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Reconstruction of mass accumulation rates (MARs) in loess deposits are widely used for interpreting long‐term aeolian transport and climate dynamics in terrestrial environments. However, these interpretations are often driven by a preponderance of reconstructions from individual or selected sites, which can bias our understanding of past climate, especially in the absence of other proxy information. Recent studies on MARs from multiple loess sites in Arid Central Asia (ACA) reveal disparities in the timing of peaks in accumulation between sites, as well as asynchronies with loess flux in the Chinese Loess Plateau (CLP). We investigate this issue by (1) dating five new sites from the western Ili Basin, therefore extending the spatial cover of loess chronologies across ACA and (2) combining that with MARs from >30 sites across ACA and the CLP over the last 60 ka. Our results indicate spatio‐temporal inhomogeneity in the timing and rate of loess deposition across the ACA, and highlight the importance of interrogating local and regional influences on dust supply and transport. Our synthesis of MARs from ACA and the CLP suggests that the timing of peak dust flux as an indicator of large‐scale climate dynamics is best derived from an aggregate of sites; this removes site‐specific bias where local processes or topographic settings outweigh the climate signature. [ABSTRACT FROM AUTHOR]

Hydrothermal venting at the Lucky Strike hydrothermal field, located on the Mid‐Atlantic Ridge, is associated with faulting linked to the tectonic dismemberment of a central axial volcano. Radium‐226/Ba dating of hydrothermal barite indicates that hydrothermal venting is at least 6,600 years old, and that Lucky Strike is one of the youngest known vent fields on the Mid‐Atlantic Ridge, which typically have ages exceeding 20 ka. Deposit volume calculations indicate that the total accumulated mass of the hydrothermal deposits on the seafloor at Lucky Strike is ∼1.3 ± 0.2 Mt, and that this mass accumulated at a maximum average rate of 194 ± 28 t/yr. This accumulation rate is comparable to other well characterized mid‐ocean ridge hydrothermal sites, such as TAG and Endeavor, but at Lucky Strike is concentrated within a relatively small area of <2.5 km2. Plain Language Summary: In this contribution we determine the age (>6,600 years) and mass (∼1.3 Mt) of metal‐rich deposits that formed at a cluster of high‐temperature seafloor hot springs called Lucky Strike, which is situated on the Mid‐Atlantic Ridge. With this information we calculate the average rate of formation (194 t/yr) of these deposits. Our results indicate that the Lucky Strike vent field is much younger than other vent fields that also occur along the Mid‐Atlantic Ridge, but the deposits form at similar rates, which are high when compared to other types of geological processes that produce metal‐rich deposits. Key Points: Hydrothermal activity at the Lucky Strike vent field has been ongoing for at least 6,600 yearsAn estimated ∼1.3 Mt of hydrothermal material has accumulated on the seafloor over an area of <2.5 km2 of seafloor, at a rate of ∼194 t/yrAccumulation rates from Lucky Strike are comparable to other seafloor sites and to analogous on‐land volcanogenic massive sulfide deposits [ABSTRACT FROM AUTHOR]

Despite the increased number of paleoceanographic studies in the SW Atlantic in recent years, the mechanisms controlling marine productivity and terrestrial material delivery to the South Brazil Bight remain unresolved. Because of its wide continental shelf and abrupt change in coastline orientation, this region is under the influence of several environmental forcings, causing the region to have large variability in primary production. This study investigated terrestrial organic matter (OM) sources and marine OM sources in the South Brazil Bight, as well as the main controls on marine productivity and terrestrial OM export. We analyzed OM geochemical (bulk and molecular) proxies in sediment samples from a core (NAP 63-1) retrieved from the SW Atlantic slope (24.8°S, 44.3°W, 840-m water depth). The organic proxies were classified into “terrestrial-source” and “marine-source” groups based on a cluster analysis. The two sources presented different stratigraphical profiles, indicating distinct mechanisms governing their delivery. Bulk proxies indicate the predominance of marine OM, although terrestrial input also affected the total OM deposition. The highest marine productivity, observed between 50 and 39 ka BP, was driven by the combined effects of the South Atlantic Central Water upwelling promoted by Brazil Current eddies and fluvial nutrient inputs from the adjacent coast. After the last deglaciation, decreased phytoplankton productivity and increased archaeal productivity suggest a stronger oligotrophic tropical water presence. The highest terrestrial OM accumulation occurred between 30 and 20 ka BP, with its temporal evolution controlled mainly by continental moisture evolution. Sea level fluctuations affected the distance between the coastline and the sampling site. In contrast, continental moisture affected the phytogeography, changing from lowlands covered by grasses and saltmarshes to a landscape dominated by mangroves and the Atlantic Forest. Our results suggest how the OM cycle in the South Brazil Bight may respond to warmer and dryer climate conditions.

