Lake-level influences on chironomid-based reconstructions of paleotemperature
Independent lines of evidence are essential for resolving the nature and dynamics of past climates. Consequently, the recent advent of chironomid (Diptera) analysis as a tool for estimating paleotemperatures is widely recognized as a major positive, if somewhat problematic, development. The temperature changes estimated by this method have frequently been surprisingly large -- substantially greater than those inferred from fossil pollen or other widely-used evidence. In the research project, we are answering several critical questions related to the method and its application in paleoclimatology. In the process we will provide improved estimates of the climate during the Younger Dryas and mid-Holocene intervals.
The reconstructions using chironomid data are based on statistical analysis of a modern calibration data set, which indicates thatthe assemblages of chironomid species are correlated most with mid- summer surface-water temperature. However, a second environmental variable " water depth " is also important in the calibration data set. We hypothesize that some of the apparently very large temperature shifts during episodes such as the Younger Dryas are related to the fact that the lakes involved changed dramatically in depth as a result of variations in water balance of the climate. Obviously, any significant changes in lake depth could greatly influence the environment experienced by the aquatic stages of the chironomid life cycle, and would also likely affect chironomid-based paleotemperature reconstructions.
Thus, the primary objective of this study is to determine the influence of lake-level changes on chironomid-based temperature estimates. Once this issue is resolved, chironomid transfer functions can be applied with greater confidence to sediments of all ages.
A transect of cores from Whited Lake in northeastern Maine is being examined for evidence of past water levels and chironomid analysis is being performed. The same analysis will be performed on sediment from Matthews Pond, north-central Maine. We are currently investigating geologic/chronologic evidence of Younger Dryas-age ice readvance in northern Maine to provide the data necessary to apply a well- developed glaciological model to determine the range of temperature and precipitation that could possibly have prevailed during this period. Chironomid estimates of temperature will be reconciled with the temperature range derived from the glaciological model, and the transfer function will also be refined with respect to lake-level. The new chironomid/lake-level transfer function will then be applied to Holocene sediments from Whited Lake and Matthews Pond, central Maine.
Long records of paleoclimate from Florida
The objectives of this research are 1) to establish a high-resolution chronology for the sediment record from Lake Tulane, Highlands County, Florida, 2) to develop a lake-level reconstruction for Lake Tulane, and 3) to extend the regional and temporal paleoclimate records from Florida. Seven complete cores were collected from Lake Tulane and one 19-m core was obtained from near-by Lake Annie. Fifty-seven AMS dates have been obtained for the Lake Tulane master core. Particle size, charcoal, macrofossil, and pollen analyses confirm the Grimm et al. (1993) interpretation of wet/dry oscillations at the site for the past 70,000 years. The evidence suggests that for several well-dated intervals (e.g., H2 and H3), warming in Florida preceded the flux of ice-rafted material into the North Atlantic sediments. The implication is that broad-scale warming led to massive discharges of icebergs, which then cooled the North Atlantic. The late-glacial portions of the Tulane and Annie cores reveal that the Younger Dryas time in Florida was warm and moist, perhaps approaching late-Holocene conditions.
Dry Valleys Late Holocene Climate Variability
The goals of this project are to collect and develop high-resolution ice core records from the Dry Valleys region of Antarctica, and provide interpretations of interannual to decadal-scale climate variability during the last 2000 years (late Holocene). In particular, we seek to test hypotheses related to ocean/atmosphere teleconnections (e.g., El Nino Southern Oscillation, Antarctic Oscillation) that may be responsible for major late Holocene climate events such as the Little Ice Age in the Southern Hemisphere. Conceptual and quantitative models of these processes in the Dry Valleys during the late Holocene are critical for understanding recent climate changes, and represent the main scientific merit of the project. We plan to collect intermediate-length ice cores (100-200m) at four sites along transects in Taylor Valley and Wright Valley, and analyze each core at high resolution for stable isotopes (ƒδ18O, ƒδD), major ions (Na+, Mg2+, Ca2+, K+, NH4+, Cl-, NO3-, SO42-, MSA), and trace elements (Al, Fe, S, Sr, B). A suite of statistical techniques will be applied to the multivariate glaciochemical dataset to identify chemical associations and to calibrate the time-series records with available instrumental data. Broader impacts of the project include: 1) contributions to several ongoing interdisciplinary Antarctic research programs; 2) graduate and undergraduate student involvement in field, laboratory, and data interpretation activities; 3) use of project data and ideas in several UMaine courses and outreach activities; and 4) data dissemination through peer-reviewed publications, UMaine and other paleoclimate data archive websites, and presentations at national and international meetings.
