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Exuma - Bahamas



Current Projects and Ongoing Interests

PLIOMAX: Pliocene Maximum Sea Levels
Milankovitch climate dynamics
Thermohaline circulation of the Atlantic Ocean
Plio-Pleistocene millennial-scale climate variability
Time scale development
Uplift-weathering hypothesis
Neogene ocean and climate history
OPD Leg 162





PLIOMAX: Pliocene Maximum Sea Levels
cape range
The Pliomax project is a multi-PI, multi-institution project with the goal of increasing the accuracy of global sea level estimates for the mid-Pliocene warm period, between 3.3 and 2.9 million years ago. Numerous proxy methods suggest that atmospheric CO2 levels at that time ranged between 350 and 400 ppm, a maximum value that will soon be exceeded. Likewise, mean global surface temperature is estimated to have been 2-3C greater than today. Thus, the mid-Pliocene warm period provides both a natural analogue for a higher CO2 world as well as a testing ground for climate and ice sheet models that are being used to predict the future response of Earth's climate to increasing levels of greenhouse gases. However, our ability to calibrate and verify model performance under different CO2 and climate conditions is limited by the accuracy of available paleoclimate data and, in particular, our knowledge of past sea level (SL), a reflection of polar ice volume. Currently, few estimates of mid-Pliocene SL exist and they range from +5m to >+30m relative to present, reflecting a large range of uncertainty in the sensitivity of polar ice sheets, including the East Antarctic Ice Sheet, to a modest, ~2-3C, global warming.

The goal of the Pliomax project is to facilitate the study of nearshore Pliocene stratigraphic sections around the world and to improve the ice sheet and crustal deformation models used in the study of past and future climate change. Other PIs on the project include Jerry Mitrovica at Harvard, Rob DeConto at U. Mass Amherst, Dave Pollard at Penn State, Paul Hearty at University of North Carolina in Wilmington, and Jeremy Inglis at the University of North Carolina in Chapel Hill. We are also collaborating with scientists in Europe, Africa, South America, and Australia, in particular Mick O'Leary of Curtin University in Perth. Numerous post-docs and graduate students are also involved with this project.

More info about the PLIOMAX project can be found on its wiki site at www.pliomax.org.

Our first papers:

Raymo, M. E., and J. X. Mitrovica, 2012, Collapse of polar ice sheets during the stage 11 interglacial, Nature, doi:10.1038/nature10891. Supplemental Material

Raymo, M. E., J. X. Mitrovica, M. J. O'Leary, R. M. DeConto, and P. J. Hearty, 2011, Departures from eustasy in Pliocene sea-level records, Nature Geoscience, doi:10.1038/NGEO1118. Supplemental Material

Raymo, M.E., P. Hearty, R. De Conto, M. O'Leary, H.J. Dowsett, M. Robinson, and J.X. Mitrovica, 2009, PLIOMAX: Pliocene maximum sea level project, PAGES News, v. 17, p. 58-59.


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Milankovitch Climate Dynamics

Although the glacial-interglacial cycles of the past 3 Ma represent some of the largest and most studied climate variations of the past, the physical mechanisms driving these cycles are not well understood. For the past thirty years, the prevalent theory has been that fluctuations in global ice volume are caused by variations in the amount of insolation received at critical latitudes and seasons due to variations in the Earth's precession, obliquity and eccentricity. Based mainly on climate proxy records from the last 0.5 Ma, but also supported by climate model results, a scientific consensus has emerged that variations in ice volume at precession (~23 kyr) and obliquity (41 kyr) frequencies are directly forced and coherent with northern summer insolation while the ~100 kyr eccentricity component of the ice age climate cycle results from non-linear amplification mechanisms possibly phase-locked to summer insolation variations (e.g., Imbrie et al., 1992, 1993 and Tziperman et al., 2006).

