HR: 09:00h
AN: PP11C-05    [Abstracts]
TI: Possible Antarctic Forcing Over Amazon Basin Climate During The LGIT
AU: * Ettwein, V J
EM: v.ettwein@ucl.ac.uk
AF: University College London, Environmental Change Research Centre, 26 Bedford Way, London, WC1H 0AP United Kingdom
AU: Maslin, M A
EM: mmaslin@geog.ucl.ac.uk
AF: University College London, Environmental Change Research Centre, 26 Bedford Way, London, WC1H 0AP United Kingdom
AU: Burns, S J
EM: sburns@geo.umass.edu
AF: University of Massachusetts, Amherst, Department of Geosciences, 233 Morrill Science Center, Amherst, MA 01003 United States
AU: Leng, M J
EM: mjl@nigl.nerc.ac.uk
AF: NIGL/NERC, Kingsley Dunham Centre, Keyworth, Nottingham, NG12 5GG United Kingdom
AU: Weyhenmeyer, C E
EM: cweyhenm@syr.edu
AF: Syracuse University, 204 Heroy Geology Laboratory, Syracuse, NY 13244 United States
AB: The Amazon Basin is the Earth's largest and most intense land-based convection centre, and plays a fundamental role in the atmospheric transport of latent heat to the higher latitudes. This is particularly significant during the austral summer months when Southern Hemisphere insolation is at a maximum, and the South American Summer Monsoon (SASM) is at its most developed. However, the Pleistocene climate history of the Amazon Basin is comparatively poorly known. Previous indicators of effective moisture have been relatively few in number and widely dispersed, often recording a highly localised signal, with many records also being fragmentary and/or having poor age control. Conversely, marine sediments from the Amazon Fan can circumvent these limitations as they have the potential to record a basin-wide average of past changes in effective moisture within single, continuous sequences that can be radiocarbon dated. Furthermore, high rates of sedimentation have the potential to yield data of a resolution comparable to the ice core records. Radiocarbon-dated δ¹⁸O records have been generated from ODP Site 942 on the Amazon Fan. By isolating the shifts in planktonic δ ¹⁸O brought about by freshwater-driven changes in salinity over the Amazon Fan (Δδ ¹⁸O), it has been possible to monitor past changes in the outflow of the Amazon River, and hence derive a proxy for the effective moisture history of the Amazon Basin. Δδ¹⁸O data imply that the Amazon Basin was more arid during the glacial period, relative to the Holocene. This is interpreted to be associated with the glacial-interglacial variation in Southern Hemisphere summer insolation and the associated intensity of the SASM. However through the Last Glacial Interglacial Transition (LGIT), effective moisture levels in the Amazon Basin appear to have co-varied with Antarctic temperature records (implied from the Vostock Ice Core ΔD, based on the timescale of Blunier et al, 1998, Nature, 384, p 739-743). The post-Last Glacial Maximum warming in Antarctica coincides with an apparent increase in effective moisture within the Amazon Basin, whereas the Antarctic Cold Reversal (~ 15-13 Cal kyr BP) is inferred to coincide with a marked phase of increased aridity. Where maximum inferred aridity appears to concur with the onset of the Younger Dryas (YD) in the Northern Hemisphere (~ 13 Cal kyr BP), the YD itself is inferred to be a period of progressively increasing effective moisture within the Amazon Basin. It is hypothesised that Northern and Southern Hemisphere temperature gradients may exert independent control over the respective northerly and southerly limits of SASM convection over the Amazon Basin, and thus influence the effective moisture availability within.
DE: 4215 Climate and interannual variability (1616, 1635, 3305, 3309, 4513)
DE: 4825 Geochemistry
DE: 4914 Continental climate records
DE: 4934 Insolation forcing
DE: 4944 Micropaleontology (0459, 3030)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005