Sediment Accumulation Rates Research Articles

Anthropogenic drivers of increasing sediment accumulation in contrasting Mexican mangrove ecosystems

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.

How much organic carbon have UK lakes stored in the Holocene? A preliminary estimate

Temperate lake sediments store a substantial amount of organic carbon (OC) over millennia. Despite the importance of quantifying terrestrial carbon budgets for Nature-based Solutions, the long-term accumulation of OC in European temperate lakes is poorly constrained. In this study, we analyzed 30 lake sediment records to generate a preliminary first-order estimate of Holocene OC accumulation rate (OCAR) and OC storage in UK lakes. We also examined the environmental variables that influence OCAR and produced synthesized Holocene records of %OC and z-scores of log-transformed OCAR and sediment accumulation rate (SAR) at 500-year resolution. Based on our estimation, we report an average Holocene OCAR of 7.4 ± 5.5 g C m−2 yr−1 and a Holocene total OC storage of 0.24 ± 0.18 Pg C in UK lakes. Apart from latitude, no relationship was found between the average Holocene OCAR and the various environmental variables (i.e. temperature, precipitation, surface area, catchment area, depth, altitude, and geology type). During the Holocene, OCAR closely resembles variations in SAR, whereas the increase in %OC is likely explained by the warming climate. Early Holocene variations in OCAR were primarily climate-driven. In contrast, the anthropogenic impact on the landscape exerted a predominant influence on OC burial during the middle-late Holocene. Our results improve the current understanding of terrestrial carbon budgets in the UK and demonstrate the under-appreciated importance of lakes as long-term OC stores.

Sedimentation on the Siberian Arctic Shelf as an indicator of the arctic hydrological cycle

Siberia occupies a significant part of the Eurasian continent and environmental changes in this region can have an important impact on the climate system of the Northern Hemisphere. The sediment flux of Siberian rivers is sensitive to changes in physical, chemical, and biological processes taking place on the continent, and these changes can be recorded in marine sediments on the Siberian Arctic Shelf. This paper presents data on grain-size distribution of the sediments, the sedimentation rates, and the mass accumulation rates on the shelf over the past 100 years. Age models are based on the decay rate of excess lead isotope 210Pb, taking into account the sorption capacity of the marine sediments, and the presence of cesium isotope 137Cs peaks in the sediment cores. The highest sedimentation and mass accumulation rates were observed prior to the 1920–40 and coincide with larger particle sizes, indicate a period of active sediment-laden sea ice and iceberg melt. Systematic decrease in the sedimentation and mass accumulation rates against the background of an increase in the proportion of silt fractions in the shelf sediments in the second half of the 20th century can be explained by an acceleration of the arctic hydrological cycle.

Astronomical time scale of the lower Miocene depositional sequences (Aquitanian-Burdigalian) in the Jambour Field, northern Iraq

The Miocene succession is considered one of the major shallow hydrocarbon reservoirs in Iraq. It consists primarily of lagoonal evaporites and carbonate alternations, with many barren intervals and non-diagnostic fauna. An astronomical time scale (ATS) was established in two wells in Jambour Field, Kurdistan, using high-resolution cyclostratigraphic analysis of GR data for the first time in Iraq to determine the absolute age of the Miocene sequences and their boundaries. Sixteen unique carbonate and evaporite facies types were discovered and classified into five facies associations, from the mid-outer ramp to the peritidal carbonate and evaporite ramps. The most significant of these implies that, after astro-climatic frequencies, sea-level change was the dominant regulator of lower Miocene deposition. The difference in GR and facies type is mostly due to third eustatic sequences, which describe a rich series of long and short-period eccentricities in orbitally defined terms. The eustatic sea-level variations of the third-order sequences correlate with the sedimentary noise model applied over the tuned GR. A sharp sediment accumulation rate (SAR) was caused by an abrupt shift in the depositional environment, as demonstrated by the applied eCOCO within the lower Aquitanian part of the Dhiban Formation; consequently, each well was split into two datasets. The SAR ranges from 3.1 to 1.97 cm/kyr in the Ja46 well and 2.3 to 3.3 in the Ja49 well. The MTM spectral analysis of the four datasets revealed the eccentricity cycles' dominance with a high degree of confidence level. The present study employs high-resolution ATS using tuning of the GR with the new merged short and long eccentricity cycle filter output method, which is supported by previous strontium isotope studies and compared to the La 2004 astronomical solution. According to the ATS, the Aquitanian-Burdigalian sequences range from 5.08 myr at Ja46 Well to 4.66 myr at Ja49 Well. The tuning output indicated the presence of two hiatuses, the first in the Dhiban Formation with a time gap of about 0.21 and 0.3 myr in the Ja46 and Ja49 wells, respectively, and the second at the top of the Jeribe Formation with a time gap of about 0.34 myr in the Ja49 well. This pause corresponds to a significant sea-level drop in the Arabian Platform Basin at 21.4–21.0 and 18.5 Ma.