41 KYR WORLD

cape range In the late Pliocene/early Pleistocene (LP/EP) interval from ~3-1 Ma, however, only weak variance at 100 kyr and 23 kyr periods is observed in proxy ice volume records such as benthic δ18O (Raymo et al., 1989; Lisiecki and Raymo, 2007). Instead, the records are dominated by 41 kyr cyclicity, the primary obliquity period. As the canonical Milankovitch model predicts that global ice volume is forced by high northern summer insolation, which at nearly all latitudes is dominated by the 23 kyr precession period, why then do we not observe a strong precession signal in LP/EP ice volume records? The lack of such a signal and the dominance of obliquity have defied understanding; most ice sheet models have been unable to reproduce the observed spectral characteristics of the LP/EP ice volume record.

In 2002, we began investigating whether variations in the insolation gradient between high and low latitudes could exert a dominant influence on high latitude climate and ice volume during the LP/EP (Raymo and Nisancioglu, 2003). The differential heating between high and low latitudes, influenced by obliquity, controls the atmospheric meridional flux of heat and moisture. In the 2-D zonal energy balance models typically used to study the long-term evolution of climate, the meridional atmospheric moisture flux was usually kept fixed. Nisancioglu (2004) constructed a simple process model that explicitly included these transports and their interactions with an ice sheet thus allowing us to test the influence of insolation gradient changes on ice sheet growth and ablation. However, while the improved meridional transports led to an increase in 41kyr power in modeled ice volume (mainly through changes in accumulation), ablation (and therefore also ice volume) remained highly sensitive to summer heating and hence precession. Thus, while insolation gradients may exert a strong influence on meridional energy transport, and thus possibly the strength of low and mid latitude wind systems, this influence does not appear to explain the dominance of 41kyr periodicity observed in δ18O.

Currently, we are using simple models of ice volume change (e.g., Imbrie and Imbrie, 1980), to explore another explanation for the "41 kyr world". The critical difference between our new experiments and previous attempts to model LP/EP ice volume is that we allow for a more dynamic Antarctic ice sheet as suggested by Pliocene sea level data (see also Mudelsee and Raymo, 2005). Raymo et al. (2006) propose that from ~3 to 1 Ma ice volume changes occurred in both the northern and southern hemispheres, each controlled by local summer insolation. Our modeled ice sheets are thus dominated by precession due to the dependence of ablation on summer temperatures. However, because Earth's orbital precession is out of phase between hemispheres, 23 kyr changes in ice volume in each hemisphere cancel in globally integrated proxies such as ocean δ18O or sea level leaving the in-phase obliquity (41 kyr) component of insolation to dominate the record. Only a modest ice mass change in Antarctica is required to "cancel" a much larger northern ice volume signal. At the Mid-Pleistocene Transition, we proposed that marine-based ice sheet margins replaced terrestrial ice margins around the perimeter of East Antarctica resulting in a shift to "in-phase" behavior of northern and southern ice sheets as well as the strengthening of 23 kyr cyclicity in the marine δ18O record.

ORIGIN OF THE 100 KYR CYCLE

It has long been recognized that the 100-kyr cycle cannot be explained as a linear response to eccentricity. Raymo (1997) suggested that the 100-kyr cycle is caused by the periodic buildup of large ice sheets during times of unusually low summer insolation maxima that occur roughly every 100,000 years as dictated by the modulation of precession by eccentricity (see also Ridgwell, Watson, and Raymo, 1999 and Raymo, Science 1998). This idea that the 100Kyr cycle of the late Pleistocene is composed of "bundles" of four or five precession cycles finds support in the chronology Kenji Kawamura has produced for the Dome Fuji and Vostok ice cores based on the O2/N2 ratio of trapped air that records local summer insolation. These records provide an accurate chronology of Antarctic climate for the past 360,000 years, covering the last four terminations, and suggest that the timing of rapid Antarctic warming at terminations falls within the rising phase of June 21 insolation at 65N. Precession pacing is statistically more significant than obliquity pacing for the last five terminations consistent with the hypothesis that high northern latitude summer insolation is the primary pacemaker of the late Pleistocene glacial cycles.

