In the last few decades, we have been witness to unprecedented changes in precipitation and temperature. Such alterations to our climate system have important implications for terrestrial ecosystems that billions of people depend on for their livelihood. The situation is especially tenuous for those living directly off the landscape via resources from natural ecosystems or subsistence agriculture as in much of tropical Africa. Studies of past climates provide potential analogues and help validate models essential for elucidating mechanisms that link changes in climate mean and variability and how they may affect ecosystem distribution and productivity. However, despite the importance of the paleo-record for insight into the future, tropical proxy records are rare, low resolution, and too short to capture important intervals that may act as analogs, such as the Last Interglacial (MIS 5e; ~130-115ka).Long, high-resolution drill cores from Lake Malawi, southeast Africa, provide a record of tropical climate and vegetation that extends back ~1.2mya, comprising many continuous glacial-interglacial cycles. My primary research involves conducting pollen analyses on these cores. First, I analyzed a high-resolution interval of the shortest Malawi core in order to better understand abrupt vegetation transitions during the Last Deglaciation. Further analysis was conducted on the longest Malawi core, beginning with an interval covering all of the Penultimate Glacial through the Last Interglacial. The resultant pollen data has shown that abrupt, large-scale landscape transitions from forest to desert follow local insolation and lake levels at the site, with a strong dependence of forest/woodland vegetation types on mean rainfall as well as rainfall seasonality. The interpretation of paleodata requires a good understanding of modern processes, thus another project has focused on using model simulations of the Last Interglacial and modern satellite NDVI time series to highlight dynamical and statistical relationships between vegetation and climate change. This work suggests that despite suggested links between monsoon intensity and SSTs in the southern African tropics, insolation controls on atmospheric circulation are the primary drivers of vegetation reorganization. In addition, this work highlights the importance of rainfall seasonality and dry season length in addition to precipitation controls on vegetation.

Stratigraphic records in Middle Park in north-central Colorado provide evidence for the late Quaternary geomorphic and environmental history of a non-glaciated Southern Rocky Mountain basin. Episodes of geomorphic instability apparent in the stratigraphic record coincide with changes in paleoenvironmental records from above 2750 m in north-central Colorado, suggesting that the western Middle Park landscape was sensitive to environmental changes affecting the region over the last ~14,000 years. Tributaries were incised prior to 14.0 ka, but deposits older than 12.0 ka are rare. Upland erosion and incision followed by rapid aggradation in alluvial settings between 12.0 and 11.0 ka coincide with evidence for regional temperatures at or above present, and is interpreted to signal the onset of Holocene summer-wet precipitation. A widespread soil-stratigraphic marker represents a long period of landscape stability between <11.0 and 6.0 ka in upland and alluvial settings. Pedologic evidence from upland settings indicates the expansion of grass and forest cover to lower elevations that today are characterized by sagebrush steppe, probably during a period of increased summer precipitation relative to present. During the late Holocene, episodes of aggradation in alluvial valleys at 6.0-1.0 ka and 0.6-0.2 ka and soil formation in uplands at 5.0-3.5 ka and 2.5-1.0 ka overlap with evidence for cooling at higher elevations. Incision of valley floors documented at 1.0-0.6 ka and during the last few centuries and episodes of erosion in uplands at 3.5-2.5 ka, after 1.0 ka, and within the last few centuries, are roughly synchronous with evidence for warming. Upland and alluvial stratigraphic records are interpreted to indicate that during cool intervals summer precipitation was diminished, resulting in relative hillslope stability and gradual valley bottom aggradation, while pulses in summer precipitation accompanying warmer episodes caused basin-wide geomorphic instability. The recent increasing frequency of geomorphic instability appears to correspond with an increase in sagebrush steppe at the expense of forest and grass cover, interpreted to represent progressive drying during the late Holocene. It stands to reason that future warming, if accompanied by similar patterns in precipitation, will result in continued erosion on a landscape already at a threshold of geomorphic instability.

