All seminars will take place from 13:00 to 14.00 in the Williamson Building G.03 lecture theatre. These seminars are open to all and are a good opportunity to meet your fellow students and staff.
For details of previous seminars please see our seminar archive.
Title: Revealing the impact of disturbance on tropical forest biota
Abstract: Tropical forests hold much of the world's terrestrial biodiversity yet are threatened by deforestation and forest disturbance. While the impacts of deforestation are well known and widely reported, we have a much poorer understanding of the more cryptic loss of biodiversity caused by to disturbances such as selective logging, fires, hunting and fragmentation. I outline their impacts using a large data set of plants, birds and dung beetles sampled in 36 catchments in the Brazilian state of Pará. Catchments retaining more than 69–80% forest cover lost more conservation value from disturbance than from forest loss. For example, a 20% loss of primary forest, the maximum level of deforestation allowed on Amazonian properties under Brazil’s Forest Code5, resulted in a 39–54% loss of conservation value. Species that were most affected by disturbance had the highest conservation or functional value. These results demonstrate why disturbance needs to be addressed by policy and management.
Title: Rifting in Iceland and in the Red Sea observed using satellite geodesy
Abstract: Extension at divergent plate boundaries is episodic and occurs during rifting events. As most divergent plate boundaries are located on the sea floor, rifting events are challenging to study and near-field data of past events are limited. In this talk, I will present our results of studying recent rifting events in the Red Sea region and in Iceland that provide a rare glimpse of this type of activity. Three volcanic eruptions occurred in the southern Red Sea during the past several years, on Jebel at Tair Island (2007-8) and within the Zubair archipelago (2011-12 and 2013). On Jebel at Tair we find evidence for temporarily varying stress field orientations within the island’s volcanic edifice that appear isolated from the regional Red Sea stress field. The two eruptions in the Zubair archipelago resulted in the formation of two new islands and were fed by dike intrusions much larger than the small size of the new islands might suggest. Together these eruptions and several seismic swarms indicate that the southern Red Sea has been experiencing an episode of rifting with multiple diking events and meter-scale extension and shows that this plate boundary is more active than previously thought. The 2014-15 Bárðarbunga rifting event in central Iceland originated from the Bárðarbunga central volcano located under the Vatnajökull ice cap. Magma propagated over 40 km to the northeast from the caldera and well beyond the periphery of the glacier where the intrusion eventually made it to the surface and produced a large lava field. We used high-resolution satellite radar images to map the near-field deformation within and around a reactivated graben between the glacier’s edge and the eruption site. We find that the meter-scale opening across the graben was accompanied with a significant amount of left-lateral shear motion. The left-lateral shear is in accordance with the mis-alignment of the rift segment to the overall plate motion in the region and implies that pre-existing fracture zones play a key role in controlling dike emplacements in rifts.
Title: How microorganisms melt glaciers
Abstract: It is now recognised that large expanses of ice in the polar regions are inhabited by active microbial communities forming one of the biomes of Earth. Microbes on ice are diverse, play an important role in the cycling of nutrients and can even modify the physical environment they live. For instance, microbial processes at the surface of glaciers and ice sheets can lead to the accumulation of labile dissolved and particulate organic carbon and this in turn have consequences to ice wastage and the delivery of nutrients to adjacent ecosystems. Liquid water also occurs at the beds of temperate and polythermal glaciers, as well as large sectors of polar ice sheets. In contrast with glacial surface environments, subglacial habitats have higher rock:water ratios, higher contact times between the bedrock and water, and a lack of light and redox potential that tend towards anoxic conditions, particularly during periods with long hydraulic residence times. Iron and sulphur reduction and oxidation, and production of methane are a few examples of processes in subglacial habitats that are important at local and potentially global scales.
Title: Cosmic Dust and the Earth’s Atmosphere
Abstract: Cosmic dust particles are produced in the solar system from the sublimation of comets as they orbit close to the sun, and also from collisions between asteroids in the belt between Mars and Jupiter. Dust particles enter the atmosphere at hyperthermal velocities (11 – 72 km s-1), and ablate at heights between 80 and 120 km in the mesosphere/lower thermosphere (MLT). The resulting metallic vapours (Fe, Mg, Si and Na etc.) then oxidize and recondense to form nm-size particles, termed “meteoric smoke particles (MSPs)”. MSPs are too small to sediment downwards and so are transported by the general circulation of the atmosphere, taking roughly 4 years to reach the surface. Smoke particles play a potentially important role as condensation nuclei of noctilucent ice clouds in the mesosphere, and polar stratospheric clouds in the lower stratosphere, where they also facilitate freezing of the clouds. There are also potential implications for climate, as the input of bio-available cosmic Fe in the Southern Ocean can increase biological productivity and stimulate CO2 drawdown from the atmosphere. However, current estimates of the magnitude of the cosmic dust mass input rate into the Earth’s atmosphere range from 2 to over 200 tonnes per day, depending on whether the measurements are made in space, in the middle atmosphere, or in polar ice cores. This nearly 2 order-of-magnitude discrepancy indicates that there must be serious flaws in the interpretation of observations that have been used to make the estimates. Furthermore, given this degree of uncertainty, the significance of these potential atmospheric impacts remains speculative.
