210Pb Chronology Research Articles

Paleoenvironmental characterization and historical trends of polycyclic aromatic hydrocarbons (PAHs) of Nutrias Lagoon, Uruguay

Concentrations of polycyclic aromatic hydrocarbons were assessed in a sediment core retrieved from Nutrias Lagoon, located within the Rocha Lagoon Protected Area along the SE Uruguayan coast. Using a 210Pb chronology, we reconstructed the historical accumulation of polycyclic aromatic hydrocarbons over the past 123 years (1895-2018). This study, the first of its kind in Uruguay, fills a research gap in understanding historical PAH accumulation and source changes. Our examination of dating, geochemical, and sedimentological data unveiled four main events, with minor instances in 1956±5 and 1964±4, and more significant occurrences in 1914±9 and 1997±2. Additionally, two prominent trend shifts were identified, one predating 1900 and the other in 1986±2. Before 1900, a dry spell was apparent, supported by all proxies, alongside a notable surge in heavy polycyclic aromatic hydrocarbons, likely attributed to fires during this arid period. Post-1986±2, a rise in sedimentation rates in the lagoon was observed, possibly due to increased rainfall. Also, the eutrophication of the lagoon over the years can be observed. Furthermore, a recent increase in polycyclic aromatic hydrocarbons influx at the core's surface was linked to the construction of a nearby lagoon bridge and associated roadwork. Our findings suggest that atmospheric deposition constitutes the primary source of polycyclic aromatic hydrocarbons in the lagoon, offering insights into its recent environmental history and basin dynamics. This study establishes a critical baseline for future research in the region and facilitates the development of effective and sustainable environmental management strategies.

Biogenic silica in sediment core indicates the historical development of off-bottom oyster farming

Sediment cores are commonly used for reconstructing historical events by determining the biogenic elements in sediment vertical profiles. The vertical flux of biogenic silica (BSi) can be enhanced by bivalve mollusks through biodeposition and can be subsequently recorded in the sediment core. However, whether BSi in sediment core can indicate the interactions between aquaculture farms and the ecosystem is unclear. In this study, sediment cores were collected from a typical off-bottom oyster farm in Sanggou Bay, China. Based on 210Pb chronology analysis of the sediment vertical profile, BSi content was determined to reflect the BSi burial flux during the farming history. The BSi biodeposition fluxes were estimated based on the biodeposition model, to identify the correspondence among BSi burial flux, BSi biodeposition flux, and annual oyster production during the historical development of the farm. The results show that the BSi density in the sediment increased obviously after 1980 when intensive oyster farming began, and reduced after 2000 when farming began to decline. Moreover, BSi burial flux had a corresponding relationship with oyster production and the simulated biodeposition rate, except for 1997–2001 when oyster production peaked. Our finding supported that the variation of BSi from biodeposition can be preserved and then recorded in the sediment, suggesting that BSi could be considered as an indicator to reconstruct the historical development of the oyster farm.

The biogenic elements retention in reservoirs of the Yangtze River basin and effect on the nutrient flux into the sea

The Yangtze River catchment is among the most human-impacted basins globally, with a population of approximately 590 million and over 60,000 dams constructed by 2020. While the effect of reservoir dams on runoff and sediment has been extensively studied, assessing the impact of biogenic element retention in reservoirs on nutrient flux into the sea remains a challenge. This study analyzed the total organic carbon (TOC), total organic nitrogen (TN), biogenic silica (BSi), grain size, and 210Pb chronology of sediment cores collected from the Pengshui, Wuqiangxi, Three Gorges, and Danjiangkou reservoirs. The analysis was combined with the database of annual reservoir area and nutrient flux into the sea of the Yangtze River. The results showed that the average annual sedimentary retention of TOC, TN, and BSi in the four reservoirs increased by 16%, 18%, and 26% after dam construction and rapid eutrophication. The total water area of large reservoirs increased from 30 to 132,000 km2 between 1960 and 2016, resulting in total accumulated retention increments of TOC, dissolved inorganic nitrogen (DIN), dissolved inorganic phosphate (DIP), and dissolved silicon (DSi) in reservoirs reaching 27, 3.5, 0.1, and 27.2 million tons, respectively. The retention increments accounted for 20.6%, 7.0%, 8.8%, and 12.1% of the total flux of TOC, DIN, DIP, and DSi into the sea during the same period, respectively. The retention of TOC and DSi in reservoirs led to a decrease in their annual flux into the sea by 67.2% and 61.4% in 2016 compared to 1960. However, the retention of DIN and DIP increased their annual flux by 6.4-fold and 4.2-fold in 2016 compared to 1960, which was attributed to the substantial emission of fertilizer and sewage in the downstream catchment area of dams. These findings provide valuable insights into biogenic element retention in reservoir catchments and their impact on nutrient flux into the sea.

