Fukushima and ocean radioactivity

Author Posting. © The Oceanography Society, 2014. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 27, no. 1 (2014): 92–105, doi:10.5670/oceanog.2014.02.The triple disaster of the March 11, 2011, earthquake, tsunami, and subsequent radiation releases from Japan's Fukushima Dai-ichi nuclear power plant were unprecedented events for the ocean and society. In this article, the radioactive releases from this event are compared to natural and prior human sources, with particular attention to cesium-137 and -134 radioisotopes. Total releases from Fukushima are not well constrained, with estimates from atmospheric fallout and direct ocean discharge spanning 4 to 90 peta Becquerels (PBq), but are most likely in the 15–30 PBq range. This source is smaller than any 137Cs remaining in the North Pacific from global and close-in fallout from the 1960s. It is of similar magnitude to 137Cs released to the ocean from the Sellafield nuclear reprocessing site on the Irish Sea, though of greater magnitude than fallout that reached the ocean from the 1986 Chernobyl nuclear power plant disaster in the Ukraine. The fate of Cs is largely determined by its soluble nature in seawater, though uptake in sediments does occur via cesium's association with both detrital particles and biological uptake and sedimentation. A mass balance of Cs supply from rivers and ongoing leakage from nuclear power plants suggests that sediments will remain contaminated for decades. This may be one reason why Cs concentrations in benthic fish stay elevated over predictions, causing fisheries to remain closed near Fukushima and ongoing concern to the public.Support for our Fukushima studies at the Woods Hole Oceanographic Institution (WHOI) has come primarily from the Gordon and Betty Moore Foundation, with additional support from the Deerbrook Foundation, US National Science Foundation, and, for outreach activities, the Japan Center for Global Partnership and the Morss Colloquia Endowed Fund at WHOI