Reconstruction of mass accumulation rates (MARs) in loess deposits are widely used for interpreting long-term aeolian transport and climate dynamics in terrestrial environments. However, these interpretations are often driven by preponderance of reconstructions from individual or selected sites, which can bias our understanding of past climate, especially in the absence of other proxy information. Recent studies on MARs from multiple loess sites in Arid Central Asia (ACA) reveal disparities in the timing of peaks in accumulation between sites, as well as asynchronies with loess flux in the Chinese Loess Plateau (CLP). We investigate this issue by (1) dating five new sites from the western Ili Basin, therefore extending the spatial cover of loess chronologies across ACA and (2) combining that with MARs from >30 sites across ACA and the CLP over the last 60 ka. Our results indicate spatio-temporal inhomogeneity in the timing and rate of loess deposition across the ACA, and highlight the importance of interrogating local and regional influences on dust supply and transport. Our synthesis of MAR's from ACA and CLP suggests that the timing of peak dust flux as an indicator of large-scale climate dynamics is best derived from an aggregate of sites; this removes site-specific bias where local processes or topographic setting outweigh the climate signature. [ABSTRACT FROM AUTHOR]

In tropical and sub‐tropical mixed siliciclastic–carbonate depositional systems, fluvial input and in situ neritic carbonate interact over space and time. Despite being the subject of many studies, controls on partitioning of mixed sediments remains controversial. Mixed sedimentary records, from Ashmore Trough shelf edge and slopes (southern Gulf of Papua), are coupled with global sea‐level curves and anchored to Marine Isotope Stage stratigraphy to constrain models of sediment accumulation at two different timescales for the past 130 kyr: (i) 100 kyr scale for last glacial cycle; and (ii) millennial scale for last deglaciation. During the last glacial cycle, carbonate production and accumulation were primarily controlled by sea‐level fluctuations. Export of neritic carbonate to the slopes was initiated during re‐flooding of previously exposed reefs and continued during Marine Isotope Stage 5e and 1 interglacial sea‐level highs. Siliciclastic fluxes to the slope were controlled by interplay of sea level, shelf physiography and oceanic currents. Heterogeneous accumulation of siliciclastic mud on the slope, took place during Marine Isotope Stage 5d to Marine Isotope Stage 3 sea‐level fall. Siliciclastics reached adjacent depocentres during Marine Isotope Stage 2. Coralgal reef and oolitic–skeletal sand resumed at the shelf edge during the subsequent stepwise sea‐level rise of the last deglaciation. Contemporaneous, abrupt siliciclastic input from increased precipitation and fluvial discharge illustrates that climate controlled deglacial sedimentation. Siliciclastic input persisted until ca 8.5 ka. Carbonate accumulation waned at the shelf edge after ca 14 ka, whereas it increased on the slopes since ca 11.5 ka, when previously exposed reef and bank tops were re‐flooded. When comparing the last sea‐level cycle sedimentation patterns of the southern Gulf of Papua with other coeval mixed systems, sea level and shelf physiography emerge as primary controls on deposition at the 100 kyr scale. At the millennial scale, siliciclastic input was also controlled by climate change during the unstable atmospheric and oceanic conditions of the last deglaciation. [ABSTRACT FROM AUTHOR]

The article is devoted to studing of the features of sedimentation on the bottom of the northwestern shelf and western deep-water area of the Black Sea based on an analysis of our own and published data obtained by bottom sediment radioisotope geochronology. It was determined that the relationship between the mass accumulation rate and primary production was linear, due to the aggregate biogeographic, hydrological, and hydrochemical conditions. The features of bottom sediment formation in the open part of the sea were associated with the presence of hydrogen sulfide (H2S) in deep waters (deeper than 100–200 m). It was shown that 20 (on the continental slope) and 17 g/(m2 year) of particulate organic matter (in the deep-sea basin) entered from the oxygen-containing zone. In this case, the predominant fractions in bottom sediments were mineralized biogenic matter: 54 and 68.5%, respectively, in these areas. The contribution of organic, mineralized biogenic, and lithogenic sedimentary matter to the formation of the mass accumulation rate was estimated, and changes in their ratio with distance from the coast and estuaries were shown. Based on the nature of the formation of the mass accumulation rate, three groups of sea areas were identified in which the ratio of biogenic and lithogenic components in absolute masses reflected a change in their role of these components in bottom sediment formation. [ABSTRACT FROM AUTHOR]

Abstract—Lithological-facies mapping of Pleistocene sediments of pelagic zone and ten key areas of the Pacific submarine margins allowed us to compile the review maps of the Neo- and Eopleistocene sediments for almost 90% of ocean basin area. The comparative analysis of quantitative sedimentation parameters for the Pleistocene sediments of the pelagic and continental margins revealed an increase of absolute mass of lithogenic matter on continental margins by more than eight times, while СаСО3 and biogenic opal, by less than five times. The increasing trend of lithogenic and СаСО3 fluxes in both megafacies zones was proved. Pelagic zone demonstrates an increase of biogenic opal accumulation in the Neopleistocene compared to the Eopleistocene, while fluxes of biogenic opal on the seafloor of continental margins were higher in the Eopleistocene. [ABSTRACT FROM AUTHOR]