Growth rate estimation by 210Pb chronology in precious corals collected off the southern coast of Japan

The Lead 210 (210Pb) concentrations were determined to estimate the skeletal growth rates in the four species of precious corals including Japanese red coral (Corallium japonicum), pink coral (Pleurocorallium elatius), white coral (P. konojoi), and a deep-sea coral (Coralliidae sp.), and in a bamboo coral (Keratoisis sp.). Colonies were collected from the southern coast of Japan, western North Pacific margin. The 210Pb concentrations typically showed the exponential decrease with distance from the edge to the center of the skeleton axis in a cross section of main stem of colonies. The mean radial growth rates for colonies were estimated from the slopes of the best fit curves for exponential decrease in 210Pb concentration along the multiple transects. The obtained mean and standard deviation of radial growth rates in the diameter (the number of transects, n) for three colonies of C. japonicum were 0.31 mm/y (n = 1), 0.21 ± 0.05 mm/y (n = 2), and 0.36 ± 0.13 mm/y (n = 2), respectively, which were broadly comparable to the previously reported growth rates obtained by growth ring counting. Those obtained for three white coral colonies were 0.52 mm/y (n = 1), 0.60 mm/y (n = 1), and 0.36 ± 0.25 mm/y (n = 2). The radial growth rate for the bamboo coral colony was 0.13 mm/y in radius. The linear growth of the main steam of some colonies was analyzed from several cross sections. The linear growth rates of colonies could be estimated from the slope of the best fit curve (1) for increasing mean 210Pb concentration along the cross transects of the axis and (2) for increasing center 210Pb concentration of the skeleton axis. The linear growth rates calculated from the mean and center concentrations for two C. japonicum colonies were 8.5 and 6.1 mm/y, and 1.8 and 1.4 mm/y, respectively. Those for a P. elatius colony were 4.7 and 3.4 mm/y. The difference between the two estimates may reflect the morphological structure of the skeleton. The growth rates measured for the radial increase and linear extension of the main stem of the colonies could provide basic information for the demographic study of these coral species thereby fostering a rational exploitation of their populations.

Recent carbon sequestration dynamics in four temperate SE European peatlands using 210Pb dating

The last two centuries’ anthropogenically-accelerated climatic changes and elevated atmospheric levels of CO2 are influencing the recent carbon sequestration dynamics of peatlands, resulting in high variations of growth rates, and a general ascending trend in apparent carbon accumulation rates. In the present work, 210Pb high-resolution chronologies and 137Cs alternative markers were employed to study the recent carbon-related peat properties and their evolution throughout the last two centuries in four Sphagnum-dominated bogs in SE Europe (Romania). The results revealed a recent apparent carbon accumulation rate ranging from 9.5 to 437.5 g C m−2 yr−1, with a mean value of 144 ± 90.1 g C m−2 yr−1, that yielded an average increase of 18.25% of the rate from 1950 to the present period, suggesting an enhanced contemporaneous C uptake and storage in the peatlands. The mean C storage per unit area was 17.6 ± 7.6 kg C m−2. The periods of decreased peat growth rates were identified and attributed to significant drought events at the regional scale. The results found in the present study confirm the observations and trends remarked by other researchers in the literature, and further reinforce the relevance of studying recent carbon dynamics in peatland ecosystems. The obtained 210Pb chronologies were validated by 137Cs markers, highlighting the suitability of this technique for peat profile dating.

