The late quaternary tectonic, biogeochemical, and environmental evolution of ferruginous Lake Towuti, Indonesia

Highlights

• A set of 130–170-m-long drill cores were recovered from Lake Towuti, Indonesia.

• The cores were analyzed to investigate lake evolution, paleoclimate, and biogeochemical changes.

• Tectonic changes, diagenesis, and paleoclimate shifts all affected the lake's sediments.

• Changes in the iron biogeochemistry document repeated wet-dry cycles through the late Quaternary.

• Regional volcanism caused large changes in the lake's primary production.

Abstract

There is a paucity of long and continuous continental records from South East Asia suitable to inform on past changes and underlying causes of the region's climate and associated diverse ecosystem evolution during the late Quaternary. In 2015, the Towuti Drilling Project (TDP) collected a series of sedimentary drill cores from the tectonic, ferruginous, and highly biodiverse Lake Towuti, Sulawesi, one of Indonesia's oldest lakes. The drill cores contain ~1 Myr of uninterrupted lacustrine sedimentation to document long-term environmental and climatic change in the tropical western Pacific, the impacts of geological and environmental changes on the biological evolution of aquatic taxa, and the geomicrobiology and biogeochemistry of metal-rich, ultramafic-hosted lake sediment. Here we use lithostratigraphic, mineralogical, geochemical, and geochronological datasets to elucidate Lake Towuti's tectonic emergence and its biogeochemical responses to climatic and volcanic forcings since lake formation. Our data document that Lake Towuti emerged during a phase of accelerated tectonic subsidence from a landscape characterized by active river channels, shallow lakes and swamps into a permanent lake at ~1 Ma. The lacustrine sediments feature quasi-rhythmic alternations of green organic rich and red sideritic clay beds reflecting changes in lake mixing and biogeochemistry as a response to temperature and hydrological changes driven by orbital-scale changes in insolation and continental ice volume through the mid- to late Pleistocene. Clay deposition is interrupted by two beds of diatomaceous oozes composed primarily of planktonic diatoms that reflect phases of substantially increased primary productivity. The occurrence of these diatomaceous oozes in close association with multiple tephra beds suggests a trophic state change driven by the addition of volcanically sourced P, possibly in combination with a lake mixing state that supports recycling of P. Data on lake age and ontogeny are also in agreement with molecular-clock estimates of ~0.7 Ma (0.18–1.37 Ma) for the divergence of Lake Towuti's Telmatherinid fishes from a riverine ancestor. Our data therefore are compatible with an evolutionary model in which Lake Towuti's endemic fauna is a result of geographic speciation in the Malili Lakes, a set of large lakes in Southeast Sulawesi, driven by physical or chemical dispersal limits imposed by the regional rivers and lakes. More detailed chronological constraints and refined climate and environmental proxy datasets are currently in preparation and will help to paint a more detailed history of the region's climate and environmental history in future studies.

Introduction

The Indo-Pacific Warm Pool (IPWP) isis home to the largest zone of deep atmospheric convection on Earth and exerts enormous influence on global climate (Cane, 2005; Chiang, 2009; Clement et al., 2001; Phillips et al., 2012). Convection over the IPWP is linked to globally important climate phenomena such as the El Niño-Southern Oscillation (ENSO), and influences the concentration of atmospheric water vapor, the Earth's most important greenhouse gas (Pierrehumbert, 2000). Our ability to understand past changes in the tropical hydrological cycle and to make accurate predictions of future changes in tropical climate therefore rests on our understanding of tropical Pacific climate under boundary conditions different from those experienced in recent time. Long drill-core records have substantially improved our understanding of the late Quaternary climate history in tropical South America and Africa (e.g. Fritz et al., 2007; Johnson et al., 2016; Lupien et al., 2018); however, proxy records of IPWP hydrology exhibit profound differences in their orbital-scale patterns that challenge our understanding of the controls on IPWP paleohydrology (Ayliffe et al., 2013; Carolin et al., 2016; Konecky et al., 2016; Krause et al., 2019; Mohtadi et al., 2011; Reeves et al., 2013; Russell et al., 2014). Thus, despite its importance, the response of Indo-Pacific hydroclimate to global climate change and forcings is uncertain.

To improve our understanding of Indo-Pacific environmental history, in 2015 an international team of scientists recovered a long and continuous sedimentary record through scientific drilling at Lake Towuti, South Sulawesi, Indonesia (the Towuti Drilling Project, or TDP; Russell et al., 2016). Lake Towuti is the largest lake within the Malili Lake System, a set of five tectonic lakes in Sulawesi (Fig. 1). Studies of shallow piston cores from Lakes Towuti and Matano have documented large hydrologic responses to global climate changes highlighted by strong drying during the last glacial maximum (LGM) reconstructed through isotopic records of terrestrial leaf waxes (Russell et al., 2014; Wicaksono et al., 2015), sediment geochemistry (Costa et al., 2015), and sedimentological reconstructions of lake level (Vogel et al., 2015). A key goal of the TDP is to extend this record over multiple glacial-interglacial cycles to investigate IPWP hydrological change over the full range of climate boundary conditions and multiple glacial-interglacial cycles that occurred during the mid- to late Pleistocene. In addition to its paleoclimatological significance, Lake Towuti harbors endemic species flocks of snails, crabs, shrimps, and fish that evolved in situ over the lake's long history (von Rintelen et al., 2012; Vaillant et al., 2011). A major goal of the scientific drilling program is to elucidate the environmental context in which these organisms evolved. Lake Towuti and vicinity is immediately underlain by the East Sulawesi Ophiolite (Monnier et al., 1995), which releases iron and other metals that catalyze biogeochemical reactions by an exotic microbial community in the lake and its sediments (Crowe et al., 2008b; Haffner et al., 2001; Vuillemin et al., 2016). Understanding the biogeochemistry of these sediments can provide insight into processes that prevailed in ancient ferruginous oceans on early Earth (Crowe et al., 2008a; Crowe et al., 2014). However, the Eurasian, Indo-Australian, Caroline and Philippine Sea plates converge at Sulawesi, giving rise to a variety of crustal processes (Hall and Wilson, 2000; Hamilton, 1979; Spakman and Hall, 2010) that influence Towuti's sedimentary record. Developing paleoenvironmental reconstructions from Lake Towuti requires disentangling the impacts of tectonics and climate, as well as geomicrobiological and diagenetic impacts, on the lake's sediments.

Here we present the first detailed sedimentological, geochemical, and biogeochemical analyses of the ~1.1 km of sediment core recovered by the TDP. We use these records and new analyses of shallow piston cores to unravel the tectonic, climatic, and biogeochemical processes controlling sedimentological change in these cores, and in particular how climate and tectonics have influenced the biogeochemistry and mineralogy of this sedimentary succession. We document profound changes in this lake ecosystem during the past ~1 million years (Ma), which have impacted the lakes' endemic organisms. This study establishes a framework for future investigations of the mid- to late Pleistocene paleoclimatic history of this region.