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Abstract Trace element (As, Co, Cr, Cu, Ni, Pb, V and Zn) enrichment trends during the past century, were assessed in thirteen 210Pb-dated sediment cores from the southern Gulf of Mexico, with the purpose to evaluate the impact on the environment, and potentially on public health, of the offshore oil industry and of oil spills such as that of the Ixtoc1 well blowout in 1979. The trace element composition was quite homogeneous among cores; and the pre-industrial concentrations of Ba, Cr, Cu and Ni are naturally high in the region, as to reach levels of potential ecological concern. The influence of multiple and simultaneous processes (e.g. industrial activities, natural seeps, fluvial discharges) on the trace element concentrations is difficult to disentangle. Some cores suggested long-term preservation of putative oil spill traces, although it was not possible to attribute their origin. The Al-normalized redox element ratios, and the crude oil contamination ratio, suggested that these events occurred along almost four decades, and that the traces attributed to the Ixtoc1 spill were comparable to background conditions, most likely owing to active natural oil seeps in the area. In most cases there was a trend towards a lowering in the supply of trace elements; this might be associated with environmental controls in the region since the 1980s. This study highlights the relevance of using dated environmental archives to reconstruct the historical trends of trace metal contamination in areas where long-term environmental studies are scarce. Graphical abstract Unlabelled Image Highlights • Metal concentrations and enrichment trends were studied in southern Gulf of Mexico. • Metal enrichment evidenced weak to intense contamination within the past 100 years. • Metals result from simultaneous sources (oil industry, seeps, fluvial discharges). • Reducing metal concentrations since 1980s likely respond to environmental regulation. • Background and recent metal concentrations might be harmful to biota and humans. [ABSTRACT FROM AUTHOR]

The Gulf of California (GC) is a unique large marine ecosystem characterized by its rich biodiversity, high biological productivity and endemism of marine life, which are the basis of Mexico's most important fisheries. However, as many other large ecosystems worldwide, it is subject to diverse anthropogenic pressures (overfishing, losses of biodiversity and habitats, pollution, climate variability and climate change (CC)). We reviewed over 180 studies dealing with the impacts of CC and climate variability in the GC region. Main issues on the impact of ENSO events, acidification, sea level rise, and water availability are discussed for the GC in a global context. Impacts of ENSO events on the GC are geographically heterogeneous, upwelling tends to be suppressed, and this in turn influences the distribution and abundance of marine mammals, fishes, shrimps, benthic species, seaweeds and phytoplankton. ENSO events strongly impact small pelagic fishes, key components of the GC ecosystem, thus affecting fisheries in general as well as non-harvested species such as marine mammals and sea birds. Probably the most well-known phenomenon associated to ENSO impact in the GC is coral bleaching, a process by which corals expel most of their microalgal endosymbionts to become pale or white (bleached). Beside shifts in the distributional limits of benthic organisms, invasions of alien species are also occuring. Harmful algal blooms (HABs) are common and recurrent in the GC. Fourteen HAB-forming species have been recorded, with Gymnodinium catenatum being the most frequent. HABs are inhibited by El Niño and promoted by La Niña. During El Niño events the size and biomass of macroalgal blooms tend to decrease. Finally, several aspects that require further research are proposed. [ABSTRACT FROM AUTHOR]

Abstract: Environmental archives, such as sediments, banded corals and tree rings, are widely used to reconstruct past environmental conditions of ecosystems. In particular, 210Pb has been used during more than 4 decades, through dating of undisturbed sediment cores, to study ecosystem changes during the last 100yr. Since its inception, diverse dating models have been proposed, developed, used and validated in numerous environments, but their nomenclature and formulation is not homogenous. In this work we emphasize that conceptual models used to date undisturbed sediment cores can be deduced from a single fundamental equation, which relates excess 210Pb concentration in sediment, its flux to the sediment surface and mass accumulation rate. From this equation, models were consistently named based on the main hypothesis used and, using a unified and logical nomenclature, dating equations were derived in detail. We applied in detail most of the described models to a sediment core from Mexico and uncertainty expressions were also included. Finally, some recommendations to use the models are proposed. We believe that this work can facilitate the use of 210Pb as a tool to date sediment cores in a more homogeneous way. [Copyright &y& Elsevier]

