Geomagnetism.org

The paper we discussed in the latest meeting of Magnetic Personalities and which motivated the piece below was Anzellini et al. (2013; Science) “Melting of Iron at Earth’s Inner Core Boundary Based on Fast X-ray Diffraction”.

They estimate the temperature of the boundary between the inner and outer core to be around 6,000 degrees Celsius based on extrapolations of the melting temperature of iron at extreme pressures and temperatures. Extrapolating from this, the top of the core would be just under 4,000°C and the heat flow to the base of the 1,000°C cooler mantle some 10 TW. For comparison, this transfer of energy is just under the 13TW present rate of energy “consumption” (energy is never consumed, only transferred and transformed) by all of human civilisation.

The Earth is hot and space is cold and the first law of thermodynamics tells us that heat must flow from the former to the latter until they are the same temperature. The Earth is far from being just a boring hot rock however and has spontaneously developed some pretty impressive ways of transferring this heat up from its depths. Earthquakes, volcanoes, tsunamis, hurricanes and the Earth’s magnetic field are all consequences of our planet trying to lose heat as fast at it can and converting (temporarily) some of this thermal energy into mechanical energy as it does so.

At the heart of thermodynamics lies the concept of the heat engine: a system that converts thermal energy into useful work (mechanical energy). The idea was formulated from considerations of man-made steam engines increasingly brought into service during the industrial revolution. Nevertheless, the pioneers of thermodynamics were also doing a great service to the Earth Sciences because heat engines are actually at work all over and inside of our planet.

The two biggest engines in the Earth’s interior are in the mantle and outer core. Both regions are undergoing vigorous convection – that is they are transferring heat by mass movement (due to buoyancy) of hot and cold bits – though at very different rates. The creeping of the continents and oceans at rates of centimetres per year, and the resulting earthquakes that ensue, are down to convection in the mantle. Simply, the crust and top of the mantle loses heat to the adjacent oceans and atmosphere, becomes dense, and sinks at subduction zones. This pulls open a gap at the surface allowing the hotter mantle down below to rise at volcanic mid-ocean ridges. This process of mantle convection via plate tectonics is an extraordinarily effective means of transferring the Earth’s heat that is both much faster and far more interesting than simple conduction. It is not our planet’s only great and beautiful internal heat engine however.

The Earth’s liquid core is a lot hotter than the solid mantle above it and so, once more, heat must flow upwards and outwards. This core-mantle heat flow is the ultimate driver of mechanical flow in the liquid core and so we have another heat engine. In detail however, things in the core are a little more complicated and uncertain than in the mantle. The core fluid (an iron alloy) is a very good thermal conductor which gets in the way of thermal convection as is happening in the mantle.

Nevertheless, the core is vigorously convecting. As the core is losing heat, it is freezing from the centre (where the pressure is greatest) outwards. This means that the solid inner core is progressively growing at the expense of the liquid outer core above. As well as changing the size of the outer core, this freezing process is also affecting its composition. Only the densest, iron part of the fluid freezes onto the inner core so the outer part is left with the lighter, residual part of the alloy. Light means buoyant, buoyant means flow (upwards), flow means convection. But this time: bottom-up compositionally driven convection rather than the top-down thermally driven convection exhibited by the mantle.

In the core, the fact that the liquid is electrically highly conductive means that things get even more interesting. The mechanical energy generated by the heat engine can undergo a further conversion before it finally gets turned back into thermal energy: this time into electromagnetic energy. As you drive your car, part of your engine’s motion is converted into electricity and used to charge your car’s battery. This dynamo process – converting mechanical energy into electrical current (with an associated magnetic field) – is also happening, quite naturally, in the core. We call it the geodynamo and it’s what generates our planet’s magnetic field.

