Robert Thompson

• PhD
• Research Geologist at United States Geological Survey

Plant macrofossils from packrat (Neotoma spp.) middens provide direct evidence of past vegetation changes in arid regions of North America. Here we describe the newest version (version 5.0) of the U.S. Geological Survey (USGS) North American Packrat Midden Database. The database contains published and contributed data from 3,331 midden samples coll...

Assemblages of fossil plant remains have been widely used to reconstruct past climatic conditions, usually through the application of methods that involve either finding vegetation analogues on the modern landscape (and using the modern associated climatic values as the basis for an estimate) or using the modern climatic ranges of individual taxa i...

During the past half century or so diverse histories of Great Salt Lake have been written from differing perspectives and all of them have contributed ideas and essential data. The published literature, however, can be confusing and misleading. In this chapter, we review and provide context for a number of those publications. This chapter is intend...

We examine the annual, seasonal, monthly, and diurnal climate responses to the land use change (LUC) in eastern United States and Cuba during four epochs (1650, 1850, 1920, and 1992) with ensemble simulations conducted with the RegCM4 regional climate model that includes the Biosphere Atmosphere Transfer Scheme (BATS1e) surface physics package (Dic...

This study presents a synthesis of century-scale hydroclimate variations in North America for the Common Era (last 2000 years) using new age models of previously published multiple proxy-based paleoclimate data. This North American Hydroclimate Synthesis (NAHS) examines regional hydroclimate patterns and related environmental indicators, including...

Sediment cores from Great Salt Lake (GSL) provide the basis for reconstructing changes in lakes, vegetation, and climate for the last ~ 40 cal ka. Initially, the coring site was covered by a shallow saline lake and surrounded by Artemisia steppe or steppe-tundra under a cold and dry climate. As Lake Bonneville began to rise (from ~ 30 to 28 cal ka)...

In the Interior western United States, the landscape is characterized by high physiographic relief, pronounced regional and local rain shadows, and gradients in temperature and precipitation across space and elevation. There is a strong gradient in the seasonality of precipitation across the region, with cool season moisture from the North Pacific...

Shorelines and surficial deposits (including buried forest-floor mats and organic-rich wetland sediments) show that Great Salt Lake did not rise higher than modern lake levels during the earliest Holocene (11.5–10.2 cal ka BP; 10–9 14C ka BP). During that period, finely laminated, organic-rich muds (sapropel) containing brine-shrimp cysts and pelle...

Apparent changes in vegetation distribution, fire, and other disturbance regimes throughout western North America have prompted investigations of the relative importance of human activities and climate change as potential causal mechanisms. Assessing the effects of Euro-American settlement is difficult because climate changes occur on multi-decadal...

This is the seventh volume in an atlas series that explores the relations between the geographic distributions of woody plant species and climatic variables in North America. A 25-kilometer (km) equal-area grid of modern climatic and bioclimatic variables was constructed from weather data. The geographic distributions of selected tree and shrub spe...

In North America, terrestrial records of biodiversity and climate change that span Marine Oxygen Isotope Stage (MIS) 5 are rare. Where found, they provide insight into how the coupling of the ocean-atmosphere system is manifested in biotic and environmental records and how the biosphere responds to climate change. In 2010-2011, construction at Zieg...

Ninety plant macrofossil taxa from the Ziegler Reservoir fossil site near Snowmass Village, Colorado, record environmental changes at high elevation (2705 m asl) in the Rocky Mountains during the Last Interglacial Period. Present-day vegetation is aspen forest (Populus tremuloides) intermixed with species of higher (Picea, Abies) and lower (Artemis...

The mutual climatic range (MCR) technique is perhaps the most widely used method for estimating past climatic parameters from fossil assemblages, largely because it can be conducted on a simple list of the taxa present in an assemblage. When applied to plant macrofossil data, this unweighted approach (MCRun) will frequently identify a large range f...

Climate-model simulations of past climates are often evaluated using both paleovegetation proxy data (e.g., pollen) and model simulations of past vegetation. These data-model comparison efforts provide important information for evaluating paleoclimate model simulations, and also for refining interpretations of paleovegetation proxy data and improvi...

Packrat (Neotoma spp.) middens are preserved for thousands to tens-of-thousands of years in dry caves and rockshelters in the western USA. Plant remains from these deposits frequently can be identified at the species level and provide excellent material for radiocarbon dating. Accordingly, assemblages of these remains provide detailed well-dated in...

