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At least 1,135 records · Page 63Linked to original sources
USGS2014

Effect of light on biodegradation of Estrone, 17β-estradiol, and 17α-ethinylestradiol in stream sediment

Biodegradation of [A-ring 14 C] Estrone (E1), 17β-estradiol (E2), and 17α-ethinylestradiol (EE2) to 14 CO 2 was investigated under light and dark conditions in microcosms containing epilithon or sediment collected from Boulder Creek, Colorado. Mineralization of the estrogen A-ring was observed in all sediment treatments, but not epilithon treatments. No difference in net mineralization between light and dark treatments was observed for 14 C-E2. Net mineralization of 14 C-E1 and 14 C-EE2 was enhanced in light treatments. Extents of 14 CO 2 accumulation and rates of mineralization were significantly greater for E2 than E1 under dark conditions, but were comparable under light conditions. These results indicate substantial differences in the uptake and metabolism of E1 and E2 in the environment and suggest biorecalcitrance of E1 relative to E2 in light-limited environments. The extent of 14 CO 2 accumulation and rate of mineralization for EE2 in dark treatments were less than half of that observed for E2 and generally lower than for E1, consistent with previous reports of EE2 biorecalcitrance. However, 14 CO 2 accumulation and rates of mineralization were comparable for EE2, E2, and E1 under light conditions. These results indicate photoactivation and/or phototransformation/photodegradation processes can substantially enhance heterotrophic biodegradation of estrogens in sunlit environments and may play an important role in estrogen transport and attenuation.

Colorado↗
USGS2013

Tree growth and competition in an old-growth Picea abies forest of boreal Sweden: influence of tree spatial patterning

Question: What factors best characterize tree competitive environments in this structurally diverse old-growth forest, and do these factors vary spatially within and among stands? Location: Old-growth Picea abies forest of boreal Sweden. Methods: Using long-term, mapped permanent plot data augmented with dendrochronological analyses, we evaluated the effect of neighbourhood competition on focal tree growth by means of standard competition indices, each modified to include various metrics of trees size, neighbour mortality weighting (for neighbours that died during the inventory period), and within-neighbourhood tree clustering. Candidate models were evaluated using mixed-model linear regression analyses, with mean basal area increment as the response variable. We then analysed stand-level spatial patterns of competition indices and growth rates (via kriging) to determine if the relationship between these patterns could further elucidate factors influencing tree growth. Results: Inter-tree competition clearly affected growth rates, with crown volume being the size metric most strongly influencing the neighbourhood competitive environment. Including neighbour tree mortality weightings in models only slightly improved descriptions of competitive interactions. Although the within-neighbourhood clustering index did not improve model predictions, competition intensity was influenced by the underlying stand-level tree spatial arrangement: stand-level clustering locally intensified competition and reduced tree growth, whereas in the absence of such clustering, inter-tree competition played a lesser role in constraining tree growth. Conclusions: Our findings demonstrate that competition continues to influence forest processes and structures in an old-growth system that has not experienced major disturbances for at least two centuries. The finding that the underlying tree spatial pattern influenced the competitive environment suggests caution in interpreting traditional tree competition studies, in which tree spatial patterning is typically not taken into account. Our findings highlight the importance of forest structure – particularly the spatial arrangement of trees – in regulating inter-tree competition and growth in structurally diverse forests, and they provide insight into the causes and consequences of heterogeneity in this old-growth system.

V�sterbotten County↗
USGS2018

Macrobenthic infaunal communities associated with deep‐sea hydrocarbon seeps in the northern Gulf of Mexico

There are thousands of seeps in the deep ocean worldwide; however, many questions remain about their contributions to global biodiversity and the surrounding deep‐sea environment. In addition to being globally distributed, seeps provide several benefits to humans such as unique habitats, organisms with novel genes, and carbon regulation. The purpose of this study is to determine whether there are unique seep macrobenthic assemblages, by comparing seep and nonseep environments, different seep habitats, and seeps at different depths and locations. Infaunal community composition, diversity, and abundance were examined between seep and nonseep background environments and among three seep habitats (i.e., microbial mats, tubeworms, and soft‐bottom seeps). Abundances were higher at seep sites compared to background areas. Abundance and diversity also differed among microbial mat, tubeworm, and soft‐bottom seep habitats. Although seeps contained different macrobenthic assemblages than nonseep areas, infaunal communities were also generally unique for each seep. Variability was 75% greater within communities near seeps compared to communities in background areas. Thus, high variability in community structure characterized seep communities rather than specific taxa. The lack of similarity among seep sites supports the idea that there are no specific infauna that can be used as indicators of seepage throughout the northern Gulf of Mexico, at least at higher taxonomic levels.

