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Archive for the ‘Science @ Goldschmidt2009’ Category

For what will probably be my last blogging post (my train leaves Davos this afternoon!), I’d love to throw another question out there to the group.
I spent this morning at the Oxygen over Earth History session, which included some great presentations by some top names in the field – Lyons, Poulton, Kirschvink, and Konhauser, just to name a few.
But as someone with a background in mathematics, I can’t help but wonder about the interpretation of proxies such as Mo, Fe, Si, Os and S quantities and isotopes.  As David Raup has shown, as well as has been shown by the work of Micheal Foote, the geologic record is incredibly biased.  Most of the geochemical work that has been done on the Proterozoic has been influenced by two things: first, the sparsity of the record and, second, the draw of big-name sections in important time intervals.
Is it possible that our entire dataset for the geochemistry of the Proterozoic is biased?  That preferential preservation has limited our view of the chemistry of Proterozoic oceans?  I don’t know myself, but I would like to quote the metaphor Darwin used in “On the Origin of Species”, which he attributed to Lyell:
“… I look at the natural geological record, as a history of the world imperfectly kept, and written in a changing dialect; of this history we possess the last volume alone, relating only two or three countries.  Of this volume, only here and there a short chapter has been preserved; and of each page, only here and there a few lines.  Each word of the slowly-changing language, in which the history is supposed to be written, being more less different in the interrupted succession of chapters…”

I’d also just like to say I’ve really enjoyed blogging at Goldschmidt; it’s been fun thinking about the science of the day and trying to say a few words about it.  I hope I’ve done an okay job, and I know that the other  bloggers have written some great stuff.   See you all at the next Goldschmidt! – Chris

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In session 19i: Bioenergetics in Geochemical Modeling today, Marc Alperin put forward the provocative idea that methane-cycling ANME archaea in consortia with sulfate-reducing bacteria are not oxidizing methane, as commonly presumed, but producing it.

Boetius

Boetius et al., 2000 Nature

The hypothesis comes from modeling the consortia in a diffusion-reaction model. When archaea (red cells in the figure) are modeled as methane-oxidizers, predicted rates of methane oxidation and sulfate reduction are orders of magnitude short of what is actually observed. However, if the model allows the archaea to produce methane instead, predicted rates of sulfate reduction are close to observed rates. The new model predicts that sulfate-reducing bacteria (green in the figure) will even have higher energy yields. They do even better by sharing H2 with methanogens.

Talks that challenge dogma are always attention-getting and provoke new thinking. Now the onus is on everyone to go out and test the new model – and to determine how the methane is being oxidized if not by ‘reverse’ methanogenesis.

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I think everyone agrees that we had some very inspiring presentations yesterday at the Earth’s future panel. Here’s what I retained:

Dr Bill Chameides said that, as a “lobbyist” for the environment, explaining complex issues about climate changes to elected peoples in positions of power is good, but that explaining simple issues to a lot of voters is even better. He joked that his “impact factor” was surely higher when he appeared on a cooking TV show to explain the meaning of “carbon footprint” than when he was publishing scientific papers. He warned that people from outside science, when they listen to scientists, are all too often left with the impression that while scientists are very intelligent, people can’t understand what they are talking about. Tackling climate change is all about communication, he said, and a scientist that takes a position on an environmental issue is not necessarily losing his or her credibility. His motto: Education, Communication, Multidisciplinary. I met him randomly today and he asked me put up a link to his blog.

Dr Veerabhadran Ramanathan warned about removing pollutant sulfur dioxide from the atmosphere without removing twelve times more CO2 at the same time. The calculation is simple: sulfur dioxide has a cooling effect on the earth climate twelve times more powerful than the warming effect of CO2. Along the same lines, he explained that emissions of other gases and particles that have greater warming effects that CO2, such as black carbon, should also be reduced. He said that global warming is about to reach thresholds that will bring iconic changes to the Earth surface. Here is the list in order of manifestation: i) the ice age oscillation switches off (this threshold is already reached; we will have no more ice ages), ii) the melting of the arctic ice cap, iii) Greenland melts, iv) the Amazon rain forest disappears, v) El Nino southern oscillation stops, vi) thermo-haline circulation shuts down, vii) the Antarctic ice cap starts to melt and viii) the Antarctic fully opens.

Dr Janet Hering also referred to three important events:

Galileo stated that the earth revolves around the sun (1610)
Darwin wrote that humans descend from apes (1859)
The term anthropocene was coined by Nobel prize winner Paul Crutzen, meaning that humankind has entered a new geological era (2000 – see his paper in Nature).