So, the Earth’s mantle and core both contain great heat engines producing work. Going back to the steam engines, the work they produced was put to good use – moving railway trains and the like. How does the Earth make use of all the work it produces? Well, if it is the aim of the Earth to lose its heat as fast as possible to space then this work is put to very good use indeed. I have already written of the massive efficiency gain in heat transfer that plate-style convection confers the mantle over simply waiting to cool down by conduction. It might surprise you to learn that the core goes to all the trouble of generating a huge magnetic field for much the same reason – to lose heat as fast as it can.

Relative motions between a conductor and a magnetic field generate electric currents in the conductor which, in turn, generate heat there. The core’s trick is to use its thermal energy to generate a moving magnetic field that, in turn, generates heat in distant conductors. Most of this magnetic-thermal energy conversion takes place within the core, but it also goes on in the mantle, the crust, the oceans and even out to space, rapidly allowing heat to migrate outwards. This is, again, a very good way of transferring heat long distances quickly.

I find it extraordinary that the creation of something as grand, complex and useful as the geomagnetic field can be neatly ascribed to the simple transfer of heat.

Yes, I know it’s a hard life but somebody has to do it……

Meet the team

Left to right, Dr. Gillian Turner and PhD student Annika Greve from Victoria University, Wellington, New Zealand. Dr. Andreas Nilsson post doc and Emma Hodgson PhD student from University of Liverpool.

My PhD project ‘Further advances in determination of past geomagnetic field strength using synthetic samples, single crystals and basalt samples from the SW Pacific’ is part of a larger targeted palaeomagnetic study of the SW Pacific with Dr. Andreas Nilsson, post doc and supervisors Dr Mimi Hill and Dr. Andy Biggin  all at the University of Liverpool. We are lucky enough to be working with Dr. Gillian Turner and her PhD student Annika Greve at Victoria University, Wellington, New Zealand who are also gathering Southern hemisphere palaeomagnetic data. They are looking to complete a palaeosecular variation curve (changes in the direction of the local geomagnetic field) for the last 10,000 years in the SW Pacific area this can then be used as a reference curve to help dating in the area. At Liverpool we look at the past intensity of the magnetic field, the methods used and modelling of the data. These projects are filling gaps in Southern hemisphere palaeomagnetic data which will in turn increase the resolution of the models and our understanding of magnetic field behaviour. A big thank you to Gillian and Annika for what must have been an awful lot of time and effort in planning.

On top of Red Crater looking down into Central Crater, the darker area on the left is the 1955 flow we sampled

In February this year we headed off to the Tongariro National Park, central North Island to collect rock cores from lava flows on the flanks of Mount Ruapehu and Tongariro. We stayed at Whakapapa village on the slopes of Mount Ruapehu, a campsite for visitors who come for the spectacular walks and skiing this area is famous for. It was an ideal location for access to Ruapehu, Tongariro and the imposing Ngauruhoe (Mount Doom to any Lord of the Rings fans).

Our biggest issues in collecting samples were identifying suitable dated lavas and accessibility.

Finding lava was not a problem but finding flows that had been dated was! The younger Holocene lavas (less than ~11,500 years old) we were collecting are notoriously difficult to date with the commonly used potassium-argon (K/Ar) radiometric dating method. So far it has only been possible to date these lava flows through bracketing by tephra (ash) layers from past eruptions with known ages. Fortunately a group of geochemists from Victoria University, Wellington, NZ were using a new method of K/Ar dating to date Holocene flows as part of a mapping project in the area. They identified flows they had already dated using this method and some they were in the process of dating.

We were aware there would be accessibility problems and a degree of hiking or ‘tramping’ as it’s known in New Zealand would be called for we weren’t disappointed! Most locations were remote and required a 2-3 hour tramp to reach the flow we wanted. Despite the effort of carrying pack, drill and sometimes large quantities of water (to cool the drill bit) the further we walked the more spectacular the views became. A five hour climb up onto the Tongariro plateau then over Red Crater into Central Crater with equipment and 20 litres of water between three of us certainly was one to remember. Accessibility was also hampered by the ongoing threat of eruption in the area the most recent from neighbouring Te Maari vents in Nov 2012.

