Theses and Dissertations from UMD
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Item Climate Change During Intervals Of The Past Millennium In The Southwestern Tropical Pacific(2018) Lopatka, Alex; Evans, Michael N; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Limited observations from the tropical Pacific over the past millennium make it difficult to assess whether different time periods had significant variations in El Nino-Southern Oscillation (ENSO) amplitude and frequency. Composited simulation results from climate models participating in the Paleoclimate Modeling Intercomparison Project suggest no difference in statistical variance and ENSO event frequency for the Medieval Climate Anomaly (MCA), Little Ice Age (LIA), and the modern Industrial Era. ENSO may not be sensitive to external radiative forcings. Unforced variability arising from the coupled ocean-atmosphere system could explain the observed past millennium results. New coral geochemical measurements were collected from Aitutaki, southern Cook Islands in the southwestern tropical Pacific and composited with existing coral geochemical observations from Rarotonga to increase the temporal coverage of climate data over the past millennium. Forward modelling of coral oxygen isotopes as a function of sea surface temperature and the oxygen isotopic composition of seawater suggests this location is sensitive to interannual variations in the position of the South Pacific Convergence Zone (SPCZ) driven by ENSO activity. Analysis of observed interannual \delo\ indicates interannual variations are driven primarily by sea surface salinity but also sea surface temperature forcings. More negative (positive) coral oxygen isotope results indicate warmer/wetter (cooler/dryer) conditions that occur at Aitutaki when La Nina (El Nino) events redistribute the South Pacific Convergence Zone away (towards) the equator. Spatial correlation of the coral \delo\ signal with regional and tropical climate variables support the interpretation that Aitutaki coral \delo\ varies according to changes in the SPCZ and ENSO activity. Results from modern Aitutaki coral oxygen isotopes may be used to interpret coral data collected from earlier periods of time. Paired coral oxygen isotopes and Sr/Ca measurements were made on diagenetically-screened samples radiometrically dated to the Medieval Climate Anomaly. These results, used to calculate interannual oxygen isotopic composition of seawater anomalies, show higher statistical variance in the fossil record relative to the modern Aitutaki/Rarotonga composite record. Singular spectrum analysis shows the first ten reconstructed components explain 79-86\% of the variability in the timeseries. Composited interannual frequency (2-10 year period) components show variable oxygen isotopic composition of seawater throughout the MCA suggesting an active ENSO period. Large variations of 0.6 permil in calculated oxygen isotopic composition of seawater suggest potential decadal shifts in oxygen isotopes from warmer/wetter to cooler/dryer conditions. Long term trends in calculated oxygen isotopic composition of seawater during the earlier MCA from more negative to more positive values suggest a transition from warmer/wetter to cooler/dryer conditions. Together, the results suggest a highly variable MCA period relative to the modern period. This new data may be used in conjunction with other observations for data/model comparisons to better understand hydroclimate variability over the past millennium.Item Dissonant Belonging and the Making of Community: Native Hawaiian Claims to Selfhood and Home(2016) Soon-Ludes, Jeannette; Kim, Seung-kyung; Women's Studies; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In 1898 the United States illegally annexed the Hawaiian Islands over the protests of Queen Liliʽuokalani and the Hawaiian people. American hegemony has been deepened in the intervening years through a range of colonizing practices that alienate Kanaka Maoli, the indigenous people of Hawaiʽi, from their land and culture. Dissonant Belonging and the Making of Community is an exploration of contemporary Hawaiian peoplehood that reclaims indigenous conceptions of multiethnicity from colonizing narratives of nation and race. Drawing from archival holdings at the University of Hawaiʽi, Mānoa and in-depth interviews, this project offers an analysis of public and everyday discourses of nation, race, and peoplehood to trace the discursive struggle over Local identity and politics. A context-specific social formation in Hawaiʽi, “Local” is commonly understood as a multiethnic identity that has its roots in working-class, ethnic minority culture of the mid-twentieth century. However, American discourses of race and, later, multiethnicity have functioned to render invisible the indigenous roots of this social formation. Dissonant Belonging and the Making of Community reclaims these roots as an important site of indigenous resistance to American colonialism. It traces, on the one hand, the ways in which Native Hawaiian resistance has been alternately erased and appropriated. On the other hand, it explores the meanings