org/10.1029/2004PA001014http://dx.doi.org/10.1029/2004PA001014http://dx.doi.org/10.1029/2000PA000567


16/17

John, C.M., Karner, G.D., Muiti, M., 2004. d18O and Marion

Plateau backstripping: combining two approaches to con-

strain late middle Miocene eustatic amplitude. Geology 32,

829–832.

Kennett, J.P., 1975. Cenozoic evolution of Antarctic glaciation,

the Circum-Antarctic Ocean and their impact on global

paleoceanography. Journal of Geophysical Research 82,3843–3860.

Kennett, J.P., 1977. Cenozoic evolution of Antarctic glaciation,

the circum-Antarctic Ocean, and their impact on global

paleoceanography. Journal of Geophysical Research 82,

3843–3860.

Kennett, J.P., Barker, P.F., 1990. Latest Cretaceous to Cenozoic

climate and oceanographic developments in the Weddell Sea,

Antarctica: an ocean-drilling perspective. In: Kennett, J.P.,

Warnke, D.A. (Eds.), The Antarctic Paleoenvironment: a

Perspective on Global Change, Part 1. Antartica Research

Series, vol. 56. AGU, Washington, DC, pp. 7–30.

Kominz, M.A., Pekar, S.F., 2001. Oligocene eustasy from two-

dimensional sequence stratigraphic backstripping. Geological

Society of America Bulletin 113, 291–304.Lawver, L.A., Gahagan, L.M., Coffin, M.F., 1992. The devel-

opment of paleoseaways around Antarctica. In: Kennett, J.P.,

Warnke, D.A. (Eds.), The Antarctic Paleoenvironment: a

perspective on Global Change, Part 1. Antartica Research

Series, vol. 56. AGU, Washington, DC, pp. 7–30.

Lea, D.W., Pak, D.K., Spero, H.J., 2000. Climate impact of Late

Quaternary equatorial Pacific sea surface temperature varia-

tions. Science 289, 1719–1724.

Lear, C.H., Elderfield, H., Wilson, P.A., 2000. Cenozoic deep-sea

temperatures and global ice volumes from Mg/Ca in benthic

foraminiferal calcite. Science 287, 269–272.

Lear, C.H., Rosenthal, Y., Slowey, N., 2002. Benthic forami-

niferal Mg/Ca-paleothermometry: a revised core-top calibra-

tion. Geochimica, et Cosmochimica Acta 66, 3375–3387.

Lear, C.H., Rosenthal, Y., Wright, J.D., 2003. The closing of a

seaway: ocean water masses and global climate change. Earth

and Planetary Science Letters 210, 425–436.

Lear, C.H., Rosenthal, Y., Coxall, H.K., Wilson, P.A., 2004.

Late Eocene to early Miocene ice sheet dynamics and the

global carbon cycle. Paleoceanography 19.

Lear, C.H., Rosenthal, Y., 2006. Benthic foraminiferal Li/Ca:

insights into Cenozoic seawater carbonate saturation state.

Geology 34, 985–988.

Lyle, M., Wilson, P., Janecek, T.R., Backman, J., Busch, W.H.,

Coxall, H.K., Faul, K., Gaillot, P., Hovan, S.A., Knoop, P.,

Kruse, S., Lanci, L., Lear, C., Moore Jr., T.C., Nigrini,

C.A., Nishi, H., Nomura, R., Norris, R.D., Pa ¨ like, H., Pare ´ s,J.M., Quinton, L., Raffi, I., Rea, B.R., Rea, D.K., Steiger,

T.H., Tripati, A., Vanden Berg, M.D., Wade, B., 2002.

Proceedings of the Ocean Drilling Program, Initial Reports,

199.

Lynch-Stieglitz, J., Curry, W.B., Slowey, N., 1999. A geostrophic

transport estimate for the Florida Current from the oxygen

isotope composition of benthic foraminifera. Paleoceanogra-

phy 14, 360–373.

Marchitto, T.M., Bryan, S.P., Curry, W.B., McCorkle, D.C.,

2007. Mg/Ca temperature calibration for the benthic for-

aminifer Cibicidoides pachyderma, Paleoceanography 22 (1),

doi:PA1203, 10.1029/2006PA001287.

