No description available.

Habilitationsschrift--Freiburg im Breisgau. / Bibliography: p. 119-127.

Proefschrift--Groningen. / "Literatuur": p. 238-271.

Thesis--University of Washington. / Vita. Bibliography: leaves [145]-154.

No description available.

In the semi-arid southwestern US, the lack of continuous records of climate over the last glacial cycle has precluded a complete understanding of the rates and timing of past regional changes in climate. Speleothems can provide high-resolution, continuous record of moisture, temperature, and, potentially, vegetation variations and can be precisely dated by uranium-series disequilibrium. We have produced two U-series dated speleothem δ¹⁸O records from Cave of the Bells (COB). COB is located in Santa Cruz County, Arizona on the east side of the Santa Rita Mountains (31°45'N, 110°45'W; 1700 m). The glacial speleothem δ¹⁸O record (53 to 8.5 ka) confirms that deglaciation in the Southwest proceeded via a stepwise shift, mirroring the Bølling-Allerød warming and Younger Dryas cooling, beginning around 15 ka. There is no evidence of early warming before the decline of the large ice sheets. In Marine Isotope Stage 3 (MIS3; 53 to 30 ka), we observe millennial variations similar to Dansgaard-Oeschger (DO) events first seen in Greenland ice core δ¹⁸O records with wet/cold conditions indicated by our cave record during glacial stadials (cold periods) and dry/warm during glacial interstadials (warmer periods). High-resolution U-series dating allows for refinement of the timing of DO events in MIS3, and spectral analysis confirms the presence of a 1515-year climate cycle during this time. The δ¹⁸O data from a Holocene stalagmite (~6.9 to 3.5 ka) average ~3‰ higher than modern and exhibit substantial multidecadal to multicentury variation. We propose that in addition to drier/warmer conditions in the winter, a stronger summer monsoon and perhaps warmer summer temperatures supplied waters with higher δ¹⁸O values to the cave during the mid-Holocene. Spectral analysis of early part of the δ¹⁸O record reveals variability at periods of 233 years and at 142 and 52. After ~4.9 ka a prominent shift from centennial to multidecadal periods of variability (a 70 to 50-year cycle) is observed and there is a slight decrease in average δ¹⁸O values. This shift is coincident with a hypothesized increase in El Niño activity, which is correlated to wet winters in the modern southwest, in the tropical Pacific at ~5 ka.

No description available.

No description available.

The post-glacial history of woodland in North Yorkshire has been studied using a wide variety of sources including existing environmental studies, archaeological data, documentary information, and place-names. A critical approach has been adopted involving comparative studies of the different sources. The environmental and archaeological data available for the prehistoric period are thought to indicate that until the end of the Atlantic climatic period the vegetation of North Yorkshire was primarily environmentally determined, though mesolithic woodland burning may have created-open spaces and encouraged the growth of hazel in the uplands. During the Neolithic and Bronze Age a gradual spread of dense-agrarian settlement and intensive clearance across areas with calcareous soils, and into some drift covered lowlands, is thought to have occurred. This was probably accompanied by pastoral exploitation of the more acidic uplands causing a structural change in some upland woodland reflected by the decline of Tilia. The Iron Age and early Roman period appear to have been a time of widespread clearance, affecting even areas such as the clay lowlands of the Vale of York. Woodland appears to have become restricted to slope and bog refugia at this time. Evidence for a post-Roman woodland recovery is patchy. Secondary woodland appears to have formed principally on steep slopes such as the moorland scarp and gill sides, and around lowland bogs. At the beginning of the medieval period there appears to have been a marked contrast between the largely woodless areas of the Vale of Mowbray and the Wolds, and the remaining areas which were relatively well wooded. With the exception of the eastern fringe of the Pennines, woodpasture appears to have been the dominant form of exploitation in most of the more wooded areas in the early Middle Ages. The expansion of coppice management appears to have been slow, accounting for only a small proportion of documentary references to woodland until the 14th century. After this coppicing appears to have become widespread while many common woodpastures were enclosed or lost their trees. By the mid-nineteenth century common woodpastures were rare, occurring mainly in the Pennine uplands, and plantation accounted for a significant proportion of woodland, particularly in areas with landscape parks. The evidence for distribution and management of woodland over a long time period has facilitated the construction of interpretive models for the influence of environment, economics, and social structure on woodland history. Whilst the interaction between the environment and economic considerations offers a good model for the broad trends in clearance, and woodland distribution, the chronology of the adoption of coppice management requires a more subtle explanation. The expansion of coppice is thought to have been delayed until after the Black Death as a result of a concerted defence of common by the tenantry, which may to a large extent have consisted of freeholders.

The aim of this study was to analyse the pattern of deglaciation in the Dee valley and, in particular, to deduce whether this occurred by active frontal retreat or by areal stagnation and downwasting. This has important implications for palaeo-environmental reconstructions of the Lateglacial period. The main techniques used were morphological mapping and construction of sediment-landform assemblages, facilitated by borehole records of the British Geological Survey. Several sections were available which have not previously been logged. The area of study has been sub-divided into three main sectors: Lower Deeside, Feughside and Upper Deeside. In each case, conclusive evidence was obtained that the last (Devensian) ice-sheet decayed predominantly by active retreat but with a stagnant margin. Linear assemblages of ice-marginal topography frequently indicate a lobate ice-front based in the main Dee valley. The closely-spaced alignment of ridges in these assemblages suggests that they represent stillstands which interrupted retreat of the ice front. The presence of ice in the main Dee valley during deglaciation meant that drainage of tributary valleys was blocked. This resulted in formation of glacial lakes as indicated by glaciolacustrine sediments, deltas and overflow channels. Topography was a major control on the pattern of deglaciation, notably in areas of compressive ice flow where supraglacial sedimentation resulted in hummocky, ice-marginal deposits. These have previously been mis-interpreted as evidence for glacial readvances initiated by climatic change. The sedimentary successions in ice-marginal ridges strongly resemble those recorded from present-day sub-polar glaciers (eg. Svalbard). This implies that deglaciation in NE Scotland occurred whilst the climate was still cold, which is consistent with evidence from the coastal zone indicating that deglaciation was in progress by 15 ka BP. Much of the ice-sheet over NE Scotland therefore disappeared before the global climatic amelioration that occurred at 13.5-13 ka BP.