Background
The authors write that "during portions of the Last Glacial stage, the climate of the high-latitude North Atlantic region was characterized by rapid transitions from cold stadial conditions to warm interstadial conditions," and they say that "these stadial and interstadial events were particularly well developed between about 60 and 20 kaBP [thousand years before present], when they had an average pacing of about 1500 years (e.g. Dansgaard et al., 1993; NGRIP, 2004) and attained nearly two-thirds of the full glacial-interglacial amplitude," noting that "millennial-scale climate variability during the Last Glacial period also is evident in many other locations worldwide (Voelker, 2002), including the tropical oceans (e.g. Arz et al., 1998; Peterson et al., 2000; Stott et al., 2002; Jennerjahn et al., 2004), as well as in the monsoon domains of Asia, East Africa, and Australia (e.g. Schulz et al., 1998; Wang et al., 2001; Altabet et al., 2002; Burns et al., 2003; Turney et al., 2004; Brown et al., 2007)."

What was done
Remarking that "it is unclear if such variation occurred in the interior of tropical South America, and, if so, how the low-latitude variation was related to its high-latitude counterpart," Fritz et al. -- in an attempt to resolve this uncertainty -- derived a high-resolution history of many climate-related parameters from the deep coring of, and retrieval of sediments from, the bottom of Lake Titicaca (15-17°S, 68.5-70°W) in the southern tropical Andes, based on their detailed analyses of multiple factors having sedimentologic, geochemical, and paleoecological significance.

What was learned
The five researchers report that their work "shows clear evidence of millennial-scale climate variation between ~60 and 20 ka BP," which was driven by variations in the degree of regional wetness; and they say that this climatic oscillation is well correlated with the stadial/interstadial oscillation of the North Atlantic region. More specifically, they write that "the correlation between the Lake Titicaca and NGRIP records suggests that the major cold periods in the North Atlantic region were synchronous with wet periods on the Altiplano."

What it means
Fritz et al. conclude that "in the southern tropics, at least in South America, the evidence now suggests that the Northern Hemisphere [Last Glacial stage] cold events were accompanied by increases in precipitation and continental runoff brought about by an apparent southward shift of the Intertropical Convergence Zone in the near-equatorial Atlantic region of the continent and also were accompanied by increases of precipitation and fluvial runoff farther from the equator in the South American summer monsoon region, including the tropical Andes." And this combined set of findings suggests that the approximate 1500-year climatic oscillation that alternately brings century-long periods of relative cold and warmth to the Northern Hemisphere impacts the hydrologic climate of the Southern Hemisphere on approximately the same time scale.

References
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Arz, H.W., Patzold, J. and Wefer, G. 1998. Correlated millennial-scale changes in surface hydrography and terrigenous sediment yield inferred from last-Glacial marine deposits off Northeastern Brazil. Quaternary Research 50: 157-166.

Brown, E.T., Johnson, T.C., Scholz, C.A., Cohen, A.S. and King, J.W. 2007. Abrupt change in tropical African climate linked to the bipolar seesaw over the past 55,000 years. Geophysical Research Letters 34: 10.1029/2007GL031240.

Burns, S.J., Fleitmann, D., Matter, A., Kramers, J., Al-Subbary, A.A. 2003. Indian Ocean climate and an absolute chronology over Dansgaard/Oeschger Events 9 to 13. Science 301: 1365-1367.

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Peterson, L.C., Haug, G.H., Hughen, K.A. and Rohl, U. 2000. Rapid changes in the hydrologic cycle of the tropical Atlantic during the Last Glacial. Science 290: 1947-1951.

Schulz, H., von Rad, U. and Erlenkeuser, H. 1998. Correlation between Arabian Sea and Greenland climate oscillations of the past 100,000 years. Nature 393: 54-57.

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