Terrestrial organic carbon accumulation on the Amazon deep sea fan during the last glacial sea level low stand

• Published in: Chemical geology Vol. 159; no. 1-4; pp. 263 - 281
• Main Authors: Schlünz, B, Schneider, R.R, Müller, P.J, Showers, W.J, Wefer, G
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 08.07.1999
• Subjects: Accumulation budget; Amazon fan; Sea level; Terrestrial organic carbon; Accumulation budget; Terrestrial organic carbon; Amazon fan; Sea level
• ISSN: 0009-2541; 1872-6836
• DOI: 10.1016/S0009-2541(99)00041-8

Sediment cores from the Amazon deep sea fan recovered during R/V Meteor cruise 16-2 show in detail the modern areal distribution of sedimentary organic carbon, stable organic carbon isotopes of the organic matter (OM), as well as variations in the depositional processes. In addition, we studied up to 300 m long drilled sediment records recovered during ODP Leg 155 which allow evaluation of temporal variations on the Amazon fan. Our results reveal new evidence for a very rapid change of fan depositional processes and organic carbon source at times of sea-level change over the middle and lower Amazon fan. To estimate the amount of terrestrial organic carbon stored in sediments from the last glacial in the Amazon fan we used stable organic carbon isotopes of the OM (δ13Corg), organic carbon content (Corg), and age models based on oxygen isotopes, faunal data, and magnetic excursions. Following our results, the organic carbon accumulation on the Amazon deep sea fan is controlled by glacio-eustatic sea-level oscillations. Interglacial sea-level high stand sediments are dominated by marine OM whereas during glacial sea-level low stands terrestrial organic carbon is transported beyond the continental shelf through the Amazon canyon and deposited directly onto the Amazon deep sea fan. Glacial sediments of the Amazon fan stored approximately 73×1015 g terrestrial Corg in 20,000 years or 3.7×1012 g terrestrial Corg yr−1 (equivalent to 7–12% of the riverine organic carbon discharge; assuming constant paleo discharge), which is about the same amount of terrestrial organic carbon as deposited on the Amazon shelf today (3.1×1012 g terrestrial Corg yr−1 or 6–10% of the modern riverine organic carbon discharge).