Margolis, S.V., 1975. Paleoglacial history of Antarctica inferred

from analysis of Leg 29 sediments by scanning electron

microscopy. In: Kennett, J.P., Houtz, R.E., et al. (Eds.),

Initial Reports DSDP 29, 1039–1048.

Martin, P.A., Lea, D.W., Rosenthal, Y., Shackleton, N.J.,

Papenfuss, T.P., Sarnthein, M., 2002. Quaternary deep sea

temperature histories derived from benthic foraminiferal Mg/

Ca. Earth and Planetary Science Letters 198 (1–2), 193–209.

Matthews, R.K., Poore, R.Z., 1980. Tertiary d

18

O record andglacio-eustatic sea-level fluctuation. Geology 8, 501–504.

Miller, K.G., Fairbanks, R.G., Mountain, G.S., 1987. Tertiary

oxygen isotope synthesis, sea-level history, and continental

margin erosion. Paleoceanography 2, 1–19.

Miller, K.G., Wright, J.D., Fairbanks, R.G., 1991. Unlocking the

icehouse: Oligocene–Miocene oxygen isotope, eustasy, and

margin erosion. Journal of Geophysical Research 96,

6829–6848.

Miller, K.G., Kominz, M.A., Browning, J.V., Wright, J.D.,

Mountain, G.S., Katz, M.E., Sugarman, P.J., Cramer, B.S.,

Christie-Click, N., Pekar, S.F., 2005. The Phanerozoic record

of global sea-level change. Science 310, 1293–1298.

Naish, T.R., Woolfe, K.J., Barrett, P.J., et al., 2001. Orbitally

induced oscillations in the East Antarctic ice sheet at theOligocene/Miocene boundary. Nature 413, 719–723.

Pa ¨ like, H., Norris, R.D., Herrle, J.O., Wilson, P.A., Coxall,

H.K., Lear, C.H., Shackleton, N.J., Tripati, A.K., Wade,

B.S., 2006. The heartbeat of the Oligocene climate system.

Science 314(5807), 1894–1898.

Pagani, M., Arthur, M.A., Freeman, K.H., 1999. Miocene

evolution of atmospheric carbon dioxide. Paleoceanography

14, 273–292.

Pagani, M., Zachos, J.C., Freeman, K.H., Tipple, B., Bohaty, S.,

2005. Marked decline in atmospheric carbon dioxide con-

centrations during the Paleogene. Science 309, 600–603.

Pearson, P.N., Palmer, M.R., 2000. Atmospheric carbon dioxide

concentrations over the past 60 million years. Nature 406,

695–699.

Prentice, M.P., Matthews, R.K., 1991. Tertiary ice sheet

dynamics: the snow gun hypotheses. Journal of Geophysical

Research 96, 6811–6827.

Raymo, M.E., 1994. The Himalayas, organic carbon burial, and

climate in the Miocene. Paleoceanography 9, 399–404.

Rea, D.K., Lyle, M.W., 2005. Paleogene calcite compensation

depth in the eastern subtropical Pacific: answers and

questions. Paleoceanography 20.

Robert, C., Kennett, J.P., 1997. Antarctic continental weathering

changes during Eocene–Oligocene cryosphere expansion: clay

mineral and oxygen isotope evidence. Geology 25, 587–590.

Rosenthal, Y., Boyle, E.A., Slowey, N., 1997. Temperature

control on the incorporation of Mg, Sr, F and Cd into benthicforaminiferal shells from Little Bahama Bank: prospects for

thermocline paleoceanography. Geochimica et Cosmochimica

Acta 61, 3633–3643.

Sanyal, A., Hemming, N.G., Hanson, G.N., Broecker, W.S.,

1995. The pH of the glacial ocean as reconstructed from

boron isotope measurements on foraminifera. Nature 373,

234–236.

Sanyal, A., Hemming, N.G., Broecker, W.S., Lea, D.W., Spero,

H.J., Hanson, G.N., 1996. Oceanic pH control on the boron

isotopic composition of foraminifera: evidence from culture

experiments. Paleoceanography 11, 513–517.

Schnitker, D., 1980. North Atlantic oceanography as possible

cause of Antarctic glaciation and eutrophication. Nature 284,

615–616.

