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  1. Marine gateways play a critical role in the exchange of water, heat, salt, and nutrients between oceans and seas. Changes in gateway geometry can significantly alter both the pattern of global ocean circulation and climate. Today, the volume of dense water supplied by Atlantic–Mediterranean exchange through the Gibraltar Strait is among the largest in the global ocean. For the past 5 My, this overflow has generated a saline plume at intermediate depths in the Atlantic that deposits distinctive contouritic sediments and contributes to the formation of North Atlantic Deep Water. This single gateway configuration only developed in the Early Pliocene. During the Miocene, two narrow corridors linked the Mediterranean and Atlantic: one in northern Morocco and the other in southern Spain. Formation of these corridors followed by progressive restriction and closure resulted in extreme salinity fluctuations in the Mediterranean, leading to the precipitation of the Messinian Salinity Crisis salt giant. International Ocean Discovery Program (IODP) Expedition 401 is the offshore drilling component of a Land-2-Sea drilling proposal, Investigating Miocene Mediterranean–Atlantic Gateway Exchange (IMMAGE). Its aim is to recover a complete record of Atlantic–Mediterranean exchange from its Late Miocene inception to its current configuration by targeting Miocene offshore sediments on either side of the Gibraltar Strait. Miocene cores from the two precursor connections now exposed on land will be obtained by future International Continental Scientific Drilling Program (ICDP) campaigns. 
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    Free, publicly-accessible full text available April 30, 2025
  2. The western South Atlantic Ocean has not been drilled since the end of the Deep Sea Drilling Program, leading to a dearth of sedimentary sequences available from this sector of the Atlantic Ocean. In 2020–2022, a transect of new sites was drilled during International Ocean Discovery Program Expeditions 390C, 395E, 390, and 393 at 31°S and spanning from 28.8°W to 15.2°W. Here, we use X-ray fluorescence data, combined with shipboard magnetic susceptibility and natural gamma radiation, to characterize the sediments below the oligotrophic South Atlantic Gyre at Site U1583. These geochemical data add to the otherwise understudied southwest Atlantic Ocean. 
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    Free, publicly-accessible full text available April 5, 2025
  3. Marine gateways play a critical role in the exchange of water, heat, salt, and nutrients between oceans and seas. The advection of dense waters helps drive global thermohaline circulation, and because the ocean is the largest of the rapidly exchanging CO2 reservoirs, this advection also affects atmospheric carbon concentration. Changes in gateway geometry can therefore significantly alter both the pattern of global ocean circulation and associated heat transport and climate, as well as having a profound local impact. Today, the volume of dense water supplied by Atlantic–Mediterranean exchange through the Gibraltar Strait is amongst the largest in the global ocean. For the past 5 My, this overflow has generated a saline plume at intermediate depths in the Atlantic that deposits distinctive contouritic sediments in the Gulf of Cadiz and contributes to the formation of North Atlantic Deep Water. This single gateway configuration only developed in the early Pliocene, however. During the Miocene, a wide, open seaway linking the Mediterranean and Atlantic evolved into two narrow corridors: one in northern Morocco, the other in southern Spain. Formation of these corridors permitted Mediterranean salinity to rise and a new, distinct, dense water mass to form and overspill into the Atlantic for the first time. Further restriction and closure of these connections resulted in extreme salinity fluctuations in the Mediterranean, leading to the formation of the Messinian Salinity Crisis salt giant. Investigating Miocene Mediterranean–Atlantic Gateway Exchange (IMMAGE) is an amphibious drilling proposal designed to recover a complete record of Atlantic–Mediterranean exchange from its Late Miocene inception to its current configuration. This will be achieved by targeting Miocene offshore sediments on either side of the Gibraltar Strait during International Ocean Discovery Program (IODP) Expedition 401 and recovering Miocene core from the two precursor connections now exposed on land with future International Continental Scientific Drilling Program (ICDP) campaigns. The scientific aims of IMMAGE are to constrain quantitatively the consequences for ocean circulation and global climate of the inception of Atlantic–Mediterranean exchange, to explore the mechanisms for high-amplitude environmental change in marginal marine systems, and to test physical oceanographic hypotheses for extreme high-density overflow dynamics that do not exist in the world today on this scale. 
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  4. Free, publicly-accessible full text available October 1, 2024
  5. This presentation will describe conditions for the use of oxygen as a reagent for the selective cleavage of thermoset composites. Carbon fiber-reinforced polymer (CFRP) composites have a prominent role in aviation, sporting goods, marine, and other manufacturing sectors and are accumulating en masse as waste, both at end-of-life and as manufacturing defects. We have recently introduced a method to use oxygen itself along with an appropriate catalyst selectively to disassemble such fully-cured composite wastes to recover both ordered carbon fiber sheets and organic materials suitable for re-manufacturing of second-life resin systems. 
