In recent years Quaternary stratigraphy has become analytically intensive, given the realisation that the sedimentary record at specific locations is sufficiently continuous and complete for examination at 100 year resolution. This paper describes methods which enable high resolution molecular stratigraphy to be carried out quickly and efficiently. The primary technique for data generation is gas chromatography (GC), validated for certain samples by gas chromatography mass spectrometry (GC-MS). GC data are reduced using a suite of programs to provide compound abundances for entry in Lotus 1-2-3 spreadsheets. xy plots of compound abundance versus sub-bottom depth are produced, prior to the use of numerically intensive methods such as Fourier transform spectral analysis and principal components analysis. The paper is illustrated with time series data for the Uk 37 parameter from ODP Leg 108, Sites 658 A and B.

HIGH-RESOLUTION palaeoclimate records based on oxygen isotope data have provided important insights into climate variability and rates of natural climate change on about a thousand-year timescale 1-3. Little is known 4, however, about the variation of climate and of palaeoceanographic conditions throughout the Quaternary on timescales of less than 1,000 years (at frequencies far greater than those of the Milankovitch orbital cycles). Here we show that such high time resolution is possible from molecular stratigraphic studies based on 'biomarker' organic molecules (alkenones). We have sampled alkenone stratigraphic records at 70- to 200-yr intervals across glacial terminations I, II and IV in sediment cores from ODP site 658, off northwest Africa 5. Sea surface temperatures (SSTs) derived from the alkenone (U37k) index 6-8 vary rapidly beyond the range of analytical noise by up to 2.5-degrees-C in 300 yr, showing hitherto unknown cycles with about 600-yr periodicities. Some of the changes parallel similar events in the oxygen isotope stratigraphy. SST oscillations may be linked, in part, to abrupt breakdowns in Atlantic deep-water ventilation resulting from meltwater events of Quaternary glacial terminations 3,9,10.

This study investigates the effects of benthic feeding upon the lipid composition of material passing through marine food chains. GC and GC-MS were used to determine the changes in dietary fatty acids and sterols in a laboratory food chain involving the dinoflagellate Scrippsiella trochoidea, the pelagic shrimp Neomysis integer and the benthic mollusc Scrobicularia plana. Herbivory of Scrippsiella by both Neomysis and Scrobicularia involves preferential removal of algal polyunsaturated fatty acids (PUFAs) from the food and addition of branched fatty acids (BFAS) to the faeces. Both species contribute 4-desmethyl sterols and remove some algal 4-methyl sterols. Coprophagy of Neomysis faeces by Scrobicularia involves the addition of further BFAs as well as further animal sterols. There is a net removal of fatty acids and a net contribution of sterol in all feeding experiments. Faeces produced coprophagously have the greatest proportion of contributed animal sterol and branched fatty acids, reflecting the feeding by both species. The results suggest that observed fatty acid and sterol distributions in sediment surface material may result primarily from pelagic crustacean feeding, though benthic molluscan feeding in conditions of a settling bloom may give similar distributions. The coprophagy experiment suggests that the lipid distributions of sediment surface material are at least partially due to successive reworking of that material by benthic animals.