of Local identity to Native Hawaiians and the ways in which indigenous conceptions of multiethnicity enabled a thriving community under conditions of colonialism.Item ON THE SUMMER TIME DEVELOPMENT OF THE NORTH PACIFIC SEA-LEVEL PRESSURE ANTICYCLONE(2008-04-16) Chan, Steven C; Nigam, Sumant; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With the exception of the North Indian Ocean, subtropical ocean basins are dominated by climatological planetary-scale sea-level pressure (SLP) anticyclones. The seasonal variability of the North Pacific subtropical SLP anticyclone is examined here. The largest ERA-40 and linear diagnostic modeled Northern Hemisphere SLP seasonal variabilities are found in the mid-latitudes with relatively less change in the subtropics; this leads to the poleward boreal summer development of the North Pacific and Atlantic subtropical SLP high. Unlike the Northern Hemisphere, the Southern Hemisphere subtropical SLP highs develop equatorward. The zonal-mean Northern Hemisphere subtropical SLP and seasonal variabilities are dominated by continental seasonality - a uniform boreal winter descent changing to a zonally asymmetric continental monsoon ascent and heat lows with relatively little change over the oceans. A linear diagnostic model is used to examine the forcing of the SLP seasonal cycle. The modeled North Pacific SLP seasonal variability is forced mainly by winter stormtracks, extra-tropical North Pacific diabatic cooling, and boreal winter ITCZ. Asian monsoon forces a SLP ridge downstream, but the monsoon response is cancelled significantly by East Pacific diabatic heating and transients. North American diabatic heating and transients are also found to have a limited upstream effect. Boreal summer ITCZ forcing has limited North Pacific SLP response, and that is possibly linked to the prescribed tropical zonal-mean easterlies. ERA-40 and TRMM CSH diabatic heating is inter-compared with other independent measures of diabatic and latent heating. Zonal-mean ERA-40 ITCZ diabatic heating is nearly twice that of NCEP and ERA-15 reanalyses, which indicates a much stronger ERA-40 Hadley Circulation. The ERA-40 Walker Circulation is also stronger than of NCEP Reanalysis, which is consistent with excessive Maritime Continent diabatic heating. Largest differences are also found in the Tropical East Pacific and Atlantic. Vertically integrated TRMM CSH heating is too weak even compare with other TRMM products. However, TRMM CSH mid-tropospheric tropical heating compares well with other datasets. The largest differences appear in the upper and lower troposphere, which implies CSH limitations in handling shallow convection (a known issue) and stratiform precipitation in deep convection.Item Emerging Infectious Disease: Host and Parasite Perspectives(2007-05-15) Beadell, Jon; Wilkinson, Gerald S; Fleischer, Robert C; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Avian malaria and related haematozoa are nearly ubiquitous parasites that can impose fitness costs of variable severity and may, in some cases, cause substantial mortality in their host populations. One example of the latter, the emergence of avian malaria in the endemic avifauna of Hawaii, has become a model for understanding the consequences of human-mediated disease introduction. The drastic declines of native Hawaiian birds due to avian malaria provided the impetus for examining more closely several aspects of host-parasite interactions in this system. Host-specificity is an important character determining the extent to which a parasite may emerge. Traditional parasite classification, however, has used host information as a character in taxonomical identification, potentially obscuring the true host range of many parasites. To improve upon previous methods, I first developed molecular tools to identify parasites infecting a particular host. I then used these molecular techniques to characterize host-specificity of parasites in the genera Plasmodium and Haemoproteus. I show that parasites in the genus Plasmodium exhibit low specificity and are therefore most likely to emerge in new hosts in the future. Subsequently, I characterized the global distribution of the single lineage of P. relictum that has emerged in Hawaii. I demonstrate that this parasite has a broad host distribution worldwide, that it is likely of Old World origin and that it has been introduced to numerous islands around the world, where it may have been overlooked as a cause of decline in native birds. I also demonstrate that morphological classification of P. relictum does not capture differences among groups of parasites that appear to be reproductively isolated based on molecular evidence. Finally, I examined whether reduced immunological capacity, which has been proposed to explain the susceptibility of Hawaiian endemics, is a general feature of an "island syndrome" in isolated avifauna of the remote Pacific. I show that, over multiple time scales, changes in immune response are not uniform and that observed changes probably reflect differences in genetic diversity, parasite exposure and life history that are unique to each species.