 The area was dominated by dense andesites andsome basalt which proved to be quite taxing for the rock drills which were custom made from chainsaws with diamond tip drill bit attachments. The cores were 2.5cm diameter and around 10cm long these can then be shortened to fit the various instruments used for their analyses. Orientating the cores in respect to north was done with a sun compass as most of these rocks were strongly magnetised and deflected the needle on a magnetic compass.

 As we were in a National Park we had to be very conscious of our impact on the natural environment so efforts were made to conceal the holes made by the drill. A before and after picture of a drill site shows effort was made to reduce any impact.

All in all we had a very successful trip to New Zealand so now it’s back to the laboratory for the next few months where we will be carrying out rock magnetic investigations to ascertain the best methods to measure the palaeointensities. The results of the of this project and associated collaborations will lead to a more comprehensive understanding of the magnetic field behaviour over the last 10ka in the SW Pacific.

Gillian, Andreas, Annika and Emma having a bit of fun!

Project Links

Targeted Palaeomagnetic Study of the SW Pacific

http://pcwww.liv.ac.uk/~nilsson/Project/Home.html

 Welcome to our project website aimed at presenting and visualizing new palaeomagnetic research from 0-5Ma rocks and pottery from in and around the SW Pacific .

We are a research group based in the Geomagnetism laboratory, University of Liverpool with collaborators in New Zealand and Australia. The project will incorporate improved geomagnetic field models with data collected from the SW Pacific. At present most of the data comes from the Northern hemisphere and Hawaii, leaving a data deficit in the Southern hemisphere. Fieldwork in New Zealand will took place in February 2012, while other samples will be donated by collaborators.

In particular palaeointensity will be used in geomagnetic field models to better understand the deep Earth processes that create the magnetic field. 

Unlocking the Secrets of the Geodynamo – the South West Pacific Key  

http://www.victoria.ac.nz/scps/research/research-groups/enviro-phys-geo/geomagnetism/projects

Days two and three of the EGU conference were packed full of interesting talks and poster sessions.  Day two was the big geomagnetism day, with open oral and poster sessions. The highlights of my third day at the conference have to be the Stephen Muller Medal Lecture by Leigh Royden of MIT and the Big Fracking Debate.

Day 2 – Tuesday 9^th April – Geomagnetism Day

I spent the majority of my second full day at the conference attending oral and poster presentations related to geomagnetism research. I liked the huge poster halls when they were quiet; with thousands of people presenting each day it can be an overwhelming experience! So, early in the morning I headed down to the poster hall to have a scout at what was on offer. I was most surprised by the variety of research being presented and some of the novel approaches being used. Two posters that really caught my attention were:

1) Is it possible to receive information about the historical geomagnetic field declination from church orientations? (A.Draxler et al.). I liked the idea because most of our information about the recent geomagnetic field comes from observatories, satellites and historical records. The approach presented in this poster is novel and with a larger dataset might provide greater resolution of the already existing models.

2) I’m a big advocate of science outreach and was really pleased to see a poster presenting a geomagnetism outreach project currently taking place in Austria (Bailey et al.). The idea of the project is study regional variations of the geomagnetic field by establishing geomagnetic observatories across three schools. The students have to choose the location for the observatory and set-up the instruments. The data collected will be available to students and researchers via an open project website.

The oral presentations were just as varied as the work being presented during the poster session, with most aspects of geomagnetism being represented. There were talks on the use of paleomagnetism to debate continental breakups during a number of geological eras; outlining the first results from a newly setup geomagnetic observatory in Croatia; using archeomagnetism to establish the deposition temperatures of the pyroclastic flows of the minoan eruption in Santorini; investigations of the Upper Jaramillo reversal from lava sequences in Tenerife; and trying to understand geomagnetic jerks better.

Day 4 – Wednesday 10^th April – Continental Collisions & to frack or not to frack?

