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Treatise of Geochemistry chapter 

A multiscale numerical framework has been developed to investigate the dispersion of deep-sea hydrothermal plumes that originate from the Endeavour Segment of the Juan de Fuca Ridge located in the Northeast Pacific. The analysis of simulation outputs presented in this study provides insights into the influences of tidal forcing and the buoyancy flux associated with hydrothermal venting on ocean circulation and plume dispersion in the presence of pronounced seafloor topography. The results indicate that tidal forcing drives anti-cyclonic circulation near the ridge-axis, while hydrothermal venting induces cyclonic circulation around vent fields within the axial rift valley. Tidal forcing has a notable impact on plume dispersion, particularly near the large topographic features to the north of the Endeavour Segment. Furthermore, plume dispersion exhibits notable inter-annual variability, with a northbound trajectory in 2016 and a southbound trajectory in 2021. The study also reveals that both buoyancy fluxes and tidal forcing enhance the mixing of hydrothermal plumes with ambient seawater. 

This paper reviews the scientific motivation and challenges, development, and use of underwater robotic vehicles designed for use in ice-covered waters, with special attention paid to the navigation systems employed for under-ice deployments. Scientific needs for routine access under fixed and moving ice by underwater robotic vehicles are reviewed in the contexts of geology and geophysics, biology, sea ice and climate, ice shelves, and seafloor mapping. The challenges of under-ice vehicle design and navigation are summarized. The paper reviews all known under-ice robotic vehicles and their associated navigation systems, categorizing them by vehicle type (tethered, untethered, hybrid, and glider) and by the type of ice they were designed for (fixed glacial or sea ice and moving sea ice). 

Abstract The noble gas signature of incoming Pacific Bottom Water (PBW), when compared to North Atlantic Deep Water, indicates the addition of 450 ± 70 GT a⁻¹glacial melt water to form AABW and subsequently PBW. The downstream evolution of this signature between the southern (20°S to equator) and northern (25°–45°N) bottom waters indicates a decrease in sea level pressure around Antarctica over the past two millennia. Vertical profiles of noble gases in the deep Pacific show exponential relationships with depth with scale heights identical to temperature and salinity. Unlike the other noble gases, helium isotopes show evidence of mid‐depth injection of non‐atmospheric helium. Using observed deviations from exponential behavior, we quantify its magnitude and isotope ratio. There is a clear latitude trend in the isotope ratio of this added helium that decreases from a high exceeding 9 R_A(atmospheric³He/⁴He ratio) in the south to around 8 R_Anear the equator. North of 30–40°N, it systematically decreases northward to a low of ∼2 R_Anorth of 50°N. This decline results from a combination of northward decline in seafloor spreading, release of radiogenic helium from increased sediment thickness, and the possible emission of radiogenic helium through cold seeps along the Alaskan and North American margins. Finally, we derive an improved method of computing the excess helium isotope concentrations and that the distributions of bottom water³He_XS/⁴He_XSare consistent with what is known about bottom water flow patterns and the input of low³He/⁴He sedimentary helium. 

Abstract. Bioactive trace metals are critical micronutrients for marinemicroorganisms due to their role in mediating biological redox reactions,and complex biogeochemical processes control their distributions.Hydrothermal vents may represent an important source of metals tomicroorganisms, especially those inhabiting low-iron waters, such as in thesouthwest Pacific Ocean. Previous measurements of primordial 3Heindicate a significant hydrothermal source originating in the northeastern (NE)Lau Basin, with the plume advecting into the southwest Pacific Ocean at1500–2000 m depth (Lupton etal., 2004). Studies investigating the long-range transport of trace metalsassociated with such dispersing plumes are rare, and the biogeochemicalimpacts on local microbial physiology have not yet been described. Here wequantified dissolved metals and assessed microbial metaproteomes across atransect spanning the tropical and equatorial Pacific with a focus on thehydrothermally active NE Lau Basin and report elevated iron and manganeseconcentrations across 441 km of the southwest Pacific. The most intensesignal was detected near the Mangatolo Triple Junction (MTJ) and NortheastLau Spreading Center (NELSC), in close proximity to the previously reported3He signature. Protein content in distal-plume-influenced seawater,which was high in metals, was overall similar to background locations,though key prokaryotic proteins involved in metal and organic uptake,protein degradation, and chemoautotrophy were abundant compared to deepwaters outside of the distal plume. Our results demonstrate that tracemetals derived from the NE Lau Basin are transported over appreciabledistances into the southwest Pacific Ocean and that bioactive chemicalresources released from submarine vent systems are utilized by surroundingdeep-sea microbes, influencing both their physiology and their contributionsto ocean biogeochemical cycling.