10-m Depth Research Articles

Extreme Value Analysis of Ocean Currents in the Mexican Caribbean Based on HYCOM Numerical Model Data

Comprehensive knowledge of extreme values is required for designing offshore structures and ocean current turbines. However, data on the return levels of ocean currents are rarely available. This is the case for the Mexican Caribbean, where enormous energy potential in the ocean currents has recently been detected. In this study, long-term numerical data from the Hybrid Coordinate Ocean Model for a depth of 50m was adjusted via linear quantile regression to short-term empirical data for a depth of 49m. The error of the results was estimated using simplified extreme value analysis. Based on the numerical data, a comprehensive extreme value analysis was conducted using the peaks over threshold method and fitting a Generalized Pareto Distribution to the data. This method relies on filtering peaks with a moving time window and an automated threshold selection based on a reparameterised scale parameter of the Generalized Pareto Distribution. The adjusted numerical model is shown to underestimate the empirical data with the error converging to almost 22% for rare events (return period > 10years). The method showed consistent results in the domain, with some anomalies only at the boundaries of the underlying numerical model. The methodology is suitable for estimating the return levels of ocean currents provided by HYCOM, although further research is needed to reduce the error of the numerical model.

Morphological analysis of Prochilodus argenteus ovaries in successful and unsuccessful hypophysation-induced reproduction.

Pampus argenteus is a species of economic importance for professional fishing and aquaculture. To analyse the quality of oocytes of P.argenteus, 10 females were kept in tanks of 200 m2 with an average depth of 1m in the Integrated Center of Fishing Resources and Aquaculture of Três Marias - CODEVASF. Specimens were submitted to hypophysation-induced reproduction with crude extract of common carp pituitary (EBHC). Females received two doses (0.8-1.0 and 5.0-6.6mg of EBHC/kg body weight, respectively), with a 12-h interval between doses. For males, a single dose (2.7mg/kg body weight) was applied at the same time as the females' second dose. Oocytes were extruded manually 8h after the second hormonal dose at 26°C. It was observed that seven females responded positively to the procedure while the other three released bloody and lumpy oocytes. For histological analysis, ovarian fragments were fixed in Bouin's liquid for 8-12 h and submitted to routine histological techniques. The protocol was considered successful for 70% of females and 100% of males. The fertilization rate of the females from the unsuccessful group was very low, and histological analyses showed that most of their oocytes were in follicular atresia, suggesting a delay in hormonal administration or extrusion could have occurred. Despite the hypophysation protocol being considered adequate for the induced reproduction of P.argenteus, complementary studies are necessary to evaluate the possible causes of this degenerative process.

Puzzling magnetic anomaly in the Barun-Khal valley (Olkhon region, western Gisbaikalia)

The Brun-Khal valley is in the Olkhon region, northwest of the village of Chernorud. Since the end of the 70s. the valley and its surroundings has been studied with geophysical methods. During magnetic survey in the central part of the valley, some round-shaped magnetic anomalies were mapped the nature of which remains unclear. Especially unusual is a negative magnetic anomaly with an amplitude of more than 1200 nT and a width of about 50m. According to the simulation, the anomaly is caused by a vertical, negatively magnetized rod or a thin cylinder, the upper and lower edges of which are located at a depth of 17m and 50m, respectively. Presumably, the anomaly is due to a stock of igneous rocks that intruded into host rocks when the polarity of the geomagnetic field was negative.

Near-Inertial Wave Energetics Modulated by Background Flows in a Global Model Simulation