Plutonium isotopes in the North Atlantic

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1986The artificial radionuclide Plutonium (Pu) has been introduced into the environment primarily as fallout from atmospheric nuclear weapons testing during the 1950's and 1960's. Earlier studies of Pu geochemistry are generally based upon the measurement of the combined activities of 239Pu and 249Pu (detected by alpha-counting and written as 239,240Pu) and assume an identical geochemical behavior for Pu from any of its fallout sources. A major focus of this thesis is the development of a mass spectrometric (m.s.) technique for the analysis of Pu in marine sediments, pore waters, sediment trap material and sea water from the North Atlantic. With the m.s. technique, not only is the detection limit for 239,240Pu increased by over an order-of-magnitude, but the 240Pu and 239Pu isotopes can be separated as well. The increased sensitivity for Pu provided by m.s. allowed me to measure Pu in deep-sea pore waters for the first time. Pore water studies are sensitive indicators of early diagenetic reactions, and can be used to examine the unresolved question of the extent of Pu remobilization out of marine sediments. Along a transect of cores ranging from highly reducing muddy sediments on the shelf to more oxic and carbonate-rich sediments in the deep-sea, I have found that the solubility of Pu is predominantly controlled by the distribution of Pu in the solid phase. The calculated 239,240Pu distribution coefficients (Kd = dpm per kg on solids/dpm per kg in solution) range from 0.2-23 x l04, with some suggestion of a trend towards lower values in the deeper cores (Kd's 2500m). Diffusive flux calculations based upon the observed Pu pore water gradients suggest that since its introduction, negligible Pu has been remobilized out of the sediments at all of the sites. On a time scale of 102 -103 years however, Pu remobilization may be significant. A large suite of sedimentary Pu and 210Pbex inventory data are also examined from the Northwest Atlantic shelf, slope and deep-sea sediments. Comparisons between Pu and 210Pb are of interest since both isotopes are predominantly supplied by atmospheric delivery to coastal waters, and since both isotopes are used to study recent accumulation and mixing processes in marine sediments. Inventories of these tracers will reflect their source function, removal efficiencies, and lateral transport in water and particles. A major conclusion is that the sediment inventories decrease with increasing water depth, reflecting a decrease in the net scavenging of these elements off-shore. Pu sediment inventories drop-off with increasing water depth much more rapidly than 210Pbex inventories, due to either the shorter residence time of 210Pb compared to Pu with respect to water column removal processes, or due to comparisons between the naturally occurring 210Pb steady-state scenario and the more recently introduced fallout Pu. When Pu and 210Pbex inventories are summed over water depths out to 4000 m in the Northwest Atlantic, the sediments can account for roughly 24 ± 8% of the expected Pu and 83 ± 15% of the expected 210Pbex inputs. The 240Pu/239Pu ratio data provided by the m.s. provide a unique insight into the relationship between the specific sources of fallout Pu and its geochemical behavior in the oceans. I find a systematic decrease in the 240Pu/239Pu ratio in sediments from 0.18 on the shelf to 0.10 in deep-sea (4500- 5000 m) sediments from the Northwest Atlantic. This trend is consistent with a model whereby Pu from surface based testing at the Nevada Test Site (240Pu/239Pu = 0.035) is carried by tropospheric fallout particles of a distinct physical/chemical form which are rapidly removed from the water column at all depths, in contrast to global stratospheric fallout (240Pu/239Pu = 0.18) which is only efficiently deposited to the sediments in the shallower cores where scavenging is more intense. This two source model was chosen since there is no evidence for the present day fractionation of 239Pu from 240Pu in the water column and sediment trap data. This two source model is supported by the analysis of 240Pu/239Pu ratios in marine sediments from the 1950's and 1960's which show lower or equivalent 240Pu/239Pu ratios than present day samples from the same locations (Nevada fallout was confined to 1951-1958 while global fallout inputs peaked in 1961/62). Also, while all of the North Atlantic deep-sea sediments show some evidence of the Nevada inputs (i.e. 240Pu/239P < 0.18), the net inventory of Pu from the Nevada source can be shown to decrease with increasing distance away from the Nevada source. Using the observed sediment 240Pu/239Pu ratios and a two end-member mixing model, the Pu supplied by the Nevada source in deep Northwest Atlantic sediments (>4500 m) is shown to account for roughly 40% of the total sediment 239,240Pu inventory. The very low inventories of 239,240Pu in the deep-sea sediments in general serves to accentuate the Nevada fallout signal at these sites. A pronounced dis-equilibrium is observed between the solid phase 240Pu/239Pu ratios (which range from 0.10-0.18) and the pore water 240Pu/23pPu ratios (which are constant at ≈ 0.18 ) at all sites. The low ratio Nevada fallout Pu is apparently more tightly bound by its solid phase carrier than Pu from global fallout sources and is therefore not participating in the general solid/solution exchange reactions. Within an individual sediment profile, the 240Pu/239Pu ratios are relatively constant from core top to core bottom. Using a sediment mixing model which combines the Pu activity data and the resulting 240Pu/239Pu ratios given the two Pu sources, I have been able to constrain the input function of Pu to the slope and deep ocean sediments. The data are consistent with a model which suggests that the bulk of the Pu deposited to the deep ocean sediments arrived early-on in the fallout record.Financial support was provided primarily by the Education Office of the Massachusetts Institute of Technology/Woods Hole Oceanographic Institution Joint Program in Oceanography, by Department of Energy contract DE-FG02-85ER60358, and by the Oak Ridge Associated Universities program for travel support to the Savannah River Laboratory

Spatial variability and the fate of cesium in coastal sediments near Fukushima, Japan

© The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biogeosciences 11 (2014): 5123-5137, doi:10.5194/bg-11-5123-2014.Quantifying the amount of cesium incorporated into marine sediments as a result of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident has proven challenging due to the limited multi-core sampling from within the 30 km zone around the facility; the inherent spatial heterogeneities in ocean sediments; and the potential for inventory fluctuations due to physical, biological, and chemical processes. Using 210Pb, 234Th, 137Cs, and 134Cs profiles from 20 sediment cores, coastal sediment inventories were reevaluated. A 137Cs sediment inventory of 100 ± 50 TBq was found for an area of 55 000 km2 using cores from this study and a total of 130 ± 60 TBq using an additional 181 samples. These inventories represent less than 1% of the estimated 15–30 PBq of cesium released during the FDNPP disaster. The time needed for surface sediment activities (0 to 3 cm) at the 20 locations to be reduced by 50% via sediment mixing was estimated to range from 0.4 to 26 yr. Due to the observed variability in mixing rates, grain size, and inventories, additional cores are needed to improve these estimates and capture the full extent of cesium penetration into the shallow coastal sediments, which was deeper than 14 cm for all cores retrieved from water depths less than 150 m.The authors would also like to acknowledge the support of the Gordon and Betty Moore Foundation, Deerbrook Charitable Trust, Woods Hole Oceanographic Institution, and Massachusetts Institute of Technology

