Hindcast

By positing that the spatial relationships between the ITCZ, BH, and TC zone have remained relatively constant over the long-term, we are able to hindcast paleoposi-tions of the BH and the TC zone based on ITCZ position. We base our hindcast on the Cariaco record of Haug et al. (2001) due to its large amplitude, high (subdeca-dal) resolution and inclusion of both rainfall and trade wind data. Although the latitudinal shifts represented by the changes in metal concentrations have not been quantified, the difference in sign and magnitude permit rough estimations.

Based on the Cariaco record, the chronology of significant changes in mean annual latitude of the ITCZ (and, by extension, location of the TC zone) is:

Northern residency: -11,000-4000 BP, -1100-600 BP (Medieval Warm Period) Present position: -2400-1100 BP

Southern residency: -4000-2400 BP, -400-200 BP (Little Ice Age)

A potential complication is the possibility of major change in the strength/ variability of ENSO frequency, which has been argued to have become more prevalent in the late Holocene (Haug et al. 2001; Koutavas and Lynch-Stieglitz, 2004). Although this should not affect the average latitude of the BH or TC zone, it might affect landfall frequency. However, it is possible that the apparent increased variability of ENSO suggested by Haug et al. (2001) for the interval between -4000-2400 BP actually results from increased instability in the general atmospheric circulation system, perhaps resulting from the establishment of a new atmospheric equilibrium.

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