Abstract:
We report high resolution molecular abundance data for alkenones, dinosterol, long chain diols and n-alkanols from ODP Site 658 (20°45′N, 18°35′W; 2263 m water depth). These data are compared with previously reported data for TOC, chlorins, opal and long chain n-alkanes. The contents and mass accumulation rates (MARs) of chlorins are used as total phytoplankton productivity proxies, while the contents and MARs of opal, dinosterol, alkenones and diols are used as productivity proxies for diatoms, dinoflagellates, haptophytes and eustigmatophytes/diatoms, respectively. Five high productivity intervals (HPIs) are identified: two at the glacial/interglacial transition boundaries of 132-122 and 15-8 ka, two within the warmer periods of MIS 3 (50-30 ka) and the late Holocene (4-0 ka), and one within the glacial period of MIS 4 (67-60 ka). Productivity was lowest during both the penultimate glacial maximum of MIS 6 (150-140 ka) and the last glacial maximum (22-18 ka), as revealed by both the total phytoplankton and individual phytoplankton productivity indicators. Phytoplankton community structure changed significantly over the last 160 kyr. The Termination I&II HPIs were characterized by higher opal content, possibly reflecting increased diatom contributions to total productivity. Eustigmatophyte/diatom and haptophyte contributions were higher during MIS 5, but decreased toward the Holocene. Dinosterol revealed an opposite trend, with the highest contribution in the Holocene. We ascribe such changes in phytoplankton communities to the effects brought about by the varying amounts and nature of nutrient inputs contributed regionally by eolian dusts, river influxes, ocean currents and upwelling water masses. © 2005 Elsevier Ltd. All rights reserved.
