Description: The precise determination of radium‐226 (226Ra) in environmental samples is challenging due to its low concentration. Seawater typically contains between 0.03 and 0.1 fg g−1 226Ra. Thus, this work addresses the need for an easy and precise methodology for 226Ra determination in seawater that may be applied routinely to a large number of samples. For this reason, a new analytical approach has been developed for the quantification of 226Ra in seawater via inductively coupled plasma mass spectrometry (ICP‐MS). Analysis by single collector sector‐field ICP‐MS was shown to be convenient and reliable for this purpose once potential molecular interferences were excluded by a combination of chemical separation and intermediate mass resolution analysis. The proposed method allows purification of Ra from the sample matrix based on preconcentration by MnO2 precipitation, followed by two‐column separation using a cation exchange resin and an extraction chromatographic resin. The method can be applied to acidified and unacidified seawater samples. The recovery efficiency for Ra ranged between 90% and 99.8%, with precision of 5%, accuracy of 95.7% to 99.9%, and a detection limit of 0.033 fg g−1 (referring to the original concentration of seawater). The method has been applied to measure 226Ra concentrations from the North Sea and validated by analyzing samples from the central Arctic (GEOTRACES GN04). Samples from a crossover station (from GEOTRACES GN04 and GEOTRACES GN01 research cruises) were analyzed using alternative methods, and our results are in good agreement with published values.

Description: 1 Kurzfassung Im Sahlenburger Wattenmeer südwestlich von Cuxhaven wurde eine Porenwasseranalyse auf- Anionen, Kationen und Nährstoffe sowie eine geoelektrische Kartierung nach Wenner zur Untersuchung des dort vorkommenden submarinen Grundwasserausstromes durchgeführt. Zudem fand an mehreren diskreten Ausstromstellen (sand boils) eine Größenkartierung sowie Volumenstromessung mittels Seapagemetern statt. Zielsetzung war es Fragen hinsichtlich der räumlichen und zeitlichen Variabilität sowie der Anreicherung durch den submarinen Grundwasserausstrom eingetragener Spezies zu beantworten. Ebenfalls von Bedeutung war die hydrogeologische Bilanz im Untersuchungsgebiet mit dem Grundwasserausstrom als potentiellem Verlustweg sowie die Ursache für dessen Auftreten. Es konnte im Rahmen dieser Untersuchung bestätigt werden, dass große Teile des Sahlenburger Wattenmeeres durch Süßwassereintrag sowie Akkumulation gelöster Spezies infolge des submarinen Grundwasserausstromes geprägt sind. Zudem konnte nachgewiesen werden, dass der Grundwasserausstrom über mehrere Jahre nahezu ortsstabil geblieben ist sowie eine zuvor postulierte wasserstauende Torf- und Kleischicht im Untergrund Hauptursache für dessen Auftreten sowie räumliche Verteilung ist. Abschließend erfolgte über einen Zusammenhang zwischen der Größe einer Ausstromstelle sowie dem ausströmenden Volumen eine hydrogeologische Bilanzierung.

Description: We propose an alternative scheme for the use of 224Ra/228Th disequilibria to investigate carbon and nutrient export from a permeable sandy seabed. Sediment profiles of dissolved 224Ra, total 224Ra and 228Th were determined at two different intertidal sand systems - an intertidal sandy beach near Weitou Bay in Fujian (China), and a tidal sand flat in the Wadden Sea near Cuxhaven (Germany). Dramatic deficit of total 224Ra relative to 228Th was identified in the upper 20 or 30 cm sand layer over the sand systems. We construct a simple two-dimensional advective cycling model to simulate interfacial fluid transport in a sand system that is subject to periodic tidal inundation and swash actions. Based on the 224Ra/228Th disequilibria in the sediment, the model gives estimates of 20.3, 9.1, and 1.9 L m−2 h−1 for water exchange flux at the high tide, mid-tide, and low tide position over the sandy beach at Weitou Bay, respectively. In comparison, the model provides an estimate of 7.2 L m−2 h−1 for water exchange flux at the tidal sand flat in the Wadden Sea. The production of dissolved inorganic carbon (DIC) in porewater is the rate-limiting step for DIC export from the sandy beach into the sea, and can be reasonably simulated as a first-order kinetic reaction. The pattern of interfacial fluid transport over the beach facilitates a horizontal zonation of redox condition in the sediment, which evolves progressively from a fully oxic state at the high tide position to a suboxic state at the low tide position. There is clear evidence of nitrogen loss via denitrification in the suboxic status, and we estimate a nitrogen removal rate of 3.3 mmolN m−2 d−1 at this site. For the two intertidal sand systems, DIC export fluxes range from 20.1 to 89.4 mmolC m−2 d−1, comparable in magnitude to fluxes determined in organic rich estuarine sediments. In the meantime, export fluxes of dissolved inorganic nitrogen (DIN) change from 0.8 to 18.6 mmolN m−2 d−1. Overall, this study suggests that the role of sandy sediments in the biogeochemical cycling of carbon and nutrients needs to be revisited.

