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ESTIMATING
GLOBAL SEA-LEVEL AND ICE VOLUME CHANGES
High-Resolution Sea-Level
and Ice Volume Records for the Cenozoic
High-Resolution Seismic
Study of the New York Bight to the Hudson River Canyon
ANDRILL
(ANtarctic DRILLing)
HUDSON
RIVER ESTUARY RESEARCH
High-Resolution
Climatic and Stratigraphic Records of the Hudson River Estuary
GREEN
HOUSE WORLDS
A
Tropical Connection to the Climatic Warmth of the Early Miocene?
Estimating the Strength of Warm Saline Intermediate Waters
in the Southern Ocean
High-Resolution Studies
of Sea-Level Changes during the "Greenhouse World"
of the Middle Eocene (51-42 Ma)
Developing Paired
High-Resolution Isotopic and Mg/Ca Ratio Records for the Late
Paleocene (59.5-55.5 Ma) from Leg 207 Site 1258
ESTIMATING SEA-LEVEL
AND ICE VOLUME CHANGES
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High-Resolution
Sea-Level Records for the Oligocene from New Jersey
Collaborators: N. Christie-Blick,
LDEO;
When I was first arrived at Lamont-Doherty
Earth Observatory in 2000, I was in the process of finishing
development of a new method to estimate global sea-level amplitudes
and implementing it for the Oligocene (34-23 Ma; Kominz and
Pekar, 2001; Pekar and Kominz, 2001). This new method was
developed largely because the only method to evaluate sea-level
amplitudes for pre-Pleistocene known so far had been considered
highly controversial (see Christie-Blick and Driscoll, 1995).
Its new approach includes integrating two-dimensional flexural
backstripping results with two-dimensional paleoslope modeling
of the margin using benthic foraminiferal biofacies. The results
from this study permitted quantitative constraints to be placed
on pre-Pleistocene sea-level amplitudes and for the first
time, permitted for pre-Pleistocene records: 1) quantitative
evaluation of how sediments and stratigraphy responded to
global sea-level changes (Pekar et al., 2001); 2) quantitative
constraints on the factors that control sedimentation on passive
margins (Pekar et al., 2003), and 3) a calibration of global
sea-level amplitudes to oxygen isotope changes (Pekar et al.,
2002; Fig. 1- SL vs d18O).
I have taken this study to the next level by beginning to
construct high-resolution (Milankovitch timescales) sea-level
records for the Oligocene by means of benthic foraminiferal
samples from the New Jersey onshore boreholes. It is the goal
of this study to generate a record with a resolution comparable
to that of the Pleistocene and of being able to investigate
directly the phase relations between the sedimentary record
and the sea-level changes that were responsible for the observed
cyclicity.
Abstracts
Pekar, S. F., Christie-Blick, N., 2003,
Estimates of Oligocene sea-level amplitudes and ice-volume
changes at Milankovitch time scales: EOS, Transactions, American
Geophysical Union, v. 84 (46), p. F-901.
Pekar, S. F., Christie-Blick, N., Miller,
K. G., and Kominz, M. A., 2003, Calibrating Oligocene eustasy
to oxygen isotope data: eustatic estimates from two-dimensional
flexural backstripping from the New Jersey continental margin
(USA): European Union of Geosciences Meeting, Nice, France,
in Geophysical Research Abstracts, v. 5, 13,654.
Invited talks:
Using a new method to estimate global sea-level
changes: results and implications from 2-D flexural backstripping
of Oligocene (34-23 Ma) strata: presented at the University
of Massachusetts, Amherst MA, 10/03 and the University of
Chicago, Chicago IL, May, 2003.
Evaluating Sea-level and Climate Change from the Greenhouse
to Icehouse Worlds: presented at the University of California
at Riverside, December, 2002.