Relatively recent papers:

Raymo, M. E. and P. Huybers, 2008, Unlocking the mysteries of the Ice Ages, Nature, v. 451, p. 284-285.

Kawamura, K., F. Parrenin, L. Lisiecki, R. Uemura, F. Vimeux, J. P. Severinghaus, M. A. Hutterli, T. Nakazawa, S. Aoki, J. Jouzel, M. E. Raymo, K. Matsumoto, H. Nakata, H. Motoyama, S. Fujita, K. Goto-Azuma, Y. Fujii, and O. Watanabe, 2007, Northern Hemisphere forcing of climatic cycles in Antarctica over the past 360,000 years, Nature, v. 448, p. 912-917, doi:10.1038/nature06015.

Lisiecki, L., and M. E. Raymo, 2007, Plio-Pleistocene climate evolution: trends in obliquity and precession responses, Quat. Sci. Revs, v. 26, p. 56-69.

Raymo, M. E., L. E. Lisiecki, and K. H. Nisancioglu, 2006, Plio-Pleistocene ice volume, Antarctic climate and the global δ18O record, Science, v. 313, p. 492, doi: 10.1126/science.1123296.   You can download this paper using link on Publications page.

Tziperman, E., M. E. Raymo, P. Huybers, and C. Wunsch, 2006, Consequences of pacing the Pleistocene 100 kyr ice ages by nonlinear phase locking to Milankovitch forcing, Paleoceanography, v. 21, PA4206, doi:10.1029/2005PA001241.

Nisancioglu, K. H., Modeling the impact of atmospheric moisture transport on global ice volume, Ph. D. thesis, MIT (2004).

Raymo, M.E. and K.H. Nisancioglu, 2003, The 41 Kyr world: Milankovitch's other unsolved mystery, Paleoceanography, v. 18, DOI 10.1029/2002PA000791.   


Some older papers on orbital-scale climate dynamics:

Ridgwell, A.J., A.J. Watson, and M. E. Raymo, 1999, Is the spectral signature of the 100 kyr glacial cycle consistent with a Milankovitch origin? Paleoceanography, v. 14, p. 437-440.

Raymo, M. E., 1998, Glacial Puzzles (Perspective). Science, v. 281, p. 1467-1468.

Raymo, M.E., D.W. Oppo, and W. Curry, 1997, The mid-Pleistocene climate transition: a deep sea carbon isotope perspective. Paleoceanography, v. 12, p. 546-559.

Raymo, M.E., 1997, The timing of major climate terminations. Paleoceanography, v. 12, p. 577-585.

Imbrie, J., A. Berger, E.A. Boyle, S.C. Clemens, A. Duffy, W.R. Howard, G. Kukla, J. Kutzbach, D.G. Martinson, A. McIntyre, A.C. Mix, B. Molfino, J.J. Morley, L.C. Peterson, N.G. Pisias, W.L. Prell, M.E. Raymo, N.J. Shackleton, and J.R. Toggweiler, 1993, On the Structure and Origin of major glaciation cycles. 2. The 100,000-year cycle. Paleoceanography, v. 8, p. 699-736.

Imbrie, J., E.A. Boyle, S.C. Clemens, A. Duffy, W.R. Howard, G. Kukla, J. Kutzbach, D.G. Martinson, A. McIntyre, A.C. Mix, B. Molfino, J.J. Morley, L.C. Peterson, N.G. Pisias, W.L. Prell, M.E. Raymo, N.J. Shackleton, and J.R. Toggweiler, 1992, On the structure and origin of major glaciation cycles. 1. Linear responses to Milankovitch forcing. Paleoceanography, v. 7, p. 701-738.

Raymo, M.E., 1992, Global climate change: a three million year perspective. In: Kukla, G. and Went, E. (eds.), Start of a Glacial, Proceedings of the Mallorca NATO ARW, NATO ASI Series I, Vol. 3, Springer-Verlag, Heidelberg, p. 207-223.

