Correction factors for δ 18 O-derived global sea surface temperature reconstructions from diagenetically altered intervals of coral skeletal density banding

Reconstruction of sea surface temperature (SST) from the δ18O and Sr/Ca composition of coral skeletal density banding (CSDB), identified with x-ray diffraction and micro computed tomography, provides invaluable centuries-long records of ocean circulation and climate change. Comparison with age-equivalent instrument measurements of SST over the last 125 years has proven these δ18O-derived SST reconstructions to be generally reliable. However, notable exceptions occur within discrete CSDB stratigraphic intervals that yield δ18O-derived SST underestimates of as much as 9°C with respect to instrument measured SST. Here we combine high-resolution optical and electron microscopy with geochemical modeling to establish correction factors for the impact of marine seafloor physical, chemical, and biological alteration (diagenesis) within these altered intervals of CSDB stratigraphy. Four cores were collected from Porites coral heads across a 4-24 m water depth bathymetric transect at Myrmidon Reef, Great Barrier Reef, Australia. Precise mapping of diagenetic aragonite cementation was completed within CSDB patterns digitally overlaid on 35 petrographic thin sections fully covering 2.1 m of core. The vast majority of core skeletal material exhibited little to no diagenetic aragonite cementation. However, extensive diagenetic alteration was observed within discrete CSDB intervals near the base of the two deeper water Porites heads. This diagenesis serves to modify skeletal density and CSDB stratigraphy in these intervals, as well as structurally reinforce the coral skeleton. Reliable δ18O-based SST correction factors for these diagenetically altered CSDB intervals are established here by applying the percent mixing of diagenetic aragonite cement to a binary mixing model. This approach, with quantitative extents of mixing established with both microscopy and existing globally distributed coral δ18O and Sr/Ca data sets, accurately restores modern and fossil coral δ18O-derived SST records. Results indicate that as little as 5% mixing of diagenetic aragonite cement with original coral skeleton will cause δ18O-based SST anomalies of 0.9°C

Corals regulate the distribution and abundance of Symbiodiniaceae and biomolecules in response to changing water depth and sea surface temperature

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Sivaguru, M., Todorov, L. G., Fouke, C. E., Munro, C. M. O., Fouke, K. W., Fouke, K. E., Baughman, M. E., & Fouke, B. W. Corals regulate the distribution and abundance of Symbiodiniaceae and biomolecules in response to changing water depth and sea surface temperature. Scientific Reports, 11(1), (2021): 2230, https://doi.org/10.1038/s41598-021-81520-0.The Scleractinian corals Orbicella annularis and O. faveolata have survived by acclimatizing to environmental changes in water depth and sea surface temperature (SST). However, the complex physiological mechanisms by which this is achieved remain only partially understood, limiting the accurate prediction of coral response to future climate change. This study quantitatively tracks spatial and temporal changes in Symbiodiniaceae and biomolecule (chromatophores, calmodulin, carbonic anhydrase and mucus) abundance that are essential to the processes of acclimatization and biomineralization. Decalcified tissues from intact healthy Orbicella biopsies, collected across water depths and seasonal SST changes on Curaçao, were analyzed with novel autofluorescence and immunofluorescence histology techniques that included the use of custom antibodies. O. annularis at 5 m water depth exhibited decreased Symbiodiniaceae and increased chromatophore abundances, while O. faveolata at 12 m water depth exhibited inverse relationships. Analysis of seasonal acclimatization of the O. faveolata holobiont in this study, combined with previous reports, suggests that biomolecules are differentially modulated during transition from cooler to warmer SST. Warmer SST was also accompanied by decreased mucus production and decreased Symbiodiniaceae abundance, which is compensated by increased photosynthetic activity enhanced calcification. These interacting processes have facilitated the remarkable resiliency of the corals through geological time.Financial support for this work was provided by the Office of Naval Research (N00014-00-1-0609), the Illinois Carl R. Woese Institute for Genomic Biology Undergraduate Summer Research Fellowship, the Illinois Carl R. Woese Institute for Genomic Biology Mark Tracy Fellowship for Translational Research, and the Illinois Department of Molecular and Cellular Biology Jenner Family Summer Research Fellowship and the Edward and Barbara Weil Research Fund provided to the University of Illinois Urbana-Champaign

