Tetraether lipids and TEX86-based temperature estimates: a case study on core-top sediments from two cross-shelf transects on the south-eastern Brazilian continental margin


Contact
Gesine.Mollenhauer [ at ] awi.de

Abstract

In the last years, core isoprenoid and branched glycerol dibiphytanyl glycerol tetraethers (GDGTs) have been increasingly used as proxies to study recent and past environmental conditions, as the TEX86 (TetraEther indeX of isoprenoid tetraethers consisting of 86 carbon atoms) to estimate seawater temperature and BIT (branched and isoprenoid tetraethers) to track the relative contribution of terrestrial and aquatic carbon to sediments (review in Schouten et al., 2013). Here we present first data of GDGTs and associated TEX86 (Kim et al., 2010) and BIT (Hopmans et al., 2004) indices in surface sediments of the Campos Basin, on the south-eastern Brazilian continental margin (Figure 1). Samples were collected in 2009 within the framework of the Habitats Project – Campos Basin Environmental Heterogeneity by CENPES /PETROBRAS – along two cross-shelf sediment transects (25 to 3000 m water depths) located under the influence of upwelling (transect B) and river discharge (transect H). Isoprenoidal GDGTs are dominated by GDGT-0 (212.1 ± 203.8 ng g-1) and crenarchaeol (327.4 ± 295.7 ng g-1), with higher concentrations at 25 m and in the middle-slope (400-100 m depths) samples, particularly at transect B (Figure 1-a). Other GDGTs (1, 2, 3 and regioisomer of crenarchaeol) and branched GDGT (I, II and III) ranged between 50 and 100 ng g-1. In transect B, the distribution of GDGT abundances is similar to that of lipid biomarkers, which in turn indicated accumulation of autochthonous OM on the shelf and slope as a result of upwelling events and/or lateral transport by mesoscale processes (Oliveira et al., 2012 and references therein). Relatively lower concentrations of GDGTs on transect H may reflect coarse sediment with low organic carbon and lipidsCorg on the shelf (Carreira et al., unpublished results). BIT index was very similar in both transects (0.12 ± 0.02 and 0.13 ± 0.02), indicating a low influence of export of terrestrial OM to the shelf, as also suggested by long-chain fatty acids and alcohols (Carreira et al., unpublished results). The TEX86 indicates low temperatures at 25 and 50 m on transect B (Figure 1-b). This is consistent with the occurrence of coastal upwelling at Cabo Frio (Valentin and Kempf, 1977), although the values are lower than historical records of seawater temperature in the region (Franchito et al., 2008). GDGTs and calculated TEX86 and BIT indices provided information consistent with ongoing evaluation of the sources and fate of OM in the studied region. The interrelationships of oceanographic and sedimentological settings and GDGT proxy signal obtained in the present study will be investigated in further details with the analysis of additional samples.



Item Type
Conference (Poster)
Authors
Divisions
Primary Division
Programs
Primary Topic
Peer revision
Not peer-reviewed
Publication Status
Published
Event Details
International Meeting on Organic Geochemistry, 15 Sep 2015 - 18 Sep 2015, Prague.
Eprint ID
39517
Cite as
Carreira, R. S. , Hefter, J. and Mollenhauer, G. (2015): Tetraether lipids and TEX86-based temperature estimates: a case study on core-top sediments from two cross-shelf transects on the south-eastern Brazilian continental margin , International Meeting on Organic Geochemistry, Prague, 15 September 2015 - 18 September 2015 .


Share

Research Platforms
N/A

Campaigns


Actions
Edit Item Edit Item