Raymo, M.E., W.F. Ruddiman, J. Backman, B.M. Clement, and D.G. Martinson, 1989, Late Pliocene variation in Northern Hemisphere ice sheets and North Atlantic deep circulation. Paleoceanography, v. 4, p. 413-446.



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Thermohaline circulation of the Atlantic Ocean

A major uncertainty concerning future climate change is the response of ocean thermohaline circulation to the redistribution of heat and moisture at the Earth's surface. Climate models predict that enhanced temperatures and runoff in the Arctic-North Atlantic region could reduce sea ice cover and impact deep water convection in the Norwegian-Greenland Sea (NGS) region, changes that could have far-reaching effects on regional and global ocean circulation and climate (e.g., Raymo, Rind and Ruddiman, 1990). Today, between 5 and 6 Sv of deep water flows over the sills east and west of Iceland and entrains a further 7-8 Sv of intermediate depth water just south of the sills. These overflows thus form the greatest volumetric component of North Atlantic Deep Water.

north atlantic
Locations of DSDP and ODP cores used in this study. Paths of major deep water flows are indicated by arrows. (Please reference Raymo et al. [2004] if you use this figure)


During the last glacial period, convection in the NGS region is thought to have been greatly reduced by the freshening of surface water due to glacial runoff. Correspondingly, the volume of NADW produced decreased, offset partially by intermediate water formation in the subpolar North Atlantic south of Iceland. Using cores recovered during ODP Leg 162, we examined much longer geochemical records from the North Atlantic Ocean. These data suggest that the vertical δ13C structure of the water column at intermediate depths did not change significantly between glacial and interglacial time over much of the Pleistocene, despite large changes in ice volume and iceberg delivery from nearby landmasses. Raymo et al. [2004] suggest that, unlike today (an extreme interglaciation), the two primary sources of northern deep water, Norwegian-Greenland Sea and Labrador Sea/subpolar North Atlantic, may have had different characteristic δ13C values over most of the Pleistocene. We speculate that the current open sea ice conditions in the Norwegian-Greenland Sea are a relatively rare occurrence and that the high δ13C deep water that forms in this region today is geologically unusual. If northern source deep waters can have highly variable δ13C, then this likelihood must be considered when inferring past circulation changes from benthic δ13C records.


Thermohaline circulation publications:

Lisiecki, L. and M. E. Raymo, 2009, Diachronous benthic δ18O responses during late Pleistocene terminations, Paleaoceanography, v. 24, PA3210, doi:10.1029/2009PA001732.

Lisiecki, L., M. E. Raymo, and W. B. Curry, 2008, Atlantic overturning responses to climate forcing in the late Pleistocene, Nature, v. 456. p. 85-88, doi:10.1038/nature07425.

Raymo, M.E., D.W. Oppo, B.P. Flower, D.A. Hodell, J. McManus, K.A. Venz, K.F. Kleiven, K. McIntyre, 2004, Stability of North Atlantic water masses in face of pronounced natural climate variability, Paleoceanography, v. 19, PA2008, doi:10.1029/2003PA000921.    

Some older papers on NADW history:

Raymo, M.E., D.W. Oppo, and W. Curry, 1997, The mid-Pleistocene climate transition: a deep sea carbon isotope perspective. Paleoceanography, v. 12, p. 546-559.    

Raymo, M.E., B. Grant, M. Horowitz, and G. H. Rau, 1996, Mid Pliocene warmth: stronger greenhouse and stronger conveyor. Marine Micropaleontology, v. 27, p. 313-326.

Dwyer, G. S., T. Cronin, P. Baker, M.E. Raymo, H. Dowsett, and T. Correge, 1995, North Atlantic deep water temperature evolution during late Pliocene and late Quaternary climatic cycles. Science, v. 270, p. 1347-1351.

Oppo, D. W., M. E. Raymo, G. P. Lohmann, A. C. Mix, J. D. Wright, and W. B. Prell, 1995, A δ13C record of Upper North Atlantic Deep Water During the Past 2.6 myrs. Paleoceanography, v. 10, p. 373-394.