From its original formulation in 1990, the International Trans Antarctic Scientific Expedition (ITASE) has had as its primary aim the collection and interpretation of a continental- wide array of environmental parameters assembled through the coordinated efforts of scientists from several nations. The primary planned product of this cooperative endeavor is the description and understanding of environmental change in Antarctica over the last ~200 years. As a demonstration of the importance of the original scientific objectives posed by ITASE, they were adopted as a key science initiative by both the International Geosphere-Biosphere Program (IGBP) and the Scientific Committee on Antarctic Research (SCAR).
DNA analysis of human paleofece
The most direct evidence of prehistoric diet is provided by the analysis of paleofeces. Recent research advances in paleofecal analysis now allow us to determine sex of depositor through fecal steroid analysis (Sobolik et al. 1996) and DNA content (Sutton et al. 1996). DNA analyses of paleofeces also identify biological affiliation of prehistoric peoples as well as plants and animals eaten (Poinar et al. 2001). Many multidisciplinary research projects are being conducted by the authors on a number of paleofecal samples throughout North America to determine prehistoric dietary diversity and bioligical relatedness between Native North Americans. Sex of depositor and identification of samples originating from different individuals will also be determined through DNA analyses. This research will allow us to identify statistically relevant dietary differences between males and females in the group who lived at the same time. Because paleofeces contain the dietary remains of specific members of a population, these interdisciplinary analyses have the potential to revolutionize prehistoric and modern investigations of gender differences in diet, health, and nutrition.
Children's health in the prehistoric southwest
Children's health in the prehistoric southwest is a subject that a number of researchers have examined, particularly given the relative abundance of well-preserved human skeletal remains that have been excavated from the region. Most researchers, however, have addressed the question of children's health from a very local, site specific perspective rather than from a broader, southwestern perspective. For this research, I synthesized data from previously analyzed human skeletal remains in different cultural contexts (Anasazi, Mogollon, Hohokam, and Sinagua), site sizes (small and large), and time periods (AD 1 - protohistoric) to address the issue of children's health from a broader, southwestern perspective. The intent of this research is to review and discuss the main health indicators observable on human skeletal material, and to ascertain patterns of children's health through time and across cultural boundaries in the prehistoric southwest. Southwestern archaeologists have long speculated on the human biological consequences to the adoption of corn agriculture in such a potentially marginal environment. There is strong evidence that the climate in the southwest was almost always marginal for trying to subsist on corn agriculture. Palkovich (1984) states that human diet and health would have suffered in that context, going from bad to worse as the agricultural subsistence base increased in importance and use through time, inducing "endemic nutritional inadequacy" (Palkovich 1984: 436) for southwestern populations. Stodder (1990) also indicates that health problems increased through time and at larger sites as populations became more sedentary, reliance on corn agriculture became more pervasive, and the rate of infectious disease transfer would have increased. Population aggregation and the subsequent increase in site size associated with increased reliance on corn agriculture has also been cited by Walker (1985) as probable cause for increased health problems such as anemia.
Therefore, researchers tend to believe that the health of prehistoric southwestern populations decreased through time as people became more sedentary, population became aggregated in larger sites, and people became more reliant on corn agriculture as a subsistence base. The health of children in such a setting is seen as potentially disastrous as infant mortality rates increased. This study is a synthesis of the analyzed human skeletal remains from a large number and variety of archaeological sites in the southwest. Differences in children's health status of populations through time, from small and large sites, and from different cultural affiliations are analyzed to discern potential differences in health status. The affects of these differences on children's health is particularly noted and discussed.
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