Record of Winter Monsoon Strength Arising From: G

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Record of winter monsoon strength Arising from: G. Yancheva et al. Nature 455, 74–77 (2007).

The Asian summer monsoon has been precisely reconstructed from It would also account for some puzzles arising from the connection the high-resolution record from the speleothem1, but reconstruction between Ti content and the Asian winter monsoon. For example, of the Asian winter monsoon is less satisfactory. Yancheva et al.2 although the Ti content indicates a southward movement of the provide such a reconstruction for the last 16,000 years from the tita- intertropical convergence zone 7.8 kyr ago2, some places further nium (Ti) content of the sediments of Lake Huguang Maar in coastal north experienced a stronger summer monsoon until about 6 kyr South China. However, we argue that the Ti is likely to have come ago14,15; the Ti content during the Holocene is comparable with those mainly from the catchment and so the Ti content may instead be during the Younger Dryas and the pre-Bølling–Allerød periods2, but related to the hydrology of the lake. other records indicate that the summer monsoon was much stronger Considering the small catchment and densely vegetated inner and that the winter monsoon was much weaker during the Holocene slope of the lake, Yancheva et al.2 overlook the Ti from the catchment than during the two cold, dry periods15,16. through runoff. However, weathering and erosion in coastal South The correspondence between the higher Ti content and occur- China are intensive, owing to high temperatures and heavy precip- remce of coarser sediments during the Younger Dryas and the pre- itation. The steep slopes surrounding the lake3 would promote sur- Bølling–Allerød periods2,4 indicates a connection between the Ti face erosion further. Sandy sediments in the lake4 are strong evidence content and the hydrology of the lake. The higher Ti content during for significant terrigenous input through runoff. This is strengthened the period 5.2–7.8 kyr ago2 may have been caused by a similar mech- by records from Tianyang Maar in the Leizhou Peninsula5 and anism because precipitation may have been lower for this period3. Shuangchi Maar in the north of Hainan6, which indicate that terri- Precipitation in coastal South China during 7.2–2.7 kyr ago may also genous input through runoff may be common for Maars in coastal have been reduced in Shuangchi Maar6. If Ti was transported into the South China. The basalts and laterite in the Leizhou peninsula, which lake mainly in particle and colloidal phases, increased input through are dominant in the catchment, have a high Ti content7 (Table 1) and runoff and reduced water depth could have contributed to the higher so should be important sources of Ti for the lake. Ti content recorded in these cores2. More importantly, the flux of the lithogenic materials to the lake, Our alternative interpretation is therefore that the Ti content may 5–10 and 10–20 mg cm22 yr21 during the Holocene and glacial have been controlled by the hydrology of the lake, rather than by the times, respectively2, is too high to be explained by a wind-blown Asian winter monsoon. Whether, and how, this mechanism could mechanism. Although it is comparable with an estimated modern influence proxies such as total organic carbon and magnetic pro- dust flux of 4.6 mg cm22 yr21 in coastal South China2, the dust flux perties, however, needs further investigation. was probably overestimated, given the atmospheric dust concentra- Houyun Zhou1,2, Huazheng Guan1,3 & Baoquan Chi1,3 tion in coastal South China8 and its settling velocity9. In addition, 1Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, modern observation indicates that mineral dust flux on the Loess Guangzhou 510640, China. 22 21 plateau ranges between 15 and 36 mg cm yr at sites close to dust 2The Earth Dynamic System Research Center, National Cheng-Kung 2 2 sources and between 9 and 10 mg cm 2 yr 1 at other sites, but only University, Tainan 701, Taiwan. about 25% of the particles are smaller than 6 mm (ref. 10). Particles e-mail: [email protected] larger than 6 mm generally have short atmospheric lifetimes owing to 3The Graduate School, Chinese Academy of Sciences, Beijing 100039, gravitational settling11. Lake Huguang Maar is about 1,500 km south China. of the Loess plateau and is not on a main dust trajectory. It should Received 25 January; accepted 20 September 2007. have a dust deposition rate much smaller than 2.5 mg cm22 yr21. , 1. Wang, Y.-J. et al. A high-resolution absolute-dated late Pleistocene monsoon record This is consistent with model-derived deposition rates of 0.2 to from Hulu Cave, China. Science 294, 2345–2348 (2001). 22 21 11,12 0.5 mg cm yr at this site . This evidence disproves wind- 2. Yancheva, G. et al. Influence of the intertropical convergence zone on the East Asian blown dust from remote North China as the main source of Ti to monsoon. Nature 455, 74–77 (2007). Lake Huguang Maar. 3. Mingram, J. et al. The Huguang maar lake—a high-resolution record of palaeoenvironmental and palaeoclimatic changes over the last 78,000 years from The Ti content of local basalts and laterite is apparently higher than South China. Quat. Int. 122, 85–107 (2004). in the loess deposit in the Loess plateau (Table 1)7,13. A source of Ti 4. Wang, W.-Y. et al. The two-step monsoon changes of the last deglaciation recorded from the catchment is therefore more reasonable. This explanation is in tropical Maar Lake Huguangyan, southern China. Chin. Sci. Bull. 45, 1529–1532 (2000). supported by the correspondence of high Ti content with the occur- 5. Zheng, Z. & Lei, Z.-Q. A 400,000 year record of vegetational and climatic changes rence of sandy sediments during two cold, dry phases, the Younger from a volcanic basin, Leizhou Peninsula, southern China. Palaeogeogr. Palaeoclimatol. Dryas episode and the period before the Bølling–Allerød warming2,4. Palaeoecol. 145, 339–362 (1999). 6. Zheng, Z. et al. High-resolution records of Holocene from the Shuangchi Maar Lake in Hainan Island. Chin. Sci. Bull. 48, 497–502 (2003). 7. Xu, Y.-F., Zhu, Z.-Y., Wen, G.-G., Liang, J.-P. & Luo, S.-W. Geochemistry and soil- Table 1 | Ti content in basalt and laterite and in loess-palaeosol forming environment of the red soil section in the southern Leizhou Peninsula, Guangdong Province. Geochimica 29, 402–408 (2000). Laterite range (%) Laterite average (%) Basalt (%) 8. Cao, J.-J. et al. Characterization of dust storms to Hong Kong in April 1998. Water Air Site 91.67–1.76 1.71 1.12 Soil Pollut. Focus 3, 213–229 (2003). Site 10 1.53–1.61 1.57 1.05 9. Reid, J. S. et al. Analysis of measurements of Saharan dust by airborne and Site 11 1.24–1.57 1.47 ground-based remote sensing methods during the Puerto Rico Dust Site 12 0.93–1.13 1.03 0.88 Experiment (PRIDE). J. Geophys. Res. 108 (D19), 8586, doi:10.1029/2002JD002493 Site 13 1.16–1.51 1.26 (2003). 10. Sun, D.-H., Chen, F.-H., Bloemendal, J. & Su, R.-X. Seasonal variability of modern dust Range (%) Average (%) over the Loess Plateau of China. J. Geophys. Res. 108 (D21), 4665, doi:10.1029/ 2003JD003382 (2003). 0 43 0 53 0 48 Loess . – . . 11. Ginoux, P. et al. Sources and distributions of dust aerosols simulated 0 42 0 51 0 44 Palaeosol . – . . with the GOCART model. J. Geophys. Res. 106 (D17), 20255–20273

