U.S. Geological Survey


Middle Pliocene Paleoenvironmental Reconstruction:  PRISM2

By Harry J. Dowsett1, John A. Barron2, Richard Z. Poore1, Robert S. Thompson3, Thomas M. Cronin1, Scott E. Ishman4 and Debra A. Willard5

1U.S. Geological Survey, 955 National Center, Reston, VA 20192
2U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA  94025
3U.S. Geological Survey, Box 25046, Mail Stop 919, Denver, CO 80225
4Department of Geology, Southern Illinois University, Carbondale, IL  62901
5U.S. Geological Survey, 926A National Center, Reston, VA 20192

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[This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards (or   with the North American Stratigraphic Code).  Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.]

1.  Introduction and Background

Anthropogenic greenhouse gas emissions and modification of land surfaces are expected to cause the earth廣 climate to warm (IPCC, 1995).  However the amount and details of the warming are still highly uncertain.  Identifying and predicting any human related changes must take into account natural climate variability and the complex interactions of the different components of the Earth廣 climate system. As part of  the USGS  Global Change Research effort,   the PRISM (Pliocene Research, Interpretation and Synoptic Mapping) Project has documented the characteristics  of middle Pliocene climate on a global scale.  The middle Pliocene was selected for detailed study because it spans the transition from relatively warm global climates when glaciers were absent or greatly reduced in the Northern Hemisphere to the generally cooler climates of the Pleistocene with expanded Northern Hemisphere ice sheets and prominent glacial-interglacial cycles.

The PRISM Project had two primary goals.  The first was to identify and characterize the nature and variability of climate during this time of past global warming as an indication of how the Earth might respond to future warming.  The second goal was to develop a series of global scale, quantitative datasets for use in experiments to model climate and environmental conditions during the mid Pliocene.   The Pliocene reconstruction is being used  to test the ability of climate models to simulate past warmer conditions on earth and to provide insights into the mechanisms and effects of global warming (Dowsett et al., 1992; Chandler et, al., 1994; Sloan et al., 1996; Haywood et al., 1999).

The purpose of this report is to document and explain the  PRISM2 mid Pliocene reconstruction.  The PRISM2 reconstruction consists of a series of 28 global scale data sets (Table 1) on a 2° latitude by 2° longitude grid.  As such, it is the most complete and detailed global reconstruction of climate and environmental conditions  older than the last glacial.

PRISM2 evolved from a series of studies that summarized conditions at a large number of marine and terrestrial sites and areas (eg. Cronin and Dowsett, 1991; Poore and Sloan, 1996).  The first global reconstruction of mid Pliocene climate (PRISM1)  was based upon 64 marine sites and 74 terrestrial sites and included data sets representing annual vegetation and land ice, monthly sea surface temperature (SST) and sea-ice, sea level and topography on a 2°x2° grid  (Dowsett et al. (1996) and Thompson and Fleming (1996)).  The current reconstruction (PRISM2) is a revision of PRISM1 that incorporates several important differences:

1)  Additional sites were added to the marine portion of the reconstruction to improve previous coverage.  Sites from the Mediterranean Sea and Indian Ocean are incorporated for the first time in PRISM2.

2)  All Pliocene sea surface temperature (SST) estimates were recalculated based upon a new core top calibration to the Reynolds and Smith (1995) adjusted optimum interpolation (AOI) SST data set.  This reduced some of the problems previously encountered when different fossil groups were calibrated to different modern climatologies (Climate / Long Range Investigation Mapping and Predictions [CLIMAP], Goddard Institute for Space Sciences [GISS], Advanced Very High Resolution Radiometer [AVHRR], etc.).

3)  PRISM2 uses a +25m rise in sea level for the Pliocene (PRISM1 used +35m), in keeping with much new data that has become available.

4)  Although the change in global ice volume between PRISM1 and PRISM2 is minor, PRISM2 uses model results from Prentice (personal communication) to guide the areal and topographic distribution of Antarctic ice.  This results in a more realistic Antarctic ice configuration in tune with the +25m sea level rise.