The main objective of this dissertation is to improve the knowledge of glacial chronology and paleoclimate of Turkey during the Late Quaternary. The 36Cl cosmogenic exposure ages of moraines show that Last Glacial Maximum (LGM) glaciers were the most extensive ones in Turkey in the last 22 ka (ka=thousands years), and they were closely correlated with the global LGM chron (between 19&plusmn;23 ka). LGM glaciers started retreating 21.3&plusmn;0.9 ka (1&sigma;) ago on Mount Erciyes, central Turkey, and 20.4&plusmn;1.3 ka ago on Mount Sandiras, southwest Turkey. Glaciers readvanced and retreated by 14.6&plusmn;1.2 ka ago (Late Glacial) on Mount Erciyes and 16.2&plusmn;0.5 ka ago on Mount Sandiras. Large Early Holocene glaciers were active in Aladaglar, south-central Turkey, where they culminated at 10.2&plusmn;0.2 ka and retreated by 8.6&plusmn;0.3 ka, and on Mount Erciyes, where they retreated by 9.3&plusmn;0.5 ka. The latest glacial advance took place 3.8&plusmn;0.4 ka ago on Mount Erciyes. Using glacier modeling together with paleoclimate proxy data from the region, I reconstructed the paleoclimate at these four discrete times. The results show that LGM climate was 8-11oC colder than today (obtained from paleotemperature proxies) and wetter (up to 2 times) on the southwestern mountains, drier (by ~60%) on the northeastern ones and approximately the same as today in the interior regions. The intense LGM precipitation over the mountains along the northern Mediterranean coast was produced by unstable atmospheric conditions due to the anomalously steep vertical temperature gradients on the Eastern Mediterranean Sea. In contrast, drier conditions along the southern Black Sea coast were produced by the partially ceased moisture take-up from the cold or frozen Black Sea and prevailing periglacial conditions due to the cold air carried from northern hemisphere's ice sheets. Relatively warmer and moister air from the south and overlying cold and dry air pooled over the northern and interior uplands created a boundary between the wet and dry LGM climates somewhere on the Anatolian Plateau. The analysis of Late Glacial advances suggests that the climate was colder by 4.5-6.4oC based on up to 1.5 times wetter conditions. The Early Holocene was 2.1oC to 4.9oC colder on Mount Erciyes and up to 9oC colder on Aladaglar, based on twice as wet as today's conditions. The Late Holocene was 2.4-3oC colder than today and the precipitation amounts approached the modern levels. Glaciers present on Turkish mountains today are retreating at accelerating rates and historical observations of the retreat are consistent with the behavior of other glaciers around the world.

Underwater (phreatic) caves are a ubiquitous landform on coastal karst terrain, but the marine geological processes operating in these systems are largely unknown. This dissertation redresses the problem by asking if Bermudian phreatic cave sediments archive sea-level and climate information? An important premise is that coastal cave environments are not identical. They can be categorized based on whether they are terrestrially-influenced (anchialine), completely flooded by saline groundwater (submarine), positioned at sea level (littoral) or in the vadose zone (vadose). For the first time the boundary between modern anchialine and submarine cave environments has been distinguished in Green Bay Cave using a multi-proxy approach (benthic foraminifera, sedimentary organic matter content and carbon isotopic composition - ?13Corg, and grain-size analysis). Twelve push cores were extracted from Green Bay Cave and dated with twenty 14C dates, recovering the first underwater cave succession spanning the Holocene (13 ka to present). Green Bay Cave transitioned through all major cave environments during Holocene sea-level rise (vadose, littoral, anchialine, and submarine), providing a sedimentary model for global cave successions. These relationships provide a novel means to solve Quaternary sea-level and climate problems. For sea level, two examples indicate that the littoral cave can be used as a sea-level indicator, distinguished stratigraphically by microfossil or sedimentary proxies. First, the elevation and timing of when Green Bay Cave was a littoral environment indicates Bermuda experienced an abrupt ~6.4 m sea-level rise at 7.7 ka, coinciding with final collapse of the Labrador sector of the Laurentide Ice Sheet. Second, microfossils preserved in elevated caves at +21 m above modern sea level and dated to marine isotope stage 11 (U-series, amino acid racemization) are consistent with modern Bermudian caves and co-stratigraphic sea level. For climate problems, annual temperature monitoring in Walsingham Cave indicates that cave water is thermally comparable to regional oceanographic conditions in the Sargasso Sea. Three sediment cores dated with sixteen radiocarbon dates indicate that Bermuda’s coldest and stormiest conditions of the last 3.2 ka occurred during the Little Ice Age (proxies: ?18Oc, grain size, bulk organic matter).

Using GIS-based tools and a review of the relevant geological and climatic literature, I attempt to identify the key implications of Quaternary glacial cycles for drainage evolution in eastern Patagonia. In doing so, the stage is set for the proper integration of existing biogeographic and phylogeographic ideas to develop a suite of inferences aimed at elucidating how these processes influenced aquatic biodiversity of Patagonian Argentina. A primary finding of this research is that the southern mainland and/or Tierra del Fuego served as an important cryptic refuge for cold-adapted species, including aquatic taxa. At least one additional aquatic refuge is likely to have existed in either central or northern Patagonia. The low position of the Atlantic shoreline during glacial periods also revealed a much larger and inter-connected drainage network in southern Patagonia. During sea-levels stands below 100m, two new drainage coalescence points on the exposed continental shelf can be recognized among the Chico/Santa Cruz, Coyle and Gallegos river basins and between the Grande and Fuego rivers. Enhanced hydrological discharge during the deglaciation period of Late-Quaternary cycles is expected to have facilitated extensive inter-drainage connections within each of the northern and southern regions of eastern Patagonia via proglacial lake and/or stream coalescence. A large proglacial lake in the Nahuel Huapi Lake region is also recognized as the most likely temporary gateway for aquatic organisms to disperse between the Neuquen and Northern Patagonian Tablelands. I also recognize climate-induced drainage reversals as a bidirectional mechanism of trans-Andean dispersal and an important factor in determining the biogeography of widespread aquatic organisms in Patagonia.

