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We describe a new on-line chromium reduction technique for the measurement of stable hydrogen (deltaD) isotopes in waters using continuous-flow isotope ratio mass spectrometry. The on-line Cr reduction method has low intersample memory effects (< 1%) and excellent precision and accuracy for deltaD (+/-0.5% and was used to analyze waters samples as small as 50 nL. The on-line Cr method has a number of significant advantages over conventional offline Zn and U reduction and on-line carbon-based pyrolysis techniques. A single Cr reactor can be used to analyze approximately 1,000 water samples using an injection volume of 0.5 microL, with an individual sample analysis time of 4 min. Intersample memory effects are negligible. The Cr reactor temperature of 1050 degree C is easily attainable on standard elemental analyzers and so does not require the specialized and costly high-temperature furnaces of carbon-based pyrolysis reactors. Furthermore, hydrogen isotopes in extremely small water samples in the 100-nL range or less can be easily measured; hence, this new method opens up a number of exciting application areas in earth and environmental sciences, for example, natural abundance deltaD measurements of individual fluid inclusions in geologic materials using a laser source and measurements of body fluids in physiological and metabolic research.

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Abstract. Re-examination of sediment cores from Deep Sea Drilling Project (DSDP) Site 277 on the western margin of the Campbell Plateau (paleolatitude of ∼ 65 • S) has identified an intact Paleocene-Eocene (P-E) boundary overlain by a 34 cm thick record of the Paleocene-Eocene Thermal Maximum (PETM) within nannofossil chalk. The upper part of the PETM is truncated, either due to drilling disturbance or a sedimentary hiatus. An intact record of the onset of the PETM is indicated by a gradual decrease in δ 13 C values over 20 cm, followed by a 14 cm interval in which δ 13 C is 2 ‰ lighter than uppermost Paleocene values. After accounting for effects of diagenetic alteration, we use δ 18 O and Mg / Ca values from foraminiferal tests to determine that intermediate and surface waters warmed by ∼ 5-6 • at the onset of the PETM prior to the full development of the negative δ 13 C excursion. After this initial warming, sea temperatures were relatively stable through the PETM but declined abruptly across the horizon that truncates the event at this site. Mg / Ca analysis of foraminiferal tests indicates peak intermediate and surface water temperatures of ∼ 19 and ∼ 32 • C, respectively. These temperatures may be influenced by residual diagenetic factors and changes in ocean circulation, and surface water values may also be biased towards warm-season temperatures.