Seasonal variation observed in microplastic deposition rates in boreal lake sediments

PurposeThe sediment trap method allows measurements of vertical microplastic flux rate into sediments and provides comparable information of the spatial microplastic deposition rates. Such data are essential for comparison of the microplastic pollution rates in different sedimentary systems and for future risk assessments.Materials and methodsWe monitored microplastic fluxes using sediment traps in a boreal lake seasonally during 1 year. The sites represent different level of exposure to anthropogenic activities, from construction work to the open water site. Microplastic fluxes were compared to sediment characteristics (organic content) and sediment accumulation rates.Results and discussionThe highest annual microplastic deposition rate (2300 items m−2 year−1) was recorded at snow disposal site, a location where the snow collected from the city streets during winter is transported. The lowest rate was observed at the control site (660 items m−2 year−1) upstream from the city. Our results reveal the seasonal variation in microplastic deposition rates. In general, the highest microplastic flux rates were measured during growing season, accompanied with higher sedimentation rate. The low microplastic deposition rate during winter is likely explained by ice cover, frozen soil, and snow cover in the catchment. In contrast, microplastic concentration was higher in winter samples due to ceased sediment transport from catchment to lake. The sediment accumulation rate did not predict microplastic accumulation rate.ConclusionOur data suggest seasonal variation in microplastic deposition rates. The microplastic flux rates compared to their concentrations indicates that sites with high sedimentation rates can lead to underestimation of microplastic deposition and hence hamper recognition of hot spots.Graphical

Hierarchical Milankovitch and sub-Milankovitch cycles in the environmental magnetism of the lower Shahezi Formation, Lower Cretaceous, Songliao Basin, northeastern China

SK-2 borehole in Songliao Basin provides unprecedented geological materials for investigating the Early Cretaceous continental paleoenvironment and paleoclimate in northeastern China. The lacustrine successions of the lower Shahezi (K1sh) Formation at the depth from 4,542 to 5,695 m was systematically studied using environmental magnetism and cyclostratigraphy in this study. Magnetic analysis reveals an inverse correlation between magnetic susceptibility (MS) and lithological ranks in fine clastic sediments, with the highest values in mudstones and the lowest in sandstones. The main magnetism carriers in the lower K1sh are pseudo-single-domain (PSD) and/or multi-domain (MD) magnetite with minor presence of hematite. MS was used to further explore the genesis of the environmental and climatic variations through cyclostratigraphic analysis. Sedimentary cycles of 113 m, 34 m, 13 m and 6 m can be identified in the power spectrum, which were interpreted as long and short eccentricity, obliquity, and precession cycles, demonstrating the impact of astronomical cyclicity on sedimentary rhythmicity. Floating astronomical time scale (FATS) of 4,090 kyr and 4,148 kyr were established by tuning the inferred long and short eccentricity cycles to the artificial 405-kyr and 105-kyr orbital eccentricity curves respectively. The estimated sediment accumulation rate around 28 cm/kyr confirms the rapid deposition process within the faulted lacustrine basin. Based on this study, the lake level oscillations in Songliao Basin are assumed to be shaped by long and short eccentricity, precession and semi-precession cycles during Early Cretaceous. This study also indicates that the sand-mudstone alternations deposition in K1sh is most likely driven by the seasonal discrepancies of summer insolation during semi-precession periods.