I was free to explore what was on offer at EGU today, as there was no sessions which would directly link to my own research. Luckily, there were some really interesting things on! Medal Lectures are great because they are aimed at a wide audience but showcase some of the best research of the past few years. This is true for Leigh Royden’s medal lecture on continental collisions and the role subduction plays in this process. The talk took the audience through some of the examples of where her work (and that of her collaborators) has made major advancements in our understanding of how geometries of subducting plates and process associated with subduction are related to the structure of systems such as the Carpathian Thrust Belt, Apennine region and the Tibetan Plato. What struck me about the lecture, as well as the quality of the research, was what a great speaker Leigh Royden was. Her slides contained only figures and the story she was trying to tell flowed skilfully well. The content of a good presentation is key, but this particular lecture highlighted to me how crucial delivery of that content is on making it a great talk.

To frack or not to frack – the big debate.

This is a hotly debated topic and unsurprisingly the lecture room (one of the largest in the conference centre) was packed. This session took the form of a panel discussion, were four experts set out their views on the subject and then the discussion was open to the floor and the panel would take questions. The panel was diverse: a Professor in hydrogeology (Spain), a member of the Energy and Climate Change Select Committee at the House of Commons (UK), the head of section at the Helmholtz Centre (Potsdam) and a representative of Greenpeace (Austria), which of course lead to heated discussions, amongst the panellist and the audience. I came out of the session a little more informed as to what the pros and cons of fracking are and educated about what the difference stances on the matter are depending on your role within the debate. The event had a designated hashtag on twitter #EGUfrack and you can find more details about the debate in this blog post by Matt Herod, of the EGU blog network.

For more EGU action from other blogs and twitter, take a look at:

GeoLog (http://geolog.egu.eu/) and the EGU Blog Network (http://blogs.egu.eu) will be updated regularly throughout the General Assembly.

Keep up to date via Twitter by following (@EuroGeosciences) with the conference hashtag (#egu2013).

All this week (7^th April -12^th April) I’m attending the European Geosciences Union (EGU) General Assembly 2013, held in Vienna, Austria.  The conference has in the region of 11000 attendees, 13,500 submitted abstracts and more than 600 sessions, workshops and short courses, all related to the geosciences.

In these next few blog posts (not sure how many I’ll get to write yet!), I’ll be giving you an insight into my time at EGU (which is extra exciting for me, as it is my first international conference). I’ll be attending a range of talks, poster sessions, short courses and panel discussions; I hope to give you highlights of my favourite bits. There is so much going on that this will only give the briefest tour of what is on offer here, but there are plenty of sources where you can keep up to date with all the rest of the geosciences action– see the bottom of this post for details on those.

Day 1 – Sunday 7^th April – Ice Breaker

I traveled to Vienna today and met up with other colleagues from Liverpool University. The seismology group have sent a number of delegates, as well as the geomorphology group at the geography department. Not much science happens at the ice breaker (at least not in my case), but we all enjoyed the free wine and food, an excellent way to start the conference !

Day 2 – Monday 8^th April – Super Earths

My day was dominated by science related to Planetary Evolution. How much do we know about the deep interior of rocky planets and what can that tell us about their ability to generate magnetic fields and how size might be related to the onset of plate tectonics.

Tilman Spohn was awarded the Runcorn-Florensky Medal for his contributions to planetary science and gave a lecture on the thermal history of planetary objects. What is the state of matter in the deep interior of planets? In most cases, it seems we have a fair handle on this. So, take the Moon, for example, from seismic data we now know it has a core and solid inner core, but at what point was it able to generate its own magnetic field? He explored the Iron Snow Regime, which provides a mechanism by which, initially no dynamo would have existed, but one could have developed later in the Moon’s history.  The lecture also presented the idea supported by many that Plate Tectonics need to operate for complex life to evolve on a planet, but is the size of a planet related to its ability to have a mobile mantle and therefore moving plates? Can plate tectonics feasibly operate in large planets know as Super-Earths? Some authors believe that there is a planetary mass range that favours the development of plate tectonics and that the probability of plate tectonics occurring may well peak at an Earth sized planet. Is it therefore, just chance that life developed on Earth?