Adsorbers for in-situ collection and at-sea gamma analysis of dissolved Thorium-234 in seawater

Two polypropylene cartridge types (Beta Pure and Hytrex II) were tested in the laboratory as adsorbers for in-situ collection of dissolved Thorium-234 (234TH) in seawater. Using a uranyl nitrate tracer, we determined that a Mn02 impregnated 3.25-inch Hytrex II cartridge with a flow rate of 8 liters/minute would collect 234TH with a greater than 60% effciency. The smaller size and composition of the 3.25 inch Hytrex II cartridge enabled it to be pressed into a permanent 1-inch "puck" for direct gamma counting. This protocol significantly reduced the handling between collection and counting. When field tested in the Gulf of Maine as a large volume (>500 liters) collector, the new adsorbers produced a greater than 80% collection effciency and a dissolved 234TH concentration which was consistent with independent samples collected at the same station and depth. These adsorbers were used successfully for the in-situ collection of 234TH in large volumes of seawater during the 1992 NOAA and NSF sponsored JGOFS EqPac program, with a mean collection efficiency of 0.79 +/- 9% (n=104 cartridge pairs).Funding was provided by the National Oceanic and Atmospheric Administration Offce of Global Programs under Contract OCE-920395200

Sources, Speciation and Mobility of Plutonium and Other Transuranics in the Groundwater at the Savannah River Site

This annual report summarizes work to date on our EMSP project: ?Sources, Speciation and Mobility of Plutonium and Other Transuranics in the Groundwater at the Savannah River Site (Sept. 2003-Sept. 2006). Our research focus is to further evaluate the sources and fate of Pu and other transuranics in groundwater at the Savannah River Site (SRS). Our overarching goal is to understand Pu speciation and mobility well enough to support safe remediation, containment and long term stewardship at any site with transuranic wastes and sources. Methods developed under prior funding for the determination Pu isotopes, oxidation state and size fractionation in groundwater are providing the best direct evidence for rejecting or not, hypotheses concerning whether colloids enhance the transport of Pu and other transuranics in groundwater. Survey samples collected in the fall of 2003 from F-area well FSB 78 had a 240/239 Pu atom ratio 7.087 +/-0.048 and reflects the continued presences of decayed 244Cm. In October 2004, we returned to the F-area and completed comprehensive field sampling of 7 wells. Field experiments included 6 different extraction rates at well 92D to test sensitivity to artifacts related to well pumping rates, and an aging experiment to evaluate Pu behavior by re-oxidation of reducing groundwater. Sampling of Pond B was included in the site visit to explore unique conditions of redox potential on Pu within the pond. To date, more than 70 Pu redox and whole water samples have been processed and are awaiting analysis at PNNL. Also, five samples from our 1998 visit are undergoing chemistry at PNNL to directly measure Cm with analysis of 2004 samples to follow. Work is continuing to evaluate particle affinity under controlled conditions and a site specific groundwater transport model which we will apply to our lab and field data to obtain a better understanding of the importance of these processes on Pu transport

Size-fractionated 234Th in continental shelf waters off New England: Implications for the role of colloids in oceanic trace metal scavenging

