Current Palynological Investigations at the University of Arizona

Neogene vegetation and climatic history of the Great Salt Lake
Archeological palynology of southern California & Arizona
History of wetlands of the Southwest
Solar variability and climate change

REGION: Southern California, Southwestern New Mexico, Northern Sonora.
STUDENTS: Andrea K. L. Freeman, Robert J. Godsoe, Thomas A. Minckley, and Thomas E. Moutoux
Wetlands are rare in the desert Southwest, and they have received intense human utilization throughout prehistoric and historic times. Comprehensive studies of eight marshes (cienegas) in California, Arizona, New Mexico, and Sonora show a consistent pattern of following European settlement: These changes suggest a dramatic decrease in the frequency and intensity of marsh fires after European settlement. Prior to the historic period, burning was frequent enough to maintain open, herb-dominated cienegas, and intense enough to eliminate the build-up of dead plant tissue. Following fire suppression, bulrushes and woody plants were able to invade the cienegas, and the buildup of senescent plant tissue resulted in the accumulation of organic sediment (peat) and the increased abundance of decay fungi.


Davis, O.K. 1994. 1994. Pollen Analysis of Borderland Cienegas, Contract Number HQ/AZ-920815-1. Report submitted to Richard P. Young, The Nature Conservency, Arizona Field Office, 300 E. University Blvd., Suite 230, Tucson, Arizona 85704. 105 p.

Davis, O.K. 1995. Pre-Columbian human impact on the wetlands of the Southwestern U.S.A. AASP 28th Annual Meeting, Oct. 10-14. Ottawa, Ontario, Canada.

REGION: Great Salt Lake Basin of Northern Utah, U.S.A.
INVESTIGATORS: O.K. Davis, A.S. Cohen, R.A. Johnson, C.G. Chase
STUDENTS: Tom Moutoux, Agata Kowalewska, Johanna Jurgens
Paleontological, sedimentological, and isotopic analysis of sediment from 15 wells drilled to bedrock in the Great Salt Lake have provided an uninterrupted record of lacustrine and terrestrial evolution over the last 6 million years, reaching 16 M yr. Chronologic control has been provided by 10 volcanic tephrae (oldest = Walcott Ash, 6.05 M yr), Ar/Ar and K/Ar dates, and fission track dates. No gaps > 10,000 yr are evident in the record to 6 M yr. The ash determinations were made by Tom Moutoux, using the extensive data on Neogene ashes collected by William Nash, University of Utah.
The upland vegetation is desert throughout the last 16 M yr with Sarcobatus and Ephedra dominating during the Miocene (< 5 M yr); Chenopodiaceae, and Artemisia dominance during the Pliocene (5 - 2.5 M yr) and early Pleistocene, and sharp increases in Pinus and Artemisia in the late Pleistocene (> 0.75 M yr). Lacustrine fossils are most prominent during the Pliocene and early Pleistocene. They abruptly decline at ca. 0.75 M yr.


Davis, O.K. 1995. The impact of climatic change on available moisture in arid lands, examples from the American Southwest. pp. 283-299 IN: "Diachronic Climatic Impacts on Water Resources." NATO ASI Series D. Reidel Publ.

Davis, O.K. 1998. Palynological evidence for vegetation cycles in a 1.5 million year pollen record from the Great Salt Lake, Utah, U.S.A. Palaeo. Palaeo. Palaeo. 138:175-185. abstract pdf Elsevier

Davis, O.K. 1999. Preliminary pollen analysis of Neogene and Quaternary sediment of the Great Salt Lake, U.S.A., Proceedings Pliocene Conference, AASP Contribution Series 34: 227-240.

Davis, O.K. 2002. Late Neogene Environmental History of the Great Salt Lake. pp. 295-307 IN: R. Hershler, D.B. Madsen, and D.R. Currey (eds.) Great Basin Aquatic Systems History. Smithsonian Contribs. to the Earth Sciences 33.

Davis, O.K. and Moutoux, T.E. 1998. Tertiary and Quaternary vegetation history of the Great Salt Lake, U.S.A. Journal of Paleolimnology. 19 (4): 417-427.