I also went along to John Tarduno’s talk on: Dynamo’s, Planetary Evolution and Life. He presented palaeomagnetic results from the Jack Hills Unit in Australia, that pass a conglomerate test (indicating they are at least the same as the depositional age of the conglomerates) and which record the weakest field intensities recorded so far in the Archaean: 7µT. Tarduno also discussed the implications of these results with relation to the ability of the Earth to retain water and it’s atmosphere at this early stage of its life. Although the evidence suggest there was an active dynamo at this time (Tarduno et al.2010, Biggin et al.,2011, as well as the data reported in the talk), it’s not clear how much protection from solar wind the early geomagnetic field would provide. It is also thought that standoff distances between the Sun and the Earth might have been much reduced and the effects of stellar activities strongly felt on the Earth’s surface. Perhaps there might be some other factors influencing the retention of an atmosphere and water early in the Earth’s history? Was there an initial super ocean on Earth, or a delivery during the Hadean/Archaean, which would allow for water loss, whilst still retaining sufficient to develop the planet into the body we know today?

Tomorrow is the big palaeomagnetism day, with both poster and oral session, watch this space for more highlights!

For more EGU action from other blogs and twitter, take a look at:

GeoLog (http://geolog.egu.eu/) and the EGU Blog Network (http://blogs.egu.eu) will be updated regularly throughout the General Assembly.

Keep up to date via Twitter by following (@EuroGeosciences) with the conference hashtag (#egu2013).

Some selected references:

Tarduno & Cotrrell, (2013) Earth and Planetary Science Letters,367, 123-132,2013.

Biggin et al., (2011), Earth and Planetary Science Letters, 302,314-328.

Tarduno et al. (2007) Nature, 446,657-660.

Tarduno et al. (2010) Science, 327 (5970).

When not conducting experiments, carrying out fieldwork, attending conferences, reading papers or writing up, it’s nice to learn new skills and meet other PhD students and early career researchers. Laura and I achieved this last Friday by attending “Standing up for Science Media Workshop” organised by the Sense About Science charity. In an increasingly interconnected world it’s important that scientists are able to communicate in a way that’s understood by all. After all, you don’t have to be an expert to be interested in a subject! In addition to Laura and myself there were students from a number of UK universities: Edinburgh, Manchester, Nottingham etc, from a number of different disciplines; Biology, Chemistry, Earth Sciences, Veterinary medicine and so on. In total there were 45 attendees which demonstrated how passionate scientists from all backgrounds are about engaging with the public regarding their science in an accurate and enjoyable way.

The workshop was split into three discussion sessions. In the first session we met two scientists who have various media experiences: from appearing on local news, to providing expert opinions for Brian Cox’s latest documentary, to appearing on ITV’s Day Break explaining their research. They both regularly talked to journalists and they shared with us their worst and best media experiences and some advice.

After lunch we had a discussion session with 3 journalists; David Derbyshire a freelance environment journalist and science writer; Rebekah Erlam, Broadcast journalist, BBC Radio 5 Live and Morwenna Grills, University of Manchester Media Relations Officer and former Sky News and BBC journalist. It was fascinating to hear their views and made me realise the amount of pressure they’re under to write a number of different science stories in an incredibly short amount of time. A science journalist probably has the same amount of time to research and write an article from scratch as I took to write this blog post! I also learnt that journalists don’t write their own headlines, sub-editors do. I found this surprising although it did explain why you get sensationalist headlines above relatively unconfirmed data. Editors want to sell newspapers after all!

In the third and final discussion session with representatives from Sense about Science and the Voice of Young Science Network we asked all the questions we had left and found out more about the network.

It was a very well organised and interesting day and I would highly recommend it to other early career researchers. The best pieces of advice I took away and will be implementing are:
• Make your work accessible
• Say yes to opportunities
• Start a blog
• Join twitter as it is a great place to network
• Practise explaining your research in 20 seconds using as little jargon as possible
Most of all I came away with the confidence that even though we’re only at the beginnings of our career, early stage career researchers can and should regularly communicate with the public and try to tackle any scientific errors that they notice in the media.