The Ti contents are calculated according to the TiO2 contents in the basalt and laterite on the (2001). Leizhou Peninsula, coastal South China7, and in the loess-palaeosol deposition at Luochuan, 12. Mahowald, N. et al. Dust sources and deposition during the last glacial North China13. maximum and current climate: A comparison of model results with paleodata E10 © 2007 Nature Publishing Group NATURE | Vol 450 | 15 November 2007 BRIEF COMMUNICATIONS ARISING

from ice cores and marine sediments. J. Geophys. Res. 104 (D13), 15895–15916 15. Dykoski, C. A. et al. A high-resolution, absolute-dated Holocene and deglacial (1999). Asian monsoon record from Dongge Cave, China. Earth Planet. Sci. Lett. 233, 71–86 13. Gallet, S. & Jahn, B.-M. Geochemical characterization of the Luochuan (2005). loess-paleosol sequence, China, and paleoclimatic implications. Chem. Geol. 133, 16. Ren, J.-Z., Ding, Z.-L., Liu, D.-S., Sun, J.-M. & Zhou, X.-Q. Climatic changes on 67–88 (1996). millennial time scales - Evidence from a high-resolution loess record. Sci. Chin. Ser. D 14. Shao, X.-H. et al. Long-term trend and abrupt events of the Holocene Asian monsoon 39, 449–459 (1996). inferred from a stalagmite d18O record from Shennongjia in Central China. Chin. Sci. Bull. 51, 221–228 (2006). doi:10.1038/nature06408

Yancheva et al. reply Replying to: H. Zhou et al. Nature 450, doi: 10.1038/nature06408 (2007).

