NATURE Vol 445 4 January 2007 LETTERS and famine,consistent with a linkage to reduced rainfall.The Tang 4. Diamond,J.Collapse (Penguin,London,2005). dynasty has been described as a high point in Chinese civilization,a 5. Fagan,B.Floods,Famines and Emperors:El Nino and the Fate of Civilizations (Pimlico London,2000). golden age of literature and art.The power of the dynasty began to 6. Haug,G.H.et al Climate and the collapse of Maya civilization.Science 299 ebb in the eighth century,starting with a defeat by the Arab army in 1731-17352003). AD 751.Rebellions further weakened the Tang empire,and it fully Kumar,K.K.,Rajagopalan,B.Cane,M.A.On the weakening of the relationship collapsed in AD 907 (ref.30). between the Indian monsoon and ENSO.Science 284,2156-2159 (1999) It is intriguing that the rise and collapse of the Classic Maya's Wang,B.The Asian Monsoon (Springer,Berlin,2006). 9. Thompson,L.G.et al.Tropical climate instability:the last glacial cycle from a coincided with the golden age and decline of the Tang dynasty in Qinghai-Tibetan ice core.Science 276,1821-1825 (1997). China.Comparison of the Ti records from Lake Huguang Maar and 10.Sirocko,F,Garbe-Schonberg,D.,Mclntyre,A.Molfino,B.Teleconnections the Cariaco basin reveals similarities,including both a general shift between the subtropical monsoons and high-latitude climates during the last towards drier climate at about AD 750 and a series of three multi-year deglaciation.Science 272,526-529 (1996). 11.Heslop,D.et ol.Sub-millennial scale variations in East Asian monsoon systems rainfall minima within that generally dry period(Fig.3),the last of recorded by dust deposits from the North-Western Chinese loess plateau.Phys which coincides with the final stage of Maya collapse as well as the Chem.Earth24,785-792(1999). end of the Tang dynasty.Given these results,it seems possible that 12. 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X-ray and magnetic measurements.Element scanning was carried out with 26.111-145(1998). a micro X-ray fluorescence spectrometer EAGLE BKA (Rontgenanalytik 15.Ding,Z.,Rutter,N.Han,J.Liu,T.A coupled environmental system formed at Meftechnik GmbH).Isothermal remanent magnetizations(IRM),saturation about 2.5 Ma in East Asia.Palaeogeogr.Palaeoclimatol.Paloeoecol.94,223-242 as well as back field,were imprinted with a 2G Enterprises pulse magnetizer in (1992). 16.Hughen,K.A.,Overpeck,J.T.Peterson,L C.Trumbore,5.Rapid climate magnetic fields of 2T and-0.3 T,respectively.All IRMs were measured on a changes in the tropical Atlantic region during the last deglaciation.Nature 380, Molyneux spinner magnetometer(Minispin).The S-ratios were calculated after 51-54(1996). ref.22.Continuous logging of magnetic susceptibility was performed with a 17. Haug G.H.,Hughen,K.A.,Sigman,D.M.,Peterson,L.C.Rohl,U.Southward Bartington MS2E sensor directly on the surface of split core halves.Magnetic migration of the Intertropical Convergence Zone through the Holocene.Science susceptibility of the discrete samples was measured with a Kappabridge KLY-3S 293,1304-1308(2001). (AGICO). 18.Wang,X.et al.Wet periods in northeastern Brazil over the past 210 kyr linked to S-ratio and TOC.The S-ratio varies between 0 for pure haematite and 1 for pure distant climate anomalies.Nature 432,740-743(2004). magnetite2.A high S-ratio indicates a predominance of oxic sedimentary con- 19. Cane,M.A.The evolution of El Nino,past and future.Earth Planet.Sci.Lett.230, 227-240(2005). ditions and the preservation of magnetite.The strong correlation between high 20.Koutavas,A.Lynch-Stieglitz,J.Marchitto Jr,T.M.Sachs,J.P.EI Nino-like S-ratio and low TOC in our record has two alternative interpretations:(1)the pattern in ice age tropical Pacific sea surface temperature.Science 297,226-230 supply of oxygen to the sediments is high,or(2)the flux oforganic matter to the (2002). lake bottom is low.In the pervasively eutrophic Lake Huguang Maar,large 21.Ivanochko,T.5.et al Va iation in tropical convection as an amplifier of changes in productivity are unlikely and difficult to cause by climate change global climate change at the millennial scale.Eorth Plonet.Sci.Lett.235,302-314 Thus,the measured changes in S-ratio and TOC are most logically interpreted as (2005). the result of wind-driven lake mixing,with more mixing and thus higher S-ratio 22.Bloemendal,J.,King.J.W.,Hall,F.R.Doh,S.J.Rock magnetism of Late Neogene and lower TOC occurring during times of strong winter monsoon winds.This and Pleistocene deep-sea sediments:Relationship to sediment source,diagenetic interpretation is supported by sedimentary manganese and biogenic opal con- processes and sediment lithology.J.Geophys.Res.97,4361-4375(1992) centrations and accumulation rates(see Supplementary Information). 