Eocene fluctuations in the CCD & climate: evidence from carbonate & oxygen isotopes

Monahan, Kyle1, Katz, Miriam E. 1, Cramer, Benjamin S.21Earth and Environmental Sciences, Rensselaer Polytechnic Institute, 110 8th St., Troy NY 12180, United States of America

2Theiss Research, Eugene OR 97401 United States of America

ABSTRACT

The transition from warm global climates in the early

Paleogene to cool global climates by the early Oligocene

was accompanied by a large-scale reorganization of

deep-sea circulation patterns (e.g., Cramer et al. 2009),

small transient Antarctic glaciations (e.g., Browning et al.

1996) and large fluctuations in the Calcite Compensation

Depth (CCD) (e.g., Coxall et al. 2005; Lyle et al. 2005).

Using CaCO3 and stable isotopic data from a central

Pacific location, Lyle et al. (2005) proposed that the

CCD changes reflected by changes in accumulation of

calcium carbonate were linked to global cooling events,

and possibly small glaciations in Antarctica.

We build on the Pacific study by analyzing the mid- to

late Eocene (~36 to 40 Ma) section from Ocean Drilling

Program (ODP) Site 1090, located in the Atlantic sector

of the Southern Ocean. At a paleodepth of ~2500-

3000m, this site is well located to monitor changes in the

CCD. We analyzed bulk sediments from Site 1090 for

(1) %CaCO3 to document changes in the CCD in this

region and (2) bulk sediment oxygen isotopes (δ18O) as

an indicator of cooling events and possible Antarctic

glaciation from ~36-40 Ma. Our CaCO3 data at Site 1090

record substantial variability in carbonate content,

indicating fluctuations in the CCD. There is good

agreement between high %CaCO3 and high δ18O,

linking a deeper CCD to cooling and possible Antarctic

ice sheet growth. Our results support the hypothesis

proposed by Lyle et al. (2005).

RESULTS

The data collected at Site 1090 is summarized in the Site 1090 graph. (Fig 5)

The %CaCO3 values show wide variation and correspond with the bulk

sediment 18O values down-core. Both fluctuate between high and low

values. Interpretations of the timescales based on the depth are provided, as

well as CCD depth interpretations to the right of the graph.

REFERENCES

1. Helen K. Coxall, Paul A. Wilson, Heiko Pälike, Caroline H. Lear, & Jan Backman. Rapid stepwise onset of

Antarctic glaciation and deeper calcite compensation in the Pacific Ocean. Nature 433, 53-57 (6 January

2005) doi:10.1038/nature03135; Received 1 September 2004; Accepted 25 October 2004

2. James V. Browning, Kenneth G. Miller, Dorothy K. Pak. Geology; July 1996; v. 24; no. 7; p. 639–642

3. Lyle, M., Olivarez Lyle, A., Backman,J., and Tripati, A., 2005. Biogenic sedimentation in the Eocene equatorial

Pacific—the stuttering greenhouse and Eocene carbonate compensation depth. In Wilson, P.A., Lyle, M., and

Firth, J.V. (Eds.), Proc. ODP, Sci. Results, 199, 1–35 [Online].

4. Cramer, B. S., J. R. Toggweiler, J. D. Wright, M. E. Katz, and K. G. Miller (2009), Ocean overturning since the

Late Cretaceous: Inferences from a new benthic foraminiferal isotope compilation, Paleoceanography, 24,

PA4216, doi:10.1029/2008PA00168

5. Coplen T. B., Kendall C. and Hopple J. (1983) Intercomparison of stable isotope reference samples. Nature

302, 236–238.

6. Coplen, T.B. and Hopple, J.A., 1995, Audit of VSMOW distributed by the United States National Institute of

Standards and Technology, in Reference and intercomparison materials for stable isotopes of light elements:

Vienna, International Atomic Energy Agency, IAEA-TECDOC-825, p. 35-38.

