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The alkalinity dynamics in coastal environments play a crucial role in controlling the global burial of carbonate minerals and the ocean's capacity to sequester anthropogenic CO2. This study presents results from high vertical resolution profiles obtained during two summers in the temperate Chesapeake Bay estuary, enabling detailed investigation of carbonate dynamics over salinity and redox gradients, along with measurement of the speciation of most redox-sensitive elements. Under oxygen-rich conditions, carbonate dissolution, primary production and aerobic respiration explain the evolution of total alkalinity (TA) versus dissolved inorganic carbon (DIC), once adjusted for fresh and oceanic water mixing. A significant flooding event in 2018 promoted carbonate dissolution. In oxygen-depleted waters, we observed a previously unreported 2.4 mol increase in DIC per 1 mol of TA production, which was consistent over the 2 years. Stoichiometric changes suggest that MnO2 reduction followed by Mn carbonate precipitation is responsible for this characteristic carbonate signature, likely produced in sediment pore water and then transferred to the water column along with other by-products of anoxic respiration at the onset of summer. Our findings highlight the critical role of Mn in alkalinity dynamics in the Chesapeake Bay and potentially other river-dominated environments where it can limit H2S oxidation to SO42- and promote sulfur burial. [ABSTRACT FROM AUTHOR]

We measured the speciation of dissolved Mn from the surface to just above the hydrothermal vents at 9°50′N East Pacific Rise in the open ocean of the Pacific over a 3‐week period. Total dissolved Mn concentrations ranged from 2.2 to 135 nmol L−1 with a significant contribution of dissolved Mn(III) bound to humic acid in one third of our samples representing up to 64% of the total dissolved Mn. These humic complexes were mostly detected in the hydrothermal vent plume and at the redox boundaries of the oxygen minimum zone in the water column. In the hydrothermal plume, the Mn(III)‐humic acid stabilized the manganese in solution up to a ~ 10,000‐fold dilution of the venting water. In the upper water column, Mn(III)‐humic acid was only detected after a squall and rain event, which indicates that it is a transient species, persistent over days to weeks. This temporal variability highlights the importance of non‐steady‐state processes in the open ocean, which may help to explain previous observations of a dissolved Mn maximum within oceanic oxygen minimum zones. [ABSTRACT FROM AUTHOR]

The coastal alkalinity cycle controls the global burial of carbonate which modulates the ability of the ocean to trap anthropogenic CO2. Twelve high vertical resolution profiles from the temperate Chesapeake Bay estuary during two summers allow precise description of carbonate dynamics over the salinity and redox gradient along with the measurement of speciation of most redox sensitive elements. In the presence of oxygen, carbonate dissolution, primary production and aerobic respiration are able to explain the evolution of total alkalinity (TA) versus dissolved inorganic carbon (DIC), once corrected for fresh and oceanic water mixing. A significant flooding event in 2018 prevented the trapping of atmospheric CO2 the estuary and favoured carbonate dissolution to balance DIC consumption from photosynthesis. In oxygen depleted waters, particularly high ratio of alkalinity versus DIC occurred (ΔTAex/ΔDICex = 2.4), that has not been previously reported in the literature, and that seemed invariant over the two years. The stoichiometric analysis agrees with Mn measurements to explain carbonate signature by the critical role of MnO2 reduction followed by Mn carbonate precipitation. Our results underline that Fe and Mn are critical elements of the alkalinity cycle, especially due to their ability to limit the H2S oxidation into SO4 2-by favouring sulphur burial. [ABSTRACT FROM AUTHOR]

The isolation of a number of diverse spore-forming manganese(II)-oxidizing Bacillus species from Guaymas Basin, a deep-sea hydrothermal vent environment in the Gulf of California, is reported. The growth and Mn(II) oxidation properties of these Bacillus species have shown that in hydrothermal sediments they are likely present as spores that are active in oxidizing Mn(II) as it emerges from the seafloor.

Bacterial Mn(II) oxidization by spores of Bacillus, sp. strain SG-I has been systematically probed over the time scale 0.22 to 77 days under in-situ conditions and at differing Mn(II) concentrations. Three complementary techniques, K-edge X-ray absorption near-edge spectroscopy (XANES), X-ray emission spectroscopy (XES), and in-situ synchrotron radiation-based X-ray diffraction (SR-XRD). have been utilized to examine time-dependent changes in Mn oxidation state, local-, and long-range structure in amorphous, crystalline, cell-bound, and solute Mn species. The primary solid biogenic product of Mn(II) oxidation is an X-ray amorphous oxide similar to [delta]-Mn[O.sub.2], which has a Mn oxidation state between 3.7 and 4.0. Reaction of Mn(II) with the primary biogenic oxide results in the production of abiotic secondary products, feitknechtite or a 10 A Na phyllomanganate. The identity of the secondary product depends upon the Mn(II) concentration as described by thermodynamic relations. A decrease in the dissolved Mn(II) concentration is followed by mineralogic transformation of the secondary products. Thus, Mn(II) appears to act as a reductant toward the biogenic oxide and to control the stability of secondary reaction products. Mineralogic changes similar to these are likely to be commonplace in natural settings where bacterial Mn(II) oxidation is occurring and may liberate sorbed metal ions or alter the rates of important Mn oxide surface-mediated processes such as the degradation of organic molecules. It is plausible that microbes may exploit such mineral transformation reactions to indirectly control specific chemical conditions in the vicinity of the cell.

The role of CumA in Mn(II) oxidation without the complications arising from polarity is assessed by generating an in-frame deletion of cumA and the ability of the resulting [DELTA]cumA strain to form Mn(IV) oxides is tested. The results have shown that cumA is dispensable for Mn(II) oxidation and have disclosed a complex two-component regulatory pathway required for Mn(II) oxidation in Pseudomonas putida GB-1.