Paleoenvironments and Proxies

Huw Jones

Characterisation of neotropical savanna ecosystems by their modern pollen rain

There is currently uncertainty about the response of Amazonian ecosystems to the environmental changes of the Quaternary. An understanding of past vegetation dynamics is important with regard to the carbon cycle, the sensitivity of ecosystems to future global change and theories concerning speciation and biogeography. However, there is debate among researchers about the degree to which forest ecosystems were replaced by more open, savanna ecosystems during the last glacial maximum. These interpretations are based on fossil pollen records and are hindered by a poor understanding of Neotropical palynology. The study of the modern pollen rain of different ecosystems can improve the interpretation of fossil pollen records by providing modern analogues for these records.

Therefore, the aim of this research is to characterise the modern pollen rain of two savanna ecosystems (an upland savanna and a lowland seasonally-flooded savanna) and the degree to which they may be differentiated from each other. These ecosystems occur under different environmental conditions, so inferring the type of savanna will be important for palaeoecological and palaeoclimatic interpretations. The study site is Noel Kempff Mercado National Park in Bolivia, in the south-west of Amazonia. Artificial pollen traps and surface lake sediments from each type of savanna will be used to sample the modern pollen rain and sampling will allow both intra-site and inter-site variability to be studied. Vegetation plot data will allow modern pollen-vegetation relationships to be defined. These results will then be available to improve the interpretation of fossil pollen records from the region.

Huw's presentation

Elsa Arrellano-Torres

Climate Response and Feedbacks on the Eastern Pacific margin at Millennial Scales

A worldwide collection of high-resolution paleoclimatic records, mainly referred to the Greenland ice-cores, have demonstrated the abrupt and widespread climatic changes at millennial time-scales in more places than the North Atlantic. In the North-Eastern Pacific, the millennial-scale climate changes were discovered in the shallow reaches off California as sequences of laminated and non-laminated sediments linked with changes in deep ocean circulation. The precise timing of the events and processes driving such changes remain unclear and some questions have to be addressed: What are the mechanistic linkages between different components of the climate system and the communication of climate signals between distant regions? How is the transmission of the climate signal? Is it through the Pacific intermediate and deep-waters, through the atmosphere, through variations in productivity or greenhouse gas exchange? The marine sediment records from the ETP provide us with a good opportunity to monitor ocean-atmospheric connections; to quantify changes in rainfall mineral inputs into the ocean; and to examine the ecological response of surface living organisms to oceanographic changes through time. Furthermore, through geochemical analyses of organic matter and microfossils we can learn about denitrification processes, changes in oxygen content, nutrient availability, deep water formation and the way in which oceans redistribute heat through basins.

Elsa's presentation

Mehmet Karatay

Modelling the Hydrology and dynamics of the Greenland Ice Sheet

Glacier hydrology is of fundamental importance to glaciology since it plays a crucial role in controlling the dynamics of ice sheets and glaciers. However, while valley glaciers have been well studied in this respect, few studies have been undertaken on larger ice-masses and up scaling these field studies to the ice sheet scale is very challenging. Modelling provides a possible method for simulating the processes occurring within an ice sheet without having to have access to it. This can provide a very useful insight to large scale systems such as the Greenland Ice Sheet.

The Greenland Ice Sheet is the second largest ice mass in the world and its future evolution is uncertain. The ice sheet has the potential to inject a vast amount of fresh water into the Atlantic which could affect oceanic circulation and climate. This fresh water can be supplied in the form of melt water runoff as well as from the melting of icebergs. Iceberg calving rates increase as ice streams feeding the ice sheet margin speed up. Once of the suspected mechanisms for fast ice stream flow involves a highly lubricated bed underneath the stream. However, it is difficult to know if this is the case as it is hard to predict the possible sources and routing of water over, through and beneath an ice sheet.

This study will create a hydrology component for the existing ice sheet model GLIMMER that will consider Darcian, efficient and inefficient drainage systems. The hydrology and dynamics of the Greenland Ice Sheet will then be investigated using this.

Mehmet's presentation

Dan Hobley

Sensitivity of Glacially-Fed Rivers to rapid climate change: Ladakh, NW Himalaya

Research into the linking of climate, earth surface processes and tectonics is essential if we wish to understand why the current landscape is the way it is and how it has changed through time. Molnar and England (1990) proposed that apparent simultaneous late Cenozoic uplift around the globe could be explained as a synchronous enhancement of erosive processes driven by global cooling, citing specifically increased glaciation, storminess, humidity and vegetation as the agents of this enhancement. This study aims to investigate some of the processes by which these agents, particularly glaciation, modify erosion rates, across both long and short timescales.

It has long been recognised that basal erosion under glaciers is an extremely powerful erosive agent. However, this effect is restricted to only those areas beneath the glaciers. However, in the Himalaya upwards of 80% of flow in the major longitudinal rivers is glacial meltwater. We wish to understand then what effect glaciers have on fluvial dynamics downstream, since it is these signals which can be readily transmitted across the whole landscape. These are also the regions where changes can have a significant socioeconomic impact.

There has long been a qualitative understanding that meltwater may increase fluvial erosion rates (e.g., Alpine slot gorges), but this has not been quantified or the processes demonstrated. I shall use the field area of Ladakh, NW Himalaya to address these deficiencies. This study area is ideal as it has clearly defined glacial/fluvial regimes (restricted area of glaciation), a relatively simple glacial chronology, high glacial outflow to precipitation ratio, relatively constant lithology, uplift and baselevels, minimal anthropogenic influence and many comparable longitudinal catchments.

A combination of digital elevation model (DEM), field, cosmogenic and modelling data shall be used to establish the differences between catchments with varying degrees of glacial influence. This shall incorporate morphometric data, moraine 10Be dates, channel parameters such as width, sediment calibre and slope, and direct cosmogenic erosion rates from side channels. From this it is hoped to obtain a fuller understanding of the processes involved in the superposition of a glacial landscape onto a fluvial one across a range of length and timescales. Will these disequilibria be preserved throughout interglacials? What will happen if anthropogenic climate change continues? The project will also hopefully improve our understanding of the response of fluvial systems to explicitly disequilibrium conditions more generally. “Non-steady state” response has profound implications for understanding of wider geomorphological modelling.

Molnar, P., and P. England, Late Cenozoic uplift of mountain ranges and global climate change: chicken or egg?, Nature, 346, 29-34, 1990

Dan's presentation