Abstract: During the reoccupation of the WOCE transect A10 at 30°S by the BEAGLE2003 cruise, the SHOTS project partners collected a large number of samples for the analysis of isotopic tracers. 137Cs was mostly deposited on the oceans surface during the late 1950s and early 1960s, after the atmospheric detonation of large nuclear devices, which mostly occurred in the Northern Hemisphere. The development of advanced radioanalytical and counting techniques allowed to obtain, for the first time in this region, a zonal section of 137Cs water concentrations, where little information existed before, thus constituting an important benchmark for further studies. 137Cs concentrations in the upper waters (0–1000m) of the south-eastern Atlantic Ocean are similar to those observed in the south-western Indian Ocean, suggesting transport of 137Cs labeled waters by the Agulhas current to the Benguela Current region. In contrast, bomb radiocarbon data do not show this feature, indicating the usefulness of 137Cs as a radiotracer of water mass transport from the Indian to the South Atlantic Ocean. [Copyright &y& Elsevier]

Abstract: A new Certified Reference Material (CRM) for radionuclides in sediment (IAEA-385) is described and the results of the certification process are presented. Eleven radionuclides (40K, 137Cs, 226Ra, 228Ra, 230Th, 232Th, 234U, 238U, 238Pu, 239+240Pu and 241Am) have been certified and information mass activities with 95% confidence intervals are given for seven other radionuclides (90Sr, 210Pb(210Po), 235U, 239Pu, 240Pu and 241Pu). Results for less frequently reported radionuclides (60Co, 99Tc, 134Cs, 155Eu, 224Ra and 239Np) and information on some activity and mass ratios are also reported. The CRM can be used for quality assurance/quality control of the analysis of radionuclides in sediment samples, for the development and validation of analytical methods and for training purposes. [Copyright &y& Elsevier]

Abstract: Society''s growing interest in environmental issues requires the production of reliable information for policy-makers, stakeholders and society in general. This information must be based on accurate data produced by qualified laboratories and data need to be comparable between numerous laboratories for joint assessments, e.g. in International Conventions. The Marine Environment Laboratories of the International Atomic Energy Agency has been providing Quality Assurance services to laboratories involved in marine radioactivity studies for the past 30 years. This has included training, organization of laboratory intercomparison exercises, production of Reference Materials (RMs) and more recently, production of Certified Reference Materials (CRMs) that comply with relevant ISO standards. Here, the overall process of Certification of Reference Materials is reviewed, past work summarized and future needs of marine radioactivity laboratories briefly discussed. [Copyright &y& Elsevier]

Abstract: A certified reference material (CRM) for radionuclides in fish sample IAEA-414 (mixed fish from the Irish Sea and North Seas) is described and the results of the certification process are presented. Nine radionuclides (40K, 137Cs, 232Th, 234U, 235U, 238U, 238Pu, 239+240Pu and 241Am) were certified for this material. Information on massic activities with 95% confidence intervals is given for six other radionuclides (90Sr, 210Pb(210Po), 226Ra, 239Pu, 240Pu 241Pu). Less frequently reported radionuclides (99Tc, 129I, 228Th, 230Th and 237Np) and information on some activity and mass ratios are also included. The CRM can be used for quality assurance/quality control of the analysis of radionuclides in fish sample, for the development and validation of analytical methods and for training purposes. The material is available from IAEA, Vienna, in 100g units. [Copyright &y& Elsevier]

210Pb was analysed in samples collected from (16) sediment traps, deployed during 1 year on the Northwestern Mediterranean continental margins, within the framework of the (MTP I)-EUROMARGE-NB programme. The traps were moored within (5) submarine canyons and their adjacent open slope, corresponding to contrasting conditions of particle inputs (fluxes and constituents). The major meso-scale observation (at the margin) is the variation in 210Pb fluxes along the slope, increasing by a factor of 2–3 between the entrance and the exit of the slope, in relation to the general (water) circulation. At a smaller scale (canyon), the 210Pb fluxes showed trends which were common to the various sites, i.e. a seaward decrease at 500 m depth and an increase, with depth, in the canyons. All these features are related to mass flux variations, except for periods with huge mass fluxes, when 210Pb fluxes reached a constant value. 210Pb activities decreased with increasing mass flux; then did not show clear relationship with the concentration of the major constituents of the flux.210Pb fluxes, obtained from the traps were mainly in excess of the theoretical 210Pb flux, available in the overlying water column. Since 210Pb inventories, measured on the basis of the shelf and slope bottom sediments, were also in excess in relation to the available flux. The margin, as a whole, appears as a sink for 210Pb. This boundary-scavenging process appears to be controlled completely by the mass flux of particles. Differences were observed between 210Pb fluxes in the near-bottom traps and in the underlying sediments; there can be linked to mass flux and/or morphobathymetry (the trap flux is higher than the sediment flux in the canyon, but lower on the open slope). Overall, the differences were not in excess of 50%, confirming good representation of data collected by the sediment traps. However, this finding must be taken into account when comparing organic carbon or other constituent fluxes, between the traps and the sediment. [Copyright &y& Elsevier]