All data sets are available by contacting hdowsett@usgs.gov  or visiting:

2.  PRISM Time Slab Concept

The PRISM2 reconstruction is a global synthesis of a period of relatively warm and stable climate lying between the transition of oxygen isotope stages M2/M1 and G19/G18 (Shackleton et al., 1995) in the middle part of the Gauss Normal Polarity Chron.  The reconstruction spans the interval of 3.29 Ma to 2.97 Ma (geomagnetic polarity time scale of Berggren et al., 1995) (Figure 1).  Previous PRISM reconstructions used the geomagnetic polarity time scale of Berggren et al. (1985) which dated the PRISM time slab at  3.15 to 2.85 Ma.  This interval occurs prior to the 2.5-2.4 Ma oxygen isotope excursion which represents a major climate step toward modern conditions (northern hemisphere ice volume increased, polar fronts were strengthened and glacial-interglacial variation intensified) (Sancetta and Silvestri, 1986; Raymo et al., 1989; Hodell and Ciesielski, 1991).
Fig. 1

Figure 1.  PRISM2 time slab correlated to the geomagnetic polarity time scale of Berggren et al. (1995) and the benthic oxygen isotope record from ODP Site 846 (Schackleton et al., 1995).  Numbers in parenthesis adjacent to magnetic polarity indicate ages of subchron boundaries according to Berggren et al. (1985).  Modern isotopic value from Schackleton et al. (1995) shown as vertical dashed line. 

While the interval of time between 3.29 and 2.97 Ma (PRISM time slab) is distinct in that mean conditions were different than the intervals immediately surrounding it, there is a high degree of variability within the time slab (Dowsett and Poore, 1991; Barron, 1992a; Hodell and Venz, 1992; Shackleton et al., 1995) (Figure 1).  Other than glacial stages KM2 (ca. 3.12 Ma) and G20 (ca. 3.01 Ma), benthic foraminiferal oxygen isotope values were either equal to or isotopically lighter than those of today (Shackleton and others, 1995).   Nevetheless, as emphasized by Tiedemann and others (1994), the 41-kyr period of Earth廣 obliquity dominates the Pliocene climate record.   For marine data points that were generated from time series studies, we have adopted a strategy whereby we develop an estimate of mean "interglacial" conditions within the time slab.  This minimizes the problems associated with point to point correlation between data sites separated by large geographic distances.  The late Pleistocene analog would be to provide a single SST value representing average winter and summer interglacial conditions at each site (e.g., average SST of isotope stages 5, 7 and 9).

The 3.29 to 2.97 Ma interval is long enough to be reliably identified and correlated between marine sequences independent of climatic characteristics because of its proximity to a number of biostratigraphic and magnetostratigraphic events (Berggren et al., 1985; 1995; Dowsett, 1989a,b).  Deep sea records and, to varying degrees, ocean margin records, can be correlated with some confidence to this interval.  Many of our terrestrial records come from short sequences that rely on limited radiometric dates and magnetostratigraphy for chronology.  The sparseness of long terrestrial time-series with multiple age control points makes identification of high frequency variability and integration of our terrestrial paleoclimate estimates into our time-slice interval less certain than our marine estimates.  This is a problem with all terrestrial paleoclimate reconstructions.

In the remainder of this report we use the terminology "3 Ma" and "middle  Pliocene" to indicate our time interval.

3.  Materials and Methods

The distribution of the 151 sites (Tables 2 and 3) from which fossil data were analysed for PRISM2 are shown in Figures2Aand2B. The terrestrial data locations have not changed from PRISM1.  The marine reconstruction benefits from the addition of sites in the Medditerranean, Indian Ocean, Southwest Pacific Ocean, and North Pacific Ocean (Figure 2A and Table 2).  These sites were chosen to fill gaps in our coverage.

3.1  Recalibration of SST estimates

A major change between this and the PRISM1 reconstruction is the recalibration of all modern marine data to the modern SST of Reynolds and Smith (1995).

