Dec 2010

On Monday 13th December, Michele Paulatto will be presenting a talk titled:

"3D image of an active magma chamber beneath Montserrat, Lesser Antilles,
from first-arrival travel-time tomography"

Abstract:

Andesitic magma erupted at island arc strato-volcanoes is stored in the shallow crust prior to eruption. Constraining the size, location and characteristics of magma reservoirs is key to forecasting the likelihood and characteristics of future eruptions. The island of Montserrat, in the Lesser Antilles, has been the subject of an active-source seismic tomography experiment (the SEA-CALIPSO experiment) with the main aim of studying the magmatic system of the active Soufriere Hills Volcano (SHV). We present the results of the three-dimensional travel-time inversion of the dataset. We are able to image the main features of the volcanic system of the island including SHV and the two older and extinct volcanoes. The shallow structure is dominated by the presence of high-velocity cores beneath the three volcanic centres. Beneath SHV at depth between 5 and 8 km we observe a negative velocity anomaly (NVA) roughly 4 km across. Checkerboard tests show that a pattern with wavelength similar to the size of the anomaly is well resolved at up to 7 km depth therefore the lower limit of the low velocity region is not constrained by our data. We show that in this case the resolution limit is in part determined by the bandwidth of the illuminating seismic source, as well as the experiment geometry. Temperature estimates at the centre of the NVA calculated with respect to the average velocity structure of the island indicate that a significant region is at temperature above the solidus of andesite and thus require the presence of melt. To further constrain the nature of the NVA we compare the observed seismic velocities with those predicted by thermal and geochemical models of melt intrusions in the upper crust. The thermal models show that the observed NVA is compatible with the presence of a magma storage region of 20-40 cubic kilometers, formed by repeated emplacement of horizontal sills over thousands of years. This shallow magma storage region is likely to correspond to the source of andesitic magma in the shallow crust feeding the current eruption.

Nov 2010

On Monday 29th November, Ben, Stephen and Tom will give Rhubarb Talks about projects past and present.

This is the second in a series of mini-talks given by 1st years about previous research they have been involved in and an insight into where they are going as their PhDs begin to take shape. It's a great opportunity to find out a little more about where people have come from and gain information about research that is being conducted in other departments.

This week we have:

Ben Russell:

Association of uranium with bituminous materials: a case study for mine site remediation

The geological occurrence of uranium with organic matter is well recognised in the subsurface, however it is unclear whether these associations hold true in surface and near-surface environments. This study focuses on the association of uranium with coal and bitumen in relation to mining pollution at two sites in the Banat district of South Western Romania. The aim was to elucidate the role that organic matter has in uranium uptake and transport, and evaluate the health risks to local populations.

Stephen Fawcett:

Mid-latitude glaciers on Mars: Volume estimates and flow observations

Recent studies have proposed the formation of late Amazonian water ice deposits on Mars at lower latitudes than are currently viable, through a process of seasonal ice migration from the poles. The ice is now buried in lobate debris aprons and lineated valley flows. Using high-resolution photos taken by the Mars Reconnaissance Orbiter of a lobate debris apron to create a Digital Elevation Model, it is possible to identify flow features, which support the theory of ice deposition. The topography of the flow can also be determined, enabling a model of the debris apron to be made, and the volume of the water ice to be estimated. This has implications for past climate change and the potential for future life on Mars.

Tom Chalk:

Tracing the Evolution of the Atlantic Thermocline and its Implications for Circulation throughout Rapid Climate Change

A multi-species analysis was undertaken on various coccolithophore and foraminifera Genera to reconstruct the thermocline structure in the Eastern Atlantic from the last glacial maximum to the present. It was found that well constrained biomarkers and their isotopic ratios provided good evidence for a shifting thermocline, indicative of global circulation change, from a surface perspective.

On Monday 22th November, Liz, Harriet and Helen will give Rhubarb Talks about projects past and present.

This is the first in a series of mini-talks given by 1st years about previous research they have been involved in and an insight into where they are going as their PhDs begin to take shape. It's a great opportunity to find out a little more about where people have come from and gain information about research that is being conducted in other departments.

This week we have:

Liz Sargent:

Assessing the species richness of the brown algal genus dictyota from the Caribbean Panama using a DNA barcoding approach.

Species distinctions are problematic in the brown algal genus Dictyota for two reasons; 1) there is difficulty in detecting cryptic diversity in morphologically convergent (but phylogenetically distinct) individuals, and 2) there is a poor understanding of the range of phenotypic plasticity intraspecifically. As part of a larger project to elucidate patterns of algal biodiversity for the Republic of Panama, this project focused on assessing diversity within the brown algal genus Dictyota using a DNA barcoding approach.

Harriet Cole:

Climate change and phytoplankton seasonality

Many studies have looked at the variability in the magnitude of the phytoplankton spring bloom but not many have focussed on the seasonality of the bloom. The physical ocean processes that control bloom timing are expected to alter with climate change. The results so far include global maps of the start date of the spring bloom and its interannual variability as well as addressing the problems with estimating phenological metrics from satellite ocean colour data. The timing of the spring bloom is an important concept when considering the timing of zooplankton/larvae spawning, length of growing season and the efficiency of the biological pump.

Helen Smith:

Ocean Acidification and Biological Carbon Pump Efficiency.

The biological carbon pump consists mainly of sinking aggregates containing organic carbon. The aim is to examine the mechanism of organic carbon export and ballasting using the Marine Snow Catcher and 234Th technique (possibly).