Reconstructing the
early Icehouse World (34-17 Ma): High-resolution constraints
on ice-volume changes in Antarctica and global sea-level amplitudes
Collaborators: N. Christie-Blick
(LDEO); R. DeConto (U-Mass-Amherst), D. Harwood
(U. of NE-Lincoln)
Recently calibrated isotopic records, global sea level estimates,
stratigraphic and biological data from Antarctica, and estimates
in atmospheric CO2 provide a new comprehensive model of cryospheric
and climate evolution between 34 and 17 Ma (Pekar et al.,
in prep.). Unlike non-calibrated isotopic records that appear
to decouple with global sea level, Antarctic stratigraphic
and CO2 records during the late Oligocene and the early Miocene
(25-16 Ma), calibrated isotopic records are in good agreement
with all of these records. This resolves previous discrepancies
between non-calibrated deep-sea oxygen isotopic records and
Antarctic stratigraphy, global sea level records, and ¡CO2
records. Calibrated isotopic records suggest that ice volume
ranged from 75 to 115% of the present-day East Antarctic Ice
Sheet across the Eocene -Oligocene boundary. Ice volume decreased
during the early Oligocene ranging from 30 to 80% of the present-day
EAIS. Ice volume then gradually increased to 50-130% of the
present-day East Antarctic Ice Sheet between 28.5 and 24.5
Ma (ATS). Estimates of atmospheric CO2 show a long-term decrease
since the middle Eocene, bottoming out by the latest Oligocene
and is consistent with the long-term cooling indicated by
both the Antarctic stratigraphic records and the calibrated
isotopic records. This supports the idea of the important
role CO2 has in climate change.
Late Oligocene composite deep-sea oxygen
isotopic records show a significant decrease (1‰), which
have long been interpreted as bottom-water warming combined
with deglaciation of Antarctica. However, a close examination
of individual oxygen isotopic records indicate a clear divergence
after 26.8 Ma between records from Southern Ocean locations
(i.e., Ocean Drilling Program sites 689, 690, 744) and those
of other ocean basins. The high oxygen isotopic values (2.9-3.3‰)
from these Southern Ocean oxygen isotopic records and by calibrating
the isotopic values to global sea level results (Pekar et
al., 2002; Pekar et al., 2006) are consistent with an ice
sheet on the East Antarctic continent (EAC) equivalent to
present-day values and cold bottom-water temperatures (2.0C).
New ice volume estimates during the early
Miocene (23-16 Ma ATS) were made by applying oxygen isotopes
to sea-level calibrations to high-resolution oxygen isotopes
records from ODP sites 1090 and 1218 (Pekar and DeConto, 2006).
These calibrated records indicate that ice volume ranged from
50% up to 125% of the present day East Antarctic Ice Sheet
(EAIS) during most of the early Miocene (23-17 Ma). Maximum
ice volume occurred at each of the early Miocene isotopic
events (i.e., Mi-events) based on isotopic values (2.9-3.6‰)
concomitant with bottom water temperatures between ~1 and
2 C.
These differences suggest a reduction in
deep waters produced near the Antarctic continent (i.e., proto-Antarctic
Bottom Waters, proto-AABW), which were quickly entrained and
mixed with warmer (and presumably more saline) bottom-waters
originating from lower latitudes. Expansion of a warmer deep
water mass and the weakening of the proto-AABW may explain
the large intra-basin isotopic gradients that developed among
late Oligocene benthic oxygen isotopic records. These conclusions
are also supported by ocean modeling suggesting a reduction
of deep-waters formed in the Southern Ocean, strengthening
of deep-waters from the northern hemisphere, and decreasing
temperatures in high southern latitudes occurred as the Drake
Passage opened to deep waters. Low oxygen isotopic values
reported from deep-sea locations other than the Southern Ocean
are shown to bias estimates of Antarctic ice volume, calling
for a re-evaluation of the notion that Antarctic ice volume
was significantly reduced during the late Oligocene.
Publications
Pekar, S. F., DeConto, R., 2006, High-Resolution
Ice-Volume Estimates for the Early Miocene: Evidence for a
Dynamic Ice Sheet in Antarctica, Palaeogeog, Palaeoclim.,
Palaeoecol. In press.
