Uppermost Sediments Research Articles

Element remobilization, "internal P-loading," and sediment-P reactivity researched by DGT (diffusive gradients in thin films) technique.

Labile P, Fe, and sulfide with the high spatial resolution in sediment porewater of five sites (A-E) of Dianchi Lake (China) were measured at same locations using AgI/Chelex-100, Chelex-100, and ferrihydrite DGT (diffusive gradients in thin films) probes. DGT derived P/Fe/S concentrations in sediment porewater on millimeter or sub-millimeter scale in order to reveal the element remobilization process and the mechanism of "internal P-loading" of sediments in Dianchi Lake. Decomposition of alga biomass in the uppermost sediment layer and the reductive dissolution of Fe-bound P in the anoxic sediment were the two main processes causing P release. A dynamic numerical model-DIFS (DGT-induced flux in sediments) was used to assess sediment-P reactivity (capacity of solid pool and rate of transfer) and P release risk by kinetic parameter-T C (1089∼20,450 s), distribution coefficient-K d (167.09∼502.0 cm(3) g(-1)), resupply parameter-R (from 0.242 to 0.518), and changes of dissolved/sorbed concentration, R and M at the microzone of DGT/porewater/sediment.

The paleohydrology of Sluice Pond, NE Massachusetts, and its regional significance

Seismic, pollen, stable isotope and lithologic stratigraphies of Sluice Pond, northeastern Massachusetts, were investigated to reconstruct local climate conditions from the latest Pleistocene to present. We present a new lake-level curve, constrained largely by acoustic reflectors and well-dated sediment cores from the deep basin and margin of the lake. Bulk δ34S data from the basin core provide valuable information regarding anoxia and water-column stratification. The lake-level history is corroborated with pollen-based, transfer-function-derived reconstructions of temperature and precipitation from the basin core. The lower stratigraphy reveals a time of cold/dry climate from ca. 11.7–8.2 ka BP (1 ka = 1,000 cal yr), with a minor lake-level increase centered at ca. 11.0 ka BP. An increase in regional temperature/moisture is apparent in sediments younger than 8.2 ka BP. A warm/dry climate is reconstructed from ca. 5.1–3.5 ka BP, concomitant with the well-established regional Tsuga (eastern hemlock) minimum. Sediments deposited since 3.5 ka BP reveal a general deepening of the pond and organic-rich conditions, with another minor dry episode from ca. 2.0–1.3 ka BP. Uppermost sediments record anthropogenic disturbance. The hydroclimate variability inferred from the Sluice Pond sediment record is consistent with previous reconstructions of lake level and vegetation in the southern portion of the northeastern US. It is not, however, consistent with reconstructions from locations farther north, many of which possess evidence of a dry period ca. 9.0–5.0 ka BP. The likely explanation for this discrepancy lies in air mass distribution associated with the position and amplitude of the circumpolar vortex throughout the Holocene. This new record of Holocene regional hydroclimate variability adds to the spatial coverage of existing reconstructions, and helps constrain forcings associated with such variability.

Interlinked seasonal variation in biogenic nutrient fluxes and pore-water nutrient concentrations in intertidal sediments

The seasonal variation in biogenic fluxes of NH4 +, PO4 3− and SiO2 calculated from the nutrient excretion rates of dominant bivalves (Ruditapes philippinarum and Arcuatula [=Musculista] senhousia), and pore-water nutrient (NH4 +, PO4 3−, SiO2 and NO3 − + NO2 −), sedimentary acid-volatile sulfide (AVS) and benthic chlorophyll-a (Chl-a) concentrations was assessed on an intertidal sandflat in the Seto Inland Sea (Japan) from summer 1994 to autumn 1995. In spite of the large variability between sampling dates and stations, significant correlations between biogenic nutrient fluxes and pore-water nutrient concentrations were found, suggesting a seasonal linkage between bivalve-mediated biological processes and chemical features of sediments. This linkage was stronger in surface (0–0.5 cm) than subsurface (0.5–2 cm) sediments, consistent with the autoecological characteristics of R. philippinarum and A. senhousia inhabiting the uppermost sediment layer. Significant temporal variation in pore-water NO3 − + NO2 −, sedimentary AVS and benthic Chl-a concentrations was also found, which was related to both occasional extreme events (e.g., dystrophy) and alternating periods of production and decomposition. This study may serve twofold in (1) contributing to unravel the ecological structure and functioning of natural tidal flats, and the scale of seasonal variability in biotic and sedimentary parameters and (2) providing useful information for assessing the effectiveness of the physico-chemical and biological structure of artificial tidal flats which are growing in number and extension worldwide.

