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  1. Data related to collaborative study of fluid rock interaction in the Nicobar Fan sampled at Sites 1480 and 1481 during IODP Expedition 362 off Sumatra 
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  2. null (Ed.)
  3. Abstract

    We use geochemical and petrographic data from anoxic sequences of the Nicobar Fan to document extensive marine silicate weathering (MSiW) in the input sediment of the Sumatra subduction zone and the conditions that result in authigenic minerals originating from this reaction: precipitation of authigenic carbonate—which sequesters carbon—and formation of authigenic clay—which releases CO2. Increase in87Sr/86Sr in pore fluids from International Ocean Discovery Program Expedition 362 (Site U1480 to 0.71376 and Site U1481 to 0.71296) reveals a radiogenic strontium contribution from alteration of the Himalayan continental sediment that dominates the Nicobar Fan. Peaks in the dissolved strontium isotope data coincide with zones of methane presence, consistent with MSiW reactions driven by CO2generation during methanogenesis. Later‐stage fan sequences from 24 to 400 mbsf (meters below seafloor) contain only minor carbonate with87Sr/86Sr ratios that deviate only slightly from the co‐eval seawater values (0.70920–0.70930); geochemical data in this zone point to a contribution of authigenic clay formation. In contrast, microscopy and elemental mapping of the carbonate‐cemented zones in the earliest fan deposits (>780 mbsf) show replacement of feldspars and dense minerals by carbonate, which ranges in volume from a few percent of the grain to near total grain obliteration. This deeper authigenic carbonate is significantly enriched in radiogenic87Sr (0.71136–0.71328). Thus, MSiW leads to distinct products, likely in response to a weathering‐derived supply of silica in the younger setting versus calcium enrichment via diffusion from oceanic basement in the older sequence.

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  4. Korea Polar Research Institute (KOPRI) installed an ionospheric sounding radar system called Vertical Incidence Pulsed Ionospheric Radar (VIPIR) at Jang Bogo Station (JBS) in 2015 in order to routinely monitor the state of the ionosphere in the auroral oval and polar cap regions. Since 2017, after two-year test operation, it has been continuously operated to produce various ionospheric parameters. In this article, we will introduce the characteristics of the JBS-VIPIR observations and possible applications of the data for the study on the polar ionosphere. The JBS-VIPIR utilizes a log periodic transmit antenna that transmits 0.5–25 MHz radio waves, and a receiving array of 8 dipole antennas. It is operated in the Dynasonde B-mode pulse scheme and utilizes the 3-D inversion program, called NeXtYZ, for the data acquisition and processing, instead of the conventional 1-D inversion procedure as used in the most of digisonde observations. The JBS-VIPIR outputs include the height profiles of the electron density, ionospheric tilts, and ion drifts with a 2-minute temporal resolution in the bottomside ionosphere. With these observations, possible research applications will be briefly described in combination with other observations for the aurora, the neutral atmosphere and the magnetosphere simultaneously conducted at JBS. 
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  6. N,N-Diborylamines have emerged as promising reagents in organic synthesis; however, their efficient preparation and full synthetic utility have yet to be realized. To address both shortcomings, an effective catalyst for nitrile dihydroboration was sought. Heating CoCl2 in the presence of PyEtPDI afforded the six-coordinate Co(II) salt, [(PyEtPDI)CoCl][Cl]. Upon adding 2 equiv of NaEt3BH, hydride transfer to one chelate imine functionality was observed, resulting in the formation of (κ4-N,N,N,N-PyEtIPCHMeNEtPy)Co. Single-crystal X-ray diffraction and density functional theory calculations revealed that this compound possesses a low-spin Co(II) ground state featuring antiferromagnetic coupling to a singly reduced imino(pyridine) moiety. Importantly, (κ4-N,N,N,N-PyEtIPCHMeNEtPy)Co was found to catalyze the dihydroboration of nitriles using HBPin with turnover frequencies of up to 380 h–1 at ambient temperature. Stoichiometric addition experiments revealed that HBPin adds across the Co–Namide bond to generate a hydride intermediate that can react with additional HBPin or nitriles. Computational evaluation of the reaction coordinate revealed that the B–H addition and nitrile insertion steps occur on the antiferromagnetically coupled triplet spin manifold. Interestingly, formation of the borylimine intermediate was found to occur following BPin transfer from the borylated chelate arm to regenerate (κ4-N,N,N,N-PyEtIPCHMeNEtPy)Co. Borylimine reduction is in turn facile and follows the same ligand-assisted borylation pathway. The independent hydroboration of alkyl and aryl imines was also demonstrated at 25 °C. With a series of N,N-diborylamines in hand, their addition to carboxylic acids allowed for the direct synthesis of amides at 120 °C, without the need for an exogenous coupling reagent. 
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