Analysis of the CLIMAP modern data set (see Prell, 1985) and the modern SST data used by the Goddard Institute for Space Science (GISS) model showed significant differences with anomalies sometimes exceeding the magnitude of estimated Pliocene temperature change.  Because of this and inter-group calibration problems, we recalibrated all modern samples and all Pliocene localities, using the 1°x1° SST of Reynolds and Smith (1995).  Foraminifer transfer functions GSF18 and GSF21 were recalibrated and their resultant coefficients are reported in Dowsett and Verardo (in prep.).   All foraminifer, diatom and ostracode estimates of SST are now based upon the same modern temperature field.


Figure 2A.  Marine localities used in this study.

Click on figure for a high-quality version in a new window.

3.2 Foraminifers

Middle Pliocene foraminifers were analyzed from 34 sites by a number of workers (Table 2).  These sites are skewed toward the Atlantic (60%) but cover all major ocean basins.  In many cases existing magnetobiostratigraphy was sufficient to create age models but in some instances new biostratigraphic analysis was employed to help scale the sequences.  Sea-surface temperatures were estimated from these sites using factor analytic transfer functions, modern analog technique (MAT), or semiquantitative comparison to modern faunas (Dowsett and Poore, 1990, 1991; Dowsett, 1991; Dowsett et al., 1996; Dowsett and Robinson, 1998; Poore, 1999).

3.3 Diatoms

Middle Pliocene diatoms were counted by Barron (1995, 1996a, b) in 16 Southern Ocean  and 6 North Pacific deep sea-cores.  Age models for these cores were based on existing magnetostratigraphy and both published and refined diatom biostratigraphy (Barron, 1996a, b).  Diatom based SST estimates for the Southern Ocean were determined by estimating the relative position of the Antarctic Polar Front (APF) relative to the various sites.  North Pacific SST was estimated using equations generated by Barron (1995) based upon the relative ratios of key taxa.

3.4 Ostracods

Middle Pliocene ostracodes were counted from 12 sites in the Northern Hemisphere including Central America, the eastern United States coastal Plain, Tjornes, Iceland, Meighen Island, Alaskan Arctic coastal Plain, North Sea, and Japan.  In each region age models were constructed using  magnetobiochronology and shallow sea bottom temperatures were quantitatively estimated by transfer function, MAT, or environmental preference matching (Cronin and Dowsett, 1990; Cronin, 1991a,b; Wood et al., 1994).

3.5 Pollen and Plants

Information on middle Pliocene vegetation was compiled from fossil pollen and plant macrofossil data from over 75 sites (Table 3, Figure 2B) from all of the continents of the world (Thompson and Fleming, 1996).  Chronological controls for these sites were provided by a variety of methods, including radiometric dating, tephrochronology, and biostratigraphy.  Quantitative estimates of past terrestrial climates are available from very few sites, and thus most middle Pliocene paleoclimates on land are expressed as qualitative estimates of changes in temperature and precipitation relative to the present-day climates at the study sites.


Figure 2B.  Terrestrial localities used in this study.

Click on figure for a high-quality version in a new window.

4.  Data Sets

The PRISM2 reconstruction is presented as a series of matrices (see Table 1), each containing 90 rows and180 columns, thereby representing the earth at a resolution of 2° latitude by 2°longitude.  Each cell in this grid is designated either land or water, based on which element comprises the majority (>50%) of the cell.  If water, a cell has either a sea surface temperature or is covered by sea ice ( -1.8°C).  If a cell is designated land, it contains one of seven land cover categories (desert, tundra, grassland, deciduous forest, coniferous forest, rain forest or ice).  In addition, land cells are given a topographic elevation.   Each data set is discussed below.

4.1  Land-Sea Distribution (Sea Level)

The initial PRISM 8x10  and PRISM1 2x2 reconstructions used a +35m sea-level rise for determining land-sea elevations  (Dowsett et al., 1994; PRISM, 1995).  For PRISM2 we have adopted a more conservative +25m sea-level rise (Figure 3) in keeping with the conclusions of Kennett and Hodell (1993).  Based upon estimates of the sea level rise equivalent of various ice masses, a 25 m rise in sea level requires significant reduction of Greenland and Antarctic ice volume.

