Browsing by Subject "Paleoecology"

Now showing 1 - 3 of 3
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    Climatic and anthropogenic influences on aquatic ecosystems in the valley of the Great Lakes, Mongolia.
    (2008-12) Shinneman, Avery Lynn Cook
    Climate warming and major land use changes have profoundly affected the Mongolian landscape in the past several decades. As in many arid and semi-arid regions, water resources are critically important for ecological, social, and economic viability. In Mongolia, traditional semi-nomadic pastoralism contributes substantially to the national economy as well as to individual subsistence and depends on limited freshwater resources to provide for grazing herds and human needs. Yet, because of substantial variability across this immense region, its remoteness, and recent political transitions, little work has been done to monitor water quality or to set baseline standards against which to measure future changes. Compounding the problem is a lack of well-resolved paleo-ecological and paleo-climatological work. These data are necessary to provide a foundation for understanding the natural variability in the aquatic systems of the region, especially with recent changes in climate and land use. This work is a contribution to developing these records by first, developing diatom-based inference models for total phosphorus and salinity, and second, applying the models to investigate lacustrine sediment records of past changes. The diatom-based inference models were based on a survey of the water chemistry, physical characteristics, and diatom flora of 64 lakes in western Mongolia. The region had a diverse diatom flora with over 300 species, nearly 100 of which had not been previously reported from Mongolia, from lakes ranging from fresh to hypersaline. The many isolated lake basins provided unique ecosystems where multiple unique communities, novel species distributions, and new and endemic flora were found. Three of these new species are described here in a careful examination of the genus Cyclotella in western Mongolia. Canonical correspondence analysis (CCA) was used to identify four variables (specific conductivity, total phosphorus, bicarbonate, and lake morphology) that were significantly related to the distribution of diatoms; predictive models were developed for specific conductivity and total phosphorus using weighted averaging regression and calibration methods. The application of these models to dated lake sediment cores, along with interpretations of other geochemical and sediment characteristics, was then used to develop records of variability in lake salinity and nutrient flux. The interpretation of diatom and sedimentary records demonstrated increases in nutrient fluxes to the lakes related to climate warming and major changes in land-use over the last 20 years. Diatom-inferred lake salinity was correlated with changes in temperature over the past 2000 years, as inferred from tree-ring records, demonstrating a positive relationship between increased warming and increased lake salinity in recent geologic history. Changes in warm-season temperature, as inferred from tree-rings, in the most recent decades were less-well correlated with inferred changes in salinity than over most of the 2000 year record. However, instrumental records of winter temperature were well correlated with recent shifts in inferred salinity, perhaps suggesting recent changes in climate that are unique from those over the past several thousand years.
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    Phylogeography of Douglas-fir: testing hypotheses from the fossil record.
    (2010-06) Gugger, Paul Francis
    Paleobotanical records and molecular data from modern forests can provide a synergistic understanding of the ecological and evolutionary history of an organism. I used the fossil record to generate hypotheses that I tested with statistical phylogeographic methods for Douglas-fir (Pseudotsuga menziesii). In Chapter 1, I describe alternative scenarios of glacial refugia and postglacial migration based on compiled fossil pollen and macrofossil evidence from the late Quaternary. In Chapter 2, I test those hypotheses using coalescent analyses of mitochondrial and chloroplast DNA sequence data. I also test the paleobotanical hypothesis that Douglas-fir’s two varieties diverged coincident with the Cascade orogeny in the late Pliocene. Finally in Chapter 3, I test whether Mexican Douglas-fir diverged from U.S. populations in the Miocene or Pleistocene, consistent with alternative interpretations of limited fossil evidence in the region. The present patterns of molecular variation in Douglas-fir are well-described by Pliocene (or early Pleistocene) divergence of its varieties, mid-Pleistocene colonization of Mexico, and restriction to multiple glacial refugia in the late Quaternary. Holocene expansion into Canada resulted in recontact among varieties and hybridization driven entirely by pollen dispersal but not seed dispersal. Douglas-fir populations have responded individualistically to past climatic and geologic change, such that some underwent expansions while others contracted to higher elevation and some diverged while others coalesced. These findings highlight the complementary insights that fossil and molecular data provide and can be used to inform the conservation and taxonomy of Douglas-fir.