In this seminar I will describe the results of a large study designed to determine the size of the cosmic dust input rate using a self-consistent treatment of cosmic dust from the outer solar system to the Earth’s surface. An astronomical model which tracks the evolution of dust from various sources into the inner solar system was combined with a chemical ablation model to determine the rate of injection of metallic vapours into the atmosphere. Constraining these coupled models with lidar measurements of the vertical fluxes of Na and Fe in the MLT, and the rate of accretion of cosmic spherules at the South Pole, indicates that about 40 tonnes of dust enters the atmosphere each day, of which ~18% ablates. The subsequent atmospheric chemistry of the ablated metallic vapours is then examined using the Whole Atmosphere Community Climate Model (WACCM), coupled with the aerosol microphysics model CARMA to treat the interplay of meteoric smoke particles with the stratospheric sulphate layer. While the optical extinction of meteoric smoke in the lower mesosphere, and of refractory material in polar stratospheric clouds is satisfactorily modelled, two problems remain. First, the injection rate of Na and Fe atoms is too large (by a factor between 5 and 10) for WACCM to replicate the observed metal atom layer densities in the MLT. It appears that vertical transport by eddy diffusion has to be significantly supplemented by chemical transport produced by unresolved (sub-grid) gravity waves (this process will significantly affect the transport of other species such as atomic O through the MLT). The second problem is that the rate of deposition of MSPs at polar latitudes is substantially underestimated by the model, indicating that there may be an efficient process for removing particles directly from the lower stratospheric winter polar vortex to the surface.
Underpinning the model development are three novel experimental systems developed at Leeds: a Meteor Ablation Simulator, which measures the evaporation of metals from cosmic dust particles that are flash heated to over 2800 K; a Time-of-Flight mass spectrometer with laser photo-ionization which is used to study the reactions of neutral metallic compounds in the gas phase; and a flowing afterglow experiment to study the dissociative recombination of metallic ions with electrons.
Title: From nano to macro: developing scalable remediation methods for problem sites and contaminants"
Abstract: The effective management of contaminated soil and waters is a major issue globally, with significant areas of land and volumes of waste and water contaminated by inorganic, organic and radioactive substances at levels that may pose a risk to human health and the wider environment. This presentation explores recent work aimed at developing scalable and practical remediation and management methods for problem sites and contaminants (including radionuclides), involving nano-based geochemical methods and large area “green” remediation strategies.
Title: Upper tropospheric water vapour and its interaction with cirrus clouds as seen from IAGOS long-term routine in-situ observations
Abstract: IAGOS (In-service Aircraft for a Global Observing System) performs long-term routine in-situ observations of atmospheric chemical composition (ozone, CO, NOx, NOy, CO2, CH4), water vapour, aerosols, clouds and temperature on a global scale by operating compact instruments on board of passenger aircraft. The unique characteristics of the IAGOS data set originate from the global-scale sampling on air traffic routes with similar instrumentation such that the observations are truly comparable and well suited for atmospheric research on a statistical basis. Here, we present the analysis of 15 months of simultaneous observations of relative humidity with respect to ice (RHice) and ice crystal number concentration in cirrus (Nice) from July 2014 to October 2015. The joint data set of 360 hours of RHice – Nice observations in the global upper troposphere and tropopause region is analysed with respect to the in-cloud distribution of RHice and related cirrus properties. The majority of the observed cirrus is thin with Nice < 0.1 cm-3. The respective fractions of all cloud observations range from 90% over the mid-latitude North Atlantic Ocean and the Eurasian continent to 67% over the subtropical and tropical Pacific Ocean. The in-cloud RHice distributions do not depend on the geographical region of sampling. Types of cirrus origin (in situ origin, liquid origin) are inferred for different Nice regimes and geographical regions. Most important, we found that in-cloud RHice shows a strong correlation to Nice with slightly supersaturated dynamic equilibrium RHice associated to higher Nice values in stronger updrafts.
Title: Earthquake histories through the Holocene from 36Cl cosmogenic exposure dating and structural geology, central Italy
Abstract: The talk will present observations of the recent Mw 6.1-6.6 earthquakes in central Italy and show how these relate to the pattern of active faults in the region and their Holocene slip-rates. 36Cl cosmogenic exposure dating of fault planes will be presented to show that earthquakes are clustered in time with periods of many thousands of years with no earthquakes interspersed with periods of the same duration containing several earthquakes. The observations and 36Cl results will be used to form an overview of how fault systems evolve and how seismic hazard ought to be conveyed to at risk populations.
Title: The role of anthropogenic aerosol in global and regional change
Abstract: There are many species of anthropogenic aerosol. The first part of this talk focuses only on sulphate aerosol. Sulphate aerosol can interact with the radiation balance directly by scattering radiation, or indirectly through their interactions with clouds. Overall, sulphate produces a negative radiative forcing of climate, causing a cooler surface and decreases in precipitation. The magnitude of the indirect effect is currently uncertain, and its representation in models is diverse. I will explore the global response to the indirect effects of sulphate changes in CMIP5, and quantify the contributions to the uncertainty in this response.
In the second half of the talk, I will quantify the role of all species of anthropogenic aerosol in historical circulation changes, with a particular focus on the position of the jets and the width of the tropics. I will also present case studies of the influence of regional aerosol changes on both local and remote climate, with a particular focus on the effects of Asian aerosol on Asian, European, and global climate.