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Department of Earth Sciences

 
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A collection of all the seminars going on at the Department, either on the downtown site, or out at the Bullard Laboratories
Updated: 46 min 44 sec ago

Wed 26 May 16:00: Title to be confirmed

Mon, 12/04/2021 - 14:04
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Wed 19 May 16:00: Title to be confirmed

Mon, 12/04/2021 - 14:03
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Wed 12 May 16:00: Title to be confirmed

Mon, 12/04/2021 - 14:02
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Wed 28 Apr 16:00: Title to be confirmed

Mon, 12/04/2021 - 14:00
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Thu 22 Apr 15:00: Reconstructing a deep time Earth system: The penultimate ice house

Wed, 24/03/2021 - 10:55
Reconstructing a deep time Earth system: The penultimate ice house

Earth system science, the study of our planet as an integrated set of subsystems that drive planetary function is applicable to the geologic past, i.e., the deep time, made possible by the advent of high precision radioisotope dating, the potential for astronomically calibrating stratigraphic intervals, and the application of Earth System (climate) Models and process-based ecosystem models to deep time studies. In this talk we discuss three components of our collective effort to develop a ‘whole-Earth’ reconstruction of the penultimate icehouse—the Late Paleozoic Ice Age (LPIA), 300 Ma. For the first component, we present a multi-proxy record of atmospheric CO2 over 40 million years of this icehouse and its turnover to a permanent greenhouse revealing CO2 variability (160 and 750 ppm) in-step with the glaciation history and with repeated restructuring of Pangaean tropical biomes on the eccentricty to million-year scales. In the second component, we couple the atmospheric composition records with plant fossil measurements and process-based ecosystem modelling to reconstruct the paleo-physiology/functioning of the extinct plants and to suggest possible ecosystem-scale vegetation-climate-CO2 feedbacks that would have influenced water cycling, surface runoff and weatherability, and organic carbon burial. In the third component, we use an isotope-enabled Earth system model to simulate the influence of glacial-interglacial fluctuations in atmospheric CO2 on epicontinental to global-scale ocean circulation and oxygen isotopic composition. This ‘systems’ perspective of the Earth’s penultimate icehouse reveals unique insights into the response of land-atmosphere-ocean interactions to a range of atmospheric CO2 within that projected for our future.

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Thu 08 Apr 15:00: The small and mighty: the role of microbes and minerals in melting the Greenland Ice Sheet

Wed, 24/03/2021 - 10:54
The small and mighty: the role of microbes and minerals in melting the Greenland Ice Sheet

The rapid melting of the Greenland Ice Sheet and the associated sea level rise is controlled by changes in albedo, which is primarily a consequence of increased light absorbing particulates (LAP) on snow and ice surfaces. Among LAPs, and included in climate models is black carbon. However, other LAPs so far not included in climate models because their role is poorly quantified, are mineral dust and pigmented glacier algae. We will show pigmented algae can reduce albedo by up to ~ 20 %, and that a necessary interplay between geochemical, mineralogical and microbiological parameters helps trigger the annual mineral-nutrient fuelled glacial algal blooms. We ground truth and link surface, airborne and satellite data and determine the role and consequences of water-mineral-microbe interface reactions in shaping large-scale processes across the Greenland Ice Sheet.

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Thu 25 Mar 15:00: Global climate change mitigation under the COVID-19 new normal

Wed, 24/03/2021 - 10:53
Global climate change mitigation under the COVID-19 new normal

The global economy is facing a serious recession due to COVID -19, with implications for CO2 emissions. Here, using a global adaptive multiregional input–output model and scenarios of lockdown and fiscal counter measures, we show that global emissions from economic sectors will decrease by 3.9 to 5.6% in 5 years (2020 to 2024) compared with a no-pandemic baseline scenario (business as usual for economic growth and carbon intensity decline). Global economic interdependency via supply chains means that blocking one country’s economic activities causes the emissions of other countries to decrease even without lockdown policies. We stimulate possible post-covid recovery pathways (grey vs. green) under different fiscal stimuli packages for developed, emerging economies and low income countries, respectively.

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Fri 26 Mar 10:35: Volcanic crystals as archives of pre-eruptive processes

Wed, 17/03/2021 - 14:11
Volcanic crystals as archives of pre-eruptive processes

Volcanic crystals provide detailed records of the inner workings of volcanoes and improve our understanding of the depths, processes and timescales of magma transport, storage and eruption. The growth stratigraphy of minerals sampled by erupted magmas provides a unique archive of processes leading to eruption, including mixing, replenishment, differentiation and mobilisation of mantle-to-crustal reservoirs. The identification of eruption triggers from the mineral record has implications for the understanding of trans-crustal magma feeder systems, the monitoring of active volcanoes and their associated hazards. This talk will interrogate magmatic systems from a crystal perspective, highlighting recent technical advances and future directions.

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Thu 18 Mar 15:00: How are water isotopes influencing our understanding of Antarctic climate variability over the past 2000 years?

Tue, 16/03/2021 - 14:09
How are water isotopes influencing our understanding of Antarctic climate variability over the past 2000 years?