What are her solutions? We need to participate in local efforts on the community scale and focus on education, outreach and the empowerment of women.

I refer to Julia’s post for comments on Sir David King’s speech

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The Earth’s future panel was very inspiring. I think I’ll have to let what we heard distillate a little before telling you more about it. I’m heading to the Banquet where discussions, and certainly good food and wine will help.

Meanwhile I’ll let you think about this quote from Sir David King during today’s panel: “A nice way to keep carbon sequestrated is to leave it in coal”. Interesting isn’t it? I wonder what the guys of the CarbFix project have to say about that.

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Yesterday I attended the Gast Lecture by Kenneth Farley, which was on a topic that is completely outside my discipline: solar system events as recorded by 3He.

Farley explained that cosmic dust – tiny particles from asteroids 3-1000 microns in diameter which rain down on Earth at a rate of 40,000,000 kg/yr – contain a unique isotopic signature that distiguishs them from the terrestrial dust.  Helium is not gravitationally bound to Earth, and so Earth is extremely 3He-depleted.  Big asteroids are also 3H-depleted because as they enter the Earth’s atmosphere, the heat causes the helium to escape.  Only the smallest of the particles, specks of dust left over from asteroid collisions that occured millions of years ago, can enter the atmosphere without heating up so much that the helium escapes. Thus, the 3He/4He ratio of dust found in ocean sediments can be used to fingerprint the origin of individual dust particles.

One result of his work is the identification of an event that happened 8 million years ago.  Out in the Oort Cloud – a cloud of comets and asteroids which surround our solar system – a 140 km hunk of rock was hit with such force that it shattered, forming the Veritas family of asteroids as well as the dust, which eventually fell to Earth, resulting in a dramatic increase in the amount of cosmic dust stored in the sediments.  While we’re all used to the idea that ocean sediments record important events on Earth, this is a wonderful demonstation that they can also record important events throughout our solar system and beyond.

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Yesterday I attended session 15a: Geochemical Processes Controlling the Fate of Radionuclides in the Environment: Radionuclide Transport processes. The session covered quite a range of subjects, from Se & I retention by concrete and mortar, to the use of extremophilic bacteria to immobilize uranium. One of the talks, entitled “Hyperaccumulation of U in Organic-Rich Alpine Soils, Dischma Valley, Davos, Switzerland,” given by P. Steinmann, was of particular interest to me because it’s story starts only a short distance from the doors of the conference center. It ends up that naturally-occurring uranium, released from the rocks found in the Dischma Valley, is immobilized to a great extent by soils in the valley floor. Maybe the most striking thing is the concentrations, in places exceeding 7000 ppm U. This is one of the highest non-anthropogenic soil U concentration ever found. If I understood correctly, the concentration is mostly controlled by the concentration of humic substances, so that the wet, histol soils hold far more uranium than dryer, meadow soils. So, there can be gigantic differences in U concentration both laterally and vertically within a relatively small field area. Around Davos, the concentrations of U in drinking water are relatively low, but the authors suggested that studies in other Swiss valleys are needed.

It’s easy to forget about the poster sessions, which are a bit of a hike from the conference center and hotel where the talks are given. The posters are a great place to have more casual and extended conversations with fellow scientists, and I’ve often learned more from a few hours of discussion in the rows of posters than attending talks. I’d encourage you to head over and engage with the people giving posters, too.

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Interesting discussion today in session 17b. New biomarker evidence for purple sulfur bacteria from the Mesoproterozoic Barney Creek Formation suggests that oceanic euxinia, previously interpreted as a global signal, may have been local. A spirited discussion ensued, hinging on the interpretation of carbonate facies as syndepositional or not. A larger question persists: can the ocean really become globally stratified? And could such an ocean persist for a billion years? This argument is unlikely to be resolved soon.

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I have attended several talks about mercury (Hg) in the atmosphere, and particularly Hg atmospheric depletion events (MDEs) in the Arctic at previous conferences. From what I understand, as the duration of the day increases during the Arctic spring, the photochemical reactivity of Hg causes most of it to be washed out of the atmosphere and deposited, either onto ice cover or into the ocean. However, as scientifically rewarding as probing these events may be, the point was made today that researchers should be aware that the real danger lurks elsewhere. Indeed, trends of Hg found in the ocean and its biota, i.e. the Hg that enters the food wed, is decoupled from trends in atmospheric Hg. This was, in essence, the take home message of the keynote talk of today’s session on Hg accumulation on aquatic foodwebs. Robbie MacDonald, from Fisheries and Oceans Canada, expressed his concerns that too much effort is being put into studying MDEs, to the detriment of a better understanding of the Hg cycle in the oceans. We all acknowledge that the Arctic is very vulnerable to global Hg emissions and that the transfer of Hg from the physical system to the biological system occurs in the ocean. Yet, very little is known about Hg geochemistry in the oceans; the Artic Ocean being the least studied. MacDonald further stressed that if the Artic permafrost, which stores a large fraction of the organic carbon on earth, is pushed towards a collapse, the recycling of its organic matter and associated Hg may lead to a massive release of Hg to the Arctic environment.

