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Mineral magnetic record of the Miocene-Pliocene climate transition on the Chinese Loess Plateau, North China

Published online by Cambridge University Press:  05 October 2017

Hong Ao*
Affiliation:
State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA
Mark J. Dekkers
Affiliation:
Paleomagnetic Laboratory ‘Fort Hoofddijk’, Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Budapestlaan 17, 3584 CD Utrecht, The Netherlands
Andrew P. Roberts
Affiliation:
Research School of Earth Sciences, The Australian National University, Canberra 2601, Australia
Eelco J. Rohling
Affiliation:
Research School of Earth Sciences, The Australian National University, Canberra 2601, Australia Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton SO14 3ZH, United Kingdom
Zhisheng An
Affiliation:
State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
Xiaodong Liu
Affiliation:
State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
Zhaoxia Jiang
Affiliation:
State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Xiaoke Qiang
Affiliation:
State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
Yong Xu
Affiliation:
Xi’an Center of Geological Survey, China Geological Survey, Xi’an 710054, China
Hong Chang
Affiliation:
State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
*
*Corresponding author at: State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China. Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA. E-mail address: aohong@ieecas.cn.

Abstract

Pre-Quaternary terrestrial climate variability is less well understood than that during the Quaternary. The continuous eolian Red Clay sequence underlying the well-known Quaternary loess-paleosol sequence on the Chinese Loess Plateau (CLP) provides an opportunity to study pre-Quaternary terrestrial climate variability in East Asia. Here, we present new mineral magnetic records for a recently found Red Clay succession from Shilou area on the eastern CLP, and demonstrate a marked East Asian climate shift across the Miocene-Pliocene boundary (MPB). Pedogenic fine-grained magnetite populations, ranging from superparamagnetic (SP)/single domain (SD) up to small pseudo-single domain (PSD) sizes (i.e., from <30 nm up to ~1000 nm), dominate the magnetic properties. Importantly, our mineral magnetic results indicate that both pedogenic formation of SP grains and transformation of SP grains to SD and small PSD grains accelerated across the MPB in the Shilou Red Clay, which are indicative of enhanced pedogenesis. We relate this enhanced pedogenesis to increased soil moisture availability on the CLP, associated with stronger Asian Summer Monsoon precipitation during an overall period of global cooling. Our study thus provides new insights into the Miocene-Pliocene climate transition in East Asia.

Type
Research Article
Copyright
Copyright © University of Washington. Published by Cambridge University Press, 2017 

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References

An, Z.S., 2014. Late Cenozoic Climate Change in Asia: Loess, Monsoon and Monsoon-Arid Environment Evolution. Springer, Amsterdam.Google Scholar
An, Z.S., Huang, Y.S., Liu, W.G., Guo, Z.T., Clemens, S., Li, L., Prell, W, et al 2005. Multiple expansions of C4 plant biomass in East Asia since 7 Ma coupled with strengthened monsoon circulation. Geology 33, 705708.Google Scholar
An, Z.S., Kukla, G.J., Porter, S.C., Xiao, J.L., 1991. Magnetic susceptibility evidence of monsoon variation on the loess plateau of central China during the last 130,000 Years. Quaternary Research 36, 2936.Google Scholar