Marine Ecology↗
USGS2017

Loss of dendritic connectivity in southern California's urban riverscape facilitates decline of an endemic freshwater fish

Life history adaptations and spatial configuration of metapopulation networks allow certain species to persist in extreme fluctuating environments, yet long-term stability within these systems relies on the maintenance of linkage habitat. Degradation of such linkages in urban riverscapes can disrupt this dynamic in aquatic species, leading to increased extinction debt in local populations experiencing environment-related demographic flux. We used microsatellites and mtDNA to examine the effects of collapsed network structure in the endemic Santa Ana sucker Catostomus santaanae of southern California, a threatened species affected by natural flood-drought cycles, ‘boom-and-bust’ demography, hybridization, and presumed artificial transplantation. Our results show a predominance of drift-mediated processes in shaping population structure, and that reverse mechanisms for counterbalancing the genetic effects of these phenomena have dissipated with the collapse of dendritic connectivity. We use approximate Bayesian models to support two cases of artificial transplantation, and provide evidence that one of the invaded systems better represents the historic processes that maintained genetic variation within watersheds than any remaining drainages where C. santaanae is considered native. We further show that a stable dry gap in the northern range is preventing genetic dilution of pure C. santaanae persisting upstream of a hybrid assemblage involving a non-native sucker, and that local accumulation of genetic variation in the same drainage is influenced by position within the network. This work has important implications for declining species that have historically relied on dendritic metapopulation networks to maintain source-sink dynamics in phasic environments, but no longer possess this capacity in urban-converted landscapes.

California↗
USGS2018

Ancient convergent losses of Paraoxonase 1 yield potential risks for modern marine mammals

Mammals diversified by colonizing drastically different environments, with each transition yielding numerous molecular changes, including losses of protein function. Though not initially deleterious, these losses could subsequently carry deleterious pleiotropic consequences. We have used phylogenetic methods to identify convergent functional losses across independent marine mammal lineages. In one extreme case, Paraoxonase 1 ( PON1 ) accrued lesions in all marine lineages, while remaining intact in all terrestrial mammals. These lesions coincide with PON1 enzymatic activity loss in marine species’ blood plasma. This convergent loss is likely explained by parallel shifts in marine ancestors’ lipid metabolism and/or bloodstream oxidative environment affecting PON1’s role in fatty acid oxidation. PON1 loss also eliminates marine mammals’ main defense against neurotoxicity from specific man-made organophosphorus compounds, implying potential risks in modern environments.

Science↗
USGS2007

Overview of issues in subsurface and landfill microbiology

To date, the majority of evidence indicates that most subsurface environments possess climax ecological communities that are well adapted to the environment in which they live. Like their counterparts on the surface, subsurface ecosystems are characterized by a high degree of microbiological diversity, they possess trophic structure, and they exhibit material cycling and energy transfer. Members of such ecosystems typically possess structural, physiological, or reproductive adaptations that allow them to disperse and survive in such habitats. Current studies argue that microbial activities influence the geochemical processes in both landfills and subsurface environments and that the altered geochemistry, in turn, influences the selection of microorganisms proliferating in the habitat. However, while microbial activity may often be limited by the availability of electron donors in uncontaminated aquifer systems, this is rarely the case with landfills. Sections in this chapter provide investigators with a greater understanding of the experimental approaches needed to study the microbiology of the terrestrial subsurface and an appreciation of interpretational limits imposed by the existing methodologies. The hope is that further study of subsurface microorganisms will provide insights into the process of microbial evolution and possibly into the origins of life itself.

Book chapter↗
USGS2014

Identification of Mn(II)-oxidizing bacteria from a low-pH contaminated former uranium mine

Biological Mn oxidation is responsible for producing highly reactive and abundant Mn oxide phases in the environment that can mitigate metal contamination. However, little is known about Mn oxidation in low-pH environments, where metal contamination often is a problem as the result of mining activities. We isolated two Mn(II)-oxidizing bacteria (MOB) at pH 5.5 ( Duganella isolate AB_14 and Albidiferax isolate TB-2) and nine strains at pH 7 from a former uranium mining site. Isolate TB-2 may contribute to Mn oxidation in the acidic Mn-rich subsoil, as a closely related clone represented 16% of the total community. All isolates oxidized Mn over a small pH range, and isolates from low-pH samples only oxidized Mn below pH 6. Two strains with different pH optima differed in their Fe requirements for Mn oxidation, suggesting that Mn oxidation by the strain found at neutral pH was linked to Fe oxidation. Isolates tolerated Ni, Cu, and Cd and produced Mn oxides with similarities to todorokite and birnessite, with the latter being present in subsurface layers where metal enrichment was associated with Mn oxides. This demonstrates that MOB can be involved in the formation of biogenic Mn oxides in both moderately acidic and neutral pH environments.

