Interhemispheric precipitation seesaw: mirror images of oxygen isotopic records from caves in S. Brazil and E. China

We have obtained a high resolution oxygen isotopic record of cave calcite from Caverna Botuverá (27° 13Ś, 49° 09Ẃ), South Brazil. The chronology was determined by 16 high-resolution U/Th ages. We interpreted our record, spanning from 40 ka through 15 ka, in terms of meteoric precipitation changes in this low-latitude location. The oxygen isotopic profile broadly follows local insolation changes and shows millennial-scale variation with amplitudes as large as 3 per mil, similar to (but not in phase with) some Northern Hemispheric observations (e.g., Wang et al., 2001; Bar-Matthews et al., 2003; Yuan et al., 2004). Using independent age scales, we compare our record to contemporary records from Hulu Cave, East China (Wang et al., 2001), and the GISP2 Ice Core, Greenland (Grootes and Stuiver, 1997). Minima in δ ¹⁸O (wet periods) at our site are synchronous with maxima in δ ¹⁸O (dry periods) in East China and vice versa. Our wet phases also correspond to minima in δ ¹⁸O (cold periods) in Greenland and vice versa. This anti-phased precipitation relationship between Botuvera and Hulu, two low-latitude locations, may be related to asymmetry in Hadley cell circulation in two hemispheres, associated not with seasonal changes as observed today, but with millennial-scale climate shifts. If the Botuvera and Hulu records are broadly representative of low-latitude rainfall in their respective hemispheres, and if rainfall is directly related to absolute humidity, then the atmospheric see-saw pattern that we observe could have important consequences because of water vapor's greenhouse properties. Reference: Bar-Matthews M. et al., 2003. Geochimica et Cosmochimica Acta 67, 3181-3199. Wang Y.J. et al., 2001. Science 294, 2345-2348. Yuan D.X. et al., 2004. Science 304, 575-578. Grootes P.M. and Stuiver M, 1997. Journal of Geophysical Research 102, 26455-26470.