An important part of being a part of the palaeomagnetic community is keeping abreast of the current research. Here at Liverpool we hold fortnightly meetings to discuss recently published papers on a wide range of geomagnetism related subjects from the modern field to the deep past. Anyone can put forward a paper for discussion and whoever is most knowledgeable on the particular subject is invited to give a short review at the start of the meeting, this can be a great opportunity to get an insight into an area of geomagnetism you might not have any previous experience of and give a wider knowledge of the field. These are very informal and also act as a good excuse to all get together, drink tea and eat cake!

As part of this blog we thought we’d give a brief summary of the papers we discuss.This week we looked at a review paper regarding relative palaeointensity and geochronology published in Quaternary Science Reviews.

http://people.rses.anu.edu.au/roberts_a/AR_Publications/152.%20Roberts%20et%20al.%202013.pdf

 Andrew, P.R., Lisa, T. and David, H., Invited review: Magnetic paleointensity stratigraphy and high-resolution Quaternary geochronology: successes and future challenges. Quaternary Science Reviews.

 This interesting review sets out the challenges faced by those using continuous high-resolution relative palaeointensity records to help constrain the chronology of sedimentary sequences, for example as an independent  tool to synchronise different palaeoclimate records. It has been shown that magnetisations acquired in marine and lake sediments can faithfully record variations in the past geomagnetic field. This (post-) depositional remanent magnetisation is produced by detrital magnetic grains that align themselves to the Earth’s magnetic field as they settle through the water column or in the top ‘slushy’ part of the sediment water interface. A lack of understanding of the precise mechanisms involved does make it difficult to isolate a palaeointensity signal and perhaps more importantly assess its reliability. This paper looks into the current research on understanding magnetisation of sediments such as sediment type, diagenesis, flocculation and the effects of salinity and the influence of these on relative paleointensity records.

 Despite not having a definitive theoretical understanding of how sediments record intensity there is compelling evidence to suggest they can be reliable.  There is the global reproducibility of the stacks, the agreement with the production of cosmogenic radionuclides and the records of ocean crust magnetisation from deep-towed magnetometer surveys.

Fig. 3. Comparison of predicted relative paleointensity from the magnetization inverted from a high-resolution marine magnetic anomaly stack (blue; data from Gee et al., 2000) and dipole moments from the PADM2M paleointensity stack (red; Ziegler et al., 2011). Ages for the magnetic anomaly record were rescaled to a common age for the Matuyama–Brunhes boundary (see discussion in the text concerning age offsets of some paleointensity features).

I’m coming to the end of a 5 week visit to The Fort Hoofddijk, the Palaeomagnetism Laboratory at the University of Utrecht, in the Netherlands.  I’ve been carrying out a number of experiments, the results of which I am hoping to present at this year’s European Geosciences Union (EGU) Assembly, in Vienna (7^th – 12^th April).

The Building

The building which houses the lab is pretty impressive, as it is a 19th Century bunker, within the grounds of the botanical gardens at the University. Most of the equipment is found at the back of the building, in what used to be the old gunpowder storage rooms. It lacks any windows, so experiments are conducted without natural light, which reminds me of this comic. Learn more about the building here.

There are strong links and collaborations between the Liverpool Geomagnetism Lab and ‘The Fort’ (as the Utrecht lab is often called). My PhD project is co-supervised by Cor Langereis, who heads up The Fort. In addition, Andy, Mimi and Megan are involved with projects with students at The Fort. I also hear that Andreas and Emma meet Wout Krijgsman (also of The Fort) during their recent sampling trip to New Zealand.

Why the Fort?

The answer is simple, doing experiments at The Fort, saves me a lot of time!

