The organic geochemistry of Peru margin surface sediments: I. A comparison of the C 37 alkenone and historical El Niño records
The alkenone-U k37 "paleothermometer" has potential as a sedimentary marker for El Niño/ Southern Oscillation (ENSO) events in the Peru upwelling regime. We assessed this potential by comparing the historical ENSO record with detailed U k37 profiles for 210Pb-dated cores from the Peru margin oxygen minimum zone (OMZ). Sediments with the greatest potential for holding a sedimentary U k37 record of El Niño events are sediments from the center of the OMZ sectioned at intervals ≤ the yearly sedimentation rate. The U k37 signals of individual El Niño events were substantially attenuated in the sediments we examined, and periods of frequent ENSO activity (e.g., 1870-1891) were more readily identified than isolated ENSO events in periods of less frequent ENSO activity. Detailed depth profiles of the C 37 alkenones in a core from ≈253 m (O 2 < 0.1 ml/l bottom water) suggest significant alkenone degradation and/or alteration (≈30%) in the 0-1 cm interval, despite the dysoxic depositional conditions. However, the similarity of the U k37 values for the five 2 mm sections from 0-1 cm suggests that the U k37 may be unaffected by the alkenone loss. Correlation between the C 37 alkenone concentration profiles in two cores from ≈15°S collected nine years apart are consistent with the use of these compounds for "molecular stratigraphy."