Variability of the Indonesian Throughflow Using Planktonic Foraminifera During the Last Glacial Maximum in the Makassar Strait Oktavira Dwi Demia Larasati1, Marfasran Hendrizan2, Rima Rachmayani3 Maharani Rachmawati Purnomo4, Niken Sitalaksmi Siagian4, Abyan Harahap4
Institut Teknologi Bandung
Abstract
Last Glacial Maximum (LGM) is a cold phase in the earth from 26 to 18 kilo years ago (kya), and a massive formation of ice mass on land and in the sea at high latitudes occurred. During the LGM, in the tropical regions, the average temperature was known to be significantly cooler, ranging between 2 - 3,5 degC below the current average temperature. These conditions could influence the global thermohaline circulation, as well as the Indonesian Throughflow (ITF), which is part of the global thermohaline circulation. 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 its main pathway (the Makassar Strait) during this period. The data used in this study include marine sediment samples and secondary data from the Community Climate System Model Version 4 (CCSM4) model output. A total of 20 sediment samples from a depth of 255 - 295 cm from marine sediment TR1926B (0,227^{\circ}N, 117,790^{\circ}E, depth 616 m) collected during the TRIUMPH 2019 expedition were used as research material. The main methods used in the analysis of TR1926B marine sediments was planktonic foraminifera abundance 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. Planktonic foraminifera abundance analysis showed that Thermocline Dwelling species was more abundant over Mixed Layer Dwelling species during 22,4 - 21,5 and 19,7 - 18 ka, 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
Keywords: Indonesian Throughflow (ITF), planktonic foraminifera, Last Glacial Maximum, depth of thermocline (DOT)
