| Indonesian Throughflow (ITF), the key part of the Global Conveyor Belt in the low latitudes, connects upper ocean waters of the Pacific and Indian Ocean and consequently regulates heat and fresh water budgets between these oceans. The ITF thus plays a crucial role in climate dynamics of the Indo-Pacific Warm Pool (IPWP) region and even over the globe. In this study, I carried out modern-and paleo-oceanographic research on the ITF region on the basis of measurements of stable isotope and Mg/Ca ratios on planktonic foraminiferal shells that were obtained from sediments of 62 core-tops and one down-core. This study investigates upper ocean water properties (?18O and ?13C) and effect of seawater salinity on planktonic foraminiferal Mg/Ca ratios for the modern ocean (?5000yr) and paleoceanographic records of the ITF since the last glacial in the ITF region. The objective of this study includes discussing water mass distribution and its controlling factors, verifying validity of Mg/Ca-thermometer in study of low-latitudes with emphasis on the Indonesian Seas, and reconstructing history of the ITF in response to tropical phenomena such as East Asian monsoon and El Nino/Southern Oscillation (ENSO). In addition, I tried in-situ microanalysis of Mg/Ca ratios on planktonic foraminiferal shells utilizing the technique of Laser Ablation-Inductively Coupled Plasma-Mass Spectrometer (LA-ICP-MS).Horizontal and vertical distribution of ?18O and 813C were investigated on shells of four planktonic foraminiferal species, Globigeronoides ruber, Globigerinoides sacculifer, Pulleniatina obliquiloculata and Neogloboquadrina dutertrei, from a total of 62 core-top sediment samples from the ITF region. Results were compared with modern hydrologic parameters, showing that, in the Makassar Strait, relatively depleted ?18O and ?13C of these four species are linked to freshwater input. Depleted ?18O and ?13C in the Bali Sea, however, point to different reasons. Depleted ?18O was possibly not only a result of freshwater input, but also due to along-shore currents, while depleted ?13C was more likely caused by the Java-Sumatra upwelling. Comparison of shell ?18O with hydrographic parameters of World Ocean Atlas 2005 suggests that G. ruber and G. sacculifer calcify within the mixed-layer at 0-50 m and 20-75 m water depth, respectively, and P. obliquiloculata and N. dutertrei within the upper thermocline both at 75-125 m water depth. It also indicates that N. dutertrei calcifies at slightly deeper water depth than P. obliquiloculata does. In general,?13C of G. ruber and G sacculifer is larger than that of P. obliquiloculata and N. dutertrei at all sites, indicating effect of vertical distribution of nutrients in the ITF region in addition to depth habitats of these species.Foraminiferal Mg/Ca-thermometer is nowadays an indispensible tool for reconstructing past ocean temperatures. Recent studies proposed that Mg/Ca ratio of planktonic foraminiferal shells is significantly biased by salinity in oceans where salinity is above a critical level, challenging validity of Mg/Ca-thermometer. I investigated ?18O and Mg/Ca on shells of four planktonic foraminiferal species, G. ruber, G. sacculifer, P. obliquiloculata and N. dutertrei, from 60 core-top sediment samples from the ITF region. My results show that salinity may exert negligible impact on shell Mg/Ca of these species in the ITF region. Combination of my G. ruber data from the ITF region with a global data compilation reinforces previous studies that G. ruber shell Mg/Ca ratio is not biased by salinity in oceans where salinity is below 35.5 psu. Besides, comparison of shell Mg/Ca-derived temperatures with temperature profiles of the upper 200 m water column from the seas of the ITF region can also indicate calcification depths of these species, as matches well with the above estimations using shell ?18O. It further indicates that G. sacculifer may be more sensitive in capturing signal of changes in depth of the mixed-layer, highlighting a potential use of Mg/Ca temperature difference between G. ruber and G sacculifer in reconstructing depth of the mixed-layer in the ITF region.The Makassar Strait as the main passage of the ITF en route is one of the most sensitive areas to monitor ITF seawater changes in association with East Asian monsoon and ENSO. This study exhibits high-resolution (around 200 yrs) isotopic and Mg/Ca records since the last glacial from Core SO18515 (3.63°S,119.54°E; water depth:688 m), recovered from the southern Makassar Strait. By comparison of Core SO18515 records with those of Cores MD98-2188 (14.82°N,123.49°E; water depth:730 m) from offshore Luzon,3cBX (8.02°N,139.6°E; water depth:2829 m) from the center of the western Pacific warm pool (WPWP) and MD01-2378 (13.08°S,121.79°E; water depth:1783 m) from the Timor Sea, this study deduced a La Nina-like phase of ENSO for the period of around 12.2 ka to 5.5 ka. In contrast, an El Nino-like phase may have occurred during the last 5.5 kyrs. Sea surface water temperature sustained a plateau (Mid-Holocene Thermal Maximum) at 11 ka through 6.8 ka in the southern Makassar Strait, central Pacific and Timor Sea, likely caused by joint work of La Nina-like climate and enhanced boreal summer insolation. Surface sea salinity (SSS) in the offshore Luzon, Makassar Strait and Timor Sea show similar changing trends to ?18O of Borneo stalagmite, indicating influence of regional precipitation on SSS. Furthermore, thermocline salinity in Cores SO18515 and MD01-2378 also shows similarities with Borneo stalagmite ?18O records, possibly pointing to intensified vertical mixing of upper ocean waters which further leads to transmission of precipitation signal by the means of seawater salinity from sea surface to thermocline. Continuous declining of thermocline temperature (TT) and shoaling of depth of thermocline (DOT) in the southern Makassar Strait and Timor Sea occurred over the last 11 kyr. Taking my data together with paleo -oceanographic and -climatic data from the studied and surrounding regions, I propose different explanations for each of the time slices of 11-5.5 ka and the last 5.5 kyr. Decline of TT and shoal of DOT during 11-5.5 ka may be caused by enhanced precipitation in association with La Nina-like climate. In contrast, for the last 5.5 kyr, decline of TT and shoal of DOT may be due to more frequent occurrence of El Nino-like events, on the one hand, and to intensified East Asian winter monsoon, on the other hand. Overall, TT in Cores MD98-2188, SO18515 and MD01-2378 closely followed boreal summer insolation since the last glacial, likely indicating relationship of ITF thermocline waters with North Pacific tropical waters.LA-ICP-MS provides an opportunity for us to perform in-situ microanalysis for depth profiling of elements and trace elements/Calcium ratios on calcite foraminiferal shells. In this study, G. ruber shells are investigated with a total of 173 ablating positions from a total of 11 core top sediment samples that retrieved from the Indonesian Seas. The results show changing compositions of Magnesium and Calcium from the inside to the outside surface for both of intra-test and inter-test. Subsequently, Mg/Ca ratios from the LA-ICP-MS microanalysis are compared with Mg/Ca ratios based on regular analyses, suggesting that LA-ICP-MS microanalysis may provide a comparatively safe and convenient way for investigating Mg/Ca ratios of planktonic foraminiferal shells with considerable reliability and accuracy. |
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