Sedimentological characteristics of ice-wedge polygon terrain in Adventdalen (Svalbard) – environmental and climatic implications for the late Holocene

Abstract. Ice wedges are widespread periglacial features in the landscape of Adventdalen, Svalbard. The networks of ice wedges have created areas with well-developed polygonal terrains in the lowest fluvial terraces in this valley. We have examined the sedimentological characteristics of the northern and southern banks of the Advent river for palaeoenvironmental purposes. The base of two sedimentary sections reported radiocarbon dates of 3.3 and 3.9 ka BP, respectively. The northern site is constituted by three very different lithostratigraphical units, which suggests that their formation should be related to different environmental and climate conditions. By contrast, the southern section shows a rather homogeneous composition, with no significant variations in grain size and organic matter content. In both cases the uppermost sediments are constituted by a thick aeolian deposit. According to our data, warmer climate conditions may have prevailed during the mid Holocene until 3.3 ka BP with widespread peat formation in the valley bottom. Subsequently, a period with alternating soil formation and aeolian sedimentation took place from 3 to 2.5 ka BP, probably due to increasing climatic severity. During the last millennium a long-term cooling trend has favoured aeolian deposition in the lowest part of Adventdalen.

Toward a better understanding of Paleocene-Eocene Thermal Maximum: A multidisciplinary record from Dababiya GSSP, Luxor, Egypt

The Paleocene-Eocene thermal maximum (PETM) shows an extraordinary drop in both δ 13 Ccarb and δ 13 Corg values, suggesting that a massive amount of 12 C-rich carbon dioxide was released into the atmosphere in a very short time (on the order of few hundred ky). The Dababiya GSSP (Luxor, Egypt) is thought to be the most complete known PETM section. The expanded sedimentary record of the Dababiya GSSP improves our understanding of the processes leading to the PETM events. Our multiproxy dataset, which includes geochemistry, mineralogy, micropaleontology and sedimentology, provided the following crucial clues for the PETM interval at Dababiya GSSP (Fig. 1). The Dababiya GSSP is deposited in the deepest part of an asymmetric submarine channel as indicated by the paleotopography, and absence of uppermost Paleocene and lowermost Eocene sediments from the Eastern section located 25m away from the main GSSP outcrop (Fig.1). At 50 m to the NW, the sediment beds thin out and finally disappear at about 150 m from the main GSSP outcrop. Thus, the Dababiya GSSP represents a localized expanded PETM sequence with a maximum extent of about 200m. At the GSSP, the PaleoceneEocene boundary (PEB) coincides therefore with a sequence Toward a better understanding of Paleocene-Eocene Thermal Maximum: A multidisciplinary record from Dababiya GSSP, Luxor, Egypt

Colonization dynamics of ciliate morphotypes modified by shifting sandy sediments

Sandy stream-bed sediments colonized by a diverse ciliate community are subject to various disturbance regimes. In microcosms, we investigated the effect of sediment shifting on the colonization dynamics of 3 ciliate morphotypes differing in morphology, behavior and feeding strategy. The dynamics of the ciliate morphotypes inhabiting sediment pore water and overlying water were observed at 3 sediment shifting frequencies: (1) stable sediments, (2) periodically shifting sediments such as migrating ripples, and (3) continuously shifting sediments as occurring during scour events of the uppermost sediment. Sediment shifting significantly affected the abundance and growth rate of the ciliate morphotypes. The free-swimming filter feeder Dexiostoma campylum was vulnerable to washout by sediment shifting since significantly higher numbers occurred in the overlying water than in pore water. Abundance of D. campylum only increased in pore water of stable sediments. On the contrary, the vagile grasper feeder Chilodonella uncinata and the sessile filter feeder Vorticella convallaria had positive growth rates and successfully colonized sediments that shifted periodically and continuously. Thus, the spatio-temporal pattern of sediment dynamics acts as an essential factor of impact on the structure, distribution and function of ciliate communities in sand-bed streams.