AbstractWe study the generation, propagation, and dissipation of wind-generated near-inertial waves (NIWs) in a global 1/25° Hybrid Coordinate Ocean Model (HYCOM) simulation with realistic atmospheric forcing and background circulation during 30 days in May–June 2019. The time-mean near-inertial wind power input and depth-integrated energy balance terms are computed for the total fields and the fields decomposed into vertical modes to differentiate between the radiative and (locally) dissipative components of NIW energy. Only 30.3% of the near-inertial wind input projects onto the first five modes, whereas the sum of the NIW energy in the first five modes adds up to 58% of the total NIW energy. Almost all of the depth-integrated NIW horizontal energy flux projects on the first five modes. The global distribution of dissipation and decay distances of NIW modes confirm that lower latitudes are a sink for NIW energy generated at higher latitudes. The locally dissipated fraction of NIW energyqlocalis found to be uniform throughout the global ocean, with a global mean value of 0.79. The horizontal NIW fluxes diverge from areas with cyclonic vorticity and converge in areas with anticyclonic vorticity; that is, anticyclonic eddies are a sink for NIW energy fluxes—in particular, for higher modes. Most of the residual energy that does not project onto modes propagates downward in anticyclonic eddies. The global near-inertial wind power input is 0.21 TW for the 30 days, of which only 19% is transmitted below 500-m depth.

Conceptual layout of a helium cooling system for the Einstein Telescope

The Einstein Telescope (ET) is a 3rd generation gravitational-wave detector planned in triangular shape with 10 km arm lengths in an underground installation at a depth of 200m to 300 m. While 2nd generation detectors and the ET high-frequency interferometer are operated at room-temperature, the ET low-frequency (LF) interferometer shall be operated at cryogenic mirror temperatures of 10K to 20K in order to reduce the thermal noise. Considering thermal dissipation limits in the heat extraction path from the mirror to the heat sink, He-II provides ultra-low-noise cooling to allow for an interferometer sensitivity at levels below 1 × 10−20 m/ in the detection band. In order to limit particle adsorption on the cold mirror surface, the total pressure in the cryostat must be reduced to p ≤ 1 × 10−10 mbar, i.e. partial pressures of water and heavier components pi ≤ 1 × 10−14 mbar, respectively, using a cryopump/shield around the mirror that is cooled with supercritical helium to T ≈ 5K.We present the conceptual layout of a helium cooling system that can provide cooling power for several ET-LF cryostats and their corresponding cryotraps, including mirror cooling at 2K as well as thermal shielding at 5K and at 50K to 80K. A process flow diagram focuses on the cooling system’s key components with their locations and their interconnections. On the diagram’s basis, we explain the cooldown process and steady-state operation, ranging from outer shield and cryotrap cooling to the formation of He-II in the mirror heat extraction path.

Slow sink rate in floated-demersal longline and implications for seabird bycatch risk.

Bycatch of birds in longline fisheries is a global conservation issue, with between 160,000-320,000 seabirds killed each year, primarily through being caught and drowned as they attempt to snatch baits off hooks as they are set. This conservation issue has received significant recognition in southern hemisphere longline fisheries over the past several decades, largely due to the impact on highly charismatic and highly threatened birds, notably Albatrosses. As a result, the use of effective mitigation measures has been subject to fisheries regulations to reduce seabird bycatch from longliners in a number of national jurisdictions and in several Regional Fisheries Management Organisations (RMFOs). While mitigation measures have been mandated in a number of north Pacific longline fisheries, this is largely not the case in north Atlantic longline fisheries. This includes vessels using floated-demersal longlines in the North-East Atlantic longline fishery targeting European Hake Merluccius merluccius, in which high levels of seabird bycatch are estimated. In this paper, we analysed the sinking speed of a floated-demersal longline used to target European Hake in the offshore waters of Scotland, to determine potential bycatch risks to seabirds. We deployed Time Depth Recorder devices at different points of the gear. We assessed how this gear performed in comparison to the best practice minimum sink rate of 0.3 m/s recommended by the Agreement on the Conservation of Albatrosses and Petrels (ACAP) to limit bird access to baited hooks. We found that the average sinking speed of the floated-demersal longline was substantially slower than the ACAP recommendation, between two and nine times slower in non-weighted parts of the gear down to 10m water depth. Our work also found that the sink rate is particularly slow in the top 2m of the water column, increasing with depth and stabilizing at depths over 10m, presumably a consequence of propeller wash behind the vessel. We calculated that the distance astern of the vessel for hooks to sink beyond susceptible seabirds' reach largely exceeds optimum coverage of best practice design Bird Scaring Lines (100 m). Our results indicate that hooks from floated-demersal longlines are therefore readily open to seabird attacks, and as a result, present a clear bycatch risk. Research is needed to adapt existing mitigation measures to floated-longlines and to develop novel mitigation approaches to improve the sink rate of the gear without impacting target fish catch.