Figure 3

Figure 3.  Emergent land areas during the mid Pliocene plotted on a 2x2 grid. 

Elevational data from the ETOPO5 five-minute topographic grid (Edwards, 1992) were used to
provide the basis for constructing a middle Pliocene land-sea distribution grid.  In this process, we determined whether the elevation of each ETOPO5 point in a given 2° x 2° cell was below, at, or above the 25 m above present-day sea level.  If the number of ETOPO5 points at or above the 25 m elevation exceeded those below that elevation, then the 2° x 2° was determined to be land during the middle Pliocene.  If the number of ETOPO5 points below the +25 m sea level exceeded those at or above this elevation, then the 2° x 2° cell was declared to be covered by water.

The digital data for sea level are provided in Appendix 1, where "1" indicates land and "0" indicates water.

4.2  Sea Surface Temperatures

Table 2 lists 77 marine localities/sections that were used for our SST reconstructions.  Included are the modern February and August SST廣 at the sites (data from Reynolds and Smith, 1995), estimated Pliocene SST廣 and the resulting anomalies (Pliocene minus Modern) of these estimates used in the PRISM2 and previous PRISM1 reconstructions.  A  reference is made to the source of the SST data, the method used (quantitative, semi-quantitative, qualitative) in making the estimates, the average temporal resolution and an indication as to whether or not the mid Pliocene section was constrained by magnetic stratigraphy.  The distribution of control points for the reconstruction is uneven and primarily  reflects the availability of suitable material for study.  Details of the techniques are given in Dowsett and Poore (1991), Dowsett (1991), Cronin and Dowsett (1991), Dowsett and Robinson (1998). Barron (1996a,b), and Dowsett and Verardo (in prep).  When available,  estimates published by other  workers were used to augment and cross check the estimates derived by the PRISM2 study.

Several new data points have been added since PRISM1.  Estimates of Mediterranean SST were derived from planktic assemblages recovered on Sicily and Crete (Spaak, 1983).  These assemblages, along with data from Thunnell (1979) suggest a positive deviation in temperatures during the mid Pliocene relative to today.   Middle Pliocene samples from ODP Site 722 in the Indian Ocean were analysed and indicate a minor warming of +1 to +2°C.  South Pacific estimates now include a sequence taken within the Wanganui Basin of New Zealand.  While there is little evidence for paleotemperature change along the west coast of South America, the southwestern Pacific shows temperature anomalies of +2 to +3°C relative to today.

modern august

[A] Modern August SST - Modern Vegetation

Pliocene August

[C] Pliocene August SST - Pliocene Vegetation

modern february

[B] Modern February SST - Modern Vegetation

Pliocene February

[D] Pliocene February SST - Pliocene Vegetation

Figure 4.  A,B  Modern SST (after Reynolds and Smith, 1995) and vegetation (modified after Matthews, 1985).  C,D  Pliocene SST and vegetation.  Sea ice distributions shown in gray; vegetation legend.

Click on maps to view high-quality versions in new windows.

To create a global data set,  SST anomalies, determined by calculating differences between Pliocene estimates and modern temperatures (Figure 4) at the location of each site, were plotted as individual points on a 2°x2° grid representing the Earth.  Modern SST contours served as a rough guide in the drawing of mid Pliocene SST contours around the control points, because it was assumed that the general pattern of modern oceanic surface current systems was present in the mid Pliocene.   Boundaries between anomaly bands were smoothed so as to make even temperature gradients.  Finally, this smoothed, contoured anomaly field was added to the modern SST of Reynolds and Smith (1995) to create a mid Pliocene SST map (Figure 4).

Because we estimated winter and summer SST (February and August), we produced two primary Pliocene SST maps in this fashion (Figure 4).  The remaining 10 months of the year were constructed by fitting a sine curve to the February and August SST estimates (Dowsett et al., 1996).