Under the current global warming trend, the Arctic is warming the fastest, and strangely, many parts of Antarctica are not warming at all. The delayed response of the high latitudes of Southern Hemisphere to the Greenhouse warming is an important observation that is not reproduced by the current generation of global climate models. One of the leading hypotheses to explain this discrepancy is that natural variability is particularly large in the southern high latitudes, masking the anthropogenic forcing, and that this large variability is not well reproduced by models. Quantifying internal variability and understanding its cause is important for our understanding of the potential response of Antarctica to climate change, and to improve projections. Here, we will review our knowledge of Antarctic climate variability from ice cores covering the past 2000 years. This is an interval sufficiently short to have observations from many places in Antarctica, and sufficiently long to investigate variability at decadal and longer timescales. Temperature reconstructions come mainly from water isotopes, but they are not a perfect temperature recorder. The central thread of this talk will be to discuss how our vision of climate variability is distorted by the water-isotopes lens. We will discuss the importance of precipitation bias on the deposited ice water isotope signal, using isotope enabled climate models over the reanalysis period (1979-present), and illustrate the impact of this sampling bias by contrasting the expression of circulation modes (such as the SAM ) on temperature and d18O. In the second part of the talk, we will review evidence from other temperature proxies, especially borehole temperature records and temperature reconstructions from inert gas isotopes (d15N-excess), and discuss how the different records can be reconciled into a coherent view of Antarctic climate evolution over the past 2ka. If time allows, we will briefly discuss model-data comparisons over the last millennium, and review hypothesis about why models (OA-GCM) under-estimate internal variability in the high latitude Southern Hemisphere.

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Fri 12 Mar 13:00: The Future Green Economy: Panel Discussion

Fri, 12/03/2021 - 15:08
The Future Green Economy: Panel Discussion

The geosciences played a key role in the hydrocarbon-fuelled economic boom of the 20th Century, and it is now poised to play an equally-key role in the transition to a green and sustainable economy. This presents a new opportunity for Geoscientists to engage with the social, political and ethical implications of the green economy and their research into green technologies. This panel discussion brings together three experts from fields outside of the geosciences to explore questions such as: how the green transition can facilitate reduced carbon emissions and social justice, whether the green economy will be structurally different to the current economic system, how should we measure activities’ green credentials, and how will societies be convinced of green economics?

  • Speaker: Prof. Gargi Bhattacharya (Professor of Sociology at the University of East London), Kate Metcalf (Co-director of the Women’s Environment Network) and Dr. Natalie Jones (Research Associate at the Cambridge Centre for the Study of Existential Risk)
  • Friday 12 March 2021, 13:00-14:00
  • Venue: Zoom.
  • Series: Geoscience in Context; organiser: Camilla Penney.

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Thu 18 Mar 13:00: 2018 Eruption of Hawaii’s Kilauea Volcano – Use of Social Media and the U.S. Department of Interior Strategic Sciences Group

Thu, 04/03/2021 - 12:02
2018 Eruption of Hawaii’s Kilauea Volcano – Use of Social Media and the U.S. Department of Interior Strategic Sciences Group

The 2018 Kilauea eruption, which began on May 3 and lasted 107 days, was one of the longest eruptions in recent history in the lower Puna district of Hawaii. Over 700 homes were destroyed, and there was additional damage to the USGS Hawaiian Volcanoes Observatory as well as to critical infrastructure within the Hawaii Volcanoes National Park. Many federal, state, and local agencies and organizations supported response to this historic event. In this seminar, the speakers will describe how the USGS used social media to deliver nearly 24/7 volcano hazards information and build trust during the crisis. The speakers will then describe how the unique approach of DOI ’s Strategic Sciences Group (SSG) provided insights to help identify potential social, environmental, and economic consequences of the eruption.

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Mon 08 Mar 17:00: The birth, death and reincarnation of Snowball Earth

Tue, 02/03/2021 - 15:03
The birth, death and reincarnation of Snowball Earth

Snowball Earth provides a wonderful case history of the complex ways in which science advances. A data-driven, somewhat inductive understanding of widespread Neoproterozoic glaciation was championed by Cambridge’s Brian Harland in the 1960s and he later facilitated relevant work in Svalbard and Greenland by Hambrey and Fairchild. Then in the late 1990s, the model-driven Snowball Earth theory exploded on the scene, becoming vigorously championed by Paul Hoffman and linked to his unrivalled field experience. The theory encouraged hypothesis-testing which guided some subsequent developments. The aspects of the theory that still stand are that glaciations were necessarily prolonged (millions of years in duration) and synchronous, that a hydrological hiatus associated with a deep-frozen state is associated with an unconformity, that atmospheric PCO ¬2 became very high during glaciation and the associated glacial sediments were deposited during the final stages of the panglaciation. The events immediately following deglaciation are still hotly disputed. Neoproterozoic glaciation and associated carbonates will be illustrated with field, petrological and geochemical data, mainly from Svalbard and Scotland. The research that has resulted from the stimulus of Snowball theory is salutary in warning us that extreme climate states, inimical to human civilization, have occurred in the past, and hence that there are dangers in the use of technology, such as shielding the sun with aerosols, to fix our current climate crisis.