Raymo, M.E., D. Hodell, and E. Jansen, 1992, Response of deep ocean circulation to the initiation of northern hemisphere glaciation (3-2 M.Y.). Paleoceanography, v. 7, p. 645-672.

Raymo, M.E., W.F. Ruddiman, and D. Rind, 1990, Climatic effects of reduced Arctic sea ice limits in the GISS-II GCM. Paleoceanography, v. 5, p. 367-382.

Raymo, M.E., W.F. Ruddiman, N.J. Shackleton, and D. Oppo, 1990, Evolution of Atlantic-Pacific δ13C gradients over the last 2.5 m.y., Earth and Planetary Science Letters, v. 97, p. 353-368.

Raymo, M.E., W.F. Ruddiman, J. Backman, B.M. Clement, and D.G. Martinson, 1989, Late Pliocene variation in Northern Hemisphere ice sheets and North Atlantic deep circulation, Paleoceanography, v. 4, p. 413-446.



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Plio-Pleistocene millennial-scale climate variability

High sedimentation rate cores spanning late Pleistocene glacial cycles show that the Earth's climate has varied significantly and continuously on time scales as short as a few thousand years. Using proxy records from the early Pleistocene and late Pliocene, we have investigated whether such millennial-scale oscillations in climate occur under significantly different climate boundary conditions; specifically, during generally warmer climates. Using cores recovered on Leg 162, Raymo et al. (1998) documented the first early Pleistocene evidence for millennial-scale climate variability in proxy records of iceberg discharge and deep water chemistry and suggested that such variability may be a pervasive and long-term characteristic of Earth's climate. Over an 80-kyr interval of the mid-Pliocene "climatic optimum", when climate was warmer and global ice volume was less than today, Draut et al. (2003) showed that the amplitude and approximate recurrence interval of sub-orbital variations was comparable to those of Holocene and Marine Isotope Stage 11 (MIS 11) records. We concluded that, like the Holocene, the mid-Pliocene warm interval was a time of relative climatic stability---conditions warmer than today do not necessarily enhance millennial-scale variability in the climate system.

I've heard from a number of colleagues that Dennis Avery and Fred Singer have been citing our work on sub-orbital climate variability as evidence that the current global warming is part of a natural 1500 year climate cycle. This is not a conclusion we have drawn from our data.

Relevant Papers:

Becker, J., L.J. Lourens and M.E. Raymo, 2006, High-frequency climate linkages between the North Atlantic and the Mediterranean during marine oxygen isotope stage 100 (MIS100), Paleoceanography, v. 21, PA3002, doi:10.1029/2005PA001168.

Draut, A., M.E. Raymo, J. McManus, and D.W. Oppo, 2003, Climate stability during the Pliocene warm period, Paleoceanography, v. 18, No. 4, 1078, DOI 10.1029/2003PA000889.    

Raymo, M.E., K. Ganley, S. Carter, D. W. Oppo, J. McManus, 1998, Millennial-scale climate instability during the early Pleistocene epoch. Nature, v. 392, p. 699-702.

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Time scale development

In 2005 Lorraine Lisiecki and I recently published a 5.3 m.y. long oxygen isotope stack composed of 57 globally distributed benthic δ18O records which had been graphically aligned and orbitally-tuned to produce the best stratigraphic depiction of global ice volume/temperature history of deep ocean over the Plio-Pleistocene. From Lorraine's web site: "Paleoclimate research has recently produced an explosion of new paleoclimate time series, but fully utilizing the acquired data requires coordinated analysis of globally distributed records. The LR04 stack and its age model provide the paleoclimate community with an important stratigraphic tool, which could be used to facilitate comparison of widely distributed marine climate records." Note that this stack also provides a more useful identification and numbering of early Pliocene marine isotope stages (see discussion and figures in paper).

The stack data can be found here along with a table for conversion between this and earlier age models. The programs Lorraine developed to generate the stack can be found here along with Lorraine's composite depth software.