This is my fourth visit to The Fort. I’ve visited often because they have equipment which we don’t, yet, have at Liverpool. Whilst at the Fort, I regularly use their2G Enterprises DC-SQUID magnetometer (which happens to be the first ever made) and also, an in house built, robotised AF demagnetiser attached to a 2G Enterprises RF-SQUID magnetometer (the Robot). The Robot

The Robot

is a nifty piece of kit, allowing you to alternating field(AF) demagentise 96 samples without you actually having to do any measuring, which any palaeomagnetist will tell you, is a GREAT advantage! It saves huge amounts of measuring man hours. You prepare the samples by placing them in cubes, which act as sample holders, and load these onto a tray made up of 12 rows, which take 8 samples each. You then produce a file which tells the computer how you want the experiment to run and press GO, and leave it to do its thing. Provided everything works fine, it takes the robot, on average, 48hrs to measure a full batch of 96 samples. The samples I’ve been working with are not standard palaeomagnetism size, (standard being 1 inch). This means I need to use special holders, of which there are only 15 available. A full AF demagentisation of two rows takes less than 12hrs. Whilst here, I’ve also been running some manual AF demagentisation experiments on the AF demagentiser, and a full experiment has taken me 36 man hours to complete.  I could conduct my experiments at Liverpool, and to some extent, I do, but they are considerably more time consuming than doing them here at the Fort!

A Typical Day

The 2G Enterprises DC-SQUID magnetometer (2G, from now on)

2G Enterprises DC-SQUID magnetometer

is usually in high demand, especially after spring and summer, when most of the field work takes place. Students and staff come back from this expeditions loaded with samples, which they are keen to get measuring asap. As a result, a shift system is in place to use the 2G. The first shift runs from 6am-3pm, the second from 3pm to midnight and the graveyard shift runs from midnight to 6am. February isn’t too busy a time, so I’ve been lucky to get the day time shift from 6am onwards.

The squids on the 2G need a little time to stabilise after being turned on, so that is my first task – get everything switched on and ready to go. In the time it takes for the squids to stabilise I can prepare breakfast and get the samples ready to be measured. I usually run two batches of samples concurrently: whilst one batch (of anything between 30 and 45 samples) is heating in the oven, I measure the other on the 2G. The samples I’m working on at the moment don’t respond well to thermal demagnetisation (TH), as I see them altering quite a lot. Therefore, I’ve been carrying out AF demagnetisations too. These only take a couple of minutes to complete, unlike the TH demagnetisations, where the samples have to sit in the oven for an hour.  I perform the AF demagenetisations and measure the samples whilst the TH batch is heating in the oven. In a nine hour shift, I repeat this process four  times, twice for AF batches and twice for TH batches. It’s a pretty repetitive task, so you have to keep yourself entertained, either by watching a film, listening to music, or writing this blog post!

A little thank you

I’d like to take this opportunity to thank everyone at The Fort for all their help during my time here (on this visit, and all my previous ones). I’d especially like to mention Tom Mullender and Maxim Krasnoperov, for all their technical support and teaching me how to use all the equipment. Also, Cor Langereis for his hospitality and valuable discussions!

