Validating the applicability of upwelling and paleotemperature proxies based on long-chain diols in a coastal region (Chile margin) over the last 150 kyr.

Abstract

During the last 10 years, two promising organic proxies based on the relative distribution of long-chain diols have been proposed: the Long chain Diol Index (LDI) and the Diol Index. The LDI is used as a proxy for past sea surface temperatures (SSTs) and the Diol Index can be used to estimate paleoproductivity. Recent application of these paleoenvironmental proxies has yielded promising result, but there are still some uncertainties that obfuscate the definitive application of these long-chain diol based proxies. In this study, a multiproxy approach is used to elucidate part of this uncertainty, related to possible disturbance of the paleoenvironmental signals by river input and extensive upwelling, but also to uncertainty related to interpretation of the Diol Index. Biomarker lipid analysis is performed on core sediments retrieved from ODP site 1234, ~65 kilometer off Concepción, Chile. This area is particularly suitable for this research, because of its proximity to large discharging river systems and its location in the Peru-Chile upwelling system.

The biolipid analysis resulted in several SST and paleoproductivity records, spanning the last ~150 kyr at a resolution of ~2 kyr. The branched isoprenoid tetraether (BIT) index is analysed to assess the impact of terrestrial input on the different diol proxies. However, low BIT values (≤ 0.05) indicate that terrestrial input has been relatively low at ODP site 1234. The LDI SST record is compared with independent records of more established SST proxies based on alkenones and glycerol dialkyl glycerol tetraethers (GDGTs), using the UK'¦37 and TEX86, respectively. The SST records of the three assessed SST proxies agree in terms of main tendencies and amplitudes, with the TEX86 generally indicating slightly colder temperatures than the UK'¦37 and LDI. The UK'¦37 SST record most closely resembles the glacial/interglacial temperature trend of the LR04 benthic global stack.

The paleoproductivity proxies assessed during this study, reveal different patterns over the last ~150 kyr. The yielded Diol Index records indicating Proboscia paleoproductivity are compared with haptophyte paleoproductivity (based on C37 alkenones). While the application of Diol Index 1 seems to be compromised by substantial SST fluctuation over the last ~150 kyr, Diol Index 2 and C37 alkenone mass accumulation rate (MAR) indicate increased paleoproductivity rates during the last interglacial. In addition to a productivity peak during marine isotope stage (MIS) 5e, Diol Index 2 indicates a second peak during MIS 5b & 5c. Further research performed at higher resolution is necessary, to more precisely constrain the encountered lag between SSTs and Antarctic atmospheric temperatures and to identify climatic events and possible (sub)millennial oscillation off the Chilean coast.