Meltwater intensive glacial retreat in polar environments and investigation of associated sediments: example from Pine Island Bay, West Antarctica

Modern Pine Island and Thwaites Glaciers, which both drain into Pine Island Bay, are among the fastest changing portions of the cryosphere and the least stable ice streams in Antarctica. Here we show that the uppermost sediment unit in Pine Island Bay was deposited from a meltwater plume, a plumite, during the late stages of ice sheet retreat ∼7–8.6 k cal yr BP and argue that this deposit records episodes of meltwater intensive sedimentation.The plumite is a hydraulically sorted, glacially sourced, draping deposit that overlies proximal glacimarine sediments and thickens towards the modern grounding line. The uppermost sediment unit is interpreted as a product of non-steady-state processes in which low background sedimentation in large bedrock-carved basins alternates with episodic purging of sediment-laden water from these basins. The inner part of Pine Island Bay contains several basins that are linked by channels with a storage capacity on the order of 70 km3 of stagnant water and significant sediment storage capacity. Purging of these basins is caused by changes in hydraulic potential and glacial reorganization. The sediment mobilized by these processes is found here to total 120 km3.This study demonstrates that episodes of meltwater-intensive sedimentation in Pine Island Bay occurred at least three times in the Holocene. The most recent episode coincides with rapid retreat of the grounding line in historical time and has an order of magnitude greater flux relative to the entire unit. We note that the final phase of ice stream retreat in Marguerite Bay was marked by a similar sedimentary event and suggest that the modern Thwaites Glacier is poised for an analogous meltwater-intensive phase of retreat.

Heavy metal records in the sediments of Nanyihu Lake, China: influencing factors and source identification

In 2008, three short sedimentary cores were collected from Nanyihu Lake in the lower Yangtze River Basin using a gravity corer. Heavy metals, including Pb, Cu, Zn, Cr, Ni, Mn, and major elements, including Al, Fe, K, Na, Mg and Ti, were measured. Radionuclides, including 210Pb and 137Cs, were analyzed to date the sediments. The significant Mn enrichment in the uppermost sediments of the three cores did not influence the distribution of Pb, Cu, Zn, Cr and Ni. The Pb, Cu, Zn, Cr and Ni contents have increased over the past 30–40 years. The decline of 206Pb/207Pb ratios toward the surface indicated increasing anthropogenic Pb loading to the lake sediments. However, the heavy metal enrichment was low overall because of the high sediment accumulation rates and the low anthropogenic heavy metal flux into the Nanyihu Lake.

Trace-fossil assemblages with a new ichnogenus in “spotted”

Abstract Highly-bioturbated “spotted” limestones and marls (Fleckenmergel-Fleckenkalk facies) of the Early Jurassic, which were deposited in broad and recurrent deep-shelf habitats of the Northern Tethys, are characterized by rare benthic carbonate-producing macroinvertebrates. To address this paradox, we analyse trace-fossil assemblages in a ~85 m-thick succession of Pliensbachian spotted deposits (Zliechov Basin, Western Carpathians). They are dominated by infaunal and semi-infaunal deposit-feeders, with 9 ichnogenera and pyritized tubes of the semi-infaunal foraminifer Bathysiphon, being dominated by Chondrites, Lamellaeichnus (new ichnogenus), and Teichichnus. Lamellaeichnus, represented by a horizontal basal cylindrical burrow and an upper row of stacked convex-up gutters, was produced by a mobile deposit-feeder inhabiting shallow tiers because it is crossed by most other trace fossils. We show that the spotty appearance of the deposits is generated by a mixture of (1) dark, organic-rich shallow- and deep-tier traces (TOC = 0.16-0.36), and (2) light grey, organic-poor mottled or structurless sediment (TOC = 0.09-0.22). The higher TOC in shallow-tier burrows of Lamellaeichnus demonstrates that uppermost sediment layers were affected by poor redox cycling. Such conditions imply a limited mixed-layer depth and inefficient nutrient recycling conditioned by hypoxic bottom-waters, allowed by poor circulation and high sedimentation rates in depocenters of the Zliechov Basin. Hypoxic conditions are further supported by (1) dominance of trace-fossils produced by infaunal deposit feeders, (2) high abundance of hypoxiatolerant agglutinated foraminifer Bathysiphon, and (3) high abundance of Chondrites with ~0.5 mm-sized branches. Oxygen-deficient bottom-conditions can thus simultaneously explain the rarity of benthic carbonate-producing macroinvertebrates and high standing abundance of tolerant soft-shell and agglutinated organisms in spotted deposits.

