Organic matter in sediments of a tropical and upwelling influenced region of the Brazilian continental margin (Campos Basin, Rio de Janeiro)

Branched GDGTs as Proxies in Surface Sediments From the South-Eastern Brazilian Continental Margin

“…The content of brGDGTs in the surface sediments showed a geographic distribution similar to the total isoGDGTs (Ceccopieri et al, 2018) and to other lipid biomarkers analyzed in the Campos Basin sediments (Oliveira et al, 2013;Cordeiro et al, 2018). Higher contents of total brGDGTs were found in the slope samples on all transects and in the middle shelf samples of the CFUS region, which are areas where preferential FIGURE 3 | Contents of (A) total brGDGTs (µg gTOC −1 ); (B) acyclic brGDGTs (µg gTOC −1 ); (C) crenarchaeol (µg gTOC −1 ), (D) BIT index; (E) #rings tetra index and (F) IR.…”

“…accumulation of OM, mostly from autochthonous processes, was already demonstrated (Oliveira et al, 2013;Albuquerque et al, 2014;Cordeiro et al, 2018). Based on the sediment TOC contents reported by Cordeiro et al (2018), the total brGDGTs contents varied from 5 to 32 µg gTOC −1 , with a sharply decreasing gradient in contents from the coastal to deeper waters ( Figure 3A). A similar trend can also be observed for the contents of the acyclic brGDGTs (sum of Ia, Ia' , IIa, IIa' , IIIa, and IIIa' , Figure 3B), with the highest contents of up to 21 µg gTOC −1 at stations near to the river mouth decreasing to 3 µg gTOC −1 in the slope region.…”

“…These values are among the highest measured in the Brazilian continental margin and contrast with the overall oligotrophic conditions induced by the warm and nutrient-poor waters transported by the Brazil Current (Silveira et al, 2017). As a consequence of the upwelling events, predominance of autochthonous OM in the basin's sediments on a regional scale is observed (Yoshinaga et al, 2008;Carreira et al, 2010;Cordeiro et al, 2018), a scenario also favored by a relatively low input of allochthonous OM (Carreira et al, 2015). The major contributor to continentally-derived materials to the Campos Basin is the Paraíba do Sul river, located to the north of the basin (Figure 2), as evidenced by isotopic and molecular markers (Souza et al, 2010;Albuquerque et al, 2014;Carreira et al, 2015), dissolved black carbon (Dittmar et al, 2012) and metals (Lacerda et al, 1993;Araujo et al, 2017).…”

“…In some places they appear to be derived from heterotrophic bacterial activity thriving in the alkaline pore waters of productive sediments (Peterse et al, 2009;Zhu et al, 2011;Weijers et al, 2014;Zell et al, 2015; Sinninghe Damsté, -Flood et al, 2019). The sediments in the depth-range where in situ production of brGDGTs seems to occur (75-400 m) are also enriched in labile organic matter (Cordeiro et al, 2018), which could support an enhanced bacterial activity in these sediments of the Campos Basin.…”

Regional palaeoenvironmental influence on organic matter sequestration and characteristics of carbon isotope segment C5 in a hemipelagic sequence, Organyà Basin, northeast Spain

“…Nonetheless, given the possible constraint associated with the use of this ratio because heterotrophic bacteria generally degrade the more labile n-alkanes before the isoprenoids, the interpretation favoured here relies on the fact that the UCM hump is almost non-existent in the chromatograms, which indicates that biodegradation is at least minimum (Wenger and Isaksen, 2002;Peters et al, 2005). The n-alkane data imply that the OM pattern of mixed origin recorded in the El Pujal lithologies is compatible with typical continental margin environments where sediments archive a complex OM signal influenced by distinct interconnected ecosystems that include rivers, estuaries and the ocean system itself (Ramaswamy et al, 2008;Schmidt et al, 2010;Bauer et al, 2013;Cordeiro et al, 2018). While the range of the n-alkanes distribution in the chromatograms suggests various sources of OM were supplied to the basin in the studied interval, it does not permit a clear conclusion concerning significant temporal variability with the lithologies because most chromatograms show only subtle differences (Figure 8).…”