Coastal vegetated habitats can be important sinks of organic carbon (C org ) and mitigate global warming by sequestering significant quantities of atmospheric CO 2 and storing sedimentary C org for long periods, although their C org burial and storage capacity may be affected by on-going sea level rise and human intervention. Geochemical data from published 210 Pb-dated sediment cores, collected from low-energy microtidal coastal wetlands in El Salvador (Jiquilisco Bay) and in Mexico (Salada Lagoon; Estero de Urias Lagoon; Sian Ka'an Biosphere Reserve) were revisited to assess temporal changes (within the last 100 years) of C org concentrations, storage and burial rates in tropical salt marshes under the influence of sea level rise and contrasting anthropization degree. Grain size distribution was used to identify hydrodynamic changes, and δ 13 C to distinguish terrigenous sediments from those accumulated under the influence of marine transgression. Although the accretion rate ranges in all sediment records were comparable, C org concentrations (0.2–30%), stocks (30–465 Mg ha −1 , by extrapolation to 1 m depth), and burial rates (3–378 g m −2 year −1 ) varied widely within and among the study areas. However, in most sites sea level rise decreased C org concentrations and stocks in sediments, but increased C org burial rates. Lower C org concentrations were attributed to the input of reworked marine particles, which contribute with a lower amount of C org than terrigenous sediments; whereas higher C org burial rates were driven by higher mass accumulation rates, influenced by increased flooding and human interventions in the surroundings. C org accumulation and long-term preservation in tropical salt marshes can be as high as in mangrove or temperate salt marsh areas and, besides the reduction of C org stocks by ongoing sea level rise, the disturbance of the long-term buried C org inventories might cause high CO 2 releases, for which they must be protected as a part of climate change mitigation efforts. [ABSTRACT FROM AUTHOR]

Coastal lagoons provide important ecosystem services worldwide but are subject to high and multiple environmental stresses. Little information exists on the inner creeks of low-flow coastal lagoons, where the low-exchange rates may exacerbate anthropogenic impacts. In this work, we used a model with high spatio-temporal resolution to describe the hydrodynamics and to estimate the accumulation of conservative contaminants in the upper estuary of the Urias sub-tropical coastal lagoon, in northwestern Mexico. The lagoon shows a weak anti-estuarine behavior and its hydrodynamics is governed by astronomical tides and topography. The mean steady-state water age in the three lagoon areas was ∼15, ∼30 and ∼70 days in the Harbor, Intermediate and Upper Areas, respectively. Thus, the Upper Area, which shelters a mangrove forest, is the most vulnerable to pollution due to the high potential for accumulation. As a best case scenario, the simulation of the release of conservative substances in the Upper area indicated that, 50 days after the release started, conservative pollutants mostly remained in the Upper Area and were not significantly exported to the open ocean. This methodology can be used to model the impact of conservative substances in coastal lagoons worldwide, and can be complementary and useful for the optimization of long-term coastal zone management activities. [ABSTRACT FROM AUTHOR]

Abstract: The accumulation, enrichment and provenance of selected trace metals (Ag, As, Cd, Cr, Cu, Hg, Ni, Pb, V and Zn) were studied in sediment cores collected from three lakes located in the Central Mexican Plateau, selected on the basis of their contrasting degree of urbanization: Santa Elena Lake, in a rural and remote area; El Tule Lake, in a rural and slightly urbanized area; and Chapala Lake, in a highly urbanized area. Grain size, magnetic susceptibility and sedimentary constituents such as organic carbon, calcium carbonate, as well as major (Al, Fe, Mn) and minor (Ca, Li, Rb, Sr, Th) elements were analyzed to explain the concentration trends of trace metals. Factor analysis (FA) was used to assess the provenance of the trace elements. The highest metal enrichment factor (EF) above natural concentration levels was found at Chapala Lake for Ag (EF=3.9), although other trace element EF in all lakes was <2.0, indicating slight contamination. However, the concentration levels of Cr and Ni in all lakes, Hg and Zn in Chapala Lake, Cu in El Tule Lake and As in Santa Elena Lake were above international benchmarks for which adverse effects are expected to occur frequently, even for those metals only slightly enriched (e.g. As, Cr). Through FA, the terrigenous contribution was identified as the most important source of trace metals to the three lakes, most likely related to deforestation and erosion of the surrounding areas, followed by atmospheric transport of volcanic ashes, rather than to direct sources. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