It is widely interpreted that there is a significant link between climate cooling at the Eocene-Oligocene Transition (EOT; ∼34 Ma) and subsequent diatom proliferation in the world's oceans during the mid to late Cenozoic. Yet, our understanding of biogenic silica flux through the EOT interval is based on limited data from a few sites, and there are many complications in making a meaningful comparison based on biogenic silica concentration data generated using different techniques. Here, we present new biogenic opal flux and diatom assemblage records across EOT from Ocean Drilling Program Site 748 (Southern Kerguelen Plateau, southern Indian Ocean), in addition to new biogenic opal flux records from the South Atlantic (Deep Sea Drilling Project Site 511, Falkland Plateau and Ocean Drilling Program Site 1090, Agulhas Ridge). Observed opal flux shifts and variability at Site 748 are consistent with published data from nearby Site 744; both sites show considerable shifts in biogenic opal accumulation rates corresponding to shifts in published benthic oxygen isotope records through the EOT. In contrast, our new opal flux record for Site 511, derived from biogenic opal concentration measurements via spectrophotometry, differs from the published record derived from insoluble residues, whereas new data generated for Site 1090 are generally consistent with previously published flux reconstructions. The South Atlantic biogenic opal flux records, however, are dissimilar from one another, and both are dissimilar from the Southern Indian Ocean records. Also, the taxonomic composition of the diatom assemblages from Sites 511, 748 and 1090 display considerable differences, with hemiauloids and rhizosolenids – generally inferred as indicative of oligotrophic conditions – being the dominant diatoms at the Southern Kerguelen Plateau (Site 748). Published records show that hemiauloid taxa are absent from the earliest Oligocene interval at Site 1090, which is widely seen as a record of deposition from nutrient-rich waters sustaining abundant diatom assemblages. These differences in diatom assemblages testify to regional differences in nutrient concentrations. In particular, the timing of biogenic opal flux pulses between Sites 1090 and 748 imply a shift in the locus of opal deposition to areas further south in the Southern Ocean across the EOT, likely related to proto-ACC development and strengthening of frontal boundaries. Thus, combined geochemical and micropaleontological evidence points to a regionally variable rather than a global, unified opal flux response to climate cooling through the Eocene-Oligocene Transition. • New biogenic opal flux data for sites 748, 511 and 1090 across EOT. • New quantitative diatom assemblage records for Site 748. • Geographically variable biogenic opal flux response to climate cooling through EOT. • High relative abundance of oligotrophic diatom taxa at Site 748. • Site 511 and 1090 diatom assemblages indicative of more eutrophic conditions. • Timing of opal flux pulses suggests southward shift of opal accumulation through EOT. [ABSTRACT FROM AUTHOR]

This study intends to review and assess the middle to late Miocene Carbonate Crash (CC) events in the low to mid latitudes of the Pacific, Indian, Caribbean and Atlantic Oceans as part of the global paleoceanographic reorganisations between 12 and 9 Ma with an emphasis on record preservation and their relation to mass accumulation rates (MAR). In the Eastern Pacific the accumulation changes in carbonate and opal probably reflect an El-Niño-like state of low productivity, which marks the beginning of the CC-event (11.5 Ma), followed by decreased preservation and influx of corrosive bottom waters (10.3 to 10.1 Ma). At the same time in the Atlantic, carbonate preservation considerably increases, suggesting basin-to-basin fractionation. The low-latitude Indian Ocean, the Pacific and the Caribbean are all characterised by a similar timing of preservation increase starting at ~9.6–9.4 Ma, while their MARs show drastic changes with different timing of events. The Atlantic preservation pattern shows an increase as early as 11.5 Ma and becomes even better after 10.1 Ma. The shallow Indian Ocean (Mascarene plateau) is characterised by low carbonate accumulation throughout and increasing preservation after 9.4 Ma. At the same time, the preservation in the Atlantic, including the Caribbean, is increasing due to enhanced North Atlantic deep-water formation, leading to the increase in carbonate accumulation at 10 Ma. Moreover, the shoaling of the Central American Isthmus might have helped to enhance Caribbean preservation after 9.4 Ma. Lower nannoplankton productivity in the Atlantic should have additionally contributed to low mass accumulation rates during the late CC-interval. Overall, it can be inferred that these carbonate minima events during the Miocene may be the result of decreased surface ocean productivity and oceanographically driven increased seafloor dissolution.