Depositional and diagenetic history of travertine deposited within the Anio Novus aqueduct of ancient Rome

Travertine deposits preserved within ancient aqueduct channels record information about the hydrology, temperature, and chemistry of the flowing water from which they precipitated. However, travertine is also chemically reactive and susceptible to freshwater diagenesis, which can alter its original composition and impact reconstructions of aqueduct operation, maintenance, and climate. Hydraulic reconstructions, in combination with a suite of high-resolution optical, laser, electron, and X-ray microscopy analyses, have been used to determine the original crystalline structure and diagenetic alteration of travertine deposited in the Anio Novus aqueduct built in A.D. 38–52 at Roma Vecchia. Age-equivalent travertine deposits, precipitated directly on the mortar-covered floor at upstream and downstream sites along a 140-m-long continuous section of the Anio Novus channel, exhibit consistent crystalline textures and stratigraphic layering. This includes aggrading, prograding, and retrograding sets of travertine linguoid, sinuous, and hummocky crystal growth ripples, as well as sand lags with coated siliciclastic grains deposited on the lee slope of ripple crests. The original aqueduct travertine, which is similar to travertine formed in analogous natural environments, is composed of shrub-like, dendritically branching aggregates of 1–3-μm-diameter euhedral calcite crystals. Dark brown organic matter-rich laminae, formed by microbial biofilms and plant debris, create stratigraphic sequences of high-frequency, dark–light layering. This hydraulic and petrographic evidence suggests that large, radiaxial calcites diagenetically replaced the original aqueduct travertine shrubs, forming upward-branching replacement crystals that crosscut the biofilm laminae. While this diagenetic process destroyed the original crystalline fabric of the calcite shrubs, the entombed biofilm laminae were mimetically preserved. These integrated approaches create the type of depositional and diagenetic framework required for future chemostratigraphic analyses of travertine deposited in the Anio Novus and other ancient water conveyance and storage systems around the world, from which ancient human activity and climatic change can be more accurately reconstructed

Physiology, Metabolism, and Fossilization of Hot-Spring Filamentous Microbial Mats

The evolutionarily ancient Aquificales bacterium Sulfurihydrogenibium spp. dominates filamentous microbial mat communities in shallow, fast-flowing, and dysoxic hot-spring drainage systems around the world. In the present study, field observations of these fettuccini-like microbial mats at Mammoth Hot Springs in Yellowstone National Park are integrated with geology, geochemistry, hydrology, microscopy, and multi-omic molecular biology analyses. Strategic sampling of living filamentous mats along with the hot-spring CaCO3 (travertine) in which they are actively being entombed and fossilized has permitted the first direct linkage of Sulfurihydrogenibium spp. physiology and metabolism with the formation of distinct travertine streamer microbial biomarkers. Results indicate that, during chemoautotrophy and CO2 carbon fixation, the 87-98% Sulfurihydrogenibium-dominated mats utilize chaperons to facilitate enzyme stability and function. High-abundance transcripts and proteins for type IV pili and extracellular polymeric substances (EPSs) are consistent with their strong mucus-rich filaments tens of centimeters long that withstand hydrodynamic shear as they become encrusted by more than 5 mm of travertine per day. Their primary energy source is the oxidation of reduced sulfur (e.g., sulfide, sulfur, or thiosulfate) and the simultaneous uptake of extremely low concentrations of dissolved O2 facilitated by bd-type cytochromes. The formation of elevated travertine ridges permits the Sulfurihydrogenibium-dominated mats to create a shallow platform from which to access low levels of dissolved oxygen at the virtual exclusion of other microorganisms. These ridged travertine streamer microbial biomarkers are well preserved and create a robust fossil record of microbial physiological and metabolic activities in modern and ancient hot-spring ecosystems