Pulsed export of carbon in the north-western Mediterranean Sea

The short term (hourly scale) variability of heterotrophic prokaryote (HP) vertical distribution and respiratory activity, was investigated in the north-western (NW) Mediterranean Sea. HP vertical distribution was determined on board by flow cytometry analysis of seawater samples collected by series of CTD casts. Cell counts and viability were determined for all samples. HP respiratory rates were determined later in the laboratory from filtered seawater samples (23 dm3) from 300–1 150-m depth. The average cell viability was 94.8%±2.2% (n=240). There was no accumulation of dead cells, due to quick decay of damaged cells. In the epipelagic layer, three HP groups were distinguished, two (HNA1, HNA2) whose cells exhibited a high nucleic acid content and one (LNA) with low nucleic acid content cells. HNA2 was most populated at 50 m but not detected at 90 m and below, presumably aerobic anoxygenic photoheterotrophic bacteria (AAPs). The variability in HP abundance was mainly confined in the upper 80 m. A few secondary peaks of HP abundance were observed (80–150 m) in connection with abundance troughs in the surface layer. HP cells were continuously present in a wide layer around 500 m (mean 191×103 cells/cm3). Below this layer, HP abundance randomly exhibited peaks, coupled to respiratory rate peaks. The HP abundance and variability in the water column was suppressed during a strong wind event. The observed sporadic variability was tentatively interpreted through a pulsed carbon-export mechanism induced by the microorganism production of dissolved polysaccharides, followed by flocculation and rapid sinking. This mechanism would thus contribute to (i) preventing organic matter accumulation in the epipelagic layer, (ii) seeding the water column with live HP cells, and (iii) supplying the aphotic water column with fresh and labile organic matter. This important vertical flux mechanism needs further observations and modelling.

Economically Important Benthic Macroinvertebrates in the Reefs of West Sulu Sea, Palawan, Philippines

Benthic macroinvertebrates are essential components of the marine ecosystem and a source of food and livelihood in many coastal communities. However, a lack of knowledge about their status has resulted in their overexploitation in many areas where they are openly harvested. In this paper, we assessed the species composition, population density, uses, and conservation status of economically important benthic macroinvertebrates in the coral reefs of the West Sulu Sea, Palawan, Philippines. A total of 100 transects from six sites (3–10-m depth) covering a reef area of 25,000 m2 were assessed using scuba diving. There were 15 species belonging to 11 families found in the surveyed sites, with the Crocus giant clam Tridacna crocea Lamarck 1819 encountered in all sites. The mean population density of each species ranged between 0.8–306.4 individuals ha–1. Based on the IUCN Red List, most of the species encountered have “Least Concern” and “Not Evaluated status,” whereas two species are listed as “Lower Risk/ Conservation Dependent.” Mostly, these organisms are harvested as a source of food, souvenirs, decorations, and jewelry. The absence of some high-value and threatened species may indicate over-harvesting of these species. The results of this study can be used as a basis for formulating a long-term management plan for these benthic macroinvertebrates and their coastal habitats.

Monitoring the effects of spatial protection on the reef fish communities of the Pondoland Marine Protected Area, Eastern Cape Province, South Africa

Monitoring marine protected areas (MPAs) is critical for evaluating their effectiveness and for improving management. In this study, a single-camera baited remote underwater video system (mono-BRUVS) was deployed quarterly at four sites (10–30-m depths) to quantify the reef fish communities in protected (no-take) and adjacent exploited areas of the Pondoland MPA on the east coast of South Africa (Indian Ocean). To assess size (biomass) of the fish communities, we used 10 years of research linefishing data (2006–2016) from the same areas. Univariate and multivariate analyses were used to compare abundance and biomass of the fish communities between protected and exploited areas. Significant differences were detected between fish communities in protected and exploited areas based on their abundance and biomass. These differences are primarily ascribed to linefishing and the removal of larger, predatory species such as yellowbelly rockcod Epinephelus marginatus, Scotsman Polysteganus praeorbitalis and black musselcracker Cymatoceps nasutus in the adjacent exploited areas. Removal of such predators may have caused trophic cascading or prey release, resulting in very different fish communities. These results highlight the importance of investigating the entire fish community and not only target fishery species when evaluating MPA effectiveness.