Benthic foraminiferal community changes and their relationship to environmental dynamics in intertidal muddy sediments (Bay of Cádiz, SW Spain)

The temporal and vertical variability of live intertidal benthic foraminifera was studied in parallel to environmental variables such as porewater and overlying water nutrients, salinity, temperature, sedimentary pigments and organic carbon. About 80% of benthic foramini - fera were concentrated in the upper 0�4 mm sediment layer, which was also the maximum oxygen penetration depth under light conditions as determined by oxygen microsensor measurements. Significant changes in the composition of the foraminiferal community over the course of the study were found in the surface layer (0�2 mm), whereas no differences were detected in the deepest sediment layers (10�30 mm). Univariate measures, such as abundance, species richness and diver- sity showed few differences over time and little relation to environmental variables. On the other hand, multivariate regression analysis for the whole community assemblage showed that the significant community composition changes over time in the surface layer could be related to fluctuations of several environmental variables, mainly those related to sediment food availability. The macroalgal bloom that occurred during the winter months had no detectable effect on benthic foraminiferal abundance or community patterns. Overall, the intertidal foraminiferal community in the Bay of Cadiz showed a highly dynamic character and a clear vertical distribution which could be effectively captured by studying the uppermost sediment layer at sub-centimetric vertical resolution.

Historical environmental pollution trend and ecological risk assessment of trace metals in marine sediments off Adyar estuary, Bay of Bengal, India

Geochemical, mineralogical and textural analyses were carried out in core sediments off Adyar estuary, Bay of Bengal, India to record the contamination trend from urban and industrial activities during the historical past. Quartz, feldspar, kaolinite, chlorite and illite were the main lithogenic and clay minerals; carbonate was the predominant biogenic mineral. Trace metals (Fe, Al, Cu, Cr, Ni, Pb and Zn) indicate more enrichment in the surface sediment layers due to recent anthropogenic activities. The mean anthropogenic factor (AF) values for trace metals in core sediments decreased in the following order: Cr > Ni > Zn > Cu > Pb. The pollution load index (PLI) values in Adyar core sediments ranged from 1 to 1.25 with an average of 1.07. Based on AF, PLI, and sediment quality guidelines values for trace metals, significant metal enrichment and ecological risk were obtained in upper-most sediment layer. Multivariate statistical methods such as correlation matrix, principal component analysis and cluster analysis were carried out to find the relationships among the texture size, metals and minerals. The pollution of Adyar estuarine sediments was started in the 1960s, responding to the rapid economic development in Chennai coastal and Adyar estuarine region in the last five decades. Despite these high concentrations in the upper layer, development and expansion of industries are still continuing. The stricter regulations for the discharge and remediation of sediments are urgent for the conservation of environments and human health.

