Hydrological connectivity and mixing of Lake Towuti, Indonesia in response to paleoclimatic changes over the last 60,000years

The Towuti Drilling Project: paleoenvironments, biological evolution, and geomicrobiology of a tropical Pacific lake

“…Previous sedimentary records from Lake Towuti span the last ∼ 60 kyr BP, and contain an intriguing record of past climate that differs markedly from that of the subtropics (Russell et al, 2014). In particular, we observed grassland expansion, lowered lake levels, and strong drying during the last glacial maximum (LGM) relative to both marine isotope stage 3 (∼ 30-60 kyr BP) and the Holocene (Costa et al, 2015;Konecky et al, 2016;Russell et al, 2014;Vogel et al, 2015). The strong glacial-interglacial signal at Lake Towuti challenges the hypothesis that tropical hydroclimate is predominantly controlled by precessional orbital forcing, with little influence of glacial-interglacial changes in climate boundary conditions (Carolin et al, 2013;Meckler et al, 2012).…”

“…The rapid transition from Unit 2, which represents sedimentation near base level, to Unit 1, which represents sedimentation permanently below base level, suggests rapid fault movement and creation of accommodation space. We interpret Unit 1 to represent sedimentation in a generally deep lake, with red/green alternations reflecting climatedriven transitions in lake level and mixing (Costa et al, 2015). Unit 1 sediments are quite similar at Sites 1 and 3, but differ substantially at Site 2, where the upper ∼ 70 m of sediment predominantly consists of distal deltaic sedimentation.…”

“…Towuti's surface water temperatures vary between ∼ 29 and 31 • C. The lake water column is thermally stratified, with seasonal mixing to a depth of ∼ 100 m (Costa et al, 2015). Lake Towuti is relatively dilute (210 µS cm −1 ) and circumneutral (pH ∼ 7.8) with a chemistry dominated by Mg and HCO − 3 (Haffner et al, 2001;Lehmusluoto et al, 1995).…”

“…The prevalence of Fe-rich sedimentary rock units in the Precambrian suggests that ferruginous conditions were a prominent feature of the deep ocean throughout the Earth's history (Poulton and Canfield, 2011), and with mounting evidence for Fe-rich Martian soils and lake sediments dominated by ultramafic weathering products (e.g., Ehlmann et al, 2008), the study of an active biosphere in environments such as Towuti is timely and critical. Moreover, Towuti's pelagic microbial ecology, biogeochemistry, and sediment mineralogy are tightly linked to climate variations through varying lake mixing regimes, soil erosion, and weathering (Costa et al, 2015;Tamuntuan et al, 2015). These processes are directly or indirectly responsible for the production and deposition of many paleoclimate proxies, and postdepositional alteration of those proxies is often linked to the activity of sedimentary microorganisms.…”

Depositional modes and lake-level variability at Lake Towuti, Indonesia, during the past ~29 kyr BP

“…The coherent signal produced by these datasets implies that the region experienced significant changes in moisture availability, with interstadial/interglacial periods of marine isotope stage 3 (MIS 3) and the Holocene being characterized by wetter and stadial/glacial periods of MIS 4 and 2 being characterized by substantially drier conditions (Russell et al 2014). These changes in moisture availability have also influenced lake water oxygenation and catchment processes at Lake Towuti (Costa et al 2015;Tamuntuan et al 2015), with deeper mixing and a well oxygenated water column as a result of enhanced evaporative surface water cooling during dry periods of MIS 4 and 2. While these datasets show a coherent pattern of hydroclimatic change associated with glacial/interglacial periods (Russell et al 2014), a dataset suitable to trace changes in lake-level driven depositional processes is still missing from Lake Towuti.…”