Measurements of 234Th (t1/2 = 24.1 days) in dissolved, colloidal, and particulate forms have been made to investigate the role of colloids in reactive metal scavenging in the surface waters of Buzzards Bay, over an annual cycle, and in the shelf and slope waters off New England. At-sea sampling involved prefiltering seawater through 0.2 μm filters followed by cross-flow filtration using a 10,000 nominal molecular weight filter to collect colloidal (10,000 NMW-0.2 μm) and dissolved (\u3c10,000 NMW) phases. Total 234Th activities increase with distance from shore, indicative of enhanced scavenging in the particle-rich nearshore waters. Clearly seen in Buzzards Bay are seasonal changes in total 234Th, with activities ranging from ≈0.7 dpm I−1 in the winter, preceeding a phytoplankton bloom, to ≈0.2 dpm I−1 in the summer. Throughout the annual cycle, 2–16% of total 234Th is colloidal, 22–40% is dissolved, and 45–75% is particulate. In the offshore waters, ≈1% of total 234Th is colloidal, 2–6% is particulate, and 93–98% is dissolved. The 234Th size-distribution exhibits a systematic increase in the association of 234Th with particulate and, to a lesser extent, colloidal matter with increasing suspended particle concentration (Cp). Moreover, a first-order prediction of the fractionation of 234Th between the various size classes is demonstrated using measured solid-solution partition coefficients. Box model calculations indicate a mean residence time of colloidal 234Th with respect to aggregation into particles of 0.3 days in Buzzards Bay, which compares with 2 days for dissolved and 4 days for particulate 234Th. In the offshore surface waters, colloidal and particulate 234Th residence times are ≈0.5 days and 2–3 days respectively, compared with 30–85 days for the dissolved phase. The short and relatively invariant residence time of colloidal 234Th suggests that colloidal aggregation may not be rate-limiting in controlling the scavenging of thorium and, by analogy, other particle-reactive trace metals. An implication of these results is that colloidal 234Th may be tracing a reactive intermediate in the bacterially mediated decomposition of large, rapidly-sinking biogenic aggregates. Using the size-fractionated 234Th data, we demonstrate that Kd values for thorium are invariant with Cp and that scavenging rate constants exhibit a first-order dependence on Cp. Thus, “particle-concentration effects” are negligible for oceanic waters (Cp ≈0.01–1 mg I−1)

A new method for the estimation of sinking particle fluxes from measurements of the particle size distribution, average sinking velocity, and carbon content

Author Posting. © Association for the Sciences of Limnology and Oceanography, 2012. This article is posted here by permission of Association for the Sciences of Limnology and Oceanography for personal use, not for redistribution. The definitive version was published in Limnology and Oceanography: Methods 10 (2012): 329-346, doi:10.4319/lom.2012.10.329.We describe a new method for estimating sinking particulate carbon fluxes at high spatial and temporal resolutions from measurements of the particle concentration size distribution taken with an in situ camera system, in this case an autonomous video plankton recorder (VPR). Paired measurements of polyacrylamide gel traps and the VPR result in depth- and size-resolved parameterizations of the average sinking velocity, which enable the estimation of the flux size distribution from the concentration size distribution. Comparisons between the gel traps and the bulk carbon flux allows for the parameterization of the particle carbon content as a function of size. Together, these parameterizations permit the estimation of carbon fluxes from high-resolution VPR surveys. This method enables greater spatial, vertical, and temporal resolution of flux measurements beyond what is possible with conventional sediment traps. We tested this method in the Sargasso Sea and found that it was capable of accurately reproducing the fluxes measured in sediment traps while offering substantial improvement in the accuracy of the estimated fluxes compared to previous global and regional parameterizations. Our results point to the importance of local calibrations of the average sinking velocity and particle carbon content when estimating carbon fluxes from measurement of the concentration size distribution. This method holds important oceanographic potential for elucidating regional or basin scale carbon flows and providing new mechanistic insights into the function of the biological pump.This project was made possible through funding from the National Science Foundation Carbon and Water Program (06028416), the Woods Hole Oceanographic Institution Academic Programs Office, ETH Zürich, and the Scurlock Bermuda Biological Station for Research Fund