• C org burial was evaluated in seagrass sediments at the northern Mexican Caribbean. • Thalassia testudinum seagrass meadows showed C org storage within ~ 40 to ~ 100 years. • C org stock increments were related with increasing sediment accumulation rates. • Seagrasses might be gradually impacted by population growth and land use changes. Carbon sequestration in seagrass meadows mitigates the currently rising CO 2 atmospheric levels, as these ecosystems are highly productive and preserve sediment organic carbon over long periods. Five 210Pb dated sediment cores, collected from seagrass meadows dominated by Thalassia testudinum in the northern Mexican Caribbean touristic corridor Cancun-Riviera Maya, were used to establish temporal trends of organic carbon (C org) content, burial rates and stock variation over the past 100 years. C org contents (0.17–1.94%) and burial rates (2.0–252 g m−2 yr−1) were generally within the lower end range reported for seagrass meadow sediments worldwide. C org stock gradually increased over the past decades, associated with increasing sediment accumulation, possibly caused by inland erosion promoted by agricultural and forestry activities and, in the recent decades, by a rapid increase of urban development due to a fast growth of the tourist industry and population, likely causing fertilization of coastal waters. Seagrass meadow sediments in the northern Mexican Caribbean coastline showed long-term C org storage and preservation, since ~ 40 to ~ 100 years depending on the core, which emphasizes the need to protect these ecosystems against impacts of global change, and their incorporation into climate change mitigation strategies should be considered. [ABSTRACT FROM AUTHOR]

The Campeche Sound is the major offshore oil producing area in the Southern Gulf of Mexico (SGoM). To evaluate the impact of oil related activities in the ocean floor sediments, we analyzed the geochemical (major and trace element, organic carbon and hydrocarbon concentrations) and biological (benthic foraminifera) composition of 62 superficial sediment samples, from 13 to 1336 m water depth. Cluster and Factor analysis of all the variables indicate that their distribution patterns are mainly controlled by differences between the terrigenous and carbonate platforms in the SGoM. Benthic foraminiferal assemblages were abundant and diverse, and their distribution patterns are mainly determined by water depth and sedimentary environment. However, most of the abundant species are opportunistic and/or low-oxygen tolerant, and many of their tests show oil stains and infillings, characteristic of oil polluted locations, suggesting the environment has been modified by natural seepage or oil-related activities. To determine if these conditions are natural or anthropogenic in origin, pre - industrial settings should be studied. Organic carbon (Corg) content (0.6–2.9%) and total hydrocarbon concentrations (PAHs 1.0–29.5 μg kg−1) were usually higher around the oil platforms area, the natural hydrocarbon seeps ("chapopoteras") area and offshore rivers, but there is no accumulation of oil related trace elements in these areas. However, the comparison with international sediment quality benchmarks indicates that Cd, Cr and Ni concentrations are above the threshold effect level, and also As, Ba and Cu are above the probable effect level benchmarks, which indicate that these element concentrations might be of potential ecological concern. Comprehensive studies involving different proxies, and assessing pre-industrial conditions, must be undertaken before assessing environmental health of marine benthic ecosystems. • Impact of oil related activities on ocean floor sediments was assessed. • Benthic Foraminifera (microbenthos) show impact of various oil derived sources. • Concentrations of As, Ba and Cu might be of potential ecological concern.. • Organic carbon and PAHs content are greater in oil exploitation and seep areas. • Campeche Bay is affected by multiple stressors, both natural and anthropogenic. [ABSTRACT FROM AUTHOR]

