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1. Physical and Biological Controls of the Drake Passage pCO ₂ Variability

   https://doi.org/10.1029/2020GB006644  

   Jersild, Annika; Ito, Takamitsu (September 2020, Global Biogeochemical Cycles)

   The Southern Ocean is an important region of ocean carbon uptake, and observations indicate its air‐sea carbon flux fluctuates from seasonal to decadal timescales. Carbon fluxes at regional scales remain highly uncertain due to sparse observation and intrinsic complexity of the biogeochemical processes. The objective of this study is to better understand the mechanisms influencing variability of carbon uptake in the Drake Passage. A regional circulation and biogeochemistry model is configured at the lateral resolution of 10 km, which resolves larger mesoscale eddies where the typical Rossby deformation radius is(50 km). We use this model to examine the interplay between mean and eddy advection, convective mixing, and biological carbon export that determines the surface dissolved inorganic carbon and partial pressure of carbon dioxide variability. Results are validated against in situ observations, demonstrating that the model captures general features of observed seasonal to interannual variability. The model reproduces the two major fronts: Polar Front (PF) and Subantarctic Front (SAF), with locally elevated level of eddy kinetic energy and lateral eddy carbon flux, which play prominent roles in setting the spatial pattern, mean state and variability of the regional carbon budget. The uptake of atmospheric CO₂, vertical entrainment during cool seasons, and mean advection are the major carbon sources in the upper 200 m of the region. These sources are balanced by the biological carbon export during warm seasons and mesoscale eddy transfer. Comparing the induced advective carbon fluxes, mean flow dominates in magnitude, however, the amplitude of variability is controlled by the eddy flux. 

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2. Synthetic Cluster Models of Biological and Heterogeneous Manganese Catalysts for O ₂ Evolution

   https://doi.org/10.1021/ic402236f  

   Tsui, Emily Y.; Kanady, Jacob S.; Agapie, Theodor (December 2013, Inorganic Chemistry)
3. Chitosan as a Canvas for Studies of Macromolecular Controls on CaCO ₃ Biological Crystallization

   https://doi.org/10.1021/acs.biomac.2c01394  

   Knight, Brenna M.; Edgar, Kevin J.; De Yoreo, James J.; Dove, Patricia M. (March 2023, Biomacromolecules)
4. Triple oxygen isotope constraints on atmospheric O ₂ and biological productivity during the mid-Proterozoic

   https://doi.org/10.1073/pnas.2105074118  

   Liu, Peng; Liu, Jingjun; Ji, Aoshuang; Reinhard, Christopher T.; Planavsky, Noah J.; Babikov, Dmitri; Najjar, Raymond G.; Kasting, James F. (December 2021, Proceedings of the National Academy of Sciences)

   Reconstructing the history of biological productivity and atmospheric oxygen partial pressure ( p O 2 ) is a fundamental goal of geobiology. Recently, the mass-independent fractionation of oxygen isotopes (O-MIF) has been used as a tool for estimating p O 2 and productivity during the Proterozoic. O-MIF, reported as Δ′ 17 O, is produced during the formation of ozone and destroyed by isotopic exchange with water by biological and chemical processes. Atmospheric O-MIF can be preserved in the geologic record when pyrite (FeS 2 ) is oxidized during weathering, and the sulfur is redeposited as sulfate. Here, sedimentary sulfates from the ∼1.4-Ga Sibley Formation are reanalyzed using a detailed one-dimensional photochemical model that includes physical constraints on air–sea gas exchange. Previous analyses of these data concluded that p O 2 at that time was <1% PAL (times the present atmospheric level). Our model shows that the upper limit on p O 2 is essentially unconstrained by these data. Indeed, p O 2 levels below 0.8% PAL are possible only if atmospheric methane was more abundant than today (so that p CO 2 could have been lower) or if the Sibley O-MIF data were diluted by reprocessing before the sulfates were deposited. Our model also shows that, contrary to previous assertions, marine productivity cannot be reliably constrained by the O-MIF data because the exchange of molecular oxygen (O 2 ) between the atmosphere and surface ocean is controlled more by air–sea gas transfer rates than by biological productivity. Improved estimates of p CO 2 and/or improved proxies for Δ′ 17 O of atmospheric O 2 would allow tighter constraints to be placed on mid-Proterozoic p O 2 . 

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5. OsO ₂ as the Contrast‐Generating Chemical Species of Osmium‐Stained Biological Tissues in Electron Microscopy

   https://doi.org/10.1002/cbic.202400311  

   Li, Ruiyu; Wildenberg, Gregg; Boergens, Kevin; Yang, Yingjie; Weber, Kassandra; Rieger, Janek; Arcidiacono, Ashley; Klie, Robert; Kasthuri, Narayanan; King, Sarah_B (September 2024, ChemBioChem)

   Abstract Electron imaging of biological samples stained with heavy metals has enabled visualization of subcellular structures critical in chemical‐, structural‐, and neuro‐biology. In particular, osmium tetroxide (OsO₄) has been widely adopted for selective lipid imaging. Despite the ubiquity of its use, the osmium speciation in lipid membranes and the process for contrast generation in electron microscopy (EM) have continued to be open questions, limiting efforts to improve staining protocols and therefore high‐resolution nanoscale imaging of biological samples. Following our recent success using photoemission electron microscopy (PEEM) to image mouse brain tissues with synaptic resolution, we have used PEEM to determine the nanoscale electronic structure of Os‐stained biological samples. Os(IV), in the form of OsO₂, generates nanoaggregates in lipid membranes, leading to a strong spatial variation in the electronic structure and electron density of states. OsO₂has a metallic electronic structure that drastically increases the electron density of states near the Fermi level. Depositing metallic OsO₂in lipid membranes allows for strongly enhanced EM signals and conductivity of biological materials. The identification of the chemical species and understanding of the membrane contrast mechanism of Os‐stained biological specimens provides a new opportunity for the development of staining protocols for high‐resolution, high‐contrast EM imaging. 

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