Middle Holocene climate change forced significant environmental response and influenced human activities throughout southern Arabia. Climate models and proxy data indicate that climate along the southern Arabian peninsula changed from a moist phase, spanning the early to middle Holocene, to an arid phase, which persisted for the last ca. 5,000 years. A weakening and southward shift of the Southwest Indian Monsoon System, forced by northern hemisphere insolation variations in the precession band and/or glacial boundary conditions, is suggested as the mechanism for the abrupt shift to more arid conditions. Geoarchaeological evidence suggests that agriculture was more widespread and evolved alongside the development of irrigation technologies during a period when rainfall was more plentiful than today. Here we investigate the surficial record of the dynamic fluvial response to the late Quaternary climate shift and reconstruct the geochronology of the geomorphic evolution of a significant portion of the ca. 125 km length of Wadi Sana, a north-flowing tributary to the Wadi Hadramout system. Using differential-corrected GPS-based survey, combined with analysis of the sedimentary record, the RASA (Roots of Agriculture in Southern Arabia) Project has created a paleohydrologic reconstruction of Wadi Sana in order to provide a context for understanding how fluvial landscapes, hydrologic regime, and human activity reacted to ivchanging middle Holocene climate. Radiocarbon and luminescence dating of remnant silt terraces suggests that fine-grained sediment began accumulating on an older (late-Pleistocene) coarse cobble surface between 12,000-7,000 years ago and continued aggrading until about 5,000 years ago. Paralleling the climate shift, Wadi Sana began incising and eroding the thick sediment infilling about 4,500 years ago, which has continued to the present time. Field reconnaissance and map analysis reveals structural and lithologic controls on the source and availability of these fluvial sediments for downstream deposition during the late Pleistocene and Holocene. Hydrologic modeling of active present-day channels within Wadi Sana estimates stream velocities at 2.2 m/s and stream discharges of 444 m3/s. We propose that a change in hydrologic regime, driven by the monsoon shift, is the cause of the middle Holocene channel adjustment from an aggradational to incising mode in Wadi Sana.

Thesis (M.S.)--Humboldt State University, 2009. / Includes bibliographical references (leaves 62-69). Also available via Humboldt Digital Scholar.

Thesis (Ph. D.)--Pennsylvania State University, 1990. / Vita. Includes bibliographical references.

Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2017-06-27T15:43:37Z No. of bitstreams: 1 DISSERTAÇÃO MESTRADO RENATA LIMA DA COSTA.pdf: 3354797 bytes, checksum: 32c50ae4ec262f98d3a557ed8afe9eaa (MD5) / Made available in DSpace on 2017-06-27T15:43:37Z (GMT). No. of bitstreams: 1 DISSERTAÇÃO MESTRADO RENATA LIMA DA COSTA.pdf: 3354797 bytes, checksum: 32c50ae4ec262f98d3a557ed8afe9eaa (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico / nstitut de Recherche pour le Développement / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geoquímica, Niterói, RJ / Sabendo-se que as condições hidrológicas de um sistema flu vial depende diretamente do clima regional, e que as mudanças climáticas do Holoceno atingiram várias regiões da Amazônia de diferentes formas, este trabalho visa r econstituir, através de estudos de sondagem lacustre, o cenário paleoambiental e as condi ções hidrológicas atuantes durante o Holoceno no lago Acarabixi, localizado na p lanície sedimentar do médio Rio Negro. A caracterização das unidades litológicas foi real izada através de medidas de densidade, teor em água, matéria orgânica, granulomet ria, e lâminas de material sedimentar bruto . A origem da matéria orgânica foi avaliada a partir da relação entre carbono e nitrogênio orgânicos e seus isótopos estáveis ( δ 13 C e δ 15 N), e de petrografia. A quantificação das frações minerais foi realizada atrav és de espectrometria de infravermelho, e a identificação através de análises de difração de raios X na fração argilosa. A cronologia foi realizada a partir de data ções radiocarbônicas ( 14 C) AMS. Os registros sedimentares de ambos os testemunhos analisados m ostraram a alternância entre ambientes de características deposicionais de maior e de menor energia hidrodinâmica. As diferenças apresentadas na sedimenta ção dos testemunhos estão relacionadas com a migração lateral do canal principal de um braço do Rio Negro que passa pelo Lago Acarabixi. Esses registros mostraram quatro fases de sedimentação: 9500-8100 14 C AP; 8100-7400 14 C AP; 7400-1600 14 C AP, e 1600 14 C AP–Presente. A ausência de registro sedimentar na terceira fase pelo test emunho ACA 02/03, está relacionada a fortes eventos de inundação, teriam remo vido o sedimento no testemunho ACA 02/03, que se localizava neste período m ais próximo do canal principal de corrente. A análise da matéria orgânica i ndicou origem pedogênica. Ela seria oriunda da lixiviação de solos podzólicos da bacia do Rio Negro, e transportada pelo Rio Negro e depositada junto com o sedimento no L ago Acarabixi. De modo geral, a planície de sedimentação estudada no Rio Negro demon strou ser um ambiente em que os centros de sedimentação variam ao longo do temp o. Estes centros de sedimentação estariam relacionados ao deslocamento latera l dos canais principais de correntes dos rios, além de seu preenchimento pelas ench entes. Podem ser reconhecidas duas fases neste preenchimento: uma fase de for te deposição com migração lateral dos canais até 8000 anos e uma fase de sedimentação mais lenta com características mais lacustres após 8000 anos AP / Knowing that the hydrologic conditions of a fluvial sy stem depends directly on the regional climate, and that the Holocene climatic chang es reached several areas of Amazonia in different ways, this work seeks to reconstitute , through studies of lacustrine survey, the paleoenvironment and the hydrologic condit ions active during Holoceno in the lake Acarabixi, located in the sedimentary plain of medium Rio Negro. The characterization of the litologics units was accomplished th rough density measures, % in water, organic matter, granulometry, and material she ets to silt up rude. The origin of the organic matter was evaluated starting from the relatio nship between carbon and organic nitrogen and δ 13 C and δ 15 N, and of petrografy. The quantification of the mine ral fractions was accomplished through infrared-espectrometry, and the identification through analyses of diffraction of rays X in the loamy fractio n. The chronology was accomplished starting from datings radiocarbônicas ( 14 C) AMS. The sedimentary registrations of both analyzed core showed the alternation among environmen ts from smaller and bigger hydrodynamic energy. The differences presented in the sedimentation of the core are related with the lateral migration of the main chann el of an arm of Rio Negro that goes by the Lago Acarabixi. Those registrations showed four sedimentation phases: 9500- 8100 14 C AP; 8100-7400 14 C AP; 7400-1600 14 C AP, and 1600 14 C AP-present. The absence of sedimentary registration in the third phase for the core ACA 02/03, is related to strong flood events, they would have removed the se diment in the core ACA 02/03, that was located closer of the main channel of current i n this period. The analysis of the organic matter indicated pedogenic origin. The organic matter would be originating from of the ‘ lixiviação’ of podzóls of Rio Negro basin, and transported by Rio Negro and deposited with the sediment in the Lago Acarabixi. In general, the sedimentation plain studied in Rio Negro demonstrated to be an environme nt in that the sedimentation centers vary along the time. These sedimentation cente rs would be related to the lateral displacement of the main channels of currents of the riv ers, besides it’s completion for the flooding. Two phases can be recognized in this comple tion: a phase of strong deposition with lateral migration of the channels to 8 000 years and a phase of slower sedimentation with more lacustrine characteristics after 8000 years AP.

Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2017-06-28T18:00:50Z No. of bitstreams: 1 moreira, 2008.pdf: 3355865 bytes, checksum: 22ec01a744345548acc67908e25fcd32 (MD5) / Made available in DSpace on 2017-06-28T18:00:50Z (GMT). No. of bitstreams: 1 moreira, 2008.pdf: 3355865 bytes, checksum: 22ec01a744345548acc67908e25fcd32 (MD5) / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geoquímica, Niterói, RJ / A Bacia Amazônica é acompanhada, ao longo do curso dos seus rios, por planícies de inundação. Sabe-se que estas regiões apresentam um grande potencial no armazenamento de matéria orgânica, que por sua vez, reservam importantes informações sobre mudanças climáticas ocorridas no passado. O conhecimento destas alterações pretéritas permite o entendimento de como os ecossistemas podem reagir a futuras mudanças no clima. Tendo em vista estas características, o objetivo deste estudo é reconstruir as mudanças pal eoambientais e paleohidrológicas do Lago Santa Ninha, na Várzea do Lago Grande de Curuai, localizada na margem direita do Rio Amazonas, à apr oximadamente 850 km da foz. Foram analisados dois testemunhos, denominados como TA12 e TA14 que apresentam, respectivamente, 2,10 e 2,70cm de compr imento. A determinação do teor de água, densidade aparente, granulometria e m ineralogia permitiram reconstruir a hidrodinâmica da região. A análise da composição da matéria orgânica, através da concentração de carbono e nitrogênio e d os isótopos estáveis δ 13 C e δ 15 N indicaram as alterações na vegetação e as dataçõe s por carbono 14 revelaram que o testemunho TA14 apresenta 5700 anos cal AP. E ste estudo colocou em evidencia diferentes ambientes sedimentares: na bas e do testemunho até 5000 anos cal AP temos uma vegetação inundada que foi gr adualmente substituída por bancos de gramíneas e por uma planície com secas sa zonais em 4000 anos cal AP até alcançar, desde 700 anos AP as condições atuais deste lago. Essas mudanças são interpretadas como a resposta a um aumento do n ível da água do rio durante as enchentes, que por sua vez são conseqüências de alt erações climáticas ocorridas na região / Amazonian Rivers are accompanied, during their cour se, by floodplains, which are named “várzeas”. It is known that these regions hav e a great potential in the storage of organic matter, which in turn, provides importan t information about climate change occurred in the past. Knowledge of these changes al lows the understanding of how ecosystem may respond to future changes in climate. The physical, chemical and geochemical characteristics of lacustrine sediments were studied to reconstructed paleohydrological control on sedimentation in an Am azonian floodplain. Two cores were collected at the Lago Grande de Curuai floodpl ain, in Santa Ninha lake, located on the right margin of the Amazon River at 850km of the estuary. Water content, granulometry, radiocarbon datation, microscopic ana lyses, organic carbon and nitrogen content and δ 13 C were used to characterize the sedimentary process es. The core TA12 is 210 cm-long and the TA14 has 270cm tha t correspond to 5700 years cal BP. The core points out different sedimentary environments: a flooded vegetation at the base of the core till 5000 cal yrs BP is sub stituted by graminea banks changing to a floodplain encompassing prolonged annual dryne ss at 4000 cal yrs BP. Since 700 BP the present day varzea lake, permanently ove rflooded, has been installed. These changes are interpreted as a response to an i ncrease in the level of water in the river during the floods, which in turn are cons equences of climate change occurring in the region

This study deploys compound-specific multi-proxy isotopic study of lipid biomarkers to understand Neogene climatic and ecological variabilities in the Himalayan foreland. The investigation of compound-specific carbon and hydrogen isotopes along with glycerol dialkyl glycerol tetraether (GDGT) is the first of its kind for the Nepalese Siwalik. A total of 49 mudstone (and some paleosol) samples were collected from the paleomagnetically age-constrained Siwalik strata in the Surai Khola and Karnali River sections. δ13C results suggest a domination of C3 trees between 12 and 8.5 Ma, and a stepwise expansion of C4 grasses starting gradually at 8.5 Ma and culminating rapidly around 5.5 Ma. δD results show an overall gradual increase in rainfall since 12 Ma, with a rapid intensification around 5.5 Ma. The negative correlation between rainfall and GDGT-derived paleotemperature prior to 5.5 Ma indicates that the region experienced higher rainfalls during colder periods and vice versa. We propose that this negative correlation could be related to the strong presence of mid-latitude westerlies in the region because of the subdued Himalayas, when summer monsoon winds were weaker, that brought enhanced winter-precipitation particularly during colder periods. After 5.5 Ma, our data show a conspicuous positive correlation between rainfall and annual temperature, indicating the onset of modern-style seasonality in rainfall in the Indian subcontinent, which generates more rainfall during summer than during winter. Notably, this initiation of the Indian monsoon around 5.5 Ma favored the dominance of C4 grasses over C3 trees that is reflected in our δ13C data.

No description available.

No description available.