The title of this post is taken from a paper by Robbie Macdonald in Nature (1996)

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What are the limits of life, and what determines the limits of where life can survive?  Today, Everett Shock from Arizona State University got us a little closer to the answer.  He has been exploring the importance of chemical affinity – the energy that has to be put into or taken out of the system for a reaction to occur – for the theoretical limits of life at high temperature and high pressure.

With characteristic enthusiasm, Shock pointed out that once upon a time we thought that there was no life above 80 C.  The reasoning was that above 80 C  proteins no longer work correctly.  However, we now see life at 100 C or more.  So he wondered: what is the real temperature limit on life?  And, maybe more importantly, what determines that limit?

The example he presented today was methanogenesis.  The methanogenic reaction has an affinity between 0 and about 30,000 cal mol-1 over a wide temperature range.  In fact, as he pointed out, the reaction has a positive affinity – i.e. is thermodynamically favored – at over 350 C.

But why then don’t we observe methanogenesis occuring at over 350 C?   Shock has an excellent reason for this.  He pointed out that the purpose of methanogenesis is energy – energy sufficient to turn ADP into ATP.  ADP is the currency of life – it is the way it stores energy to be used in all major biologic process.  But ATP is a way to store energy.  Thus, the reaction which turns ADP into ATP has a negative affinity.

By modeling these affinities across a range of temperatures and pressures, Shock has shown that at very high temperatures – over 200 C – the amount of methanogenesis that you need to support ATP formation goes up dramatically, to the point where at very high temperatures thousands of moles of CH4 have to be produced to create 1 mole of ATP.  This is not metabolically efficient, and, therefore, methanogenesis does not occur at these temperatures.  In his mind, it’s not the limits of the proteins, but the inherent thermodynamic limits on the system which prevent life from thriving at these high temperatures.

He concluded his lecture with an observation that would be truely wise for any biogeochemist to remember: for far too long protons have been the prima donnas of biogeochemistry.  Perhaps now it’s time for the electrons to step up and take center stage.

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Wow, what a day. 

It would be lie to say I didn’t wake up a little nervous this morning knowing my first talk at an international conference was but hours away. Although the nerves were there, they didn’t get in the way of the thorough enjoyment and interest I had listening to the other presentations in the session themed “Microbial Cycling of Iron Minerals” with a particular focus on Fe(II) oxidation. It was such an experience to hear cutting edge research directly related to my field of research, delivered from peers I hold in high esteem from reading of their published work. 

The keynote address by Katrina Küsel on “Iron Cycling at the Oxic-Anoxic Interface in Acidic Peatlands” was great. She presented some novel methods for redox gradient analysis and iron oxidizing bacterial characterization using inoculation by gradient tube methods (methods I hope to pursue her about and relate to my own work). Her sophisticated yet simple to follow talk offered excellent insight into bacterial mediated iron cycling over a redox gradient in a peat land environment. It was great to hear in the majority of the talks a discussion on the iron oxidizing bacteria Leptothix ochracea, a bacteria close to my heart.

 My talk focused on biomineralisation of nano-particulate Fe(III) phases in circumneutral environments. I don’t think I’ll be wearing the same shirt again for the remainder of the conference after the nervous sweat that was perspired during the talk, but I was extremely gratified to be offered an oral presentation. It was an excellent learning experience, and although being nervous, I enjoyed delivering it and believe it was well received. It was nice to have one of the session chairs, Thilo Behrends approach me after the session to congratulate me on my talk and propose further discussion with him and one of his PhD students who was studying a similar topic….an opportunity I definitely won’t miss. 

The same session in the afternoon was equally interesting, however more focused on the bioreduction of Fe(III) phases. It really is a fascinating and hot topic at the moment (illustrated by the standing room only crowd in both sessions). 

Looking forward to tomorrows plenary by the él presidenté, Marty Goldhaber and will report in at some stage post plenary.

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