Preindustrial levels and temporal enrichment trends of mercury in sediment cores from the Gulf of Thailand.

Four sediment cores in the middle of Gulf of Thailand (GOT) and one core close to Bang Pakong River mouth were examined for total mercury (T-Hg) using direct thermal decomposition coupled with the atomic absorption spectrometry (DTD-AAS) method and acid digestion (acid-CVAAS) method, and sediment chronologies using 210Pb dating. T-Hg in the river mouth core ranged 44.49-52.76µg/kg and higher than the cores from the middle of GOT (18.26-36.68µg/kg). The age span obtained from the cores dated back to the 1940s with the sediment accumulation rates of 0.15-0.76cm/year. The preindustrial levels of T-Hg showed an initial slow increase followed by a rapid elevation since the 1960s which marked the start of the industrialized period in the country. To this end, we posit that T-Hg in the GOT sediment can be attributed to not only land-based sources but also offshore activities including petroleum exploration and frequent accidental oil spills.

Microfaunal Recording of Recent Environmental Changes in the Herschel Basin, Western Arctic Ocean

ABSTRACTMicrofaunal assemblages of benthic foraminifera, ostracods, and tintinnids from two marine sediment cores retrieved from the Herschel Basin of the Canadian Beaufort Sea shelf document relationships with environmental parameters such as salinity, sea-ice cover, and turbulence. Cores YC18-HB-GC01 and PG2303-1 were collected at 18 and 32 m water depth, respectively. At these sites, sediment accumulation rates range between 0.6 and 1.7 cm yr–1 allowing a near-annual temporal resolution over the last 50 years. Multivariate analyses indicate that benthic foraminiferal assemblages respond primarily to food supply. Dissimilarities between the microfaunal assemblages of the two cores are mainly the result of bottom water salinity levels linked to water depth. High abundance of the benthic foraminiferal species Elphidium clavatum and occurrences of Elphidium bartletti point to varying, but relatively low, salinities at the shallow core site YC18-HB-GC01, which may be affected by variations in the summer halocline depth. Higher species diversity and more abundant Cassidulina reniforme and Stainforthia feylingi characterize the deeper core PG2303-1, which might reflect more stable conditions and higher bottom-water salinities throughout the studied time interval. The most important microfaunal shift of the last 50 years, observed in the shallower longer core YC18-HB-GC01, occurred at the turn of the 21st century. Prior to ∼2000 CE, the presence of Islandiella norcrossi indicates more stable and saline conditions. Since ∼2000 CE, increased abundances of Haynesina nivea and of the ciliate Tintinnopsis fimbriata suggest decreased salinity and increased turbidity. An increased abundance of Eoeponidella pulchella after ∼2000 CE suggests a concurrent increase in productivity in the last two decades. This shift is nearly synchronous with a decrease in mean summer sea-ice concentration, which can play an important role in bottom water stability on the shelf. Easterly winds can induce a reduction in the sea-ice cover, but also foster a westward spreading of the Mackenzie River plume and the upwelling of nutrient-rich Pacific waters onto the shelf. Both factors would explain the increased freshening and productivity of the Herschel Basin. The last two decades were also marked by a decrease in ostracod abundance that may relate to higher water turbidity. This study shows that combining information from benthic foraminifera, ostracods, and tintinnids provides a comprehensive insight into recent hydrographic/climatic changes in nearshore Arctic habitats, where productivity is critical for the food security of local communities.

Anthropogenic impacts on tidal creek sedimentation since 1900.

