Thursday, 17 May 2018

Understanding methane dynamics: working towards dual isotope analysis at the BGS…by Andi Smith

A recent collaborative venture between the stable isotope facility at the BGS and UK based mass spectrometer company Sercon Ltd has resulted in the development of the UK’s first automated system for the analysis of both hydrogen and carbon isotopes in methane. Here Andi Smith tells a bit more about the new instrument and potential applications…

Understanding subsurface methane dynamics is something that is going to become increasingly important to several areas of BGS, especially with ongoing developments with UKGEOs and groundwater monitoring projects in the Vale of Pickering, North Yorkshire and Fylde, Lancashire. One of the most promising tracers for understanding methane sources in groundwater is duel isotope analysis of the dissolved gas. Most surface methane is produced by methanogenic bacteria within the near subsurface, large isotope fractionations are associated with this process lead to very negative isotope values for both carbon and hydrogen (δ13C –70 to –110‰; δ2H –160 to –340‰).

Thermogenically produced methane on the other hand is formed by the thermal decomposition of kerogen, a process which is normally associated with isotope values of δ13C between –20 to –50‰ and δ2H between –110‰ to –250‰. These differences allow us to provenance where methane collected during monitoring projects was formed and start to understand potential migration pathways within the subsurface.

Whilst this dual isotope tracer technique has been undertaken many years, traditional systems require very labour intensive/ expensive sample clean up and preparation methods. This has meant that the number of samples that can be analysed has been very limited for most studies. To overcome this limitation staff at the stable isotope facility and Sercon Ltd embarked on a joint innovation project to develop a sample preparation and mass spectrometer system which is capable of running far greater numbers of samples at a reduced cost.

The developed instrument is now on site at the BGS and is being put through its paces. Once the system is fully functional it will be able to analyse large numbers of samples at very high precision. This will be ideal for baseline investigations at a number of BGS research sites and should help us identify if subsurface activities have any impact on methane release into aquifers.

There are many other potential applications for this instrument, if you think you may have an interesting application for this technique get in contact with me andrews@bgs.ac.uk.

Monday, 14 May 2018

Brazilian Bahia Blues...by Clive Mitchell


Clive presenting at the Global Stone Congress
BGS Industrial minerals geologist Clive Mitchell ventured to Brazil for the Global Stone Congress where he made many new friends, saw some amazing geology and learnt approximately 12 words of Brazilian Portuguese… 

Ola! (there that’s the first word!) Towards the end of April I was lucky enough to travel the 6000 or so miles to Brazil to take part in the 6th Global Stone Congress in the coastal resort of Ilhéus in the north-eastern state of Bahia.

I was an invited speaker at a conference I had never heard of, in a place I’d never been and with people I didn’t know. Yes you may have picked up a little apprehension. It wasn’t the presentation I was worried about (I actually enjoy that bit) but the travelling to a big, new, slightly scary sounding place. Anyway I went, otherwise this would be a very short blog…

En route (Nottingham – Heathrow – Sao Paolo – Ilhéus) I met some other delegates who quickly became my new best friends and were pretty much in the same boat as me (in the sense they were new to this, not an actual boat). Thirty hours after leaving home I arrived at the conference venue, the Jardim Atlantico Beach Resort in Ilhéus, approx. 800 miles NE of Sao Paolo.

Over the next 4 days I got to know everyone at the conference, was made to feel very welcome and quickly became part of the natural stone family. We took over the resort for a week – the conference venue was a marquee set up in the grounds. A large rain cover was hastily set up when the rain proved too much for the marquee (yes it rained every day, typical!)

The beach at the Jardim Atlantico Beach Resort in Ilhéus
The Global Stone Congress has been held every few years since 2005, when it was first held in Brazil as the International Congress on Dimension Stone. The objective is to gather internationally renowned natural stone experts in order to share knowledge, promote technical cooperation and discuss the latest advances in the industry. Since 2005 it has travelled to Italy (2008), Spain (2010), Portugal (2012) and Turkey (2014).