Pekar, S.F., Harwood, D., DeConto, R., 2006, Resolving a late
Oligocene conundrum: deep-sea warming versus Antarctic glaciation:
submitted to Palaeogeog, Palaeoclim., Palaeoecol. In press.
Invited talks:
Pekar, S.F., Christie-Blick, N., DeConto,
R.M., Reconstructing the early Icehouse World (34-16 Ma):
High-resolution constraints on ice-volume changes in Antarctica
and global sea-level amplitudes: Geoitale 2005 - Quinto
Forum Italiano di Scienze della Terra, Sept., 2005.
Reconstructing the Early Icehouse World (34-16 Ma): Constraining
Ice-Volume Changes in Antarctica and Global Sea-Level Amplitudes,
Department of Geosciences, Pennsylvania State University,
April, 2005.
Reconstructing the Early Icehouse World (34-16 Ma): Constraining
Ice-Volume Changes in Antarctica and Global Sea-Level Amplitudes,
Marine Geology and Geophysical Seminar, Lamont Doherty
Earth Observatory of Columbia University, February, 2005.
Pekar, S. F., Harwood D., Deconto R., 2004, [Key lecture]
Resolving a late Oligocene conundrum: deep-sea warming
versus Antarctic glaciation: 32nd International Geological
Congress, Florence, Italy.
ANDRILL (ANtarctic
DRILLing)
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ANDRILL (ANtarctic DRILLing) is a
multinational initiative with the objective to recover stratigraphic
core records for the use of interpreting Antarctic’s
climatic, glacial, and tectonic history for the past 50 Ma.
NSF has already provided support for ANDRILL’s drilling
program in the Ross Sea for the first two years, with the
goal of extending this commitment to at least the year 2010.
I am one of 6 scientists selected to be on the final site
survey committee for Southern McMurdo Sound (SMS) drilling
project. A workshop convened by D. Harwood revisited the geological
history of the SMS area using reprocessed seismic profiles
and new age dates from nearby cores, resulting in new exciting
hypotheses on the geological evolution of the SMS region.
This resulted in an abstract submitted to IGC (Pekar et al.)
as well as the preparation of a manuscript to Marine Geology
(Harwood, Pekar et al., in prep.). This project is planned
to be drilled by ANDRILL either in late 2005 or 2006.
Publications
Harwood, D., Florindo, F., Fielding, C.,
Levy, R., Pekar, S.F., Southern McMurdo Sound Drilling Prospectus,
2005, published by the ANDRILL Program.
Harwood, D., Florindo, F., Fielding, C., Levy, R., Pekar,
S.F., Southern McMurdo Sound Project, 2004. Andrill, v. 2,
p. 3-4.
Harwood, D., Pekar, S.F., Florindo, F.,
Levy, R., Fielding, C.R., ANDRILL Program drilling in Southern
McMurdo Sound (SMS): obtaining proximal archives of Antarctic
environmental changes for the past 19 million years: to be
submitted to Marine Geology.
Abstracts:
Pekar, S.F., Speece, M.A., DeConto, R.M.,
Using new tools to explore undiscovered country: understanding
the tectonic and stratigraphic history of greenhouse to icehouse
worlds of Offshore New Harbor, Ross Sea, Antarctica: Geoitale
2005 - Quinto Forum Italiano di Scienze della Terra, Sept.,
2005.
Pekar, S. F., Harwood D., Florindo F., Fielding
C., Levy, 2004, ANDRILL Program drilling in Southern McMurdo
Sound (SMS): obtaining proximal archives of Antarctic environmental
changes for the past 17 million years: 32nd International
Geological Congress, Florence, Italy.
Harwood D., Florindo F., Fielding C., Levy
R., Pekar S., and ANDRILL Science Committee, 2004, ANDRILL
Program stratigraphic drilling project in Southern McMurdo
Sound (SMS): An overview of site surveys and scientific objectives:
XXVIII SCAR Science and XVI COMNAP/SCALOP Meeting, Bremen,
Germany.