Land cover and use around the margins of estuaries has shifted since 1950 at many sites in North America due to development pressures from higher population densities. Small coastal watersheds are ubiquitous along estuarine margins and most of this coastal land-cover change occurred in these tidal creek watersheds. A change in land cover could modify the contribution of sediments from tidal creek watersheds to downstream areas and affect estuarine habitats that rely on sediments to persist or are adversely impacted by sediment loading. The resilience of wetlands to accelerating relative sea-level rise depends, in part, on the supply of lithogenic sediment to support accretion and maintain elevation; however, subtidal habitats such as oyster reefs and seagrass beds are stressed under conditions of high turbidity and sedimentation. Here we compare sediment accumulation rates before and after 1950 using 210Pb in 12 tidal creeks across two distinct regions in North Carolina, one region of low relief tidal-creek watersheds where land cover change since 1959 was dominated by fluctuations in forest, silviculture, and agriculture, and another region of relatively high relief tidal-creek watersheds where land-use change was dominated by increasing suburban development. At eight of the creeks, mass accumulation rates (g cm-2 y-1) measured at the outlet of the creeks increased contemporaneously with the largest shift in land cover, within the resolution of the land-cover data set (~5-years). All but two creek sites experienced a doubling or more in sediment accumulation rates (cm yr-1) after 1950 and most sites experienced sediment accumulation rates that exceeded the rate of local relative sea-level rise, suggesting that there is an excess of sediment being delivered to these tidal creeks and that they may slowly be infilling. After 1950, land cover within one creek watershed changed little, as did mass accumulation rates at the coring location, and another creek coring site did not record an increase in mass accumulation rates at the creek outlet despite a massive increase in development in the watershed that included the construction of retention ponds. These abundant tidal-creek watersheds have little relief, area, and flow, but they are impacted by changes in land cover more, in terms of percent area, than their larger riverine counterparts, and down-stream areas are highly connected to their associated watersheds. This work expands the scientific understanding of connectivity between lower coastal plain watersheds and estuaries and provides important information for coastal zone managers seeking to balance development pressures and environmental protections.

Capturing of organic carbon and nitrogen in eelgrass sediments of southern Scandinavia

AbstractThe ability of seagrass meadows to filter nutrients and capture and store CO2 and nutrients in the form of organic carbon (OC) and nitrogen (N) in their sediments may help to mitigate local eutrophication as well as climate change via meadow restoration and protection. This study assesses OC and N sediment stocks (top 50 cm) and sequestration rates within Danish eelgrass meadows. At four locations, eelgrass‐vegetated and nearby unvegetated plots were studied in protected and exposed areas. The average OC and N sediment 50 cm stocks were 2.6 ± 0.3 kg OC m−2 and 0.23 ± 0.01 kg N m−2, including vegetated and unvegetated plots. In general, OC and N stocks did not differ significantly between eelgrass meadows and unvegetated sediments. Lack of accumulation of excess 210Pb suggested sediment erosion or low rates of sediment accumulation at most sites. OC accumulation rates ranged from 6 to 134 g m−2 yr−1 and N from 0.7 to 14 g m−2 yr−1. Generalized additive models showed that ≥ 80% of the variation in sediment OC and N stocks was explained by sediment grain size, organic matter source, and hydrodynamic exposure. Long cores, dated with 210Pb, showed declining OC and N densities toward present time, suggesting long‐term declines in eelgrass OC and N pools. Estimates of potential nation‐wide OC and N accumulation in eelgrass sediments show that they could annually capture up to 0.7% ± 0.5% of CO2 emissions and 6.9% ± 5.2% of the total terrestrial N load.

Fluvial responses to late Holocene hydroclimate variability in the midcontinental United States