• Sediment accumulation in contrasting mangrove areas showed similar temporal trends. • Mass accumulation rates (MAR) increased exponentially over the last century. • MAR mainly accelerated since the 1950s and it was attributed to continental erosion. • Continental erosion was associated with land-use changes and population growth. • Mangroves accumulated sediments at pace with local sea-level rises. Mangrove sediments are valuable records to reconstruct the impacts of human-induced changes on the coastal zone. Seven lead-210 dated sediment cores were used to evaluate temporal trends of sedimentation rates over the past century in Mexican mangrove areas at Términos Lagoon (TL; southern Gulf of Mexico) and El Verde Camacho Lagoon (EV; northern Mexican Pacific coast). We hypothesized that the contrasting characteristics (e.g., meteorological, demographic, and land-use change) would lead to significant differences in sedimentation rates between the study sites. Sediment accumulation rates (SAR) in both sites (TL 0.03–2.1 cm yr−1; EV 0.04–4 cm yr−1) were comparable to the global SAR range for mangrove forests. Mass accumulation rates (MAR) in the TL cores (0.03–0.47 g cm−2 yr−1) were consistent with previous studies of the region. Excluding conspicuous MAR maxima, attributed to meteorological events, MAR values in the EV cores (0.04–0.9 g cm−2 yr−1) were higher than in other mangrove areas of the Mexican Pacific coast, but comparable to other sites in the world. Similar exponentially increasing MAR values towards present in both sites were attributed to general factors driving sediment accumulation in mangroves, mainly continental erosion promoted by land-use changes, which has accelerated since the 1950s, associated with (i) population growth and the consequent expansion of human activities and (ii) sea-level rise, similar in the studied regions and from which mangrove ecosystems seem to adapt. Intensifying population growth and land-use change are already reducing the extent of mangrove coverage in some parts of the study areas. Adaptation to an accelerating sea-level rise depends on maintaining conditions that allow mangroves to accrete vertically. However, both global change pressures may pose future threats to these ecosystems. Efforts to monitor sediment accretion and adapt the management of mangrove conservation areas are required to understand better mangrove response to global change impacts. [ABSTRACT FROM AUTHOR]

Abstract: Since 1998 the highly polluted Havana Bay ecosystem has been the subject of a mitigation program. In order to determine whether pollution-reduction strategies were effective, we have evaluated the historical trends of pollution recorded in sediments of the Bay. A sediment core was dated radiometrically using natural and artificial fallout radionuclides. An irregularity in the 210Pb record was caused by an episode of accelerated sedimentation. This episode was dated to occur in 1982, a year coincident with the heaviest rains reported in Havana over the XX century. Peaks of mass accumulation rates (MAR) were associated with hurricanes and intensive rains. In the past 60 years, these maxima are related to strong El Niño periods, which are known to increase rainfall in the north Caribbean region. We observed a steady increase of pollution (mainly Pb, Zn, Sn, and Hg) since the beginning of the century to the mid 90s, with enrichment factors as high as 6. MAR and pollution decreased rapidly after the mid 90s, although some trace metal levels remain high. This reduction was due to the integrated coastal zone management program introduced in the late 90s, which dismissed catchment erosion and pollution. [Copyright &y& Elsevier]

Abstract: The anthropogenic radionuclides such as 137Cs, 90Sr, 99Tc, 129I and some transuranics are important tracers of transport and biogeochemical processes in the ocean. 137Cs, with a half-life of 30years, a major fission product present in a dissolved form in seawater, is a good tracer of oceanic circulation at a time scale of several decades. At WOCE P6 line along 30°S during the BEAGLE cruise in 2003, surface seawater (around 80L) was collected a few meters below the ocean surface by a pumping system. Water column samples (from 5 to 20L) were collected using a Rosette multisampling system and Niskin bottles. 137Cs was separated from seawater samples using ammonium phosphomolybdate (AMP) and analysed for 137Cs in low-level HPGe gamma-ray spectrometers. Results allowed to draw a detailed picture of the distribution of 137Cs in the South Pacific Ocean along P6 line. A 137Cs depth section was depicted from about 160 samples. 137Cs concentrations in the subsurface layers ranged from 0.07±0.04Bqm−3 to 1.85±0.145Bqm−3, high in the Tasman Sea and very low in the eastern region where upwelling occurs. Water column inventories of 137Cs from surface to 1000dbar depth ranged from 270±104 to 1048±127Bqm−2. It was concluded that the source of higher 137Cs concentration and inventories in the Tasman Sea was 137Cs deposited in the mid latitude of the North Pacific Ocean and transported across the equator during four decades. [Copyright &y& Elsevier]

Abstract: Vertical profiles of dissolved plutonium activity concentration in South Pacific Ocean water columns were determined using ICP-SF-MS after Fe co-precipitation and radiochemical purification. The water samples were collected in the central South Pacific mid-latitude region (32.5°S) during the BEAGLE2003 expedition conducted in 2003–2004 by the Japan Agency for Marine-Earth Science and Technology. 239Pu concentrations in surface water were around 1mBqm−3. Concentrations reached a maximum (6mBqm−3) at 600–800m, and then decreased with increasing depth. The vertical profile pattern was similar to that observed in the North Pacific subtropical gyre, although concentrations of 239Pu in the deep South Pacific were significantly lower than those in the North Pacific subtropical gyre. The 239Pu/137Cs activity ratios, which reflect biogeochemical processes in seawater, increased exponentially from the surface to 1500m depth, whereas in deep waters they were almost constant. The estimated 239,240Pu inventories in the South Pacific water column (0–2300m) were of the same order of magnitude as previous estimates in 1996 (15°S, 148°W); however they were about one order of magnitude lower than those in the western North Pacific. [Copyright &y& Elsevier]

