Impacts of the Fukushima nuclear power plants on marine radioactivity

Author Posting. © American Chemical Society, 2011. This article is posted here by permission of American Chemical Society for personal use, not for redistribution. The definitive version was published in Environmental Science and Technology 45 (2011): 9931–9935, doi:10.1021/es202816c.The impacts on the ocean of releases of radionuclides from the Fukushima Dai-ichi nuclear power plants remain unclear. However, information has been made public regarding the concentrations of radioactive isotopes of iodine and cesium in ocean water near the discharge point. These data allow us to draw some basic conclusions about the relative levels of radionuclides released which can be compared to prior ocean studies and be used to address dose consequences as discussed by Garnier-Laplace et al. in this journal.(1) The data show peak ocean discharges in early April, one month after the earthquake and a factor of 1000 decrease in the month following. Interestingly, the concentrations through the end of July remain higher than expected implying continued releases from the reactors or other contaminated sources, such as groundwater or coastal sediments. By July, levels of 137Cs are still more than 10 000 times higher than levels measured in 2010 in the coastal waters off Japan. Although some radionuclides are significantly elevated, dose calculations suggest minimal impact on marine biota or humans due to direct exposure in surrounding ocean waters, though considerations for biological uptake and consumption of seafood are discussed and further study is warranted.Funding for this work to KOB is from the Gordon and Betty Moore Foundation as well as the Chemical Oceanography Program of the US National Science Foundation

How Data Set Characteristics Influence Ocean Carbon Export Models

Ocean biological processes mediate the transport of roughly 10 petagrams of carbon from the surface to the deep ocean each year and thus play an important role in the global carbon cycle. Even so, the globally integrated rate of carbon export out of the surface ocean remains highly uncertain. Quantifying the processes underlying this biological carbon export requires a synthesis between model predictions and available observations of particulate organic carbon (POC) flux; yet the scale dissimilarities between models and observations make this synthesis difficult. Here we compare carbon export predictions from a mechanistic model with observations of POC fluxes from several data sets compiled from the literature spanning different space, time, and depth scales as well as using different observational methodologies. We optimize model parameters to provide the best match between model‐predicted and observed POC fluxes, explicitly accounting for sources of error associated with each data set. Model‐predicted globally integrated values of POC flux at the base of the euphotic layer range from 3.8 to 5.5 Pg C/year, depending on the data set used to optimize the model. Modeled carbon export pathways also vary depending on the data set used to optimize the model, as well as the satellite net primary production data product used to drive the model. These findings highlight the importance of collecting field data that average over the substantial natural temporal and spatial variability in carbon export fluxes, and advancing satellite algorithms for ocean net primary production, in order to improve predictions of biological carbon export

Sources, Speciation and Mobility of Plutonium and Other Transuranics in the Groundwater at the Savannah River Site (Sept. 2003-Sept. 2006)

The intent of this research effort is to: (1) provide the basis for accurate modeling and prediction of actinide transport; (2) allow for remediation strategies to be planned that might use in-situ manipulations of geochemical variables to enhance (for extraction) or retard (for immobilization) Pu mobility in the groundwater zone; (3) identify specific Pu sources and the extent of far field, or long-term migration of transuranics in groundwater; (4) reduce costly uncertainty in performance and risk assessment calculations. This new knowledge is essential to ensure continued public and worker safety at the DOE sites and the efficient management of cleanup and containment strategies

Beryllium-7 analyses in seawater by low background gamma-spectroscopy

Author Posting. © Akadémiai Kiadó, 2008. 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 277 (2008): 253-259, doi:10.1007/s10967-008-0739-y.7Be is a cosmogenic isotope produced in the stratosphere and troposphere. 7Be has a half-life of 53.4 days and decays to 7Li emitting a 477 keV gamma line with a branching ratio of 0.104. It is predominantly washed out of the atmosphere through wet deposition. It is a tool for oceanographers to study air sea interaction and water mass mixing. Beryllium’s largely non-reactive nature in the open ocean makes it an excellent conservative tracer. Its conservative nature and extreme dilution in seawater also makes it difficult to concentrate and analyze. Early experiments at WHOI with Fe(OH)3 cartridges to directly collect 7Be by insitu underwater pumps proved ineffective. Collection efficiencies of the cartridges were too low to be consistently useful. At sea chemistry of whole water samples became the method of choice. The use of stable 9Be as a yield monitor further improved the accuracy of the procedure. The method was optimized at WHOI in 2005 using a seawater line that enters WHOI’s coastal research lab. The procedure was then used on an oceanographic cruise on the R/V Oceanus out of Bermuda in the oligotrophic Sargasso Sea.The authors would like to thank DOE, ONR and NSF for funding of this research