23.Mingram,J.et al.The Huguang maar lake-a high-resolution record of Magnetic susceptibility.The sharp increase in magnetic susceptibility at palaeoenvironmental and palaeoclimatic changes over the last 78,000 years from South China.Quat.Int.122,85-107 (2004). -7.8 kyr ago,which is simultaneous with a saturating increase in S-ratio and a 24.Wang,L.et ol.East Asian monsoon climate during the Late Pleistocene:high- decrease in TOC content,requires that increasing wind mixing caused a thresh- resolution sediment records from the South China Sea.Mar.Geol.156,245-284 old in lake oxygen content to be crossed,such that magnetite is subsequently 1999). preserved in the sediments (Supplementary Fig.4).However,the continued 25.Hastenrath,5.Greischar,L.Circulation mechanisms related to northeast Brazil gradual increase in magnetic susceptibility over the mid-to late Holocene has rainfall anomalies.J.Geophys.Res.98,5093-5102 (1993). two potential explanations.It may result from a continued increase in the annual 26.Wang,L.et al.Holocene variations in Asian monsoon moisture:a bidecadal mean oxygen content of the lake,due to a continued increase in wind mixing.In sediment record from South China Sea.Geophys.Res.Lett.26,2889-2892(1999) this case,the lack ofchange in S-ratio would be due to saturation of this index at a 27.Fleitmann,D.et al.Holocene forcing of the Indian Monsoon recorded in a stalagmite from Southern Oman.Science 300,1737-1739 (2003). value close to 1 (Supplementary Fig.4).Alternatively,the gradual increase in 28. deMenocal,P.B.Cultural responses to climate change during the late Holocene magnetic susceptibility may result from an increase in the aeolian delivery of Science292,667-673(2001). magnetic minerals because of stronger winter winds,as magnetic minerals such 29.Hodell,D.A.Brenner,M.,Curtis,J.H.Guilderson,T.Solar forcing of drought as magnetite are much (roughly two times)denser than most aluminosilicates frequency in the Maya lowlands.Science 292,1367-1370(2001). The gradual decrease in TOC content through the mid-to late Holocene may 30.Blunden,C.Elvin,M.Cultural Atlos of China (Checkmark Books,New York, indicate either an increasing wind-driven ventilation of the lake or progressively 1998). greater dilution by aeolian inputs.In either case-an increase in lake mixing and/ or an increase in aeolian input-the combined data require a Holocene strength- Supplementary Information is linked to the online version of the paper at www.nature.com/nature. ening of the winter monsoon. Acknowledgements We thank M.Cane,R.Seager,P.deMenocal and S.Clemens Received 27 January;accepted 6 November 2006. for discussions,comments and reviews.This work was supported by the Deutsche Forschungsgemeinschaft (DFG).D.M.S.and G.H.H.thank the Humboldt 1.Wang Y.J.et al.A high-resolution absolute-dated Late Pleistocene monsoon Foundation for support.D.M.S.was also supported by BP and Ford Motor Company record from Hulu Cave,China.Science 294,2345-2348 (2001). through the Princeton Carbon Mitigation Initiative. 2.Yuan,D.et ol.Timing,duration,and transitions of the Last Interglacial Asian Monsoon.Science 304,575-578(2004). Author Information Reprints and permissions information is available at 3.Dykoski,C.A.et al.A high-resolution,absolute-dated Holocene and deglacial www.nature.com/reprints.The authors declare no competing financial interests. Asian monsoon record from Dongge Cave,China.Earth Planet.Sci.Lett.233, Correspondence and requests for materials should be addressed to G.H.H. 71-86(2005). (haug@gfz-potsdam.de). 