Showing papers by "Paul J. Valdes published in 2003"

Constant elevation of southern Tibet over the past 15 million years

Abstract: The uplift of the Tibetan plateau, an area that is 2,000 km wide, to an altitude of about 5,000 m has been shown to modify global climate and to influence monsoon intensity. Mechanical and thermal models for homogeneous thickening of the lithosphere make specific predictions about uplift rates of the Tibetan plateau, but the precise history of the uplift of the plateau has yet to be confirmed by observations. Here we present well-preserved fossil leaf assemblages from the Namling basin, southern Tibet, dated to approximately 15 Myr ago, which allow us to reconstruct the temperatures within the basin at that time. Using a numerical general circulation model to estimate moist static energy at the location of the fossil leaves, we reconstruct the elevation of the Namling basin 15 Myr ago to be 4,689 +/- 895 m or 4,638 +/- 847 m, depending on the reference data used. This is comparable to the present-day altitude of 4,600 m. We conclude that the elevation of the southern Tibetan plateau probably has remained unchanged for the past 15 Myr.

The effect of ocean dynamics in a coupled GCM simulation of the Last Glacial Maximum

Abstract: General circulation models (GCMs) of the climate system are powerful tools for understanding and predicting climate and climate change. The last glacial maximum (LGM) provides an extreme test of the model's ability to simulate a change of climate, and allows us to increase our understanding of mechanisms of climate change. We have used a coupled high resolution ocean–atmosphere GCM (HadCM3) to simulate the equilibrium climate at the LGM. The effect of ocean dynamics is investigated by carrying out a parallel experiment replacing the dynamic three-dimensional ocean GCM with a static thermodynamic mixed-layer ocean model. Changes to the ocean circulation, and feedbacks between the ocean, atmosphere and sea ice have an important influence on the surface response, and are discussed. The coupled model produces an intensified thermohaline circulation and an increase in the amount of heat transported northward by the Atlantic Ocean equatorward of 55°N, which is at odds with the interpretation of some proxy records. Such changes, which the thermodynamic mixed-layer ocean model cannot produce, have a large impact around the North Atlantic region, and are discussed in the study.

Insolation forcing of the Australian monsoon as controls of Pleistocene mega-lake events

Abstract: [1] During the last c. 300,000 years mega-lakes with areas an order of magnitude greater than those of today occurred in the monsoon region of northern Australia. The results of an Atmosphere Global Circulation Model (AGCM) sensitivity experiment show that the repeated occurrence of mega-lake phases during the Pleistocene, and the strong monsoon flow that this implies, can be related to Milankovitch insolation forcing. The AGCM experiment is centred on the Southern Hemisphere low-latitude, summer insolation high of 115,000 years ago. The details of the results indicate a strong response of the Australian monsoon to the higher insolation at that time, with a longer monsoon season, increased precipitation and higher resultant runoff than at present.

The human presence in Europe during the last glacial period: III. Site clusters, regional climates and resource attractions

Abstract: For the past seven years a team of international experts have worked together to provide a detailed study of the world occupied by the European Neanderthals 60,000 - 25,000 years ago (Oxygen Isotope Stage 3). The new chronological and archaeological datab For the past seven years a team of international experts have worked together to provide a detailed study of the world occupied by the European Neanderthals 60,000-25,000 years ago (Oxygen Isotope Stage 3). The new chronological and archaeological database constructed by the Project sets the Neanderthal and modern human sites in a continent-wide framework of space and time. A mammalian data base maps the ecology and fauna of the period, providing fresh insights into the availability of plant and animal foods in different parts of the European landscape as Ice Age climate changed and fluctuated. New high-resolution computer simulations give detailed estimates of temperature and rainfall, and above all of the wind-chill and snow cover that would have had such an impact on both humans and on the resources they needed for survival. The results provide revolutionary insights into the glacial climate of Stage 3 and the landscapes and resources that influenced late Palaeolithic life-styles. New hypotheses are offered to explain why and how Neanderthal and modern human societies chose where to settle and why they moved on in the face of ever-changing conditions.

GENIE: Delivering e-Science to the environmental scientist

Abstract: The GENIE project aims to deliver a Grid-based, modular, distributed and scalable Earth System Model for long-term and paleo-climate studies to the environmental sciences community. In this paper we address the scientific problem of the vulnerability of the thermohaline circulation to the global climate, and describe our e-scientific solution using a Grid-based architecture involving Condor computational resources, web service oriented data management mechanisms and the employment of a web portal. We find that the scientific results of our e-science efforts are useful to the environmental science community, and provide a means of fulfilling the longer-term aims of the GENIE project.