The 2018 congress attracted 165 delegates from 11 countries – 70% from Brazil with the remainder mostly from Portugal, Italy and Spain, and a small representation from Chile, the Czech Republic, Finland, Iran, Saudi Arabia, Sweden and one from the UK (me!). For my part, I gave a presentation on ‘Dimension stone in the United Arab Emirates’ – the UAE is an important market for natural stone in the Middle East and is one of the largest importers per capita in the world. It also has the potential to produce its own natural stone. It has mountains of limestone resources equal to that imported from neighbouring Oman.

After the conference, we spent a couple of days visiting dimension stone quarries, which turned out to be a very long way from Ilhéus! The state of Bahia it turns out is twice the size of the UK, with a quarter of the population.

The blue granite of Potiraguá is a sodalite-rich syenite worked as a dimension stone by Somibras and marketed as ‘Azul Bahia’. This is probably the most famous naturally blue stone from Brazil. I have come across it in use in the new terminal building at Dubai International Airport.

Field trip delegates at the Macarani pegmatite dimension stone quarry
The Precambrian Macarani pegmatite is hosted in a metavolcanosedimentary sequence of banded and strongly folded biotite paragneiss. The pegmatite is mostly coarsely crystalline feldspar and quartz often displaying graphic texture, with occasional crystals of aquamarine and beryl. Both the pegmatite and host rocks are worked as dimension stone by Ouro Campo.

An important phrase to learn for those tea drinkers out there: chá com leite frio, por favour or tea with cold milk please (not that you will get black tea of course, you’ll need to take that out with you I learnt!).

The congress social programme introduced me to the three C’s: Caipirinha (the Brazilian national drink), Capoeira (a form of mock-fight dancing) and Cerveja (beer of course, I knew that one as I am a geologist after all!).

The 6th Global Stone Congress took place from 27th to 29th April 2018, and was followed by two days of dimension stone quarry visits. Further information: www.globalstonecongress2018.com.br/ing/

Obrigado e tchau!

Tuesday, 8 May 2018

My first paper about improving methodologies in ostracod research…by Lucy Roberts

Ostracods, small animals which live in all aquatic environments, build shells (see image) that reflect the temperature and salinity of the water in which they formed. When the shells fossilise they can be used to understand past conditions of the lake or climate at that time. The ratio of certain trace elements (magnesium and strontium) to calcium (Sr/Ca and Mg/Ca) and the oxygen and carbon isotopes (δ18O and δ13C) within the shell is used to relate to the water conditions. The magnesium, strontium and oxygen isotopes relate to the past temperature and salinity of the water; carbon isotopes relate to the productivity of the lake. Here PhD student Lucy Roberts from UCL tells about her research on improving cleaning methodologies…

To obtain the most accurate reconstructions of past conditions, the ostracod shells must be cleaned of mud and/or remaining parts of their internal limbs. There are, however, a range of methods used across different laboratories. All the methods used have been proven to effectively clean the shells, but until now it has not been clear if the methods are also removing parts of the shell surface and causing an alteration to the trace element and/or isotope signal that is preserved in the shell.

A valve of the species Cyprideis torosa. A carapace is formed
of two valves – left and right held together by hinge along the
top of the shell. The species was used in the study because
it is found in a range of habitats across Europe, Asia and
Africa and has been used extensively for trace element and
 isotope based reconstructions
Alongside the BGS stable isotope laboratories, we designed an experiment to test this using a range of cleaning methods. For isotopic work, cleaning was performed using chemical oxidation, vacuum roasting and plasma ashing; for trace element work we used sonication, chemical oxidation and reductive cleaning. These methods were compared to simple ‘manual’ cleaning using a paint brush to remove visible material. Cleaning methods were compared by undertaking analyses on a single ostracod carapace (two separate ‘valves’, similar to a mussel, which together form the ‘shell’); in modern ostracods, the two valves should have identical trace element and isotope ratios. One valve was cleaned using one of the methods above, and the other was manually cleaned using a paintbrush. Any difference between the two valves after cleaning could be assigned to the effect of the treatment method.

We found that some cleaning methods have the potential to cause alteration to the signal and can therefore affect the values obtained for climate reconstructions. For trace element reconstructions we calculated that reductive cleaning can alter the Mg/Ca temperature reconstruction up to −12°C and the Sr/Ca conductivity reconstruction up to +4.5 mS cm−1 by removing parts of the surface of the shell. Isotope-based reconstructions are less affected by the cleaning method. However, the concentration and length of exposure to chemicals was an important factor in the extent of alteration.

