Late Holocene Expansion/Contraction of the Indo-Pacific Tropical Rain Belt

Tuesday, July 28, 2015: 2:10 PM
Rhawn Flavell Denniston1, Caroline Ummenhofer2, Alan D Wanamaker3, Gabriele Villarini4, Matthew S Lachniet5, Yemane Asmerom6, Victor J Polyak6 and William F Humphreys7, (1)Cornell College, Mt. Vernon, IA, United States, (2)WHOI, Woods Hole, MA, United States, (3)Iowa State University, Ames, IA, United States, (4)University of Iowa, Civil and Environmental Engineering, Iowa City, IA, United States, (5)UNLV-Geosciences, Las Vegas, NV, United States, (6)University of New Mexico Main Campus, Albuquerque, NM, United States, (7)Western Australian Museum, Perth, Australia
Abstract:
The ITCZ marks the ascending (wet) arm of the Hadley Circulation, and migrates cross-equatorially on a seasonal basis, defining the tropical rain belt (TRB). Millennial variations in tropical precipitation are attributed to changes in mean latitude of the ITCZ, and in many regions, the TRB shifted as a coherent package, resulting in anti-phasing of monsoon rainfall between the Northern and Southern Hemispheres. However, rainfall dynamics along the southern margin of the TRB are not well understood, particularly in areas such as the Indo-Pacific where the majority of such research has been conducted at Northern Hemisphere sites.

We reconstructed late Holocene (the last 3000 yr) variability of the Indo-Pacific TRB by enhancing a published stalagmite-based monsoon reconstruction from northern Australia (cave KNI-51) (Denniston et al., 2013) and integrating it with the Dongge Cave record from southern China (Wang et al., 2005). Stalagmites are widely utilized paleomonsoon proxies because they can be precisely dated, offer high temporal resolution, and preserve evidence of monsoon strength via their oxygen isotopic ratios which are dominated by amount effects in regional precipitation.

Our results reveal that rather than shifting meridionally, the Indo-Pacific TRB expanded and contracted over multi-decadal/centennial time scales during the late Holocene, with symmetric weakening/strengthening of summer monsoons in the Northern and Southern Hemispheres of the Indo-Pacific (the East Asian Summer Monsoon in China and the Indo-Australian Summer Monsoon in northern Australia). Drought periods in southern Asia, such as those linked to the collapse of the Khmer Empire and Chinese dynasties also impacted the Australian tropics, with implications for ecosystems and human societies across the Southern Hemisphere of the Indo-Pacific. Last Millennial climate simulations from the Coupled Model Intercomparison Project, phase 5 (CMIP5) support Hadley Cell expansion and suggest that the Indo-Pacific may be somewhat anomalous in this behavior.

1 – Denniston R. et al. (2013) Quaternary Science Reviews, v. 78, 155-168.

2 – Wang Y. et al. (2005) Science, v. 308, 854-857.

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