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Radium isotopes are continuously produced at ocean boundaries and are soluble in seawater. Radium therefore serves as an analogue for similarly sourced shelf-derived materials, including biologically important elements such as carbon, nutrients, and trace metals. To test the hypothesis that climate change is leading to increased delivery of terrestrially-derived solutes to the Arctic Ocean, radium levels are measured on bi-annual cruises along the Laptev and East Siberian Sea margins (to capture interannual changes) and on a first-of-its kind in situ radium isotope sampler (to capture seasonal changes). These sampling efforts are complemented by an international network of collaborators that will contribute data to create an Arctic Radium Isotope Observing Network (ARION) that spans the Arctic Ocean and will serve the greater scientific community.\n This dataset contains the (1) results of the water column measurements made on the second ARION cruise, which took place in August-October 2023 along the slopes of the East Siberian and Laptev Seas in collaboration with the Nansen and Amundsen Basin Observational Systems (NABOS) program, and (2) results from two moored radium in situ samplers (MoRIS) deployed on the Laptev and East Siberian Slopes from 2021-2023. Parameters measured include radium-228, radium-226, oxygen-18, deuterium, salinity, and barium. 

Abstract. The Siberian Arctic Ocean (SAO) is the largest integrator and redistributor of Siberian freshwater resources and acts to significantly influence the Arctic climate system. Moreover, the SAO is experiencing some of the most notable climate changes in the Arctic, and advection of anomalous Atlantic- (atlantification) and Pacific-origin (pacification) inflow waters and biota continue to play a major role in reshaping the SAO in recent decades. In this study, we use a large collection of mooring data to create a coherent picture of the spatiotemporal patterns and variability of currents and shear in the upper SAO during the past decade. Although there was no noticeable trend in the upper SAO's current speed and shear from 2013 to 2023, their seasonal cycle has significantly strengthened. The cycle reveals a strong relationship between upper ocean currents and their shear with sea ice conditions – particularly during transitional seasons – evidenced by a strong negative correlation (−0.94) between seasonal sea ice concentration and current shear. In the shallow (< 20–30 m) summer surface mixed layer, currents have increased because strong stratification prevents wind energy from propagating into the deeper layers. In this case, strong near-inertial currents account for more than half of the summertime current speed and shear. In the winter, a thicker surface layer is created by deep upper SAO ventilation due to atlantification, which distributes wind energy to far deeper (> 100 m) layers. These findings are critical to understanding the ramifications for mixing and halocline weakening, as well as the rate of atlantification in the region. 

This dataset includes measurements of the dissolved isotope radium-226 in the South Pacific and Southern Ocean. Samples were collected on the US GEOTRACES GP17-OCE cruise (Papeete, Tahiti to Punta Arenas, Chile) on R/V Roger Revelle from December 2022 to January 2023. Radium-223, radium-224, and radium-228 data will be made available in the future. 

Abstract Fresh submarine groundwater discharge (FSGD) can deliver significant fluxes of water and solutes from land to sea. In the Arctic, which accounts for ∼34% of coastlines globally, direct observations and knowledge of FSGD are scarce. Through integration of observations and process‐based models, we found that regardless of ice‐bonded permafrost depth at the shore, summer SGD flow dynamics along portions of the Beaufort Sea coast of Alaska are similar to those in lower latitudes. Calculated summer FSGD fluxes in the Arctic are generally higher relative to low latitudes. The FSGD organic carbon and nitrogen fluxes are likely larger than summer riverine input. The FSGD also has very high CO₂making it a potentially significant source of inorganic carbon. Thus, the biogeochemistry of Arctic coastal waters is potentially influenced by groundwater inputs during summer. These water and solute fluxes will likely increase as coastal permafrost across the Arctic thaws. 

Abstract Distributions of the natural radionuclide²¹⁰Po and its grandparent²¹⁰Pb along the GP15 Pacific Meridional Transect provide information on scavenging rates of reactive chemical species throughout the water column and fluxes of particulate organic carbon (POC) from the primary production zone (PPZ).²¹⁰Pb is in excess of its grandparent²²⁶Ra in the upper 400–700 m due to the atmospheric flux of²¹⁰Pb. Mid‐water²¹⁰Pb/²²⁶Ra activity ratios are close to radioactive equilibrium (1.0) north of ∼20°N, indicating slow scavenging, but deficiencies at stations near and south of the equator suggest more rapid scavenging associated with a “particle veil” located at the equator and hydrothermal processes at the East Pacific Rise. Scavenging of²¹⁰Pb and²¹⁰Po is evident in the bottom 500–1,000 m at most stations due to enhanced removal in the nepheloid layer. Deficits in the PPZ of²¹⁰Po (relative to²¹⁰Pb) and²¹⁰Pb (relative to²²⁶Ra decay and the²¹⁰Pb atmospheric flux), together with POC concentrations and particulate²¹⁰Po and²¹⁰Pb activities, are used to calculate export fluxes of POC from the PPZ.²¹⁰Po‐derived POC fluxes on large (>51 μm) particles range from 15.5 ± 1.3 mmol C/m²/d to 1.5 ± 0.2 mmol C/m²/d and are highest in the Subarctic North Pacific;²¹⁰Pb‐derived fluxes range from 6.7 ± 1.8 mmol C/m²/d to 0.2 ± 0.1 mmol C/m²/d. Both²¹⁰Po‐ and²¹⁰Pb‐derived POC fluxes are greater than those calculated using the²³⁴Th proxy, possibly due to different integration times of the radionuclides, considering their different radioactive mean‐lives and scavenging mean residence times. 

