Diatom-inferred productivity changes in the eastern equatorial Pacific: The Quaternary record of ODP Leg 111, Site 677

Abstract

Recent marine planktonic diatom assemblages from 47 sediment surface samples retrieved from the eastern equatorial Pacific yielded four significant Q-mode factors that are related to surface water properties. They include a northern subtropical (Factor 1), a southern subtropical (Factor 2), a Peru Current (Factor 3) and an eastern Equatorial Pacific (Factor 4) factor.A transfer function (based on 42 surface sediment samples) with a productivity range of 109 to 210 gC m−2 y −1 was defined using the geographic distribution of the northern and southern subtropical assemblages (Factor 1 and 2) and their relation to “mapped” surface water primary productivity. This transfer function has a standard error of estimate of 11.9 gC M−2 y −1 and it is used to estimate late Pleistocene paleo-productivity changes at ODP Leg 111 Site 677 off Ecuador.The Site 677 samples (usually spaced 10 cm apart and with a linear sedimentation rate of 4.3 cm y −3) were the same samples that were used for stable oxygen/carbon isotopic analysis from planktonic Foraminifera. The well constrained oxygen isotope stratigraphy permitted assignment of accurate ages to downcore samples.The interval between oxygen isotope stages 3 and 9 had variable productivity that is generally higher than present values of 175 gC m −2 y −1. A major decline in paleo-productivity below the present value occurred in stage 9, the early part of stage 8 and in the early and late stage 5.Key wordseastern equatorial PacificproductivityQuaternarydiatoms