Decoupling of Net Community Production and Export Production at Submesoscale Fronts in the Sargasso Sea

Determinations of the net community production (NCP) in the upper ocean and the particle export production (EP) should balance over long time and large spatial scales. However, recent modeling studies suggest that a horizontal decoupling of flux-regulating processes on submesoscales (≤10 km) could lead to imbalances between individual determinations of NCP and EP. Here we sampled mixed-layer biogeochemical parameters and proxies for NCP and EP during 10, high-spatial resolution (~2 km) surface transects across strong physical gradients in the Sargasso Sea. We observed strong biogeochemical and carbon flux variability in nearly all transects. Spatial coherence among measured biogeochemical parameters within transects was common but rarely did the same parameters covary consistently across transects. Spatial variability was greater in parameters associated with higher trophic levels, such as chlorophyll in \u3e5.0 µm particles, and variability in EP exceeded that of NCP in nearly all cases. Within sampling transects, coincident EP and NCP determinations were uncorrelated. However, when averaged over each transect (30 to 40 km in length), we found NCP and EP to be significantly and positively correlated (R = 0.72, p = 0.04). Transect-averaged EP determinations were slightly smaller than similar NCP values (Type-II regression slope of 0.93, standard deviation = 0.32) but not significantly different from a 1:1 relationship. The results show the importance of appropriate sampling scales when deriving carbon flux budgets from upper ocean observations

Bacterial vs. zooplankton control of sinking particle flux in the ocean\u27s twilight zone

The downward flux of particulate organic carbon (POC) decreases significantly in the oceanÂs mesopelagic or ‘twilight’ zone due both to abiotic processes and metabolism by resident biota. Bacteria and zooplankton solubilize and consume POC to support their metabolism, but the relative importance of bacteria vs. zooplankton in the consumption of sinking particles in the twilight zone is unknown. We compared losses of sinking POC, using differences in export flux measured by neutrally buoyant sediment traps at a range of depths, with bacteria and zooplankton metabolic requirements at the Hawaii Ocean Time‐series station ALOHA in the subtropical Pacific and the Japanese times‐series site K2 in the subarctic Pacific. Integrated (150‐1,000 m) mesopelagic bacterial C demand exceeded that of zooplankton by up to 3‐fold at ALOHA, while bacteria and zooplankton required relatively equal amounts of POC at K2. However, sinking POC flux was inadequate to meet metabolic demands at either site. Mesopelagic bacterial C demand was 3‐ to 4‐fold (ALOHA), and 10‐fold (K2) greater than the loss of sinking POC flux, while zooplankton C demand was 1‐ to 2‐fold (ALOHA), and 3‐ to 9‐fold (K2) greater (using our ‘middle’ estimate conversion factors to calculate C demand). Assuming the particle flux estimates are accurate, we posit that this additional C demand must be met by diel vertical migration of zooplankton feeding at the surface and by carnivory at depth—with both processes ultimately supplying organic C to mesopelagic bacteria. These pathways need to be incorporated into biogeochemical models that predict global C sequestration in the deep sea

Speciation, Mobility and Fate of Actinides in the Groundwater at the Hanford Site

Plutonium and other actinides represent important contaminants in the groundwater and vadose zone at Hanford and other DOE sites. The distribution and migration of these actinides in groundwater must be understood so that these sites can be carefully monitored and effectively cleaned up, thereby minimizing risks to the public. The objective of this project was to obtain field data on the chemical and physical forms of plutonium in groundwater at the Hanford site. We focused on the 100-k and 100-n areas near the Columbia River, where prior reactor operations and waste storage was in close proximity to the river. In particular, a unique set of technical approaches were combined to look at the details of Pu speciation in groundwater, as thus its chemical affinity for soil surfaces and solubility in groundwater, as these impact directly the migration rates off site and possible mitigation possibilities one might undertake to control, or at least better monitor these releases