In present research, fifteen surficial and two profile sediment samples were studied in terms of sediment chronology and pollution degree on the ground of pollution indexes such as enrichment factor (EF), contamination factor (CF), Pollution Load Index (PLI) and lead isotope ratios (206Pb/207Pb, 208Pb/206Pb). Lead-210 (polonium-210) activity concentrations were measured by utilizing alpha spectrometry. Sediment chronology was determined via modified CRS mathematical model. Average mass accumulation rates are 0.301 and 0.227 g cm−2 year−1 in Bakırçay River mouth and Ayvalık offshore stations respectively. Mass accumulation rates do not display the systematic increases along the cores from bottom layers to top layers. In Bakırçay River mouth station 210Pb flux is higher than the range of global atmospheric 210Pb flux value. Due to the high CF and EF values of Sr both of stations have hydrothermal features. Ayvalık offshore station has displayed Na, Cd pollution since 1945, but Na, Cd, As, Mo, Ag pollutions have existed in Bakırçay River mouth station since 1983 in terms of CF and EF values. According to PLI index, Bakırçay River mouth station has “starting level pollution” degree and it displayed an “acute corruption” in 1981. 206Pb/207Pb ratios range from 1.17 to 1.25, 208Pb/206Pb ratios range from 1.99 to 2.16 in study area. When 206Pb/207Pb and 208Pb/206Pb ratios are evaluated with together, it is seen that both of the stations have had the natural (geologic) sediments since 2011. [ABSTRACT FROM AUTHOR]

Geochemistry, total organic carbon and total nitrogen of three sediment cores collected in the Gulf of Cádiz and the Guadalquivir prodelta areas in Spain were investigated. The C/N ratio, mostly around 10, seems to indicate a predominantly marine origin for the sedimentary organic matter. Major and minor elements (Si, Ti, Al, Fe, Mg, Ca, K, Na, P, S) and trace elements (Mn, Sc, V, Cr, Ni, Cu, Zn, Rb, Sr, Y, Zr, Ba, Ce, Pb, Hg) showed significant differences in bulk chemical composition between the two areas. Despite the effects of bioturbation, vertical changes in downcore profiles of heavy metals occur only in the cores of the Cádiz area, although the concentrations keep to low levels. The relatively high concentrations of Zr and Y, elements commonly associated with the heavy minerals fraction, at the top of cores from the Cádiz area are attributed to an enrichment of heavy minerals related to selective transport that concentrates this fraction. 137Cs and 210Pb activities in one of the two sediment cores collected in the Gulf of Cádiz were also measured. The distribution of excess 210Pb was used to determine the modern (last 100 yr) mass accumulation rate and the depth of sediment mixing on the continental shelf of the gulf. Estimated sediment accumulation rate was 0.1 g cm-2 yr-1. The uppermost 4 cm had uniform excess 210Pb activity profiles above a region of steadily decreasing 210Pb activity, and this phenomenon was attributed to sediment mixing (bioturbation). 137Cs activity was lower than 3 Bq kg-1 and the profile does not show evidence of fallout peaks.

Minerals and elements are important proxies that can provide information about variations in the delivery and deposition of coastal ocean sediments associated with past climate changes. In this study, postglacial changes in the accumulation of sediments on the upper shelf of southeastern Brazil are linked to the evolution of regional paleoceanographic and continental paleoclimatic conditions during the last 14.4 kyr CAL BP. Mineralogical and major and trace element analyses of a 14 C-dated sediment core identify three main lithostratigraphic units of this core that reveal a succession of changes in sediment delivery and accumulation as postglacial sea level rose and Holocene climate on land evolved. The depositional setting has transitioned in response to the large sea level rise prior to 9.9 kyr CAL BP from being a shallow water high energy environment to a deeper water one. This location has since then been a lower energy environment that has persisted into modern times. Due to the high marine productivity associated with the Cabo Frio upwelling system in an oxygenated water column, the sediments have shown a complex and dynamic redox condition, making variations in redox-sensitive trace elements indicative of changes in primary production and organic matter diagenesis at this location. After sea level stabilized ~ 9 kyr CAL BP, variations in fluxes of Al, Fe, Ca, and minerals were small, indicating that climate driven changes had only secondary controls on delivery of detrital sediment components to the Cabo Frio shelf. Modern coastal upwelling conditions and the onset of mid-shelf organic-rich sediment deposition were established after 9.9 CAL kyr BP. [ABSTRACT FROM AUTHOR]

