Oceanic surface conditions recorded on the sea floor of the Southwest Pacific Ocean through the distribution of foraminifers and biogenic silica

Abstract

Over 180 surface sediment samples from the Southwest Pacific Ocean were investigated for their planktonic foraminiferal (> 149 μm), opaline and terrigenous sediment content, with the aim to determine the oceanic conditions at the sea surface above the sampling sites. High concentrations of biogenic opal are related to high productivity levels recognised in tropical surface waters. The abundance of this biogenic opal found within the sediments on the ocean floor shows a slight decrease as one approaches the Australian landmass, and also poleward from the equatorial belt. The distribution of major species of planktonic foraminifers reflects different surface water masses. Q-mode factor analysis of planktonic foraminiferal percentage data from 63 core tops permits identification of several characteristic foraminiferal assemblages for the Southwest Pacific Ocean. Four factors explain up to 95.5% of the total variance. Factor 1 (66%) is dominated by the tropical-subtropical species Globigerinoides sacculifer and Globigerinoides tuber. The transitional to subpolar species Globorotalia inflata is important in factor 2 (12%). The temperate-cool factor 3 (13%) is characterised by Turborotalia quinqueloba and Globigerinita glutinata. Factor 4, which explains 3% of the total variance and which is represented by several species, is assigned to the high productive equatorial and coastal waters off the Australian continental margin. Palaeoecological equations permitting an estimate of sea-surface temperatures and salinities are presented. The correlation coefficients between modern data adapted from literature and estimated by transfer function FP 4 (transfer function for planktonic foraminifers) are 0.95 (for temperature) and 0.77 (for salinity). Show more