Every year, the UK magnetism community gets together at a conference to showcase the most recent advances in the field, establish collaborations and discuss (sometimes heatedly) new projects and findings.
This year, Magnetic Interactions, was hosted by the Lancaster Environment Center. They certainly did a great job! An interesting program of talks was put together, alongside a good poster session and an excellent curry for dinner!
All of us at Liverpool Geomagnetism attended the conference, with much of our recent work on display (more on that later). Labs from other Universities were represented too, including Oxford, Imperial, Plymouth, Leeds and Cambridge. Talk and poster topics ranged from discussion on geomagnetic excursions and jerks, through nanopalaeomagnetism and magnetic tracing of particulate pollutants.
Work from other labs
For the most part, the attendees are based at UK Labs, but this year, the invited speaker was none other than Ted Evans (University of Alberta, Canada) who gave a very interesting talk on what he has called the cryptonchron enigma. So what is a cryptonchron? It is described as a tiny wiggle seen in the Geomagnetic Polarity Time Scale (GPTM) which is smaller than the major chrons, a small feature of dimensions on the scale of:40-80nT, 10-20Km. Their underlying cause is currently unexplained, although recent studies suggest they might be attributed to short reversal periods or intensity fluctuations of the geomagnetic field (Boulingand et al. 2006). But the enigma remains: what are cryptochrons? With his collaborator G.Hoye, Ted has developed a computer model which calculates the magnetic anomaly over a section of oceanic crust. The output of this model suggests that cyptochrons could be considered subchrons which could indicate that the field might be reversing more regularly than was previously thought.
A pick of other interesting talks and posters included: Sarah Dodd (Imperial) & Conall Mac Niocaill, (Oxford), who propose that magentostratigraphic data can help in understanding the eruption rate and exact chronology of Large Igneous Provinces (LIPs), which a particular focus on the Etendeka Flood Basalts of Namibia. Richard Harrison, from Cambridge, presented his new approach to palaeomagnetic measurements, where the source of uncertainty introduced during bulk rock measurements, is removed by performing paleomagnetic measurements at sub micron length scales, in what is being called: nanopalaeomagnetism. One of the hosts, Barbara Maher talked about how magnetic particles found in particulate pollutants which accumulate on tree leaves allows monitoring of pollution in urban areas.
What the Geomag Lab has been up to
As I mentioned earlier, the Liverpool Geomagnetism Lab had a strong presence at the conference:
• Andy gave a talk in which he discussed the findings of his recently published article in Nature Geoscience were he and his collaborators link long term variations of the geomagnetic field to whole-mantle convection processes.
• I also presented the latest findings of my research on Archean age rocks of the Barberton Greenstone Belt. Combined with data previously published by Andy (Biggin et al. 2011), I’ve been able to constrain the age of the magnetic signal recorded in the rocks of the Hooggenoeg Formation, to 3.2Gyr.
• Emma Hodgson has been researching non-ideal behaviour in interacting single and multi-domain grains, using synthetic magnetic samples. She presented a poster with experimental results from her recent work which indicates that there is violation of Néel’s Laws of thermoremanent behaviour in interacting single domain samples.
• Wilbor Poletti (a visiting student from the University of Sao Paulo, Brazil) has compared classical Thellier-Thellier(TT), Triaxe (TR) and Microwave (MW) methods for determining palaeointensities using Brazilian baked clays. In his work, he has improved the experimental protocol for the MW method. He also shows that the MW method is significantly affected by the “cooling-rate effect” and a pseudo-single domain bias, but these are easily accounted for, performing an experimental correction, which means all three methods for determining palaeointensities are now comparable.
• Keeping with the paleointensity theme; Megan (who also contributes to the blog) has been working on determining the past geomagnetic field intensity using Turkish pottery fragments has found that, as is well known, experiment success rate is very variable. Putting aside methodology issues, she discussed other potential issues e.g. dating uncertainty, pottery compositional variability and kiln design.
• Andy also presented the PINT database (which has been recently updated with 227 new records taken from 14 references) with the aim to reach a consensus on what the properties of the most reliable paleointensity measurements are.
• In his work, Andreas Nilsson, has used data from the Pint database, using archaeological artefacts/lavas and lake/marine sediments, has constructed a new continuous spherical harmonic model for the geomagnetic filed over the past 9000 years.
• Finally, Neil has been questioning if how we calculate pole positions (from Fisher distribution statistics) is actually the best way to go about things? He proposes a new method which defines the virtual geomagnetic pole (VGP) from the expectation of angle between VGP and spin-axis of the Earth, adopting a spherical exponential distribution. This method consistently gives confidence limits that are smaller than those derived from Fisher, yet more likely to contain the true pole position.
The conference was a huge success. The conference organisers did a brilliant job, and it provides a great platform for us all to showcase the best of our work. Already looking forward to the next one – Cambridge here we come!

Sorry about the lack of posts in recent times. Here at least is what I’ve been busy with…

https://news.liv.ac.uk/2012/07/30/scientists-probe-links-between-magnetic-polarity-reversals-and-mantle-processes/