Abstract: Hydrothermal sulfide deposits that form on the seafloor are often located by the detection of hydrothermal plumes in the water column, followed by exploration with deep-towed cameras, side-scan sonar imaging, and finally by visual surveys using remotely-operated vehicle or occupied submersible. Hydrothermal plume detection, however, is ineffective for finding hydrothermally-inactive sulfide deposits, which may represent a significant amount of the total sulfide accumulation on the seafloor, even in hydrothermally active settings. Here, we present results from recent high-resolution, autonomous underwater vehicle-based mapping of the hydrothermally-active Endeavour Segment of the Juan de Fuca Ridge, in the Northeast Pacific Ocean. Analysis of the ridge bathymetry resulted in the location of 581 individual sulfide deposits along 24 km of ridge length. Hydrothermal deposits were distinguished from volcanic and tectonic features based on the characteristics of their surface morphology, such as shape and slope angles. Volume calculations for each deposit results in a total volume of 372,500 m3 of hydrothermal sulfide–sulfate–silica material, for an equivalent mass of ∼1.2 Mt of hydrothermal material on the seafloor within the ridge's axial valley, assuming a density of 3.1 g/cm3. Much of this total volume is from previously undocumented inactive deposits outside the main active vent fields. Based on minimum ages of sulfide deposition, the deposits accumulated at a maximum rate of ∼400 t/yr, with a depositional efficiency (proportion of hydrothermal material that accumulates on the seafloor to the total amount hydrothermally mobilized and transported to the seafloor) of ∼5%. The calculated sulfide tonnage represents a four-fold increase over previous sulfide estimates for the Endeavour Segment that were based largely on accumulations from within the active fields. These results suggest that recent global seafloor sulfide resource estimates, which were based mostly on the sizes and distribution of hydrothermally-active deposits, may be similarly underestimating the amount of sulfide along the global submarine neovolcanic zones. [Copyright &y& Elsevier]

Mass accumulation rates (MAR; g cm-2 y-1), linear sedimentation rates (LSR; cm y-1), and core geochronology derived from excess lead-210 (210Pb) profiles and inventories measured in six sediment cores collected from marsh sites from the MobileTensaw River Delta and Mobile Bay region record the importance of both continuous and event-driven inorganic sedimentation over the last 120 years. MAR in freshwater marshes varied considerably between sites and through time (0.24 and 1.31 g cm-2 y-1). The highest MARs occurred in the 1950s and 1960s and correspond to record discharge events along the Mobile and Tensaw Rivers. In comparison, MAR at salt marsh sites increased almost threefold over the last 120 years (0.05 to 0.18 g cm-2 y-1 or 0.23 to 0.48 cm y-1). From 1880 to 1960, organic accumulation remained fairly constant (∼20%), while intermittent pulses of high inorganic sedimentation were observed following 1960. The pulses in inorganic sedimentation coincide with several major hurricanes (e.g., Hurricanes Camille, Fredric, Georges, and Ivan). The nearly threefold increase in MAR in salt marshes during the last 120 years would thus appear to be partially dependent on inorganic sedimentation from storm events. This study shows that while hurricanes, floods, and other natural hazards are well-known threats to human infrastructure and coastal ecosystems, these events also transport sediment to marshes that help abate other pressures such as sea-level rise (SLR) and subsidence. [ABSTRACT FROM AUTHOR]

Four sediment cores were collected from selected locations of Sundarbans mangroves and Hooghly estuary, northeast coast of India to establish Pb geochronology and trace metal distribution in sediments. Core sites were chosen to reflect a matrix of variable anthropogenic input and hydrological conditions. The vertical distribution of Pb (Pb-Ra) provided reliable geochronological age to calculate the mass accumulation rates and historic trace element inputs and their variations. The mass accumulation rates ranged from 0.41 g cm year (estuarine region) to 0.66 g cm year (mangrove region). Both in mangroves and estuarine systems, Fe-Mn oxy-hydroxides are observed to be a major controlling factor for trace metal accumulation when compared to organic carbon. Core collected from Hooghly estuary shows less contamination when compared to the mangrove region due to high energy and mostly coarse grained. Fe-normalized enrichment factors (EFs) of trace metals were calculated based on crustal trace element abundances. The EFs are typically >1 for Cd, Pb, Co, and Cu indicating that these metals are highly enriched while other metals such as Zn, Ni, Cr, and Mn show no enrichment or depletion. Both Sundarbans mangroves and Hooghly estuary have been receiving considerable pollution loads from anthropogenic sources such as industrial, domestic, and shipping activities in recent times, indicating high concentration of metals in the top few layers. This study suggests that the variation in trace metals content with depth or between mangrove and estuarine system results largely from metal input due to anthropogenic activities rather than diagenetic processes. [ABSTRACT FROM AUTHOR]

Abstract: Submarine canyons play an important role in the transfer of contaminated sediments from shelf areas to the deeper ocean. To evaluate the importance of submarine canyons adjacent to the Tagus and Sado estuaries (Portuguese Margin) as sediment pathway major and trace elements, 210Pb radionuclides, organic carbon, calcium carbonate and grain size were analyzed in fifteen short sediment cores from the Cascais and Lisboa–Setúbal submarine canyons and neighbor slopes at the Estremadura Spur and off Sines. Mass accumulation rates (MAR) vary between 0.02 and 0.40g cm−2 y−1 with the highest values in the upper Cascais and Lisboa canyons. Mercury and Pb enrichment factors exceed 2 and show a continuously increasing trend since 1950AD in the upper sections of the Cascais Canyon and in the Lisboa–Setúbal Canyon system, implying an anthropogenic source. Mercury and Pb anthropogenic inventories also present highest values in the canyon heads, which is consistent with its proximity to the Tagus and Sado river mouths. To a lesser extent, the Estremadura and Sines slopes and the deeper sections of the canyons also have slightly increasing Hg and Pb enrichment factor trends towards the present-day. For these areas, with a major influence of pelagic sedimentation, we infer atmospheric transport as a complementary source of contaminants. Therefore, our data suggest that although canyons are preferential conduits to transport sediments to the deep sea when compared to the slopes, Hg and Pb derived from human activities have reached both domains with different intensities down to a depth of 2000mwd. [Copyright &y& Elsevier]

