Carbonate dissolution and planktonic foraminiferal assemblages observed in three piston cores collected above the lysocline in the western equatorial Pacific

Abstract

Planktonic foraminiferal assemblages were analyzed in three piston cores recovered from depths above the recent sedimentary lysocline (3.5 km) in the western Pacific Ocean for the purposes of (1) evaluating the effects of carbonate dissolution on fossil assemblages and (2) the impact of dissolution on paleoceanographic reconstructions for the past 300 kyr. We used the perfect test ratio (PTR) of Globorotalia menardii as an indicator of carbonate dissolution. Down-core variations of the PTR indicate that significant dissolution occurred during reglaciation steps represented by isotope stages 7–6, 5–4, and 3–2. The results of principal component analysis (PCA) based on the relative abundances of dominant species of planktonic foraminifera indicate that down-core changes in factor 1 loadings correlate with variations in PTR and with variations in the percentage of coarse fraction (>63 μm) present in the sediments. These correlations indicate that foraminiferal assemblages were apparently altered by dissolution events despite the fact that they were deposited at water depths shallower than the modern lysocline. We also estimated variations in paleo-sea surface temperature (paleo-SST) using the transfer function FP-12E. A negative correlation was found in communality as calculated from PCA and factor 1 loadings; this trend is distinct for the case of communality lower than 0.9. Thus, we conclude that estimated paleo-SST values based upon analysis of planktonic foraminifera are biased by carbonate dissolution.