EGU Blogs

Geochemistry

Geology Photo of the Week # 20 – Feb 3-9

This week we have a photo of the something that has been on my mind a lot for the last little while and will continue to be on my mind in the comings years months weeks. Of course I am speaking of lab work and particularly the new iodine extraction line that I have been developing. Over the past few months I have had a 0% success rate with this damn thing. However, thanks to the fresh ideas and experience of a new radiochemistry professor in our department I have now had some success. In fact, I was so excited by this success that I did one of these:

Anyway, now that some progress has been made it is time to duplicate, refine and start using the line for actual samples. Thus, the photo of the week is a picture of the line that I now get a warm fuzzy feeling looking at as opposed to the former sinking and depressed feeling. Hopefully it lasts…..

My iodine extraction line for solid samples.

Cheers,

Matt

 

Guest Lecture – Dr. Tim Lowenstein

Our department was recently lucky enough to have Dr. Tim Lowenstein from SUNY Binghamton come give a guest lecture on the changes in the chemistry of seawater throughout geologic time.

Originally, we thought that the major ion chemistry in the past was more or less the same as it is today. However, over the last 10 years this long standing belief has been challenged by many researchers and championed by Dr. Lowenstein. Honestly, when you see the changes in sea water chemistry over geologic time it is pretty mind blowing. Especially when these changes are related to some pretty important events in earth history. I know that the fact that the ocean is really important should not come as a surprise, but it is still amazing when you realize that small thinks like the concentration of magnesium relative to calcium can have a huge global impact.

I don’t want to steal Dr. Lowenstein’s thunder by revealing everything, but I would like to provide some of the key points of his talk and the paper’s that it came from, as well as the innovative methods that his lab uses to find these results.

The whole premise of this research is based on salt and more specifically, where does the salt come from and how does it change over time? The salt in the ocean comes from two main sources. The first is rivers. Rivers carry sediment and dissolved salts from weathering of the continent into the ocean. Should this input of salt to the ocean from the rivers of the world change, so would the salinity of the ocean. There is another important source as well: hydrothermal vents/black smokers/mid-ocean ridges. Basically, sea floor volcanic activity and spreading is responsible for dumping a lot of dissolved minerals and ions into the ocean. These two sources mix to create the salinity of the ocean and control the chemistry of seawater. Should these inputs change over time, so would the chemical composition of the oceans. This is not really that far-fetched an idea, but it is still catching on within the scientific community.

File:Sea salt-e-dp hg.svg

A good image showing both the modern salinity of sea water and the ionic composition of the salts. What if these proportions varied over time? (Source: Wikipedia)

In order to determine the chemistry of ancient seawater Dr. Lowenstein’s lab attempts to find places where seawater could have been trapped from its deposition to now. Obviously, this is a difficult task as there are very few ways to preserve water since, as we all know, it has a tendency to evaporate or flow away. To overcome this hurdle they use fluid inclusions in halite (salt) crystals.

This is pretty ingenious. Halite is formed from evaporating ocean water. As the crystals form they incorporate some of the water they’re forming from in tiny bubbles in the crystal structure, called fluid inclusions. This water is literally trapped forever, or until it is released by breaking the crystal. Therefore, in order to find old seawater all Dr. Lowenstein has to do is find old evaporite deposits, which are scattered all over the globe. I know of one that is Silurian in age not far from Ottawa, which means the fluid inclusions trapped in that halite are 445 million year old ocean water.

Halite from Potash Corporation of Saskatchewan Mine in Rocanville, Saskatchewan, Canada (Source: Wikipedia)

Once the halite has been collected it is examined under a microscope for the fluid inclusions, which occur along growth lines in the crystal. If they are present, the crystal is placed inside a scanning electron microscope, frozen using liquid N and cleaved along the growth line, exposing the frozen fluid inclusion to the electron beam. The microscope is able to analyse the composition of the ice bubble by producing x-ray spectra that vary based on dissolved ions. This is done 5 times for each inclusion. Using this method Dr. Lowenstein has been able to analyze ancient water throughout the geologic time scale and as far back as 830 million years!!

