Stable Isotope Geochemistry - Science topic

Thanks Fernando. When I ask them a few weeks ago, they said that UC Davis is not doing this analysis (MIMS) any more since a year.

PLEASE  ASK DR E. KEREPERTZIS DEPARTMENT OF GEOLOGY

Additional link from IAEA

On stable ground: tackling soil erosion with nuclear techniques in Viet Nam

No idea, Russ, sorry

Gerald,

Very interesting.  The problem we have is.........there is very little fentanyl in most samples.  Purity is usually 1-5% and we may get only 10 mg maximum via LC prep (of isolated and non-fractionated material) from a seizure.  Carfentanil concentrations are in the range of 0.05-0.5% and usually have less than 1 mg total carfentanil in the sample.  EA-IRMS and TCEA-IRMS only consume about 2 mg total fentanyl, but we are doing many signature profile methods similar to what is done in cocaine signature that requires 5-50 mg equivalents of fentanyl.  Feel free to test your approach on the molecule. Solvent would need to be non-aqueous and the fentanyl would need to be the free base, so that fentanyl can be recovered for other techniques.  Pat Hays (NMR guru here) is familiar with your work.......If you get some promising results......maybe we can collaborate?....The problem will be getting my management to agree to send samples to your lab.........John

Hi Klaus-Holger,

we are using the 15N2 labelling in my lab, since the publication of the Dabundo paper we checked our gases for contamination and it turns out that Campro gases and Cambridge isotope gases were not contaminated since then. In addition to the contaminatio nissue, SA gases are very expensive- so I personally buy now from the other two suppliers..

Best,

Carolin

In addition to being the customary reference isotope, it is one of the high-abundance Nd isotopes (therefore easy to measure). Typically, we want to reference radiogenic isotopes of an element to stable isotopes of the same element that aren't affected by ingrowth or decay. While 144Nd isn't actually stable and undergoes alpha decay, the decay rate is so slow (t1/2 on the order of 10^15 yr) that you wouldn't see significant change in 144Nd in geologic samples.

With regard to the isobaric 144Sm interference, we get around that by separating Nd from Sm and other elements in the sample. If the separation is imperfect and there is still a tiny amount of Sm present, it is possible to monitor other, uninterfered Sm isotopes during analysis. Assuming natural Sm ratios, you can then subtract the 144Sm part of the total measured 144 amu signal, isolating what should be just purely the 144Nd part of the signal in order to calculate your ratio.

I am searching a way to prove the age of some sediment strata which presumably are upper Miocene or Pliocene( C 14 is not working). This strata are reach of  Flora fossils, but so far can not determine the age only by them. They aslo are reach of iron oxides, that is why if we can date the oxide, than we can date the flora and the strata as well.

I am really sorry for not being able to get back to you sooner (I was out of station). The d¹³C values for the limestone cluster around -6 permil, much depleted than expected from marine origin. Also I have measured bulk d¹³C  which cluster around -22 permil, which is again enriched if we consider only C3 vegetation. The TOC content is rather high. These samples are from inter-trappeans layers in a place close to the western margin of peninsular India. The atmospheric CO2 should be more enriched compared to what we have today, and likewise the deposits should also reflect that.

Department of Earth Sciences at Western Ontario University, Canada has an excellent stable isotope lab. Contact. Dr. Neil Panerjee

Dear Jiawei Da,

Although HCl does not change isotope results you should remove it from the sample because it can damage spectrometer.

pH of your sample should be around 6.

Best wishes,

Karina

Dear James,

I presume you are referring to the equations used to estimate water temperatures from calcite d18O values.

Originally Epstein et al. (1951) proposed

t (°C) = 11.88 - 5.91 * (d18O calcite - d18O water)

(Epstein, S., Buchsbaum, R., Lowenstam, H., Urey, H., 1951. Carbonate-water isotopic temperature scale. Bulletin of the Geological Society of America 62, 417-426)

This equation was revised and became generally known as the "Epstein equation":

t (°C) = 16.5 - 4.3 (d18O calcite - d18O water) + 0.14 (d18O calcite - d18O water)²

(Epstein, S., Buchsbaum, R., Lowenstam, H., Urey, H., 1953. Revised carbonate-water isotopic temperature scale. Bulletin of the Geological Society of America 64, 1315-1326)

In these equations d18O calcite is in the PDB scale and d18O water in the SMOW scale.

Hope that answers your question.

Cheers,

Clemens

A good review of d18O of minerals and rocks in mafic eclogites is in the work of Miller, Buick and Cartwright et al.

Miller, J. A., Cartwright, I., Buick, I. & Barnicoat, A. (2001). An O-isotope profile through the HP-LT Corsican ophiolite, France and its implications for fluid flow during subduction. Chemical Geology 178, 43-69.

Miller, J. A. & Cartwright, I. (2000). Distinguishing between seafloor alteration and fluid flow during subduction using stable isotope geochemistry: examples from Tethyan ophiolites in the Western Alps. Journal of Metamorphic Geology 18, 467-482.

For d18O in garnet from eclogites nice works are below, not all of them are oceanic crust but you will see a variety of d18O due to oceanic alteration, interaction with serpentinite and sedimentary fluids during subduction.

Errico, J. C., Barnes, J. D., Strickland, A. & Valley, J. W. (2013). Oxygen isotope zoning in garnets from Franciscan eclogite blocks: Evidence for rock-buffered fluid interaction in the mantle wedge. Contributions to Mineralogy and Petrology 166, 1161-1176.