Subfossil pollen and plant macrofossil data derived from 14C-dated sediment profiles can provide quantitative information on glacial and interglacial climates. The data allow climate variables related to growing-season warmth, winter cold, and plant-available moisture to be reconstructed. Continental-scale reconstructions have been made for the mid...

We are using a regional climate model to conduct time-slice simulations of paleoclimate over North America, and comparing these with syntheses of paleoclimatic data to examine the performance of the regional modeling system and to diagnose the potential controls of the climatic variations recorded by the data. The base climate simulations are 50-ye...

The method of modern analogs is widely used to obtain estimates of past climatic conditions from paleobiological assemblages, and despite its frequent use, this method involved so-far untested assumptions. We applied four analog approaches to a continental-scale set of bioclimatic and plant-distribution presence/absence data for North America to as...

Pollen records from western North America and the eastern Pacific Ocean reveal the amplitude and timing of changes in vegetation and climate during the late Pleistocene (ca. 130 to 10 ka). Cooler-than-present conditions prevailed through most of this time, punctuated by shorter intervals of warmth. The dominance of pollen types reflecting open vege...

The USGS/NOAA North American Packrat Midden Database is a standardized archive of published paleobotanical data derived from packrat middens in western North America. We use midden age, location, and species presence-absence data from this dataset to generate maps illustrating the past occurrence of important woody plant taxa in western North Ameri...

The Upper Colorado Basin (UCB) is an important source of water and power for cities, farms, and other interests from the plains of Colorado to the Pacific Ocean. The region is currently experiencing a multi-year drought that is affecting Colorado River flows and is implicated in the high mortality rate of pinyon pines in the region among other ecos...

Archival databases seek to faithfully represent published data, although sometimes with slight modifications for updated taxonomy or standard descriptions. Over the past decade NOAA, the USGS, other agencies, and groups have produced archival databases for present-day and late-Quaternary North American pollen, woody plant distributions, plant trait...

Ecoregion classification systems are increasingly used for policy and management decisions, particularly among conservation and natural resource managers. A number of ecoregion classification systems are currently available, with each system defining ecoregions using different classification methods and different types of data. As a result, each cl...

As the international community ponders the potential course of future climate changes and their impacts, studies of past climatic changes and their environmental effects provide a way to understand the processes involved in environmental change, the interactions among elements of the ocean-atmosphere-land surface system, and the rates and amplitude...

This chapter explores the strengths and shortcomings of the major sources of data on Quaternary vegetation and climate change and discusses the use of models as a means to explore past and potential future environmental changes. The flora and major vegetation types of the western United States are present for several million years. Ongoing changes...

Plant macrofossils provide a unique resource in paleoclimatology: They can usually be identified to the species level, can be directly dated by radiocarbon analysis, and can be related to modern living relatives whose ranges are usually well-known. Fossil packrat middens provide a spatially and temporally rich data set of well-dated species-level p...

Simulations of the climatic response to mid-Holocene (6 ka BP) orbital forcing with two coupled ocean-atmosphere models (FOAM and CSM) show enhancement of monsoonal precipitation in parts of the American Southwest, Central America and northernmost South America during Northern Hemisphere summer. The enhanced onshore flow that brings precipitation i...

Paleoclimatologic studies usually employ a "modern" climatic data set as the baseline against which to measure the differences between past climates and those of today. Weather records for the past century indicate that climate has not been stationary, and thus the selection of the baseline time-interval from the past hundred years will affect the...

A newly identified tephra in stratified deposits in southwestern Utah, dated ∼14,000 14C yr B.P., may aid in correlating late Pleistocene deposits across parts of the southern Great Basin and west-central Colorado Plateau. Geochemical analyses of the ash suggest the tephra originated from Mono Craters, California, and most probably correlates with...

BIOME 6000 is an international project to map vegetation globally at mid-Holocene (6000 14C yr bp) and last glacial maximum (LGM, 18,000 14C yr bp), with a view to evaluating coupled climate-biosphere model results. Primary palaeoecological data are assigned to biomes using an explicit algorithm based on plant functional types. This paper introduce...

Spatial patterns of plant species richness vary greatly at continental scales. The environmental and bioclimatic controls on these patterns are still not fully understood. A recently completed data set of the distributions of over 500 species of trees and shrubs in North America (U.S. Geological Survey Professional Paper 1650A-D) allows us to explo...

