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Palaeo-El Nino activity on the Peru margin over the past 20,000 yr BP.

Project Member(s): Skilbeck, C.

Funding or Partner Organisation: Australian Institute of Nuclear Science & Engineering (AINSE 2004 Awards)

Start year: 2004

Summary: This proposal seeks funding for twenty one 14C dates to infill the Holocene-Late Pleistocene chronology for two of three cores recovered during Leg 201 of the Ocean Drilling Program. The three cores contain sub-annual resolution laminations which we believe represent El Nino variation along the Peru continental margin, over at least the period from Last Glacial Maximum (LGM) to present. This request for extended support is critical to capitalise on our initial findings from the Leg 201 data set (AINSE grant 02/169 and commercial grant AMS-03-04) that have allowed us to 1) define a consistent chronology over 13,000 to 20,000yrBP in core 1227B (&diagram0), 2) recognise a diastem covering the Holocene in 1227B, and 3) confirm and broadly define the extent of Holocene sedimentation in cores 1228B and 1229E (&diagram1). Two Holocene ages from each of cores 1228B and 1229E, and one deglaciation age (11,330 yrBP) from 1228B do not provide a sufficiently constrained chronology, because sedimentation rates vary inconsistently between the early and late Holocene (between 9 and 36 cm/ka) (dashed lines on &diagram2).

Despite these constraints, we have carried out a preliminary analysis of Holocene redcolour intensity variation in 1228B and 1229E, using simple linear interpolation of ages between tie points. Although we are yet to prove laminations are indeed related to ocean temperature (tropical vs upwelling), our analyses show a remarkably similar pattern with Holocene El Nino data recently published by Moy et al. (2002) (&diagram3).

In addition, our well-constrained chronology over the deglaciation period in 1227B has yielded results showing the current pattern of El Nino variation seen in instrumental records (2-7.5 yr base period, with ~100 yr intensity cycle) was also probably operating immediately after LGM for at least 1300 yr (&diagram4).

Successful dating of the intervals requested will allow us to complete the project.

FOR Codes: Climatology (incl. Palaeoclimatology), Climate variability