Abstract: The Japan Agency for Marine Earth Science and Technology conducted in 2003–2004 the Blue Earth Global Expedition (BEAGLE2003) around the Southern Hemisphere Oceans, which was a rare opportunity to collect many seawater samples for anthropogenic radionuclide studies. We describe here sampling and analytical methodologies based on radiochemical separations of Cs and Pu from seawater, as well as radiometric and mass spectrometry measurements. Several laboratories took part in radionuclide analyses using different techniques. The intercomparison exercises and analyses of certified reference materials showed a reasonable agreement between the participating laboratories. The obtained data on the distribution of 137Cs and plutonium isotopes in seawater represent the most comprehensive results available for the Southern Hemisphere Oceans. [Copyright &y& Elsevier]

Abstract: The distribution of 239Pu in Atlantic and Indian Ocean waters about four decades after their main injection from atmospheric nuclear weapons tests is discussed. Recent data obtained in the framework of the SHOTS (Southern Hemisphere Ocean Tracer Studies) projects are evaluated and compared with previous investigations. Seawater samples were collected during the round the globe BEAGLE2003 (Blue Ocean Global Expedition) along the 30°S transect in the Atlantic and the 20°S transect in the Indian Ocean. The results indicate transport of surface waters labelled with 239Pu from the western North Pacific via the Indonesian Seas to the South Indian Ocean and then to the South Atlantic Ocean. Along the whole BEAGLE2003 sampling route, the Atlantic Ocean has the lowest 239Pu content due to its particle scavenging on the long way from the western North Pacific. On the other hand, concentrations of the conservative 137Cs tracer are in all three oceanic basins comparable. The primary productivity reflected by the chlorophyll content in surface waters has similar longitudinal distribution as 239Pu. Radioactive and chlorophyll tracers revealed that the most important current system in each southern oceanic basin is represented by the Subtropical gyre. While the main streams of the gyres maintain high concentrations of tracers, inside the loops the tracer concentrations are the lowest. [Copyright &y& Elsevier]

Abstract: The measurement of plutonium isotopes, 239Pu and 240Pu, at 670kV on the compact accelerator mass spectrometry (AMS) system at the Centro Nacional de Aceleradores (CNA) in Seville, Spain, is now a reality. In this work, we present first Pu AMS results for environmental samples: a sediment core collected in a submarine canyon in the Mediterranean coast of the Spanish region of Palomares, affected by a nuclear accident in 1966. From the study of the 240Pu/239Pu atomic ratio profile, showing on average levels lower than 11%, we confirm that the weapon-grade plutonium released on land during the accident, with a characteristic 240Pu/239Pu atomic ratio of 5.8%, has found its way into the marine environment. A two-plutonium sources mixture model (Palomares and fallout) is used to elucidate the percentage of the plutonium coming from the accident. As a validation exercise of the Pu AMS measuring technique and in order to obtain the 238Pu/(239+240)Pu activity ratios, samples were also studied by alpha-spectrometry (AS). The obtained AS 239+240Pu activity concentration results fit in with the AMS ones in a wide dynamic range, thus validating the AMS technique. [Copyright &y& Elsevier]

Artificial radionuclides enter the Mediterranean Sea mainly through atmospheric deposition following nuclear weapons tests and the Chernobyl accident, but also through the river discharge of nuclear facility effluents. Previous studies of artificial radionuclides impact of the Mediterranean Sea have focussed on shallow, coastal sediments. However, deep sea sediments have the potential to store and accumulate pollutants, including artificial radionuclides. Deep sea marine sediment cores were collected from Mediterranean Sea abyssal plains (depth >2000 m) and analysed for 239,240Pu and 137Cs to elucidate the concentrations, inventories and sources of these radionuclides in the deepest areas of the Mediterranean. The activity — depth profiles of 210Pb, together with 14C dating, indicate that sediment mixing redistributes the artificial radionuclides within the first 2.5 cm of the sedimentary column. The excess 210Pb inventory was used to normalize 239,240Pu and 137Cs inventories for variable sediment fluxes. The 239,240Pu/210Pb xs ratio was uniform across the entire sea, with a mean value of 1.24×10−3, indicating homogeneous fallout of 239,240Pu. The 137Cs/210Pb xs ratio showed differences between the eastern (0.049) and western basins (0.030), clearly significant impact of deep sea sediments from the Chernobyl accident. The inventory ratios of 239,240Pu/137Cs were 0.041 and 0.025 in the western and eastern basins respectively, greater than the fallout ratio, 0.021, showing more efficient scavenging of 239,240Pu in the water column and major sedimentation of 137Cs in the eastern basin. Although areas with water depths of >2000 m constitute around 40% of the entire Mediterranean basin, the sediments in these regions only contained 2.7% of the 239,240Pu and 0.95% of the 137Cs deposited across the Sea in 2000. These data show that the accumulation of artificial radionuclides in deep Mediterranean environments is much lower than predicted by other studies from the analysis of continental shelf sediments. [Copyright &y& Elsevier]