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Thu 04 Mar 15:00: Structural and magnetic transitions in minerals and functional materials: the pervasive roles of strain and elasticity

Fri, 26/02/2021 - 11:03
Structural and magnetic transitions in minerals and functional materials: the pervasive roles of strain and elasticity

Lattice distortions, formally described as “strain”, accompany almost all types of phase transitions in crystalline materials, either as the driving order parameter (acoustic mode instability) or by coupling with some other driving mechanism, which may be structural (soft mode, atomic ordering, hydrogen bonding, …), ferroelectric (displacive, order/disorder, relaxor, …), magnetic (ferro/antiferromagnetic, spin-glass …), or electronic (charge order, Jahn-Teller, spin state, superconducting, metal-insulator, …). The underlying physics is the same for minerals as for functional materials used in device applications: critical fluctuations are suppressed, coupling between multiple order parameters occurs via common strains, and microstructures such as twin walls, vortices and skyrmions interact with point defects or with each other. If there are changes in strain, it is inevitable that there will also be changes in elastic moduli and these provide clear insights into the dynamics and mechanisms of any phase transition of interest. Amongst minerals, transitions in quartz and stishovite give rise to large and characteristic patterns of elastic softening which should be detectable in seismic data. Recent focus, however, has been on materials which undergo more than one phase transition. Amongst minerals with such multiple instabilities are feldspars (displacive transitions, Al/Si ordering) and pyrrhotites (vacancy ordering, magnetic transitions). Landau theory provides a coherent and robust description of how these materials will evolve with temperature, while Resonant Ultrasound Spectroscopy provides a convenient experimental method for following the variations of elastic moduli through the phase transitions. Current focus, in particular, is on the strength of magnetoelastic coupling and examples provided by pyrrhotite, hematite and ilmenite show that this can be highly variable in minerals. As an example of a functional material, the interacting structural, magnetic and superconducting transition in the pnictide Ba(Fe1-xCox)2As2 will be described. Future directions for work on functional materials relate to the use of twin walls for device applications on a nanoscale.

References

Carpenter, M.A. and E.K.H.Salje (1998) Elastic anomalies in minerals due to structural phase transitions. European Journal of Mineralogy 10, 693–812.

Carpenter, M.A., R.J.Hemley and H.K.Mao (2000) High-pressure elasticity of stishovite and the P42 /mnm – Pnnm phase transition. Journal of Geophysical Research 105, 10807–10816.

Carpenter, M.A. (2006) Elastic properties of minerals and the influence of phase transitions. American Mineralogist 91, 229–246.

Oravova, L., Z.Zhang, N.Church, R.J.Harrison, C.J.Howard, M.A.Carpenter (2013) Elastic and anelastic relaxations accompanying magnetic ordering and spin-flop transitions in hematite, Fe2O3. Journal of Physics: Condensed Matter 25, 116006.

Carpenter, M.A. (2015) Static and dynamic strain coupling behaviour of ferroic and multiferroic perovskites from Resonant Ultrasound Spectroscopy. Journal of Physics: Condensed Matter 27, 263201.

Salje, E.K.H, M.A.Carpenter (2015) Domain glasses: twin planes, Bloch lines, and Bloch points. Physica Status Solidi B 252 , 2639–2648.

Evans, D.M., J.A.Schiemer, T.Wolf, P.Adelmann, A.E.Böhmer, C.Meingast, S.E.Dutton, Y.-T.Hsu, M.A.Carpenter (2019) Strain relaxation behaviour of vortices in a multiferroic superconductor. Journal of Physics: Condensed Matter 31, 135403.

Carpenter, M.A., D.L.Evans, J.A.Schiemer, T.Wolf, P. Adelmann, A.E.Böhmer, C.Meingast, S.E.Dutton, P.Mukherjee, C.J.Howard (2019) Ferroelasticity, anelasticity and magnetoelastic relaxation in Co-doped iron pnictide: Ba(Fe0.957Co0.043)2As2. Journal of Physics: Condensed Matter 31, 155401.

Haines, C.R.S., C.J.Howard, R.J.Harrison, M.A.Carpenter (2019) Group theoretical analysis of structural instability, vacancy ordering and magnetic transitions in the system troilite (FeS) – pyrrhotite (Fe1−xS). Acta Crystallographica B 75 1208 –1224.

Haines, C.R.S., S.E.Dutton, M.W.R.Volk, M.A.Carpenter (2020) Magnetoelastic properties and behaviour of 4C pyrrhotite, Fe7S8, through the Besnus transition. Journal of Physics: Condensed Matter 32, 405401.

Haines, C.R.S., G.I.Lampronti, M.A.Carpenter (2020) Magnetoelastic coupling associated with vacancy ordering and ferrimagnetism in natural pyrrhotite, Fe7S8. Journal of Physics: Condensed Matter 32 385401.

Zhang, Y., S.Fu, B.Wang, J.-F.Lin (2021) Elasticity of a pseudoproper ferroelastic transition from stishovite to post-stishovite at high pressure. Physical Review Letters 126, 025701

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