THE INFLUENCE OF VOLCANIC ERUPTION ON CLIMATE AND ECOLOGY CHANGES IN THE LATE PLEISTOCENE IN BENGKULU BASIN, INDONESIA

• Main Author: Wiguna, Taufan
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/57592
• Institution: Institut Teknologi Bandung

Volcanic eruption may influence global climate, cooling or warming. Both are affected by SO2 or CO2 domination. The domination of volcanic SO2 emission is the reason of climate cooling, while CO2 is the opposite. Nevertheless, global cooling or warming as effect of volcanic eruption is still debatable. Accordingly, it is necessary to have a better understanding of the volcanic eruptions impact on climate and ecological changes for disaster mitigation in the future. This study aims to determine the influence of volcanic eruptions to climate and ecological changes. The research location is southern water in west Sumatra, Indonesia, specifically in Bengkulu Basin. The datasets are conducted on sediment core SO189/2_04KL retrieved from Bengkulu Basin, extracted from water depth 1705 meter. Another data is come from GeoB 10038-4, 150 km southeast of SO189/2_04KL, that extracted from water depth 1892 meter. SO189/2_04KL’s data are element composition (obtained from XRF analysis) and foraminifera abundance interval 600-800 cm below sea floow (cmbsf), both are primary data, while lightness (L*) and magnetic susceptibility (Mag) interval 0-1000 cmbsf as secondary data. To reconstruct age model, secondary data of marine core sediment GeoB 10038-4 interval dept 0-898 cmbsf was used. Sedimentation rate between SO189/2 and GeoB 10038-4 is assumed same. To get the aim of research, volcanic product in sediment succession (VSU: Volcanogenic Sediment Unit) is determinated. Its determination applies five elemental ratio, peak of ln (Fe/Ca), ln (Mn/Ca), and (Fe+Mn)/(Ca+Sr), well sorting shown by high Sr/Ca ratio, and low weathering represented by low Rb/Sr ratio. General ecology condition are shown by Shannon Index (H) and evenness (E), more detail by indicator value (IndVal). Climate condition is represented by tropic foraminifera is represented by tropic species, Gr. menardii abundance, and ratio thermocline dweller and mixed dweller. Marine productivity is represented by Pulleniatina group abundance. Upwelling event is shown by Globigerina bulloides. Climate periodic and IndVal on interval 600-800 cmbsf according to biozonation result by single linkage clustering on distance 150. IndVal is also calculated on VSU interval. Primary VSU layers are found on 740-742 cmbsf (VSU-1, thichness 3 cm, 106.000 BP) and 661-664 cmbsf (VSU-2, thickness 2 cm, 92.000 BP). The volcanic eruption that occurred during this time was an eruption originating from the Sunda Caldera at 105,000 years BP, after which it was recorded that the Old Tangkuban Perahu (OT) deposit which was 83,000 years old BP occurred long after VSU-2. The VSU-2 eruption is close to the Aso-4 eruption (Japan) which is 87,000 ± 7,080 years BP, the second largest eruption after YTT in a period of 100,000 years resulting in a distribution of eruptions with a maximum radius of 3,500 from the center of the eruption, so it does not reach south Sumatra. Therefore, VSU-1 and VSU-2 are interpreted as originating from the Sunda Caldera. In relation to climate and ecological changes, VSU-1 deposit is in the period 2, which relative cooupwelling. In the VSU-1 layer interval, the IndVal value indicates cooler climate compared to its top and bottom. VSU-2 deposit is in the period 4, which relative cooler and on upwelling, as well as VSU-1, shown by G. bulloideas increasing on 645-670 cmbsf. Upwelling may be influenced by austral winter wind from SE. The results of paleoclimate and paleoecological reconstructions show that at the two VSU intervals, both volcanic eruptions can cause climate and ecology changes. In general, volcanic antivity during these 2 VSUs had induced cooling climate condition, which are characterized by thermocline shoaling, Gr. menardii relative abundance decreasing. Both intervals are also show increasing of marine productivity which indicated by the increase of Pulleniatina group and IndVal values of P. obliquiloculata and N. dutertrei. In addition, diversity and evenness decreased as indicated by a decrease in the Shannon diversity index (H) and Evenness (E). Thermocline shoaling in VSU interval does not correlate to upwelling, so that thermocline shoaling represent stratification weakening may be affected by volcanic eruption.