Growth of modern branched columnar stromatolites in Lake Joyce, Antarctica

Abstract

Modern decimeter-scale columnar stromatolites from Lake Joyce, Antarctica, show a change in branching pattern during a period of lake level rise. Branching patterns correspond to a change in cyanobacterial community composition as preserved in authigenic calcite crystals. The transition in stromatolite morphology is preserved by mineralized layers that contain microfossils and cylindrical molds of cyanobacterial filaments. The molds are composed of two populations with different diameters. Large diameter molds (>2.8 μm) are abundant in calcite forming the oldest stromatolite layers, but are absent from younger layers. In contrast, <2.3 μm diameter molds are common in all stromatolites layers. Loss of large diameter molds corresponds to the transition from smooth-sided stromatolitic columns to branched and irregular columns. Mold diameters are similar to trichome diameters of the four most abundant living cyanobacteria morphotypes in Lake Joyce: Phormidium autumnale morphotypes have trichome diameters >3.5 μm, whereas Leptolyngbya antarctica, L. fragilis, and Pseudanabaena frigida morphotypes have diameters <2.3 μm. P. autumnale morphotypes were only common in mats at <12 m depth. Mats containing abundant P. autumnale morphotypes were smooth, whereas mats with few P. autumnale morphotypes contained small peaks and protruding bundles of filaments, suggesting that the absence of P. autumnale morphotypes allowed small-scale topography to develop on mats. Comparisons of living filaments and mold diameters suggest that P. autumnale morphotypes were present early in stromatolite growth, but disappeared from the community through time. We hypothesize that the mat-smoothing behavior of P. autumnale morphotypes inhibited nucleation of stromatolite branches. When P. autumnale morphotypes were excluded from the community, potentially reflecting a rise in lake level, short-wavelength roughness provided nuclei for stromatolite branches. This growth history provides a conceptual model for initiation of branched stromatolite growth resulting from a change in microbial community composition.

Microbial Mat Communities along an Oxygen Gradient in a Perennially Ice-Covered Antarctic Lake

“…This is evident in the accumulation of annual laminations (11,13), with accrual on the order of millimeters on the ridges where D. contenta and Phormidium were concentrated, whereas both were rare in the pit bases, where annual accrual was Ͻ Ͻ1 mm. Our observations thus support the view that the macroscopic morphology of microbial mats is affected by differential growth, community composition, and behavioral traits (17).…”

“…The mechanism underlying the difference between the low topographic growth of the ridge-pit mat and the high topographic growth form of the pinnacles may relate to the shift in dominance from Leptolyngbya to diatoms and Phormidium. In the pinnacle mats, vertical extension into pinnacles appears to be characteristic of mats with a higher abundance of Leptolyngbya, as documented in previous studies (17,68), whereas high abundance of Phormidium has been more commonly associated with flat prostrate microbial mats in Antarctic lakes (17,68).…”

“…Two distinct mats zones are recognized. Below the ice cover, where liquid water persists year round, mats are rich in lightharvesting pigments (12) and extracellular polysaccharides, are laminated (11), and often take the form of complex, three-dimensional structures (13,16,17). During summer, solar heating melts the shallow margins of most MDV lakes to some extent, creating shallow "moats" that seasonally alternate between ice free and frozen.…”

The role of biology in planetary evolution: cyanobacterial primary production in low‐oxygen Proterozoic oceans

“…However, microbial fossils older than ∼2.5 Gyr are both rare and potentially obscured by multiple generations of geologic events, and linking them to specific metabolisms or taxonomic groups remains difficult. Furthermore, the biogenicity of stromatolites and microbially induced sedimentary structures dating to the Archean are still controversial (Bosak et al ., ) and these structures rarely contain definitive microbial body fossils (Mackey et al ., ). In addition, recent analyses indicate that previously sampled Archean sedimentary rocks host biomarker contaminants accumulated during sample collection and processing and overmature hydrocarbons (French et al ., ).…”

Microbial carbonation in natural and engineered environments

“…Studying microbial carbonation in dissimilar environments provides an opportunity to appreciate the ubiquitous nature of this biogeochemical process. It occurs in fresh and salt water environments, in aquatic and terrestrial habitats, and in polar and tropical climates Andersen et al, 2011;Braissant et al, 2003;Dittrich et al, 2003;Gerard et al, 2013;Mackey et al, 2015;Sumner et al, 2016;. As a subset of this range of possibilities, the Heron Island beachrock represents a natural tropical marine environment that, due to its intertidal nature, is both aquatic and terrestrial, and hosts microbial calcium carbonate mineral precipitation.…”