Reconstructing the climate variation of Eastern Peru over the last millennium

The delta18O of two speleothems from northeastern Peru provides a 1000 year history of precipitation variability at subannual to decadal resolution. The speleothem delta18O varies in response to shifting North Atlantic SSTs that bring about a southward or northward bias in the Intertropical Convergence Zone. A southward bias in the ITCZ leads to increased precipitation over eastern Peru. Wetter periods cause lower speleothem delta 18O due to the 'amount effect'. The 1000 year speleothem reconstruction documents a multi-century increase in the amount of precipitation during the "Little Ice Age". There has been a progressive decrease in precipitation over the past two centuries. These observations do not agree with earlier reconstructions of rainfall variability that relied upon river runoff proxies from northern South America. It is proposed that this discrepancy is a result of decreased river runoff in wetter periods because precipitation is stored at higher elevations as ice.