Zhou et al.1 raise the possibility that the titanium (Ti) record at Lake minerogenic particles, as well as more prominent siderite enrich- Huguang Maar is controlled by local erosion and runoff to the lake, ments, but without any major changes, even when including the or through hydrological changes in the lake such as level fluctuations, glacial termination in the analysis. There are no sandy sediments in rather than by changes in the inputs of airborne material2. The the entire Lake Huguang Maar section: the interpretation of Wang authors come to this conclusion by considering the Ti record in et al.3 is incorrect. isolation. They ignore the redox-sensitive parameters of the S-ratio, One aspect of the comment is valid and important. Given the total organic-matter content, the Mn/Fe ratio, and magnetic current understanding of large scale dust distributions4, regional dust susceptibility records. We believe that their case against our inter- deposition seems to be significantly lower than siliciclastic flux rates pretation of the Ti record is weak, and that their interpretation can be in Lake Huguang Maar sediments. This discrepancy may be ruled out if the other measurements are taken into account2. explained by sediment focusing in similar lake environments, which Zhou et al.1 argue that the high Ti content during times of weak has been measured as up to fivefold5. summer monsoon, such as the Younger Dryas cold period, may be Gergana Yancheva1, Norbert R. Nowaczyk1, Jens Mingram1, the result of runoff from the catchment. On the basis of runoff alone, Peter Dulski1, Georg Schettler1,Jo¨rg F. W. Negendank1, Jiaqi Liu2, one would expect the opposite signal, with lower Ti values in times of Daniel M. Sigman3, Larry C. Peterson4 & Gerald H. Haug5 reduced rainfall and runoff, and not higher values. The authors argue 1GeoForschungsZentrum Potsdam, Telegrafenberg, D-14473 Potsdam, that lake-level changes may explain the higher Ti values during drier Germany. climates. However, major lake-level changes can be excluded in the 2Institute of Geology and Geophysics, Chinese Academy of Sciences, PO case of Lake Huguang Maar for the study interval. Box 9825, Beijing 100029, China. The lake is today about 21 m deep, and it is characterized by a 3Department of Geosciences, Princeton University, Princeton, New strong thermocline at about 10 m water depth. Below the thermo- Jersey 08544, USA. cline, the lake is suboxic. Our transect of cores spans the depth 4Rosenstiel School of Marine and Atmospheric Science, University of range between 10 and 20 m water depth2. For all cores at all depths, Miami, Miami, Florida 33149, USA. we observe a continuous sediment sequence during the past 5Geological Institute, Department of Earth Sciences, ETH Zu¨rich, 20,000 years, as indicated by parallel high-resolution magnetic sus- CH-8092 Zu¨rich, Switzerland. ceptibility records in all cores. This argues that the lake level has not e-mail: [email protected] fluctuated by as much as 10 m, because this would have exposed the shallowest core to the atmosphere. Moreover, suboxic to anoxic con- 1. Zhou, H., Guan, H. & Chi, B. Records of winter monsoon strength. Nature 450, doi: ditions are recorded in our magnetic susceptibility and S-ratio 10.1038/nature06408 (2007). 2. Yancheva, G. et al. Influence of the intertropical convergence zone on the East Asian records throughout the record at all cores and at all water depths. monsoon. Nature 455, 74–77 (2007). Even a modest drop in lake level would have exposed the shallowest 3. Wang, W.-Y. et al. The two-step monsoon changes of the last deglaciation recorded core (at 10 m water depth) to the oxic lake conditions in the epilim- in tropical Maar Lake Huguangyan, southern China. Chin. Sci. Bull. 45, 1529–1532 (2000). nion above the thermocline, which would have markedly altered the 4. Mahowald, N. et al. Dust sources and deposition during the last glacial maximum and redox sensitive signals of this core. current climate: A comparison of model and results with paleodata from ice cores and Zhou et al.1 argue that the correspondence of higher Ti with marine sediments. J. Geophys. Res. 104 (D13), 15895–15916 (1999). 5. Schettler, G., Liu, Q., Mingram, J. & Negendank, J. F. W. Palaeovariations in the East- coarser sediments during the Younger Dryas and the pre-Bølling/ Asian monsoon regime geochemically recorded in varved sediments of lake Allerød periods indicates a connection between Ti content and the Sihailongwan (northeast China, Jilin province). Part 1: Hydrological conditions and hydrology of the lake. However, microscopic quantification of dust flux. J. Paleolimnol. 35, 239–270 (2006). minerogenic matter of local origin shows only scattered silt-sized doi:10.1038/nature06409