Description: The precise determination of radium-226 (226Ra) in environmental samples is challenging due to its low con- centration. Seawater typically contains between 0.03 and 0.1 fg g−1 226Ra. Thus, this work addresses the need for an easy and precise methodology for 226Ra determination in seawater that may be applied routinely to a large number of samples. For this reason, a new analytical approach has been developed for the quantification of 226Ra in seawater via inductively coupled plasma mass spectrometry (ICP-MS). Analysis by single collector sector-field ICP-MS was shown to be convenient and reliable for this purpose once potential molecular interfer- ences were excluded by a combination of chemical separation and intermediate mass resolution analysis. The proposed method allows purification of Ra from the sample matrix based on preconcentration by MnO2 precipi- tation, followed by two-column separation using a cation exchange resin and an extraction chromatographic resin. The method can be applied to acidified and unacidified seawater samples. The recovery efficiency for Ra ranged between 90% and 99.8%, with precision of 5%, accuracy of 95.7% to 99.9%, and a detection limit of 0.033 fg g−1 (referring to the original concentration of seawater). The method has been applied to measure 226Ra concentrations from the North Sea and validated by analyzing samples from the central Arctic (GEOTRACES GN04). Samples from a crossover station (from GEOTRACES GN04 and GEOTRACES GN01 research cruises) were analyzed using alternative methods, and our results are in good agreement with published values.

Description: Mapping radon (222Rn) distribution pat- terns in the coastal sea is a widely applied method for localizing and quantifying submarine groundwater discharge (SGD). While the literature reports a wide range of successful case studies, methodical problems that might occur in shallow wind-exposed coastal settings are generally neglected. This paper evalu- ates causes and effects that resulted in a failure of the radon approach at a distinct shallow wind-exposed location in the Baltic Sea. Based on a simple radon mass balance model, we discuss the effect of both wind speed and wind direction as causal for this fail- ure. We show that at coastal settings, which are domi- nated by gentle submarine slopes and shallow waters, both parameters have severe impact on coastal radon distribution patterns, thus impeding their use for SGD investigation. In such cases, the radon approach needs necessarily to allow for the impact of wind speed and wind direction not only during but also prior to the field campaign.

Description: In search for critical elements, polymetallic nodules at the deep abyssal seafloor are targeted for mining operations. Nodules efficiently scavenge and retain several naturally occurring uranium-series radioisotopes, which predominantly emit alpha radiation during decay. Here, we present new data on the activity concentrations of thorium-230, radium-226, and protactinium-231, as well as on the release of radon-222 in and from nodules from the NE Pacific Ocean. In line with abundantly published data from historic studies, we demonstrate that the activity concentrations for several alpha emitters are often higher than 5 Bq g−1 at the surface of the nodules. These observed values can exceed current exemption levels by up to a factor of 1000, and even entire nodules commonly exceed these limits. Exemption levels are in place for naturally occurring radioactive materials (NORM) such as ores and slags, to protect the public and to ensure occupational health and radiation safety. In this context, we discuss three ways of radiation exposure from nodules, including the inhalation or ingestion of nodule fines, the inhalation of radon gas in enclosed spaces and the potential concentration of some radioisotopes during nodule processing. Seen in this light, inappropriate handling of polymetallic nodules poses serious health risks.