公 2007 Nature Publishing Groupand famine, consistent with a linkage to reduced rainfall. The Tang dynasty has been described as a high point in Chinese civilization30, a golden age of literature and art. The power of the dynasty began to ebb in the eighth century, starting with a defeat by the Arab army in AD 751. Rebellions further weakened the Tang empire, and it fully collapsed in AD 907 (ref. 30). It is intriguing that the rise and collapse of the Classic Maya4,5 coincided with the golden age and decline of the Tang dynasty in China30. Comparison of the Ti records from Lake Huguang Maar and the Cariaco basin reveals similarities, including both a general shift towards drier climate at about AD 750 and a series of three multi-year rainfall minima within that generally dry period (Fig. 3), the last of which coincides with the final stage of Maya collapse as well as the end of the Tang dynasty. Given these results, it seems possible that major circum-Pacific shifts in ITCZ position catalysed simultaneous events in civilizations on opposite sides of the Pacific Ocean. METHODS X-ray and magnetic measurements. Element scanning was carried out with a micro X-ray fluorescence spectrometer EAGLE BKA (Ro¨ntgenanalytik Meßtechnik GmbH). Isothermal remanent magnetizations (IRM), saturation as well as back field, were imprinted with a 2G Enterprises pulse magnetizer in magnetic fields of 2 T and 20.3 T, respectively. All IRMs were measured on a Molyneux spinner magnetometer (Minispin). The S-ratios were calculated after ref. 22. Continuous logging of magnetic susceptibility was performed with a Bartington MS2E sensor directly on the surface of split core halves. Magnetic susceptibility of the discrete samples was measured with a Kappabridge KLY-3S (AGICO). S-ratio and TOC. The S-ratio varies between 0 for pure haematite and 1 for pure magnetite22. A high S-ratio indicates a predominance of oxic sedimentary con￾ditions and the preservation of magnetite22. The strong correlation between high S-ratio and low TOC in our record has two alternative interpretations: (1) the supply of oxygen to the sediments is high, or (2) the flux of organic matter to the lake bottom is low. In the pervasively eutrophic Lake Huguang Maar, large changes in productivity are unlikely and difficult to cause by climate change. Thus, the measured changes in S-ratio and TOC are most logically interpreted as the result of wind-driven lake mixing, with more mixing and thus higher S-ratio and lower TOC occurring during times of strong winter monsoon winds. This interpretation is supported by sedimentary manganese and biogenic opal con￾centrations and accumulation rates (see Supplementary Information). Magnetic susceptibility. The sharp increase in magnetic susceptibility at ,7.8 kyr ago, which is simultaneous with a saturating increase in S-ratio and a decrease in TOC content, requires that increasing wind mixing caused a thresh￾old in lake oxygen content to be crossed, such that magnetite is subsequently preserved in the sediments (Supplementary Fig. 4). However, the continued gradual increase in magnetic susceptibility over the mid- to late Holocene has two potential explanations. It may result from a continued increase in the annual mean oxygen content of the lake, due to a continued increase in wind mixing. In this case, the lack of change in S-ratio would be due to saturation of this index at a value close to 1 (Supplementary Fig. 4). Alternatively, the gradual increase in magnetic susceptibility may result from an increase in the aeolian delivery of magnetic minerals because of stronger winter winds, as magnetic minerals such as magnetite are much (roughly two times) denser than most aluminosilicates. The gradual decrease in TOC content through the mid- to late Holocene may indicate either an increasing wind-driven ventilation of the lake or progressively greater dilution by aeolian inputs. In either case—an increase in lake mixing and/ or an increase in aeolian input—the combined data require a Holocene strength￾ening of the winter monsoon. Received 27 January; accepted 6 November 2006. 