HR: 14:05h
AN: PP13D-01 INVITED    [Abstracts]
TI: Holocene variability in the North American monsoon and links to other monsoon systems
AU: * Cole, J E
EM: jecole@email.arizona.edu
AF: Dept of Geosciences, University of Arizona, 1040 E 4th St, Tucson, AZ 85721, United States
AU: Wagner, J
EM: miller_jend@hotmail.com
AF: Dept of Geosciences, University of Arizona, 1040 E 4th St, Tucson, AZ 85721, United States
AU: Overpeck, J
EM: jto@email.arizona.edu
AF: Dept of Geosciences, University of Arizona, 1040 E 4th St, Tucson, AZ 85721, United States
AU: Beck, J W
EM: wbeck@physics.arizona,.edu
AF: Dept. of Physics, University of Arizona, PAS Building, Tucson, AZ 85721, United States
AU: Patchett, P J
EM: patchett@email.arizona.edu
AF: Dept of Geosciences, University of Arizona, 1040 E 4th St, Tucson, AZ 85721, United States
AU: Henderson, G
EM: Gideon.Henderson@earth.ox.ac.uk
AF: Department of Earth Sciences, Oxford University, Parks Road, Oxford, OX1 3PR, United Kingdom
AB: Unlike the Asian and African monsoon systems, with relatively rich Holocene paleoclimate histories, the history of the North American monsoon (NAM) remains poorly documented. One reason for this lack of explicit paleoclimate resolution may be that the NAM influences a region that also receives significant non-monsoonal precipitation. Thus records of past aridity can be ambiguous in their seasonal attribution and related mechanisms. In the Southwestern US, monsoon moisture makes up half at most of the seasonal precipitation, with the balance coming in from westerly storms in the winter half-season. Holocene records from this region are divided on whether the mid-Holocene was wetter or drier; the balance of evidence is consistent with a scenario that involves an intensified monsoon and drier winters. However, continuous, well-dated records of the NAM spanning the Holocene are virtually nonexistent. Here we present a Holocene record of stable isotope variability from a cave in southeastern Arizona, Cave of the Bells, that appears to track at least partly the long-term variations in the NAM. Precipitation isotope data from the modern system indicates a monsoon influence that is subtle and only appears in the wettest of recent monsoon seasons. Speleothem oxygen isotopic data from the mid- Holocene parallel insolation forcing on Milankovich time scales and show substantial higher-frequency variance whose period changes over the 3300-6400 yr BP record. In particular, we note a shift from century-scale to multidecadal variance around 4500 yr BP that coincides with variance changes in other records from the tropical/subtropical Americas. We argue that as the ITCZ shifted southward in the mid-Holocene, in response to orbital forcing, subtropical dry zones expanded and climate in these marginal areas became more variable. This interval is an important time of change in other monsoon systems, and we will discuss how the NAM record from Arizona compares with well-documented shifts in the Asian and African monsoons.
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1637 Regional climate change
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4958 Speleothems
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting