The 68-year monthly resolved time series of delta(18)O from ice cores retri
eved from the glaciated col of Nevado Huascaran; Peru (9 degrees S, 77 degr
ees W, 6050 m) reflects climate variability over Amazonia and the western t
ropical Atlantic. Over the 25-year period (1968-1993) of midtroposphere obs
ervations: the interannual variations in Huascaran delta(18)O relate closel
y with the zonal wind Variations over tropical South America at the 500 hPa
level. Additionally, there is some evidence that the spatial distribution
of temperature anomalies in the western tropical Atlantic has influence on
the 500 hPa circulation and hence the isotopic fractionation of moisture ad
vected across Amazonia. During El Nino warming, the moisture convergence ax
is over the Atlantic Ocean is commonly diverted northward, leading to unusu
al warm and dry conditions over northeast Brazil, and O-18-enriched snowfal
l at Huascaran. This enrichment phase is enhanced when the peak Pacific war
ming occurs during the first half of the calendar year, coincident with the
wet season over Amazonia, Approximately 12 months later, the El Nino demis
e is affiliated with a reprisal of strong trade wind circulation; and the r
esultant cool, pluvial environment over Amazonia triggers a reversal to str
ongly depleted isotope anomalies.