Applied and Environmental Microbiology↗
USGS2024

Krumholzibacteriota and Deltaproteobacteria contain rare genetic potential to liberate carbon from monoaromatic compounds in subsurface coal seams

Biogenic methane in subsurface coal seam environments is produced by diverse consortia of microbes. Although this methane is useful for global energy security, it remains unclear which microbes can liberate carbon from the coal. Most of this carbon is relatively resistant to biodegradation, as it is contained within aromatic rings. Thus, to explore for coal-degrading taxa in the subsurface, this study reconstructed relevant metagenome-assembled genomes (MAGs) from coal seams by using a key genomic marker for the anaerobic degradation of monoaromatic compounds as a guide: the benzoyl-CoA reductase gene ( bcrABCD ). Three MAGs were identified with this genetic potential. The first represented a novel taxon from the Krumholzibacteriota phylum, which this study is the first to describe. This Krumholzibacteriota MAG contained a full set of genes for benzoyl-CoA dearomatization, in addition to other genes for anaerobic catabolism of monoaromatics. Analysis of Krumholzibacteriota MAGs from other environments revealed that this genetic potential may be common, and thus, Krumholzibacteriota may be important organisms for the liberation of recalcitrant carbon in a broad range of environments. Moreover, the assembly and characterization of two Syntrophorhabdus aromaticivorans MAGs from different continents and a Syntrophaceae sp. MAG implicate the Deltaproteobacteria class in coal seam monoaromatic degradation. Each of these taxa are potential rate-limiting organisms for subsurface coal-to-methane biodegradation. Their description here provides some understanding of their function within the coal seam microbiome and will help inform future efforts in coal bed methane stimulation, anoxic bioremediation of organic pollutants, and assessments of anoxic, subsurface carbon cycling and emissions.

mBio↗
USGS2000

Stratigraphy, correlation, depositional setting, and geophysical characteristics of the Oligocene Snowshoe Mountain Tuff and Creede Formation in two cored boreholes

Core descriptions and geophysical logs from two boreholes (CCM-1 and CCM-2) in the Oligocene Snowshoe Mountain Tuff and Creede Formation, south-central Colorado, are used to interpret sedimentary and volcanic facies associations and their physical properties. The seven facies association include a mixed sequence of intracaldera ash-flow tuffs and breccias, alluvial and lake margin deposits, and tuffaceous lake beds. These deposits represent volcanic units related to caldera collapse and emplacement of the Snowshoe Mountain Tuff, and sediments and pyroclastic material deposited in the newly formed caldera basin, Early sedimentation is interpreted to have been rapid, and to have occurred in volcaniclastic fan environments at CCM-1 and in a variery of volcaniclastic fan, braided stream shallow lacustrine, and mudflat environments at CCM-2. After an initial period of lake-level rise, suspension settling, turbidite, and debris-flow sedimentation occurred in lacustrine slope and basin environments below wave base. Carbonate sedimentation was initially sporadic, but more continuous in the latter part of the recorded lake history (after the H fallout tuff). Sublacustrine-fan deposition occurred at CCM-1 after a pronounced lake-level fall and subsequent rise that preceded the H tuff. Variations in density, neutron, gamma-ray, sonic, and electrical properties of deposits penetrated oin the two holes reflect variations in lithology, porosity, and alteration. Trends in the geophysical properties of the lacustrine strata are linked to downhole changes in authigenic mineralology and a decrease in porosity interpreted to have resulted primarily from diagenesis. Lithological and geophysical characteristics provide a basis for correlation of the cores; however, mineralogical methods of correlation are hampered by the degree of diagenesis and alteration.

