Distribution of terrigenous and marine material along the Southeastern Brazilian continental margin

Abstract

Coastal marine sediments are a complex mixture originated from both terrestrial and marine sources characterized by terrestrial runoff, high primary production, and atmospheric deposition. Organic material and the trace elements from these sources are delivered to the ocean and a significant portion of them sink through the water column and ultimately get stored in sediments. In order to evaluate the source and distribution of the sedimentary material and variations of the marine productivity of the Southeastern Brazilian continental margin between 23° S and 28° S, contents for n-alkanes, alkenones, chlorins, fatty acids, trace elements were analyzed. Alkenone-based sea surface temperatures lower than 24.2 °C were found only southwest to São Sebastião Island while in the northeast the temperatures were higher than 24.2 °C. The distribution of organic material in sediments showed a predominance of terrigenous material and was ruled by the grain size. A correlation analysis indicates significant, positive values between the terrigenous and marine organic compounds, indicating the promotion of marine productivity by the input of terrigenous material (nutrient). Barium content was influenced by water depth as a result of an abiotic process in the formation of marine barite. Calcium and strontium were not correlated to the primary production proxies exhibited by the organic compounds.