(In)coherent multiproxy signals in marine sediments: Implications for high-resolution paleoclimate reconstruction

Abstract

Accurate chronologies are the backbone of paleoclimate research, yet for marine sedimentary records the same age model is often applied to co-eval components that may have experienced different pre-depositional histories, leading to aliasing in corresponding proxy signals. Here we demonstrate 14C age discrepancies among several proxy carriers and use them to highlight spatio-temporal disparities among different components of the sediment. Total organic carbon (TOC), alkenones, and alkanoic (fatty) acids have older ages than co-occurring planktonic foraminifera in corresponding depth intervals of a sediment core retrieved from the so-called ‘Shackleton Sites’ on the southwest Iberian margin off Portugal. Temporal differences are explained by the addition of pre-aged material that is transported to the site by lateral advection, rivers or wind. We then modeled the age structure and relative abundance of the different pools that might have contributed to the older ages of TOC and alkenones. Results suggest the addition of a moderate (15-20%) proportion of very old allochthonous material (18,500-49,900 yr). This information was used to deconvolve the alkenone-derived sea surface temperature (SST) record and assess the impact of allochthonous inputs on paleoclimate signals.