LR04 stack
The LR04 benthic δ18O stack [Lisiecki and Raymo, 2005]


In 2003, Bill Ruddiman and I proposed a new time scale for the Vostok ice core based on tuning the Vostok methane signal to mid-July 30N insolation. Using this time scale Bill later proposed his hypothesis that human activities have been increasing atmospheric carbon dioxide and methane levels for over 5000 years [Ruddiman, W. F., The Anthropogenic Greenhouse Era Began Thousands of Years Ago, Climatic Change, v. 61, p. 261-293 , doi:10.1023/B:CLIM.0000004577.17928.fa, 2003]. According to Bill's hypothesis, we may have already averted an ice age!

Timescale papers:

Lisiecki, L. and M. E. Raymo, 2009, Diachronous benthic δ18O responses during late Pleistocene terminations, Paleaoceanography, v. 24, PA3210, doi:10.1029/2009PA001732.

Lisiecki, L.E. and M.E. Raymo, 2005, A Plio-Pleistocene stack of 57 globally distributed benthic δ18O records, Paleoceanography, 20, PA1003, doi:10.1029/2004PA001071.    

Ruddiman, W.F., and M.E. Raymo, 2003, A methane-based time scale for Vostok ice, Quaternary Science Reviews, v. 22, p. 141-155.    

Channell, J.E.T., J. Labs, and M.E. Raymo, 2003, The Reunion subchronozone at ODP Site 981 (Feni Drift, North Atlantic), Earth Planetary Science Letters, v. 215, p. 1-12.   

Channell, J.E.T. and M.E Raymo, 2003, Paleomagnetic record at ODP Site 980 (Feni Drift, Rockall) for last 1.2 Myrs, Geochemistry, Geophysics, Geosystems, v. 4, DOI 10.1029/2002GC000440.   

Channell, J.E.T., A. Mazaud, P. Sullivan, S. Turner, and M. E. Raymo, 2002, Geomagnetic excursions and paleointensities in the Matuyama Chron at ODP Sites 983 and 984 (Iceland Basin), J. of Geophysical Research, v. 107, 10.1029/2001JB000491.    

Hodell, D., J. Curtis, F. Sierro, and M. E. Raymo, 2001, Correlation of Late Miocene-to-early Pliocene sequences between the Mediterranean and North Atlantic. Paleoceanography, v. 16, p. 164-178.    

Raymo, M.E., 1997, The timing of major climate terminations. Paleoceanography, v. 12, p. 577-585.    

Raymo, M.E. and M. Horowitz, 1996, Organic carbon paleo-pCO2 and marine-ice core correlations and chronology. Geophys. Res. Letts., v. 23, p. 367-370.

Berggren, W., F. Hilgen, C. Langereis, D. Kent, J. Obradovich, I. Raffi, M.E. Raymo and N.J. Shackleton, 1995, Late Neogene chronology: New perspectives in high resolution stratigraphy. Geol. Soc. Amer. Bull., v. 107, p. 1272-1287.

Raymo, M.E., W.F. Ruddiman, J. Backman, B.M. Clement, and D.G. Martinson, 1989, Late Pliocene variation in Northern Hemisphere ice sheets and North Atlantic deep circulation, Paleoceanography, v. 4, p. 413-446.

Weaver, P.P.E., J. Backman, J.G. Baldauf, J. Bloemendal, H. Manivit, E.M. Pokras, M.E. Raymo, L. Tauxe, J-P. Valet, A. Cheptow-Lusty, and G. Olafsson, 1989, Biostratigraphic synthesis, Leg 108, eastern equatorial Atlantic. Proceedings of the Ocean Drilling Program, (Part B), v. 108, p. 455-462.