Long-term relationships between mean-state climatic conditions and flood frequencies in the midcontinental United States (US) are not well established because instrumental records of fluvial processes are limited to the current warm period (CWP; the last ca. 150 years) and continuous paleo-flood records are exceedingly rare. Here, we investigate climate-flood relationships in the midcontinental US by reconstructing flood frequencies at Half Moon Pond, a 1600-year-old oxbow lake on the lower White River, Indiana (watershed = ca, 29,000 km2). We used sediment accumulation rates and clastic fluxes constrained by high-resolution radiocarbon (14C) dating. Frequent flooding, as indicated by high sedimentation rates and clastic fluxes to Half Moon Pond, occurred leading up to and during the Medieval Climate Anomaly (MCA; 950–1250 CE) when paleoclimate records suggest the predominance of ocean-atmosphere mean states resembling the negative phases of the Pacific Decadal Oscillation (-PDO-like) and Pacific North American Mode (-PNA-like). Reductions in sedimentation rates and clastic fluxes, indicating reduced flooding, subsequently occurred during the transition out of the MCA and into the Little Ice Age (LIA; 1250–1830 CE) as ocean-atmosphere conditions shifted to + PDO-like and +PNA-like mean states. Sedimentation rates and clastic fluxes increased again after ca. 1800 CE, indicating increased flooding during the CWP as ocean-atmosphere conditions returned to -PDO-like and -PNA-like mean states. The White River trends were notably antiphased with sedimentation-rate-based flood frequencies for the lower Ohio River (500,000 km2 watershed) prior to 1830 CE. This antiphased relationship is consistent with flooding in moderate to small watersheds in the Midwest being sensitive to the occurrence of rainstorm events, which were more frequent leading up to and during the MCA, and flooding in large watersheds being more sensitive to large spring melts associated with extensive snowpacks, which characterized the LIA. That both the White and Ohio rivers experienced their most frequent flooding during the CWP suggests deforestation and changing land use practices increased flooding on Midwestern watersheds across scales despite a current climatic mean state that in the past only resulted in increased flooding on moderate to small watersheds. Continued increased in midcontinental rainfall are therefore likely to enhance the occurrence of floods in Midwestern watersheds across different geographic scales.

Sources and chemical stability of soil organic carbon in natural and created coastal marshes of Louisiana

Coastal marshes are globally important for sequestering carbon, yet sea-level rise and anthropogenic stressors can reduce their capacity as carbon sinks. Marsh restoration can offset a portion of carbon loss through the degradation of natural marshes, but potential differences in the sources and stability of soil organic carbon (SOC) between created and natural marshes may affect their function as a long-term carbon sink. Here, we examine the sources and chemical stability of SOC in natural and created marshes across the Gulf coast of Louisiana, USA. Marshes were examined along an estuarine salinity gradient in a former interdistributary basin of the Mississippi River Delta and in six created marshes across a 32-year chronosequence and a natural reference marsh (n = 6) in the Chenier Plain. Carbon source was assessed using δ13C analysis and chemical stability was determined through an acid hydrolysis digestion that removed labile carbon (LC). Soil δ13C values suggested that the local vegetation dominated SOC in all natural marshes although brackish marshes had a mix of sources and degradation of SOC. Recalcitrant carbon (RC) was 72.2 ± 0.5 % of SOC across fresh, brackish and saline marshes. The depth-averaged RC accumulation rate was almost three times greater than LC accumulation rate, yet both contributed significantly to accretion and long-term SOC accumulation (124–132 g m−2 y−1 in natural marshes). RC and SOC accumulation rate increased with mineral sediment accumulation rate. For the created marshes, SOC became increasingly recalcitrant due to an increase in in-situ plant inputs, but accumulation rates were lower than the natural marshes. Overall, this study illustrates that natural marshes have a large stock of RC from the vegetation while dredge sediment created marshes have no plant-derived carbon initially, which accumulates slowly thereafter. Restoration practices may be improved by preserving and augmenting these deteriorating but carbon-rich natural marshes.

Evaluating the effectiveness of sediment retention by comparing the spatiotemporal burial of sediment carbon, nitrogen and phosphorus in a plateau lake and its affiliated reservoirs

