Distinguished Lecture Program

Tailings are wastes comprising mixtures of crushed rock and processing fluids from mills, washeries, or concentrators that remain after the extraction of economic metals, minerals, mineral duels or coal from the mined resource. They contain potentially toxic metals and metalloids and can be very reactive, generating acidity or alkalinity and affecting ecosystem and human health. To understand their impacts we must ask the what, where, how and why questions.

Recorded at the Geological Survey of Slovenia, Ljubljana, Slovenia.

Mining is a vital part of the global economy, but unmanaged releases of mine wastes can affect the health of humans, ecosystems, water, soil and Earth surface environments such as rivers, estuaries, oceans and the atmosphere. New technological developments and multi-disciplinary collaborations are leading to new insights into the relationship between mining and the health of the Earth, and the effect of mining on global biogeochemical cycles.

Recorded at the Geological Survey of Slovenia, Ljubljana, Slovenia.

Iron fertilisation of the oceans, injecting particles high into the atmosphere and other methods that might reduce the effects of climate change. However their interactions go far beyond that for which they are designed, we must fully understand the whole cycle of such actions before committing ourselves to them.

Recorded at the Department of Geophysics, University of Zagreb, Croatia.

Major historic eruptions such as Krakatoa, Laki and Tambora had huge implications across the planet far beyond their immediate impact on the local region. These will be described and we will discuss how they have helped our understanding of nature’s power. More recently, eruptions such as Pinatubo and El Chichón have allowed us to test our understanding of the global atmosphere whilst significant financial losses associated with the eruption of the Icelandic volcano, Eyjafjallajökull in 2010 have resulted in significant focus in our efforts to monitor and predict such eruptions including systems to monitor post eruption allowing impacted airspace to reopen as soon as possible.

Recorded at the Institute of Geography and Earth Sciences, Eötvös Loránd University, Budapest.

Mineral dust blowing off the Sahara produces a number of changes in local marine geochemistry resulting in algal blooms that can change the oceanic ecosystems, which can have a profound effect upon the global albedo both near field and at significant distance from the emission.

Recorded at the Department of Geophysics, University of Zagreb, Croatia.

Natural contamination of aquifers with arsenic (As) affects over 150 million people around the globe. Most severely affected regions are located in South and Southeast Asia but also areas in Europe (e.g., the Pannonian Basin) are affected. Exposure to elevated levels of arsenic occurs through drinking contaminated water but also via eating food prepared with arsenic-enriched water, among other exposure routes. Long-term exposure to arsenic can lead to chronic arsenic poisoning, referred to as arsenicosis, which leads to serious health effects (e.g., skin lesions and cancers) and eventually to death. This talk will focus on the biogeochemical factors controlling the release of arsenic in groundwaters. It will also show how human actions, such as extensive groundwater pumping in areas affected by natural arsenic contamination, can lead to contamination of previously uncontaminated aquifers. Finally, methods of removing arsenic from groundwater will be discussed.

Recorded at the Institute of Geography and Earth Sciences, Eötvös University Budapest (ELTE)

Selenium (Se) is an important micronutrient for humans and animals as it is a key component of selenoproteins that serve a wide range of biological functions. Understanding selenium cycling in the environment is complex as selenium is a redox sensitive element that can occur in many chemical forms (i.e., species) in all Earth’s spheres (i.e., lithosphere, biosphere, hydrosphere and atmosphere). Since the environmental distribution and chemical speciation of selenium is closely related to environmental health issues, it is of major importance to better understand the factors that control its distribution and biogeochemical cycling, from the molecular to global scale. Climate plays a key role in global selenium cycling, firstly by controlling soil properties and thus selenium retention in soils and secondly, the atmosphere itself is an important reservoir of selenium and thus a potential source of selenium to terrestrial ecosystems and agricultural soils. Climatic processes and atmospheric cycling can thus affect selenium status of soils and finally of food crops. However, the effect of climate on terrestrial selenium distributions as well as atmospheric cycling of selenium and deposition to the surface is still largely unknown. This talk will give new insights in the atmospheric sources, sinks and fluxes of selenium and how these are linked. Furthermore, it will be shown how various geochemical techniques can be used to analyse selenium speciation and concentrations in a wide range of environmental matrices.