Metrics that matter for assessing the ocean biological carbon pump

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Buesseler, K. O., Boyd, P. W., Black, E. E., & Siegel, D. A. Metrics that matter for assessing the ocean biological carbon pump. Proceedings of the National Academy of Sciences of the United States of America, (2020): 201918114, doi: 10.1073/pnas.1918114117.The biological carbon pump (BCP) comprises wide-ranging processes that set carbon supply, consumption, and storage in the oceans’ interior. It is becoming increasingly evident that small changes in the efficiency of the BCP can significantly alter ocean carbon sequestration and, thus, atmospheric CO2 and climate, as well as the functioning of midwater ecosystems. Earth system models, including those used by the United Nation’s Intergovernmental Panel on Climate Change, most often assess POC (particulate organic carbon) flux into the ocean interior at a fixed reference depth. The extrapolation of these fluxes to other depths, which defines the BCP efficiencies, is often executed using an idealized and empirically based flux-vs.-depth relationship, often referred to as the “Martin curve.” We use a new compilation of POC fluxes in the upper ocean to reveal very different patterns in BCP efficiencies depending upon whether the fluxes are assessed at a fixed reference depth or relative to the depth of the sunlit euphotic zone (Ez). We find that the fixed-depth approach underestimates BCP efficiencies when the Ez is shallow, and vice versa. This adjustment alters regional assessments of BCP efficiencies as well as global carbon budgets and the interpretation of prior BCP studies. With several international studies recently underway to study the ocean BCP, there are new and unique opportunities to improve our understanding of the mechanistic controls on BCP efficiencies. However, we will only be able to compare results between studies if we use a common set of Ez-based metrics.We thank the many scientists whose ideas and contributions over the years are the foundation of this paper. This includes A. Martin, who led the organization of the BIARRITZ group (now JETZON) workshop in July 2019, discussions at which helped to motivate this article. We thank D. Karl for pointing us in the right direction for this paper format at PNAS and two thoughtful reviewers who through their comments helped to improve this manuscript. Support for writing this piece is acknowledged from several sources, including the Woods Hole Oceanographic Institution’s Ocean Twilight Zone project (K.O.B.); NASA as part of the EXport Processes in the global Ocean from RemoTe Sensing (EXPORTS) program (K.O.B. and D.A.S.). E.E.B. was supported by a postdoctoral fellowship through the Ocean Frontier Institute at Dalhousie University. P.W.B. was supported by the Australian Research Council through a Laureate (FL160100131)

The value of scientific research on the ocean's biological carbon pump

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Jin, D., Hoagland, P., & Buesseler, K. O. The value of scientific research on the ocean's biological carbon pump. Science of the Total Environment, 749, (2020): 141357, doi:10.1016/j.scitotenv.2020.141357.The ocean's biological carbon pump (BCP) sequesters carbon from the surface to the deep ocean and seabed, constituting one of Earth's most valuable ecosystem services. Significant uncertainty exists surrounding the amounts and rates of organic carbon sequestered in the oceans, however. With improved understanding of BCP sequestration, especially its scale, world policymakers would be positioned to make more informed decisions regarding the mitigation of carbon emissions. Here, an analytical model of the economic effects of global carbon emissions—including scientific uncertainty about BCP sequestration—was developed to estimate the value of marine scientific research concerning sequestration. The discounted net economic benefit of a putative 20-year scientific research program to narrow the range of uncertainty around the amount of carbon sequestered in the ocean is on the order of $0.5 trillion (USD), depending upon the accuracy of predictions, the convexities of climate damage and economic output functions, and the initial range of uncertainty.This research is supported by WHOI's Ocean Twilight Zone program which is part of the Audacious Project, a collaborative endeavor, housed at TED. DJ was also funded by National Oceanic and Atmospheric Administration (NOAA) Cooperative Institutes (CINAR) award NA14OAR4320158. KB was also funded by National Aeronautics and Space Administration (NASA) as part of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) program award 80NSSC17K0555. We thank Ankur Shah for research assistance and three anonymous reviewers for their constructive suggestions

Observations of Carbon Export by Small Sinking Particles in the Upper Mesopelagic

Carbon and nutrients are transported out of the surface ocean and sequestered at depth by sinking particles. Sinking particle sizes span many orders of magnitude and the relative influence of small particles on carbon export compared to large particles has not been resolved. To determine the influence of particle size on carbon export, the flux of both small (11–64 μm) and large (\u3e 64 μm) particles in the upper mesopelagic was examined during 5 cruises of the Bermuda Atlantic Time Series (BATS) in the Sargasso Sea using neutrally buoyant sediment traps mounted with tubes containing polyacrylamide gel layers and tubes containing a poisoned brine layer. Particles were also collected in surface-tethered, free-floating traps at higher carbon flux locations in the tropical and subtropical South Atlantic Ocean. Particle sizes spanning three orders of magnitude were resolved in gel samples, included sinking particles as small as 11 μm. At BATS, the number flux of small particles tended to increase with depth, whereas the number flux of large particles tended to decrease with depth. The carbon content of different sized particles could not be modeled by a single set of parameters because the particle composition varied across locations and over time. The modeled carbon flux by small particles at BATS, including all samples and depths, was 39 ± 20% of the modeled total carbon flux, and the percentage increased with depth in 4 out of the 5 months sampled. These results indicate that small particles (\u3c 64 μm) are actively settling in the water column and are an important contributor to carbon flux throughout the mesopelagic. Observations and models that overlook these particles will underestimate the vertical flux of organic matter in the ocean