02426nas a2200241   4500008004100000022001400041245010000055210006900155260001200224490000800236520166500244653001501909653001701924653002901941653002401970653002201994653001902016100002202035700002202057700001502079700002102094856006902115       2025                        eng d  a2169-895300aMorphology and distribution of bubble-supported microbial mats from ice-covered Antarctic lakes0 aMorphology and distribution of bubblesupported microbial mats fr  c03/20250 v1303 a<p>Gas bubbles directly influence the macromorphology of benthic microbial mats resulting in preservable biosedimentary structures. This study characterizes the morphology and distribution of microbial mats growing in gas-supersaturated, perennially ice-covered lakes Fryxell, Joyce, and Hoare of the McMurdo Dry Valleys of Antarctica. Photosynthetic benthic mats within the gas-supersaturated zone trap oxygen-rich bubbles and become buoyant, tearing off the bottom as &ldquo;liftoff mats.&rdquo; These liftoff mats form a succession of morphologies starting with bubble-induced deformation of flat mats into tent, ridge, and finger liftoff mat. With progressive deformation, mats tear, forming sheet liftoff, while multiple cycles of deformation and tearing transform sheet into strip liftoff. Some mats detach from the substrate and float to the underside of the ice. The depth range of the liftoff zone has varied over time at each lake. Downslope expansion of bubble formation brings previously bubble-free, deep-water pinnacle mats into the liftoff zone. When the liftoff zone shallows, liftoff mats at the deeper end deflate and can become scaffolding for additional mat growth. The superposition and relative orientation of liftoff and pinnacle mats can be used to track the maximum depth of the liftoff zone and changes in gas saturation state in these lakes through time. Our results demonstrate that gas bubbles, even when they are transitory, can exert a significant impact on the morphology of microbial mats at larger scales. This provides a way to identify similar structures and gas supersaturated environments in the biosedimentary record.</p>10aAntarctica10abiosediments10abubble-driven morphology10agas-supersaturation10aice-covered lakes10amicrobial mats1 aJuarez-Rivera, M.1 aMackey, Tyler, J.1 aHawes, Ian1 aSumner, Dawn, Y.  uhttps://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024JG00851603274nas a2200313   4500008004100000245011700041210006900158260001200227300001100239490000700250520227300257653001502530653002502545653001802570653002702588653002802615653002302643653001902666100002202685700002802707700002302735700002302758700002502781700002202806700002202828700001502850700002302865856007202888       2022                        eng d00aLipid biomarkers from microbial mats on the McMurdo Ice Shelf, Antarctica: Signatures for life in the cryosphere0 aLipid biomarkers from microbial mats on the McMurdo Ice Shelf An  c06/2022  a9036210 v133 a<p>Persistent cold temperatures, a paucity of nutrients, freeze-thaw cycles, and the strongly seasonal light regime make Antarctica one of Earth&rsquo;s least hospitable surface environments for complex life. Cyanobacteria, however, are well-adapted to such conditions and are often the dominant primary producers in Antarctic inland water environments. In particular, the network of meltwater ponds on the &lsquo;dirty ice&rsquo; of the McMurdo Ice Shelf is an ecosystem with extensive cyanobacteria-dominated microbial mat accumulations. This study investigated intact polar lipids (IPLs), heterocyte glycolipids (HGs), and bacteriohopanepolyols (BHPs) in combination with 16S and 18S rRNA gene diversity in microbial mats of twelve ponds in this unique polar ecosystem. To constrain the effects of nutrient availability, temperature and freeze-thaw cycles on the lipid membrane composition, lipids were compared to stromatolite-forming cyanobacterial mats from ice-covered lakes in the McMurdo Dry Valleys as well as from (sub)tropical regions and hot springs. The 16S rRNA gene compositions of the McMurdo Ice Shelf mats confirm the dominance of Cyanobacteria and Proteobacteria while the 18S rRNA gene composition indicates the presence of Ochrophyta, Chlorophyta, Ciliophora, and other microfauna. IPL analyses revealed a predominantly bacterial community in the meltwater ponds, with archaeal lipids being barely detectable. IPLs are dominated by glycolipids and phospholipids, followed by aminolipids. The high abundance of sugar-bound lipids accords with a predominance of cyanobacterial primary producers. The phosphate-limited samples from the (sub)tropical, hot spring, and Lake Vanda sites revealed a higher abundance of aminolipids compared to those of the nitrogen-limited meltwater ponds, affirming the direct affects that N and P availability have on IPL compositions. The high abundance of polyunsaturated IPLs in the Antarctic microbial mats suggests that these lipids provide an important mechanism to maintain membrane fluidity in cold environments. High abundances of HG keto-ols and HG keto-diols, produced by heterocytous cyanobacteria, further support these findings and reveal a unique distribution compared to those from warmer climates.</p>10aAntarctica10abacteriohopanepolyol10acyanobacteria10aheterocyte glycolipids10ahomeoviscous adaptation10aintact polar lipid10amicrobial mats1 aEvans, Thomas, W.1 aKalambokidis, Maria, J.1 aJungblut, Anne, D.1 aMillar, Jasmin, L.1 aBauersachs, Thorsten1 aGrotheer, Hendrik1 aMackey, Tyler, J.1 aHawes, Ian1 aSummons, Roger, E.  uhttps://www.frontiersin.org/articles/10.3389/fmicb.2022.903621/full