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Uplift-Weathering Hypothesis

Himalayas        In 1988, Bill Ruddiman, Flip Froelich and I published the first of an eventual series of papers (listed below) proposing that the late Cenozoic cooling of climate, the Ice Age, was caused by enhanced chemical weathering and consumption of atmospheric CO2 in the mountainous regions of the world, in particular the Himalayas. About 40 to 50 million years ago, the Indian subcontinent collided with the underside of Asia. This collision, which continues to this day, resulted in the uplift of the Himalayas and the formation of the Tibetan Plateau, the largest geographic feature on the Earth's surface (above the waves). The uplift of the plateau would likely have intensified the Asian monsoon (see a series of papers by Ruddiman and Kutzbach) and this rainfall, combined with the steep relief and high mechanical erosion rates in the Himalayas, may have resulted in dramatically higher chemical weathering rates in the region. It is these chemical weathering reactions that, over 40 million years, would have consumed atmospheric CO2 thus weakening the global greenhouse effect and leading to the growth of continent-spanning ice sheets at both poles.

        Raymo et al. (1988) originally proposed that the marine strontium isotope record showed that chemical weathering rates had increased over the Cenozoic, but by 1992 this record was shown to be ambiguous and hence not suitable for testing the hypothesis. A major criticism of the hypothesis was that chemical weathering rates could not increase in the absence of enhanced metamorphic delivery of CO2 to the atmosphere, otherwise CO2 would be completely stripped from the atmosphere within a few hundred thousand years and the Earth would become a frozen "snowball" planet. We agreed that a negative feedback was needed to stabilize atmospheric CO2 levels and argued that this feedback may have operated through the organic carbon subcycle.

       Hopefully, new paleo-CO2 and silicate weathering proxies now being developed, along with high resolution geochemical records of the last 60 Ma, will help unravel the secrets of Cenozoic climate change. Did silicate weathering rates increase or decrease since the Eocene?!


Uplift-related links:

A book "Tectonic Uplift and Climate Change", edited by Bill Ruddiman, is aimed at scientists and graduate students and contains many interesting and useful papers.

PBS NOVA made a documentary about our work. If you'd like a DVD copy of "Cracking the Ice Age" send me an email.


Some articles in the popular press:

Paterson, D. (1993) "Did Tibet cool the world?" New Scientist. v. 139 No. 1880, pp 29-33.

Wilson, J. (1999) "The Big Chill Solved: the mystery of the first ice age", Popular Mechanics.

Watson, T. (1997) "What Causes Ice Ages?", U.S. News and World Report, August 18.


Our papers on uplift-weathering hypothesis:

Raymo, M.E., W.F. Ruddiman, and P.N. Froelich (1988) Influence of late Cenozoic mountain building on ocean geochemical cycles. Geology, v. 16, p. 649-653.

Raymo, M.E. (1991) Geochemical evidence supporting T.C. Chamberlin's theory of glaciation. Geology, v. 19, p. 344-347.

Raymo, M.E. and W.F. Ruddiman (1992) Tectonic forcing of late Cenozoic climate. Nature, v. 359, p. 117-122.

Raymo, M.E. and W.F. Ruddiman (1993) Cooling in the late Cenozoic-Scientific Correspondence. Nature, v. 361, p. 123-124.

Raymo, M.E. (1994) The initiation of Northern Hemisphere glaciation. Annual Reviews of Earth and Planetary Science, v. 22, p. 353-383.

Raymo, M.E. (1994) The Himalayas, organic carbon burial, and climate in the Miocene. Paleoceanography, v. 9, p. 399-404.
Raymo, M.E. (1997) Carbon cycle models: how strong are the constraints? In: Global Tectonics and Climate Change (eds. W.F. Ruddiman and W. Prell), Plenum Press, p. 368-382.

Ruddiman, W.F., M.E. Raymo, W. Prell, and J.E. Kutzbach (1997) The uplift-climate connection: a synthesis. In: Global Tectonics and Climate Change (eds. W.F. Ruddiman and W. Prell), Plenum Press, p. 471-515.