An, Z.S., Kutzbach, J.E., Prell, W.L., Porter, S.C., 2001. Evolution of Asian monsoons and phased uplift of the Himalaya-Tibetan plateau since Late Miocene times. Nature 411, 6266.Google Scholar
An, Z.S., Wu, G.X., Li, J.P., Sun, Y.B., Liu, Y.M., Zhou, W.J., Cai, Y.J., et al 2015. Global monsoon dynamics and climate change. Annual Review of Earth and Planetary Sciences 43, 2977.Google Scholar
Anwar, T., Kravchinsky, V.A., Zhang, R., 2015. Magneto- and cyclostratigraphy in the Red Clay sequence: new age model and paleoclimatic implication for the eastern Chinese Loess Plateau. Journal of Geophysical Research 120, 67586770.CrossRefGoogle Scholar
Ao, H., An, Z.S., Dekkers, M.J., Wei, Q., Pei, S.W., Zhao, H., Zhao, H.L., Xiao, G.Q., Qiang, X.K., Wu, D.C., Chang, H., 2012. High-resolution record of geomagnetic excursions in the Matuyama chron constrains the ages of the Feiliang and Lanpo Paleolithic sites in the Nihewan Basin, North China. Geochemistry Geophysics Geosystems 13, Q08017. http://dx.doi.org/08010.01029/02012GC004095.Google Scholar
Ao, H., Dekkers, M.J., Deng, C.L., Zhu, R.X., 2009. Paleoclimatic significance of the Xiantai fluvio-lacustrine sequence in the Nihewan Basin (North China), based on rock magnetic properties and clay mineralogy. Geophysical Journal International 177, 913924.Google Scholar
Ao, H., Roberts, A.P., Dekkers, M.J., Liu, X.D., Rohling, E.J., Shi, Z.G., An, Z.S., 2016. Late Miocene-Pliocene Asian monsoon intensification linked to Antarctic ice-sheet growth. Earth and Planetary Science Letters 444, 7587.Google Scholar
Bloemendal, J., Liu, X.M., 2005. Rock magnetism and geochemistry of two Plio-Pleistocene Chinese loess-palaeosol sequences–implications for quantitative palaeoprecipitation reconstruction. Palaeogeography, Palaeoclimatology, Palaeoecology 226, 149166.Google Scholar
Clift, P.D., 2006. Controls on the erosion of Cenozoic Asia and the flux of clastic sediment to the ocean. Earth and Planetary Science Letters 241, 571580.Google Scholar
Clift, P.D., Blusztajn, J., 2005. Reorganization of the western Himalayan river system after five million years ago. Nature 438, 10011003.Google Scholar
Clift, P.D., Hodges, K.V., Heslop, D., Hannigan, R., Van Long, H., Calves, G., 2008. Correlation of Himalayan exhumation rates and Asian monsoon intensity. Nature Geoscience 1, 875880.Google Scholar
Clift, P.D., Wan, S.M., Blusztajn, J., 2014. Reconstructing chemical weathering, physical erosion and monsoon intensity since 25 Ma in the northern South China Sea: a review of competing proxies. Earth-Science Reviews 130, 86102.CrossRefGoogle Scholar
Deng, C.L., 2008. Paleomagnetic and mineral magnetic investigation of the Baicaoyuan loess-paleosol sequence of the western Chinese Loess Plateau over the last glacial-interglacial cycle and its geological implications. Geochemistry, Geophysics, Geosystems 9, Q04034. http:/dx.doi.org/04010.01029/02007GC001928.Google Scholar
Deng, C.L., Shaw, J., Liu, Q.S., Pan, Y.X., Zhu, R.X., 2006. Mineral magnetic variation of the Jingbian loess/paleosol sequence in the northern Loess Plateau of China: implications for Quaternary development of Asian aridification and cooling. Earth and Planetary Science Letters 241, 248259.Google Scholar
Deng, C.L., Vidic, N.J., Verosub, K.L., Singer, M.J., Liu, Q.S., Shaw, J., Zhu, R.X., 2005. Mineral magnetic variation of the Jiaodao Chinese loess/paleosol sequence and its bearing on long-term climatic variability. Journal of Geophysical Research 110, B03103. http://dx.doi.org/03110.01029/02004JB003451.Google Scholar