The scanning electron microscope at the University of Ottawa. (Source)

So what are the results and implications of knowing how the composition of seawater changes over time?

Dr. Lowenstein proposes a link between the chemistry of seawater and the types of skeletons that coral and benthic organisms such as molluscs can form. It is common knowledge to those familiar with the fossil record that the skeletal composition of corals and other reef building organisms has changed over time between calcite and aragonite. These cycles operate on roughly 100-200 million year timescales and it was believed that they were due to changes in the major ion chemistry of seawater in the past. However, these ideas were based on the rock record, which is subject to major chemical change during lithification, and as such the smoking gun to prove this was missing. Enter Dr. Lowenstein. The measurements presented by Dr. Lowenstein in his talk and his paper in Science show that the fluctuations in ancient seawater chemistry correlate very well with the timing of the calcite and aragonite seas and greatly reinforce our understanding of how important the chemistry of seawater is to sustaining and controlling life.

File:CalciteAragonite.jpg

A graph showing the timing of calcite and aragonite seas. The graph by Lowenstein uses actual measurements to substantiate the timing. (Source)

The biggest implication of understanding the history of seawater is the fact that we now know that seawater chemistry has changed! The oceans play such an integral role in sustaining life on Earth and controlling the climate that understanding this system and how it can change over geologic time is crucial to making future predictions about the ocean and how things like climate change or tectonism could affect it. It is no longer acceptable to just think of the ocean as a salty bowl of soup. Indeed, we must now think of it in terms of a fluctuating system that has profound and basic linkages to the way our planet operates.

Thanks for reading,

Matt

References

Lowenstein, T. K., Timofeeff, M. N., Brennan, S. T., Hardie, L. A., & Demicco, R. V. (2001). Oscillations in Phanerozoic seawater chemistry: evidence from fluid inclusions. Science (New York, N.Y.), 294(5544), 1086–8. doi:10.1126/science.1064280

Timofeeff, M. N., Lowenstein, T. K., Brennan, S. T., Demicco, R. V, Zimmermann, H., & Horita, J. (2008). Evaluating seawater chemistry from fluid inclusions in halite : Examples from modern marine and nonmarine environments. Geochimica et Cosmochimica Acta, 65(14), 2293–2300.

Translate Radioisotope Hydrogeochemist – #1000simplewords

There is a new craze sweeping twitter…at least among those that I follow, which is mostly geoscientists. This is of course the #1000simplewords challenge. In essence the challenge is to explain your profession using only the 1000 most common words in the English language. The most complex/specific title that I could come up with for myself was radioisotope hydrogeochemist. What a mouthful of jargon! I have tried to simplify this in the paragraph below. If you would like to try it out for yourself go here. There is a nice little collection of job descriptions being posted at the Highly Allocthonous blog and that is great place to go see the attempts of others.

I have to say that this is not the easiest thing in the world. Words like earth, soil, rock are not allowed. Words that I take for granted when I describe what I do like: contaminant, groundwater, radioactive, analyze, etc. are all not allowed. This made the challenge a lot harder than I expected. It was also a very rewarding experience and got me thinking about what I do in the simplest terms possible, which was pretty eye opening.

 Water is every place and in everything. We need water to live and we use water to drink, make power and grow food. I study the amazing field of what is in our water. I look at where our water comes from, how it moves and if there is anything in our water that should not be there. I pick up water from all over the world and try to find out what is in it. If I find something that should not be in the water I try to explain how it got there and what we can do to clean it. I also use what I have learned to understand how bad things get in our water in the first place and how they move with the water. Knowing this can help us keep our water clean and how to keep bad things from hurting our water. Keeping our water clean is something that we should all care about and I try to talk about this with as many people as I can.

Cheers and let me know what you think of my attempt.

