Centennial-scale Holocene climate variability revealed by a high-resolution speleothem delta 18O record from SW Ireland.

Evaluating the significance of Holocene submillennial delta18O variability in the Greenland ice cores is crucial for understanding how natural climate oscillations may modulate future anthropogenic warming. A high-resolution oxygen isotope record from a speleothem in southwestern Ireland provides evidence for centennial-scale delta18O variations that correlate with subtle delta18O changes in the Greenland ice cores, indicating regionally coherent variability in the early Holocene. Evidence for previously undetected early Holocene cooling events is presented, but mid- to late-Holocene ice rafting in the North Atlantic appears to have had little impact on delta18O at this ocean margin site.

Sulfur isotope analysis of sulfide and sulfate minerals by continuous flow-isotope ratio mass spectrometry.

A continuous flow method (CF-IRMS) for the rapid determination of the sulfur isotope composition of sulfide and sulfate minerals has significant advantages over the classic extraction method in terms of the reduced sample quantity and a rapid analytical cycle of less than 8 min/ analysis. For optimum performance, the technique is sensitive to a number of operating parameters, including sample weight and the O2 saturation of the Cu-reduction reactor. Raw data are corrected using a calibration based on five international and internal standards ranging from -17.3 to +20.3 per thousand, which requires monitoring in order to correct the effect of changing delta18O of the sample gas on the measured mass 66 values. Measured sulfur contents are within 1-1.5% of expected values and the reproducibility of delta34S values is +/-0.1 per thousand (1sigma). The technique has been used successfully for more than 1000 analyses of geological samples with a wide range of delta34S from -20 to +20 per thousand.

Antiquity of the biological sulphur cycle: evidence from sulphur and carbon isotopes in 2700 million-year-old rocks of the Belingwe Belt, Zimbabwe.

Sulphur and carbon isotopic analyses on small samples of kerogens and sulphide minerals from biogenic and non-biogenic sediments of the 2.7 x 10(9) years(Ga)-old Belingwe Greenstone Belt (Zimbabwe) imply that a complex biological sulphur cycle was in operation. Sulphur isotopic compositions display a wider range of biological fractionation than hitherto reported from the Archaean. Carbon isotopic values in kerogen record fractionations characteristic of rubisco activity methanogenesis and methylotrophy and possibly anoxygenic photosynthesis. Carbon and sulphur isotopic fractionations have been interpreted in terms of metabolic processes in 2.7 Ga prokaryote mat communities, and indicate the operation of a diverse array of metabolic processes. The results are consistent with models of early molecular evolution derived from ribosomal RNA.

Galapagos hydrothermal mounds: stratigraphy and chemistry revealed by deep-sea drilling.

The Galápagos mounds sea-floor hydrothermal system is at least 300,000 years old and once produced manganese-poor sediments, which nearly blanketed the area of the present mounds field. Present-day mound deposits are limited manganese-rich exposures, suggesting that the system has changed from rock-to water-dominated and has diminished in intensity with time.