The present plutonium and 137Cs concentrations in South Pacific Ocean surface waters were determined. The water samples were collected in the South Pacific mid-latitude region (32.5 °S) during the BEAGLE expedition conducted in 2003–04 by JAMSTEC. 239,240Pu concentrations in surface seawater of the South Pacific were in the range of 0.5 to 4.1 mBq m−3, whereas 137Cs concentrations ranged from 0.07 to 1.7 Bq m−3. The observed 239,240Pu and 137Cs concentrations in the South Pacific were almost of the same level as those in the North Pacific subtropical gyre. The surface 239,240Pu in the South Pacific subtropical gyre showed larger spatial variations than 137Cs, as it may be affected by physical and biogeochemical processes. The 239,240Pu/137Cs activity ratios, which reflect biogeochemical processes in seawater, were generally smaller than that observed in global fallout, except for the most eastern station. The 239,240Pu/137Cs ratios in the South Pacific tend to be higher than that in the North Pacific. The relationships between anthropogenic radionuclides and oceanographic parameters such as salinity and nutrients were examined. The 137Cs concentrations in the western South Pacific (the Tasman Sea) and the eastern South Pacific were negatively correlated with the phosphate concentration, whereas there is no correlation between the 137Cs and nutrients concentrations in the South Pacific subtropical gyre. The mutual relationships between anthropogenic radionuclides and oceanographic parameters are important for better understanding of transport processes of anthropogenic radionuclides and their fate in the South Pacific. [Copyright &y& Elsevier]

Abstract: The Late Holocene fine-grained sedimentation in the deep central Balearic Abyssal Plain, Western Mediterranean Sea, has been studied after the analysis of high quality sediment cores from three multicoring stations, named A, B and C. The coring stations are 25 km apart from each other and form a triangle that is at the greatest distance from the nearest landmasses. The sediments consist of foraminifer–pteropod oozes (layers U1 and U4 from bottom to top), two pteropod oozes (U2 and U5) and a turbidite layer (U3). The same sequence has been identified in the three cores. The turbidite layer U3 that lies on top of U2 (14C AMS dated at 1814 cal yrs BP) ranges from 5 to 11 cm thick and is clearly distinguished from the dominating hemipelagic sediments by colour variations, higher water content and the absence of planktonic foraminifer shells. Rather uniform values of organic carbon and nitrogen are also characteristic of the U3 turbidite unit, likely because of homogenisation during transport and emplacement. In addition, U3 unit shows higher contents of terrigenous elements such as K and Fe. Otherwise, the presence of zeolites in the turbidite layer supports the hypothesis of the Sardinian continental margin, where pyroclastic deposits are known, as the most likely source area for U3. Our results demonstrate the ability of turbidity currents originating on the margins surrounding the Balearic Abyssal Plain to reach the very centre of the basin during high sea level still stands as the present one. [Copyright &y& Elsevier]