Matt

Research Highlight – Variations of 129I in the atmospheric fallout of Tokyo, Japan: 1963-2003

ResearchBlogging.org I occasionally like to focus in on what I view as a key paper either in my particular field of iodine geochemistry or in the geochemical world at large. In this instance I have decided to highlight a paper in my field that releases a fantastic wealth of data that is matched nowhere else in the literature I have seen. This paper also reflects incredible dedication and planning to answer a scientific question that far exceeds that of most papers in terms of patience and structure. The reason I say this is because most datasets in papers today may reflect a few years of sampling. In my opinion the average is around 2-5 years of data for papers that concern modern processes. This is great, however, datasets such as this only represent a small snapshot of these processes and do not allow one to observe long term trends with much confidence. Indeed, most of these papers finish by saying more data is needed to reach conclusions about long term changes. The reason for this is usually money, grad students wanting to finish, etc. These are good reasons, particularly the latter, which I can really empathize with, however, the problem is that such short time periods are not really long enough to make robust conclusions about changes in the environment or that factors that are causing such changes. Most researchers overcome their piddly datasets by adding in the work of others to broaden their time periods. Obviously, there are problems with doing this such as differences in sampling location, sampling techniques, lab practices…the list goes on and on with reasons why two datasets from different researchers may not be exactly comparable. This practice is very common nonetheless. However, rarely papers come out that present many years worth of data all analysed by the same person, in the same place, and collected the same way. Such datasets are invaluable in the geochemistry world! The paper I review here is such a paper.  In fact, it presents data for a 40 year period!!

The paper is by the AMS research group in the department of chemistry at Gakushin University in Tokyo, Japan. The authors are: Chiaki Toyama, Yasuyuki Muramatsu, Yuka Uchida, Yasuhito Igarashi, Michio Aoyama, and Hiroyuki Matsuzaki.

Why 129I

I thought this might be a good introductory section to add in order to bring everyone up to speed on what the value of researching 129I is. The main reason is that 129I levels are continually increasing globally and it is an emerging contaminant which we don’t want our environment, particularly 129I, which we don’t understand very well. The next reason is that we are still learning how iodine and 129I behave in the environment. They are tricky little elements that just won’t stay put no matter what the chemical conditions. Therefore, we need to better understand how they move and over what time scales. Lastly, 129I is produced by nuclear reactors and is present in large amounts in radioactive waste. This means that when we dispose of it and store it there is a very mobile isotope in there with a 16 million year half life. It is essential that we understand how it behaves and where it comes from.

Purpose

The purpose of this paper, that is to say the research questions that they authors are attempting to answer is:

1. What variations exist in the fallout rate of iodine-129 over time in Tokyo and what factors influence this fallout?

2. What are the sources of 129I in Tokyo?

3. How have nuclear accidents, such as Chernobyl, affected 129I concentrations in Tokyo?

4. What is the background concentration of 129I in Tokyo?

Sampling Methods

The samples were collected by the Japanese Meteorological Research Institute. Precipitation and particulate fallout samples were collected on a monthly basis from 1963 to 2003 and iodine was extracted as silver iodide and analyzed using accelerator mass spectrometry. Total iodine was analyzed with ICP-MS.

Results and Discussion

Unfortunately I cannot reproduce any figures from the paper…even though it has a graphical abstract…since Elsevier wants to charge me $20/figure to use them.

Anyway, I’ll make do without and try and describe the results without being too long winded.

– The 129I/127I ratio increased drastically during the 70’s and 80’s. It peaked at 4 orders of magnitude, or 10,000 times higher than the pre-anthropogenic ratio of 1.5 x 10^12. This increase is likely initially due to bomb testing, but the steady increase through the 80’s, which post dates most bomb testing means there is another cause.

– The deposition of 129I initially mimics the deposition of strontium-90 and cesium-137, both produced exclusively by bomb testing and nuclear reactor accidents. However, over time the 90Sr and 137Cs inputs decrease while the 129I remains steady. Also, there is a visible Chernobyl pulse for 90Sr and 137Cs, but not for 129I, although this is mainly since very little 129I was released from Chernobyl.

