Comment on "Absence of Cooling in New Zealand and the Adjacent Ocean During the Younger Dryas Chronozone"

doi:10.1126/science.1152098

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Atmospheric Science

Science 9 May 2008:
Vol. 320. no. 5877, p. 746
DOI: 10.1126/science.1152098

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Technical Comments

Comment on "Absence of Cooling in New Zealand and the Adjacent Ocean During the Younger Dryas Chronozone"

Patrick J. Applegate¹^*, Thomas V. Lowell² and Richard B. Alley³

¹ Department of Geosciences, Pennsylvania State University, University Park, PA 16802, USA.
² Department of Geology, University of Cincinnati, Cincinnati, OH 45221, USA.
³ Department of Geosciences and Earth and Environmental Systems Institute, Pennsylvania State University, University Park, PA 16802, USA.

Fig. 1. Comparison of eight ¹⁰Be exposure dates from the Waiho Loop moraine (black curves) (1) to the distribution of 10⁶ exposure dates predicted by the updated degradation model (red curves) (5, 10, 11). The best fit between the model and the data occurs at a model age of 11,600 yr B.P. (dashed red line), corresponding to the end of the Younger Dryas. Our preferred age assignment is thus $~$ 1100 years older than that given in (1) (black, dashed line). This best fit was found by adjusting the modeled age of the moraine until both the sum of squared errors and the maximum vertical distance between the cumulative density curves (inset) were minimized. The probability density curve for the observed exposure dates was constructed by summing the Gaussian curves of the individual dates and normalizing the total curve to 1. We assumed that the moraine's initial height and slope were 50 m and 34°, respectively; topographic diffusivities are from (5). Although these diffusivities are probably too small for the wet West Coast of New Zealand (9), multiplying the diffusivities by 10 does not change the fundamental resemblance of the model results to the ¹⁰Be dates. [View Larger Version of this Image (38K GIF file)]