25th International Meeting on Organic Geochemistry IMOG 2011

P-166
The role of two submarine canyons in the transport and
accumulation of organic matter in the south-eastern Brazilian
continental margin
Renato Carreira 1,2 , Lívia Cordeiro 2 , Dulce Oliveira 2
1 Department of Chemistry, Pontifical Catholic University, Rio de Janeiro, Brazil, 2 School of Oceanography,
Rio de Janeiro State University, Rio de Janeiro, Brazil (corresponding author:rscarreira@gmail.com)
The geochemistry of organic matter in recent
sediments from the South-Eastern Brazilian
Continental Margin (SEBCM; 20-29°S, 39-48°W) has
been considered in detail only in the last 5-10 years.
Studies using isotopic and sedimentological
information [p.ex, 1] as well as lipid biomarker
distributions [2, 3] suggest that organic matter (OM)
accumulating in these sediments is mainly derived
from autochthonous production, which is enhanced by
the occurrence of coastal and shelf-break upwelling
events of the cold and nutrient-rich South Atlantic
Central Water (SACW) [4]. On the other hand, the
presence of only small to medium estuaries in this
region results in low input of continental sources of
OM.
Under the ―Habitats Project – Campos Basin
Environmental Heterogeneity by CENPES
/PETROBRAS‖ we used lipid biomarkers (fatty acids,
n-alcohols and sterols) to evaluate the origin and
bioavailable fraction of organic matter in superficial
sediments from two canyons and two adjacent
transects in the slope (400 to 1300 m water-depths) of
the Campos Basin, in the SEBCM. Assignment of
lipids to distinct sources of organic matter,
considering all the data in two samplings (winter/2008
and summer/2009), revealed preferential
accumulation in the canyons (compared to adjacent
transects) of organic matter derived from primary and
secondary production in the water column. Our results
support the hypothesis that these topographical
features are responsible for the accumulation and
transport of labile organic matter to deeper portions of
the continental margin.
Figure 1. Results from two samplings (median=bar,
25 th and 75 th percentis=box and min/max=whisker)
for the grouping of lipids according to distinct sources
of organic matter: (i) terrestrial: sum of long-chain
(>C23) fatty acids and n-alcohols; (ii) zoo/fauna:
cholesterol, 18:1 fatty acid; (iii) primary production:
C27, C28, C30 sterols and C18,C20 polyunsaturated fatty
acids; (iv) bacterial: iso and anteiso-C15/C17 and 10methyl-C16
fatty acids. CANG = Grussaí canyon
CANAC = Almirante Câmara canyon.
References:
1. Mahiques, M.M., et al., Anais da Academia
Brasileira de Ciências, 2005. 77(3): p. 535-548.
2. Yoshinaga, M.Y., P.Y.G. Sumida, and S.G.
Wakeham, Organic Geochemistry, 2008. 39(10):
p. 1385-1399.
3. Carreira, R.S., et al., Organic Geochemistry, 2010.
41: p. 879-884.
4. Valentin, J.L., D.L. André, and S.A. Jacob,
Continental Shelf Research, 1987. 7(1): p. 77-88.
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