Ages of continental shelf waters determined from <sup>223</sup>Ra and <sup>224</sup>Ra

Moore, Willard S.

doi:10.1029/1999jc000289

Cited by 188 publications

(165 citation statements)

References 20 publications

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“…Tritium present in the environment is mostly of global fallout origin (Livingston and Povinec, 2002), and due to its peak input to the atmosphere (1963) and suitable half-life (12.32 y) is frequently used for dating of groundwater (Povinec et al, 2008c). Radium has four isotopes of varying half-lives ( 223 Ra, t 1/2 = 11.4 d; 224 Ra, t 1/2 = 3.66 d; 226 Ra, t 1/2 = 1600 y and 228 Ra, t 1/2 = 5.75 y) and is ideally suited to estimate water exchange rates in coastal zones, as well as to assess coastal integrated SGD fluxes (Moore, 1996(Moore, , 2000(Moore, , 2006Moore and Wilson, 2005). Radon ( 222 Rn) is a conservative tracer, suitable for studying the dynamics of groundwater-seawater interactions.…”

Section: Introductionmentioning

confidence: 99%

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

Povinec¹,

Burnett²,

Beck³

et al. 2012

Journal of Environmental Radioactivity

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Submarine groundwater discharge (SGD) into a shallow lagoon on the west coast of Mauritius Island (Flic-en-Flac) was investigated using radioactive ( 3 H, 222 Rn, 223 Ra, 224 Ra, 226 Ra, 228 Ra) and stable ( 2 H, 18 O) 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 m 3 /m day, which was in a reasonable agreement with results obtained from hydrologic water balance calculation (26 m 3 /m day). SGD calculated from the radon inventory method using in situ radon measurements were between 5 and 56 m 3 /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.

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Section: Introductionmentioning

confidence: 99%

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

Povinec¹,

Burnett²,

Beck³

et al. 2012

Journal of Environmental Radioactivity

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“…In addition to the measurement of radionuclides derived from the NPP, radium isotopes were measured to trace the pathway of the cesium derived from direct ocean discharges. In marine environments, radium isotopes are produced from the decay of thorium isotopes, which are abundant in sediments along the coastline (Moore, 2000). Unlike thorium, radium is soluble in seawater, making leakage from continental margin sediments a continuous source of radium isotopes to the ocean.…”

Section: Introductionmentioning

confidence: 99%

Radium-based estimates of cesium isotope transport and total direct ocean discharges from the Fukushima Nuclear Power Plant accident

et al. 2013

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Radium has four naturally occurring isotopes that have proven useful in constraining water mass source, age, and mixing rates in the coastal and open ocean. In this study, we used radium isotopes to determine the fate and flux of runoff-derived cesium from the Fukushima Dai-ichi Nuclear Power Plant (FNPP). During a June 2011 cruise, the highest cesium (Cs) concentrations were found along the eastern shelf of northern Japan, from Fukushima south, to the edge of the Kuroshio Current, and in an eddy ~ 130 km from the FNPP site. Locations with the highest cesium also had some of the highest radium activities, suggesting much of the direct ocean discharges of Cs remained in the coastal zone 2–3 months after the accident. We used a short-lived Ra isotope (²²³Ra, t_1/2 = 11.4 d) to derive an average water mass age (T_r) in the coastal zone of 32 days. To ground-truth the Ra age model, we conducted a direct, station-by-station comparison of water mass ages with a numerical oceanographic model and found them to be in excellent agreement (model avg. T_r = 27 days). From these independent T_r values and the inventory of Cs within the water column at the time of our cruise, we were able to calculate an offshore ¹³⁴Cs flux of 3.9–4.6 × 10¹³ Bq d⁻¹. Radium-228 (t_1/2 = 5.75 yr) was used to derive a vertical eddy diffusivity (K_z) of 0.7 m² d⁻¹ (0.1 cm² s⁻¹); from this K_z and ¹³⁴Cs inventory, we estimated a ¹³⁴Cs flux across the pycnocline of 1.8 × 10⁴ Bq d⁻¹ for the same time period. On average, our results show that horizontal mixing loss of Cs from the coastal zone was ~ 10⁹ greater than vertical exchange below the surface mixed layer. Finally, a mixing/dilution model that utilized our Ra-based and oceanographic model water mass ages produced a direct ocean discharge of ¹³⁴Cs from the FNPP of 11–16 PBq at the time of the peak release in early April 2011. Our results can be used to calculate discharge of other water-soluble radionuclides that were released to the ocean directly from the Fukushima NPP

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“…Open seawater is relatively radium deplete; therefore, radium activity above that of open seawater suggests a coastal source that in many cases is groundwater. Because radium isotopes behave conservatively in the nearshore after accounting for radioactive decay, the radium quartet is useful for characterizing ocean mixing and rates of submarine groundwater discharge (Charette et al 2001;Moore 1996Moore , 1999Moore , 2000aMoore , b, 2003.…”

Section: Introductionmentioning

confidence: 99%

Submarine Groundwater Discharge to a High-Energy Surf Zone at Stinson Beach, California, Estimated Using Radium Isotopes

Sieyes

Yamahara

Paytan

et al. 2010

Estuaries and Coasts

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Two 14-day experiments conducted in the dry summer (July 2006) and wet winter (March 2007) seasons, respectively, examined tidal, wave-driven, and seasonal variability of submarine groundwater discharge (SGD) at Stinson Beach, CA, using natural radium tracers. Tide stage, tide range, breaker height, and season each explained a significant degree of radium variability in the surf zone. A mass balance of excess radium in the surf zone was used to estimate SGD for each season, confirming larger discharge rates during the wet season. Our results indicate median groundwater discharge rates of 6 to 8 L min

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Ages of continental shelf waters determined from ²²³Ra and ²²⁴Ra

Cited by 188 publications

References 20 publications

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

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

Radium-based estimates of cesium isotope transport and total direct ocean discharges from the Fukushima Nuclear Power Plant accident

Submarine Groundwater Discharge to a High-Energy Surf Zone at Stinson Beach, California, Estimated Using Radium Isotopes

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Ages of continental shelf waters determined from 223Ra and 224Ra

Cited by 188 publications

References 20 publications

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

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

Radium-based estimates of cesium isotope transport and total direct ocean discharges from the Fukushima Nuclear Power Plant accident

Submarine Groundwater Discharge to a High-Energy Surf Zone at Stinson Beach, California, Estimated Using Radium Isotopes

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Ages of continental shelf waters determined from ²²³Ra and ²²⁴Ra