Core Depth Research Articles

Water Masses and Ocean Currents Over the Continental Slope off Northern Baja California

AbstractOcean currents and thermohaline properties over the continental slope off northern Baja California are analyzed with data collected between 2008 and 2012. The data set is composed of 3‐year‐long time series of two moorings with current meter profilers and one chain of conductivity‐temperature‐depths, as well as data collected during 13 synoptic hydrographic surveys. The upper layer (<100 m) was characterized by low salinity Subarctic Waters. Geostrophic velocities suggest that waters of the lighter layer are advected equatorward by near‐surface flows. Below 50 m, poleward flow dominates, so the denser Subarctic Waters recirculates back north along the slope. The combination of geostrophic velocities derived from the hydrographic surveys and the current meter data confirm the presence of the California Undercurrent (CUC), a narrow subsurface poleward flow with a high‐velocity core confined to the continental slope. Mean core speeds were 12–15 cm/s at an average depth of ~150 m. Below the CUC, the core of spicy North Pacific Equatorial Water (NPEW) was found at a mean depth of ~200 m. The analysis of the continuous time series provides strong evidence of the seasonal signal in speed, spiciness, and depth of the CUC and NPEW cores, with a time resolution unprecedented to date. Most of the variance of water mass and flow properties is explained by the annual cycle. The phase shift between the depth of the NPEW core and the strength of the CUC suggests that remotely generated Kelvin waves are responsible for the seasonal variability observed off northern Baja California.

Intra annual Variability of the Arabian Sea high salinity water mass in the South Eastern Arabian Sea during 2016 17

Intra-annual variability of the Arabian Sea high salinity water mass (ASHSW) in the South Eastern Arabian Sea (SEAS) and Gulf of Mannar (GoM) are addressed in this paper by utilisng the monthly missions carried out onboard INS Sagardhwani during 2016-17. Our observations revealed that the ASHSW was evident along the SEAS irrespective of seasons, whereas in the GoM the presence of ASHSW was observed during winter. The processes such as downwelling/up-welling, coastal currents, intrusion of low saline waters, stratification are clearly affects the spreading of the ASHSW. The characteristics such as core salinity value, depth and thickness of ASHSW exhibited remarkable spatio-temporal variability. Lateral mixing with the low saline waters in the region during winter reduces its core salinity. The intrusion of low saline waters was clearly seen upto 15 ON but the intrusion of low saline waters is not flowing through the GoM. The interface between the ASHSW and the prevailing low saline waters showed strong horizontal gradients of salinity. The presence of the ASHSW makes difference in the SLD and the below layer gradient which is sufficient to complicate or influence sound transmission. The spatio temporal variability of the ASHSW and its acoustic relevance are documented in this paper.

Holocene tropical reef accretion and lagoon sedimentation: A quantitative approach to the influence of sea‐level rise, climate and subsidence (Belize, Maldives, French Polynesia)

AbstractAccretion rates of Holocene tropical coral reefs in three areas in the Atlantic, Pacific and Indian Oceans have been quantified in 79 dated core sections in 34 reef cores from Belize, the Maldives and French Polynesia. Holocene vertical reef accretion rate averages 5.05 m/kyr and has decreased during the past 10 kyr. Accretion rates in branched and massive coral facies are statistically similar. Reef accretion rate is positively correlated with the rate of sea‐level rise, that is the degree of creation of accommodation space, and with climate as expressed in a Holocene sea surface temperature anomaly. Accommodation space is also created by subsidence, but at a rate one to two orders of magnitude lower than that created by glacio‐eustasy (0.04 to 0.16 m/kyr). Lagoonal background sedimentation in adjacent reef lagoons averages 0.89 m/kyr as measured in 72 dated core sections in 28 cores. Lagoonal carbonate sedimentation on top of underlying mangrove peat usually starts after a considerable hiatus of ca 3 kyr on average. The lagoonal background sedimentation rate increased during the Holocene, probably due to deepening. The differences between vertical reef accretion and lagoonal background sedimentation rates are a major factor in the production of the widely known saucer shapes typical of tropical reefs and carbonate platforms, that is the creation of unfilled accommodation space. Reef core recovery, used as a proxy for reef consolidation, and core depth exhibit a statistically negative correlation based on data from 326 core barrels. Recovery and marine cement abundance (average volume 8.6%) also decrease from windward to leeward core positions. These observations are presumably a result of both a decrease in the rate of sea‐level rise that is the increase in time available for submarine cementation during the Holocene and the amount of flushing of reef interstices by marine waters.