Invited talk:
Pekar, S. F., Harwood D., Deconto R., Resolving
a late Oligocene conundrum: deep-sea warming versus Antarctic
glaciation: 32nd International Geological Congress, Florence,
Italy.
Bringing Antarctic Research to Queens College
and Expanding CUNY Research and Educational Programs to Governors
Island, Presidential Roundtable Lecture Series, Queens College,
December 12, 2005.
High-Resolution
Seismic Study of the New York Bight to the Hudson River Canyon
Collaborators: N. Christie-Blick
(LDEO); G. Mountain (Rutgers U.); C. McHugh (LDEO and Queens
College)
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The objective of this project is to develop
new models to evaluate the stratigraphic response to eustatic
change at time and length scales for which changes in global
ice volume operates. This will be accomplished by examining
two contrasting periods from the New York Bight and New Jersey
region: 1) well-documented unconformities of Cretaceous and
early Paleogene age, which developed during a span of time
lacking evidence for significant continental glaciation; and
2) Quaternary sediments from the mid to outer shelf, successions
for which eustasy is known independently and typically deviate
from a simple one-for-one relationship between eustatic fluctuation
and stratigraphic response (e.g., sequence boundary development).
The key to this plan is high-resolution physical stratigraphy,
precise chronology, and quantitative analysis of stratigraphic
data. Specifically, the research will consist of the following
elements:
1. Acquisition of coincident side-scan data for surface texture;
Chirp sonograms for sub-meter resolution in the upper several
tens of meters below seafloor; a new generation of 48-fold
HiRes MCS profiles for meter-scale resolution to 200 mbsf
where needed; and 24-fold HiRes MCS for a region requiring
penetration to 600 mbsf.
2) Collection of Vibracores to ground-truth the age, provenance
and paleoenvironment of strata, and to map these features
at unprecedented resolution.
3) High-resolution chronology at ODP Site 1073 (radiocarbon
and racemization dating), coupled with provenance studies
to constrain slope processes.
4) Two-dimensional backstripping of coastal plain borehole
data, in the context of stratal geometries inferred from our
offshore MCS data, to place constraints on amplitudes of eustatic
change during Late Cretaceous to early Paleogene time.
My focus will be to place constraints on amplitudes of eustatic
change and how sediments response to these changes for the
Cretaceous through early Paleogene. This will be done by determining
the stratal geometry of the sediments from the seismic data
and integrating it with two-dimensional flexural backstripping
techniques and stratigraphic data from the onshore boreholes.
I will be also developing high-resolution isotopic records
from the vibracores that were obtained during the cruise.
Abstracts:
Brownlee, S J., McHugh, C., Burckle,
L., and Pekar, S, 2004, Diatoms as proxies for climate change
in the Hudson River estuary, New York: Geological Society
of America Abstracts with Programs v. 36, No. 2.
Christie-Blick, N., Mountain, G.
S., Ghosh, A., McHugh, C. M. G., Pekar, S. F., Schock, S.
G., 2002, New insights on late Pleistocene sedimentation at
the New Jersey margin based on chirp sonar profiles and vibracores:
EOS, Transactions, American Geophysical Union, F-727.
Ghosh, A., Christie-Blick, N., Mountain,
G. S., McHugh, C. M. G., Pekar, S. F., Late Pleistocene sequence
geometry beneath the Long Island shelf from CHIRP sonar data:
10th Annual Geology of Long Island and Metropolitan New York,
SUNY Stony Brook, NY.
Gould, H., McHugh, C. M. G., Mountain,
G. S., Christie-Blick, N., Pekar, S., Gurung, D., Hartin,
C., 2004, Evidence for the latest Pleistocene-Holocene shoreline
along the New York-New Jersey continental margin: Geological
Society of America Abstracts with Programs v. 36, No. 2.
McHugh, C. M. G., Gould, H., Mountain,
G. S., Christie-Blick, N., Pekar, S., Gurung, D., Hartin,
C., 2004, Evidence of the latest Pleistocene-Holocene shoreline
along the New York-New Jersey, U.S., continental margin: 32nd
International Geological Congress, Florence, Italy.
