Cosmogenic nuclide dating, from a rock to a date…

1 11 2011

The main objective of my PhD is to reconstruct the retreat of the Uummannaq Ice Stream System, a large system of coalescent ice streams in West Greenland.  To constrain the timing of the retreat of this ice, we are using a technique known as cosmogenic nuclide dating.

Cosmic rays, originating from outer space, bring  rare cosmogenic nuclide isotopes (I am using 10Beryllium and 26Aluminium) to the Earth’s surface, where they build up in exposed rock surfaces at known rates. The total concentration of these isotopes in a rock surface therefore represents the length of time that the surface has been exposed to the atmosphere. This provides an ideal method for determining when a glacier retreated from a region, hence exposing the ground beneath. Technological developments in the last few decades have allowed more precise measurements of their concentration in terrestrial rock samples and this dating technique is becoming increasingly popular.

I collected the samples in the field in 2010 and 2011:

Rock sampling for cosmogenics at 900m a.s.l on Karrat Island

Rock sample after being cut with the rock saw

Having collected the samples in the field and received funding to run them, I went up to the Scottish Universities Environmental Reserach Centre (SUERC) laboratories in East Kilbride to start the process!

As 10-Beryllium and 26-Aluminium preferentially build up in quartz, the aim of the first week was to crush down the samples and extract as pure quartz as we could.  Firstly I had to crush the samples in the workshop to shards, and then grind them down on a disc miller. This was very noisy and dusty, and fairly hard work, but good fun.

Crushed rocks before being milled

The ground up rock was then sieved, and we retained the 250-500µm size fraction, keeping the rest in case we didn’t have enough quartz in these.

Crushed rock having been crushed and sieved. Note how different in mineral content the rock samples can be!

The final step for this week in the labs was using the Frantz machine.  A hopper slowly releases the grains of crushed rock onto a track which vibrates past a very strong electro-magnet.  Any magnetically charged particles are attracted to this and taken down a separate track, into a separate container.  The non-magnetic particles (such as quartz), aren’t attracted, and take a separate route (see video below).

So, I’ve now left my samples there with the lab staff for a series of etches with hydrofluoric and nitric acid.  I’m heading back in about a month to finish the samples off and then run them on the mass spectrometer.  Hopefully then it will spit out some nice dates which I can use to develop a deglacial chronology for the northern half of the Uummannaq Ice Stream System!





Any Questions? – with Tim Lane

6 10 2011

This is the first of what we hope will become a regular feature, in which we interview someone working in the Quaternary Science field to find out what they do and what they like about doing it (and more importantly what they don’t). First up is the co-author of this blog Mr Timothy Lane, a PhD student at Durham University in the UK.

IQSB: Can you explain for our readers what you are researching?

TL:  Essentially I am trying to reconstruct the thickness, extent and behaviour of a large ice stream in central west Greenland, from about 20,000 years ago to the present day.  An ice stream is a fast flowing glacier, and about 20,000 years ago, during the last glaciation, the ice in Greenland was far more extensive.  We’re using a variety of methods to reconstruct this ice stream.  We look at the sediment and landscape it leaves behind so we can tell where the ice was, and in which direction it flowed, and we can use material from both lakes and rocks to try and constrain a date on when the ice retreated.

Hopefully this will help other scientists who are trying to look at the entire Greenland Ice Sheet, and reconstruct its behaviour.  It will also help to feed information into models of sea level change.

IQSB: Cool, got any good photos?

TL: Yeh!

There are more here from 2010:

Greenland

And here from 2011:

Greenland 2011

IQSB: What made you want to undertake a PhD?

TL: While I was doing my Masters at Royal Holloway and UCL, I realised that I loved research, and it was the only thing I really wanted to do in the future.  Funding is always an issue, and I was lucky enough to get a fair amount of funding.  I’ve had to scrape together money for the fieldtrips, but I count myself as lucky!  It took me a bit of time to decide I definitely wanted to go ahead with one, but I knew it was right, and loved the project.

IQSB: What have you found hardest about the process thus far?

TL: Hmm.  I’d say that the complete independence can be a curse as well as a blessing.  If you’re having a bad week, or get knocked back by negative feedback/results not working etc it can be hard to drag yourself back to get on with your work.  The trouble is that there’s no one else to tell you to do it, other than your supervisor.  Similarly, it can be a lonely experience.  I’m lucky in Durham as they have a strong postgraduate community, both through the department and Ustinov College (a sort of halls of residence with a bar and social/sports community attached).

IQSB: Can you describe a typical day?