The naturally smooth surface of the shell after cleaning with a paintbrush and no
chemicals is pictured in A and C. After exposure to hydrogen peroxide for 30 minutes,
the smooth surface shows evidence of being removed (D) altering the trace element
and isotope signal of the shell. After 15 minutes, there is no evidence of the
treatment affecting the shell (B).
To establish a universal method which allows comparison between reconstructions, we recommend sonication for trace element analysis and oxidation by hydrogen peroxide for stable isotope analysis. We believe these methods are effective at cleaning the shells, but do not significantly alter the signal preserved in the shell.

For more information on the study and the recommended methods, the open access paper is reference is: Roberts, L.R., Holmes, J.A., Leng, M.J., Sloane, H.J., Horne, D.J. Effects of cleaning methods upon preservation of stable isotopes and trace elements in ostracod shells: Implications for palaeoenvironmental reconstruction. Quaternary Science Reviews, 189, 197-209. The paper can be download for free here.

Wednesday, 2 May 2018

A new Post Doctoral Research Associate in shale gas geochemistry at the BGS…by Joe Emmings

Joe Emmings presenting research at the European
Geosciences Union General Assembly
Joe Emmings is the new Post Doctoral Research Associate in shale gas geochemistry at the British Geological Survey’s Stable Isotope Facility and Centre for Environmental Geochemistry. Here, Joe tells us about his PhD at Leicester University and future research at the British Geological Survey…

The world is gradually turning to renewables, such as wind and solar, as the main source of energy. This is great news for the environment, particularly for reducing greenhouse gas emissions. Yet all sources of energy, such as natural gas, nuclear energy, but even renewables, have pro’s and con’s. The expansion of renewables and batteries used to store this ‘green’ electricity is increasing the demand for metals, such as Co and Ni. These will need to be mined somewhere in the world.

Renewables cannot entirely replace the demand for hydrocarbons, either. For example, hydrocarbons are used as fertilisers and gas central heating in UK households, will be difficult to replace. So the transition to renewables must proceed now, but gradually – if it is done too quickly, the environmental and economic costs are large.

It is in this context that locally extracted natural gas is potentially a ‘bridge’ between coal, oil and gas and sustainable sources of energy. In a global context, locally extracted gas is preferable over imported gas, because in the UK we have strict regulations which protect the environment, and the fugitive emissions by long gas pipelines is significant. The method of extracting natural gas from shale, hydraulic fracturing, is contentious. Yet much of the science that informs our understanding of the pro’s and con’s of this technique has not been conducted.

I have been and will be continuing to work on the science that contributes to this debate, by shedding light on the composition of black shales in the UK that are of interest to exploration companies. On a microscopic scale, black shales are incredibly varied. No two shales are the same; the amount of gas stored in the rock varies substantially. This ultimately comes down to the environment of deposition – in other words – what did the environment look like millions of years ago?

Through my PhD research, we know Mississippian black shales in the UK were deposited in shallow seaways. By studying the geochemical composition of UK black shales, we know these were deposited in seawaters that lacked oxygen (termed ‘anoxic’), an environment that is similar to the modern Black Sea. Understanding when and how seawaters became oxygenated is important for understanding the amount of gas that is now trapped in the shale. The geochemical proxy record also shows that seawaters were also rich in hydrogen sulphide (H2S), a gas that is highly toxic to aerobic organisms. H2S is produced when other ‘electron acceptors’, such as oxygen, are absent. Anaerobes that live in the water instead respire using dissolved sulphate (SO4) and produce H2S as a product. This means UK black shales contain lots of pyrite (FeS2, ‘fools gold’) and are enriched in many ‘redox-sensitive’ metals, including Co and Ni. So black shales in the UK may represent an important resource of metals, which are used in renewable technologies, and this is something that I will be looking at.

Overall, Joe is interested in understanding ancient marine biogeochemical processes, by integration of sedimentology and organic and inorganic geochemistry. Please contact Joe if you are interested in his research field at josmin65@bgs.ac.uk