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Rationale: The carbon (δ13C) and oxygen (δ18O) isotope composition of siderite (FeCO3) is used widely to understand and quantify geochemical processes to reconstruct past climate and environmental change. However, few laboratories follow precisely the same protocol for the preparation and analysis of siderite‐bearing materials, which combined with the absence of international reference materials and mineral‐specific acid fractionation factors, leads potentially to significant differences in isotope data generated by individual laboratories. Here we examine procedures for the isotope analysis of siderite and discuss factors potentially contributing to inconsistencies in sample measurement data. Methods: Isotope analysis of siderite is first assessed using similar versions of the classical off‐line, sealed vessel acid digestion method by comparing data sets obtained from intercomparison materials measured at two participating laboratories. We then compare data from the classical method against those generated using an automated preparation technique using data produced from an independent set of test materials. Results: Measurement of siderite δ13C is generally both repeatable and reproducible, but measurement of δ18O may be subject to large (~1‰), method‐dependent bias for siderite reacted at differing temperatures (70°C and 100°C) under classical and automated CO2 preparation conditions. The potential for poor oxygen isotope measurement reproducibility is amplified by local differences in sample preparation protocols and procedures used to calibrate measurement data to international reference scales. Conclusions: We offer suggestions for improving the repeatability and reproducibility of δ13C and δ18O analysis on siderite. The challenge of producing consistent isotope data from siderite can only be resolved by ensuring the availability of siderite reference materials to facilitate identical treatment as a basis for minimising method‐dependent contributions to data inconsistency between laboratories. [ABSTRACT FROM AUTHOR]

Abrupt cooling events are features of Holocene climate and may recur in the future. We use lake records from Hawes Water, NW England, to quantify the impact of two prominent early Holocene climatic events. Subdecadal oxygen isotope records from sedimentary carbonate ([[delta].sup.18][O.sub.c]), dated using thermal ionization mass spectrometry (TIMS) U-series analyses, provide evidence for abrupt cold events, lasting ~50 and ~150 yr at 9350 and 8380 yr ago, which correlate with the 9.3 ka and 8.2 ka events recognized in Greenland ice cores. At Hawes Water, mean July air temperatures, inferred from chironomid assemblages, decreased by ~1.6 [degrees]C during each event. Calculations show that the isotopic excursions were dominantly caused by decreases in the isotopic composition of meteoric precipitation ([[delta].sup.18][O.sub.p]) by ~1.3%o; this is interpreted as a direct downstream response to cooling and freshening of northeast Atlantic surface water by melting ice sheets. Intermediate in magnitude between events observed in Greenland and central Europe, the effects are consistent with a partial shutdown of the North Atlantic thermohaline circulation. Keywords: abrupt climate change, Holocene, 8200 event, 9.3 ka event, stable isotopes, lacustrine record.

Scanning electron microscopy of sediments, microfossils, and polished thin sections from the Cenomanian-Turonian boundary section at Dover, England, demonstrates that cement is concentrated within large pores such as foraminifera and calcispheres, whereas the surrounding coccolith-rich sediments are largely lacking in cement. Isotope analysis of single microfossils and cement samples indicates the presence of mixing lines between primary (paleoceanographic) compositions and cements. Consequently, paleoceanographic and stratigraphic interpretations of these sediments, and perhaps other similar sediments based on similar data, may be suspect.