Ding, Z.L., Xiong, S.F., Sun, J.M., Yang, S.L., Gu, Z.Y., Liu, T.S., 1999. Pedostratigraphy and paleomagnetism of a ~7.0 Ma eolian loess-red clay sequence at Lingtai, Loess Plateau, north-central China and the implications for paleomonsoon evolution. Palaeogeography, Palaeoclimatology, Palaeoecology 152, 4966.Google Scholar
Dunlop, D.J., Özdemir, Ö., 1997. Rock Magnetism: Fundamentals and Frontiers. Cambridge University Press, Cambridge.CrossRefGoogle Scholar
Egli, R., Chen, A.P., Winklhofer, M., Kodama, K.P., Horng, C.S., 2010. Detection of noninteracting single domain particles using first-order reversal curve diagrams. Geochemistry Geophysics Geosystems 11, Q01Z11. http://dx.doi.org/10.1029/2009GC002916.Google Scholar
Eronen, J.T., Ataabadi, M.M., Micheels, A., Karme, A., Bernor, R.L., Fortelius, M., 2009. Distribution history and climatic controls of the Late Miocene Pikermian chronofauna. Proceedings of the National Academy of Sciences of the United States of America 106, 1186711871.CrossRefGoogle ScholarPubMed
Evans, M.E., Heller, F., 1994. Magnetic enhancement and palaeoclimate: study of a loess/palaeosol couplet across the Loess Plateau of China. Geophysical Journal International 117, 257264.CrossRefGoogle Scholar
Evans, M.E., Heller, F., 2001. Magnetism of loess/palaeosol sequences: recent developments. Earth-Science Reviews 54, 129144.Google Scholar
Evans, M.E., Heller, F., 2003. Environmental Magnetism: Principles and Applications of Enviromagnetics. Academic Press, New York.Google Scholar
Filippelli, G.M., 1997. Intensification of the Asian monsoon and a chemical weathering event in the late Miocene-early Pliocene: implications for late Neogene climate change. Geology 25, 2730.Google Scholar
Florindo, F., Zhu, R.X., Guo, B., Yue, L.P., Pan, Y.X., Speranza, F., 1999. Magnetic proxy climate results from the Duanjiapo loess section, southernmost extremity of the Chinese loess plateau. Journal of Geophysical Research 104, 645659.Google Scholar
Geiss, C.E., Zanner, C.W., 2006. How abundant is pedogenic magnetite? Abundance and grain size estimates for loessic soils based on rock magnetic analyses. Journal of Geophysical Research 111, B12S21. http://dx.doi.org/10.1029/2006JB004564.Google Scholar
Heller, F., Evans, M.E., 1995. Loess magnetism. Reviews of Geophysics 33, 211240.Google Scholar
Hilgen, F.J., Lourens, L.J., van Dam, J.A., 2012. The Neogene Period. In: Gradstein, F.M., Ogg, J.G., Schmitz, M., Ogg, G. (Eds.), The Geologic Time Scale. Elsevier, Amsterdam, pp. 923978.Google Scholar
Hu, P.X., Liu, Q.S., Torrent, J., Barrón, V., Jin, C.S., 2013. Characterizing and quantifying iron oxides in Chinese loess/paleosols: implications for pedogenesis. Earth and Planetary Science Letters 369, 271283.Google Scholar
Huang, Y.S., Clemens, S.C., Liu, W.G., Wang, Y., Prell, W.L., 2007. Large-scale hydrological change drove the late Miocene C4 plant expansion in the Himalayan foreland and Arabian Peninsula. Geology 35, 531534.Google Scholar
Kim, D., Lee, Y.I., Hyeong, K., Yoo, C.M., 2016. Terrestrial biome distribution in the Late Neogene inferred from a black carbon record in the northeastern equatorial Pacific. Scientific Reports 6, 32847. http://dx.doi.org/32810.31038/srep32847.Google Scholar
Kukla, G., Heller, F., Ming, L.X., Chun, X.T., Sheng, L.T., Sheng, A.Z., 1988. Pleistocene climates in China dated by magnetic susceptibility. Geology 16, 811814.Google Scholar