Dean, W., Rosenbaum, J., Haskell, B., Kelts, K., Schnurrenberger, D., Valero-Garces, B., Cohen, A., Davis, O., Dinter, D. and Nielson, D. 2002. Progress in global lake drilling holds potential for global change research. EOS 83: 85, 90-91.

Moutoux, T.E. Davis, O.K., Perkins, M., and Nash, W.P. (in prep). Palynological and tephra correlations among deep wells in the Modern Great Salt Lake, Utah, U.S.A. G.S.A. Bulletin.

Moutoux, T. and Davis, O.K. 1995. Neogene through Pleistocene paleoclimate of the Great Salt Lake region, Northeastern Great Basin, U.S.A. Proceedings 11th PACLILM Workshop, Calif. Dept. Water Res. Ecol. Stud. Progr. Techn. Rep. 40:127-135.

REGION: Southern Arizona, Southern California
STUDENTS: Andrea K. L. Freeman, Robert H. Dayhuff, Robert J. Godsoe, Thomas A. Minckley, Thomas E. Moutoux, and Maria Sanchez de Carpentier
In the last decade, the analysis of pollen from archaeological sites has become one of the most active fields of palynology. Pollen, the most-resistant of plant fossils, provides keys to the understanding of a host of human activities. Bryant and Holloway have listed the benefits as including the reconstruction of prehistoric diet, funary practices, artefact function and source, archaeological feature use, and environmental reconstruction. To this list can be added the study of the cultivation and domestication of plants, and the study of the history of human impact on vegetation.

The Palynology Laboratory at the University of Arizona is currently involved in 3 large projects including the analysis of 98 pollen samples from excavations on the Calfiornia State University at Longbeach, 300 samples from a series of 5 cores from Ballona Lagoon, and 200 samples from freshwater and lagoon cores from Newport Bay. Recently-complete projects are listed below.


Davis, O.K. 1995. Pollen analysis the Prado flood control basin, CA-RIV-653 -1098 -2798. Report Submitted to Donn R. Grenda, Statistical Research, Redlands, CA 92373. 25 p.

Davis, O.K. 1995. Pollen analysis of sites near Copper Butte and the Ray complex, AZ V:13:127 AND AZ U:16:246. Report Submitted to Mary Lou Heuett, Cultural & Environmental Systems, Tucson, Az. 12 pp.

Davis, O.K. 1995. Pollen analysis of a mid-lake core from Lake Tahoe, California: Historic vegetation change. Report Submitted to Don Erman, SNEP Team Leader and Director Centers for Water and Wildlands Resources, Univ. California, Davis. 19 pp.

Davis, O.K. 1995. Pollen analysis of the Sugarloaf Fault Project. Report submitted to Dr. Kirk Vincent, Arizona Geological Survey. 9 pp.

Davis, O.K. and Overs, J. (Editors) 1994. Archeological Palynology: An International Perspective. American Assoc. of Stratigraphic Palynologists Contrib. Ser. 29, 221 p.

REGION: Global
INVESTIGATORS: O.K. Davis, R.M. Kalin, J.L. Jirikowic
Davis, O.K. 1992. Rapid climatic change in coastal southern California inferred from Pollen Analysis of San Joaquin Marsh. Quaternary Research. 37:89-100.
Pollen analysis and 5 radiocarbon dates of a 687 cm core provide a detailed chronology of environmental change in a marsh at the head of Newport Bay, Orange County, California. Sediment deposition kept pace with sea-level rise during the early history of the marsh. From ca. 7000 to 4500 yr B.P. the site was a freshwater marsh, trees were more abundant than today, and grassland was the regional vegetation. As sea level rose, salt marsh gradually invaded the site. Brief periods of fresh-water marsh 3800, 2800, 2300 and after 560 yr B.P., correlate with episodes of global cooling during the Neoglacial. The historic period is marked by the appearance of exotic species (particularly Erodium cf. cicutarium and Eucalyptus) and the spores of fungi (Sporormiella and Thecaphora). Peak influx of pollen, spores, and charcoal probably reflect greater frequency of flooding and erosion ca. 5000 yr B.P. and during the last 1000 yr.