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  6. ABSTRACT

    The low-J rotational transitions of 12CO are commonly used to trace the distribution of molecular gas in galaxies. Their ratios are sensitive to excitation and physical conditions in the molecular gas. Spatially resolved studies of CO ratios are still sparse and affected by flux calibration uncertainties, especially since most do not have high angular resolution or do not have short-spacing information and hence miss any diffuse emission. We compare the low-J CO ratios across the disc of two massive, star-forming spiral galaxies NGC 2903 and NGC 3627 to investigate whether and how local environments drive excitation variations at GMC scales. We use Atacama Large Millimeter Array (ALMA) observations of the three lowest-J CO transitions at a common angular resolution of 4 arcsec (190 pc). We measure median line ratios of $R_{21}=0.67^{+0.13}_{-0.11}$, $R_{32}=0.33^{+0.09}_{-0.08}$, and $R_{31}=0.24^{+0.10}_{-0.09}$ across the full disc of NGC 3627. We see clear CO line ratio variation across the galaxy consistent with changes in temperature and density of the molecular gas. In particular, towards the centre, R21, R32, and R31 increase by 35  per cent, 50  per cent, and 66  per cent, respectively, compared to their average disc values. The overall line ratio trends suggest that CO(3–2) is more sensitive to changes in the excitation conditions than the two lower J transitions. Furthermore, we find a similar radial R32 trend in NGC 2903, albeit a larger disc-wide average of $\langle R_{32}\rangle =0.47^{+0.14}_{-0.08}$. We conclude that the CO low-J line ratios vary across environments in such a way that they can trace changes in the molecular gas conditions, with the main driver being changes in temperature.

     
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  7. Nitrogen hydrides such as NH3 and N2H+ are widely used by Galactic observers to trace the cold dense regions of the interstellar medium. In external galaxies, because of limited sensitivity, HCN has become the most common tracer of dense gas over large parts of galaxies. We provide the first systematic measurements of N2H+ (1-0) across different environments of an external spiral galaxy, NGC 6946. We find a strong correlation (r > 0.98, p < 0.01) between the HCN (1-0) and N2H+ (1-0) intensities across the inner ∼8 kpc of the galaxy, at kiloparsec scales. This correlation is equally strong between the ratios N2H+ (1-0)/CO (1-0) and HCN (1-0)/CO (1-0), tracers of dense gas fractions (fdense). We measure an average intensity ratio of N2H+ (1-0)/HCN (1-0) = 0.15 ± 0.02 over our set of five IRAM-30m pointings. These trends are further supported by existing measurements for Galactic and extragalactic sources. This narrow distribution in the average ratio suggests that the observed systematic trends found in kiloparsec-scale extragalactic studies of fdense and the efficiency of dense gas (SFEdense) would not change if we employed N2H+ (1-0) as a more direct tracer of dense gas. At kiloparsec scales our results indicate that the HCN (1-0) emission can be used to predict the expected N2H+ (1-0) over those regions. Our results suggest that, even if HCN (1-0) and N2H+ (1-0) trace different density regimes within molecular clouds, subcloud differences average out at kiloparsec scales, yielding the two tracers proportional to each other. 
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    Free, publicly-accessible full text available August 1, 2024
  8. The South Atlantic Transect (SAT) is a multidisciplinary scientific ocean drilling project that will recover complete sedimentary sections and the upper ~250 m of the underlying oceanic crust along a slow/intermediate spreading rate Mid-Atlantic Ridge crustal flow line at ~31°S. These cores were originally scheduled to be collected during International Ocean Discovery Program (IODP) Expeditions 390 and 393 in October–December 2020 and April–June 2021, respectively. In 2020 and 2021, the global COVID-19 pandemic resulted in the postponement of several IODP expeditions, including Expeditions 390 and 393, chiefly because science parties were unable to travel to the R/V JOIDES Resolution. In response, the ship was used to conduct preparatory work for the postponed expeditions that did not require a science party aboard but could be carried out by the ship’s crew and a team of technicians from the JOIDES Resolution Science Operator. Two of these expeditions (390C and 395E) were in service of the SAT drilling project, to reduce the operational risks and expedite basement drilling during the rescheduled Expeditions 390 and 393. Expeditions 390C and 395E visited five of the six primary SAT sites and successfully cored a single advanced piston corer/extended core barrel hole penetrating the entire sediment section and <10 m into the underlying basalt before installing a reentry system in a second hole at each site visited. Given these accomplishments, the operations plans for the rescheduled Expeditions 390 and 393 have been revised. 
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