The role of microorganisms in the formation of a stalactite in Botovskaya Cave, Siberia – paleoenvironmental implications

Abstract

Calcitic speleothems in caves can form through abiogenic or biogenic processes, or through a combination of both. Many issues conspire to make the assessment of biogenicity difficult, especially when focusing on old speleothem deposits. This study reports on a multiproxy analysis of a Siberian stalactite, combining high-resolution microscopy, isotope geochemistry and microbially enhanced mineral precipitation laboratory experiments. The contact between growth layers in a stalactite exhibits a biogenic isotopic signature; coupled with morphological evidence, this supports a microbial origin of calcite crystals. SIMS δ¹³C data suggest that microbially mediated speleothem formation occurred repeatedly at short intervals before abiotic precipitation took over. The studied stalactite also contains iron and manganese oxides that have been mediated by microbial activity through extracellular polymeric substance (EPS)-influenced organomineralization processes. The latter reflect paleoenvironmental changes that occurred more than 500 000 yr ago, possibly related to the presence of a peat bog above the cave at that time. Microbial activity can initiate calcite deposition in the aphotic zone of caves before inorganic precipitation of speleothem carbonates. This study highlights the importance of microbially induced fractionation that can result in large negative δ¹³C excursions. The microscale biogeochemical processes imply that microbial activity has only negligible effects on the bulk δ¹³C signature in speleothems, which is more strongly affected by CO₂ degassing and the host rock signature

Carbonate Neoformations on Modern Buildings and Engineering Structures in Tyumen City, Russia: Structural Features and Development Factors

“…Apart from the mycelium, remains of bacterial colonies, which are often reported as an important factor of speleothem development in caves [33], were found in all studied samples. In general, the typical structure of carbonate crusts formed at the engineering constructions and buildings represents an alternation of interlayers consisting of tubular aggregates formed by the fungal hyphae and interlayers consisting of concentric spherical aggregates resulting from the activity of microbial communities (Figure 8a,b).…”

A new Chinese national reference material (GBW04481) for calcite oxygen and carbon isotopic microanalysis

“…Carbonate geochemistry and isotope compositions are the most important tracers for studies of paleoceanography, paleoenvironment and paleoclimate changes . Isotopic variations at micrometer scales are robust archives for reconstructing palaeoenvironment and paleoclimate changes at annual and seasonal resolution or even higher temporal resolution …”

“…[8][9][10][11] Isotopic variations at micrometer scales are robust archives for reconstructing palaeoenvironment and paleoclimate changes at annual and seasonal resolution or even higher temporal resolution. [12][13][14][15][16][17][18] SIMS (secondary ion mass spectrometer) is thought to be the most powerful technique for high-precision stable isotopic analysis at micrometer scales. However, matrix effects are demonstrated as the major limitations of SIMS carbonate isotopic microanalysis.…”

Molecular signatures of dissolved organic matter in a tropical karst system

“…The distinct provenance of the recharge water and the absence of light in karst systems, provides a unique opportunity to study non-photic processes acting on DOM (Birdwell and Engel, 2009). Karst systems, and especially caves, have been the subject of a number of studies on biological activity in the aphotic zone (Shabarova and Pernthaler, 2010;Baskar et al, 2011;Pacton et al, 2013;Shabarova et al, 2014;Tisato et al, 2015). These environments are generally nutrient-limited, and DOM fluxes represent an important source of carbon for karst fauna (Einsiedl et al, 2007;Simon et al, 2007).…”