Table of Contents
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The ARAMIS systemAll JRAS sets have been prepared using the ARAMIS system at BGC-Jena. ARAMIS (‘Acid Reaction and Air Mixing System’) was built to enable the production of well defined SRMs (Standard Reference Materials). It is designed to minimize variability between different preparations/batches and to ensure a consistent production of reference CO2 mixed into CO2 free air. (for details see http:\\...). JRAS preparations/batchesEach digestion of calcite results in three flasks of mixed gas. These three flasks are filled simultaneously from the mixing volume and represent a preparation or batch. The CO2 and N2O concentrations in each flask are measured by the BGC Gas-Lab prior to isotope analysis in BGC Iso-Lab. Isotope analysis of δ13C and δ18O are repeated three times for each flask providing a total of nine measurements per batch. Below are the results of the batches prepared within the IMECC project (which funds this activity). Each data point represents the average of the nine measurements with the error bars showing one standard deviation.Figure 1.
Batch wise averages (n=9) from the MAR-J1
preparations made since the beginning of the IMECC project. The overall
average
for δ13C is 1.956 ‰ with a standard deviation of 0.012 ‰ .
The δ18O
average is -2.58 ‰ , σ = 0.035 ‰. The
time scale refers to the batch production dates. The average δ13C values for both MAR-J1 and OMC-J1 show a variability that is comparable or better than the average flask to flask variability obtainable by the BGC IsoLab (±0.02 ‰ as opposed to tank measurements which has a long term precision of ~0.013 ‰). The oxygen values are as expected not quite as precise, although the overall variability is also less than the average precision for flask measurements (±0.04‰). Based on these observations we can conclude that the preparation process is not adding any detectable variability when comparing the batch averages. Also, even though only a limited number of batches have been prepared so far, no systematic trend in time is visible as more preparations are added, indicating that the working reference air-based analysis is consistent and stable. Figure 2. Batch wise averages (n=9) from the OMC-J1 preparations made since the beginning of the IMECC project. The overall average for δ13C While this is all good
news for JRAS, it
does not leave much room for improvements. On the other hand, if we
take a
closer look at the two isotopic values for each calcite together we
still find
a correlation between δ13C and δ18O for both calcites (Figure 3). Although the ranges are
too small to
allow for a quantification of the correlation with any certainty, the
sign of
the slope and to some degree the magnitude suggest that this is a
consequence
of mass dependent isotope fractionation. Where this fractionation could
take
place is not clear. Any of the expansion steps when the CO2
formed
during digestion is moved within the ARAMIS system is a possible
culprit. Figure
3. Batch wise average values of δ13C and δ18O for
each
calcite, error bars are one standard deviation of the
averages (n=9)
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