Increases in atmospheric greenhouse gases are driving significant changes in global climate. To project potential vegetation response to future climate change, this study uses response surfaces to describe the relationship between bioclimatic variables and the distribution of tree and shrub taxa in western North America. The response surfaces illus...

A new compilation of pollen and packrat midden data from western North America provides a refined reconstruction of the composition and distribution of biomes in western North America for today and for 6000 and 18,000 radiocarbon years before present ( ¹⁴ C yr bp ). Modern biomes in western North America are adequately portrayed by pollen assemblag...

Initial interpretation of the sediments from the Burmester core (Eardley et al. (1973). Geological Society of America Bulletin 84, 211-216) indicated that 17 deep-lake cycles, separated by shallow-lake and soil-forming intervals, occurred in the Bonneville basin during the Brunhes Chron (the last 780 x 103 yr). Our re-examination of the core, along...

This atlas explores the continental-scale relations between the geographic ranges of woody plant species and climate in North America. A 25-km equal-area grid of modern climatic and bioclimatic parameters was constructed from instrumental weather records. The geographic distributions of selected tree and shrub species were digitized, and the presen...

Maps of upper-level and surface winds and of surface temperature and precipitation illustrate the results of a sequence of global paleoclimatic simulations spanning the past 21,000 years for North America. We review a) the large-scale features of circulation, temperature, and precipitation that appear in the simulations from the NCAR Community Clim...

Maps of upper-level and surface winds and of surface temperature and precipitation illustrate the results of a sequence of global paleoclimatic simulations spanning the past 21,000yr for North America. We review (a) the large-scale features of circulation, temperature, and precipitation that appear in the simulations from the NCAR Community Climate...

Historical and geological data indicate that significant changes can occur in the Earth's climate on time scales ranging from years to millennia. In addition to natural climatic change, climatic changes may occur in the near future due to increased concentrations of carbon dioxide and other trace gases in the atmosphere that are the result of human...

The general characteristics of global vegetation during the middle Pliocene warm period can be reconstructed from fossil pollen and plant megafossil data. The largest differences between Pliocene vegetation and that of today occurred at high latitudes in both hemispheres, where warming was pronounced relative to today. In the Northern Hemisphere co...

Sedimentological, palynological, and magnetic susceptibility data provide paleoenvironmental and paleoclimatic information from a 989 ft (301 m) core of sediments from the upper Glenns Ferry and Bruneau Formations from near the town of Bruneau, Idaho. Chronology is based on stratigraphic position, paleomagnetism, and biostratigraphic data. Palynolo...

Marine microfaunal data and terrestrial pollen records indicate that the middle Pliocene (ca. 3 Ma) climate is the most recent period in geologic history with global temperatures nearly as warm as those predicted for the coming century. We used the GISS GCM to examine the Pliocene climate by specifying sea surface temperatures and vegetation distri...

The Pliocene epoch represents an important transition from a climate regime with high-frequency, low-amplitude oscillations when the Northern Hemisphere lacked substantial ice sheets, to the typical high-frequency, high-amplitude Middle to Late Pleistocene regime characterized by glacial—interglacial cycles that involve waxing and waning of major N...

The Middle Pliocene ( approximately 3 million years ago) has been identified as the last time the Earth was significantly warmer than it was during the Last Interglacial and Holocene. A quantitative micropaleontological paleotemperature transect from equator to high latitudes in the North Atlantic indicates that Middle Pliocene warmth involved incr...

Palynological data from sediment cores from the Ruby Marshes provide a record of environmental and climatic changes over the last 40,000 yr. The modern marsh waters are fresh, but no deeper than ∼3 m. A shallow saline lake occupied this basin during the middle Wisconsin, followed by fresh and perhaps deep waters by 18,000 to 15,000 yr B.P. No sedim...

The available evidence from the western United States suggests that the climate of the Early and Middle Pliocene (prior to ∼2.4 Ma) was less seasonal (more equable) and generally more humid than now. Along the Pacific coast, summer drought was less pronounced than today. In the interior of the Pacific Northwest rainfall was more abundant and mild w...

Pleistocene lake sediments in the Great Basin typically contain little organic carbon, and thus are difficult to date reliably by conventional radioccarbon methods. Paleoenvironmental data are abundant in these sediments, but are of limited value without adequate age controls. With the advent of accelerator-mass spectrometer (AMS) radiocarbon datin...