As part of the FRUELA experiment, 11 sediment cores were recovered from the Bellingshausen Sea, the western Bransfield and Gerlache Straits (Antarctic Peninsula) to determine the spatial distribution of organic carbon (OC), biogenic silica (BSi), and nitrogen (N) in the sediment under regions of known irregular primary production rates (PPRs).OC, BSi, and N contents ranged from 0.3% to 1.2%, from 5.7% to 20.4%, and from 0.03% to 0.17%, respectively. Apparent mean sediment accumulation rates (SARs) varied between 0.25 and 3.11 mm year-1 (220 and 1750 g m-2 year-1). Central Gerlache and western Bransfield Straits (the Orleans Canyon) had the highest biogenic constituents contents and sediment accumulation rates, whereas the northern coast off Snow Island (Bellingshausen Sea) showed the lowest values.Central Gerlache Strait, with the highest primary production rates in the study area, was the only region where the OC and BSi contents in the sediment corresponded to the photosynthetic activity in the euphotic zone above it. At the extremes of Gerlache Strait as in western Bransfield Strait, sediment focusing by currents enhanced by depressions in the sea floor contributed to develop regions with high biogenic constituent concentrations, whereas at the Bellingshausen Sea and western Gerlache Strait, winnowing by currents may drift away the biogenic material exported from the euphotic zone. Apparently, bottom relief and currents rather than solely depth determined the modern distribution and accumulation rates of biogenic particulate matter in the study area. Paleoceanographic interpretations of the sedimentary record from Antarctic marginal seas, such as Gerlache and Bransfield Straits, should consider that focusing due to lateral transport and sea floor morphology and the preferential degradation of OC relative to BSi may increase to an important degree the biogenic contents in the sediment, especially the opal. OC and BSi accumulation in Antarctic marginal seas could be as important as the broad continental shelves despite large spatial differences. [Copyright &y& Elsevier]

The accumulation rates of sediment and major constituents in three different geographic areas of the Alboran Sea have been assessed by means of 210Pb and 137Cs concentration profiles. Mixing is present in the top layer of the sedimentary column, with mixing coefficients estimated to range from 0.2 to 15 cm2 yr−1. Overall, apparent sedimentation rates for the last 100 years range from 0.014 to 0.182 g cm−2 yr−1 and show a tendency to decrease with distance to the coast and water column depth. However, specific characteristics of the sea floor for each physiographic environment govern the actual patterns of sediment accumulation. Particularly noticeable are the feeding role of submarine canyons, the trapping effect of slope terraces and the isolation caused by ridges. Sediment accumulation induced by turbiditic flows is also observed north of the Almeria–Oran area. Excess 210Pb inventories and surface concentrations reveal a net effect of sediment focussing and point to the role of bottom nepheloid layers in supplying a significant fraction of sediments to the deep areas. This is also evidenced by comparison of bottom sediment with the sediment trap data available from the Malaga area. We estimate that the particle advective input below 30 m above the bottom accounts for as much as 50–70% of the material that is ultimately deposited onto the sea floor. The greater abundance of lithogenic material in the Malaga zone (∼80%) reflects its larger input in the western Alboran Sea. Conversely, carbonate contents increase from less than 20% in this area to about 30% in the Almeria–Oran zone, reflecting the lesser importance of the dilution by lithogenic components. Biogenic silica was only detected in some surface samples, and no significant preservation was observed below the Eh boundary. Abundance and accumulation rates of organic matter are in accordance with the spatial patterns of primary production in the Alboran Sea: higher in the western part, due to the presence of the Western Alboran Gyre. However, near-bottom redistribution leads to the homogenisation of organic matter concentrations in bottom sediments of any given area. Finally, from comparisons with sediment trap data, the degradation of organic matter has been estimated to be approximately 30–40% of what reaches the bottom. [Copyright &y& Elsevier]

Discusses a study which assessed the sediment, carbon and nitrogen accumulation rates along a high-productivity area, Gerlache Strait, Antarctica. Sample collection and analytical methods; Results; Discussion.

The Ixtoc-1 oil spill (1979–80) released 475 million liters of petroleum into the Southern Gulf of Mexico (sGoM) likely causing Marine Oil Snow Sedimentation and Flocculent Accumulation (MOSSFA) to occur. A multiproxy approach including short-lived radioisotopes (210Pb xs), benthic foraminifera stable isotopes (δ13C CaCO3), and volcanic sediment grains was used to investigate regional events (e.g. oil spills and volcanic eruptions) recorded in sedimentary records. Depleted δ13C CaCO3 from 1979 to 80 outside of natural variability most likely results from petrogenic carbon deposition 100–250 km west of Ixtoc-1, possibly associated with MOSSFA. An event, characterized by increased volcanic input, depleted δ13C CaCO3 , and increased mass accumulation rates was consistent with the El Chichón eruption (1982) 80–100 km north of Ixtoc-1. Many factors confound the uniform distribution and preservation of these events in the sGoM. However, a multiproxy approach may aid to distinguish multiple events in the sGoM sedimentary record. • Event identified in recent sediments consistent with preserved Ixtoc-1 oil spill (1979–80), MOSSFA. • Event identified in recent sediments consistent with El Chichón volcanic eruption (1982). • Multiproxy approach is necessary to disentangle and identify events in recent sediments. [ABSTRACT FROM AUTHOR]