Heavy-mineral-based provenance and environment analysis of a Pliocene series marking a prominent transgression in the south Yellow Sea

Detrital minerals in sediments can provide insight into sedimentary provenance and depositional environments. Here we report a record of heavy minerals of a 300.1 m long core recovered from the western south Yellow Sea, which was dated back to the late Pliocene (~3.5 Ma). Results of detrital mineral analysis show that sediments are dominated mainly by silicate minerals sourced from the Chinese mainland through river inputs. Heavy minerals suggest that marine transgression occurred around 76–84 m depth of the core depth, about at 792–840 ka BP. The upper part of the core (0–76 m) is dominantly marine and the lower part (below 84 m) is terrestrial. From the Miocene to Early Pleistocene, the Yellow Sea area generally subsided; the deposition center began to move from west to east, therefore the content of fine sand increased relatively in the core sediment. Meanwhile, under the influence of depression evolution in the Subei Basin, the paths of rivers were shifted, as a result the contents of augite and garnet changed, sediments in the study area were dominated by proximal sediments sourced from the Subei Basin, possibly of mixed sediments of the Yellow River and Yangtze River. The lower part of the core was characterized by a dramatic increase in augite with hornblende and epidote as dominant minerals. In the Early Pleistocene, under the background of subsidence in the Yellow Sea area, while transgression occurred, rivers shifted southward. Comparison with the mineral composition of adjacent core NHH01 and surface sediments from the region suggests the Yellow River dominated the study area, and the old Yangtze River input being occasionally dominant. The heavy mineral assemblage was dominated by hornblende and epidote, as well as mica, garnet and authigenic pyrite in some sediment layers.

In Situ Microbial Degradation of PBDEs in Sediments from an E-Waste Site as Revealed by Positive Matrix Factorization and Compound-Specific Stable Carbon Isotope Analysis.

In the present study, positive matrix factorization (PMF) and compound-specific isotope analysis were used to investigate the in situ biodegradation of polybrominated diphenyl ethers (PBDEs) in sediment cores collected from a pond at an e-waste recycling site in South China. The potential microorganisms relevant to the degradation of PBDEs were also assessed to aid in the understanding of in situ biodegradation. The PMF results suggested that reductive debromination took place in the sediments. The debromination signal (ratio of the concentration of factor 5 (PMF result) to the total PBDE content) was positively correlated with the relative abundance of Dehalococcoidetes at different core depths. The clear 13C enrichment of five PBDE congeners (BDE 28, 47, 49, 99, and 153) with increasing core depth indicated that a measurable change in isotope fractionation might have occurred during PBDE biodegradation. The in situ biodegradation was further validated by the widespread detection of mono-BDE congeners (BDE 2, BDE 3) and diphenyl ether in the sediments. This study provides new evidence to enhance our understanding of the in situ biodegradation of PBDEs and suggests that the extensive removal of bromine from PBDEs was mediated by indigenous microorganisms at the e-waste site.

Experimental study on the 3D-flow field of a free-surface vortex using stereo PIV

ABSTRACTIn order to analyse the flow characteristics of free-surface vortexes and to validate the Burgers vortex model by using stereo particle image velocimetry, experiments are conducted in a 600 mm diameter vortex tank. Measured axial velocities indicate that 10–25% of the flow is transported through the vortex core. The velocity profiles show that the axial flow is concentrated in a domain bounded by two times the core radius. Despite Burgers’ assumption of radially independent axial velocity profiles, the model quantifies the tangential velocity profile within a relative uncertainty of circa 10%. The measurements show that it seems valid to use Burgers’ model to obtain an estimate for the core radius by taking the average axial velocity over a radial domain of approximately 2.2 times the core radius. The Burgers model quantifies the air core depth with an uncertainty of 20% relative to the measurements. When compared with the magnitude of vorticity diffusion by molecular viscosity, the experiments show that there is no significant diffusion by radial turbulence.

Vertical Stratification of Sediment Microbial Communities Along Geochemical Gradients of a Subterranean Estuary Located at the Gloucester Beach of Virginia, United States.