Global assessment of ocean carbon export by combining satellite observations and food-web models

The export of organic carbon from the surface ocean by sinking particles is an important, yet highly uncertain, component of the global carbon cycle. Here we introduce a mechanistic assessment of the global ocean carbon export using satellite observations, including determinations of net primary production and the slope of the particle size spectrum, to drive a food-web model that estimates the production of sinking zooplankton feces and algal aggregates comprising the sinking particle flux at the base of the euphotic zone. The synthesis of observations and models reveals fundamentally different and ecologically consistent regional-scale patterns in export and export efficiency not found in previous global carbon export assessments. The model reproduces regional-scale particle export field observations and predicts a climatological mean global carbon export from the euphotic zone of ~6 Pg C yr−1. Global export estimates show small variation (typically < 10%) to factor of 2 changes in model parameter values. The model is also robust to the choices of the satellite data products used and enables interannual changes to be quantified. The present synthesis of observations and models provides a path for quantifying the ocean's biological pump

Global assessment of ocean carbon export by combining satellite observations and food-web models

The export of organic carbon from the surface ocean by sinking particles is an important, yet highly uncertain, component of the global carbon cycle. Here we introduce a mechanistic assessment of the global ocean carbon export using satellite observations, including determinations of net primary production and the slope of the particle size spectrum, to drive a food-web model that estimates the production of sinking zooplankton feces and algal aggregates comprising the sinking particle flux at the base of the euphotic zone. The synthesis of observations and models reveals fundamentally different and ecologically consistent regional-scale patterns in export and export efficiency not found in previous global carbon export assessments. The model reproduces regional-scale particle export field observations and predicts a climatological mean global carbon export from the euphotic zone of ~6 Pg C yr⁻¹. Global export estimates show small variation (typically <10%) to factor of 2 changes in model parameter values. The model is also robust to the choices of the satellite data products used and enables interannual changes to be quantified. The present synthesis of observations and models provides a path for quantifying the ocean’s biological pump.Keywords: remote sensing, biological pump, food webs, carbon cycle, carbon expor

An assessment of the use of sediment traps for estimating upper ocean particle fluxes

Author Posting. © Sears Foundation for Marine Research, 2007. This article is posted here by permission of Sears Foundation for Marine Research for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 65 (2007): 345–416, doi: 10.1357/002224007781567621This review provides an assessment of sediment trap accuracy issues by gathering data to address trap hydrodynamics, the problem of zooplankton "swimmers," and the solubilization of material after collection. For each topic, the problem is identified, its magnitude and causes reviewed using selected examples, and an update on methods to correct for the potential bias or minimize the problem using new technologies is presented. To minimize hydrodynamic biases due to flow over the trap mouth, the use of neutrally buoyant sediment traps is encouraged. The influence of swimmers is best minimized using traps that limit zooplankton access to the sample collection chamber. New data on the impact of different swimmer removal protocols at the US time-series sites HOT and BATS are compared and shown to be important. Recent data on solubilization are compiled and assessed suggesting selective losses from sinking particles to the trap supernatant after collection, which may alter both fluxes and ratios of elements in long term and typically deeper trap deployments. Different methods are needed to assess shallow and short- term trap solubilization effects, but thus far new incubation experiments suggest these impacts to be small for most elements. A discussion of trap calibration methods reviews independent assessments of flux, including elemental budgets, particle abundance and flux modeling, and emphasizes the utility of U-Th radionuclide calibration methods.WG meetings and production of this report was partially supported by the U.S. National Science Foundation via grants to the SCOR. Individuals and science efforts discussed herein were supported by many national science programs, including the U.S. National Science Foundation, Swedish Research Council, the International Atomic Energy Agency through its support of the Marine Environmental Laboratory that also receives support from the Government of the Principality of Monaco, and the Australian Antarctic Science Program. K.B. was supported in part by a WHOI Ocean Life Institute Fellowship