HUDSON RIVER
ESTUARY RESEARCH
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High
resolution climatic and stratigraphic records of the Hudson
River Estuary
Collaborators: C. McHugh, LDEO and
Queens College; L. Burkle, LDEO
The primary goal of this project is to develop
climate records for the lower Hudson River during the past
7,000 years that will allow us to evaluate how these climate
changes influence the long-term sedimentation patterns of
the estuary. To accomplish this, twelve long (up to 7.5 m)
vibracores recently obtained (9/02) from the Hudson River
between Alpine and Storm King Mountain were strategically
positioned to sample intervals containing high sedimentation
rate, large salinity changes, and older strata. Geophysical
imagery (side-scan sonar, high-resolution CHIRP, and multibeam
bathymetry) and our prior experience in investigating sedimentation
patterns in the estuary guided the positioning of these cores.
Salinity in the Hudson River is controlled primarily by runoff,
which is in turn due to precipitation/climate. Thus, paleosalinity
ought to serve as a proxy for long-term climate variability
(i.e., long-term precipitation patterns). It can be estimated
by an integrated approach using benthic foraminiferal biofacies
and oxygen isotopes from juvenile bivalves. Sedimentological
data (sedimentary structures and physical properties) will
be used to determine the paleoenvironmental conditions under
which the sediments were deposited (i.e., tidal influence
and energy regime). Age constraints will be developed using
14C chronology. Taken together, the resulting data will provide
a means to evaluate the factors that control sediment transport
patterns in the Hudson River at long timescales. The objectives
of this study include the following:
1) Determine long-term runoff changes due
to climate variability using two proxies for estimating salinity.
2) Evaluate the significance of a paleo-estuarine turbidity
maximum in sedimentary patterns (an important phenomenon in
the Hudson River today).
3) Estimate the energy (tidal and wave energy) of the Hudson
River system back through time, determine the paleoenvironments
of deposition, and propose a model for estuarine sedimentation.
Initial results from this project include that four biofacies
were recognized in the cores and were correlated to present
day assemblages, which living in the Hudson River have been
calibrated to salinity. Elphidium species abundances were
also calibrated to salinity. Preliminary results indicate
a good agreement between salinity estimates based on benthic
foraminiferal studies and oxygen isotopes records obtained
from the juvenile shells (first year growth) of the bivalve
species Gemma gemma, permitting them to used as salinity proxies
(Fig. 2 HR salinity). Another aspect of this research is the
long-term migration of the salt wedge and the deposition record
related to the turbidity maximum zone. Results indicate that
the turbidity maximum is preserved in the sedimentary record
and can be traced in the Hudson Estuary through time. This
has important implications for possible sedimentation pattern
changes as a result of the migration of the salinity wedge
intruding further into the Hudson Estuary due to future sea-level
rises.
Papers and Manuscripts:
Pekar, S. F., McHugh, C., Christie-Blick, N., Jones, M., Carbotte,
S., Bell, R. E., and Lynch-Stieglitz, J., 2004. Estuarine
processes and their stratigraphic record: paleosalinity and
sedimentation changes in the Hudson Estuary: Marine Geology,
209:113-129..
McHugh, C., Pekar, S. F., Christie-Blick, N., Ryan, W B. F.,
Carbotte, S., Bell, R., and Burckle, L., 2004, Spatial variation
in a condensed interval between estuarine and open-marine
settings: Holocene Hudson River estuary and adjacent continental
shelf: Geology, 32:169-172.
Abstracts:
Brownlee, S J., McHugh, C., Burckle, L., and Pekar, S, 2004,
Diatoms as proxies for climate change in the Hudson River
estuary, New York: Geological Society of America Abstracts
with Programs v. 36, No. 2.