LaRiviere, J.P., Ravelo, A.C., Crimmins, A., Dekens, P.S., Ford, H.L., Lyle, M., Wara, M.W., 2012. Late Miocene decoupling of oceanic warmth and atmospheric carbon dioxide forcing. Nature 486, 97100.Google Scholar
Li, F.J., Rousseau, D.D., Wu, N.Q., Hao, Q.Z., Pei, Y.P., 2008. Late Neogene evolution of the East Asian monsoon revealed by terrestrial mollusk record in Western Chinese Loess Plateau: from winter to summer dominated sub-regime. Earth and Planetary Science Letters 274, 439447.Google Scholar
Li, F.J., Wu, N.Q., Rousseau, D.D., Dong, Y.J., Zhang, D., Pei, Y.P., 2014. Late Miocene-Pliocene paleoclimatic evolution documented by terrestrial mollusk populations in the western Chinese Loess Plateau. Plos One 9, e95754. http://dx.doi.org/10.1371/journal.pone.0095754.Google Scholar
Liu, Q.S., Deng, C.L., Torrent, J., Zhu, R.X., 2007. Review of recent developments in mineral magnetism of the Chinese loess. Quaternary Science Reviews 26, 368385.Google Scholar
Liu, Q.S., Deng, C.L., Yu, Y.J., Torrent, J., Jackson, M.J., Banerjee, S.K., Zhu, R.X., 2005. Temperature dependence of magnetic susceptibility in an argon environment: implications for pedogenesis of Chinese loess/palaeosols. Geophysical Journal International 161, 102112.Google Scholar
Liu, Q.S., Jackson, M.J., Banerjee, S.K., Maher, B.A., Deng, C.L., Pan, Y.X., Zhu, R.X., 2004. Mechanism of the magnetic susceptibility enhancements of the Chinese loess. Journal of Geophysical Research 109, B12107. http://dx.doi.org/12110.11029/12004JB003249.Google Scholar
Liu, Q.S., Jin, C.S., Hu, P.X., Jiang, Z.X., Ge, K.P., Roberts, A.P., 2015. Magnetostratigraphy of Chinese loess-paleosol sequences. Earth-Science Reviews 150, 139167.Google Scholar
Liu, Q.S., Roberts, A.P., Larrasoaña, J.C., Banerjee, S.K., Guyodo, Y., Tauxe, L., Oldfield, F., 2012. Environmental magnetism: principles and applications. Reviews of Geophysics 50, RG4002. http://dx.doi.org/4010.1029/2012RG000393.Google Scholar
Liu, Q.S., Torrent, J., Morrás, H., Ao, H., Jiang, Z.X., Su, Y.L., 2010. Superparamagnetism of two modern soils from the northeastern Pampean region, Argentina and its paleoclimatic indications. Geophysical Journal International 183, 695705.Google Scholar
Liu, T.S., 1985. Loess and the Environment. China Ocean Press, Beijing.Google Scholar
Liu, X.M., Rolph, T., An, Z.S., Hesse, P., 2003. Paleoclimatic significance of magnetic properties on the Red Clay underlying the loess and paleosols in China. Palaeogeography, Palaeoclimatology, Palaeoecology 199, 153166.CrossRefGoogle Scholar
Liu, Z.F., Liu, Q.S., Torrent, J., Barron, V., Hu, P.X., 2013. Testing the magnetic proxy χFD/HIRM for quantifying paleoprecipitation in modern soil profiles from Shaanxi Province, China. Global and Planetary Change 110, 368378.Google Scholar
Lu, H.Y., Yi, S.W., Liu, Z.Y., Mason, J.A., Jiang, D.B., Cheng, J., Stevens, T., Xu, Z.W., Zhang, E.L., Jin, L.Y., Zhang, Z.H., Guo, Z.T., Wang, Y., Otto-Bliesner, B., 2013. Variation of East Asian monsoon precipitation during the past 21 k.y. and potential CO2 forcing. Geology 41, 10231026.CrossRefGoogle Scholar
Ma, Y.Z., Wu, F.L., Fang, X.M., Li, J.J., An, Z.S., Wang, W., 2005. Pollen record from Red Clay sequence in the central Loess Plateau between 8.10 and 2.60 Ma. Chinese Science Bulletin 50, 22342243.CrossRefGoogle Scholar