Profiling the below ground biomass of an emergent macrophyte using an adapted ingrowth core method

In the context of our work exploring the role of Sparganium erectum as a physical ecosystem engineer, we aimed to test our hypothesis that the root and rhizome biomass of this species would be largely confined to the uppermost sediment layers, thereby having the effect of reinforcing newly deposited material and facilitating the growth of in-channel macrophyte stands and sediment accumulations. Detailed measurements of the below ground structures of linear emergent macrophytes, in terms of their biomass and architecture, are complicated by difficulties associated with sampling in the highly saturated sediments that these morphotypes typically occupy. In this paper, we describe the development of an adapted ingrowth core method, which allows the extrusion of an undisturbed root-soil matrix from highly saturated environments. The approach combines an ingrowth core, which is commonly used to measure fine-root production in forest topsoil, with an outer casing that facilitates the retention of a sample representative of field conditions, and a laboratory protocol that enables extrusion and measurement of biomass at different depth increments. The new approach enabled detailed depth profiling of S. erectum, and confirmed our hypothesis by demonstrating that root and rhizome biomass was predominantly located in the 10cm of sediment closest to the sediment–water interface throughout our study.

Submarine Groundwater Discharge as a Source of Mercury in the Bay of Puck, the Southern Baltic Sea.

Both groundwater flow and mercury concentrations in pore water and seawater were quantified in the groundwater seeping site of the Bay of Puck, southern Baltic Sea. Total dissolved mercury (HgTD) in pore water ranged from 0.51 to 4.90 ng l−1. Seawater samples were characterized by elevated HgTD concentrations, ranging from 4.41 to 6.37 ng l−1, while HgTD concentrations in groundwater samples ranged from 0.51 to 1.15 ng l−1. High HgTD concentrations in pore water of the uppermost sediment layers were attributed to seawater intrusion into the sediment. The relationship between HgTD concentrations and salinity of pore water was non-conservative, indicating removal of dissolved mercury upon mixing seawater with groundwater. The mechanism of dissolved mercury removal was further elucidated by examining its relationships with both dissolved organic matter, dissolved manganese (Mn II), and redox potential. The flux of HgTD to the Bay of Puck was estimated to be 18.9 ± 6.3 g year−1. The submarine groundwater discharge-derived mercury load is substantially smaller than atmospheric deposition and riverine discharge to the Bay of Puck. Thus, groundwater is a factor that dilutes the mercury concentrations in pore water and, as a result, dilutes the mercury concentrations in the water column.

Holocene vegetation history and fire regimes of Pseudotsuga menziesii forests in the Gulf Islands National Park Reserve, southwestern British Columbia, Canada

Pollen analysis of a 9.03-m-long lake sediment core from Pender Island on the south coast of British Columbia was used to reconstruct the island's vegetation history over the last 10,000years. The early Holocene was characterized by open mixed woodlands with abundant Pseudotsuga menziesii and a diverse understory including Salix and Rosaceae shrubs and Pteridium aquilinum ferns. The establishment of Quercus garryana savanna-woodland with P. menziesii and Acer macrophyllum followed deposition of the Mazama tephra until ~5500calyr BP, when these communities gave way to modern mixed P. menziesii forest. Charcoal analyses of the uppermost sediments revealed low charcoal accumulation over the last 1300years with a mean fire return interval (mFRI) of 88years. Fires were more frequent (mFRI=50yr) during the Medieval Climate Anomaly (MCA) with warm, dry conditions facilitating a higher fire frequency than during the Little Ice Age, when fires were infrequent. Given the projected warming for the next 50–100years, land managers considering the reintroduction of fire to the Gulf Islands National Park Reserve may want to consider using the mFRI of the MCA as a baseline reference in prescribed burning strategies.

Sulfate reduction, methanogenesis, and methane oxidation in the upper sediments of the Vistula and Curonian Lagoons, Baltic Sea

Microbiological, biogeochemical, and isotope geochemical investigations of the upper sediments of the Vistula and Curonian lagoons, Baltic Sea, were carried out. High content of organic matter in the sediments was responsible for the high numbers (over 1010 cells cm−3) and activity of heterotrophic microorganisms. The calculated integral rates of dark CO2 assimilation for the upper 30 cm of the sediments varied 12.5 to 38.8 mmol m−2 day−1 and were somewhat higher in the Curonian Lagoon than in the Vistula Lagoon. Integral rates of sulfate reduction were higher in the more saline Vistula Lagoon. Rapid consumption of sulfates of the pore water resulted in intensified methanogenesis, with significantly higher rates detected in the silts of the Curonian Lagoon. High rates of methanogenesis in the Curonian Lagoon correlated with higher methane levels in its upper sediments and near-bottom water. The highest rates of methane oxidation were detected in the uppermost sediment horizons (oxidized or slightly reduced), which was an indication of the barrier role of aerobic methanotrophic bacteria. The calculated methane flows from the sediments into the water column were 0.45 and 0.007 mmol m−2 day−1 for the Vistula and Curonian Lagoons, respectively. Low methane flow from the sediments of the Curonian Lagoon resulted probably from the specific weather (wind) conditions during sampling. The near-stormy conditions in the Curonian Lagoon caused sediment detachment, resulting in methane release into the water column.