7. Ruddiman, William F. Earth's Climate: Past and Future, Second Edition. W. H. Freeman. 2008.

8. Gersonde, R., Hodell, D.A., Blum, P., et al., 1999. Proc. ODP, Init. Repts., 177: College Station, TX

9. “Map of World.” Diagram. International Student Handbook. Coastal Carolina University . 26 Oct 2010.

[http://www.coastal.edu/international/students/handbook.html ]

10. Katz, Miriam E. Class Lecture. Micropaleontology. Rensselaer Polytechnic Institute. Troy, NY. 27 Sept. 2010.

METHODS

Samples were analyzed for %CaCO3 at Lamont-Doherty

Earth Observatory with the UIC, Inc. Carbon CO2

coulometer attached to an Automate FX automatic

acidification preparation system. Approximately 10mg of

dried sediment was mixed with ~0.5mL distilled water.

Accuracy was confirmed by running a standard sample

of reagent-grade (99.9% pure) CaCO3 for every twenty

Site 1090 samples run. If the standard %CaCO3wt was

less than 90.0%, the samples were re-run.

Stable isotope analyses on Hole 1090B samples were

performed in the Stable Isotope Laboratory at Rutgers

University using a multi-prep peripheral device and

analyzed on an Optima mass spectrometer. Samples

were reacted in 100% phosphoric acid at 90°C for 13

minutes. Values are reported versus V-PDB through the

analysis of an internal standard calibrated with NBS-19

(1.95‰ for δ13C) as reported by (Coplen et al., 1983)

and (Coplen, 1995).

Figure 1. Location of the ODP Site 1090 sediment

core in the white box. (Map, 2010)

CONCLUSIONS

Our CaCO3 data at Site 1090 record substantial variability in carbonate

content, indicating fluctuations in the CCD. (Fig 4 and 5) As %CaCO3

increases the Calcite Compensation Depth (CCD) becomes shallower, as a

shallower CCD allows more CaCO3 to be preserved. A shallow CCD and a

high %CaCO3 value are associated with a higher temperature and lower ice

volume through the covariance of %CaCO3 and δ18O. This agreement

between high %CaCO3 and high δ 18O, links a deeper CCD to cooling and

possible Antarctic ice sheet growth. This growth is also supported by the

current-induced unconformities which show a deepening CCD and colder

climate (Fig 3.) Our results support the hypothesis proposed by Lyle et al.

(2005).

Figure 2. Location map. Site 1090 is

highlighted in red (Gersonde, 1999).

1

ACKNOWLEDGEMENTS

• This research was supported by NSF grant OCE 09- 28607

• This research used samples provided by the Integrated Ocean Drilling

Program (IODP), which is sponsored by the U.S. National Science

Foundation (NSF) and participating countries under management of the

Joint Oceanographic Institutions (JOI), Inc.

• This poster was partially funded by the Charles McMorrow Award for

Undergraduate Research in Geology.

2

Fig 3 outlines the

relationship between

δ18O and climate. The 16O

is more readily

evaporated because it is

the lighter isotope.

During glacial climates

(where the 16O is

preferentially stored in

glaciers) the seawater

(and the marine

carbonate) are enriched

with 18O, resulting in a

higher δ18O .

When the glaciers melt in

during interglacial

climates the 16O returns

o the oceans lowering

the δ18O of marine

carbonates.(Ruddiman, 2008)

6

Figure 3. Deep-sea hiatuses from the Atlantic

sector of the Southern Ocean (Wright & Miller,

1993). Middle and late Eocene hiatuses indicate

an increase in ocean ventilation.

3

5

4

Figure 4. CCD paleodepth fluctuated in the middle

to late Eocene at Pacific ODP Sites 1220, 1219 and

1218 before deepening permanently near the

Eocene-Oligocene boundary. (Katz, 2010)

SITE 1090Fig 5 provides

the data for

Site 1090. The

bulk sediment 18O and

%CaCO3 are

plotted

downcore.

Interpretations

are provided

for ice

volume,

temperature

and relative

CCD depth .

Timescale

interpretations

are also

provided.

low δ18O