INDONESIAN THROUGHFLOW DYNAMICS ANALYSIS DURING THE LAST GLACIAL MAXIMUM USING PLANKTONIC FORAMINIFERA IN THE MAKASSAR STRAIT

• Main Author: Dwi Demia Larasati, Oktavira
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/84573
• Institution: Institut Teknologi Bandung

Last Glacial Maximum (LGM) is a period when the Earth is in a cold phase and there is a massive formation of ice mass on land and in the sea at high latitudes. During the LGM, the climate conditions at high latitudes in the Northern Hemisphere were much colder compared to current conditions. The global average temperature was estimated to be 3–6 °C lower than modern temperatures. Even in tropical regions, the average temperature was known to be significantly cooler, ranging between 2 and 3,5 °C below the current average temperature. These conditions can influence the global thermohaline circulation, as well as the Indonesian Throughflow (ITF), which is part of the global thermohaline circulation. Studies have shown that the intensity and vertical structure of the ITF varied significantly on glacial-interglacial timescales. Previous studies have shown that the ITF weakens during the LGM period. However, little is known about the changes in the vertical structure and intensity of the ITF in the Makassar Strait during this period. This study presents a proxy-based analysis using planktonic foraminifera at the main entrance of the ITF in the Makassar Strait. The data used in this study include marine sediment samples and secondary data from the Couple Climate System Model Version 4 (CCSM4) model output. A total of 20 sediment samples from a depth of 255 – 295 cm from marine sediment coded TR1926B (0°13,664' N / 117°47,436' E, depth 616 m) collected during the TRIUMPH 2019 expedition were used as research material. The methods used in the analysis of TR1926B marine sediments include absolute age dating using AMS14C, Sea Surface Temperature (SST) analysis through Mg/Ca geochemistry in Globigerinoides ruber, planktonic foraminifera abundance analysis, and Log (Zr/Rb) ratio analysis. The CCSM4 model output includes potential temperature and current velocity data from the LGM and Pre-Industrial (PI) periods. Potential temperature data were used to determine the Depth of Thermocline (DOT) and calculate the South-North (S – N) temperature gradient, while current velocity data were used to calculate the volume transport of the Indonesian Throughflow. Paleoceanographic analysis was conducted by examining the range of LGM cooling periods, SST, DOT changes, and ITF intensity at the study site The DOT analysis was conducted based on the ratio of Thermocline Dwellers (TD) planktonic foraminifera abundance to Mixed Layer Dwellers (MLD) and the vertical profile of potential temperature, while the ITF intensity analysis was based on the S – N temperature gradient, volume transport, and Log (Zr/Rb) proxy. This analysis was conducted to understand the dynamics of the ITF and the mechanisms that affect it during the LGM period. The LGM period in the Makassar Strait, particularly at the TR1926B marine sediment research location, occurred around 22 to 18 kilo years ago (kya), with the peak cooling occurring around 19,7 kya. The average SST during the LGM, obtained through Mg/Ca geochemical analysis, was 25,72°C, which is 3,33°C lower than the modern SST which reached 29,05°C. Planktonic foraminifera abundance analysis showed that TD were dominant over MLD during the LGM planktonic foraminifera was abundant during 22,4 – 21,5 and 19,7 – 18 kya, indicating the shallowing of the DOT at the study site. These results were confirmed by vertical temperature profile data from the CCSM4, which showed a shallowing of the DOT by 10 meters compared to PI conditions. Furthermore, the intensity of ITF is known to be weaker during the LGM, as indicated by the low S–N temperature gradient and a decrease in ITF transport of 0,24 Sv. The Log (Zr/Rb) analysis shows that the intensity of the ITF increased during the LGM, with higher Log (Zr/Rb) values compared to modern conditions. However, this increase in Log (Zr/Rb) values is more likely related to the increase in river runoff. During the LGM, river runoff increased freshwater input to the Makassar Strait, which caused a decrease in salinity and an increase in buoyancy, thereby reducing transport in the Makassar Strait.