Wind strength variability in Australia during the last glacial maximum

Lynda Petherick 1 ,2, Hamish McGowan2, Patrick Moss2, Sam Marx3
1Xi'an-Jiaotong-Liverpool University, Suzhou, Jiangsu, China, 2The University of Queensland, Queensland, Australia, 3The University of Wollongong, New South Wales, Australia

A continuous multi-decadal to centennial scale resolution record of deposition of local dune sands and far travelled aeolian dusts encompassing the termination of the Last Glacial Cycle (defined here as ca. 31,000-18,000 years BP) has been developed from organic-rich lake sediments from Tortoise Lagoon, North Stradbroke Island, Australia. Grain size analysis of the aeolian sediment deposited in the lake showed three dominant modes (ca. 221 μm, 64 μm and 14 μm), interpreted as reflecting fluvial/aeolian transport . Based on modal grain size of the fine clay (i.e. far-travelled dust) fraction, we quantitatively estimate wind strength using a based on Tsoar and Pye's (1997) equation:

L = Ūt = Ū2ε

Rearranged to solve for Ū:

Ū = K2D4L

Ū = Mean wind velocity (cms-1)
D = Modal grain size (cm)
L = Horizontal distance travelled by suspended particle (cm)
K = Constant
ε = Coefficient of turbulent exchange

Pollen grains archived in the lake sediment indicate relatively cool climate with mean air temperatures during the Last Glacial Maximum ca. 6 C cooler than modern. As such, equation variables were calculated based on a relatively cool atmosphere. Results indicate that not only was there a higher frequency of dust storms during the Last Glacial Maximum, but also that dust may have been transported by higher intensity winds. Estimated wind strengths based on modal grain size during the two peaks in inorganic sediment flux at ca. 29,000 yr BP and ca. 21,000 yr BP indicate a maximum wind speed of 32 ms-1. This value is over twice the average wind speed of modern dust storms, and roughly equivalent to maximum wind gusts of modern storms associated with the passage of cold fronts.