How large peak ground acceleration by large earthquakes could generate turbidity currents along the slope of northern Japan Trench

Deep-sea turbidite has been used to determine the history of occurrence of large earthquakes. Surface-sediment remobilization is a mechanism of the generation of earthquake-induced turbidity currents. However, the detailed mechanism of surface-sediment remobilization caused by earthquake ground shaking is unclear. To understand how high peak ground acceleration (PGA) caused by a large earthquake can remobilize surface sediments, we determined the age of a surface-sediment core recovered from the mid-slope terrace (MST) of the inner slope of the Japan Trench in northern Sanriku to determine turbidites generated by large historical earthquakes and calculate the PGAs of these earthquakes using an empirical attenuation relation commonly used in Japan. Small offsets in radiocarbon ages and excess 210Pb activities between turbidite and hemipelagic muds suggest that the turbidites in the core resulted from surface-sediment remobilization. 137Cs and excess 210Pb chronologies indicate that the three uppermost turbidites in the core are correlated with three large historical earthquakes, namely the 1968 common era (CE) Tokachi-oki, the 1933 CE Showa–Sanriku, and the 1896 CE Meiji–Sanriku earthquakes. Calculation of PGAs for large historical earthquakes along the northern Japan Trench indicates that a PGA of > 0.6 g is necessary for turbidite deposition in the MST basin. This threshold is larger than that reported for central Sanriku and may vary spatially. Moreover, turbidites in the MST deposits are more frequent in the northern Japan Trench than in the central Japan Trench, suggesting that the occurrence of three types of large M8-class earthquakes in the northern Japan Trench might have contributed to the frequent occurrence of large PGAs.

Geochemical mobility of 137Cs in marine environments based on laboratory and field studies

Cesium-137, a unique geochemical tracer, behaves as a particle-reactive species in freshwater that is useful as a geochronometer, and soluble in seawater that is used as a water mass tracer, as evidenced by higher solid-solution partition coefficient, Kd, in freshwater and much lower Kd values in seawater. A suite of sediment cores were collected from the Southern Yellow Sea and coastal regions of Croatia in 2014 and analyzed for vertical profiles of excess 210Pb (210Pbex), 239+240Pu, and 137Cs. A set of laboratory experiments were also conducted to investigate the partitioning of 137Cs between a suite of solid material comprised of commonly occurring minerals in the environment and solution under different contact times, pH, and salinity. The partition coefficient showed that for illite Kd sharply increased during the first two hours and then slowly increased after 4 h. Overall, the salinity significantly affects the 137Cs behavior in aqueous environments. The Kd values of 137Cs were higher (6.5 × 103–1.1 × 104 mL g−1) when the salinity was below 0.5 psu but drastically decreased to 9.0 × 102 mL g−1 when salinity was 3.6 psu and then slowly decreased to 2.7 × 102 mL g−1 with the salinity of 27.5 psu. Combining with the previously published results, it is observed that higher suspended particle (SPM) concentration could enhance the Kd values of 137Cs when SPM was below 12 mg L−1. Our results show that post-depositional mobility of 137Cs in the marine environment, except for river-dominated coastal areas, result in the 137Cs chronology is not suitable to validate the 210Pbex-based chronology. The penetration depths of 137Cs were found to be much deeper than it was expected based on the 137Cs and 239+240Pu peak and 210Pb chronology. Chitin showed a higher affinity for 137Cs than clay particles (e.g., smectite and illite). The desorption experiment showed that the NH4+ could leach 5.6% of sorbed 137Cs, accounting for 79% of the total exchangeable fraction while 2.8% of the total 137Cs was bound to organic matter. These observations support the field observation degradation of organic matter in anoxic marine sediment could enhance the mobility of 137Cs.

Investigation of self-attenuation of 210Pb (46 keV) gamma ray in sediment, certified reference material and high-density minerals: Implication to precise measurement of 210Pb

High resolution gamma spectrometry is one of the most widely used techniques in the measurements of environmental level 210Pb in sediment from coastal and freshwater environments and such measurements are needed to establish 210Pb chronology for the past 100–150 years. Precise measurement of 210Pb in sediment and soil requires appropriate self-absorption correction for its low-energy (46.5 keV) gamma radiation due to differences in the matrix between the sample and standard used to calibrate the instrument. Here we report a method that involves precise determination of 210Pb activity in sediment sample by calibrating the HPGe well detector with RGU-1-IAEA Certified Reference Material for well-defined geometries. A comparison of the 210Pb activity obtained from gamma-ray spectrometry with that obtained from alpha spectrometry via 210Po, using 209Po as yield tracer, indicates good agreement. We propose an empirical relation between the absolute efficiencies and packing densities of sample in a well-defined geometry (cylindrical counting vial) by affecting the count rate of 210Pb and its progenitor, 226Ra (via 214Pb and 214Bi). The effects of self-attenuation of 46.5 keV (210Pb), for naturally-occurring high-density minerals (apatite, titanite, monazite, and cerite) are evaluated. Specific activity of 210Pb on apatite measured by alpha and gamma spectrometry are compared. This study is relevant and useful for precise measurements of gamma-emitting environmental radionuclides such as 210Pb, 7Be, 137Cs as well as 226Ra.

Submarine Geomorphology and Glacimarine Sedimentary Processes Associated to Deglaciation in Europa Fjord, Chilean Patagonia

In a period of high rates of glacier retreat, increasing meltwater discharge from tidewater glaciers can influence marine fjord ecosystems due to increase sediment delivery and accumulation rates in the proglacial environment. Glacier variations and associated changes in glacimarine processes are recorded in the sedimentary record and submarine geomorphology of fjords. In October-November 2017, CIMAR23 Cruise surveyed several fjords adjacent to the Southern Patagonian Icefield (SPI). In this study, we show detailed results of the multibeam bathymetry, backscatter and sub-bottom seismic profiles, and sediment core samples from Europa Fjord, located west of the central SPI area, to improve the analysis of the fjord glacial and sedimentary evolution and to connect its behavior with the other fjords in the region. For the cores 210Pb chronology, magnetic susceptibility, organic carbon, total nitrogen, and stable isotopes (δ13Corg, δ15N) were performed. The seafloor geomorphology showed that the most prominent submarine landforms are transverse morainal ridges, which indicate past stillstand glacier positions; these features formed during the deglaciation of the fjord (latest Pleistocene), and some, perhaps more recently during short episodic advance/retreat events. In the central and mouth fjord areas, erosional features such as lineations are found on the rocky bottom and interpreted as formed by past grounded glaciers. Several submarine moraines are generally well preserved, but some parts are crumbled by slope failures and erosion. Most of the seismic sections are interpreted as the expected subglacial-ice proximal-ice distal succession of facies, characteristic of single retreat environments. The sedimentary record includes bioturbed muds with muddy laminations and variable amounts of coarse sediments interpreted as ice rafted debris, suggesting a proglacial environment, punctuated by calving. From the beginning of the twentieth century there is a tendency to an increase in the terrigenous organic material content, including an abrupt increase during the 80–90s, and a decline in the last decade. This behavior is indicating possibly a general increase of surface terrestrial runoff and, for the last decade, an increase of glacial meltwater input which would be caused by an accelerated deglaciation.

Coastal Wetland Surface Elevation Change Is Dynamically Related to Accommodation Space and Influenced by Sedimentation and Sea-Level Rise Over Decadal Timescales

The fate of mangroves and saltmarshes under conditions of accelerating sea-level rise is dependent upon sedimentation and surface elevation gain that is sufficient to maintain substrate positions within a shifting tidal frame. This study focuses on coastal wetlands fringing Westernport Bay, a large tidal embayment of southeastern Australia where mangroves occupy lower tidal positions than saltmarshes. Estimates of vertical accretion, surface elevation change, and autocompaction derived from a 20-year record of observations were integrated with estimates of sedimentation at the decadal to century time-scale derived from 210Pb chronology to model the relationship between surface elevation gain and accommodation space at timescales relevant to management and decision-making. This model was validated against records of shoreline changes extracted from time-series aerial photography. Sedimentation and surface elevation gain vary spatially on the basis of available accommodation space and sediment supply, which are influenced by hydrodynamic conditions within the bay. Since sea-level rise increases available accommodation space, these relationships provided the means to project the outcome of accelerating sea-level rise on equilibrium accommodation space of mangroves and saltmarshes. Sea-level rise will generally deepen substrate positions within the tidal frame, creating conditions favorable for mangrove forests. Where sediment supply is high, maintenance (and some progradation) of mangrove shorelines may occur under projected low rates of sea-level rise; these conditions are limited to shorelines near sedimentary basins and where there is considerable lateral accommodation space. The same fate is not likely under a high sea-level rise scenario where shoreline retreat is projected in all settings. Given the limited accommodation space within saltmarshes at Westernport Bay, sedimentation will not be sufficient to maintain tidal positions and landward retreat will be critical for maintenance of saltmarsh biodiversity. This will require planning decisions to facilitate tidal incursions and conserve retreat pathways.