On Appendices 2.1 - 2.12, each cell in a 2°x2° global grid designated as water (see section 4.1) is given a SST in degrees Celsius.  Cells designated land are given the code -999.  Sea-ice  is designated with SST set to -1.8°C.

4.3  Sea-Ice Distribution

Northern Hemisphere sea-ice distribution is unchanged from PRISM1 except for adjustments to accommodate the newer +25m sea level. (see Dowsett et al., 1996).  Southern Hemisphere sea-ice is slightly modified from PRISM1 (Barron, 1996a,b).  The PRISM2 August (peak winter) sea ice for the mid Pliocene has been arbitrarily placed at between 4 and 6° of latitude further to the south than the present day (Figure 4).  To obtain a  Pliocene winter sea ice coverage we started with the average summer sea ice coverage derived from the 14  year monthly sea-ice NOAA satellite data (Schweitzer, 1995).   The modern average summer coverage was  incorporated into a 2 x 2 degree matix and modified to fit the + 25 meter sea-land boundary and the Pliocene sea surface temperature projections discussed in the previous section (Figure 4).

The  model experiments require a sea ice configuration for each of the twelve months of the year.   In order to create 12 sets of sea-ice distribution we took  the winter and summer end-member distributions for each polar area and then used the modern monthly average sea-ice data compiled in  Schweitzer, (1995) and the PRISM2 Pliocene monthly sea surface temperature projections to guide modification of the  winter and summer end- members into  12 monthly intervals  of sea-ice coverage.

Twelve 2°x2° global grids are provided with estimated average monthly sea-ice distributions (Appendices 3.1 - 3.12).  Sea ice is designated with "1", land with "8" and water without sea-ice as "0".  Sea-ice can also be read off the SST fields where cells with SST set to -1.8°C are designated as sea-ice.

4.4  Land Ice Distribution

In the PRISM2 reconstruction, ice volume and areal coverage on Greenland was reduced by 50%.  All other Northern Hemisphere ice (Iceland and mountain glaciers) were removed.  The PRISM2 reconstruction uses model results from Prentice (personal communication) to guide the areal and topographic distribution of Antarctic ice.  This results in a more realistic distribution of ice.

The areal distribution of ice can be read from Appendix 5 which designates vegetation and land cover categories for each cell in the 2°x2° global grid (see section 4.6).

4.5  Land Surface Topography

As discussed in Thompson and Fleming (1996), Pliocene elevations were apparently lower than present-day in the western Cordillera of western North America and in the Andes of South America (Figure 5).  The reduction in the size of the Greenland and Antarctica Ice Sheets also resulted in a net reduction in elevation in those areas.  On the other hand, data discussed in Thompson and Fleming (1996) suggest that the east African rift zone was elevationally higher than at present.  Following these authors, we set Pliocene elevations in parts of North and South America at half of their modern values, and the elevation of portions of the Greenland Ice Sheet were reduced.  The elevations of Antarctica were taken directly from Prentice (personal communication).  The elevations of grid points in the east African rift zone were set at 500 m above those on the modern grid.

Figure 5

Figure 5.  Pliocene topography.  Contour Interval 500m.

Appendix 4 provides elevation in meters above sea level for each cell in the 2°x2° global grid.

4.6  Vegetation Distribution

PRISM2 vegetation is identical to that in PRISM1 (see Thompson and Fleming,1996).  We use seven land cover categories that are a simplification of the 22 land cover types of Matthews (1985).  The distribution of vegetation or land cover categories can be found in Figure 4 and Appendix 5 where cells designated 0 = water, 1 = desert, 2= tundra, 3= grassland, 6= deciduous forest, 7= coniferous forest, 8= rainforest, and 9= land ice ( See Figure 4).

5.  Summary

The PRISM2 reconstruction is an internally consistent  global summary of many important components of the earth廣 climate and surface conditions during the mid Pliocene.  It is the most complete summary of the earth廣 climate and environmental condition beyond the last interglacial and provides an opportunity to test and refine our ability to decipher past environments and model climates that are different from the present.

