Multi-decadal to centennial-scale development of the Indonesian-Australian summer monsoon over the last 6,000 years
Final Report Abstract
The Australian-Indonesian monsoon (AIM) has a governing influence on the agricultural practices and livelihood in the highly populated islands of Indonesia. However, little is known about the factors that have influenced past monsoon activity in southern Indonesia. This project investigated the development and variability of the AIM during the last ~6000 years. To this end, Australian-Indonesian summer monsoon (AISM) rainfall variations have been investigated using bulk sediment element analysis in a sediment archive retrieved offshore northwest Sumba Island (Indonesia). The bulk sediment element analyses record and climate model simulations reveal that variations in solar activity exert a significant influence on monsoonal rainfall at multi-decadal timescales. On the basis of planktonic foraminiferal faunal composition and planktonic foraminiferal Mg/Ca-based sea-surface temperature (SST) as proxies for monsoon-controlled austral winter upwelling intensity (Australian-Indonesian winter monsoon; AIWM) in the same archive, it has been shown that lower percentages of G. bulloides during the Little Ice Age (LIA) suggest less upwelling and thus weaker AIWM winds. Higher percentages of G. bulloides during the Current Warm Period (CWP) suggest enhanced upwelling and thus stronger AIWM winds. A weaker AIWM during the LIA corresponds to a weaker Indian summer monsoon (ISM) and a weaker East Asian Summer monsoon (EASM). The link between the three monsoon sub-systems is most likely through cross-equatorial winds consistent with their modern linkage. The data for the last 1000 years suggest a synchronous development of the AIWM with its Northern Hemisphere counterparts. However, the close correspondence between changes in AIWM, ISM and EASM is less distinct between AD 150 and AD 1000 or even reveals an opposite pattern, i.e. around AD 600. In contrast, the G. bulloides Mg/Ca-based SST estimates reveal lower (higher) temperatures during the LIA (CWP), which would suggest enhanced (decreased) upwelling activity and stronger (weaker) AIWM winds. It is speculated that the G. bulloides Mg/Ca-based SSTs reflect changes in the temperature of the upwelled subsurface Indonesian Throughflow (ITF) water rather than variations in upwelling intensity.
Publications
- (2010). East Asian summer monsoon weakening after 7.5 Ma: Evidence from combined planktonic foraminifera Mg/Ca and δ 18O (ODP Site 1146; northern SCS). Palaeogeography, Palaeoclimatology, Palaeoecology 289, 33-43
Steinke, S., Groeneveld, J., Johnstone, H., Rendle-Bühring, R.
- (2010). Evolution and variability of the East Asian summer monsoon during the Pliocene: Evidence from clay mineral records of the South China Sea. Palaeogeography, Palaeoclimatology, Palaeoecology 239, 237-247
Wan, S., Tian, J., Steinke, S., Li, A., Li, T.
- (2010). Glacial to Holocene surface hydrography of the tropical eastern Indian Ocean. Earth and Planetary Science Letters 292, 89-97
Mohtadi, M., Steinke, S., Lückge, A., Groeneveld, J., Hathorne, E.C.
- (2010). Late Pleistocene surface and thermocline conditions of the eastern tropical Indian Ocean. Quaternary Science Reviews 29, 887-896
Mohtadi, M., Lückge, A., Steinke, S., Groeneveld, J., Hebbeln, D., Westphal, N.
- (2010). Reconstructing the southern South China Sea upper water-column structure since the Last Glacial Maximum (LGM): Implications for the East Asian winter monsoon development. Paleoceanography 25
Steinke, S., Mohtadi, M., Groeneveld, J., Lin, L-C., Löwemark, L., Chen, M-T., Rendle-Bühring, R.
(See online at https://doi.org/10.1029/2009PA001850) - (2010). Strontium/Calcium ratio, carbon and oxygen stable isotopes in coccolith carbonate from different grain-size fractions in South Atlantic surface sediments. Geobios 43, 151-164
Fink, C., Baumann, K.-H., Groeneveld, J., Steinke, S.
- (2011). Glacial to Holocene swings of the Australian-Indonesian monsoon. Nature Geoscience 4, 540-544
Mohtadi, M., Oppo, D.W., Steinke, S., Stuut, J-B W., De Pol-Holz, R., Hebbeln, D., Lückge, A.
- (2011). Millennial-scale dynamics of the winter cold tongue in the southern South China Sea over the past 26 ka and the East Asian winter monsoon. Quaternary Research 75, 196-204
Huang, E., Tian, J., Steinke, S.
- (2011). Past dynamics of the East Asian monsoon: No inverse behaviour between the summer and winter monsoon during the Holocene. Global and Planetary Change 78, 170-177
Steinke, S., Glatz, C., Mohtadi, M., Groeneveld, J., Li, Q., Jian, Z.
- (2011). Reconstructing the thermal structure of the upper ocean: insights from planktic foraminifera shell chemistry and alkenones in modern sediments of the tropical eastern Indian Ocean. Paleoceanography 26
Mohtadi M., Oppo, D.W., Lückge A., De Pol-Holz, R., Steinke, S., Groeneveld, J., Hemme, N., Hebbeln, D.
(See online at https://doi.org/10.1029/2011PA002132) - (2011). Stable oxygen isotopes from the calcareous-walled dinoflagellate Thoracosphaera heimii as a proxy for changes in mixed layer temperatures off NW Africa during the last 45,000 years. Palaeogeography, Palaeoclimatology, Palaeoecology 302, 311-322
Kohn, M., Steinke, S., Baumann, K.-H., Donner, B., Meggers, H., Zonneveld, K.A.F.
- 2011). Impact of abrupt climate change in the tropical southeast Atlantic during Marine Isotope Stage (MIS) 3. Paleoceanography 26
Hessler, I., Steinke, S., Groeneveld, J., Dupont, L., Wefer, G.
(See online at https://doi.org/10.1029/2011PA002118)