Biogenic matter content in marine sediments in the vicinity of the Antarctic Peninsula: Recent sedimentary conditions under a diverse environment of production, transport, selective preservation and accumulation

Burial fluxes of organic carbon and biogenic silica were determined in 17 continental shelf sediment cores collected from the northern Weddell Sea, the Bransfield Strait, and the southern Drake Passage. Coring sites included open-shelf stations as well as slope and glacial trough environments, with water depths varying from 220 to 760 m. Apparent 210Pb accumulation rates from these cores ranged from 0.04 g m−2y−1 to 0.21 g m−2y−1 (1 to 3 mm y−1), with organic carbon burial rates ranging from 3 to 15 g OC m−2y−1 and biogenic silica accumulation rates ranging from 15 to 126 g SiO2 m−2y−1. OC contents below the surface mixed layer ranged from 0.26 to 1.51 wt. % (avg. 0.64 %). Biogenic silica contents at depth ranged from 2.3 to 11.2 wt. % (avg. 7.5%), with an average bSi/OC ratio (wt. %/wt. %) at depth of 12. Annual OC primary production rates and biogenic silica production rates in the euphotic zone were estimated from satellite chlorophyll-a data in the literature and from a seasonal model for biogenic particle export from surface waters. Based on these biogeochemical data, preservation efficiencies (i.e., mass burial rate/water column production rate) were calculated for organic carbon and biogenic silica. These preservation efficiency values ranged from 2 to 18% (avg. 9%) for OC and 8 to 106% (avg. 54%) for bSi. These relatively high preservation efficiencies resulted from extensive lateral sediment focusing (210Pb Psi (Ψ) values [burial flux/water column production rate] ranging from 2 to 33; avg. of 16), cold bottom water temperatures (2 to −2°C), and relatively high biogenic Si and OC production rates in the euphotic zone. The enhanced preservation efficiency for bSi relative to OC (i.e., 54% vs. 9%) in these Antarctic settings is consistent with the change in the phytoplankton bSi/OC (wt. %/wt. %) value of 2 for this area to the burial bSi/OC value of 12. Excess 210Pb activities in surface sediments varied from 4 to 47 dpm g−1. The surface mixed layer in the seabed varied in thickness from 0 to 4 cm. The penetration of excess 210Pb into these Antarctic Peninsula sediments varied from 6 to 28 cm (avg. 18 cm). The inventory of excess 210Pb in the seabed varied from 13 to 230 dpm cm−2 (avg. 110 dpm cm−2). Although 210Pb was the only radionuclide measured in this study, “apparent” 210Pb sediment accumulation rate (SAR) values from these 17 cores (assuming that deep bioturbation is negligible) are believed to be accurate SAR values because of good agreement between 210Pb and 14C chronologies from nearby cores reported in the literature.

Depositional time trends of phosphorous accumulation in a dated sediment core from the northwestern Arabian Gulf: Can phosphorous be used to support 210Pb chronologies in coastal aquatic sediments?