Experimental study on the effects of sediment size and porosity on contaminant adsorption/desorption and interfacial diffusion characteristics

The joint effects of the sediment size and porosity on the contaminant adsorption/desorption and interfacial diffusion characteristics were experimentally investigated. The adsorption of Phosphorus (P) on the natural and artificial sediment suspensions was measured with respect to the P adsorption isotherms and kinetics in the experiment. The obtained adsorption isotherms for different grain-sized sediment suspensions fit well with the Langmuir equation, dependent on the initial aqueous concentration and sediment content. The P kinetic adsorption behaviors for cohesive fine-grained and non-cohesive coarse-grained sediment suspensions clearly show the size-dependent feature. On the other hand, the P kinetic release feature of a porous sediment layer is affected by not only the direct desorption of the uppermost sediments, but also the diffusivity in the pore-water within the underlying sediment layer, characterized by the sediment size and porosity, respectively. Furthermore, the temporal contaminant release from the permeable sediment layer into the overlying water column increases with the increasing flow velocity, while this enhancement in mediating the interfacial diffusion flux is somewhat insignificant in an immediate release stage, largely due to the resistance of the diffusive boundary layer on the hydrodynamic disturbance.

Sedimentary lead pollution history: Lead isotope ratios and conservative elements at East Taihu Lake, Yangtze Delta, China

In 2009, two short sedimentary cores (DJZ and DQG) were collected from the East Taihu Lake at the lower Yangtze River Basin using a gravity corer. Lead isotopes and metals including Pb, Al, Fe, and Ti were measured. Radio nuclides including 210Pb and 137Cs were also analyzed for dating of the sediments at both cores. The averaged sedimentation rate at DQG site was 0.32 cm/a since the early 1960s, while at DJZ it was at least 1 cm/a. Significant decline of 206Pb/207Pb ratios were observed in DQG from the deeper sediments to near-surface sediments, indicating increased anthropogenic lead load to the lake sediments due to human impact since the 1970s. The uppermost sediments' lead contents were 2.3 times of those before the 1950s. Trends of anthropogenic lead in both cores inferred from a lead isotope mixing model were found to be similar to those from Al, Fe, and Ti normalization methods. Ti was found to be the best passive tracer element, highly in accordance with Pb isotope mixing model results. In DQG, anthropogenic lead increased sharply since the 1970s and reached a maximum in 2000s (28 mg/kg from lead isotope mixing model), while at DJZ the highest value was 20 mg/kg. These results revealed significant anthropogenic lead influx into the lake caused by human activities, in good agreement with the economic development in the past three decades in China.

The Last Glacial: Insights from continuous coring on the New Jersey continental shelf