Recorded at the Institute of Geography and Earth Sciences, Eötvös University Budapest (ELTE)

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. The accumulation of cells often seen at the surface of the ice clearly results in ‘biological darkening’ of glacier surfaces. Such darkening increases the amount of incident shortwave radiation available for ice ablation, and could be a contributing element to glacier thinning and wastage. Nitrogen fixation is also potentially important as a source of nitrogen to microbial communities in the debris rich marginal zone close to the terminus of the glaciers and ice sheets, where this may aid the colonization of subglacial and moraine-derived debris as glaciers retreat as a result of climate change. More recently, data have shown that viruses are both abundant and dynamic at the surface of glaciers too. Viruses at the surface of glaciers cause significant mortality to bacterial communities and consequently, they have an important effect on the cycling of nutrients of these habitats. 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.

Recorded at the Institute of Geological Sciences, Jagiellonian University, in Krakow, Poland.

Biogeochemistry as a discipline deals with the chemical composition of the Earth (and beyond) and it is an integrated field that includes chemical, physical, geological, and biological processes and reactions. Microbial processes have a particularly important role in defining the geochemical characteristics of natural habitats. Through knowledge of the microbial community in a habitat and their activities, transformations at the micro scale can sometimes be scaled up to understand major shifts in ocean, continent and atmospheric chemistry. Next-generation sequencing (NGS), also known as high-throughput sequencing has revolutionised the way microbes can be investigated in their natural system. Microbial diversity and function are now commonly investigated in a variety of systems revealing key chemical reactions that are mediated by microbes. This knowledge combined with the chemical composition of natural habitats helps our understanding of natural reactions, particularly in habitats that are remote and difficult to conduct in situ experiments or collect large volumes of samples (e.g., hydrothermal vents, subglacial lakes). Measurements of microbial activity are also important and vital to show where bacterial populations are important drivers of e.g., carbon and nitrogen fixation, organic carbon transformations, weathering with implications for biogeochemical cycles at local and global scales. A combination of microbial measurements and biogeochemical modelling can also further our understanding of the chemical composition of natural ecosystems and increase the power for predicting chemical transformations in the future in response
to climate change. In this talk, I will cover a variety of microbiological methods used to improve our understanding of the interactions between Earth, environmental systems, and microbial life.

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Many lines of evidence, from both marine and terrestrial records, suggest that there have been dramatic changes in the Earth’s climate system during the last 65 Myr that occur on both long (geological) and short timescales. The mechanisms that are responsible for these changes are less well established, but there is growing evidence that amongst the primary controls is the concentration of atmospheric carbon dioxide (CO₂), the principal greenhouse gas.

Weathering of continental rocks leads to drawdown of atmospheric CO₂. Weathering rates are controlled primarily by temperature and rainfall, creating a dynamic link between weathering and climate that represents an important feedback process in the Earth’s climate system. As weathering products are ultimately delivered to the oceans via rivers, weathering also regulates ocean chemistry which, in turn, affects primary productivity and also levels of atmospheric CO₂.

We have identified a number of metal stable isotopes, including lithium and magnesium, which are sensitive to changes in continental weathering and erosion. In this talk, we will discuss their strengths and weaknesses, their potential for preservation in marine sedimentary records, and how these analyses have opened up new perspectives in understanding the linkages between weathering and climate.

Recorded in Budapest (Hungary) at the Institute for Geological and Geochemical Research, Hungarian Academy of Sciences.

Methane hydrate is a solid ice-like substance composed of methane and water molecules. Methane hydrates occur naturally in marine environments, where methane gas is available and temperatures are relatively low and pressure is relatively high. Estimates of the quantity of hydrate-bound gas in marine sediments range from 500 to 3000 Gt of carbon; additionally, hydrates are frequently underlain by free gas reservoirs that may contain another ~1800 Gt of carbon. Together, the hydrate and underlying free gas reservoirs comprise almost half of the Earth’s organic carbon. Release of methane from hydrate may have contributed to rapid climate change in the past, and it is considered to be a significant natural hazard because hydrate decomposition could destabilize sediments, creating landslide and tsunami risk.

