(Table 1) TOC, δ¹³C, concentrations of C37 alkenones, crenarchaeol and GDGTs of turbidites

• Main Authors: Huguet, Carme, Kim, Jung-Hyun, de Lange, Gert J, Sinninghe Damsté, Jaap S, Schouten, Stefan
• Format: Dataset
• Language: English
• Published: PANGAEA 2009
• Subjects: 157-951; 157-952; Alkenone; C37; standard deviation; C37 total (C37:2+C37:3); unsaturation index UK'37; Atlantic; Branched glycerol dialkyl glycerol tetraether; Canarias Sea; Carbon; organic; total; Comment; COMPCORE; Composite Core; Crenarchaeol; DEPTH; sediment/rock; Event label; Joides Resolution; Leg157; North Atlantic Ocean; Ocean Drilling Program; ODP; PC; Piston corer; Tetraether index of 86 carbon atoms; Tyro_90P22; Zone; δ13C; organic carbon; North Atlantic
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.818285; https://doi.org/10.1594/PANGAEA.818285

One of the primary prerequisites for the application of organic proxies is that they should not be substantially affected by diagenesis. However, studies have shown that oxic degradation of biomarker lipids can affect their relative distribution. We tested the diagenetic stability of the UK'37 and TEX86 palaeothermometers upon long term oxygen exposure. For this purpose, we studied the distributions of alkenones and glycerol dialkyl glycerol tetraethers (GDGTs) in different sections of turbidites at the Madeira Abyssal Plain (MAP) that experienced different degrees of oxygen exposure. Sediments were deposited anoxically on the shelf and then transported by turbidity currents to the MAP, which has oxic bottom water. This resulted in partial degradation of the turbidite organic matter as a result of long term exposure to oxic bottom water. Concentrations of GDGTs and alkenones were reduced by one to two orders of magnitude in the oxidized parts of the turbidites compared to the unoxidized parts, indicating substantial degradation. High-resolution analysis of the Pleistocene F-turbidite showed that the UK'37 index of long chain alkenones increased only slightly (0.01, corresponding to <0.5 °C) in the oxidized part of the turbidite, suggesting minor preferential degradation of the C37:3 alkenone, in agreement with previous studies. TEX86 values showed a small increase (0.02, corresponding to ~2 °C) in the F-turbidite, like UK'37 , while for other Pliocene/Miocene turbidites it either remained unchanged or decreased substantially (up to 0.06, corresponding to ~6 °C). Previous observations showed that the BIT index, a proxy for the contribution of soil organic matter to total organic carbon, was always substantially higher in the oxidized part in all the turbidites, as a result of preferential degradation of marine-derived GDGTs. This relative increase in soil-derived GDGTs affects TEX86, as the isoprenoid GDGT distribution on the continent can be quite different from that in the marine environment. Our results ...