Colorado↗
USGS2015

The modern muds of Laguna Mar Chiquita (Argentina): Particle size and geochemical trends from a large saline lake in the "thick-skinned" Andean foreland

Laguna Mar Chiquita (central Argentina; ~latitude 31°S, longitude 63°W) provides an outstanding opportunity to examine organic facies development and petroleum source-rock potential in a modern thick-skinned foreland basin lake. In this case study, we define profundal, paleodelta, and lake-margin depositional environments based on trends in bathymetry and lake-floor sediment particle size. Sedimentary geochemical analyses indicate that organic carbon–rich muds accumulate in profundal environments during the extant lake-level highstand. The lateral variability of organic facies is minimal. The quality of organic facies is controlled by lake level and depositional environment, both of which dictate patterns of algal productivity, siliciclastic dilution, and early diagenesis. We present conceptual models of lacustrine source rocks in both thick-skinned and thin-skinned foreland basins based on modern analog data from both Laguna Mar Chiquita and other lakes in the central Andean foreland. Over relatively short time intervals (10 2 –10 4 yr), climatically driven water-level fluctuations influence the source-rock potential of these basins. Over time intervals >10 5 yr, contraction and lateral migration of the basin flexural profile control stratal stacking patterns and the potential for hydrocarbon play development.

Laguna Mar Chiquita↗
USGS2016

The Maryland Coastal Plain Aquifer Information System: A GIS-based tool for assessing groundwater resources

Groundwater is the source of drinking water for ∼1.4 million people in the Coastal Plain Province of Maryland (USA). In addition, groundwater is essential for commercial, industrial, and agricultural uses. Approximately 0.757 × 109 L d –1 (200 million gallons/d) were withdrawn in 2010. As a result of decades of withdrawals from the coastal plain confined aquifers, groundwater levels have declined by as much as 70 m (230 ft) from estimated prepumping levels. Other issues posing challenges to long-term groundwater sustainability include degraded water quality from both man-made and natural sources, reduced stream base flow, land subsidence, and changing recharge patterns (drought) caused by climate change. In Maryland, groundwater supply is managed primarily by the Maryland Department of the Environment, which seeks to balance reasonable use of the resource with long-term sustainability. The chief goal of groundwater management in Maryland is to ensure safe and adequate supplies for all current and future users through the implementation of appropriate usage, planning, and conservation policies. To assist in that effort, the geographic information system (GIS)–based Maryland Coastal Plain Aquifer Information System was developed as a tool to help water managers access and visualize groundwater data for use in the evaluation of groundwater allocation and use permits. The system, contained within an ESRI ArcMap desktop environment, includes both interpreted and basic data for 16 aquifers and 14 confining units. Data map layers include aquifer and ­confining unit layer surfaces, aquifer extents, borehole information, hydraulic properties, time-series groundwater-level data, well records, and geophysical and lithologic logs. The aquifer and confining unit layer surfaces were generated specifically for the GIS system. The system also contains select groundwater-quality data and map layers that quantify groundwater and surface-water withdrawals. The aquifer information system can serve as a pre- and postprocessing environment for groundwater-flow models for use in water-supply planning, development, and management. The system also can be expanded to include features that evaluate constraints to groundwater development, such as insufficient available drawdown, degraded groundwater quality, insufficient aquifer yields, and well-field interference. Ultimately, the aquifer information system is intended to function as an interactive Web-based utility that provides a broad array of information related to groundwater resources in Maryland’s coastal plain to a wide-ranging audience, including well drillers, consultants, academia, and the general public.

Special Paper of the Geological Society of America↗
USGS1971

The geochemist’s involvement with the pollution problem

The geochemist can contribute much information of value toward assessing the effect of environment, including inorganic pollution, on health. The average composition of rocks, soils, plants, and water and also the increments of inorganic substances that can be expected in geologic environments of high-metal content are essential for comparison with metal contents of these components of the environment in areas contaminated by various types of inorganic air and water pollution. Background levels of lead, zinc, nickel, chromium, copper, and manganese in soils and in four classes of vegetation have been estimated from collections that were made in remote areas presumed to be free from inorganic contamination. The trace-metal content of soils and plants varies widely in different geologic provinces of the United States; in those areas of high natural mineralization, additions of metals from man-made pollution may compound a possible hazard. Results of sampling in urban areas show that contamination of vegetation by gasoline lead can be expected for at least 1000 ft back from transportation lanes, and that the lead burden is increasing greatly with time. Ore-treatment plants can also be a source of air contamination for several miles downwind and several thousand feet in other directions. Soils of naturally high metal content in a mining district may be further contaminated with both major and minor elements from smelting operations. Recent studies show that volatile elements are released directly to the air from ore deposits in place. Concentrations of mercury, for instance, may be as much as 20 times background for several hundred feet in altitude over ore deposits in which mercury occurs as a relatively minor constituent. The source of inorganic pollution in surface drainage and also in ground water is commonly geologic, as rivers may be contaminated from coal and metal deposits in place and also from mining and smelting operations. More information of the type illustrated should be accumulated and made available to scientists who are working in environmental health, and, in particular, to those involved in the pollution problem. Only by these means can we provide a scientific basis for the enactment of realistic and effective legislation for pollution control.