Abstract Sedimentation on the Pleistocene New Jersey (NJ) shelf is complex, and results from the interaction of processes chiefly driven by glacioeustatic change. Erosion, non-deposition, downcutting and infilling combine to produce a complicated set of reflectors and sedimentary units that are best interpreted in the shallow subsurface with the aid of high resolution seismic reflection profiling. The highly variable lithology on the shelf has historically been an impediment to significant core recovery in this challenging environment. Coring using the AHC-800 drilling system provided continuous downcore recovery at three sites on the outer shelf. The sites targeted fluvial incisions, channel fill and exposure surfaces associated with glacial lowstands. The exceptional cores were analyzed using an integrated approach. Textural and benthic foraminiferal data were evaluated to determine the environment of deposition and estimate paleodepth. Carbon dating of wood and shell material provides the temporal framework for interpretation and K–Ar dating of hornblende crystals provides insights into the source region of sediments. Our integrated analysis indicates the NJ shelf was a dynamic environment from at least 45 ka. Estimates of sea level from this study are consistent with other studies from the Pleistocene NJ Margin. The oldest sediments (> 36 k.y.) recovered by drilling came from below (Site 3) and above (Site 1) R, a time-transgressive regional unconformity. Best estimates are for formation of R on the mid shelf, between MIS3b and the MIS3b/a transition, ~ 45 ka, under neritic conditions. Channels were incised during late MIS2, between ~ 30 and 16 ka. Channel infill was focused in a narrow time frame, during latest MIS 2 (16–14 ka), shortly after the shoreline began to migrate landward. Rates of 1–2 cm/yr are consistent with modern fluvial/ estuarine sedimentation rates. Reinvigoration and infilling of the channels around 14 ka is associated with meltwater pulse 1A. We find no evidence at our study area for jokelhlaup deposition associated with the Intra-Allerod cold period ~ 13 ka. Regional deposition (channel infill and interfluvial regions) was underway by latest MIS2/early MIS1 as sea level transgressed the shelf. The uppermost sediments are of Holocene to Recent age and are routinely and likely rapidly reworked, eroded and mixed by shelf processes. The sediment source during MIS3, as determined by hornblende age dates, was bimodal. Older sediments were derived from the Reading Prong/NJ Highlands and younger sediments were sourced from along the Hudson River. Delivery to the study area was through a more southerly paleo-Hudson position that may have resulted in formation of the outer shelf wedge through deltaic sedimentation during at least MIS 3b–3a.

A new sediment slicer for rapid sectioning of the uppermost sediment cores from marine and freshwater habitats

The new sediment slicer described herein provides an easy and time-efficient way of sectioning cores of varying length, diameter, and composition from a wide range of habitats and sediment types. It is designed to process sediments collected by means of any soft-sediment core sampler with the core tube detachable from the sampler head and trigger unit. It is useful for sectioning core samples that include both the undisturbed sediment/water interface and highly consolidated sediments. The slicer is composed of three parts: (1) a supporting block, (2) a gliding block with the incorporated 10 cm sub-sampler holder designed to glide freely in the grooves along the supporting block, and (3) a metal blade for sediment slicing.

Bacterial Diversity and Geochemical Profiles in Sediments from Eutrophic Azorean Lakes

In the Azores, the advanced trophic state of the lakes requires a fast intervention to achieve the good ecological status prescribed by the Water Framework Directive. Despite the considerable effort made to describe the phytoplankton growing on the water column, the lack of information regarding the microbial processes in sediments is still high. Thus, for the successful implementation of internal management actions, the present work explored the relationships between geochemical profiles and dominant members of the bacterial community in sediments from eutrophic Azorean lakes. Lake Azul geochemical profiles were quite homogeneous for all parameters, while in lake Furnas the total iron profile presented a peak below the aerobic layer. For lake Verde, the concentrations of all studied parameters (20 ± 2% loss-on-ignition; 2.10 ± 0.08 mg g−1 total phosphorus; 1.31 ± 0.50 mg g−1 total nitrogen; 8.06 ± 0.13 mg g−1 total iron) in the uppermost sediment layer were approximately two times higher than the ones in sediments from other lakes, decreasing with sediment depth. The higher amounts of phosphorus and organic matter in lake Verde suggested a higher internal contribution of phosphorus to eutrophication. The dominant members of the sediment bacterial community, investigated by denaturing gradient gel electrophoresis, were mostly affiliated to Proteobacteria phylum (Alpha-, Delta-, and Gamma-subclasses), group Bacteroidetes/Chlorobi and phylum Chloroflexi. The Cyanobacteria phylum was solely detected in sediments from lake Verde and lake Furnas that presented the highest amounts of nitrogen and phosphorus both in the water column and sediments, while the other phyla were detected in sediments from the three studied lakes. In conclusion, management measurers to achieve the good ecological status until 2015 should be distinct for the different lakes taking into account the relative magnitude of the nutrient sources and the bacterial diversity in sediments.