Sea surface paleotemperature errors in UK′₃₇ estimation due to alkenone measurements near the limit of detection

Major errors (> 0.5°C) are produced in paleotemperature estimation with the C 37 alkenone method when the amount of the diunsaturated or triunsaturated species, C 37:2 and C 37:3 , respectively, approaches the limit of detection. These errors are more commonly encountered with C 37:3 because of its higher adsorption to gas chromatographic (GC) columns. They are particularly relevant at low sedimentary C 37 alkenone concentrations and may easily increase to temperature differences of 2°–4°C depending on the U K′ 37 values and the ratio between the C 37:3 signal and limit of detection. Mathematical expressions for the description of the analytical constraints derived from this detection limit problem are given. A quality assurance guideline based on sample dilution (three times) and calculation of the sea surface temperature error is proposed for assessment of reliable measurements. Reevaluation of literature data in the light of the equations reported in the present study suggest that some previously reported alkenone geochemical effects, such as variation in U K′ 37 temperatures due to postdepositional oxidation, may reflect deviations in the GC measurements due to changes in C 37 alkenone concentration.