Abstract: The modern distribution of biogenic silica (SiO2biog) in Baikal surface (0–0.2 and 0–0.5 cm) sediments, its mass accumulation rates (MAR), and the processes responsible for this distribution were studied. The contents of SiO2biog were determined in samples from 87 stations evenly distributed throughout the lake water area. These data were used to calculate the MAR of SiO2biog and compile SiO2biog and MAR distribution maps. The maps showed that the MAR varies significantly throughout the study area. Its highest values have been established in North Baikal. In Central and South Baikal the MAR values are much lower, and the minimum values are observed in the Selenga shoal. This MAR distribution pattern is consistent with the distribution of frustules of Aulacoseira baicalensis endemic diatoms throughout the surface sediments. Compared with other modern diatom species, this one has the most massive and heaviest frustules, which undergo the least dissolution when settling. This suggests that the above species plays a leading role in the accumulation of biogenic silica in modern Baikal bottom sediments, whereas the role of thin-walled species is minor because of their small mass and partial or complete dissolution in water on settling. Dilution of the sediments with terrigenous material is less significant for the SiO2biog accumulation. [Copyright &y& Elsevier]

Abstract: Sediment input to the deep ocean, off the New Zealand collisional plate boundary, is large and variable as revealed by a 139 kyr-old record from the 34.92 m-long core, MD97 2121. Mass accumulation rates (MARs) were derived for terrigenous and biogenic (carbonate and silica) sedimentary components, with temporal control from a stable isotope age model verified by tephra and radiocarbon ages. Terrigenous MARs changed in phase with glacio-eustatic fluctuations of sea level. Highest rates (≥30 g/cm2/kyr) coincided with the late regressive-lowstand-early transgressive phase of marine isotope stage (MIS) 2 when rivers discharged at or near the shelf edge. Lesser, but still high terrigenous rates (20–30 g/cm2/kyr) characterized peak warm phases of early MIS 5 and 1, when a strengthened Subtropical Inflow probably introduced sediment from fluvial and seabed sources to the north of MD97 2121. However, during prolonged highstands the flux declined as more sediment was retained on a tectonically subsiding shelf with a shore-parallel current. Paradoxically, the lowest MARs (10–5 g/cm2/kyr) occurred in MIS 4; either sea level was too high to allow much sediment to escape off-shelf, or the fluvial input was modest, or both these factors. Despite the terrigenous dominance, biogenic MARs are high, and are 2–4 times larger than SW Pacific Ocean rates. MARs were lowest during MIS 4 and 3, possibly due to reduced marine production under a lowered input of fluvial micronutrients. In contrast, MARs increased irregularly though glacial maxima to peak at 5–6 g/cm2/kyr carbonate and 2–2.5 g/cm2/kyr silica in early-mid MIS 5 and 1. Such rates reflected the interaction of macronutrient-rich subantarctic waters, sourced from the south, with local, micronutrient-rich subtropical waters. Production also responded to warmer temperatures, elevated nutrient runoff and a more stratified surface ocean. Later in MIS 5 and 1, fluxes reduced as less productive subtropical waters prevailed. That biogenic and aeolian MAR profiles are out of phase, suggests Fe-fertilization by aerosolic dust was not a major influence. [Copyright &y& Elsevier]

Abstract: To obtain a quantitative estimate of the sediment accumulating on the muddy belt extending along the western Adriatic continental shelf, a budget was calculated based on the mass accumulation rates measured from more than one hundred activity–depth profiles of 210Pb. 137Cs depth-distributions were used, when possible, to support 210Pb results. 210Pb profiles show quasi-monotonic declines in the foreset region of the central Adriatic clinoform. In the prodelta of the rivers Po and Isonzo, 210Pb profiles are characterized by intervals of low and uniform activity, which are thought to be produced by flood deposition. Since the north Adriatic is shallow and occasionally affected by storms from Bora wind, sediments are not in steady-state and their accumulation is the net result of recurring deposition, resuspension and winnowing events. In the western Adriatic, mass accumulation rates range between 0.04 and 6.6 g cm−2 yr−1. Peak values were recorded in the Po and Isonzo prodeltas and along a narrow belt between Pescara and the Gargano promontory. Furthermore, the latter depocentre is located immediately seaward of the offlap break (40–50 m water depth) and parallels that of the most recent sigmoid of the HST. The integration of mass accumulation rates throughout the mud wedge of the north and central Adriatic gave a value of ∼42.0 Tg yr−1 of sediment accumulating along the Italian coast. The balance between sediment accumulation and riverine sediment supply (∼46.6 Tg yr−1) suggests an export of 4.6 Tg yr−1 to the south Adriatic basin and/or the Mediterranean Sea. The along-shore sediment transport is very effective and, in particular, 16.2 Tg yr−1 of sedimentary material (∼35% of the riverine supply) is transferred from north to central Adriatic, through the Ancona section. [Copyright &y& Elsevier]

