Synchronous timing of abrupt climate changes during the last glacial period.

Abrupt climate changes during the last glacial period have been detected in a global array of palaeoclimate records, but our understanding of their absolute timing and regional synchrony is incomplete. Our compilation of 63 published, independently dated speleothem records shows that abrupt warmings in Greenland were associated with synchronous climate changes across the Asian Monsoon, South American Monsoon, and European-Mediterranean regions that occurred within decades. Together with the demonstration of bipolar synchrony in atmospheric response, this provides independent evidence of synchronous high-latitude-to-tropical coupling of climate changes during these abrupt warmings. Our results provide a globally coherent framework with which to validate model simulations of abrupt climate change and to constrain ice-core chronologies

Synchronous timing of abrupt climate changes during the last glacial period

Many geographically dispersed records from across the globe reveal the occurrence of abrupt climate changes, called interstadial events, during the last glacial period. These events appear to have happened at the same time, but the difficulty of determining absolute dates in many of the records have made that proposition difficult to prove. Corrick et al. present results from 63 precisely dated speleothems that confirm the synchrony of those interstadial events. Their results also provide a tool with which to validate model simulations of abrupt climate change and calibrate other time series such as ice-core chronologies.Science, this issue p. 963Abrupt climate changes during the last glacial period have been detected in a global array of palaeoclimate records, but our understanding of their absolute timing and regional synchrony is incomplete. Our compilation of 63 published, independently dated speleothem records shows that abrupt warmings in Greenland were associated with synchronous climate changes across the Asian Monsoon, South American Monsoon, and European-Mediterranean regions that occurred within decades. Together with the demonstration of bipolar synchrony in atmospheric response, this provides independent evidence of synchronous high-latitude–to-tropical coupling of climate changes during these abrupt warmings. Our results provide a globally coherent framework with which to validate model simulations of abrupt climate change and to constrain ice-core chronologies

Magnesium in subaqueous speleothems as a potential palaeotemperature proxy

Few palaeoclimate archives beyond the polar regions preserve continuous and datable palaeotemperature proxy time series over multiple glacial-interglacial cycles. This hampers efforts to develop a more coherent picture of global patterns of past temperatures. Here we show that Mg concentrations in a subaqueous speleothem from an Italian cave track regional sea-surface temperatures over the last 350,000 years. The Mg shows higher values during warm climate intervals and converse patterns during cold climate stages. In contrast to previous studies, this implicates temperature, not rainfall, as the principal driver of Mg variability. The depositional setting of the speleothem gives rise to Mg partition coefficients that are more temperature dependent than other calcites, enabling the effect of temperature change on Mg partitioning to greatly exceed the effects of changes in source-water Mg/Ca. Subaqueous speleothems from similar deep-cave environments should be capable of providing palaeotemperature information over multiple glacial-interglacial cycles

Millennial-scale climate events in an Italian speleothem: a pilot study covering the last glacial period

Millennial-scale climate events are the best example of naturally occurring rapid climate change. However, the absolute timing and underlying cause of these events remains unknown, largely due to the absence of long continuous records of the events that are anchored in radiometric time. Speleothems (cave deposits such as stalagmites) can preserve long, continuous and precisely dated records of millennial-scale climate events, thus providing vital information on their timing and underlying cause. A subaqueous speleothem from Corchia Cave, NW Italy, contains a palaeoclimate record spanning the last 1 million years, presenting an unprecedented opportunity to investigate the long-term pattern of millennial-scale climate events. The pilot study presented here tests the potential of this speleothem to record millennial-scale climate events by focusing on the last glacial period (120-12 ka), a period already well captured in Greenland ice cores (the current reference record of the events). Due to its slow growth rate, microanalytical techniques were applied to the speleothem to measure three potential climate proxies: Mg (a proxy for temperature), Zn (a proxy for cold climate intervals) and 5180 (a proxy for rainfall amount). Uranium-thorium (U-Th) dating was undertaken to provide the temporal framework. Mg and Zn provide an impressive record of fluctuations consistent with millennial time scales, whilst the 8180 analysis is limited by the resolution and precision of the technique applied. Unexpectedly, the U-Th results reveal an age offset, whereby the timing of high-amplitude regional climate events is at least 2 kyr too old. This age offset, possibly due to a process known as `thorium scavenging', casts serious doubt over the integrity of the chronology, precluding any robust comparison with the Greenland ice-core record. To partly overcome the age offset issue, a first-order correction was performed by tying the speleothem series to well-constrained Corchia Cave stalagmite records. This correction is only possible over a short interval (100-60 ka), which contains few millennial-scale climate events. However, based on this correction, fluctuations in Zn and Mg are broadly in alignment with the higher-magnitude events recorded in Greenland ice, suggesting that the speleothem does record evidence of millennial-scale climate events, and, with further analysis, could yield a 1 Myr record of such events. Meanwhile, the dating problem could potentially resolve a long-standing debate over the chronology of a high-profile palaeoclimate record published in the 1980s and 1990s from Devils Hole (USA), and has important implications for future studies focusing on subaqueous speleothems

Speleothem records of millennial scale climate events during the last glacial period: implications for ice core chronologies

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Speleothem-based chronologies for Greenland ice cores

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A precise chronology of millennial-scale climate events from French speleothems

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A global comparison of the timing of millennial-scale climate events from published speleothem records

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Abrupt climate changes during the early Last Glacial period recorded in French speleothems

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Widespread evidence for the synchronous timing of millennial-scale climate events

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