Isotopic, geophysical and biogeochemical investigation of submarine groundwater discharge : IAEA-UNESCO intercomparison exercise at Mauritius Island

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Journal of Environmental Radioactivity 104 (2012): 24-45, doi:10.1016/j.jenvrad.2011.09.009.Submarine groundwater discharge (SGD) into a shallow lagoon on the west coast of Mauritius Island (Flic-en-Flac) was investigated using radioactive (3H, 222Rn, 223Ra, 224Ra, 226Ra, 228Ra) and stable (2H, 18O) isotopes and nutrients. SGD intercomparison exercises were carried out to validate the various approaches used to measure SGD including radium and radon measurements, seepage-rate measurements using manual and automated meters, sediment bulk conductivity and salinity surveys. SGD measurements using benthic chambers placed on the floor of the Flic-en-Flac Lagoon showed discharge rates up to 500 cm/day. Large variability in SGD was observed over distances of a few meters, which were attributed to different geomorphological features. Deployments of automated seepage meters captured the spatial and temporal variability of SGD with a mean seepage rate of 10 cm/day. The stable isotopic composition of submarine waters was characterized by significant variability and heavy isotope enrichment and was used to predict the contribution of fresh terrestrially derived groundwater to SGD (range from a few % to almost 100 %). The integrated SGD flux, estimated from seepage meters placed parallel to the shoreline, was 35 m3/m day, which was in a reasonable agreement with results obtained from hydrologic water balance calculation (26 m3/m day). SGD calculated from the radon inventory method using in situ radon measurements were between 5 and 56 m3/m per day. Low concentrations of radium isotopes observed in the lagoon water reflected the low abundance of U and Th in the basalt that makes up the island. High SGD rates contribute to high nutrients loading to the lagoon, potentially leading to eutrophication. Each of the applied methods yielded unique information about the character and magnitude of SGD. The results of the intercomparison studies have resulted a better understanding of groundwater-seawater interactions in coastal regions. Such information is an important pre-requisite for the protection management of coastal freshwater resources.The financial support provided by the IOC and IHP of UNESCO for travel arrangements, and by the IAEA’s Marine Environment Laboratories for logistics is highly acknowledged. MAC and MEG were supported in part by the US National Science Foundation (OCE-0425061 and OCE-0751525). PPP acknowledges a support provided by the EU Research & Development Operational Program funded by the ERDF (project No. 26240220004), and the Slovak Scientific Agency VEGA (grant No. 1/108/08). The International Atomic Energy Agency is grateful to the Government of the Principality of Monaco for support provided to its Marine Environment Laboratories

Reference material for radionuclides in sediment IAEA-384 (Fangataufa Lagoon sediment)

Author Posting. © Springer, 2007. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Journal of Radioanalytical and Nuclear Chemistry 273 (2007): 383-393, doi:10.1007/s10967-007-6898-4.A reference material designed for the determination of anthropogenic and natural radionuclides in sediment, IAEA-384 (Fangataufa Lagoon sediment), is described and the results of certification are presented. The material has been certified for 8 radionuclides (40K, 60Co, 155Eu, 230Th, 238U, 238Pu, 239+240Pu and 241Am). Information values are given for 12 radionuclides (90Sr, 137Cs, 210Pb (210Po), 226Ra, 228Ra, 232Th, 234U, 235U, 239Pu, 240Pu and 241Pu). Less reported radionuclides include 228Th, 236U, 239Np and 242Pu. The reference material may be used for quality management of radioanalytical laboratories engaged in the analysis of radionuclides in the environment, as well as for the development and validation of analytical methods and for training purposes. The material is available from IAEA in 100 g units

Reference Material for Radionuclides in Sediment, IAEA-384 (Fangataufa Lagoon Sediment)

