Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Micallef, A., Person, M., Berndt, C., Bertoni, C., Cohen, D., Dugan, B., Evans, R., Haroon, A., Hensen, C., Jegen, M., Key, K., Kooi, H., Liebetrau, V., Lofi, J., Mailloux, B. J., Martin-Nagle, R., Michael, H. A., Mueller, T., Schmidt, M., Schwalenberg, K., Trembath-Reichert, E., Weymer, B., Zhang, Y., & Thomas, A. T. Offshore freshened groundwater in continental margins. Reviews of Geophysics, 59(1), (2021): e2020RG000706, https://doi.org/10.1029/2020RG000706.

Description: First reported in the 1960s, offshore freshened groundwater (OFG) has now been documented in most continental margins around the world. In this review we compile a database documenting OFG occurrences and analyze it to establish the general characteristics and controlling factors. We also assess methods used to map and characterize OFG, identify major knowledge gaps, and propose strategies to address them. OFG has a global volume of 1 × 106 km3; it predominantly occurs within 55 km of the coast and down to a water depth of 100 m. OFG is mainly hosted within siliciclastic aquifers on passive margins and recharged by meteoric water during Pleistocene sea level lowstands. Key factors influencing OFG distribution are topography-driven flow, salinization via haline convection, permeability contrasts, and the continuity/connectivity of permeable and confining strata. Geochemical and stable isotope measurements of pore waters from boreholes have provided insights into OFG emplacement mechanisms, while recent advances in seismic reflection profiling, electromagnetic surveying, and numerical models have improved our understanding of OFG geometry and controls. Key knowledge gaps, such as the extent and function of OFG, and the timing of their emplacement, can be addressed by the application of isotopic age tracers, joint inversion of electromagnetic and seismic reflection data, and development of three-dimensional hydrological models. We show that such advances, combined with site-specific modeling, are necessary to assess the potential use of OFG as an unconventional source of water and its role in sub-seafloor geomicrobiology.

Description: This study has received funding from the European Research Council (ERC), under the European Union's Horizon 2020 research and innovation program (grant agreement No. 677898 (MARCAN) to A. M.) and the U.S. National Science Foundation (NSF FRES 1925974 to M. P.; NSF OCE 0824368 to B. D.; and NSF EAR 1151733 to H. A. M.). T. M., B. W. and Y. Z. were funded by the SMART project through the Helmholtz European Partnering Initiative (Project ID Number PIE-0004) involving GEOMAR and the University of Malta.

Description: ABSTRACT Hereditary hemochromatosis, which is characterized by inappropriately low levels of hepcidin, increased dietary iron uptake, and systemic iron accumulation, has been associated to mutations in the HFE, TfR2, or HJV genes. However, it is still not clear whether these molecules intersect in vivo with BMP6/SMAD signaling, the main pathway upregulating hepcidin expression in response to elevated hepatic iron. To answer this question, we produced mice double knockout for Bmp6 and β2-microglobulin (a surrogate for the loss of Hfe) and for Bmp6 and Tfr2, and we compared their phenotype (hepcidin expression, Bmp/Smad signaling, hepatic and extrahepatic tissue iron accumulation) with that of single Bmp6 -deficient mice and that of mice deficient for Hjv, alone or in combination with Hfe or Tfr2. Whereas the phenotype of Hjv -deficient females was not affected by loss of Hfe or Tfr2, that of Bmp6 -deficient females was considerably worsened, with decreased Smad5 phosphorylation, compared with single Bmp6 -deficient mice, further repression of hepcidin gene expression, undetectable serum hepcidin, and massive iron accumulation not only in the liver but also in the pancreas, the heart and the kidneys. Conclusion : These results show that (i) BMP6 does not require HJV to transduce signal to hepcidin in response to intracellular iron, even if the loss of HJV partly reduces this signal, (ii) another BMP ligand can replace BMP6 and significantly induce hepcidin expression in response to extracellular iron, and (iii) BMP6 alone is as efficient to induce hepcidin as the other BMP in association with the HJV/HFE/TfR2 complex. They provide an explanation for the compensatory effect of BMP6 treatment on the molecular defect underlying Hfe-hemochromatosis in mice. This article is protected by copyright. All rights reserved.

Description: Expression of phenol oxidases (PO) in bacteria is often observed during physiological and morphological changes; in the nitrogen-fixing strain Azotobacter chroococcum SBUG 1484, it is accompanied by the formation of encysted cells and melanin. Herein, we studied the effects of copper and the depletion of the nitrogenase-relevant metals molybdenum and iron on physiological characteristics such as culture pigmentation, release of ortho -dihydroxylated melanin precursors, and expression of PO activity in A. chroococcum . Biomass production and melanogenic appearance were directly affected by the depletion of either iron or molybdenum, or in the absence of both metals. Only nitrogen-fixing cells growing in the presence of both metals and cultures supplemented with iron (molybdenum starved) showed the ability to produce an intensively brown-black melanin pigment typically associated with A. chroococcum . Accordingly, PO production was only detected in the presence of both metals and in iron-supplemented cultures starved of molybdenum. The total amount of catecholate siderophores produced by nitrogen-fixing melanogenic cells was considerably higher than in cultures starved of metal ions. Induction of enhanced PO activity was stimulated by additional copper sulfate, possibly related to cellular processes involved in the detoxification of this particular metal, and revealed distinct release of the ortho -dihydroxylated melanin precursors catechol and 3,4-dihydroxybenzoic acid (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)