Gould, H., McHugh, C. M. G., Mountain, G. S., Christie-Blick,
N., Pekar, S., Gurung, D., Hartin, C., 2004, Evidence for
the latest Pleistocene-Holocene shoreline along the New York-New
Jersey continental margin: Geological Society of America Abstracts
with Programs v. 36, No. 2.
Pekar, S. F., Gonzalez-McHugh, C.
M., Christie-Blick, N., Jones, M. C., Lynch-Stieglitz, J.,
2002 Using salinity estimates and sedimentary data to evaluate
the processes that controlled the evolution of Hudson River
estuary during the mid-Holocene: EOS, Transactions, American
Geophysical Union, F-787.
McHugh, C. M. G., Pekar, S. F., Ryan, W. B. F., Carbotte,
S., Bell. R., and Burckle, L., 2002, Infilling of the Hudson
River Estuary during the latest Holocene (3,000 BP to present):
implications for estuarine stratigraphic models: EOS, Transactions,
American Geophysical Union, F780.
Jones, M. C., McHugh, C. M. G., Burckle, L., Pekar, S. F.,
Pereira, G., Ryan, W. B. F., Bell, R., and Carbotte, S., 2002,
Decadal to millennial sedimentation patterns of the Hudson
River estuary: EOS, Transactions, American Geophysical Union,
F-787.
McHugh, C. M. G., Ryan, B., Pekar, S. F., Zheng, Bell, R.
E., Carbotte, S., Chillrud, S., Rubenstone, J.L., 2001, Dynamic
equilibrium of the Hudson Estuary revealed by the sedimentary
record: Geological Society of America Abstracts with Programs,
A-453.
Jones, M. C., Pekar, S. F., Gonzalez-McHugh, C. M., Lynch-Stieglitz,
J., Rubenstone, J. L., Bell, R. E., and Carbotte, S., 2001,
Developing an integrated approach in understanding the evolution
of the Hudson Estuary: Geological Society of America Abstracts
with Programs, A-453.
GREEN HOUSE
WORLDS
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In the spring of 2000, I participated as
a sedimentologist on an eight-week expedition south of Tasmania
in Ocean Drilling Program Leg 189. One of the fundamental
questions of this leg was to investigate how the southern
ocean influenced climate and paleoceanography globally. I
focused on two intervals that were dominated by unusually
warm climates: the early Miocene (21-16 Ma) and the middle
Eocene (51-42 Ma). I am also developing late Paleocene records
from participating as a land based scientists for Leg 207.
A
Tropical Connection to the Climatic Warmth of the Early Miocene?
Estimating the Strength of Warm Saline Intermediate Waters
in the Southern Ocean
Collaborators: T. Marchitto, LDEO;
J. Lynch-Steigleig, LDEO; P. deMenocal
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This project will evaluate climatic and
paleoceanographic changes during the early Miocene, the oldest
and perhaps most significant warm interval of the Neogene.
Although the causal factors for this mini-greenhouse event
are still unresolved, an overall consensus that deep and intermediate
water changes coupled with expanding and contracting oceanic
gateways must have played a critical role in the resulting
warmth. One theory is that the warm saline deep waters forming
in the Tethys Sea played a pivotal role in the creation of
this mini-greenhouse world. However, up until now there has
been a paucity of paleoceanographic data sets from the southern
ocean for the early Miocene, a pivotal region in understanding
this warm period.
This project is generating high-resolution
stable isotope and Mg/Ca ratio records that will rectify this
apparent gap in current data sets, providing a greater understanding
how deep waters in the southern ocean during the early Miocene
operated and possibly controlled global climate changes. Site
1168 contains a remarkable continuous early Miocene record
of deep-water sedimentation, which includes excellent recovery
of the sediment and preservation of the calcareous microfossils.
This research is, for the first time, improving age resolution
of early Miocene strata in the southern ocean to Milankovitch
time scales using stable isotopic data from Site 1168. This
site is critical in evaluating potential penetration of warm
saline intermediate waters originating from the Tethys Sea
and Indian Ocean due to its paleowater depth (middle bathyal)
location that makes it perhaps the first and only area to
monitor warm saline intermediate waters entering the Southern
Ocean.