The IAEA Marine Environment Laboratory (IAEA-MEL) in Monaco has conducted intercomparison exercises on radionuclides in marine samples for many years as part of its contribution to the IAEA's program of Analytical Quality Control Services (AQCS). An important part of the AQCS program has been a production of Reference Materials (RMs) and their provision to radioanalytical laboratories. The RMs have been developed for different marine matrices (sediment, water, biota), with accuracy and precision required for the present state of the art of radiometrics and mass spectrometry methods. The RMs have been produced as the final products of world-wide intercomparison exercises organized during last 30 years. A total of 44 intercomparison exercises were undertaken and 39 RMs were produced for radionuclides in the marine environment. All required matrices (seawater, biota, sediment) have been covered with radionuclide concentrations ranging from typical environmental levels to elevated levels affected by discharges from nuclear reprocessing plants. The long-term availability of RMs (over 10 years) requires the use of very specific techniques to collect and pretreat large quantities of material (e.g., in excess of 100 kg) in order to ensure sample stability and homogenization of any analytes of interest. The production of a RM is therefore a long process, covering the identification of needs, sample collection, pre-treatment, homogenization, bottling, distribution to laboratories, evaluation of data, preliminary reporting, additional analyses in expert laboratories, certification of the material, and finally issuing the RM. In this paper we describe a reference material IAEA-384, Fangataufa lagoon sediment, designed for determination of anthropogenic and natural radionuclides in the marine environment. This RM has been prepared with the aim of testing the performance of analytical laboratories to measure the activity of these radionuclides in a sediment sample contaminated by elevated levels of fallout from nuclear weapons tests. Participating laboratories were requested to determine as many radionuclides as possible by radiometric (alpha, beta and gamma-spectrometry) as well as by mass spectrometry methods (e.g., ICPMS - Inductively Coupled Plasma Mass Spectrometry, TIMS - Thermal Ionization Mass Spectrometry, AMS - Accelerator Mass Spectrometry)

Sediment remobilization by open sea deep convection in the northwestern Mediterranean

VIII Congreso Geológico de España (Oviedo, 2012). -- 4 pages, 5 figures.-- Versión pre-print[ES] El Mediterráneo noroccidental es una importante zona de formación invernal de agua profunda, un proceso que ocurre en dos variantes: la convección en mar abierto y el hundimiento de agua densa de plataforma en forma de cataratas submarinas (“cascading”). La relevancia del cascading en la dinámica sedimentaria de la cuenca y los márgenes del Mediterráneo noroccidental es hoy ampliamente reconocida, mientras que la convección de mar abierto ha recibido más atención desde un punto de vista hidrológico. En este trabajo se presentan datos de flujos de partículas y corrientes a 200 m, 1000 m de profundidad y cerca del fondo (2350 m) en la estación DYFAMED, durante un notable episodio de formación de agua profunda (invierno 2005-2006). Durante este evento, las corrientes se intensificaron en toda la columna de agua, alcanzando valores similares hasta el fondo (máximo 39 cm s-1). Al mismo tiempo, el flujo de partículas medido cerca del fondo se incrementó en dos órdenes de magnitud (máximo 9 g m-2 d-1). Estos resultados sugieren que la convección en mar abierto es un mecanismo relevante en la resuspensión y redistribución de sedimentos en la cuenca profunda del Mediterráneo noroccidental.[EN] The northwestern Mediterranean is a well known area of deep water formation via dense shelf water cascading and offshore convection. The impact of the former in the sediment dynamics of the deep basin has been highlighted in recent years, while open sea convection has been solely studied from a hydrological perspective. Particle fluxes and hydrodynamics were monitored at the DYFAMED site (Ligurian Sea, northwestern Mediterranean) at 200, 1000 m and near the seafloor (2350 m depth) during winter 2005-2006 and the following spring. From February to April 2006, and in coincidence with a remarkable episode of deep water formation, currents intensified throughout the entire water column to the bottom, where particle flux increased up to two orders of magnitude (maximum 9 g m-2 d-1). These observations suggest that open-sea deep convection is to be considered, together with cascading, as a relevant driving force for sedimentary dynamics in the northwestern Mediterranean basin.Este trabajo fue financiado por INSU (Francia), el Organismo Internacional de la Energía Atómica y el Proyecto HERMES (EC contract GOCE-CT-2005-511234).Peer reviewe

Sediment remobilization by open sea deep convection in the northwestern Mediterranean

