Paper No. 69-27
Presentation Time: 9:00 AM-5:30 PM
CONSTRAINING THE OUTFLOW OF THE AMAZON RIVER FOR THE PAST ~40 KA USING BA/CA
DIX, Jamie1, DIXIT, Yama1, DOSS, Whitney C.2, DILL, Ryan2, CHANG, Fengming3 and TRIPATI, Aradhna K.4, (1)Earth, Planetary, and Space Sciences, University of California, Los Angeles, 3806 Geology Building Box 951567, los angeles, CA 90095, (2)Geological Sciences, Univ of Colorado-Boulder, INSTAAR, Boulder, CO 80309, (3)Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China, (4)Department of Earth, Planetary, and Space Sciences, Departments of Atmospheric and Oceanic Sciences, Institute of the Environment and Sustainability, Institute of Geophysics and Planetary Physics, University of California, Los Angeles, 595 Charles Young Drive East, Box 951567, Los Angeles, CA 90095, jamiedix@ucla.edu
The Amazon River is a critical part of the global water cycle and is associated with a region of high biodiversity. It is the world’s largest river by discharge amount, has the largest drainage basin, and holds approximately 20% of the world’s fresh water. Although dramatic changes in Amazon River outflow could have devastating effects regionally and worldwide, it is unclear how the outflow of the Amazon will respond to short and long-term climate change. However, the geochemical record of foraminifera from the Amazon Fan can be used to determine past behavior of this system caused by climate change. Understanding conditions associated with large reductions in Amazon River outflow can help us evaluate the likelihood of such a devastating scenario occurring in the future in response to anthropogenic carbon emissions.
Previous work used oxygen isotope ratios in foraminifera to infer a >60% reduction in Amazon River outflow around 12 kya in response to abrupt climate changes in the high latitudes of the Northern Hemisphere. This dramatic reduction in outflow is believed to have occurred on timescales of only decades to centuries. Using oxygen isotope ratios to reconstruct river outflow can be ambiguous due to its dependence on the hydrologic cycle and glacial meltwater. Here, barium/calcium ratios were used to determine freshwater outflow, and magnesium calcium ratios were used to determine temperature. Ba/Ca results are consistent with a significant decrease in river outflow around 12 ka during the Younger Dryas, and we will present a quantitative reconstruction of changes in outflow to evaluate the potential for this river system to undergo abrupt changes.
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