We established sediment geochronologies for cores from eight deltaic areas in Lake Tanganyika (the Lubulungu, Kabesi, Halembe, Malagarasi, Nyasanga/Kahama, Mwamgongo, Nyamusenyi, and Karonge/Kirasa River deltas), recording a range of watershed disturbance histories from the eastern margin of this African rift valley lake. Cores from currently disturbed sites on the central Tanzanian coast display remarkably uniform and low rates of sediment accumulation from the 18th century until the early 1960s, when a synchronous and dramatic rise in rates occurs. Through this same time interval sedimentation rates offshore from undisturbed Tanzanian watersheds either remain unchanged or decline. Further north, at disturbed sites along the northern Tanzania and Burundi coasts, the pattern of sedimentation rate increase is more complex. Although a mid-late 20th century increase is also evident in these sites, indications of earlier periods of increasing sediment erosion, dating from the mid-late 19th century, are also evident. Synchronous changes in sediment accumulation rates dating from the early 1960s may be the result of exceptionally wet years triggering an increase in the discharge of previously eroded and unconsolidated alluvium and stream/beach terrace deposits, previously accumulated in the deltas and stream valleys of impacted watersheds. Sedimentation rate impacts of deforestation on lake ecosystems are likely modulated by short-term climatic forcing events, which can impact the specific timing and location of sediment discharge to lakes. [ABSTRACT FROM AUTHOR]

Molecular abundances of n-nonacosane are reported for a suite of 44 surface sediments and four deep sea cores distributed throughout the South China Sea (SCS), covering the last 220 ky at different time resolutions. The patterns of glacial to interglacial variability of the concentrations of this terrigenous marker are parallel for all cores, taking values linearly inversely correlated to the U37K′ index sea surface temperatures (SST), with high concentrations during cold-glacial intervals and low concentrations during warm-interglacial periods. The oscillations of this terrigenous marker likely result from the emergence and flooding of the shelves caused by sea-level variations which, together with SCS SSTs, have a clear dependency on the Northern Hemisphere climate evolution. Calculation of accumulation rates for the northernmost core together with the modern distribution of n-nonacosane concentrations in surface sediments evidences the complexity of sedimentation patterns in the northern SCS. In particular, and in agreement with recent studies, terrigenous materials deposited there might originate from areas different than the highly loaded Pearl River. For paleoceanographic purposes, the noticeable general pattern of the n-alkane concentration down-core profiles for the four cores studied, a parameter apparently unaffected by changes in sedimentation rates, prompts its use as a tracer of variations in terrigenous input into this basin over glacial to interglacial times. [Copyright &y& Elsevier]

Glacier-fed river systems represent potentially significant sediment sources for aeolian processes owing to sediment production, flow seasonality, and winds within mountain settings. We investigate the timing and rates of Holocene loess and aeolian sand deposition in three major river valleys (Bow, North Saskatchewan and Athabasca) of the southeastern Canadian Cordillera through aeolian stratigraphy and dating of sedimentary materials. Source sediments are glacially-derived, seasonally-exposed alluvial deposits. Variation in river morphology promotes source-sediment deposition influenced by bedrock configuration, tributary stream deposition and alluvial fans. Two main settings for aeolian deposition are source-proximal valley-bottom sites and more distal lower-valley sites in sub-alpine and montane forest ecozones. Dating is well-constrained by radiocarbon ages and tephrochronology. Quartz optical dating is complicated, likely owing to minimal recycling of grains and quartz provenance. Mass accumulation rates (MARs) indicate that aeolian deposition was initiated soon after deglaciation and has occurred nearly continuously for at least 10000 years. Loess MARs ranged between 100 and 2500 g·m−2·a−1 during the Holocene. Rates in the last 3000 years are generally two to three times higher than those observed for earlier periods, and are highest in most recent times. We attribute Holocene accumulation at these sites in general to fluvial source sediment availability and the efficacy of forested valleys as sediment traps. The late Holocene increase in MARs is primarily attributed to increased glacial silt and alluvial sediment supply during neoglacial fluctuations including the Little Ice Age. [ABSTRACT FROM AUTHOR]