The use of 210Pb dating for the reconstruction of contaminant profiles in undisturbed sediments is the most widely acceptable technique historically. Due to the uncertainties associated with the technique, dating of sediments have often been supported by ancillary evidence such as an alternative historical marker in the catchment that is preserved in the sedimentary records. The most widely used verification marker is 137Cs, which is attributed to global fallout from past nuclear weapons testing, and the Chernobyl accident. In the southern hemisphere, and the mid-latitudes, the 137Cs signal from Chernobyl fallout is often absent from the sedimentary records making it very difficult to verify the 210Pb chronologies in these natural archives. This study reports the spatial and temporal variability of total phosphorus (TP) and its forms in sediments from Kuwait Bay and provides evidence of the possibility of using Phosphorous as a potential marker to support dates derived from 210Pb dating.In the current study we report the spatial and temporal variations in the concentrations of Phosphorus from near-shore sediments from Kuwait. The mean (and range) of TP concentration in surficial sediments is 19.4 (12.2 to 24) μmol-P g−1 dry weight. The highest concentrations were measured in the deepest portions of the Bay which is characterized by fine grained sediments. The vertical profile of TP in the sediments was characterized by a gradual increase in concentration from lower layers to a subsurface maximum (at approximately 4–5 cm) followed by an exponential decrease to the sediment-water interface. The sedimentary TP profile correlated remarkably well with changes in the population of Kuwait over the last three decades, suggesting that wastewater inputs into the Bay from treatment plants are an important source of phosphorus in the coastal waters. The decrease in concentration in sediment deposited over the last five years of the core is explained by the commissioning of an improved wastewater treatment plant with higher phosphorus removal efficiency. These fluctuations preserved in the sedimentary records linked to identifiable historical events provides powerful evidence that this nutrient associated with wastewater inputs in coastal aquatic environments can be used as ancillary information to support 210Pb dating.

Long-term and recent ecohydrological dynamics of patterned peatlands in north-central Quebec (Canada)

Peatlands are natural ecosystems that provide archives of the hydrological cycle, ecological processes and terrestrial carbon dynamics. In the north-central region of Quebec (eastern Canada), patterned peatlands developed in topographic depressions of the Precambrian Shield following the Laurentide Ice Sheet retreat. These peatlands display characteristics similar to appa mires and other peatlands that developed at the ecotone between the open (taiga) and closed boreal forest biomes of the Northern Hemisphere, and also correspond to the biogeographic limit between ombrotrophic and minerotrophic peatlands. During the Neoglacial cooling period in northeastern Canada, patterned peatlands, mainly oligotrophic fens, registered a hydrological disequilibrium expressed by an increase in surface wetness as aquatic microforms expanded to the detriment of terrestrial surfaces. Ecohydrological trajectories were reconstructed from a detailed study of two patterned peatlands in order to document their sensitivity to climate variations. To do this, plant macrofossil and testate amoeba data were combined with peat carbon accumulation rates, C:N ratios,210Pb and14C chronologies. Data show that peatlands initiated ca 6500 cal. y BP as ombrotrophic or minerotrophic systems depending on site-specific conditions, followed by a general increase in surface wetness during the Neoglacial cooling until the end of the Little Ice Age. A relatively synchronous ecosystem state shift from oligotrophic to more ombrotrophic conditions was registered at the beginning of the 20th century in central and lateral cores of both study sites, evoking the likely influence of recent warming on peat accumulation. These results suggest a potential northward migration of the biogeographic limit of the ombrotrophic peatland distribution during the 20th century, which could have implications for the role of these ecosystems as C sinks at the continental scale. Overall, these peatlands have stored a mean carbon mass of ca 100 kg m−2.

Atmospheric fallout of radionuclides in peat bogs in the Western Segment of the Russian Arctic.

This article presents the results of studies of the activity of radionuclides in peat-bog profiles of the European subarctic of Russia. Two peat profiles were collected in different areas of the Arkhangelsk region. The peat cores were used to determine 210Pb, 137Cs, 241Am, 239Pu, 240Pu, 238U, and 234U content. To estimate the relationship between radionuclide activity and physicochemical parameters of peat, the content of organic matter, water-soluble salts, carbonates and ash, and the pH of aqueous and salt extracts were studied. Radionuclide activity concentrations in peat samples were measured using inductively coupled plasma mass spectrometry (ICP-MS), low-background semiconductor gamma spectrometry with a high-purity germanium (HPGe) detector, and alpha spectrometry. The 210Pb chronology of peat cores was studied using a constant flow model based on the Monte Carlo simulation method. Comparison of 210Pb dating data showed that the position of the maximum activity peaks of anthropogenic radionuclides shifted along the peat profile. This is probably due to the relative mobility of different radionuclides in the peat massif. Measurement of the atomic ratio 240Pu/239Pu showed that the main sources of pollution in the peatlands of the European subarctic of Russia are global fallout from atmospheric tests from the 1950s through 1980 and fallout from the Chernobyl nuclear accident in 1986. This study shows that a complex of radioactive isotopes in peat deposits can provide valuable information on the environmental pollution loads of subarctic territories.