Davis, O.K. 1994. The correlation of summer precipitation in the southwestern U.S.A. with isotopic records of solar activity during the Medieval Warm Period. Climate Change. 26:271-287.
Decreased solar activity correlates with positive cosmogenic isotope anomalies, and with cool, wet climate in temperate regions of the world. The relationship of isotope anomalies to climate may be the opposite for areas influenced by monsoonal precipitation, i.e., negative anomalies may be wet and warm. Petersen (1988) has found evidence for increased summer precipitation in the American Southwest that can be shown to be coincident with negative 14C anomalies during the Medieval Warm Period. The present study compares palynological indicators of lake level for the Southwest with Petersen's data and with the 14C isotope chronology. Percentages of aquatic pollen and algae from three sites within the Arizona Monsoon Boundary record greater lake depth or fresher water from A.D. 700 - 1350, between the Roman IV and Wolf positive isotope anomalies, thereby supporting Petersen's findings. Maximum summer moisture coincides with maximum population density of prehistoric People of the Southwest. However, water depth at a more northern site was low at this time, suggesting a climate - isotope relationship similar to that of other temperate regions. Further analysis of latitudinal patterns is hampered by inadequate 14C dating.

Davis, O.K., Dai, K., Dean, J.S., Parks, J., and Kalin, R.M. (In press.). Radiocarbon dating of buried trees, and climatic change in west-central Oklahoma. Radiocarbon.
The production of cosmogenic isotopes, especially as revealed in the tree-ring record of radiocarbon anomalies, provides a detailed chronology for rapid global climatic change. Solar variability modulates production of 14C and 10Be and influences global climate. Large (>10 ) -14C excursions in tree-ring records from North America, the British Isles, and Germany coincide with brief, intense cold periods in dated paleoclimatic time series. Although the climate - 14C-anomaly correspondence can be demonstrated in long (5000 yr) series (Sonett and Suess, 1984), detailed comparisons are needed to more-precisely test the relationship, particularly before the Little Ice Ages. The coincidence of cold periods and -14C anomalies first was suggested by de Vries (1958) and Eddy (1977) for the Little Ice Ages; however, the origin of the solar - climate hypothesis can be traced to the 19th century. The 14C and 10Be records allows the comparison of solar variability and climate over much longer timescales. Detailed comparisons of tree-ring analysis and radiocarbon dating by Schmidt and Gruhle (1988) demonstrate coincident cool-wet climate and -14C anomalies during the Homeric (880-600 BC) and Greek (460-260 BC) "Dendroklic" events. If the 14C-climate association is global, then Schmidt and Gruhle's (1988) results should be replicable in North America. We propose to repeat the study of Schmidt and Gruhle, using 64 well-preserved trees from Carnegie Canyon, Oklahoma (Hall and Lintz, 1984). Through detailed dendroclimatic study and high-precision radiocarbon dating of these trees, we will test the global nature of the 14C-climate "Dendroklic" phenomenon.

Davis, O.K., Jirikowic, J.L., and Kalin, R.M., 1992. The Radiocarbon record of solar variability and Holocene climatic change in coastal southern California. Proceedings 8th PACLILM Workshop, Calif. Dept. Water Res. Ecol. Stud. Progr. Techn. Rep. 31:19-33
The tree-ring calibration of radiocarbon dates may provide a chronology for high-frequency global climatic change. Large (ca. 10o/oo) delta -14C excursions in tree-ring series from North America, Great Britain, and Germany, are associated with brief, intense cold periods throughout the Holocene. The coincidence of cold periods and delta -14C anomalies first was suggested by de Vries (1958) for the Little Ice Ages. Schmidt and Gruhle (1988) have combined dendrochronologic analysis and radiocarbon dating to demonstrate coincident cool-wet climate and increased 14C production during the Homeric (880-600 BC) and Greek (460-260 BC) Minima. Many western North America sites record cold-wet climate at this time. Pollen analysis and 5 radiocarbon dates for a 687 cm core provide a detailed chronology of environmental change for San Joaquin Marsh at the head of Newport Bay, Orange County, California. Sediment deposition kept pace with sea-level rise during the mid-Holocene, but after 4500 yr B.P. sea water regularly reached the coring site, and salt marsh was the local vegetation. Brief periods of dominance by fresh-water vegetation 3800, 2800, 2300 and after 560 yr B.P., correlate global cooling events and (except the 3800 yr B.P. event) with 14C production anomalies. The coincidence of climate change and 14C anomalies support a causal connection with solar variability; but regardless of the causal mechanism(s) the delta -14C curves provide a chronology for global, high-frequency climatic change comparable to that of Milankovitch cyclicity for longer time scales.