ARTICLE IN PRESS


http://dx.doi.org/10.1029/2006PA001287http://dx.doi.org/10.1029/2006PA001287


17/17

Shackleton, N.J., 1974. Attainment of isotopic equilibrium

between ocean water and benthonic foraminifera genus

Uvigerina: isotopic changes in the ocean during the last

glacial Colloq. Int. CNRS No. 219, Les Mthodes Quanti-

tative d’Etudes des Variations du Climat au cours du

Plkistoc6ne, pp. 203–209.

Shackleton, N.J., Kennett, J.P., 1975. Paleotemperature historyof the Cenozoic and the initiation of Antarctic glaciation:

oxygen and carbon isotopic analyses in DSDP Sites 277, 279,

and 281. In: Kennett, J.P., Houtz, R.E., et al. (Eds.), Initial

Reports DSDP, vol. 29. U.S. Government Printing Office,

Washington, DC, pp. 143–156.

Shackleton, N.J., Opdyke, N.D., 1973. Oxygen isotope and

palaeomagnetic stratigraphy of equatorial Pacific core V28-

238: oxygen isotope temperatures and ice volumes on a 105

and 106 year scale. Quaternary Research 3, 39–55.

Shevenell, A.E., Kennett, J.P., Lea, D.W., 2004. Middle Miocene

Southern Ocean cooling and Antarctic cryosphere expansion.

Science 305, 1766–1770.

Shevenell, A.E., Kennett, J.P., Lea, D.W. in review. Middle

Miocene ice sheet dynamics, deep-sea temperatures, andcarbon cycling: a Southern Ocean perspective (G3, 2007).

Stanley, S.M., Hardie, L.M., 1998. Secular oscillations in the

carbonate mineralogy of reef-building and sediment produ-

cing organisms driven by tectonically forced shifts in seawater

chemistry. Palaeogeography Palaeoclimatology Palaeoecol-

ogy 144, 3–19.

Sugden, D.E., Denton, G.H., 2004. Cenezoic landscape evolution

of the Convoy Range to Mckay Glacier area, Transantarctic

Mountains: onshore to offshore synthesis. Geological Society

of America Bulletin 116, 840–857.

Van Andel, T.H., 1975. Mesozoic/Cenozoic calcite compensation

depths and he global distribution of calcareous sediments.

Earth and Planetary Science Letters 26, 187–194.

Vincent, E., Berger, W.H., 1985. Carbon dioxide and polar

cooling in the Miocene. In: Sundquist, E.T., Broecker, W.S.

(Eds.), The carbon cycle and atmospheric CO2: natural

variations Archean to Present, Geophysical Monographyvol. 32. AGU, Washington, DC, pp. 455–468.

Wilkinson, B.H., Algeo, T.J., 1989. Sedimentary carbonate

record of calcium–magnesium cycling. American Journal of

Science 289, 1158–1194.

Woodruff, F., Savin, S.M., 1989. Miocene deepwater oceano-

graphy. Paleoceanography 4, 87–140.

Woodruff, F., Savin, S.M., 1991. Mid-Miocene isotope stratigraphy

in the deep sea: high-resolution correlations, paleoclimatic cycles,

and sediment preservation. Paleoceanography 6, 755–806.

Wright, J.D., Miller, K.G., Fairbanks, R.G., 1992. Evolution of

modern deepwater circulation: evidence from the late

Miocene Southern Ocean. Paleoceanography 6, 275–290.

Zachos, J.C., Lohmann, K.C., Walker, J.C.G., Wise, S.W., 1993.

Abrupt climate change and transient climates in the Paleogene: amarine perspective. Journal of Geology 100, 191–213.

Zachos, J.C., Flower, B.P., Paul, H., 1997. Orbitally paced

climate oscillations across the Oligocene/Miocene boundary.

Nature 388, 567–570.

Zachos, J.C., Pagani, M., Sloan, L.C., Thomas, E., Billups, K.,

2001a. Trends, rhythms, and aberrations in global climate

65 Ma to present. Science 292, 686–693.

Zachos, J.C., Shackleton, N.J., Palike, H., Flower, B.P., 2001b.

Climate response to orbital forcing across the Oligocene–-

Miocene boundary. Science 292, 274–278.

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