Environmental and anthropic variabilities at Guanabara Bay (Brazil): A comparative perspective of metal depositions in different time scales during the last 5,500 yrs

The determination of age-dated metal sediment accumulation rates in a representative South American bay is able to portray the dimension of human impacts during the colonial occupation and industrial periods. Many studies have assessed metal distribution and chronology at Guanabara Bay, in Brazil. However, understanding natural variabilities associated to paleoclimatic changes and comparing these natural variabilities to anthropogenic processes are not well established to date. Accurate geochronological control integrating ages determined by 210Pb and 14C chronologies through an exponential spline fit model allowed for a precise definition of changes associated to the holocene marine transgression, as well as the colonial period, leading to intense land use changes, and the industrial period. The reference values of the system were defined based on their concentrations and the accumulation rates of ecotoxicologically important metals. Al, Ba, Fe, Cd, Cu, Cr, Li, Ni, Mn, Pb, Si, Ti, V, and Zn distributions were determined in a Guanabara Bay core (BG-28) by the EPA 3051 method. Elemental distribution profile assessment allowed for the identification of variabilities associated to weathering processes, predominantly of lithogenic origin, mainly for Al, Ba, Fe, Li, Si, and V. Weathering processes occurred simultaneously to land use changes in the drainage basin since the colonial period, at 400 cal yr BP, and during the industrial period, mainly after the 1960s, denoted by Cd, Cr, Cu, Mn, Pb and Zn increases. The highest average metal enrichment values metals associated to industrial processes reached 5.95, with 119.1-fold higher accumulation rates than the background accumulation values observed between 4200 and 500 cal yr BP.

Geochemical markers of the Anthropocene: Perspectives from temporal trends in pollutants

Determining stratigraphic markers of the Anthropocene is important for demarcating Global Stratotype Section and Point (GSSP). Heavy metals and persistent organic pollutants (POPs) are candidate geochemical markers of the Anthropocene, but no study has comprehensively evaluated temporal trends in these pollutants in sediment cores globally. 454 data points for 8 heavy metals and 8 POPs were compiled to reconstruct their temporal trends and evaluate their global consistency. The heavy metals did not increase rapidly in the 20th century, and their temporal trends were locally but not globally consistent, which are not suitable geochemical markers of the Anthropocene. POPs rapidly increased beginning in the mid-20th century but have declined in the past decade, and these data are more consistent globally. The time of the peak concentration and period of rapid increase for polychlorinated biphenyls (PCBs) occur near the boundary of the Anthropocene and are consistent globally. Forty-five percent of the studies evaluated used only 210Pb chronology for dating, which creates definite uncertainty in the analysis. In GSSP candidate sections, PCBs could be considered candidate markers of the Anthropocene.

A persistent increase in primary productivity east off Hainan Island (northwestern South China Sea) over the last decades as inferred from sediment records

Sediment cores were analyzed from the continental shelf of the northwestern South China Sea aiming to understand the change history of primary productivity and provide insights into key changes of environmental conditions in this region over the past ~100 years. Multiple proxies including stable carbon isotopic composition (δ13C) of sedimentary organic matter, diatom abundance and biogenic silica burial flux were applied along with 210Pb chronology. Notably, these independent evidences consistently point to a steady increase of primary production in this region only after ~1960s. We propose that increasing atmospheric deposition due to dramatically enhanced human activities especially from China supplies essential nitrogen nutrients to the N-poor region and probably acts a major reason for the observed enhancement of marine primary production. Our study provides insights into better understanding how human perturbation may have profoundly impacted biogeochemical cycling in marginal seas in the last decades.