VIII Congreso Geológico de España, 17-19 de julio de 2012, OviedoPeer Reviewe

Approaches to

The determination of 90Sr in seawater, sediment and biota is carried out by radiochemical analysis. The choice of method is dependent on the amount of sample to be analyzed, the Ca/Sr mass ratio and the natural Sr content of the sample. For large volumes of seawater and sediment samples (e.g., coral) of high Ca content, 1 g (minimum) of Sr carrier and 85Sr tracer are used. The Sr fraction is separated and purified chiefly by Sr(NO3)2 precipitations. After 2 - 3 weeks, the ingrown 90Y is separated from the parent 90Sr, and the 90Y beta activity is measured by a gas-flow proportional counter. The detection limits obtained are 36 µBq/L for seawater and 0.36 Bq/kg for corals. For sediment and biota samples of low to moderate Ca content and low natural Sr content, 10 - 20 mg of stable Sr carrier are used without 85Sr. The Sr fraction is separated and purified using crown ether extraction chromatography. The purified Sr fraction itself (containing 90Sr together with in-growing 90Y) is measured immediately using liquid scintillation counting. The detection limit obtained is 0.66 Bq/kg for 10g of sediment or biota ash

Temporal (<SUP>3</SUP>H) and spatial variations of <SUP>90</SUP>Sr, <SUP>239,240</SUP>Pu and <SUP>241</SUP>Am in the Arabian Sea: GEOSECS stations revisited

In order to study the spatial and temporal variations of radionuclides in the world ocean, five Geochemical Ocean Sections (GEOSECS) stations, located in the different areas of the Arabian Sea, were revisited in 1998, 20 years after the GEOSECS expedition. Water samples were collected to study the vertical and horizontal distributions of 3H, 90Sr, 239,240Pu and 241Am. 239,240Pu and 241Am profiles generally showed subsurface maxima at 400-800 m water depth, while 3H and 90Sr profiles decreased smoothly with depth. 3H profiles measured in 1998 showed higher 3H levels at surface and intermediate depths as expected from the decay-corrected GEOSECS results. 239,240Pu and 241Am inventories increased towards the south, reaching a maximum at GEOSECS Station 419, situated in the southern Arabian Sea. 90Sr inventories showed the same tendency as transuranics, while 3H inventories were lowest at Station 419 and highest at Stations 413 (close to the Gulf of Aden). It appears that there are several processes viz. water transport from the Red Sea, different monsoon regimes (summer and winter), transport of tritium from the atmosphere to the ocean via isotope exchange with atmospheric moisture, rain and river inputs, and finally, circulation processes specific to the Arabian Sea and the Indian Ocean

Impact of the Fukushima accident on tritium, radiocarbon and radiocesium levels in seawater of the western North Pacific Ocean: A comparison with pre-Fukushima situation

International audienceTritium, radiocarbon and radiocesium concentrations in water column samples in coastal waters offshore Fukushima and in the western North Pacific Ocean collected in 2011–2012 during the Ka'imikai-o-Kanaloa (KoK) cruise are compared with other published results. The highest levels in surface seawater were observed for 134Cs and 137Cs in seawater samples collected offshore Fukushima (up to 1.1 Bq L−1), which represent an increase by about three orders of magnitude when compared with the pre-Fukushima concentration. Tritium levels were much lower (up to 0.15 Bq L−1), representing an increase by about a factor of 6. The impact on the radiocarbon distribution was measurable, but the observed levels were only by about 9% above the global fallout background. The 137Cs (and similarly 134Cs) inventory in the water column of the investigated western North Pacific region was (2.7 ± 0.4) PBq, while for 3H it was only (0.3 ± 0.2) PBq. Direct releases of highly contaminated water from the damaged Fukushima NPP, as well as dry and wet depositions of these radionuclides over the western North Pacific considerably changed their distribution patterns in seawater. Presently we can distinguish Fukushima labeled waters from global fallout background thanks to short-lived 134Cs. However, in the long-term perspective when 134Cs will decay, new distribution patterns of 3H, 14C and 137Cs in the Pacific Ocean should be established for future oceanographic and climate change studies in the Pacific Ocean

Tracing the 1887 Ligurian earthquake in the sedimentary record of the Var Ridge

The Deep-sea & Sub-Seafloor Frontiers Conference project (DS3F), 11-14 March 2012, Sitges, Barcelona, SpainPeer Reviewe