No description available.

This study examined samples part of a larger project exploring environmental changes at Lake Hawdon, mid Canterbury, involving Queen’s University Belfast and the University of Canterbury. The author was responsible for the analysis of 85 fossil diatom samples from Lake Hawdon to create a high resolution study to assess their use as a biological proxy of past environmental changes through the Late Glacial Inter-Glacial Transition. Qualitative interpretations suggest three main phases of environmental change in Lake Hawdon during ~17,000 to 10,000 cal. BP. The first is a cool stage where taxa such as Cocconeis placentula and fragilarioid complex taxa Staurosirella pinnata and Pseudostaurosira brevistriata suggest a cool shallow lake with increasing macrophyte growth. The second phase suggests cold deepening water from at 13,928 +/- 142 to 12,686 +/- 166 cal. BP, dominated by Pseudostaurosira brevistriata, which coincides with the Antarctic Cold Reversal. The third phase represents a warm deep water phase after 12,686 +/- 166 cal. BP, dominated by planktonic taxon Cyclotella stelligera and epiphytic taxon Epithemia sorex, suggesting that Lake Hawdon does not exhibit the Younger Dryas event. Pollen and chironomid data from Lake Hawdon, generated by other project members, are included in the quantitative analyses to further inform palaeoenvironmental inferences generated from diatom data. Chironomid temperature reconstructions complement diatom interpretations for all three phases of change in the lake however diatom resolution allows changes to be detected earlier than other proxies suggest. Stabilisation of the landscape ~12, 686 +/- 166 cal. BP is suggested by tree pollen appearing near the end of the diatom cold phase, confirming with the diatoms and chironomid data that there was a warming out of the cold phase. Interpretations from Lake Hawdon add to other proxy studies in New Zealand that suggest an Antarctic Cold Reversal type event, but fail to highlight the Younger Dryas event. The generation of a transfer function was attempted with the diatom data based on Northern Hemisphere datasets, but a Principal Component Analysis plot highlighted major dissimilarities between the New Zealand fossil data and modern European data. This raised the issue of having morphologically similar but genetically separate taxa, potentially displaying convergent environmental adaptation, a crucial area for further research globally, and particularly in isolated areas like New Zealand.

During the last main phase of glaciations (26-13kaBP) an ice cap developed in south west Ireland and ice, from a dispersal centre in the vicinity of Kenmare, flowed north and diverged on the southern slopes of the Macgillycuddy’s Reeks. On these slopes, a weathering limit separates ice-moulded bedrock, on low ground, from frost-weathered terrain above. Assessment of bedrock dilation joint characteristics, Schmidt hammer R-value data, clay-sized mineral contents and magnetic properties of basal soil samples confirms significant contrasts in the degree of weathering above and below this limit. The weathering limit declines in altitude along former ice flow-lines and is confluent with morainic deposits on the eastern side of the Gap of Dunloe and on the western slopes of Skregbeg. This evidence supports the assertion that the high-level weathering limit is a periglacial trimline that marks the former maximum upper limit of the body of ice, which occupied this area of southwest Ireland during the LGM. This evidence, however, does not confute the notion that cold based, non-erosive plateau ice may have covered some or all of the upland surfaces that occur above the recorded weathering limits. Reconstruction of the former ice surface profile from periglacial trimline limits along three former flow lines yielded mean estimates for basal shear stress that ranged from 104.2 to 125.9 kPa. Although these values are high, they are within the range deemed normal for glaciers and ice sheets. The values suggest that the reconstructed areas of the ice cap were warm based and flowing on a bedrock substrate. This is supported by the geomorphological evidence of these areas, which shows that a landform – sediment association has developed consisting of zones of glacial scour and a thin, discontinuous drift cover. This contrasts with the glacial geomorphology of northern parts of the study area, where drift cover is largely continuous, and extensive in valley bottoms and on surrounding hillsides, and is associated with large lateral moraines.