Large fluctuations in the isotope and Mg/Ca
ratio records suggest changes in the water masses that bathed
the Tasmanian slope during the early Miocene. Temperature
estimates based on Mg/Ca ratios contain a surprisingly high
range, from 4° to 10° C. Low temperatures (4°-6°
C) are associated with high carbon isotope values (>1.4‰)
and are interpreted to be Southern Component Waters (SCW).
The high carbon isotope values also suggest a proximal source
for SCW. High water temperatures (7°-10°C) indicate
a warm-water mass and are interpreted to be due to the penetration
of WSDW into this area, replacing SCW at various times. Large
high-frequency isotopic excursions (low oxygen and carbon
isotope values) occurred between 18.7 and 18.4 Ma were originally
thought to be due to either localized effects (e.g., disassociation
of hydrates) or possible diagensis. However, a recently published
high-resolution isotopic record from the Southern Ocean (Site
1090) also contains large isotopic excursions (e.g., >1‰
decrease in oxygen isotope values) at this time, suggesting
that these events may not due to diagensis but may be transient
global events. We interpret that the changes observed in the
isotopic and Mg/Ca ratio records are the result of both changes
in the cryosphere and water-mass changes in the vicinity of
Tasmania, the latter being due to the penetration of WSDW
into the Southern Ocean.
Abstract:
Pekar, S.F., Marchitto, T., Lynch-Steiglitz,
J., White, T., Ennyu, A., 2002, Evidence for a tropical source
for climate change during the early Miocene (19-16 Ma): Stable
isotopic and Mg/Ca records from ODP Leg 189 Site 1168, EOS,
Transactions, American Geophysical Union, F927.
Invited talk:
Evaluating Sea-level and Climate
Change from the Greenhouse to Icehouse Worlds: University
of California at Riverside, December, 2002.
High-Resolution
Studies of Sea-Level Changes during the "Greenhouse World"
of the Middle Eocene (51-42 Ma)
Collaborators: M. Fuller (U. of
Hawaii), A. Hucks (Rice U.)
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The other greenhouse world I am interested
is the middle Eocene. I am currently developing high-resolution
sea-level records from cores obtained ODP Site 1171 from between
Australia and Antarctica. The middle Eocene is a time of slow
long-term climatic deterioration (global cooling) following
the warmest period of the Cenozoic, the early Eocene. A debate
exists whether these coolings included significant ice-volume
increases in Antarctica and in a related issue whether high
frequency (< 1 m.y.) sea-level changes observed in shallow
water sections are due to ice-volume changes. However, no
records exist from shallow water sites that can properly address
these issues at high-resolution.
Sequence boundaries identified in shallow-water
sediments obtained from ODP Leg 189 Site 1171 were correlated
to oxygen isotope records and other stratigraphic records
indicating that significant global sea-level changes occurred
during the late early to middle Eocene (51-42 Ma). Six sequence
boundaries were identified using lithostratigraphy, age control
(bio- and magnetostratigraphy), CaCO3 content and physical
properties (e.g., photospectrometry). Benthic foraminiferal
biofacies and planktonic/benthic foraminiferal ratios were
used to estimate water depth changes.
A comparison of sequence boundaries from
Site 1171 to oxygen isotope increases shows a good correlation.
Additionally, sequence boundaries identified
in Eocene studies from Leg 150X onshore boreholes (New Jersey,
USA) compare well with the timing of sequence boundary development
at Site 1171. The synchronous nature of sequence boundary
development from globally distal sites and oxygen isotope
increases indicates a global control. The only mechanism that
can explain these large rapid changes is glacioeustasy. This
is supported by modeling studies (Deconto and Pollard, 2003)
and CO2 estimates (Pearson et al., 2000) showing that the
first time CO2 levels decreased below a threshold that would
support the development of an ice sheet in Antarctica was
at ~51 Ma. Finally, using constraints established for the
Oligocene from oxygen isotope records, estimates of sea-level
amplitudes range from 20±10 m for the early Eocene
(51 and 49 Ma) with higher amplitudes (25±10 m to 45±20)
for the middle Eocene (48 and 42 Ma).
