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We constructed an 800,000-year synthetic record of Greenland climate variability based on the thermal bipolar seesaw model. Our Greenland analog reproduces much of the variability seen in the Greenland ice cores over the past 100,000 years. The synthetic record shows strong similarity with the absolutely dated speleothem record from China, allowing us to place ice core records within an absolute timeframe for the past 400,000 years. Hence, it provides both a stratigraphic reference and a conceptual basis for assessing the long-term evolution of millennial-scale variability and its potential role in climate change at longer time scales. Indeed, we provide evidence for a ubiquitous association between bipolar seesaw oscillations and glacial terminations throughout the Middle to Late Pleistocene.

The El Niño-Southern Oscillation (ENSO) drives large changes in global climate patterns from year to year, yet its sensitivity to continued anthropogenic greenhouse forcing is uncertain. We analyzed fossil coral reconstructions of ENSO spanning the past 7000 years from the Northern Line Islands, located in the center of action for ENSO. The corals document highly variable ENSO activity, with no evidence for a systematic trend in ENSO variance, which is contrary to some models that exhibit a response to insolation forcing over this same period. Twentieth-century ENSO variance is significantly higher than average fossil coral ENSO variance but is not unprecedented. Our results suggest that forced changes in ENSO, whether natural or anthropogenic, may be difficult to detect against a background of large internal variability.

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Oxygen isotope records of stalagmites from China and Oman reveal a weak summer monsoon event, with a double-plunging structure, that started 8.21 ± 0.02 kyr B.P. An identical but antiphased pattern is also evident in two stalagmite records from eastern Brazil, indicating that the South American Summer Monsoon was intensifi ed during the 8.2 kyr B.P. event. These records demonstrate that the event was of global extent and synchronous within dating errors of <50 years. In comparison with recent model simulations, it is plausible that the 8.2 kyr B.P. event can be tied in changes of the Atlantic Meridional Overturning Circulation triggered by a glacial lake draining event. This, in turn, affected North Atlantic climate and latitudinal position of the Intertropical Convergence Zone, resulting in the observed low-latitude monsoonal precipitation patterns. INTRODUCTION A prominent abrupt climate event ca. 8.2 kyr B.P. (the 8.2 kyr B.P. event) is evident in Greenland ice cores and other climate proxy records from across the Northern Hemisphere (Alley et al. , 1997). However, due to a distinct lack of highly resolved and precisely dated records, the timing, structure, and geographical extent of the event are not well documented (Alley and Ágústsdóttir, 2005;Rohling and Pälike, 2005). A key question is whether climatic anomalies ca. 8.2 kyr B.P. are indeed representative of one synchronous event with similar structure, different events, or of one time-transgressive event in different geographical regions (Alley and Ágústsdóttir, 2005). Precisely dated stalagmite records from Asia and Brazil can help to answer this question. In order to accurately characterize the 8.2 kyr B.P. event in Asian Monsoon (AM) and South American Summer Monsoon (SASM) records, we present new and revised sets of precisely dated stalagmite records from China, Oman, and Brazil. Improved 230 Th dating techniques with very small age errors of 15-45 years (2σ) for ca. 8.2 kyr B.P. allow us to: (1) correlate AM records from widely separate locations; (2) test the relationship between the AM and SASM and their correlations to Greenland ice core records on decadal time scales; (3) provide a benchmark for global correlation and age calibration of the event; (4) characterize the common structure of the 8.2 kyr B.P. event; and (5) probe the mechanism underlying the event in comparison with model simulations.