Subterranean estuaries (STEs) have been recognized as important ecosystems for the exchange of materials between the land and sea, but the microbial players of biogeochemical processes have not been well examined. In this study, we investigated the bacterial and archaeal communities within 10 cm depth intervals of a permeable sediment core (100 cm in length) collected from a STE located at Gloucester Point (GP-STE), VA, United States. High throughput sequencing of 16S rRNA genes and subsequent bioinformatics analyses were conducted to examine the composition, diversity, and potential functions of the sediment communities. The community composition varied significantly from the surface to a depth of 100 cm with up to 13,000 operational taxonomic units (OTUs) based on 97% sequence identities. More than 95% of the sequences consisted of bacterial OTUs, while the relative abundances of archaea, dominated by Crenarchaea, gradually increased with sediment core depth. Along the redox gradients of GP-STE, differential distribution of ammonia- and methane-oxidizing, denitrifying, and sulfate reducing bacteria was observed as well as methanogenic archaea based on predicted microbial functions. The aerobic-anaerobic transition zone (AATZ) had the highest diversity and abundance of microorganisms, matching with the predicted functional diversity. This indicates the AATZ as a hotspot of biogeochemical processes of STEs. The physical and geochemical gradients in different depths have attributed to vertical stratification of microbial community composition and function in the GP-STE.

Holocene climate dynamics derived from pollen record of Jiulongchi wetland in Fanjing Mountain, southwest China

An alpine wetland core was obtained to a depth of 4.0 m from the Fanjing Mountain in southwest China. Sections of the core were dated with 14C data obtained with high resolution mass spectrometry (AMS), and Holocene climate changes were inferred by categorizing predominant tree and fern vegetation identified from pollen and spore counts at various core depths. The temperature increased during 11.9–8.0 cal ka BP, and the warmest period was during 8.0–4.6 cal ka BP. Then, it gradually became cooler during the late Holocene. Our temperature estimates were in good agreement with the previous studies of the Holocene temperature in the Asian monsoon areas. There were two relatively wet periods of 10.7–8.0 cal ka BP and 4.6–2.6 cal ka BP. There was an asynchronous precipitation trend in the south, north and southwest China, which was probably due to the different monsoon impacts. In East Asian summer monsoon (EASM) area, the monsoon precipitation gradually transgressed northward during the early to middle Holocene and regressed southward during the late Holocene. Our results will be useful to improve the understanding of the coherent spatio-temporal patterns of climate evolution in EASM region in China.

A Borehole Record of Late Quaternary Permafrost on Kurungnakh Island (Lena Delta, Northeastern Siberia): Reconstruction of Deposition Environments

Abstract —Paleoenvironmenal reconstructions have been made from a multidisciplinary study of a borehole permafrost record on Kurungnakh Island (Lena delta). According to data on palynomorphs and ostracods, the clay silt units from the 10.58 to 13.54 m and 1.58 to 10.3 m core depth intervals were deposited in the Late Pleistocene (during the Karginian interstadial) and Early–Middle Holocene, respectively. The sediments were studied in terms of moisture contents, grain size distribution, mineralogy, and magnetic susceptibility, and the results were compared with published evidence from nearby natural outcrops. Quite a cold oligotrophic lake existed in the area during the Karginian period, and the deposition was interrupted by a gap recorded at a core depth of about 11 m. In the Early and Middle Holocene, the area was covered with shrub tundra vegetation.