Evaluating the effectiveness of sediment retention by comparing the spatiotemporal burial of sediment C, N, and P in a plateau lake and its affiliated reservoirs is critical in dealing with global eutrophication in freshwater ecosystems. The objective of the study was to estimate the spatial–temporal of C, N and P accumulation rates (CAR, NAR and PAR) in sediment cores of a plateau Lake Dianchi (DC) and its four affiliated reservoirs (Dashiba-DSB, Xibaisha-XBS, Baoxianghe-BXH, and Shuanlong-SHL). The results indicated that the average sediment accumulation rates (SARs) ranged from 0.040 to 1.187 g cm−2 a−1 in DC and 0.201 to 3.965 g cm−2 a−1 in its affiliated reservoirs. Spatially, all of the values of CAR, NAR and PAR exhibited similar distribution characteristics, along with two high-value regions concentrated in the southern and northern parts of the lake DC. Temporally, these three values of Lake DC and its affiliated reservoirs showed upward trends from bottom to top over the past ∼ 150 years, especially occurring in the 1950s. The change in the C/N ratio indicated that intensive anthropogenic factors promoted the CAR, NAR and PAR in sediments. Based on a developed proportional model, the ratios of sediment retention by each reservoir on TOC, TN and TP were calculated to be 2.15 %, 4.38 % and 9.01 % for DSB, 0.14 %, 0.18 % and 0.14 % for XBS, 1.61 %, 5.77 % and 1.23 % for BXH, and 0.97 %, 2.07 % and 0.46 % for SHL, respectively. Reservoirs located in the upper and middle reaches of the lake catchment play a critical role in sediment retention and prevent a potential risk from water deterioration of the downstream Lake DC. Linkages between reservoir-sources and lake-sinks not only provide valuable information for managing the environmental changes within the catchment, but also contribute to new insight into the regulation of water eutrophication in global lake ecosystem.

Synoptic observations of sediment transport and exchange mechanisms in the turbid Ems Estuary: the EDoM campaign

Abstract. An extensive field campaign, the Ems-Dollard Measurements (EDoM), was executed in the Ems Estuary, bordering the Netherlands and Germany, aimed at better understanding the mechanisms that drive the exchange of water and sediments between a relatively exposed outer estuary and a hyper-turbid tidal river. More specifically, the reasons for the large up-estuary sediment accumulation rates and the role of the tidal river on the turbidity in the outer estuary were insufficiently understood. The campaign was designed to unravel the hydrodynamic and sedimentary exchange mechanisms, comprising two hydrographic surveys during contrasting environmental conditions using eight concurrently operating ships and 10 moorings measuring for at least one spring–neap tidal cycle. All survey locations were equipped with sensors measuring flow velocity, salinity, and turbidity (and with stationary ship surveys taking water samples), while some of the survey ships also measured turbulence and sediment settling properties. These observations have provided important new insights into horizontal sediment fluxes and density-driven exchange flows, both laterally and longitudinally. An integral analysis of these observations suggests that large-scale residual transport is surprisingly similar during periods of high and low discharge, with higher river discharge resulting in both higher seaward-directed fluxes near the surface and landward-directed fluxes near the bed. Sediment exchange seems to be strongly influenced by a previously undocumented lateral circulation cell driving residual transport. Vertical density-driven flows in the outer estuary are influenced by variations in river discharge, with a near-bed landward flow being most pronounced in the days following a period with elevated river discharge. The study site is more turbid during winter conditions, when the estuarine turbidity maximum (ETM) is pushed seaward by river flow, resulting in a more pronounced impact of suspended sediments on hydrodynamics. All data collected during the EDoM campaign, but also standard monitoring data (waves, water levels, discharge, turbidity, and salinity) collected by Dutch and German authorities are made publicly available at 4TU Centre for Research Data (https://doi.org/10.4121/c.6056564.v3; van Maren et al., 2022).

Age‐Depth Models for Tropical Marine Hemipelagic Deposits Improve Significantly When Proxy‐Based Information on Sediment Composition Is Included

