ABSTRACT:
Sulfur isotopes are classically measured as either SO2 or SF6 using gas-source isotope-ratio mass spectrometry. We have recently developed an alternative approach utilizing multicollector ICP-MS, which has the principle benefit of lowering detection limits by several orders of magnitude. In this seminar I will present data from two projects highlighting unique advantages of the technique. Carbonate-associated sulfate from Archaean rocks can now be measured in microdrilled samples, and reveals that ? contrary to expectations ? Archaean seawater sulfate carried a positive 33S anomaly. This is in direct contradiction to current thinking about the importance of short-wavelength photodissociation in the Archaean sulfur cycle. Organosulfur compounds isolated from marine sediments and separated by gas chromatography can also be measured by ICPMS, providing the first compound-specific capability. In Cariaco Basin, we show that there is a dichotomy in d34S values between sulfurized lipids and sugars, which potentially explains the anomalous d34S values of most kerogens and highlights the importance of carbohydrates in organic matter accumulation.