Stability of planed and precision planed solid wood surfaces due to wetting

The upper cell layers of machined solid wood surfaces will usually be damaged and compacted due to cutting forces. The deformation zone may be instable due to temperature and moisture variations as a consequence of artificial surface treatment or environmental interaction. Therefore, an evaluation method of surface stability in this respect would be desirable. In the frame of the new developed surface roughness evaluation method an individual wetting procedure has been developed, whilst surfaces have been characterized by 3D roughness measurement. The stability of surfaces is characterized by appropriate roughness ratios measured before and after wetting. The core depth Sk of the Abbott parameters is the most sensitive indicator to any changes in the deformation zone. Different machining processes may produce surfaces with different stability but wood species have also definite influence on the surface stability, probably due to their density and moisture conduction properties. Latter is supported by the fact that the half-time of moisture evaporation from surfaces may differ considerably. In these experiments, planed and precision-planed surfaces were compared. According to the working principle of the precision planers the planing tool is held stationary whilst the work piece does the feeding motion, thus the blade produces a very thin slice. Using this machine, the machining roughness can be reduced to minimum as it is possible to avoid formation of cycloid arcs (like in case of traditional planing) and also possible to avoid dust formation (like in case of sanding). Investigations were conducted on Norway spruce (Picea abies), larch (Larix decidua), scots pine (Pinus sylvestris), sessile oak (Quercus petraea), black locust (Robinia pseudoacacia), aspen (Populus tremula) and beech (Fagus sylvatica). Black locust and the sessile oak have had most stable surfaces by both machining methods. The deformation zone of precision planed surfaces has been proven to be more stable than the one of planed surfaces for all wood species. Keywords: Cutting parameters, deformation zone, planed surface, roughness, surface stability

ОСОБЕННОСТИ РАСПРЕДЕЛЕНИЯ ЭЛЕМЕНТОВ В МНОГОЛЕТНЕМЕРЗЛЫХ ПОРОДАХ ПОЛУОСТРОВА ГЫДАН

This paper presents the chemical and mineral composition of the soil core of the Gydan Peninsula near the Parisento Lake. The changes in the K, Ca, Mn, Fe, Ti, Cu, Pb, Br, As concentrations over the core depth depending on its structure, mineralogical and granulometric composition are discussed.

Stable Isotope Clues to the Formation and Evolution of Refrozen Melt Ponds on Arctic Sea Ice

AbstractSea ice is one of the determining parameters of the climate system. The presence of melt ponds on the surface of Arctic sea ice plays a critical role in the mass balance of sea ice. A total of nine cores was collected from multiyear ice refrozen melt ponds and adjacent hummocks during the 2015 Arctic Sea State research cruise. The depth profiles of water isotopes, salinity, and ice texture for these sea ice cores were examined to provide information about the development of refrozen melt ponds and water balance generation processes, which are otherwise difficult to acquire. The presence of meteoric water with low oxygen isotope values as relatively thin layers indicates melt pond water stability and little mixing during formation and refreezing. The hydrochemical characteristics of refrozen melt pond and seawater depth profiles indicate little snowmelt enters the upper ocean during melt pond refreezing. Due to the seasonal characters of deuterium excess for Arctic precipitation, water balance calculations utilizing two isotopic tracers (oxygen isotope and deuterium excess) suggest that besides the melt of snow cover, the precipitation input in the melt season may also play a role in the evolution of melt ponds. The dual‐isotope mixing model developed here may become more valuable in a future scenario of increasing Arctic precipitation. The layers of meteoric origin were found at different depths in the refrozen melt pond ice cores. Surface topography information collected at several core sites was examined for possible explanations of different structures of refrozen melt ponds.

In situ measurements of fine sediment infiltration (FSI) in gravel‐bed rivers with a hydropeaking flow regime

AbstractThe overpresence of fine sediment and fine sediment infiltration (FSI) in the aquatic environment of rivers are of increasing importance due to their limiting effects on habitat quality and use. The habitats of both macroinvertebrates and fish, especially spawning sites, can be negatively affected. More recently, hydropeaking has been mentioned as a driving factor in fine sediment dynamics and FSI in gravel‐bed rivers. The primary aim of the present study was to quantify FSI in the vertical stratigraphy of alpine rivers with hydropeaking flow regimes in order to identify possible differences in FSI between the permanently wetted area (during base and peak flows) and the so‐called dewatering areas, which are only inundated during peak flows. Moreover, we assessed whether the discharge ratio between base and peak flow is able to explain the magnitude of FSI. To address these aims, freeze‐core samples were taken in eight different alpine river catchments. The results showed significant differences in the vertical stratification of FSI between the permanently wetted area during base flow and the dewatering sites. Surface clogging occurred only in the dewatering areas, with decreasing percentages of fine sediments associated with increasing core depths. In contrast, permanently wetted areas contained little or no fine sediment concentrations on the surface of the river bed. Furthermore, no statistical relationship was observed between the magnitude of hydropeaking and the sampled FSI rate. A repeated survey of FSI in the gravel matrix revealed the importance of de‐clogging caused by flooding and the importance of FSI in the aquatic environment, especially in the initial stages of riparian vegetation establishment. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