AbstractAccurate age‐depth models for marine sediment cores are crucial for understanding paleo‐oceanographic and ‐climatic changes derived from these archives. To date, information on bulk sediment composition is largely ignored as a potential source of information to improve age‐depth models. In this study, we explore how bulk sediment composition can be qualitatively used to improve age‐depth models. We developed the BomDia algorithm, which produces age‐depth models with realistic sediment accumulation rates that co‐vary in harmony with the bulk sediment composition. We demonstrate that changes in the marine versus terrigenous sediment deposition, based on bulk sediment composition, can be used to significantly improve age‐depth models of hemipelagic marine deposits. Based on two marine records—each containing more than 20 radiocarbon (AMS 14C) dated levels—we show that the mean error of prediction of unused AMS 14C ages significantly improves from 3.9% using simple linear interpolation, to 2.4% (p = 0.003), when bulk sediment composition is included. The BomDia age‐depth modeling approach provides a powerful statistical tool to assess the validity of age control points used and also may assist in the detection of hiatuses. Testing and further development of the BomDia algorithm may be needed for application in depositional settings other than tropical hemipelagic.

Organic carbon and planktic foraminifera radiocarbon derived Holocene sediment accumulation rates in the northern slopes of the Gulf of Mexico

In the context of climate regulation and anthropogenic waste detoxification (e.g. oil spills), estimates of deep ocean sedimentation and carbon sequestration are of the utmost importance. Radiocarbon (14C) is a common radioisotope that can be used to establish millennial scale sediment accumulation rates. The objectives of this study were to: 1) establish ages for co-occurring total organic carbon (TOC) and planktic foraminifera (carbonate) in the northeastern Gulf of Mexico (GoM), 2) use these ages to estimate accumulation rates independently, 3) identify any evidence of redistribution, and 4) examine any offset between TOC and carbonate 14C ages as a tool to potentially identify selective TOC transport. Sediment samples were collected in May 2018 from the RV Point Sur using an Ocean Instruments MC-800 multi corer. Radiocarbon measurements of both planktic foraminifera and TOC subsamples were made at the National Ocean Science Accelerator Mass Spectrometry Facility (NOSAMS). Radiocarbon ages, calibrated using the OxCal 4.4, ranged from recent to 6407 BP. Linear (LAR: 4–24 cm/kyr) and mass accumulation rates (MAR: 1.5–11.5 g/cm2/kyr) were generally consistent with those reported by other recent studies in the GoM. At two sites, C14 ages decreased from the surface to the second sampling increment which was consistent with sediment redistribution. The TOC-carbonate offsets, which are indicative of lateral advection and organic matter aging, were lower than those found in the majority of other regions, which was consistent with less lateral transport or a more oligotrophic setting. The magnitude in radiocarbon age offsets with depth could potentially be used as a relative aging or transport assessment tool in areas with little resuspension.

Vegetation changes and sediment dynamics in the Lake Alaotra region, central Madagascar

Madagascar is known for its high erosion rates in the central highlands, yet the role of human disturbance versus natural processes is not well understood and is a topic of ongoing debate. At present the necessary quantitative data to couple vegetation dynamics and sediment fluxes over time in Madagascar is scarce. This study aims to provide more insight in vegetation changes and sediment transfers over the last millennia in the Lake Alaotra region, and specifically on the role of human disturbances and natural processes. Our vegetation reconstruction is based on pollen records from two lake sediment cores, covering the last 2600 years. Sediment accumulation rates were calculated from cores obtained from the floodplains, from wetlands surrounding the lake, and from Lake Alaotra itself. Our data show an early opening in the landscape, between 2050 and 1700 cal a BP, with a transition from a wooded grassland or woodland/grassland mosaic towards open grassland and an increase in charcoal accumulation rates. (Indirect) human impact is suggested as the main driver for these vegetation changes. Floodplain and wetland sediment accumulation rates only increase in the last 1000 years and peak in the last 400 years. This increased accumulation can mainly be linked to the increased anthropogenic pressure (grazing and farming activities) that triggered increased lavaka (gullies) activity. No changes in accumulation rate were observed in Lake Alaotra, indicating that most sediments are buffered in the floodplains and wetlands. Overall, our pollen and charcoal data suggest an indirect effect of human disturbance on vegetation shifts whilst strong evidence was found for a direct effect of human disturbance on sediment accumulation through intensified use of the grasslands.