Book chapter↗
USGS1969

Modern coastal mangrove swamp stratigraphy and the ideal cyclothem

The general stratigraphy of the “ideal” cyclothem of Late Paleozoic age can be recognized in a modern succession of sedimentary units underlying the coastal mangrove swamps of southwestern Florida. Because coal deposition is associated with the formation of cyclothems, this stratigraphic similarity has geologic importance with respect to coal formation. The lower part of the succession in Florida consists of nonmarine sediments, the middle part of brackish-water or fresh-water mangrove peat, and the upper part of brackish-water and marine units. This sequence of sediments records a relative rise in sea level. In comparison, the lower part of the ideal cyclothem consists basically of nonmarine units, the central sedimentary member is coal, and the upper units are brackish-water and marine sediments. The ideal cyclothem is thought to have formed in part in a deltaic environment and to record a periodic fluctuation in terrigenous sediment supply and a relative rise in sea level. In contrast, southwestern Florida has essentially no deltas, as most of its paralic sediments are derived from coastal sources. In view of this, the stratigraphic similarity noted above must reflect a partial duplication of sedimentary environments brought about by a relative rise in sea level across a low coastal platform supporting peat-depositing paralic and fresh-water swamps and forests. This conclusion tends to support the point of view that the coal member of some cyclothems formed in a swampy environment penecontemporaneously with a relative rise in sea level. The coal member, therefore, is in part a transgressive unit.

Florida↗
USGS2015

Mechanics of sediment suspension and transport within a fringing reef

Large bottom roughness is a characteristic of most coral reef environments and this has been shown to have a substantial impact on hydrodynamic processes in these environments. In this paper, we evaluate suspended sediment concentration (SSC) data as well detailed hydrodynamic data over a coral reef flat in Ningaloo Reef, Western Australia, to understand how this bottom roughness affects these processes. A well-developed logarithmic velocity layer consistently developed above a canopy layer during the experiment. Estimates of bottom stresses from these logarithmic profiles were comparable with estimates obtained directly from turbulent Reynolds stresses, and an order of magnitude greater than those typically reported for sandy beach environments having similar flow. Nevertheless, the sediment grain size distribution of the suspended load was very fine relative to what should be mobilized by these stresses, indicated the large roughness substantially suppressed sediment transport.

Tantabiddi↗
USGS2010

Biocomplexity in mangrove ecosystems

Mangroves are an ecological assemblage of trees and shrubs adapted to grow in intertidal environments along tropical coasts. Despite repeated demonstration of their economic and societal value, more than 50% of the world's mangroves have been destroyed, 35% in the past two decades to aquaculture and coastal development, altered hydrology, sea-level rise, and nutrient overenrichment. Variations in the structure and function of mangrove ecosystems have generally been described solely on the basis of a hierarchical classification of the physical characteristics of the intertidal environment, including climate, geomorphology, topography, and hydrology. Here, we use the concept of emergent properties at multiple levels within a hierarchical framework to review how the interplay between specialized adaptations and extreme trait plasticity that characterizes mangroves and intertidal environments gives rise to the biocomplexity that distinguishes mangrove ecosystems. The traits that allow mangroves to tolerate variable salinity, flooding, and nutrient availability influence ecosystem processes and ultimately the services they provide. We conclude that an integrated research strategy using emergent properties in empirical and theoretical studies provides a holistic approach for understanding and managing mangrove ecosystems.

Annual Review of Marine Science↗
USGS1993

The use of NOAA AVHRR data for assessment of the urban heat sland effect

A vegetation index and a radiative surface temperature were derived from satellite data acquired at approximately 1330 LST for each of 37 cities and for their respective nearby rural regions from 28 June through 8 August 1991. Urban–rural differences for the vegetation index and the surface temperatures were computed and then compared to observed urban–rural differences in minimum air temperatures. The purpose of these comparisons was to evaluate the use of satellite data to assess the influence of the urban environment on observed minimum air temperatures (the urban heat island effect). The temporal consistency of the data, from daily data to weekly, biweekly, and monthly intervals, was also evaluated. The satellite-derived normalized difference (ND) vegetation-index data, sampled over urban and rural regions composed of a variety of land surface environments, were linearly related to the difference in observed urban and rural minimum temperatures. The relationship between the ND index and observed differences in minimum temperature was improved when analyses were restricted by elevation differences between the sample locations and when biweekly or monthly intervals were utilized. The difference in the ND index between urban and rural regions appears to be an indicator of the difference in surface properties (evaporation and heat storage capacity) between the two environments that are responsible for differences in urban and rural minimum temperatures. The urban and rural differences in the ND index explain a greater amount of the variation observed in minimum temperature differences than past analyses that utilized urban population data. The use of satellite data may contribute to a globally consistent method for analysis of urban heat island bias.