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    Stable isotopic investigation of late Neogene terrestrial paleoecology and paleoclimate of the circum-Mediterranean region
    (2010-08) Matson, Samuel Dean
    The late Neogene was an interval of important global change, in which gradual cooling and aridification resulted in terrestrial ecosystems over much of the world that became essentially modern. The geologic record of the circum-Mediterranean region presents an exceptional opportunity to examine the interplay of tectonics, biology, and climate during this important transition, because the paleogeography of this region was influenced heavily by a unique tectonic situation governed by both large-scale convergence between Europe and Africa and smaller-scale extension within the Mediterranean Basin. Effects of this distinct tectonic regime include the establishment of land bridges that allowed migration of animals between Europe, Africa, and Asia, large-scale desiccation of inland seas due to tectonic closure of seaways connecting the Mediterranean Sea and the Atlantic Ocean, and development of intramontane basins that preserve an extensive sedimentary record of past continental environments. In combination with this unique tectonic situation, regional climatic and ecological effects in the circum-Mediterranean region resulted in a late Neogene transition to modern terrestrial ecosystems that was in many ways different than general global patterns. In order to better undstand the late Neogene transition both regionally and globally, the research presented here focuses on reconstruction of terrestrial paleoclimate and paleoecology in Spain and Italy through the development of a stable isotopic record from biogenic and and authigenic minerals preserved in fossil mammals and continental sediments. vii A reconstruction of Late Miocene to Pleistocene paleoclimate and paleoecology in Spain was developed through analysis of the oxygen isotopic composition (δ18O) of biogenic phosphate in tooth enamel and dentine from fossil mammals. Comparisons of δ18O between clades are consistent with morphological interpretations of habitat and physiology, and suggest a semi-aquatic habitat for anthracotheres, hippopotamids, and castorids, and open or mixed habitats for most gracile taxa such as equids and cervids. Comparisons of enamel and dentine δ18O indicate slight diagenetic alteration of dentine, but also suggest that such comparisons can be used to reconstruct reasonable values of diagenetic water δ18O. Since the δ18O of modern horses has been demonstrated to be a reasonable proxy for the δ18O of local meteoric water, which is in turn strongly dependent on mean annual temperature (MAT) for modern mid- to high-latitudes, the δ18O of fossil horses from Spain was used to reconstruct terrestrial paleotemperature. These reconstructions are consistent with global cooling during the late Cenozoic, with MAT for the late Miocene that is warmer than today by ~1–2 ºC in NE Spain and by ~4–5 ºC in SE Spain. The difference of ~8–9 ºC between NE and SE Spain for the Late Miocene is ~60% greater than the MAT difference between these same areas today. To examine the ways in which a desiccated Mediterranean Basin affected surrounding terrestrial environments during the Messinian Salinity Crisis (MSC), a paleoclimatic record of this event was developed through integrated analyses of sedimentology, δ18O, and the stable carbon isotopic composition (δ13C) of latest Miocene authigenic carbonates from the Baza Basin in southern Spain. A transition from dolomite- and calcite-rich palustrine and distal alluvial fan sediments to lacustrine diatomites and calcite-rich limestones is accompanied by a decrease in both δ13C and δ18O, reflecting increased lake level under a wetter climate. The mean δ18O of latest Miocene lacustrine calcite is significantly lower than that of modern closed-basin lakes in the Iberian Peninsula, and likely represents overflow or through-flow conditions with inflow waters derived from the surrounding Betic mountains. This result is consistent with some aspects of climate model reconstructions of the MSC, which suggest strengthened storm tracks from the Atlantic Ocean over southern Europe. Orographic uplift of these air masses along the Betic Cordillera may have resulted in enhanced precipitation and runoff in southern Spain. To examine the interplay between tectonics, environmental change, and biological evolution, a paleoecological record was developed from the δ13C of Late Miocene paleosols from the Baccinello Basin in northern Italy. These paleosols span the extinction of Oreopithecus bambolii, which was the only European hominoid to survive an important extinction event ca. 9.6 Ma. Oreopithecus is important for understanding the evolutionary history of Late Miocene hominoids, since its peculiar morphology precludes a simple interpretation of its phylogenetic position. The paleosol δ13C values show very low temporal and spatial variability (indicating plant ecosystem stability through time) and provide no evidence for ecologically significant changes in floral composition spanning the Oreopithecus extinction event. These results validate assumptions about the importance of tectonics and species interaction as an underlying cause for the extinction of Oreopithecus and its associated fauna. The paleosol δ13C values fall entirely within the range of isotopic variability for modern plants following the C3 photosynthetic pathway, indicating that C4 vegetation was not an important component of biomass. The research presented in this dissertation underscores the importance of the Mediterranean region for consideration of the interplay of climate, tectonics, and ecology during important global transitions occurring in the Late Miocene. The results of this research validate the utility of stable isotopic approaches to paleoenvironmental reconstruction, and provide a powerful complement to independent means of reconstructing terrestrial systems that are complex and often poorly understood, but nevertheless an extremely important component of the Earth System.