Sedimentation Rate and Contamination Levels Profile of Potentially Toxic Elements in the Limoncocha Lagoon RAMSAR Wetland in the Ecuadorian Amazon

The aim of this study is to analyze the recent sedimentation rate in the center of the Limoncocha lagoon, a Ramsar site in the Ecuadorian Amazon, using the 210Pb dating method and identifying the potentially toxic elements along a 50 cm sediment core. A strategy based on the application of three single and four integrated indices is used to evaluate trace element contamination with depth. Single indices show mainly As and Mo, and Cu, Ba, Cd, Ni, and Pb to a lesser extent, as responsible elements of a minor enrichment between −10 and −40 cm. The multielement slight pollution shows a mixture of potential contamination sources, probably due to agricultural, oil activities, and urban wastewater discharges. However, integrated indices applied, classify the complete core as without potential risk. The 210Pbexcess profile shows three differentiated sections. A surface section where new materials with lower concentrations have been found, probably due to the underground currents that connect the lagoon and the nearby Napo River; a central section where CF-CS model and mass accumulation rate calculations provide a sediment accumulation rate of 0.56 ± 0.03 cm y−1; finally, a deeper section with a constant 210Pbexces profile, showing sediment reworking probably due to local flooding’s.

A rare record of the early and middle Holocene dust export history of the Mongolian Plateau obtained from a crater lake on its southern boundary

The dust export from the interior Mongolian Plateau to downwind regions is key to identifying environmental changes in the source areas of Asian dust and the dust forcing in climate system. Due to the lack of ideal aeolian sediment materials and the imprecise indication ability of grain-size index, dust export from the Mongolian Plateau during the Holocene is still unclear. Diaojiaohaizi Lake is a closed crater lake located at the summit of the Yinshan Mountains, and on the southern boundary of the Mongolian Plateau. Compared with other lakes inside the dust source area or distant downwind areas, the unique location and geographic features make it possible for this lake to record the dust export history of the Mongolian Plateau more directly. Comparing the properties of chemical elements, Sr-Nd isotopes, magnetic minerals, mineral compositions and grain sizes between lake sediments, lakeshore materials and bedrock of Diaojiaohaizi Lake, we deduced that the lake sediments was relatively pure aeolian materials. Therefore, the mass accumulation rate of the lake sediments was further used as an ideal index to indicate the dust export history from the Mongolian Plateau during the Holocene, which had an average deposition of 29.1 g/cm2/ka at ∼ 11500–9200 cal. a BP, decreased to 16.0 g/cm2/ka at ∼ 9200–7400 cal. a BP and decreased sharply to 7.6 g/cm2/ka at ∼ 7400–4000 cal. a BP. This indicates that the dust export activity of the Mongolian Plateau was much stronger in the early Holocene than in the middle Holocene.

Response of Magnetic Minerals to the Mid-Brunhes Climate Event Recorded in Deep-Sea Sediments of the West Philippine Sea

The Mid-Brunhes Event (MBE) was one of the most important global climate events since 800 ka. The deep-sea palaeoceanographic changes in the Western Pacific might have been more sensitive to the MBE and they have not been well documented yet. In this study, we investigated a deep-sea core collected from the Western Philippine Sea and then obtained the magnetism record since around 900 ka. The MBE signal in the deposition process was derived from the concentration-dependent (χ, χARM and SIRM) and the grain-size-dependent magnetic parameters (χARM/χ and χARM/SIRM). Across the MBE, the content of magnetic minerals and the fluctuation of the grain size decreased. Both the content and grain-size indices calculated from magnetic parameters are well correlated with the glacial–interglacial alternations and display a major shift at the MBE. The decreased grain size of magnetic minerals may be associated with the flourishing biota in the tropical Pacific during interglacial intervals. The accumulation of magnetic minerals in the Western Philippine Sea was mainly regulated by the sediment accumulation rate, which may be related to the shoaling of the carbonate compensation depth. Overall, this study expanded the environmental magnetism record for the MBE, suggested a new possible influence of this critical climatic event on the deep-sea deposition process in Western Philippine Sea and inferred the interactions between various environmental systems on glacial–interglacial timescales.