Los Andes ecuatorianos, ubicados en el noroeste de América del Sur son considerados un “hot-spot” con una alta diversidad mundial de plantas vasculares, debido a su compleja topografía (elevación de la cordillera), variaciones de las condiciones climáticas y los distintos tipos de vegetación. A pesar de su elevado nivel de biodiversidad, los Andes ecuatorianos presentan uno de los paisajes más amenazados y poco estudiados. Especialmente los ecosistemas de páramo y montaña están sujetos a sobrepastoreo, quemas, cultivos y la deforestación causada por la expansión de la actividad humana en las últimas décadas. El conocimiento sobre paleoecología y la dinámica del paisaje es clave para entender los procesos del pasado que tuvieron un papel importante en el desarrollo de los ecosistemas y los paisajes ecuatorianos actuales. Sin embargo sólo un número limitado de estudios paleoecológicos de los Andes ecuatorianos están disponibles. En esta tesis se presentan análisis palinológicos que se llevaron a cabo en tres sitios diferentes en la región centro y sur de los Andes de Ecuador, con el fin de comprender mejor los últimos cambios en la vegetación, el clima y la dinámica del fuego; así como el impacto humano desde finales del Pleistoceno. El análisis del núcleo de sedimento El Cristal, ubicado en la ladera oriental de la cordillera Oriental en el Bosque Protector Corazón de Oro en el sureste del Ecuador, revela cambios en la distribución de la vegetación, el clima, el régimen de incendios y el impacto humano desde finales del Pleistoceno. Durante el Pleistoceno tardío el bosque montano fue el principal tipo de vegetación. Especialmente, hay evidencia de bosque de Polylepis lo que no ocurre en la actualidad. Sin embargo pruebas de proporciones relativamente altas de páramo sugiere que un bosque montano abierto ocupó la región. Por otro lado la presencia de taxones de páramo durante el Pleistoceno tardío, propone que la línea superior del bosque se encontraba a una altura inferior. Así mismo, la transición del Pleistoceno tardío al Holoceno temprano y medio se caracteriza por la presencia de bosque montano y una proporción estable de la vegetación de páramo. Sin embargo, después de aproximadamente 4000 cal yr BP, el bosque de Polylepis disminuyó, probablemente debido a un aumento en la frecuencia de incendios. Durante el Holoceno medio y tardío la composición de la vegetación cambió, el bosque montano fue menos frecuente y la vegetación de páramo se expandió. Altas proporciones de Asteraceae y Muehlenbeckia/Rumex (desde ca. 1380 cal yr BP) reflejan alteraciones del paisaje, probablemente por el impacto humano. Además, se registraron incendios durante todo el Pleistoceno tardío, pero fueron más frecuentes durante el Holoceno tardío, esto sugiere que eran de origen antropogénico. Por otro lado, El registro de polen Cajanuma valle, en la ladera occidental de la cordillera Oriental del Parque Nacional Podocarpus, sur de Ecuador, revela los cambios ambientales desde el último Glacial. Durante el último Glacial, páramo herbáceo principalmente dominado por Poaceae, Cyperaceae y Gentianaceae cubrió la zona. La línea superior del bosque se localizó a una altura más baja que la actual. El Holoceno temprano y medio se caracterizó por una sustitución parcial de páramo por bosque montano (Symplocos), el cual cambió su posición a elevaciones más altas donde está actualmente. Durante el Holoceno medio y tardío hay evidencia de un cambio de la vegetación, el páramo se re-expande con el predominio de Poaceae y alta presencia de Huperzia y Cyatheaceae. Durante el Holoceno tardío el páramo fue el principal tipo de vegetación que cubrió la zona. Los incendios se hicieron frecuentes desde el Holoceno tardío. Finalmente, el récord de polen Anteojos valle, que se encuentra en la ladera occidental del Parque Nacional Llanganates, en los Andes ecuatorianos centrales, presenta una reconstrucción ambiental detallada de aproximadamente los últimos 4100 años. La vegetación de páramo tuvo una ocurrencia dominante y estable en el área de estudio (Poaceae, Cyperaceae y Asteraceae); especialmente entre ca. 4100 - 3100 cal yr BP. Entre ca. 3100 - 2100 cal yr BP hubo una disminución de la vegetación de páramo seguido de una ligera expansión del bosque montano (Moraceae/Urticaceae, Trema, Celtis y Macrocarpaea). Desde ca. 2100 cal yr BP hasta la actualidad, la vegetación de páramo una vez más se hizo frecuente con una incidencia estable de los taxones del bosque montano. Se evidenció una baja frecuencia de incendios a lo largo del núcleo de sedimento; sin embargo, es evidente un ligero aumento entre ca. 4100 - 3100 años cal BP.

No description available.