Manuscript submitted
Pekar, S. F., Hucks, A., Fuller, M., and
Li, S., Glacioeustatic changes in the early and middle Eocene
(51-42 Ma) greenhouse world based on shallow-water stratigraphy
from ODP Leg 189 Site 1171 and oxygen isotope records: Geological
Society of America Bulletin, in review.
Invited Abstract:
Pekar, S.F., Hucks, A., Fuller, M., Li,
S., 2003, Glacioeustatic changes in the early and middle Eocene
(51-42 Ma) greenhouse world based on shallow-water stratigraphy
from ODP Leg 189 Site 1171 and oxygen isotope records: EOS,
Transactions, American Geophysical Union, v. 84 (46), F-900.
Developing
Paired High-Resolution Isotopic and Mg/Ca Ratio Records for
the Late Paleocene (59.5-55.5 Ma) from Leg 207 Site 1258 back to top
The early Paleogene represents a time of
dramatic climatological and paleoceanographic changes that
include the recovery after the K/T Event, the cooling of the
mid to late Paleocene (e.g., Francis and Poole, 2002) and
the ephemeral global hothouse world of the Late Paleocene
Thermal Maximum (LPTM). However, with the K/T Boundary and
LPTM having garnered the attention of much scientific study
in recent years, fundamental questions concerning paleoceanographic
and climatic changes during the late Paleocene have remained
unanswered. In particular, little is known about the extent
of cooling that took place during the late Paleocene (59-57
Ma; Fig. 1). It has also been speculated that small ephemeral
ice sheets may have existed in Antarctica during this time
(Prentice and Matthews, 1988; Miller et al., 1998). Furthermore,
the mechanisms for the long-term warming (57-55 Ma) that preceded
the LPTM remain uncertain. Gaps in knowledge regarding the
Paleocene paleoceanography and climate are mainly due to a
paucity of deep-sea isotope records; in particular, the absence
of Mg/Ca ratio and high-resolution isotope records that could
evaluate paleoceanographic and climate changes at time scales
that typically control climate and oceans. New high-resolution
studies of the Paleocene would fill in the missing link between
the high-resolution studies of the Cretaceous and the early
Eocene in reconstructing the long-term paleoclimate and paleoceanographic
history.
This proposal will attempt to fill the above
gaps by developing high-resolution paired isotope and Mg/Ca
ratio records for the late Paleocene (59.5-55.5 Ma) from benthic
foraminifers from Leg 207 at Site 1258. The main goal is to
develop deep-sea records from the late Paleocene at Milankovitch
time scales, which will provide the means of evaluating potential
ice sheet development, bottom-water temperatures and circulation
in the western Atlantic at the necessary time lengths. These
records will then be correlated to isotopic records from other
sites around the globe to gain a better understanding of the
global climatic and paleoceanographic changes.
The following sampling strategies
will be implemented for this study.
1) Moderately high-resolution (~40
k.y.) late Paleocene (59.5-55.5 Ma) isotope and Mg/Ca ratio
records will be developed from benthic foraminifers. This
will provide a paleoceanographic framework to investigate
trends in the late Paleocene in the western tropical Atlantic,
plus assist in identifying the target intervals for high-resolution
studies.
2) High-resolution (5. k.y.) isotope and Mg/Ca ratio records
will be developed from benthic foraminifers from two 0.5 m.y.
time intervals once the moderate resolution study is completed.
Specific objectives of the project
will include both the 40 and 5 k.y. records and are as follows.
1) To determine bottom-water temperatures
using Mg/Ca ratios and estimate the isotopic composition of
seawater. This would allow evaluation of whether significant
ice growth occurred in Antarctica.
2) To correlate the above results to other isotopic records
for the purpose of creating time series and time slice reconstructions.
This would permit developing a global composite picture of
the paleoceanographic circulation during this time.
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