Journal of Applied Meteorology and Climatology↗
USGS2013

Tracking animals in freshwater with electronic tags: past, present and future

Considerable technical developments over the past half century have enabled widespread application of electronic tags to the study of animals in the wild, including in freshwater environments. We review the constraints associated with freshwater telemetry and biologging and the technical developments relevant to their use. Technical constraints for tracking animals are often influenced by the characteristics of the animals being studied and the environment they inhabit. Collectively, they influence which and how technologies can be used and their relative effectiveness. Although radio telemetry has historically been the most commonly used technology in freshwater, passive integrated transponder (PIT) technology, acoustic telemetry and biologgers are becoming more popular. Most telemetry studies have focused on fish, although an increasing number have focused on other taxa, such as turtles, crustaceans and molluscs. Key technical developments for freshwater systems include: miniaturization of tags for tracking small-size life stages and species, fixed stations and coded tags for tracking large samples of animals over long distances and large temporal scales, inexpensive PIT systems that enable mass tagging to yield population- and community-level relevant sample sizes, incorporation of sensors into electronic tags, validation of tag attachment procedures with a focus on maintaining animal welfare, incorporation of different techniques (for example, genetics, stable isotopes) and peripheral technologies (for example, geographic information systems, hydroacoustics), development of novel analytical techniques, and extensive international collaboration. Innovations are still needed in tag miniaturization, data analysis and visualization, and in tracking animals over larger spatial scales (for example, pelagic areas of lakes) and in challenging environments (for example, large dynamic floodplain systems, under ice). There seems to be a particular need for adapting various global positioning system and satellite tagging approaches to freshwater. Electronic tagging provides a mechanism to collect detailed information from imperilled animals and species that have no direct economic value. Current and future advances will continue to improve our knowledge of the natural history of aquatic animals and ecological processes in freshwater ecosystems while facilitating evidence-based resource management and conservation.

Animal Biotelemetry↗
USGS2025

Rapid Holocene deposition in the Mackenzie Trough and Barrow Canyon areas in the western Arctic Ocean

The Arctic Ocean and terrestrial environment have recently been reported to be changing drastically, but it is unclear whether these changes are similar to natural variations in the past or how sudden and large the changes are compared to natural variations. This premise served as motivation to collect sediment cores during the summer of 2022 at four sites on the Canadian continental shelf and Alaskan upper continental slope to reconstruct changes in the marine and terrestrial environments to provide a comprehensive picture of the ocean environment during the preindustrial period before anthropogenic influences. We dated the sediments based on the 137 Cs radioactivity of bulk sediments and the 14 C concentrations of mollusk shells. The 137 Cs radioactivity shows a distinct onset corresponding to 1950 Common Era (CE) and the most prominent peak corresponding to 1963 CE. Multiple peaks appeared above the most prominent one, coinciding with nuclear power plant accidents in 1986 and 2011. Inventories of excess 210 Pb in all cores exceed the estimated supply of excess 210 Pb from atmospheric deposition, likely due to the scavenging supply of excess 210 Pb. By comparing 137 Cs and radiocarbon conventional ages, we estimated the local radiocarbon reservoir age value of each site. Using these local radiocarbon reservoir age and the conventional ages of mollusk shell samples, we established the age-depth models by the Bayesian method. The optimal ΔR values were 598, 511, 65, and –60 years at the MT1, MT2, BC2, and BC2-2 sites, respectively. The cores consist of clayey silts continuously deposited with uniquely high sedimentation rates of 0.17 to 0.74 cm y −1 . Variation in the Ca/Ti ratio indicates ~ 20, ~ 30, 50–60, 100–125, and 300-year cycles, likely attributed to the variation in the Aleutian Low that controls the Bering Strait inflow of Pacific waters influencing our core sites. These sediments will be used for further high-resolution, multi-proxy studies with forthcoming results.

western Arctic Ocean↗