Variations in isotopes of oxygen, hydrogen, and carbon in modern and subfossil plant cellulose are related to spatial and temporal patterns in temperature, humidity, seasonality and amount of rainfall. Stable isotope chronology suggests major warming at c13 ka which is coincident with deglaciation of regional ice sheets and alpine glaciers and with...

The basin and range topography creates a situation where montane vegetation is discontinuous and separated into habitat islands of various sizes. Packrat Neotoma midden coverage is heavily skewed toward the late Wisconsinan and Late Holocene. The full glacial flora of the basin was impoverished and the shift from a Late Wisconsinan to modern vegeta...

Changes in solar radiation arising from changes in the orientation of the earth's axis had pronounced effects on tropical monsoons and mid-latitude climates as well as on ice-sheet configuration during the last 18,000 years. COHMAP (Cooperative Holocene Mapping Project) has assembled a global array of well-dated paleoclimatic data and used general-...

Diatoms, crustaceans, and pollen from sediment cores, in conjunction with dated shoreline tufas provide evidence for lake level and environmental fluctuations of Walker Lake in the late Quaternary. Large and rapid changes of lake chemistry and level apparently resulted from variations in the course and discharge of the Walker River. Paleolimnologic...

The western United States is a mountainous land with strong climatic gradients and vegetation ranging from subtropical desert-scrub to tundra. The region has a dynamic past, especially over the last 20,000 years, when large lake-systems developed and then desiccated to the few modern remnants in the now-arid interior, and alpine glaciers and ice-ca...

Selected radiocarbon data on surficial materials from the Lahontan basin, Nevada and California, provide a chronology of lake-level variation for the past 50,000 yr. A moderate-sized lake connected three western Lahontan subbasins (the Smoke Creek-Black Rock Desert subbasin, the Pyramid Lake subbasin, and the Winnemucca Dry Lake subbasin) from abou...

Radiocarbon dates of plant materials from packrat middens in caves below the elevation of the last high stand of Pleistocene Lake Lahontan, in conjunction with radiocarbon dates of ancient archaeological materials, provide evidence that the last high stand terminated before 12,070 yr B.P. This new information suggests that the last major fluctuatio...

Sediments of Balsam Meadow have produced a 11,000-yr pollen record from the southern Sierra Nevada of California. The Balsam Meadow diagram is divided into three zones. (1) The Artemisia zone (11,000–7000 yr B.P.) is characterized by percentages of sagebrush (Artemisia) and other nonarboreal pollen higher than can be found in the modern local veget...

Analyses of well-preserved plant remains from ancient packrat (Neotoma) middens have yielded much information on the history of vegetation, fauna and climate from the more arid portions of North America over the past 40,000 years1,2. In most of the modern deserts, woodland or forest communities were present during the last glacial age, the Wisconsi...

Occupation of this site by man was relatively brief and began after 10 700 yr BP. The surrounding vegetation then was a mosaic of dense scrub and juniper woodland, but Pinyon pine had not yet migrated into the area. By this stage Lake Bonneville had disappeared. -K.Clayton

Plant and animal remains found in packrat (Neotoma spp.) middens and cave fill from the eastern and southern Great Basin region reveal the presence of subalpine conifers and boreal mammals at relatively low elevations during the Late Wisconsin. Limber pine (Pinus flexilis) and bristlecone pine (P. longaeva) were important in the late Pleistocene pl...

During the late Pleistocene, montane glaciers in the Snake Range, eastern Nevada reached an elevation as low as 2900m and pluvial Lake Bonneville rose to approximately 1580m, only 130m below the entrance of the east-facing Smith Creek Canyon. It is not known whether the two events coincided. Packrat midden macrofossils indicate that bristlecone pin...

Seven coprolites of the extinct Shasta ground sloth ( Nothrotheriops shastense ) were recently discovered in the Los Angeles County Museum collection from Shelter Cave, New Mexico. Three dung balls provided radiocarbon ages of 11,330, 12,330 and 12,430 yr B.P. Packrat ( Neotoma ) middens disclose a xeric juniper woodland at Shelter Cave during the...

The carbon isotope analyses reported here include all radiocarbon dates run on packrat middens in the United States and Mexico by the Arizona radiocarbon laboratory through October 1977. All samples described below report dates by CO 2 (0.5 or 2.0L) counting. Age calculations are based on a 14 C half-life of 5568 years, using 0.949 NBS oxalic acid...