10² to 10³ year scale variability of the El Niño/Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) in the eastern Indian Ocean over the last 30,000 years
Final Report Abstract
One of the main outcomes of this project is that millennial scale climate variability of the Northern Hemisphere high latitude exerts a significant influence on the eastern tropical Indian Ocean hydroclimate, regardless if within or outside of the Australian-Indonesian monsoon domain. This climate change in the northern high latitudes is supposed to modify the Hadley Circulation and the meridional position of the ITCZ, which in turn affect the amount of rainfall over the entire eastern Indian Ocean. Combined results of this project and other studies from the tropical Indian Ocean realm reveal a meridional pattern in temperature and rainfall changes during abrupt climate events of the last glacial period and support the hypothesis of a Hadley Cell reorganisation (ITCZ shift) caused by changes in the Atlantic Meridional overturning circulation. Reconstructing centennial to millennial scale variability of the (zonal) IOD remains a difficult task, not only because the above mentioned scenario favors a meridional (Hadley Cell) rather than a zonal (Walker Cell) modification of the atmospheric circulation on centennial to millennial timescales. If any, evidence for an IOD variability exists only for the Holocene, yet with conflicting results from the available proxies of its characteristic atmospheric (rainfall) or oceanic (thermocline structure) features. Future work will have to concentrate on generating various proxy records from the same archives in order to exclude potential biases introduced by different localities, archives, age models, etc. Additionally, time-series analyses of various proxies are vital but yet missing in order to assess the sensibility and appropriateness of each proxy in this region (W off Sumatra) with respect to the IOD. Finally, well-dated, high-resolution records of SST and rainfall from the western Indian Ocean are required to support the inferred IOD scenarios from the eastern Indian Ocean but yet missing. Another important outcome of this project is that the hitherto existing data do not support any significant effect of ENSO on the hydroclimate of the tropical eastern Indian Ocean, probably because ENSO has been outcompeted by monsoon and the IOD in this region. This has been also inferred from recent observations of the outflow passages of the Indonesian Throughflow in the eastern Indian Ocean suggesting that “Indian Ocean dynamics likely win out over Pacific Ocean dynamics” (Sprintall and Révelard, 2014).
Publications
- 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. 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, PA3219
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) - 2014. Indonesian vegetation response to changes in rainfall seasonality over the past 25,000 years. Nature Geoscience 7, 513-517
Dubois N., Oppo D.W., Galy V., Mohtadi M., van der Kaars S., Tierney J., Rosenthal Y., Eglinton T., Lückge A., Linsley B.
(See online at https://doi.org/10.1038/NGEO2182) - 2014. Mid- to Late-Holocene Australian-Indonesian summer monsoon variability. Quaternary Science Reviews 93, 142-154
Steinke S., Mohtadi M., Prange M., Varma V., Pittauerova D., Fischer H.W.
(See online at https://doi.org/10.1016/j.quascirev.2014.04.006) - 2014. North Atlantic forcing of tropical Indian Ocean climate. Nature 509, 76-80
Mohtadi M., Prange M., Oppo D.W., De Pol-Holz R., Merkel U., Zhang X., Steinke S., Lückge A.
(See online at https://doi.org/10.1038/nature13196)