This study intends to review and assess the middle to late Miocene Carbonate Crash (CC) events in the low to mid latitudes of the Pacific, Indian, Caribbean and Atlantic Oceans as part of the global paleoceanographic reorganisations between 12 and 9 Ma with an emphasis on record preservation and their relation to mass accumulation rates (MAR). In the Eastern Pacific the accumulation changes in carbonate and opal probably reflect an El-Niño-like state of low productivity, which marks the beginning of the CC-event (11.5 Ma), followed by decreased preservation and influx of corrosive bottom waters (10.3 to 10.1 Ma). At the same time in the Atlantic, carbonate preservation considerably increases, suggesting basin-to-basin fractionation. The low-latitude Indian Ocean, the Pacific and the Caribbean are all characterised by a similar timing of preservation increase starting at ~9.6–9.4 Ma, while their MARs show drastic changes with different timing of events. The Atlantic preservation pattern shows an increase as early as 11.5 Ma and becomes even better after 10.1 Ma. The shallow Indian Ocean (Mascarene plateau) is characterised by low carbonate accumulation throughout and increasing preservation after 9.4 Ma. At the same time, the preservation in the Atlantic, including the Caribbean, is increasing due to enhanced North Atlantic deep-water formation, leading to the increase in carbonate accumulation at 10 Ma. Moreover, the shoaling of the Central American Isthmus might have helped to enhance Caribbean preservation after 9.4 Ma. Lower nannoplankton productivity in the Atlantic should have additionally contributed to low mass accumulation rates during the late CC-interval. Overall, it can be inferred that these carbonate minima events during the Miocene may be the result of decreased surface ocean productivity and oceanographically driven increased seafloor dissolution. [ABSTRACT FROM AUTHOR]

Thick and widespread loess deposits in southern Tajikistan provide insight into the regional climatic changes in arid Central Asia (ACA) during the Quaternary. However, because of the lack of robust chronological constraints, the environmental implications of these deposits are not yet fully understood. Here, we report a detailed medium-grained quartz optically stimulated luminescence (OSL) dating analysis on a loess sequence deposited since the Lateglacial in southern Tajikistan. The single-aliquot regeneration (SAR) and standardized growth curve (SGC) methods were used for equivalent dose determination. Quartz OSL measurements showed that both the SAR and SGC methods can be used for equivalent dose determination for Tajik loess. On the basis of the obtained OSL ages, we reconstructed the dust accumulation rates and mass accumulation rates. Our results show that the dust flux continued to decline whereas the precipitation increased stepwise after the end of the Last Glacial Maximum. Changes in the dust flux and precipitation in ACA were sensitive to the gradual warming since the Lateglacial. • Both the SAR and SGC methods can be used for De determination in Tajik loess. • A continuous decline trend of past dust flux since the end of the LGM. • Dust activities have been sensitive to gradual warming since the Lateglacial. [ABSTRACT FROM AUTHOR]

Blue carbon (BC) ecosystems provide important and multiple ecosystem services, including climate change mitigation through carbon storage. However, these ecosystems are under the pressure of numerous anthropogenic stressors, such as population growth and industrialization, which jeopardize the benefits they provide. Although the common methodology is based on the use of a linear depth scale, this work highlights the need of sediment dating to evaluate temporal variation of organic carbon (C org) stocks and burial rates, since sedimentation patterns can be variable even between sites within a single ecosystem. Temporal records of C org stocks and burial rates during the past 100 years were determined in mangrove, seagrass and salt marsh ecosystems, from five representative areas of the Mexican marine coastal systems, by using 210Pb-dated sediment cores. Carbon stocks during the past 100 years (C org stock (100 years)) ranged from 67 to 269 Mg C org ha−1 in mangroves, 8–53 Mg C org ha−1 in seagrasses and 32–56 Mg C org ha−1 in salt marshes, and burial rates were 8–426 g m−2 yr−1, 2–252 g m−2 yr−1 and 1–60 g m−2 yr−1, respectively. Most of the stored C org (60–86%) accumulated during the Anthropocene (since 1950), and in mangrove cores recent C org stocks were up to six times higher than before the Anthropocene onset (1900–1950), most likely as a result of land use changes. Increased C org burial rates in seagrass ecosystems were mostly driven by mass accumulation rate changes (promoted by catchment erosion and sea level rise), and in mangroves and salt marshes by changes in C org content, likely promoted by an increase in productivity associated with nutrient enrichment by fertilizer runoff and sewage disposal. Despite the multiple anthropogenic stressors that positively affected C org stocks and burial rates in BC ecosystems, worldwide destruction of these valuable habitats will cause losses of long-term buried C org through significant CO 2 releases, thus conservation and/or restoration are effective actions for climate change mitigation. • C org burial and stock temporal change in Mexican blue carbon habitats are reviewed. • Notable differences in C org accumulation were observed within and among study sites. • Highest accumulation in seagrasses, mangroves and salt marshes occurred after 1950s. • Land use changes have enhanced C org burial rates and stock during the Anthropocene. • 210Pb dating is relevant for blue carbon stock evaluations in a global context [ABSTRACT FROM AUTHOR]