Technological aspects of improving adhesion of TiNiZr coating materials with thermoelastic phase transformations formed by high-velocity oxygen-fuel spraying

The authors discuss technological aspects of increasing the adhesion of coatings made of materials with thermoelastic phase TiNiZr transformations formed by high-velocity oxygen-fuel spraying (HVOF) with a steel base by means of using a combined method, including HVOF and electromechanical treatment (EMT). The authors presented the results of the structure and elemental composition of the surface-modified layer before and after high-frequency impulse action in the EMT process and established new possibilities of modification of the structure and properties. It is shown that in the optimal modes of EMT, the fusion zone of the coating and the base is 10-20 microns. The authors designed the statistical models of technological process, which allowed defining fusion depth and diameter of a contact core depending on technological modes of EMT, as well as a current density and frequency or pulse duration. Adhesion tests according to State Standard 98844-99 showed that the strength of the coating with the base reaches (0.3-0.4) from the tensile strength of the base, depending on the depth and size of the fusion zone. It is recommended to perform additional thermomechanical processing to ensure the functional properties of materials with shape memory effect in the TiNiZr surface layer.

Evidence for a recent increase in delivery of atmospheric 210Pb to Oualidia lagoon, coastal Morocco.

Two sediment cores were collected from the Oualidia lagoon, on the Atlantic coast of Morocco, and analyzed for 210Pb and 137Cs activity by gamma spectrometry. The 210Pb profiles were characterized by high activity at specific depths in each core, which were attributed to substantial increases in atmospheric 210Pb input to the sediment. A modified CRS model was applied to develop age-depth relations (chronologies) for the cores and calculate sediment accumulation rates, taking into account changing unsupported 210Pb delivery and specifying the year when the increase began. Calculated 210Pb inventories (activity/area) and fluxes (activity/area/time) depend strongly on sedimentation rates and were much higher than mean values in similar coastal systems worldwide. We attempted to use 137Cs as a time marker to support the modified CRS chronologies for both cores. The 137Cs profiles, however, were affected by post-depositional cesium migration in the sediment which made it difficult to identify the 1963 atmospheric bomb-testing peak, especially in the core with low sedimentation rate. We conclude that the high activities of 210Pb detected at specific depths in the Oualidia lagoon sediment cores are a consequence of decay of radioactive 222Rn, which displayed periodic high concentrations in the overlying atmosphere.

A comparison of Gaussian, Student-t and vine copulas for modelling geophysical measurements along a rock drill core

This case study is a based on measurements made approximately at 20cm lengths along a down-the-hole diamond drill core from a pyrite mine in South Australia. The measurements are the P-wave velocity, magnetic susceptibility and impedance. The trivariate distribution is modelled using Gaussian, Student-t and vine copulas and the results are compared in terms of goodness of fit and differences in extreme values from distributions obtained by simulation from the copulas. The vine copula provides the best fit for the variables. Trivariate linear spatial Gaussian, Student-t and vine copulas are used to predict magnetic susceptibility one step below the depth of the drill core. The vine copula allows for more detailed modelling of the error structure, and so provides more accurate 90% prediction intervals. The 90% prediction interval for the vine copula is wider than that for the Student-t copula, and both are wider than the interval obtained with the Gaussian copula. In general, copulas provides a more realistic modelling of geological variables and hence allows for accurate assessment of risk and uncertainty.

A \u201cmirror layer\u201d of temperature and salinity in the ocean

Using the newly available 13-year Argo float data for the period 2004–2016, a three-dimensional temperature–salinity (T–S) correlation field is constructed for the global upper ocean. It is revealed that the layer-averaged correlation between T and S time series has a significant peak (~ 0.7) at a depth of approximately 300 m, suggesting that the density-compensated thermohaline covariation may lead to a maximum T–S coupling in the vicinity of the pycnocline. This argument is supported by subsequent findings that the spatial distributions of temperature and salinity have excellent consistencies in terms of both climatology and seasonality around this depth, which we call a “T-S mirror layer”. Since mass, heat and salt are mainly transported by dynamic events and processes, dominant currents and prevailing eddies in the pycnocline zone are found to determine the fundamental patterns of the global T/S climatologies which are characterized by a unified pattern of six well-defined warm/salty pools with collocated centroids and a clear west preference. Our results also suggest that the climatological ocean circulations transport heat/salt as a conveyor belt, meanwhile heat and salt parcels are discretely transported by numerous migrating mesoscale eddies, the combined effects of which lead to the formation of six well-defined “warm/salty pools” in the western subtropical oceans with a core depth of ~ 300 m at the “mirror layer”.