TL: I guess it depends really.  I am normally in the office by about 8.45-9.00am, and if I have nothing else on will work at my computer all day (Split up by coffee breaks of course!)!  If I have lab work to do I will spend the day in the Geography department labs, or in the GIS room.  We also tutor undergraduates, and demonstrate on modules, so my day is often broken up with helping them.  Obviously when I’m on fieldwork it’s quite a different daily routine…..

IQSB: What are your plans for when you graduate?

TL:  I’m not entirely sure yet.  I’d love to stay in academia or research, but it’s a competitive field so we’ll see how it goes.  Ideally I’d like to work as a postdoctoral researcher overseas somewhere.  At the moment I’m thinking of Norway, Canada, America or New Zealand.  I like the idea of moving country to change scene, meet new people, and experience the ways research works in other institutions and countries.

IQSB: And finally, what is the coolest thing about being a glaciology PhD student at Durham University?

TL: Well Durham itself is a great town, small and beautiful.  The flexibility the PhD offers is another massive positive, and as long as you’re prepared to put the hard work in then the rewards are massive.  The best part of the PhD has got to be the fieldwork though.  Getting the chance to go to remote areas of Greenland as part of my “job” is incredible.  Spending a month camping in complete isolation with just two other people is a great experience, and the fact that we’re researching areas which have really never been studied before is very rewarding.  You see some incredible places that 99.9% of the world will never see, and have numerous experiences which you will remember for the rest of your life.





Greenland – The Times Atlas vs Scientists

28 09 2011

There has been a big furore over the past few weeks regarding the publication of the new, 13th Edition of the Times Comprehensive Atlas of the World.  Specifically, the depiction of the Greenland Ice Sheet (GIS), and the associated press release, which said that the GIS had lost 15% of its permanent ice cover.

Different in the permanent ice cover in Greenland between 1999 (left) and 2011 (right)

This figure is a gross over-exagerration (Greenland has actually lost about 0.1% over the last decade), and was picked up by a number of scientists almost immediately.  Emails were being fired around mailing lists rapidly, as glaciologists attempted to find the best way to remove this figure from the mass media, before it became public knowledge and damaged the reputation of glaciologists working in Greenland (of which there are a lot).  The Times Atlas publishers (Harper Collins) initially refuted the claims, saying  that they:

“are the best there is … Our data shows that it has reduced by 15%. That’s categorical.”

Initially it was unclear where the “15%” figure had appeared from, but it soon emerged that the new map bared a striking resemblance to an online map of the GIS on the National Snow and Ice Data Centre’s website.  Those working on Greenland for the Times Atlas had clearly misinterpreted this map, and taken it to be an absolute measure of all ice cover in Greenland, when it actually represented something else.

The reason that this cartographer’s error spiralled out of control is simple – scientists were not consulted.  Had consultation taken place, the error on the map, and the consequent ice loss figure of 15% would have been immediately spotted and corrected.  The error, if left uncorrected would have discredited what a number of scientists from institutions across American and Europe have been working on for a number of years.  The actual picture of what is happening to the GIS is extremely complex, and remains poorly understood in areas.  It is a story of variability, with extreme thinning and increased in melting in areas, counterpoised with slight thickening in other areas.

The details are too complex to do justice in this post, but maybe another time….

The main issue that arose from this “crisis” was not the actual error made by the cartographers, this was relatively easily rectified in the end, but the ease at which this information got into the public domain with no input from scientific experts.  Such experts, who have built their career working on monitoring changes of the GIS, are subject to the rigorous peer-review system when disseminating their work to the wider scientific community. The problem with this however, is that this information is largely only available to the academic community, whose institutions provide paid subscriptions to the content. ‘Scientific’ information reaching the public through popular media is subject to no such scrutiny and due to the far greater reach of such outlets, errors can propagate much further much more quickly. With recent “fiascos” tarnishing science’s reputation (Climategate, the IPCC), science needs all the help it can get to stay favouring in the public’s eyes.  Thankfully this episode was resolved quickly, and if anything, demonstrated the ability of scientists to quash rumours with scientific evidence quickly.

At no point did the writers think to contact any scientists over the alarmingly large 15% ice loss Greenland had experienced.  Instead they simply put it to print and made a fool of themselves as a result.  They have now agreed to work with scientists in the future to correct this issue, and ensure it doesn’t happen again.

Hopefully this will be the standard position for those publishing material that should (and does) have a grounding in scientific work.

For an interesting alternative visualisation of melting in Greenland visit Cryocity.