Miao, Y.F., Herrmann, M., Wu, F.L., Yan, X.L., Yang, S.L., 2012. What controlled Mid-Late Miocene long-term aridification in Central Asia? Global cooling or Tibetan Plateau uplift: a review. Earth-Science Reviews 112, 155172.Google Scholar
Muxworthy, A.R., Dunlop, D.J., 2002. First-order reversal curve (FORC) diagrams for pseudo-single-domain magnetites at high temperature. Earth and Planetary Science Letters 203, 369382.Google Scholar
Nie, J.S., King, J., Jackson, M., Fang, X.M., Song, Y.G., 2008. AC magnetic susceptibility studies of Chinese red clay sediments between 4.8 and 4.1 Ma: paleoceanographic and paleoclimatic implications. Journal of Geophysical Research 113, B10106. http://dx.doi.org/10110.11029/12008JB005654.Google Scholar
Nie, J.S., King, J.W., Fang, X.M., 2007. Enhancement mechanisms of magnetic susceptibility in the Chinese red-clay sequence. Geophysical Research Letters 34, L19705. http://dx.doi.org/19710.11029/12007GL031430.Google Scholar
Nie, J.S., Song, Y.G., King, J.W., 2016. A review of recent advances in Red-Clay environmental magnetism and paleoclimate history on the Chinese Loess Plateau. Frontiers in Earth Science 4. http://dx.doi.org/10.3389/feart.2016.00027.Google Scholar
Nie, J.S., Song, Y.G., King, J.W., Zhang, R., Fang, X.M., 2013. Six million years of magnetic grain-size records reveal that temperature and precipitation were decoupled on the Chinese Loess Plateau during ~4.5–2.6 Ma. Quaternary Research 79, 465470.Google Scholar
Nie, J.S., Stevens, T., Song, Y.G., King, J.W., Zhang, R., Ji, S.C., Gong, L.S., Cares, D., 2014. Pacific freshening drives Pliocene cooling and Asian monsoon intensification. Scientific Reports 4, 5474. http://dx.doi.org/5410.1038/Srep05474.Google Scholar
Qiang, X.K., Li, Z.X., Powell, C.M., Zheng, H.B., 2001. Magnetostratigraphic record of the Late Miocene onset of the East Asian monsoon, and Pliocene uplift of northern Tibet. Earth and Planetary Science Letters 187, 8393.Google Scholar
Quade, J., Cerling, F.E., Bowman, J.R., 1989. Development of Asian monsoon revealed by marked ecological shift during the latest Miocene in northern Pakistan. Nature 342, 163166.Google Scholar
Rea, D.K., Snoeckx, H., Joseph, L.H., 1998. Late Cenozoic eolian deposition in the North Pacific: Asian drying, Tibetan uplift, and cooling of the northern hemisphere. Paleoceanography 13, 215224.Google Scholar
Roberts, A.P., 2015. Magnetic mineral diagenesis. Earth-Science Reviews 151, 147.Google Scholar
Roberts, A.P., Heslop, D., Zhao, X., Pike, C.R., 2014. Understanding fine magnetic particle systems through use of first-order reversal curve diagrams. Reviews of Geophysics 52, 557602.Google Scholar
Roberts, A.P., Pike, C.R., Verosub, K.L., 2000. First-order reversal curve diagrams: a new tool for characterizing the magnetic properties of natural samples. Journal of Geophysical Research 105, 2846128475.Google Scholar
Rommerskirchen, F., Condon, T., Mollenhauer, G., Dupont, L., Schefuss, E., 2011. Miocene to Pliocene development of surface and subsurface temperatures in the Benguela Current system. Paleoceanography 26, PA3216. http://dx.doi.org/3210.1029/2010PA002074.Google Scholar
Schouten, S., Hopmans, E.C., Schefuss, E., Damste, J.S.S., 2002. Distributional variations in marine crenarchaeotal membrane lipids: a new tool for reconstructing ancient sea water temperatures? Earth and Planetary Science Letters 204, 265274.Google Scholar
Sanyal, P., Bhattacharya, S.K., Kumar, R., Ghosh, S.K., Sangode, S.J., 2004. Mio-Pliocene monsoonal record from Himalayan foreland basin (Indian Siwalik) and its relation to vegetational change. Palaeogeography, Palaeoclimatology, Palaeoecology 205, 2341.Google Scholar