The disintegration of the Classic Maya throughout the Terminal Classic (750-900 C.E.) is a complex loss of human population that has presented many questions about climate change and its impact on humanity. With droughts proposed as a prominent cause, understanding the quality and availability of groundwater resources at the time is pivotal to further determining the spatial and temporal distributions of population deterioration. The Yucatan aquifer consists of karstic cave systems, with a small number of inland lakes, which have previously been termed closed to the aquifer. It is important to understand how both of these types of water bodies react to long- and short-term forcing mechanisms such drying climate, sea-level rise and precipitation events. Using a variety of spatial and temporal records to determine aquifer evolution, changes and connectivity throughout the Holocene it will further understanding of how the aquifer reacts to changes in climate and the implications this may have had on the Classic Maya. Four sediment cores from Pac Chen Lake and two sediment cores from Carwash Cenote were collected to investigate Holocene paleoclimatic trends on the Yucatan Peninsula in Mexico. Records of past climate, groundwater conditions and flooding history at both sites were determined through microfossil and micro X-Ray fluorescence data. In Pac Chen Lake, elevation and timing of flooding of the lake coincided with sea-level rise. Using Ti, Fe and K records to determine wet vs dry conditions, dry periods through the terminal classic coincided with other paleoclimate records, but with no evidence of draw-down within the lake. Both of these observations imply connection of the lake to the aquifer. The Cl record from Carwash was used alongside a core from the Yax Chen cave system to observe spatial and temporal potability of the aquifer. An overall freshening trend in the coastal groundwater occurred throughout the Holocene. The largest amount of this freshening transpired through the Terminal Classic. At this time, populations inland were experiencing deterioration, while coastal populations along the coast continued to survive. Comparing Cl records at various depths and distances from the coast proved that Cl is impacted by proximity to the halocline. / Thesis / Master of Science (MSc)

Long-duration records are necessary to understand and assess the long-term dynamics of natural systems. The purpose of this research was to use dendrochronologic modelling to construct proxy histories of hydroclimatic conditions and Pacific salmon abundance in west central British Columbia. A multi-species regional network of tree ring-width and ring-density measurements was established from new and archived tree-ring chronologies. These chronologies were then used in multivariate linear regression models to construct proxy records of nival river discharge, summer temperature, end-of-winter snow-water equivalent (SWE), the winter Pacific North America pattern (PNA) and Pacific salmon abundance. All proxy hydroclimate records provide information back to 1660 AD. Reconstructions of July-August mean runoff for the Skeena and Atnarko rivers describe below average conditions during the early- to mid-1700s and parts of the early-, mid- and late-1900s. Models describe intervals of above average river discharge during the late-1600s, the early-1700s and 1800s, and parts of the early- and mid-1900s. Fluctuations in proxy reconstructions of July-August mean temperature for Wistaria and Tatlayoko Lake, May 1 SWE at Mount Cronin and Tatlayoko Lake and October-February PNA occurred in near synchrony with the shifts described in runoff records. Episodes of above average runoff were typically associated with periods of enhanced end-of-winter SWE, below average summer temperature and positive winter PNA. A history of Pacific salmon abundance was reconstructed for four species of salmon (chinook, sockeye, chum and pink) that migrate to coastal watersheds of west central British Columbia. Proxy records vary in length and extend from 1400 AD, 1536 AD and 1638 AD to present. Salmon abundance reconstructions varied throughout the past six centuries and described significant collapse in population levels during the early-1400s, the late-1500s, the mid-1600s, the early-1700s, the early-1800s and parts of the 1900s. Wavelet analyses of reconstructed hydroclimate and salmon population records revealed low- and high-frequency cycles in the data. Correlation analyses related reconstructions to atmospheric teleconnection indices describing variability in North Pacific sea surface temperatures and the Aleutian Low pressure centre. To a lesser degree, relationships were also established between reconstructions and the El Niño-Southern Oscillation. Results thus confirm the long-term influence of large-scale ocean and atmospheric circulation patterns on hydroclimate and Pacific salmon abundance in west central British Columbia. The reconstructions introduced in this thesis provide insights about the long-term dynamics of the west central British Columbia environment. Several reconstructions presented in this thesis provide novel contributions to dendrohydroclimatic and paleoecologic research in Pacific North America. Proxy runoff records for the Skeena and Atnarko rivers are the first to be constructed for nival-regime basins in British Columbia. The models of Skeena River runoff and Mount Cronin SWE are additionally the first reconstructions of runoff and snowpack in Pacific North America based on a ring-density chronology, demonstrating the significant contribution that wood density measurements can make to dendrohydroclimate research. The models of Pacific salmon stocks are the first to utilize climate-sensitive tree-ring records to construct a history of regional salmon abundance and thus represent a significant advancement to paleoecological modelling. / Graduate