Davis, O.K. and Shafer, D.S. 1992. An early-Holocene maximum for the Arizona monsoon recorded at Montezuma Well, central Arizona. Palaeogeography Palaeoclimatology Palaeoecology. 92:107-119.
Pollen and macrofossil analyses of a radiocarbon-dated core, 1125 cm long, from Montezuma Well, elev. 1125 m, Yavapai County, Arizona, provide a record of summer precipitation similar to that of other monsoonal regions of the world. Precipitation was least from 4000 to 5000 yr B.P., and generally was greater than today before 8400 yr B.P. During the early-Holocene moist period, oak and grass pollen are abundant, and the best modern analogs are within the Arizona Monsoon boundary, so increased summer precipitation is indicated. Climatic parameters are estimated with the technique of best modern analogs for fossil samples. Temperature was highest ca. 3400 and 5700 yr B.P., and generally was cooler than today before 6800 yr B.P. Brief cold intervals in the Holocene match periods of global cooling and of positive 14C and 10Be anomalies.

Jirikowic, J.L., Kalin, R.M. and Davis, O.K. 1993. Tree-Ring 14C as an indicator of climate change. Climatic Change in Continental Isotopic Records. AGU Geophysical Monograph 78:353-366.
Analyses of the tree-ring delta-14C data set shows intermittent high 14C anomalies. During these anomalies, the time series nature of the 14C data set changes markedly. Such non-stationarity suggests 14C variation results from a dynamic non-linear set of processes. The latest 14C anomaly occurs during the past millennium and coincides with the historic profound solar activity minima. To test the hypotheses of solar modulation of global climate and cosmogenic isotope anomalies, we sought evidence for brief climatic events coincident with major anomalies in a rapid deposition site which had not been previously reported. Using detailed pollen analysis and precise 14C dating, we have studied climatic change during the Homeric-Greek (1830-2550, 2360 - 2160 cal B.P.) And Noachan (4880-4660 cal B.P.) Anomalies at Mission Cross Bog, Elko Co., Nevada. Through "wiggle-matching" with the 14C calibration curve, we could date the precise interval in the sediment record which corresponds to the Homeric and Greek 14C production anomalies. We located the exact age of the Greek anomaly only, corresponding to a wet period in the pollen diagram. We also discovered two wet periods that do not match any cosmogenic isotope anomalies. The presence of brief climatic episodes cannot be used to date the sequence. By dating and analyzing pollen during the Homeric and Noachan anomalies, we may confirm or refute the climate-cosmogenic isotope anomaly association.

Leroux, M., Petit-Maire, N, and Davis, O.K. (In press.) Differential insolation at north and south high latitudes explains palaeoclimatic changes in tropical Africa for the last 30,000 years. Palaeogeography Palaeoclimatology Palaeoecology.
In the last decades, the close connection between orbital insolation pseudo-periodicities and short and long-term terrestrial climatic records has verified Milankovitch's theories (Hays & Imbrie 1975; Bernard 1977; Berger 1978, 1981; Kutzbach and Otto-Bliesner, 1982, Kutzbach, 1987), especially the alternation of humid and arid phases of the world's deserts and their sensitive margins (Petit-Maire 1986, 87, 88). Cyclicities of ca. 115,000, 40,000, and 19-23,000 years have been recognized, even over long time spans (Thiedeman et al., 1988). However, the many complex variations and rapid changes in the tropical belt cannot be explained by these slow cosmic evolutions. For example, the movement of the Saharo-Sahelian margins by 10o between 19,000 and 9,000 BP and by ca. 6o between 7,000 BP and the present (Petit-Maire 1988, 1989). Furthermore, on longer time scales, climatic change lags thousands of years behind the orbitally-induced insolation changes.