Important features of PRISM2 compared to modern are:

1.  Greatly reduced continental ice volume with a small ice cap on Greenland being the only continental ice in the Northern Hemisphere.

2.  Greatly reduced sea-ice with the Arctic being seasonally ice free.

3.  Sea level change of + 25 meters which requires substantial reduction of the Antarctic Ice Sheet.

4.  Increased SST in high latitudes and unchanged SST in low latitudes.  Warming is most pronounced in the northeastern North Atlantic sector.

5.  Expansion of evergreen forests to the margins of the Arctic Ocean,  a reduction of desert area in equatorial Africa and essential elimination of polar desert and tundra regions in the Northern Hemisphere.  A small amount of deciduous vegetation occurred at the edge of the Antarctic continent.

6.  Acknowledgements

Earlier versions of this text were read and reviewed by Mark Chandler (NASA), Thomas Crowley (Texas A&M) and Milan Pavich (USGS).  We thank these individuals for their comments which greatly improved the final product.  Over the course of this study scores of researchers from around the world kindly provided their time, data and expertise.  Any attempt to list these individuals would be impossible.  To all of you, both critics and supporters, we thank you.  It was your input that helped make the PRISM2 reconstruction possible.  The PRISM effort was supported by the USGS Global Change Program.  The marine reconstruction would not have been possible without the cooperation of the Ocean Drilling Program.

7.  References

This section contains all references cited in the text as well as publications related to data or interpretations used in the reconstructions.

Adam, D.P., 1994.  Pliocene pollen data set dynamics:  Tulelake, California and Lost Chicken Mine, Alaska.  In:  Thompson, R.S. (Editor), Pliocene terrestrial environments and data/model comparisons.  U.S. Geological Survey Open-File Report 94-23: 6-10.

Adam, D.P., Bradbury, Rieck, H.J., and Sarna-Wojcicki, A.M., 1990.  Environmental Changes in the Tulelake basin, Siskiyou and Modoc Counties, California, from 3 to 2 million years before present.  U.S. Geological Survey Bulletin 1933: 1-13.

Adam, D.P., Sarna-Wojcicki, A.M., Rieck, H.J., Bradbury, J.P., Dean, W.E., and Forester, R.M., 1989.  Tulelake, California:  the last 3 million years.  Palaeogeography, Palaeoclimatology, Palaeoecology, 72: 89-103.

Ager, T.A., 1994.  Terrestrial palynological and paleobotanical records of Pliocene age from Alaska and Yukon Territory.  In:  Thompson, R.S. (Editor), Pliocene terrestrial environments and data/model comparisons.  U.S. Geological Survey Open-File Report 94-23:  2-3.

Akhmetiev, M. A., 1991. Flora, vegetation, and climate of Iceland during the Pliocene. Pliocene Climates of the Northern Hemisphere:   abstracts of the Joint US/USSR Workshop on Pliocene Paleoclimates, Moscow, USSR, April, 1990. U.S. Geological Survey Open-File Report 91-447:  8-9.

Akhmetiev, M. A., G. M. Bratoeva, Giterman, R.E., Golubeva, L.V., and Moiseeya, A.I., 1978.  "Late Cenozoic stratigraphy and flora of Iceland." Transactions, Academy of Sciences of the USSR 316.

Andersson, C., 1997.  Transfer function vs. modern analog technique for estimating Pliocene sea surface temperatures based on planktic foraminiferal data, western equatorial Pacific Ocean.  Journal of Foraminiferal Research, 27: 123-132.

Axelrod, D.I., 1944.  The Sonoma flora (California).  Carnegie Institute of Washington Publication, 553: 167-206.

Ballog, R.A., and Malloy, R.E., 1981.  Neogene palynology from the southern California continental borderland, Site 467, Deep Sea Drilling Project Leg 63.  In:  Yeats, R.S., Haq, B.U., et al. (Editors), Initial Reports of the Deep Sea Drilling Project, 28:  565-576.  U.S. Government Printing Office, Washington, D.C.

