Upwelling and productivity along the Peru-Chile Current derived from faunal and isotopic compositions of planktic foraminifera in surface sediments

We report on the spatial distribution of isotopic compositions of the two planktic foraminifera species Globigerina bulloides and Neogloboquadrina pachyderma (dex.), and the faunal assemblages of planktic foraminifera in 91 surface sediment samples along the Chilean continental slope between 23 degrees S and 44 degrees S. Both delta C-13 and delta O-18 data of N. pachyderma (dex.) show little variability in the study area. North of 39 degrees S, the isotopic values of N. pachyderma (dex.) are heavier than those of G. bulloides, whereas south of 39 degrees S, this relation inverses. This is indicative for a change from a well-mixed, deep thermocline caused by coastal upwelling north of 39 degrees S to well-stratified water masses in a non-upwelling environment south of 39 degrees S. In addition, the faunal composition of planktic foraminifera marks this change by transition from an upwelling assemblage north of 39 degrees S to a high-nutrient-non-upwelling assemblage south of 39 degrees S, which is characterized by decreased contributions of upwelling indicators such as G. bulloides, N. pachyderma (sin.), and Globigerinita glutinata. In general, we can conclude that food and light rather than temperature are the primary control of the planktic foraminiferal assemblage between 23 degrees S and 44 degrees S off Chile. Our data point to higher marine productivity at upwelling centers north of 25 degrees S and at 30-33 degrees S. South of 39 degrees S, significant supply of nutrients by fluvial input most likely boosts the productivity. (c) 2005 Elsevier B.V All rights reserved.