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The photolytic reduction of amorphous iron hydroxide [am-Fe(OH)3], lepidocrocite ( -FeOOH), goethite (a-FeOOH), hematite (ct-FeaOsband natural iron-containing aerosol particles in the presence of formaldehyde, formate, acetate, oxalate, and butyrate has been investigated. Important parameters in the photoreduction experiments are the pH, wavelength of the irradiating light, nature of the electron donor, characteristics of the iron phase. The present results show that the fastest rates of photoreduction of Fe(III) to Fe(II) are achieved with am-Fe(OH)3 as the electron acceptor and formate as the electron donor.Maximum rates of photoreduction were observed at 330 nm with a continuous decrease to 405 nm. Natural ironcontaining aerosol particles show photochemical behavior similar to am-Fe(OH>3 and -FeOOH. These results suggest that a significant fraction of the reactive atmospheric iron in urban aerosol could be present as am-Fe-(OH)s and -FeOOH. Ambient iron-containing aerosol particles with oxalate as the electron donor resulted in a significant photochemical production of H2O2.

Climate change is driving an expansion of marine oxygen-deficient zones, which may alter the global cycles of carbon, sulfur, nitrogen, and trace metals. Currently, however, we lack a full mechanistic understanding of how oxygen deficiency affects organic carbon cycling and burial. Here, we show that cryptic microbial sulfate reduction occurs in sinking particles from the eastern tropical North Pacific oxygen-deficient zone and that some microbially produced sulfide reacts rapidly to form organic sulfur that is resistant to acid hydrolysis. Particle-hosted sulfurization could enhance carbon preservation in sediments underlying oxygen-deficient water columns and serve as a stabilizing feedback between expanding anoxic zones and atmospheric carbon dioxide. A similar mechanism may help explain more-extreme instances of organic carbon preservation associated with marine anoxia in Earth history.

Recent discoveries of nonintegumentary melanosomes in extant and fossil amphibians offer potential insights into the physiological functions of melanin not directly related to color production, but the phylogenetic distribution and evolutionary history of these internal melanosomes has not been characterized systematically. Here, we present a holistic method to discriminate among melanized tissues by analyzing the anatomical distribution, morphology, and chemistry of melanosomes in various tissues in a phylogenetically broad sample of extant and fossil vertebrates. Our results show that internal melanosomes in all extant vertebrates analyzed have tissue-specific geometries and elemental signatures. Similar distinct populations of preserved melanosomes in phylogenetically diverse vertebrate fossils often map onto specific anatomical features. This approach also reveals the presence of various melanosome-rich internal tissues in fossils, providing a mechanism for the interpretation of the internal anatomy of ancient vertebrates. Collectively, these data indicate that vertebrate melanins share fundamental physiological roles in homeostasis via the scavenging and sequestering of metals and suggest that intimate links between melanin and metal metabolism in vertebrates have deep evolutionary origins.