Most climate models predict a rapid increase in Arctic air and surface water temperatures within the next decades, and direct observations of waters at 250 m depth in the eastern Fram Strait record a +1˚C increase between 1998 and 2006. In 2008, we discovered more than 250 plumes of methane gas bubbles rising from the seabed west of Svalbard. Many of these plumes were discovered close to the depth at which the gas hydrate stability zone is predicted to intersect with the seafloor in this area (close to 400 m water depth) suggesting that the bubble plumes may be the result, at least in part, of methane release by the dissociation of gas hydrates beneath the seabed, due to increases in water temperature.

A key question, which will be addressed in this talk, is how much of this methane escapes into the atmosphere where it has the potential to affect climate? To this end, we assess the extent to which fluxes of methane from Arctic sediments are modified by anaerobic oxidation (in sediments) and aerobic oxidation (in the water column). We will also discuss the evidence for gas hydrate as a source of Arctic methane, and characterise the carbon isotopic signature of the methane flux to the atmosphere from the Arctic seafloor.

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Isotope measurements belong to the most important tracers to study the Earth system. In atmospheric research, isotope effects are used to identify and quantify individual production and removal processes of atmospheric trace gases. For oxygen, with three stable isotopes, ¹⁶O, ¹⁷O and ¹⁸O, measurements show that the variations between these three isotopes in the atmosphere are anomalous, also called “non-mass-dependent”. The most important example for an anomalous oxygen isotope effect is the formation reaction of ozone (O₃).

At the same time, non-mass dependent oxygen isotope compositions have been detected in many other atmospheric molecules. In fact, there is almost no atmospheric species for which an anomaly has not been detected, or at least postulated. This is because O₃ is at the center of atmospheric oxidation reactions. Via chemical reactions the oxygen isotope anomaly is transferred from O₃ to other atmospheric compounds. Measuring the isotope anomaly therefore opens new opportunities to investigate chemical reaction mechanisms on the one hand, and mass fluxes between different species and reservoirs on the other hand. What started out as a peculiar isotope anomaly almost three decades ago has grown into a new research field that spans the full range from molecular physics studies to the reconstruction of climate parameters in the past.

In many cases, direct and comprehensive measurements on atmospheric composition are only available for the last 2-3 decades. To obtain information on changes before that time, air archives are needed, and polar ice cores are excellent archives of past atmospheric composition. Whereas available ice core records can go almost a million years back in time, air extracted from the firn, the top part of an ice sheet, can be used to cover the period of several decades to a century back in time.  We have measured mixing ratio and isotopic composition of numerous trace gases on air samples extracted from firn at the NEEM ice core drilling site in Greenland. These data are combined with previously published measurements to reconstruct consistent time series of isotope variations over the past 6 decades using a state of the art firn air model. It is important to take into account gravitational and diffusive fractionation in the firn air, which are in some cases of the same order as the actually isotope changes in the atmosphere. For example, for ¹³C in methane (CH₄), reconstructions from individual sites are not always mutually consistent among the different sites, which emphasizes that the precise knowledge of the diffusive properties in the firn is very important. On the other hand, for nitrous oxide (N₂O) the isotope reconstructions between different sites agree well and allow reconstruction of a consistent isotope history that can be used to reconstruct the variations of the sources of N₂O in the past.

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Gold has value for its intrinsic rarity and noble beauty. Other more economically useful metals such as platinum (Pt) also have their intrinsic value enhanced by their scarcity.  Yet, the abundance of these rare metals is actually much larger than simple models of the evolution of the Earth would predict. The so-called highly siderophile elements, such as gold and platinum should be efficiently incorporated into the core and thus locked within the inaccessible interior of the Earth since its formation at the beginning of Earth History.