Sun, D.H., An, Z.S., Shaw, J., Bloemendal, J., Sun, Y.B., 1998. Magnetostratigraphy and palaeoclimatic significance of late Tertiary aeolian sequences in the Chinese Loess Plateau. Geophysical Journal International 134, 207212.Google Scholar
Sun, Y.B., An, Z.S., 2002. History and variability of Asian interior aridity recorded by eolian flux in the Chinese Loess Plateau during the past 7 Ma. Science in China 45, 420429.Google Scholar
Verosub, K.L., Fine, P., Singer, M.J., Tenpas, J., 1993. Pedogenesis and paleoclimate: interpretation of the magnetic susceptibility record of Chinese loess-paleosol sequences. Geology 21, 10111014.Google Scholar
Wang, P.X., Clemens, S., Beaufort, L., Braconnot, P., Ganssen, G., Jian, Z.M., Kershaw, P., Sarnthein, M., 2005. Evolution and variability of the Asian monsoon system: state of the art and outstanding issues. Quaternary Science Reviews 24, 595629.Google Scholar
Webster, P.J., 1994. The role of hydrological processes in ocean-atmosphere interactions. Reviews of Geophysics 32, 427476.Google Scholar
Wei, G., Li, X.H., Liu, Y., Shao, L., Liang, X.R., 2006. Geochemical record of chemical weathering and monsoon climate change since the early Miocene in the South China Sea. Paleoceanography 21, PA4214. http://dx.doi.org/4210.1029/2006PA001300.Google Scholar
White, A.F., Blum, A.E., 1995. Effects of climate on chemical weathering in watersheds. Geochimica et Cosmochimica Acta 59, 17291747.Google Scholar
White, A.F., Blum, A.E., Bullen, T.D., Vivit, D.V., Schulz, M., Fitzpatrick, J., 1999. The effect of temperature on experimental and natural chemical weathering rates of granitoid rocks. Geochimica et Cosmochimica Acta 63, 32773291.Google Scholar
Xu, Y., Yue, L.P., Li, J.X., Sun, L., Sun, B., Zhang, J.Y., Ma, J., Wang, J.Q., 2009. An 11-Ma-old red clay sequence on the Eastern Chinese Loess Plateau. Palaeogeography, Palaeoclimatology, Palaeoecology 284, 383391.Google Scholar
Xu, Y., Yue, L.P., Li, J.X., Sun, L., Sun, B., Zhang, J.Y., Ma, J., Wang, J.Q., 2012. Red clay deposits on the Chinese Loess Plateau during 11.0–2.6 Ma and its implications for long-term evolution of East Asian monsoon. Environmental Earth Sciences 66, 20212030.Google Scholar
Yang, S.L., Ding, Z.L., 2003. Color reflectance of Chinese loess and its implications for climate gradient changes during the last two glacial-interglacial cycles. Geophysical Research Letters 30, 2058. http://dx.doi.org/2010.1029/2003GL018346.Google Scholar
Yang, S.L., Ding, Z.L., Li, Y.Y., Wang, X., Jiang, W.Y., Huang, X.F., 2015. Warming-induced northwestward migration of the East Asian monsoon rain belt from the Last Glacial Maximum to the mid-Holocene. Proceedings of the National Academy of Sciences of the United States of America 112, 1317813183.Google Scholar
Zachos, J., Pagani, M., Sloan, L., Thomas, E., Billups, K., 2001. Trends, rhythms, and aberrations in global climate 65 Ma to present. Science 292, 686693.Google Scholar
Zhang, Y.G., Pagani, M., Liu, Z.H., 2014. A 12-million-year temperature history of the tropical Pacific Ocean. Science 344, 8487.Google Scholar
Zhao, X., Heslop, D., Roberts, A.P., 2015. A protocol for variable-resolution first-order reversal curve measurements. Geochemistry, Geophysics, Geosystems 16, 13641377.Google Scholar
Zhou, L., Oldfield, F., Wintle, A.G., Robinson, S.G., Wang, J.T., 1990. Partly pedogenic origin of magnetic variations in Chinese loess. Nature 346, 737739.Google Scholar