– The authors then compare the 129I deposition to the releases of 129I from the nearby Tokai Reprocessing Plant. The correlation is excellent. In order to guage the influence of European reprocessing plants the authors compared their results to another study looking at 129I in ice cores from the Alps, which found that there was a strong relationship to reprocessing releases. The Japanese deposition fluxes did not match the European very well. The suggests that 129I deposition in Tokyo is mainly from the Tokai plant.

– There was a consistent seasonal variation in 129I deposition in Tokyo. Indeed, the deposition of 129I was about 2 times higher in the spring than in the fall. This is consistent with other studies that have noticed a “spring peak” in radioactive fallout in mid-latitude regions. This is explained by a change in stratosphere-troposphere mixing in the spring (I have the reference if you want it). However, the authors also note that the air mass above Tokyo in the spring comes from Europe the higher levels could represent an influence of the European or Russian fuel reprocessing plants.

Conclusions

The principle conclusions of this article are:

1. The current ratio of 129I/I in atmospheric fallout is 10,000 times higher than the pre-anthropogenic, natural 129I/I ratio.  This is primarily due to atmospheric weapons testing in the 1950’s and 60’s.

2. There is no detectable influence of the Chernobyl accident in atmospheric fallout in Tokyo. This is likely because the signal is hidden rather than not present.

3. The high deposition of 129I in the 1980’s is due to the influence of the nearby Tokai Nuclear Fuel Reprocessing Plant. There is no correlation between 129I and 137Cs and 90Sr, which indicates the recent rise in 129I concentrations are not due to bomb testing.

4. There is also a possibility of distant transport of 129I from overseas reprocessing facilities in Europe, Russia and China and the authors intend to assess this by carrying out further sampling in places throughout Japan.

These conclusions are not especially novel. Many other papers have clearly demonstrated the impact of nuclear fuel reprocessing on 129I fallout and the ease with which 129I can be transported atmospherically. Indeed, I have published a paper demonstrating this in the Yukon Territory. However, most papers, mine included, do not present the quantity of data to verify this conclusion that this one does. This makes this paper a fantastic addition to the body of 129I literature as well as provides an excellent starting point for future conclusions about changes in 129I fallout with time and the factors responsible for them. It also provides excellent context for future work. It is difficult to put 129I deposition fluxes in context over time and this data set opens that door.

Some Speculation

So many papers come out every day in the research community. I have often wondered what each one represents financially. I mean, how much does it cost to produce all this research? How much do the analyses cost, the sampling, the preparation, the time, the analytical equipment? None of these components is cheap, except maybe the grad student hours, and therefore, every paper that comes out represents a substantial financial investment on the part of the supervisor and the funding agencies. So I thought it might be an interesting thought experiment to guess what this paper may have cost to produce. I have no actual knowledge regarding what this paper cost to produce, but I can speculate a bit since I am familiar with the cost of AMS analysis and lab work. So here is my very, very rough cost breakdown. It is likely on the low side though since I am not going to factor in human labour hours, the cost of sampling, or the cost of using the lab equipment besides the AMS.

# of Samples: 80

AMS sample prep: ~$75/sample = $6000

Cost of AMS analysis per sample: ~$250/sample = $20,000

Cost of ICP-MS per samples: ~$25 x 80 = $2000

Grand Total: $28,000

I believe that the paper is sadly trapped behind a paywall. Therefore, if you would like to read the paper in full let me know in the comments below and leave me your email so I can pass it on to you.

Thanks for reading! If you have any questions or concerns I’d love to hear from you. Also, if you have an opinion on the paper or dataset I’d love to hear it as well

Citation

Toyama, C., Muramatsu, Y., Uchida, Y., Igarashi, Y., Aoyama, M., & Matsuzaki, H. (2012). Variations of 129I in the atmospheric fallout of Tokyo, Japan: 1963–2003 Journal of Environmental Radioactivity, 113, 116-122 DOI: 10.1016/j.jenvrad.2012.04.014

Matt

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