As part of a wider palaeoclimate and palaeoceanographic study of Holocene-Late Pleistocene laminated sediments from the Peru continental margin, we completed 33 AMS 14C dates from 3 cores (1227,1228 and 1229) recovered during Leg 201 of the ODP to reconstruct a history of sediment accumulation over the past 20,000 years. Although the sediments are predominantly diatomaceous oozes they contain sufficient inorganic (e.g. foraminifer tests and nannofossil plates) and organic carbon to allow 14C dating. The Peru margin cores are located below a well-developed oxygen minimum zone where distinct laminated diatomaceous oozes contain a multiproxy geochemical signature of interannual El Niño variability Sample preparation and measurement were carried out at the ANTARES AMS facility. Our recent analyses of these marine sediment cores from the Peru continental margin have yielded new evidence for multidecadal to century-scale ENSO variability over the past 20,000 years.. Well preserved sections of the core dated by AMS C-14 have provided continuous, high-resolution records for the intervals 2,800-0 cal yrBP and 17,200-15,700 cal yrBP. Average sedimentation rates during the late Holocene are ~70 cm/ka and exceedingly high accumulation rates (~265 cm/ka) have been calculated for the early Deglaciation period. For one core, 1228, 14C dating is progressing over the transition period of 9 to 12 yrBP . In order to investigate an El Nino origin for the laminae on this part of the Peru shelf, we have undertaken two independent lines of study : (1) high resolution (0.1 mm per pixel) scanned colour images to carry out time series analysis of ENSO-band (2-8 year) base variability and (2) given the mixed volcaniclastic - upwelling setting, selected geochemical and mineralogical analyses of dark and light laminae to determine if they contain a climate signal. These include del-13C analyses of bulk sediments and planktonic foraminifer, del-18O of the latter, as well as bulk organic carbon, carbonate, quartz and feldspar percentages of representative “dark” and “light” laminae. Layer counting of the ~1500 year deglacial sequence reveals that each couplet of dark (El Niño) and light (La Niña) layers (~8 mm per couplet) represents a mean time duration of 5.6 years, well within the 2-7 year periodicity of the interannual ENSO cycle. Frequency analysis of the down-hole high-resolution red colour intensity variation reveals strong spectral peaks at 4.8 and 7.1 years, and additional but significant peaks at 11, 21 and 149 years, strongly suggestive of a solar influence on long-term ENSO variability
See more of Poster Session I
See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)