Page, F. Z., Essene, E. J., Mukasa, S. B. & Valley, J. W. (2014). A garnet-zircon oxygen isotope record of subduction and exhumation fluids from the Franciscan complex, California. Journal of Petrology 55, 103-131.

Russell, A. K., Kitajima, K., Strickland, A., Medaris Jr, L. G., Schulze, D. J. & Valley, J. W. (2013). Eclogite-facies fluid infiltration: Constraints from d18O zoning in garnet. Contributions to Mineralogy and Petrology 165, 103-116.

Rubatto, D. & Angiboust, S. (2015). Oxygen isotope record of oceanic and high-pressure metasomatism: a P-T-time-fluid path for the Monviso eclogites (Italy) Contributions to Mineralogy and Petrology in press.

I use Li YH and Gregory S, Geochim. Cosmochim. Acta 38, 703 (1974) which also gives ion diffusivities in pure water. The article have 1000+ citations, some of these may provide revised data, but I have not checked.  

Dear Imran,

Large grain sizes like pebbles, cobbles and boulders would allow more accurate inferences on the provenance (the source of detritus), particularly based on the Rb-Sr system. Large grain sizes suggest that, (a) limited physical break down of the source has taken place and the chemical weathering is at a minimum, thus, fractionation of Rb/Sr during the weathering  and the sedimentary process is at a minimum. (b) the sediments are lying more closer the source area. Thus, one could expect that a pebbly, cobbly or bouldery sediment to preserve the Rb-Sr isotopic signature of the source to a larger extent. As chemical weathering is having extremely limited influence on the Sm-Nd system, inferences about the source (provenance) based on that system in coarse sediments is very accurate as it is almost unaffected. Contrary, the small grain sizes (sand, silt and clay) mean that the physical break down is at a maximum promoting chemical weathering, thus fractionation of elements during sedimentary processes (particularly Rb/Sr) is very heavy, and the source is far away from the sediment and there was plenty of time available for chemical modification. Thus, isotopic signature of the provenance has been significantly altered. One has to remember, however, that even the coarse sediments are not fully sorted, thus, there are plenty of fine to medium-grained material admixed with it allowing some deviations from the true provenance age. Hope this will be of help to you.

Best Wishes!

LRK

I would suggest getting in touch with Geoff McDonnell, mentioned by Douglas Burns above, for a more balanced approach to the question. Bootstrap and similar techniques (like Monte-Carlo) may not be the best approach, depending on the processes occurring in your system, and the available data.

Hi Wieslawa,

Yes it is possible, but as Jay already states, it is difficult. If you have mono-specific assemblages, it becomes easier. If you have relatively large dinocysts, you can hand-pick (a large number of) cysts. This does take a lot of work.

CaCO₃ precipitation decreases the carbonate alkalinity (HCO₃^-+2*CO₃^2-) and not the CO₃^2- alone. Precipitation of CaCO₃ however increases the partial pressure of CO₂ in the sea (Ca²⁺+HCO₃^-=CaCO_3(s)+CO_2(aq)+H₂O) that may l escape to the atmosphere and taken up by the phytoplankton population both leading to increase in the ¹³C/¹²C of seawater DIC (dissolved inorganic carbon) and no significant change in the ¹⁸O/¹⁶O ratio, as indicated by Julie in the answer above. In epeiric sea the situation is more complicated because also changes in the alkalinity input from the nearby land masses may shift the carbon balance of the sea. 

Hope that it helped,

Boaz

Dear Jean-Michel, 

Thank you to your opinion/suggestion. We will try to split the dataset and to use separate trophic enrichment factor for primary and secondary consumers, but how to deal with intermediate consumers?

And of course, I agree with you that a deep knowledge of the trophic web is necessary before to use mixing models.

Merci.

Hi you can proceed by analyzing hydrochemical composition, ionic ratios (Na+/Cl–, Ca2+/Cl–, Mg2+/Cl–, SO42-/Cl- and especially Br–/Cl– molar ratios; Ca2+/Mg2+ weight ratio; and chloride concentrations) and calcite-saturation index (SIcalcite) of seawater and groundwater from selected wells. Also, isotope analysis of (2H/18O, 3H, 14C, 34S).

Chloride/Br ratios are used to determine the causes of groundwater salinisation for water.

Given the chemical make-up of ceramic / porcelain drill bits one would have thought it is the other way 'round. The only way I can think of a metal drill bit changing the 18O signature of bone or tooth bioapatite would be through heat stress (too much pressure being applied while drilling or drill set to too high a speed or both).  In all my work we have always used diamond-tipped drill bits in concjunction with a variable-speed dental drill.  If the correlation we got between bioapatite 18O and source water 18O is anything to go by, this combination of tools (and using a moderate drill speed) does not cause any 18O artefacts.  BTW, if you do not have a dental drill (with foot pedal for speed control) buy one; it is worth it.  However, do not purchase an NHS-for-human-dentistry approved model since they are beastly expensive. Look for a dental drill in veterinary supplies companies.  What they sell is exactly the same article (sometimes even from the same Swiss manufacturer) but at a fraction of the cost what NHS supplies companies charge.

Here is a solution practises (has a practice), if you have only the coupling EA-IRMS, you can proceed in this way:

- On a sample of homogeneous sediment you measure global 13C (carbonate + organic matters)

- On one other fraction acidified with the HCl with pH 2 and washed well and dried to measure you again the organic 13C.

From the intensities of peaks CO2, to calculate you the quantity of the CACO3 in your sediments.

So to calculate you the values of the 13C of carbonates.