Barron, J.A., 1992a. Pliocene paleoclimatic interpretation of DSDP Site 580 (NW Pacific) using diatoms. Marine Micropaleontology, 20:23-44.

Barron, J.A., 1992b. Paleoceanographic and tectonic controls on the Pliocene diatom record of California. In Tsuchi, R., and Ingle, J.C., Jr., eds., Pacific Neogene: Environment, Evolution, and Events. Univ. of Tokyo Press: Tokyo: 25-41.

Barron, J.A., 1995.  High resolution diatom paleoclimatology of the middle part of the Pliocene of the northwest Pacific.  In Rea, D.K., Basov, I.A., Scholl, D.W., and Allan, J.F., eds., Proc. ODP, Sci. Results, 145: 43-53. College Station, TX (Ocean Drilling Program)

Barron, J.A., 1996a. Diatom constraints on the position of the Antarctic Polar Front in the middle part of the Pliocene.   Marine Micropaleontology, 27:195-213.

Barron, J. A., 1996b.  Diatom constraints on sea surface temperatures and sea ice distribution during the middle part of the Pliocene.  U.S. Geological Survey Open-File Report, 96-713: 1-45.

Berggren, W.A., Kent, D.V. and Couvering, J.A., Van, 1985.  Neogene geochronology and chronostratigraphy.  In, Snelling, N.J., ed., The Chronology of the Geological Record.  London, Geological society of London Memoir 10: 211-260.

Berggren, W.A., Kent, D.V., Swisher, C.C. and Aubry, M.-P., 1995.  A revised Cenozoic geochronology and chronostratigraphy.  In, .Berggren, W.A., Kent, Aubry, M.-P. and Hardenbol, J. eds., Geochronology, time scales and global stratigraphic correlation.  Tulsa, Society for sedimentary geology special publication 54: 129-212.

Bertolani Marchetti, D., 1975.  Preliminary palynological data on the proposed Plio-Pleistocene boundary type-section of La Castella.  L'Atheneo Parmense Acta Naturalia, 11: 467-485.

Bertolani Marchetti, D., Accosi, C.A., Pelosio, G., and Raffi, S., 1979.  Palynology and stratigraphy of the Plio-Pleistocene sequence of the Stirone River (northern Italy).  Pollen et Spores, 21: 149-167.

Bint, A.N., 1981.  An Early Pliocene Pollen assemblage from Lake Tay, south-western Australia, and its Phytogeographic implications.  Australian Journal of Botany, 29: 277-291.

Bonnefille, R., Vincens, A., and Buchet, G.,  1987.  Palynology, stratigraphy and palaeoenvironment of a Pliocene hominid site (2.9-3.3 M.Y.) at Hadar, Ethiopia.  Palaeogeography, Palaeoclimatology, Palaeoecology, 60: 249-281.

Borisova, O.K., 1991.  Neogene temperature fluctuations on the southeastern Russian Plain. Pliocene Climates of the Northern Hemisphere:   abstracts of the Joint US/USSR Workshop on Pliocene Paleoclimates, Moscow, USSR, April, 1990. U.S. Geological Survey Open-File Report. 91-447:  14-15.

Borisova, O.K., 1994.  Landscape and climate of the south-central and southeastern Russian Plain in the Pliocene.  In:  Thompson, R.S. (Editor), Pliocene terrestrial environments and data/model comparisons.  U.S. Geological Survey Open-File Report 94-23: 61-64.

Brouwers, E.M., Jorgensen, N.O. and Cronin, T.M., 1991.  Climatic significance of the ostracode fauna from the Pliocene Kap Kobenhavn Formation, north Greenland.  Miropaleontology 37: 245-276

Brouwers, E.M., 1994.  Late Pliocene paleoecologic reconstructions based on ostracode assemblages from the Sagavanirktok and Gubik Formations, Alaskan North Slope.  Arctic 47(1): 16-33.