Variation in sedimentary 210Pb over the last 60 years in the Yangtze River Estuary: New insight to the sedimentary processes

Anthropogenic activities have decreased the sediment transport from catchment to the river-dominated continental margin mainly through river damming that controlled the estuarine and associated shelf modern sedimentation. In this study, radioisotopes 210Pb (210Pbex and 226Ra) and 137Cs, grain size, and X-radiograph were combined to evaluate the modern sedimentary processes in the Yangtze River Estuary (YRE). We found that seabed cores collected on the estuary and associated shelf show a direct temporal correlation between decreases in initial activity and burial flux of 210Pbex and suspended sediment load in relation to river damming and soil conservation from 1950 to 2016. Most of sediment cores are characterized by low, uniform and reverse 210Pb patterns at surface and negligible sediment accumulation rates (SARs), indicating that due to the limited sediment supply following the construction of the Three Gorges Dam in 2003, erosion and remobilization of fine-grained sediments by energetic tidal currents and biological mixing tends to have become determinant forces in controlling the fate of modern sediment burial in the YRE. Moreover, these results indicated that decline in sediment load and additional input of eroded materials will largely violate the basic assumption of constant 210Pb flux, raising a substantial challenge for 210Pb chronology in the river-dominated continental margins. However, we suggest that radiotracer 210Pb could provide critical information for understanding the complex the sedimentary processes (e.g., terrestrial sediment supply and redistribution by tidal currents) and assessing past environmental status on the river- and/or tidal-dominated estuaries subject to human modification.

The rapid increases in microplastics in urban lake sediments

Microplastics have received widespread attention as an emerging global pollutant. However, the research on the abundance and characteristics of microplastics entering the environment throughout history has been limited. Meanwhile, the determination of the start of the Anthropocene is important because humans have become a vital force affecting the environment and Earth surface processes. It is unclear whether the plastic can be used as an artefact to indicate the start of the Anthropocene. In this study, combined with 137Cs, 210Pb, and spherical carbonaceous particles (SCP) high-resolution chronology, a microplastics-time curve was established by using the sedimentary record from an urban lake in Wuhan city. The microplastic abundance increased from 741 items·kg−1 to 7707 items·kg−1 over the past 60 years. The microplastics were mainly fibres and composed of polyester and rayon polymers, which indicated that the microplastics most likely originated from textiles. The surfaces of the older microplastics were rough and weathered with many absorbed elements. Microplastics are similar to fossils belonging to the Anthropocene, and may be used as an indicator. The comparison of microplastic-time curves in different records on a global scale will be necessary in the future.

Geochemical distribution, fractionation, and sources of heavy metals in dammed-river sediments: the Longjiang River, Southern China

In the present study, six sediment cores were collected from six river-dammed reservoirs to reveal the geochemical distribution of heavy metals (As, Cd, Pb, Sb, and Zn) in the Longjiang River, South China, which is highly impacted by nonferrous metal mining and smelting activities. The sediments were geochemically characterized, combining geochemical analysis, sequential extractions, and 210Pb chronology. The results indicated that the river sediments were severely polluted by heavy metals in the order of Cd > Zn ≈ Pb ≈ Sb > As. These heavy metals generally exhibited relatively low enrichment in the upstream sediments because of the limited anthropogenic impact, but their abundances drastically increased in the midstream sediments due to local smelting activities. In downstream sediments, the heavy metal concentrations (except for Cd) decreased, owing to the effect of dam interception and detrital inputs. Cadmium levels tended to increase in downstream sediments, which were attributed to the intensive discharge of Cd during the pollution event in 2012. The sedimentary records were traced back to 1985, and a significant decrease of heavy metal enrichments could be found after the year 2000, suggesting the enhancement of environmental management in this period. The statistical results indicated that local metal smelting and mining activities were the main anthropogenic contributors for the enrichment of heavy metals in the dammed-river sediments. High enrichment factor and non-residual fractions of heavy metals in local sediments may pose a direct threat to aquatic organisms. Cd presents significant danger because of its extreme enrichment and high labile fractions.