Browsing by Author "Betzler, C."
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- Refinement of Miocene sea level and monsoon events from the sedimentary archive of the Maldives (Indian Ocean)Publication . Betzler, C.; Eberli, G. P.; Luedmann, T.; Reolid, J.; Kroon, D.; Reijmer, J. J. G.; Swart, P. K.; Wright, J.; Young, J. R.; Alvarez-Zarikian, C.; Alonso-Garcia, Montserrat; Bialik, O. M.; Blattler, C. L.; Guo, J. A.; Haffen, S.; Horozal, Senay; Inoue, Mayuri; Jovane, L.; Lanci, L.; Laya, J. C.; Mee, A. L. Hui; Nakakuni, M.; Nath, B. N.; Niino, K.; Petruny, L. M.; Pratiwi, S. D.; Slagle, A. L.; Sloss, C. R.; Su, X.; Yao, Z.International Ocean Discovery Program (IODP) Expedition 359 cored sediments from eight borehole locations in the carbonate platform of the Maldives in the Indian Ocean. The expedition set out to unravel the timing of Neogene climate changes, in particular the evolution of the South Asian monsoon and fluctuations of the sea level. The timing of these changes are assessed by dating resultant sedimentary alterations that mark stratigraphic turning points in the Neogene Maldives platform system. The first four turning points during the early and middle Miocene are related to sea-level changes. These are reliably recorded in the stratigraphy of the carbonate sequences in which sequence boundaries provide the ages of the sea-level lowstand. Phases of aggradational platform growth give precise age brackets of long-term sea-level high stands during the early Miocene and the early to middle Miocene Climate Optimum that is dated here between 17 to 15.1 Ma. The subsequent middle Miocene cooling coincident with the eastern Antarctic ice sheet expansion resulted in a long-term lowering of sea level that is reflected by a progradational platform growth. The change in platform architecture from aggradation to progradation marks this turning point at 15.1 Ma.& para;& para;An abrupt change in sedimentation pattern is recognized across the entire archipelago at a sequence boundary dated as 12.9-13 Ma. At this turning point, the platform sedimentation switched to a current-controlled mode when the monsoon-wind-driven circulation started in the Indian Ocean. The similar age of the onset of drift deposition from monsoon-wind-driven circulation across the entire archipelago indicates an abrupt onset of monsoon winds in the Indian Ocean. Ten unconformities dissect the drift sequences, attesting changes in current strength or direction that are likely caused by the combined product of changes in the monsoon-wind intensity and sea level fluctuations in the last 13 Ma. A major shift in the drift packages is dated with 3.8 Ma that coincides with the end of stepwise platform drowning and a reduction of the oxygen minimum zone in the Inner Sea.& para;& para;The strata of the Maldives platform provides a detailed record of the extrinsic controlling factors on carbonate platform growth through time. This potential of carbonate platforms for dating the Neogene climate and current changes has been exploited in other platforms drilled by the Ocean Drilling Program. For example, Great Bahama Bank, the Queensland Plateau, and the platforms on the Marion Plateau show similar histories with sediment architectures driven by sea level in their early history (early to middle Miocene) replaced by current-driven drowning or partial drowning during their later history (Late Miocene). In all three platform systems, the influence of currents on sedimentations is reported between 11 and 13 Ma.
- Sea-surface temperature, productivity and hydrological changes in the Northern Indian Ocean (Maldives) during the interval similar to 575-175 ka (MIS 14 to 7)Publication . Alonso-Garcia, Montserrat; Rodrigues, Teresa; Abrantes, Fatima; Padilha, M.; Alvarez-Zarikian, C. A.; Kunkelova, T.; Wright, J. D.; Betzler, C.The South Asian Monsoon (SAM) drives seasonal changes in the atmospheric and ocean circulation of the tropical Indian Ocean, affecting precipitation on land and oceanic primary productivity. This work examined sediments from the International Ocean Discover Program (IODP) Site U1467 (IODP Expedition 359) located in the Maldives Inner Sea (Northern Indian Ocean) at a water depth of 487 m. The Maldives Inner Sea is a perfect location to study past changes in tropical climate and ocean circulation related to monsoon dynamics in the Equatorial Indian Ocean. This study focuses on the similar to 575-175 ka interval, from Marine Isotope Stage (MIS) 14 to 7, an important period for human evolution and dispersal to Eurasia. We reconstructed sea-surface temperature (SST), based on alkenone unsaturation index (U-37(K')), hydrological changes, based on terrestrial input of n-alkanes, and past surface ocean productivity, based on total C-37 alkenones concentration. The U-37(K')-SST record shows a difference of about 1.5 degrees C between glacial and interglacial periods, clearly showing all stages and substages from MIS 14 to 7, and revealing a connection between ice sheets extension and SST at the equatorial region. The n-alkanes concentration and average chain length index indicate vegetation changes at the Indian Peninsula with drier conditions generally associated with glacial periods. Precipitation increases abruptly at the end of terminations, lasting for a variable time interval in each interglacial period, except for MIS 13. However, other mechanisms superimposed to the glacial-interglacial forcing, such as the Indian Ocean Dipole (IOD) mode, have been invoked to explain shorter-scale variability in precipitation over India. The total alkenone concentration record indicates that primary productivity at Site U1467 is strongly associated with orbital changes, probably related to the summer inter-tropical insolation gradient (SITIG, 23N-23S on June 21st). High primary productivity occurred during intervals of low SITIG, which resulted in strong inter-monsoon (April-May and October-November) Indian Ocean Equatorial Westerlies (IEW) and reduced precipitation in the equatorial region. This mechanism may also be related to the IOD, which affects the strength of the IEW.