Raymo - current projects

Ph.D., Columbia University
Research Professor, Dept. of Earth Sciences, Boston University
685 Commonwealth Avenue • Boston • Massachusetts • 02215
e-mail: raymo@bu.edu

Home
Current Projects
Data/Figure Archives
Publications/CV
Foraminifera Taxonomy
Links/Misc.

Current Projects

Milankovitch climate dynamics
Thermohaline circulation of the Atlantic Ocean
Plio-Pleistocene millennial-scale climate variability
Time scale development
Neogene ocean and climate history
OPD Leg 162
Uplift-Weathering Hypothesis

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 loose scientific consensus has emerged that variations in ice volume at precession (~23 kyr) and obliquity (41 kyr) frequencies appear to be directly forced and coherent with northern summer insolation while the ~100 kyr 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).

Benthic δ¹⁸O record from DSDP Site 607 in the North Atlantic (solid line) plotted to a paleomagnetic time scale. The magnetic field reversals are marked, as well as the transition from a dominant 41 kyr to a 100 kyr world. B=Brunhes; M=Matuyama; J=Jaramillo; TOld=top of Olduvai; G=Gauss. Also shown is orbital obliquity (red dashed line).

41 KYR WORLD

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; no ice sheet-climate model that we are aware of has been successful in reproducing 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.

Power spectra of Site 607 δ¹⁸O record (a) plotted using a paleomagnetic time scale. Power spectra of the benthic δ¹⁸O record of ODP Site 846 [(b) Mix et al., 1995] plotted to orbitally tuned time scale of Shackleton et al. [1990].

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 propose 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. In 1997, I suggested that the 100-kyr cycle is caused by skipping of higher frequency beats that results in the bundling of either 4 or 5 precession cycles (Raymo, 1997, Paleoceanography; see also Ridgwell, Watson, and Raymo, 1999). More recently, Huybers and Wunsch (2005) proposed that it was the bundling of 2 or 3 obliquity cycles that resulted in an average 100 kyr periodicity. Verification of these competing hypotheses requires accurately dated climate proxies. Recently, Kenji Kawamura has produced new chronologies 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, with phase modulation by obliquity and ice volume.

Here is a link to Kenji's abstract that he presented at Fall 2006 AGU.

Recent collaborators on these projects are Lorraine Lisiecki (BU), Kerim Nisancioglu (Bjerknes Centre for Climate Research), Eli Tziperman (Harvard U.), and Kenji Kawamura (Tohoku U.).

Recent papers:

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.

back to top

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 (NADW; total volume flux estimated at 20 Sv).

Locations of DSDP and ODP cores used in this study. Paths of major deep water flows are indicated by arrows.

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.

I am currently collaborating with Delia Oppo (WHOI) and Jerry McManus (WHOI) on this project.

A recent publication:

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.

back to top

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 evidence for millennial-scale climate variability, in proxy records of iceberg discharge and deep water chemistry, from sediments older than the late Pleistocene and suggest 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.

Currently, we are looking at various timeslices throughout the LP/EP to study the response of iceberg discharge and thermohaline circulation on centennial to millennial timescales as well millennial-scale climate linkages between the North Atlantic and Mediterranean Region (Becker et al., in press).

Finally, 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 and I hope they are not implying we endorse this view in any way. In my opinion, the pronounced warming of the last few decades is almost certainly due to anthropogenic alterations of the composition of the atmosphere due primarily to the combustion of fossil fuel.

I am currently collaborating with Delia Oppo (WHOI), Jerry McManus (WHOI), and Julia Becker (U. of Cardiff) on these projects.

Millenial-scale climate change 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.

back to top

Time scale development

Lorraine Lisiecki (BU) and I recently published a 5.3 m.y. long oxygen isotope stack composed of 57 globally distributed benthic δ¹⁸O records which have 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.

Congratulations to Lorraine for being awarded the prestigious Joukowsky Dissertation Award from Brown University as well as a NOAA Global Change postdoctoral fellowship for 2005-2007.

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 30°N insolation. This time scale provided the basis for Bill's 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.

Recent papers:

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.

Other time scale-related papers:

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.

back to top

Neogene ocean and climate history

Unraveling the dynamics of the Northern Hemisphere glaciation (NHG) in the Pliocene is a key step toward a quantitative theory of 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.

Manfred Mudelsee currently works at the University of Leipzig. Please contact him for more information about this study.

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

*************

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 and provides a framework for the interpretation of geochemical tracer data.

Kerim Nisancioglu and Peter Stone were collaborators on this project. Contact K. Nisancioglu for more information on this study.

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.

*************

The Cenozoic history of the calcite compensation depth (CCD) for the major basins of the world has also been reconstructed using available DSDP and ODP databases. The abrupt shoaling of the Pacific CCD in the middle Miocene may be related to the shoaling of the Panamanian Isthmus which prevented young North Atlantic deep water from entering the Pacific basin.

Susan Carter (Harvard) collaborated on this project.

Other Neogene ocean and climate history papers (see also Uplift Hypothesis page):

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., 1994, The Himalayas, organic carbon burial, and climate in the Miocene. Paleoceanography, v. 9, p. 399-404.

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.

back to top