High resolution planktic foraminiferal record of the last 13,300 years from the upwelling area off Chile

A high resolution sedimentary record spanning the last deglacial and Holocene periods was obtained by studying the deep-sea sediment core GIK 17748-2 retrieved from 2545 m water depth in the Valparaiso Basin (Chilean continental slope, Southeast Pacific - 32 degrees 45.00'S; 72 degrees 02.00'W). AMS-(14)C measurements and oxygen-isotope analyses of the planktic foraminifera species Globigerilla bulloides and Neogloboquadrina pachyderma (dex.) indicate an age of 13.3 AMS-(14)C kyr B.P. at the base of the core (383 cm) and sedimentation rates ranging between 9 and 92 cm/kyr. Foraminiferal assemblages and accumulation rates were analysed in order to investigate variations in paleoceanography and paleoproductivity in the southern Peru-Chile Current during the last 13 kyr. Changes in foraminiferal assemblages indicate a sequence of three major hydrographic regimes at the site of the core: (1) deglacial sediments are characterised by variable faunal compositions generally reflecting strong upwelling and high productivity. (2) During the early and middle Holocene upwelling and, thus, productivity decreased, as indicated by an elevated relative abundance of N. pachyderma (dex.), and the importance of the Subtropical Surface Water of the Peru-Chile Countercurrent increased, as indicated by higher relative amounts of N. dutertrei. (3) For the last 3 kyr, variable faunal assemblages indicate variable competing environmental conditions characterised on one hand by increased upwelling, reflected by an elevated relative abundance of N, pachyderma (sin.), and on the other hand, by warmer conditions, deduced from a higher relative abundance of N. dutertrei, probably due to more frequent and more intense El Nino events. In addition, hints for slightly cooler conditions between 11.4 and 10.7 kyr B.P, might be related to a Younger Dryas event in this region. (C) 1999 Elsevier Science B.V. All rights reserved.