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Neogene ocean and climate history

       Unraveling the dynamics of the Northern Hemisphere glaciation (NHG) in the late Pliocene is necessary if we are to understand the climate transition from a greenhouse to an icehouse world. Extracting the ice volume signal from marine oxygen isotope (δ18O) records corrupted with "temperature noise" can be accomplished using statistical time series analysis. Mudelsee and Raymo [2005] use 45 δ18O records from benthic and planktonic foraminifera and globally distributed sites to reconstruct the dynamics of NHG initiation. We compare δ18O amplitudes with those of temperature proxy records and estimate a global ice volume-related increase of 0.4 per mil, equivalent to an overall sea level lowering of 43 m. We find the NHG started significantly earlier than previously assumed, as early as 3.6 Ma, and ended at 2.4 Ma. This long-term increase points to slow, tectonic forcing such as closing of ocean gateways or mountain building as the root cause of the NHG.

       Did the uplift of the Panamanian Isthmus influence ocean circulation and global climate? As part of an ongoing effort to reconstruct the Neogene history of thermohaline circulation, Nisancioglu et al. [2003] used the MIT Ocean General Circulation Model to test the response of ocean circulation to the shoaling of the Central American Isthmus. We found that significant amounts of deep water formed in the North Atlantic prior to the closure of the Central American Seaway (CAS) although the circulation pattern contrasts with the modern ocean. In the upper layers of the CAS there is strong geostrophic flow from the Pacific to the Atlantic, controlled by the pressure difference across the seaway. At depth, a significant amount of NADW passes through the CAS to the deep Pacific traversing the basin from east to west in a relatively narrow zonal jet before becoming a southward flowing boundary current in the western Pacific (red arrows in figure below). This implies that Miocene sediment records from the western Pacific Ocean could have been influenced by relatively young NADW.

CAS_model


Papers on Neogene climate history and the initiation of northern hemisphere glaciation:

Mudelsee, M., and M.E. Raymo, 2005, Slow dynamics of the Northern Hemisphere Glaciation, Paleoceanography, 20, PA4022, doi:10.1029/2005PA001153.

Nisancioglu, K. H., M. E. Raymo, and P. H. Stone, 2003, Reorganization of Miocene Deep Water Circulation in response to the shoaling of the Central American Seaway, Paleoceanography, v. 18, DOI 10.1029/2002PA000767.

Lawrence, K. T., T. D. Herbert, C. M. Brown, M. E. Raymo, and A. M. Haywood, 2009, High amplitude variations in North Atlantic sea surface temperature during the early Pliocene warm period, Paleoceanography, v. 24, PA2218, doi:10.1029/2008PA001669.

Raymo, M.E., B. Grant, M. Horowitz, and G. H. Rau, 1996, Mid Pliocene warmth: stronger greenhouse and stronger conveyor. Marine Micropaleontology, v. 27, p. 313-326.

Dwyer, G. S., T. Cronin, P. Baker, M.E. Raymo, H. Dowsett, and T. Correge, 1995, North Atlantic deep water temperature evolution during late Pliocene and late Quaternary climatic cycles. Science, v. 270, p. 1347-1351.

Raymo, M.E., 1994, The initiation of Northern Hemisphere glaciation. Annual Reviews of Earth and Planetary Science, v. 22, p. 353-383.

Raymo, M.E., 1992, Global climate change: a three million year perspective. In: Kukla, G. and Went, E. (eds.), Start of a Glacial, Proceedings of the Mallorca NATO ARW, NATO ASI Series I, Vol. 3, Springer-Verlag, Heidelberg, p. 207-223.

Raymo, M.E., W.F. Ruddiman, and D. Rind, 1990, Climatic effects of reduced Arctic sea ice limits in the GISS-II GCM. Paleoceanography, v. 5, p. 367-382.

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ODP Leg 162: North Atlantic Gateways


Jansen, E., Raymo, M.E., Blum, P., et al., 1996. Proceedings of the Ocean Drilling Program, Initial Reports, vol. 162: College Station, TX (Ocean Drilling Program). A link to leg-related citations can also be found here.

Raymo, M.E., Jansen, E., Blum, P., and Herbert, T.D., Eds., 1999, Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 162: College Station, TX (Ocean Drilling Program).


162 Map
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