Mittelmiozäne Dynamik des indischen Monsuns
Zusammenfassung der Projektergebnisse
This study presents a middle to late Miocene record of the radiogenic Sr, Nd, Hf and Pb isotope compositions of detrital clays obtained from IODP Site U1443 in the southern Bay of Bengal. Tectonics, climate and regional monsoon strength controlled weathering and erosion regimes of the watersheds feeding into the Bay of Bengal and these factors played an important role in the global climate evolution via carbon cycle feedbacks. Radiogenic isotope compositions that were used to infer the provenance and the prevailing weathering regime of the sediments supplied to the Ninetyeast Ridge, are affected by all these factors on different timescales. Therefore, the approach of this project was to disentangle the roles of climate, tectonics, monsoon strength and weathering and erosion intensity using multiple isotope systems and higher temporal resolution records than in previous studies to advance the understanding of major controls of past SAM intensity. The study of orbital-resolution intervals of the middle Miocene (15.8-9.5 Ma) as well as of a 100 kyr resolution record of the late Miocene (9-5 Ma) now allows to distinguish between tectonic and climatic forcing of changes recorded in the detrital clay radiogenic isotope record. The high resolution of individual intervals even allowed the identification of orbital cycles in radiogenic isotopes in the Miocene for the first time. The use and combination of multiple isotope systems to trace the sources of detrital sediments and the weathering regime provided insights that were not accessible by single isotope systems. The coupling of Nd and Hf isotope systems was applied as a novel tracer of silicate weathering and provides new insights into tropical environmental changes. Major findings achieved in this project were: The combination of Sr, Nd and Pb isotope compositions demonstrated that the mix of clay sources contributing to the Ninetyeast Ridge remained largely invariant throughout the middle to late Miocene despite major tectonic reorganizations in the Himalayas. - A marked decrease in detrital Sr, Nd and Pb isotope variability at ~13.5 Ma was attributed to a major restriction in the supply of High Himalayan erosion products. The change in variability coincided with global climate cooling, which likely had a major impact on precipitation patterns, restricting peak precipitation to the frontal domains of the Himalayas and the Indo-Burman Ranges. - Transient orbital-scale fluctuations of the radiogenic isotope compositions were mainly triggered by climatically-driven changes in the balance of source contributions, which was supported by the presence of a significant 30 kyr periodicity in the Nd isotope record, a heterodyne typically associated with monsoon variability. - A late Miocene increase in 87Sr/86Sr between 6 and 5 Ma likely indicates an increase in the chemical weathering intensity in the Ganges-Brahmaputra and Irrawaddy basins. This may have resulted from increased exposure of the continental shelves due to larger floodplains and the expansion of C4 plants. - To better disentangle the silicate weathering intensity signal from changes in source provenance, Nd and Hf isotope compositions were combined, using the relatively new ∆εHf clay proxy. This indicated highly intense chemical weathering in the catchment area recorded by some of the highest ∆εHf clay values measured to date, suggesting a combination of highly weathered sediments and substantial erosion in tropical environments with intense and seasonal precipitation.
Projektbezogene Publikationen (Auswahl)
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(2017) South Asian Monsoon induced erosion during the Miocene. In: Expedition 353 Science Meeting, 06.-08.11.2017, Bengaluru, India
Bretschneider, L., Hathorne, E.C., Frank, M., Ali, S., Lübbers, J., Kochhann, K., Holbourn, A., Kuhnt, W. and Andersen, N.
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(2018) Asian Monsoon induced erosion during the Miocene recorded at IODP Site U1443 (Exp. 353). In: AGU Fall Meeting 2018, 10.-14.12.2018, Washington D.C., USA
Bretschneider, L., Hathorne, E.C., Frank, M., Lübbers, J., Kochhann, K., Holbourn, A. and Kuhnt, W.
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(2018) Asian Monsoon induced erosion during the Miocene. In: IODP/ICDP Kolloquium 2018, 14.-16.03.2018, Bochum, Germany
Bretschneider, L., Hathorne, E.C., Frank, M., Lübbers, J., Kochhann, K., Holbourn, A., Kuhnt, W. and Andersen, N.
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(2019) Indian Monsoon induced erosion during the Miocene recorded at IODP Site U1443 (Exp. 353). In: IODP/ICDP Kolloquium 2019, 18.-20.03.2019, Köln, Germany
Bretschneider, L., Hathorne, E.C., Frank, M., Lübbers, J., Kochhann, K., Holbourn, A. and Kuhnt, W.
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(2019) Miocene radiogenic isotope record of Indian monsoon induced erosion and its link to global climate and tectonics (IODP Site U1443). In: 13th International Conference on Paleoceanography, 02.-06.09.2019, Sydney, Australia
Bretschneider, L., Hathorne, E.C., Frank, M., Bolton, C., Gray, E., Lübbers, J., Kochhann, K., Holbourn, A., Kuhnt, W. and Andersen, N.
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(2021), Provenance and weathering of clays delivered to the Bay of Bengal during the middle Miocene: Linkages to tectonics and monsoonal climate. Paleoceanography and Paleoclimatology
Bretschneider, L., Hathorne, E.C., Huang, H., Lübbers, J., Kochhann, K.G.D., Holbourn, A., Kuhnt, W., Thiede, R., Gebregiorgis, D., Giosan, L. and Frank, M.
