Pockmark asymmetry and seafloor currents in the Santos Basin offshore Brazil

Inorganic and organic geochemical fingerprinting of sediment sources and ocean circulation on a complex continental margin (São Paulo Bight, Brazil)

“…Vegetation dominated by grasses and herbs (C 4 plants) normally presents AI values larger than 0.5. On the other hand, forest assemblages show AI values less than 0.5 (Schefuß et al, 2003). Accordingly, the organic matter of cores 61 and 62, located on the shelf, is dominated by input of C 3 vegetation derived from the Atlantic rainforest adjacent to the sampling site.…”

“…The South Atlantic Subtropical Gyre, during its movement toward the Brazilian continental margin, is influenced by both the wind field and the southern circulation in the South Atlantic. At the near-surface level (carrying Tropical Water -TW), the gyre is centred at 15 • S. At the level of the thermocline (carrying South Atlantic Central Water -SACW), the gyre is centred at 20 • S. Finally, at the underlying intermediate level, between 500 and 1200 m water depth (carrying Antarctic Intermediate Water -AAIW), the gyre approaches the margin at 28 • S (Schmid et al, 2000).…”

“…1). From a hydrodynamic point of view, the Santos Bifurcation leads to the formation of a permanent western boundary current (Intermediate Western Boundary Current -IWBC) (Boebel et al, 1999;Silveira et al, 2004;Legeais et al, 2013;Biló et al, 2014;Schattner et al, 2016) which leads to a reversed flow compared to the regional southward-directed circulation (Brazil Current -BC). Thus, a unique situation in the global ocean occurs.…”

“…In fact, previous studies (de Mahiques et al, 2008;Franco-Fraguas et al, 2014;Razik et al, 2015) provide different and contradictory interpretations for the sources and transport of sediment in the south-western Atlantic; this is especially due to a complex hydrodynamics of the Subtropical Gyre (Boebel et al, 1999;Schmid et al, 2000;Biló et al, 2014) between 23 and 35 • S.…”

“…The terrigenous / aquatic ratio (TAR) (Bourbonniere and Meyers, 1996) and the average chain length (ACL) (Ficken et al, 2000) are frequently used as proxies for the terrestrial versus marine sources. Also, the Alkane Index (AI) (Schefuß et al, 2003) is considered a useful tool for the evaluation of the relative contribution of C 3 and C 4 plants. Finally, the Carbon Preference Index (CPI) (Eglinton et al, 1962), originally used as an indicator of natural and anthropogenic sources, can also be used in the determination of the terrigenous or marine character of the organic matter.…”