Burckle, L.H. and Cirilli, J., 1987.  Origin of diatom ooze belt in the Southern Ocean:  Implications for Late Quaternary paleoceanography.  Micropaleontology 33: 82-86.

Burckle, L.H. and Potter, N., Jr., 1996. Pliocene-Pleistocene diatoms in Paleozoic and Mesozoic sedimentary and igneous rocks from Antarctica: A Sirius problem solved. Geology, 24:235-238.

Burckle, L.H., Stroeven, A.P., Bronge, C., Miller, U., and Wassel, A., 1996.  Deficiencies in the diatom evidence for a Pliocene reduction of the East Antarctic Ice Sheet.  Paleoceanography, 11:379-390.

Caratini, C., and Tissot, C., 1988, Paleogeographical evolution of the Mahakam Delta in Kalimantan, Indonesia during the Quaternary and Late Pliocene.  Review of Palaeobotany and Palynology, 55: 217-228.

Cerling, T. E., J. R. Bowman, J.R., and O'Neil, J.R., 1988.  An isotopic study of a fluvial-lacustrine sequence:  the Plio-Pleistocene Koobi Fora Sequence, East Africa.  Palaeogeography, Palaeoclimatology, Palaeoecology, 63: 335-356.

Cerling, T.E., 1992.  Development of grasslands and savannas in East Africa during the Neogene.  Palaeogeography, Palaeoclimatology, Palaeoecology (Global and Planetary Change Section), 97: 241-247.

Chandler, M., Rind, D. and Thompson, R., 1994.  Joint investigations of the middle Pliocene climate II: GISS GCM Northern Hemisphere results.  Global and Planetary Change 9: 197-219.

Choi, D.K. and Bong, P.Y., 1986.  Neogene palynomorphs from lignite beds of Bugyeong and Yeonghae areas, Korea.  Journal of the Paleontological Society of Korea, 2:  1-17.

Clapperton, C. and Sugden, D.E., 1990.  Late Cenozoic glacial history of the Ross Embayment, Antarctica.  9(2/3): 253-272.

Committee on Glaciology, 1984.  Environment of West Antarctica:  potential CO2-induced changes.  Rep. Workshop held at Madison, Wisconsin, July 1983.  National Academy Press, Washington D.C., 236p.

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8.  Appendices

Only Appendices 2, 4 and 5 are included with hard copy version of this report to save space.  All data can be derived from these appendices.  All appendices are stored in Microsoft® EXCEL or ASCII TEXT format.  These files are available at  http://geology.er.usgs.gov/eespteam/prism/prism_data.html  or by contacting  Harry Dowsett.
Appendix 1.  PRISM2.LAND

2x2 global grid showing ocean cells as "0",  land cells as "1", and land cells covered by land ice as "9".  Based upon a +25m sea level.

Appendices 2.1 - 2.12.  PRISM2.SST

subdirectory contains 12 2x2 global grids with estimated average monthly pliocene sea surface temperatures.  Sea ice is designated as -1.8 degrees C.  Land cells are designated with -999.

Appendices 3.1 - 3.12.PRISM2.SEAICE

subdirectory contains 12 2x2 global grids with estimated average monthly pliocene sea ice distributions.  Sea ice is designated as "1", land cells as '8' and  water cells as '0.'  This information can alternatively be extracted from the 12 SST grids descibed in Appendix 2.

Appendix 4. PRISM2.TOPO

2x2 global grid showing Pliocene topography  in meters above sea level.

Appendix 5.  PRISM2.VEG

2x2 global grid showing Pliocene vegetation cover using the following categories:  0-water, 1-desert,  2-tundra, 3-grassland, 6-deciduous forest, 7-coniferous forest, 8-rainforest, 9-land ice.

Appendices 6.1 - 6.7  MODERN.DATA

subdirectory contains assorted modern data including SST (6.1 & 6.2), vegetation (6.3), and topography (6.4).  Other modern data can be derived from these appendices.

Approved for publication October 26, 1999

This site is http://pubs.usgs.gov/openfile/of99-535/
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Last revised 07-08-08