DOI: 10.1594/pangaea.873377
title: Long chain n-alkanes deposited from borehole PRGL1P (ROMESS1) in the upper slope of the Gulf of Lions

description: During the PROMESS campaign (summer 2004) a borehole (PRGL1) was drilled in the upper slope of the Gulf of Lions. Previous studies showed that the deposition of the sedimentary units at borehole PRGL1 was determined by changes in the discharge of the Rhone river, induced by sea level and climate variability with a strong 100 ka imprint. However, there are no detailed studies that focus on the glacial/interglacial transitions (i.e. Terminations) that define 100 ka Quaternary ice-age cycles. Here we present a high-resolution record of terrestrial long chain n-alkanes (C21 to C33) from MIS 3 to MIS 11 in order to monitor changes in the sediments deposited on the upper slope of the Gulf of Lions with the aim to provide new insight into the climatic events occurring during Terminations in the western Mediterranean Sea.Principal component analysis grouped n-alkane on the basis of the degree of maturation of organic matter (fresh/degraded) that allowed to monitor past variability in the source of the sediment deposited in the upper slope as a consequence of sea level and climate change. This information was used to estimate the impact that northern ice-sheet variability had on the western Mediterranean basin. As sea level started to fall, fresh terrestrial organic matter increased owing to the seaward migration of Rhone's mouth. Simultaneously, the decrease in sea level exposed old and reworked organic material from the Rhone's catchment, including the delta plain and the continental shelf, that was eroded and transported into our study site. This resulted in an increase in the proportion of degraded terrestrial organic matter together with sea level decrease. Aside from sea level changes, the proportion of fresh vs degraded organic matter seems to be affected by the amount of continental runoff, with an increasing proportion of fresh terrestrial organic matter occurring at times of reduced continental runoff. During the last glacial, the increase of fresh terrestrial organic matter was contemporaneous with Heinrich events (HEs), suggesting dry and cold conditions on the western Mediterranean basin. These dry and cold millennial-scale episodes were reproduced during Terminations II, III and IV preceding flood events, most probably due to weakening/reinforcement of Atlantic Meridional Overturning Circulation (AMOC) that caused dry/humid conditions in western Mediterranean.
description: The age model used in this paper was derived from two previous studies on borehole PRGL1: for 19.25 to 157.10 mbsf the age model published by Sierro et al. (2009; doi:10.1016/j.quascirev.2009.07.019) was used, whereas for 157.10 to 230.90 mbsf, the age model published by Frigola et al. (2012; doi:10.5194/cp-8-1067-2012) was applied. In both cases the age model was mainly based on comparison of the G. bulloides ?18O record with the LR04 benthic stack (Lisiecki and Raymo, 2005 (doi:10.1029/2004PA001071)).
description: Supplement to: Cortina, Aleix; Grimalt, Joan O; Rigual-Hernandez, Andrés S; Ballegeer, Anne-Marie; Martrat, Belén; Sierro, Francisco Javier; Flores, José-Abel (2016): The impact of ice-sheet dynamics in western Mediterranean environmental conditions during Terminations. An approach based on terrestrial long chain n-alkanes deposited in the upper slope of the Gulf of Lions. Chemical Geology, 430, 21-33