1. Wang, Y. J. et al. A high-resolution absolute-dated Late Pleistocene monsoon record from Hulu Cave, China. Science 294, 2345–2348 (2001). 2. Yuan, D. et al. Timing, duration, and transitions of the Last Interglacial Asian Monsoon. Science 304, 575–578 (2004). 3. Dykoski, C. A. et al. A high-resolution, absolute-dated Holocene and deglacial Asian monsoon record from Dongge Cave, China. Earth Planet. Sci. Lett. 233, 71–86 (2005). 4. Diamond, J. Collapse (Penguin, London, 2005). 5. Fagan, B. Floods, Famines and Emperors: El Nino and the Fate of Civilizations(Pimlico, London, 2000). 6. Haug, G. H. et al. Climate and the collapse of Maya civilization. Science 299, 1731–1735 (2003). 7. Kumar, K. K., Rajagopalan, B. & Cane, M. A. On the weakening of the relationship between the Indian monsoon and ENSO. Science 284, 2156–2159 (1999). 8. Wang, B. The Asian Monsoon (Springer, Berlin, 2006). 9. Thompson, L. G. et al. Tropical climate instability: the last glacial cycle from a Qinghai-Tibetan ice core. Science 276, 1821–1825 (1997). 10. Sirocko, F., Garbe-Schonberg, D., McIntyre, A. & Molfino, B. Teleconnections between the subtropical monsoons and high-latitude climates during the last deglaciation. Science 272, 526–529 (1996). 11. Heslop, D. et al. Sub-millennial scale variations in East Asian monsoon systems recorded by dust deposits from the North-Western Chinese loess plateau. Phys. Chem. Earth 24, 785–792 (1999). 12. Porter, S. C. & An, Z. Correlation between climate events in the North Atlantic and China during the last glaciation. Nature 375, 305–308 (1995). 13. Oppo, D. W. & Sun, Y. Amplitude and timing of sea-surface temperature change in the northern South China Sea: Dynamic link to the East Asian monsoon. Geology 33, 785–788 (2005). 14. Liu, T. & Ding, Z. Chinese loess and the paleomonsoon. Annu. Rev. Earth Planet. Sci. 26, 111–145 (1998). 15. Ding, Z., Rutter, N., Han, J. & Liu, T. A coupled environmental system formed at about 2.5 Ma in East Asia. Palaeogeogr. Palaeoclimatol. Palaeoecol. 94, 223–242 (1992). 16. Hughen, K. A., Overpeck, J. T., Peterson, L. 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Rock magnetism of Late Neogene and Pleistocene deep-sea sediments: Relationship to sediment source, diagenetic processes and sediment lithology. J. Geophys. Res. 97, 4361–4375 (1992). 23. Mingram, J. et al. The Huguang maar lake – a high-resolution record of palaeoenvironmental and palaeoclimatic changes over the last 78,000 years from South China. Quat. Int. 122, 85–107 (2004). 24. Wang, L. et al. East Asian monsoon climate during the Late Pleistocene: high￾resolution sediment records from the South China Sea. Mar. Geol. 156, 245–284 (1999). 25. Hastenrath, S. & Greischar, L. Circulation mechanisms related to northeast Brazil rainfall anomalies. J. Geophys. Res. 98, 5093–5102 (1993). 26. Wang, L. et al. Holocene variations in Asian monsoon moisture: a bidecadal sediment record from South China Sea. Geophys. Res. Lett. 26, 2889–2892 (1999). 27. Fleitmann, D. et al. Holocene forcing of the Indian Monsoon recorded in a stalagmite from Southern Oman. Science 300, 1737–1739 (2003). 28. deMenocal, P. B. Cultural responses to climate change during the late Holocene. Science 292, 667–673 (2001). 29. Hodell, D. A., Brenner, M., Curtis, J. H. & Guilderson, T. Solar forcing of drought frequency in the Maya lowlands. Science 292, 1367–1370 (2001). 30. Blunden, C. & Elvin, M. Cultural Atlas of China (Checkmark Books, New York, 1998). Supplementary Information is linked to the online version of the paper at www.nature.com/nature. Acknowledgements We thank M. Cane, R. Seager, P. deMenocal and S. Clemens for discussions, comments and reviews. This work was supported by the Deutsche Forschungsgemeinschaft (DFG). D.M.S. and G.H.H. thank the Humboldt Foundation for support. D.M.S. was also supported by BP and Ford Motor Company through the Princeton Carbon Mitigation Initiative. Author Information Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests. Correspondence and requests for materials should be addressed to G.H.H. (haug@gfz-potsdam.de). NATURE| Vol 445| 4 January 2007 LETTERS 77 ©2007 NaturePublishingGroup