EVALUATION OF EFFECTING FACTORS OF TRADITIONAL AND SUPER PLASTICIZER CONCRETE CORE STRENGTH

This paper deals with the investigation factors effecting core strength estimation by conducting an experimental study which included casting of six plain concrete beams. For each beam, 12 cubes were cast in addition to twenty-four core samples were extracted. The investigated factors involved the concrete compressive strength, concrete type, core extracting direction, core location, core depth in the beam, and the damage factor. It obtained results showed that the ratio of compressive strength in the vertical to horizontal cast direction is (1.075) and (1.080) for the traditional and superplasticizer concrete, respectively. Also, the depth factor of bottom to top zone strength in vertical cast direction is (1.110) and (1.066) for traditional concrete and the super plasticizer concrete respectively, while the location factor of center zone in vertical cast direction corresponding to (1.088) and (1.103). Finally, the damage factor is directly proportional with the concrete strength for both concrete types.

HEAVY METAL CONCENTRATIONS IN SEDIMENT CORES FROM DIFFERENT MANGROVE FORESTS IN DA LOC COMMUNE, HAU LOC DISTRICT, THANH HOA PROVINCE, VIETNAM

In order to clarify heavy metal concentration profiles in different mangrove forest ages, four sediment cores (up to 100 cm in depth) were collected and tested for their physicochemical characteristics (pH, Eh, organic matters and grain size) and heavy metal concentrations. Results showed that mangrove sediments were composed mainly of sandy silt, silty sand, silt, sandy mud and mud. The average mud content in the sediment cores continuously increased with mangrove forest ages from one, nine, nineteen and twenty years old, whereas the mud content highly fluctuated with the core depth. pH, Eh and organic matter content implied that the sedimentary depositional environments were classified as weak alkaline and anaerobic. The Cu and Zn concentrations in the sediment cores from the intertidal zone exceeded the TEL values in Canadian Interim Marine Sediment Quality Guideline (ISQGs) values, while, Pb concentration exceeded the PEL level. When compared with National Technical Regulation on Sediment Quality QCVN43:2012/BTNMT, sediment samples were polluted by Cu and Pb.

Determinants of atrial bipolar voltage: Inter electrode distance and wavefront angle

BackgroundLocal bipolar electrogram (EGM) peak-to-peak voltage (Vpp) is currently used to characterise mapped myocardial substrate. However, how interelectrode distance and angle of wavefront incidence affect bipolar, Vpp values, in the current era of multi-electrode mapping is unknown. ObjectivesTo elucidate the effects of tissue and electrode geometry on bipolar Vpp measurements, when mapping healthy versus diseased atrial regions. MethodsA bidomain model of human atrial tissue was used to quantify the influence on Vpp values of various electrode configurations in healthy tissue, and tissue containing an unexcitable region. The orientation angle and interelectrode spacing of a surface bipole, and thickness and depth of the unexcitable core were serially varied. Results were validated with data obtained from isolated porcine hearts. ResultsIn healthy tissue, bipolar Vpp values increased with increasing interelectrode spacing and plateaued beyond a spacing of approximately 4 mm. The bipolar Vpp values in healthy tissue were relatively less sensitive to wavefront orientation angle with large interelectrode spacing. In diseased tissue, on the contrary, with increasing interelectrode spacing, bipolar Vpp values increased linearly without a plateau and were more sensitive to orientation angle. The bipolar Vpp values decreased with increasing thickness of the scar, with larger relative decrease in small bipoles than larger ones. Bipolar Vpp values increased with a progressively intramural location of fixed-size scar and became less distinguishable from healthy tissue especially for smaller interelectrode spacings. ConclusionsThe scalable relationship established for interelectrode distances favour an electric-field-based assessment as opposed to traditional Vpp values as a tool for physiologically relevant measurement for mapping catheters with interelectrode spacing up to 4 mm. This will allow for universal assessment of myocardial health across catheters with varied spacing.