Biogeochemistry of an Iron- and Manganese-Rich Stratified Lake: Tasik Biru, Malaysia, as a Modern Model Habitat for the Ancient Ocean

Muammar, Mansor and Andreas, Kappler and Tomás Israel Grijalva, Rodriquez and Samuel, Lihan and Sergei, Katsev (2025) Biogeochemistry of an Iron- and Manganese-Rich Stratified Lake: Tasik Biru, Malaysia, as a Modern Model Habitat for the Ancient Ocean. Geobiology, 23 (5). pp. 1-19. ISSN 1472-4669

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Abstract

Tasik Biru is a ~70 m-deep tropical lake in Malaysia, originating from a water-filled open pit mine. We investigated the biogeo-chemistry and microbial community of the lake as a modern model habitat to the stratified ancient ocean. We found that a sharpredoxcline exists at around 50 m depth, related to the decrease of O 2 and pH (7.2–6.8) going down into the monimolimnion.Despite being relatively sulfate-rich (~320 μM), only a slight decrease of sulfate (to ~240 μM) was observed coupled with an in-crease of dissolved sulfide to 4 μM, attributed to microbial sulfate reduction in the monimolimnion. Comparatively, dissolvedFe and total Mn rose to ~50 μM in the anoxic layer with an unusual 1:1 concentration ratio. Other nutrients (PO 43−, Si) and tracemetal(loid)s (As, Mo, Sb, Co, U, and V) depth profiles increased or decreased across the chemocline, indicating controls via cy-cling of redox-sensitive elements. Microbial community analysis based on 16S rRNA amplicon sequencing reflects various metab-olisms, from aerobic metabolisms in the mixolimnion to putative nitrite-dependent methane oxidation (e.g., by Methylomirabilis)at the chemocline, to sulfate reduction, methanogenesis, and fermentation in the monimolimnion. Tasik Biru is not in steady-state, and its anoxic water is predicted to shift from being Fe/Mn-rich to sulfide-rich, perhaps lending it as a model habitat toinvestigate biogeochemical changes from the metal-rich Archean to the Proterozoic oceans with expanding zones of sulfide-richmargins. An overview of the current biogeochemical cycles in the lake is presented, and open questions regarding partial sulfateconsumption, methane, and Mn cycling and mineralogical distribution are highlighted to guide future studies.

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