Paleoenvironmental records derived from two ferruginous lakes on Sulawesi, Indonesia
BORIS DOI
Abstract
The primary objective of this thesis is to extract paleoenvironmental information in the Indo-Pacific Warm Pool (IPWP) from two ferruginous lakes on Sulawesi, Indonesia: Lake Towuti and Lake Poso. This thesis comprises two parts, each dedicated to a separate lake. The motivation for this division is twofold: (1) the assessment of molybdenum (Mo) as a paleoredox proxy in ferruginous Lake Towuti and (2) the investigation of modern hydrology, hydrochemistry, and land-use conditions of Lake Poso. Part I falls within the framework of the Towuti Drilling Project (TDP), an advanced project aiming to uncover in-depth insight into the long-term environmental changes of Lake Towuti. In contrast, Part II introduces key findings that identify Lake Poso as a promising site for paleoenvironmental reconstructions in IPWP.
Given the smaller dissolved Mo inventory in lakes, the assessment of Mo as a paleoredox proxy in a ferruginous setting was conducted using a source-to-sink approach including the Mo mobility and isotope variability in weathering profiles overlying ultramafic bedrock, lake surface sediments, and a sediment piston core that spanned ~30 kyr. The Mo mobility during weathering is likely associated with Mo redistribution within the weathering profile leading to larger Mo isotope variation compared to the bedrock. The near-complete scavenging of Mo onto Fe (oxyhydr)oxides phases from the porewater leads to high Mo concentration and Mo isotopic composition close to bedrock in strongly weathered conditions. The transport of Mo to the lake is dominantly in particulate Fe (oxyhydr)oxides phases which releases previously bound Mo in the reducing conditions of Lake Towuti’s hypolimnion. Released Mo was found to be rescavenged subsequently by available newly formed amorphous Fe (oxyhydr)oxides in the oxic parts of the lake. Therefore, the Mo isotope signature in Towuti sediments is predominantly influenced by redox processes with isotopically light Mo sedimentary signatures indicating oxic conditions and heavy Mo isotopic compositions correspond to sediments deposited under anoxic conditions. The understanding of these contemporaneous conditions was applied to ~30 kyr spanning sediment core to reconstruct climate-induced water column oxygenation changes caused by glacial-interglacial climate changes. These results underscore the potential of Mo as a paleoredox proxy and thus have the potential to be implemented in longer records (~1 Myr) from the TDP project which reacts sensitively to climate-induced changes in water column mixing.
Investigation of Lake Poso's modern hydrology and hydrochemistry was combined with a geographic information system (GIS) analysis to assess the land use and anthropogenic impact on Lake Poso. The hydrochemical results revealed a composition primarily attributed to the weathering and dissolution of calcareous and calcareous-siliceous bedrock lithologies, with minimal to no anthropogenic impact on nutrient and metal loadings. These studies underscore the considerable potential of Lake Poso as a site for paleoenvironmental reconstructions, and potentially for the reconstruction of ENSO-induced climate extremes.
Given the smaller dissolved Mo inventory in lakes, the assessment of Mo as a paleoredox proxy in a ferruginous setting was conducted using a source-to-sink approach including the Mo mobility and isotope variability in weathering profiles overlying ultramafic bedrock, lake surface sediments, and a sediment piston core that spanned ~30 kyr. The Mo mobility during weathering is likely associated with Mo redistribution within the weathering profile leading to larger Mo isotope variation compared to the bedrock. The near-complete scavenging of Mo onto Fe (oxyhydr)oxides phases from the porewater leads to high Mo concentration and Mo isotopic composition close to bedrock in strongly weathered conditions. The transport of Mo to the lake is dominantly in particulate Fe (oxyhydr)oxides phases which releases previously bound Mo in the reducing conditions of Lake Towuti’s hypolimnion. Released Mo was found to be rescavenged subsequently by available newly formed amorphous Fe (oxyhydr)oxides in the oxic parts of the lake. Therefore, the Mo isotope signature in Towuti sediments is predominantly influenced by redox processes with isotopically light Mo sedimentary signatures indicating oxic conditions and heavy Mo isotopic compositions correspond to sediments deposited under anoxic conditions. The understanding of these contemporaneous conditions was applied to ~30 kyr spanning sediment core to reconstruct climate-induced water column oxygenation changes caused by glacial-interglacial climate changes. These results underscore the potential of Mo as a paleoredox proxy and thus have the potential to be implemented in longer records (~1 Myr) from the TDP project which reacts sensitively to climate-induced changes in water column mixing.
Investigation of Lake Poso's modern hydrology and hydrochemistry was combined with a geographic information system (GIS) analysis to assess the land use and anthropogenic impact on Lake Poso. The hydrochemical results revealed a composition primarily attributed to the weathering and dissolution of calcareous and calcareous-siliceous bedrock lithologies, with minimal to no anthropogenic impact on nutrient and metal loadings. These studies underscore the considerable potential of Lake Poso as a site for paleoenvironmental reconstructions, and potentially for the reconstruction of ENSO-induced climate extremes.
Date of Publication
2024
Year of graduation
2024
Theses Type
dissertation
Subject(s)
Language(s)
en
Author(s)
Faculty/Graduate School
Access(Rights)
open.access
Primary OA Publication
true