This dataset includes measurements of dissolved barium (Ba) concentrations in the South Pacific and Southern Ocean from the US GEOTRACES GP17 section (GP17-OCE, Papeete, Tahiti to Punta Arenas, Chile) on R/V Roger Revelle from December 2022 to January 2023. 

Radium is a useful tracer of sediment‐derived materials, improving our understanding of the geochemical cycling of elements at ocean boundaries. We have developed an autonomous in situ sampler to collect time series samples of radium isotopes on mooring deployments. Samplers were deployed for 2 yr in the Arctic Ocean, a region particularly hard to access outside of the summer season, and collected monthly samples to create the first annual time series of radium‐228 and radium‐226 in the Arctic. Results from the Laptev Slope show increased radium‐228 and radium‐228/radium‐226 ratios in spring/summer, concomitant with increased meteoric water and brine influence. Together, these tracers indicate seasonal periods of increased influence of shelf‐ and river‐derived materials, findings which would not be possible to discern from summertime shipboard surveys alone. The development of this in situ sampler has therefore expanded our capability to use radium as a tracer to discern temporal changes in the geochemistry of remote areas of the ocean. 

Abstract Supra‐permafrost submarine groundwater discharge (SGD) in the Arctic is potentially important for coastal biogeochemistry and will likely increase over the coming decades owing to climate change. Despite this, land‐to‐ocean material fluxes via SGD in Arctic environments have seldom been quantified. This study used radium (Ra) isotopes to quantify SGD fluxes to an Arctic coastal lagoon (Simpson Lagoon, Alaska) during five sampling periods between 2021 and 2023. Using a Ra mass balance model, we found that the SGD water flux was substantial and dependent on environmental conditions. No measurable SGD was detected during the spring sampling period (June 2022), when the lagoon was partially ice‐covered. During ice‐free periods, the main driver of SGD in this location is wind‐driven lagoon water level changes, not tides, which control surface water recirculation through sediments along the lagoon boundary. A combination of wind strength and direction led to low SGD fluxes in July 2022, with an SGD flux of (6 ± 3) × 10⁶ m³ d⁻¹, moderate fluxes in August 2021 and July 2023, which had an average flux of (17 ± 9) × 10⁶ m³ d⁻¹, and high fluxes in October 2022, at (79 ± 16) × 10⁶ m³ d⁻¹. This work demonstrates how soil and environmental conditions in the Arctic impact Ra mobilization, laying a foundation for future SGD studies in the Arctic and shedding light on the major processes driving Ra fluxes in this important environment. 

{"Abstract":["This data set was acquired during cruise RR2106 using 3 separate CTD systems (referred to as "Hydrothermal", "Trace Metal", and "Pump") that all utilized Seabird 911plus CTD systems with various integrated analog sensors (see the associated documentation that identifies the instrument configuration of each system). The data files are in ASCII format and column headers define the fields. Navigation is included in the files. The aim of the study was to evaluate the contribution of low-temperature hydrothermal venting as an important, but overlooked, source of stabilized dissolved iron to the ocean. Operations included near-bottom (20-40 m above the seafloor) CTD tows (using the "Hydrothermal" CTD only) along with vertical casts that were completed using all 3 systems. The CTD data has been processed using Seabird Data Processing modules and averaged to 5-second intervals. Navigation for the tows was calculated using a lay-back method. Primary plume tracers are potential temperature anomaly (ΔTheta, °C), turbidity anomaly (optical backscatter, ΔNTU), and oxidation-reduction potential anomaly (ΔE, mV). Users should refer to the continuous CTD data files (i.e., those with "CTDdata" in the file names) for ΔTheta and ΔE values at the time the bottle samples were obtained; ΔNTU values are included in the "BottleFile" files, which are subsets of the continuous data from the times each bottle sample was obtained (generated by Seabird Data Processing "Bottle Summary" module). The data set was generated as part of the projects called "Are Low-Temperature Hydrothermal Vents an Important but Overlooked Source of Stabilized Dissolved Iron to the Ocean?" and "Low temperature hydrothermal vent fluxes as traced by radium isotopes". Funding was provided by NSF awards OCE17-56402 and OCE18-29431."]} 

Atlantification—the northward inflow of anomalous waters and biota from the Atlantic into the polar basins—has wide-ranging climatological ramifications. We present previously unknown observational evidence that the atlantification processes are strengthening in the eastern Eurasian Basin. The primary example is the diminishing sea ice, which is related to a powerful ocean-heat/ice-albedo feedback, which accelerates sea-ice losses. Furthermore, we observe that atlantification is extending far beyond the Lomonosov Ridge into the Makarov Basin of the Arctic Ocean where upper ocean ventilation creates a new and unique ecological environment. The eastern part of the Siberian Arctic Ocean is still strongly stratified, but the atlantification-driven shoaling of warm, salty, and nutrient-rich intermediate waters already has important ecological consequences there. Disentangling the role of atlantification in multiple and complex high-latitude changes should be a priority in future modeling and observational efforts.