Late Quaternary Paleoclimatology and Paleoceanography of the Amazon Continental Margin, Brazil

• Main Author: Nace, Trevor
• Other Authors: Baker, Paul A
• Format: Doctoral or Postdoctoral Thesis
• Language: unknown
• Published: 2012
• Subjects: Geology; Geochemistry; Amazon Basin; equatorial Atlantic; paleoceanography; sedimentology; South America; Nordeste; Methane hydrate
• Online Access: https://hdl.handle.net/10161/5556

The tropics are a significant source of heat and moisture export, which drive global circulation patterns, thus it is vital to systematically understand the land, ocean and sedimentological interactions within the tropics. The Brazilian continental margin is an ideal region to characterize the tropics due to its unique local oceanography and proximity to the atmospheric engine that is the Amazon Basin. A combination of: 1) terrestrial organics and hydrology; 2) oceanographic temperature, isotopic composition, and salinity and 3) early diagenesis and geochemistry of sedimentary interstitial water and methane hydrate, provide a detailed understanding of the primary constituents that influence the South American tropics. Sedimentological, organic and paleoceanographic reconstructions of the Amazon Basin, Brazilian Nordeste, and western equatorial Atlantic have been undertaken on two sediment cores located on the Brazilian continental slope representing 30 and 110 ka, respectively. High-resolution XRF analyses of Fe, Ti, K and Ca are used to define the sedimentological history of the Amazon Basin and northern Nordeste. Here we present elemental ratios of Ti/Ca and Fe/K, in addition to magnetic susceptibility, to determine variability in Amazon Basin and Nordeste hydrology. Bulk organic proxies d13C and d15N of sedimentary organic carbon are used to define the organic history of the Amazon Basin. Peaks in Ti/Ca and Fe/K ratios largely correlate in both the Amazon Basin and in the Nordeste Record. These excursions correlate with commonly modeled global slowdown of the Atlantic meridional overturning circulation (AMOC) during increased northern hemisphere glaciation. Differences in the Fe/K and Ti/Ca records suggest periods of increased chemical weathering independent of precipitation driven sediment discharge in the Brazilian Nordeste. Bulk organic geochemistry indicates the vegetative history of the Amazon Basin has been relatively stable during the late Quaternary. High-­resolution stable oxygen isotopic analysis ...