Abstract:
[Abstract from the online documentation]
A glacial varve chronology from New England spanning the 4000-year
period from 17,500 to 13,500 calendar years before present was
analyzed for evidence of climate variability during the late
Pleistocene. The chronology shows a distinct interannual (3 to 5
years) band of enhanced variability suggestive of El Nino-Southern
Oscillation (ENSO) teleconnections
... into North America during the late
Pleistocene, when the Laurentide ice sheet was near its maximum extent
and climatic boundary conditions were different than those of
today. This interannual variability largely disappears by the young
end of the 4000-year chronology, with only the highest frequency
components (roughly 3-year period) persisting. This record provides
evidence of ENSO-like climate
The 4022 year continuous annual chronology is roughly dated between
17.5 and 13.5 kyr before present, in calibrated radiocarbon
years. Varve year 1 is oldest, and varve year 4022 is most recent.
The continuous chronology has been obtained (as described in Rittenour
et al, Science, 2000) by (1) log-normal transformation to yield
roughly Gaussian distribution, (2) high-pass filtering of non-climatic
influences (timescales longer than 200 years) which represent
variation in deposition due to change from ice-proximal to ice-distal
environment of glacial lake following migration of Laurentide ice
sheet) of constituent segments, (3) standardization of constituent
segments and (4) merging of constituent segments, after verifying the
significance of correlations in the overlap interval between different
segments. 
