Glacial geomorphology, fluvial geomorphology, hillslope geomorphology, submarine geomorphology, tectonic geomorphology...

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Monday, 13 September 2010

NZ-YD#1: No evidence for a Southern Hemisphere Younger Dryas?

Irishman's Stream, New Zealand
The presence of a Younger Dryas (YD, ~13-12 ka) cooling event in New Zealand has been much discussed as it would provide a useful correlation to the Northern Hemisphere cooling at this time, and so indicate if glacial-interglacial cycles in either hemisphere occur synchronously or sequentially. South Island's Waiho Loop moraine was previously considered to represent the YD, but recent research by Tovar et al. at Canterbury University revealed its landslide origin. A paper in Nature this week by Kaplan et al. has shown from an investigation of glacial events in Irishman's Stream, using very high resolution 10Be dating, that this glacier retreated consistently throughout the period of the YD. This suggests that during a Northern Hemisphere glacial the Southern Hemisphere is warming, which may be due to a southward shift in warm climate systems, or a more extreme seasonality between the poles during cooling. In fact, our understanding of the climate of this area is changing rapidly; Shulmeister et al. extend the start of the Last Glacial Maximum in New Zealand by 2 kyr to ~24 ka, again using cosmogenic dating.