However, the abundance of gold in the outer portion of the Earth is several orders of magnitude greater than that expected after core formation. This has long been attributed to the ‘late’ addition of meteoritic material to the Earth, after the core formed. This so-called Late Veneer could have replenished the mantle with a fresh inventory of precious metals. Yet, this model has been disputed, as newer experimental data of core formation at high pressures can also potentially explain the over-abundance of highly siderophile elements.

We have been able to resolve this debate using high precision isotopic measurements, showing clearly that the late delivery of meteorites to Earth is responsible for the economic bounty of precious metals we currently enjoy. I will explain the utility of isotope measurements in this endeavour and how these analyses also open up new perspectives in understanding the behaviour of the ancient Earth.

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Material that makes up the solar system represents the end-product of many different stellar explosions. This blend of material is to a first order well mixed and the individual components are hard to identify. There has been much progress identifying the type of star from which individual pre-solar grains derived from their isotopic signatures.  However, the relative importance of each grain type within the mix is hard to discern.  We have taken a different approach. Rather than looking for large isotopic variations in tiny grains, we have looked for tiny isotopic variation within large, bulk samples. The rationale is that any signature that has survived complete homogenisation should reflect material from a recent input to the solar system. We have identified pre-solar signatures in several elements in bulk meteorites. These point to material derived from a type II super nova. This is reassuringly in keeping with independent lines of evidence and points to a possible ‘super-nova’ trigger for solar nebula collapse.

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Iron-oxidizing bacteria can induce the formation of iron minerals by their metabolic activity and by forming nucleation surfaces. This process has diverse implications such as the trapping of inorganic pollutants in soils and rivers or possibly the formation of huge sedimentary iron deposits  the Precambrian Earth called Banded Iron formations. The first discovery of bacteria able to oxidize Fe(II) under anoxic and neutrophilic conditions was made only less than 20 years ago. Hence, much remains to be understood on detailed Fe-biomineralization processes. For example among Fe-oxidizing bacteria that can be cultured, some localize mineral precipitation outside the cells while others get encrusted by Fe-mineral formation and we do not know what makes the difference between these strains.  Here, I will present results from a combined use of cryo-transmission electron microscopy and synchrotron-based x-ray spectromicroscopy on laboratory cultures of diverse Fe-oxidizing bacteria. With such analyses, it is possible to follow the evolution of Fe redox in these cultures, detect Fe redox heterogeneities at the ~40 nm scale, as well as characterize and image organic molecules associated with these minerals.  As a result, it allows to uniquely discussing Fe-oxidation processes mediated by bacteria.

Recorded at the Institute of Biology, Bucharest, Romania

Geomicrobiology studies interactions between microorganisms and minerals. Working at the nanoscale on such systems is not just a methodological challenge and the use of new fancy tools. Here, I will show how we can combine Scanning Transmission X-ray Microscopy (STXM) and Transmission Electron Microscopy (TEM) to perform high spatial and energy resolution near-edge x-ray absorption fine structure (NEXAFS) and high resolution imaging on diverse samples of geomicrobiological interest. I will consider diverse samples including naturally and experimentally biomineralized bacteria, and bioweathered silicates. Spectroscopy was performed at the C K-edge, Al K-edge, Ca L2,3-edge, Fe L3-edge, and N K-edge offering the possibility to characterize diverse biochemical compounds, unique bacterial spectroscopic signatures, and iron oxidation state at microorganism-mineral interfaces. Combination of TEM and STXM provides remarkably clear chemical state-specific images of fossilized microorganisms and microorganism-mineral interfaces at the nanometer scale. This allows finding yet unreported chemical and mineralogical heterogeneities at the submicrometer-scale in ancient and recent rocks, and also reveals in experimental samples a more complex picture of a given process than that observed at a rougher scale. By reviewing studies performed on Archean stromatolites, modern Fe-oxidizing bacteria, fossils preserved in metamorphic rocks or pathological calcifications, I will show how the methodology presented here should be helpful in assessing the importance of microorganisms in the evolution of Earth’s surface chemistry and in identifying them in early Earth and planetary materials.

Recorded at Charles University, Prague, Czech Republic.