INVASION OF ZEBRA MUSSEL DREISSENA POLYMORPHA PALLAS,1771) INTO THE COOLING SYSTEM WATER SUPPLY OF AL-MUSAYAB THERMAL POWER PLANT / IRAQ

Zebra mussels Dreissena polymorpha are tiny bivalve mollusca , invade water supply of cooling system unit in Al- Musayab power plant, 60 km south-west Baghdad and grow to dense clusters. Its ability to rapidly colonize intake structures, such as pipes and screens causing reduction in water pumping capabilities .Some biological aspects of zebra mussel Dreissena polymorpha have been studied and some physical & chemical parameters were examined as alimenting factors for the species Samples collecting was done monthly from two sites within the water system , the first was the traveling band screen (TBS ) and the other site was small canal collecting excess water passing from TBS .Biological studies revealed that the samples collected from the canal includes five size groups with average length of 5.7 ; 11.3 ; 16.7 ; 21.9 & 27.3 mm. In TBS , the individuals found all over the year with highest number of 135 individuals recorded in August . Individuals of a length of 11.3 & 16.7mm were the dominant.In general, from total number of 799 individuals collected from TBS, 388 individuals were of size of 11.3mm and 239 individual were of size 16.7mm while no large specimens of large size group of 27.3mm were recorded in TBS.To study the settlement rate of larvae, several concreat tiles of (25X25cm) were suspended at depths of 2,4& 6 m. in the sedimentation pond (12m depth). The number of juveniles were counted monthly . The result showed that there were two peaks of settlement , one in June and the other in September and October .Depth of 6m was the most suitable for settlement.The average length of settled juveniles ranged between 3.5-6.1mm. Water temperature in the site ranged between 11-32o C , Dissolved oxygen was 4.8-8.3ml/L . The highest value of turbidity was 49NTU.Ca++ was 68-136mg/l and Mg++ was 34- 72mg/l

Free surface features of submarines moving underwater: Study of Bernoulli Hump

Submarines are known to produce certain surface manifestations, primary among them being a feature known as Bernoulli Hump (BH). BH is a rise and fall of sea surface height above the submarine, when the vessel cruises close to surface. This feature has been noted by many researchers but scant information is publically available on the same due to the classified nature of the data. A major part of the Wide Area Surveillance program for submarines of the world navies uses the detection of this BH. In this work, our objective is to detect and establish the presence of BH characteristics. After calibrating a known CFD code using experimental data, we make model simulations which clearly depict the BH and its features. We then show the path ahead for submarine detection using BH from observations of sea surface heights. Value of BH height for a submarine at 10m depth moving at 5 knots is about 20cm which falls within the 2 cm vertical resolution of altimeters. Though most of the studies were for calm waters, an introduction to the presence of regular wind waves is given at the end.

CARBON STOCK, SOIL CO2 FLUX AND CARBON BUDGETS OF DIFFERENT FOREST ECOSYSTEMS OF MANIPUR, NORTHEAST, INDIA

Carbon stock and soil CO 2 flux in the vegetation-soil components were assessed in tropical, sub-tropical and temperate forest ecosystems of Manipur, Northeast India. Carbon stock in the aboveground biomass was recorded to be highest in the sub-tropical forest (319.18 Mg ha -1 ) followed by temperate (54.45 Mg ha -1 ) and tropical forest (38.35 Mg ha -1 ) whereas soil organic carbon stock was highest in temperate forest (65.13 Mg ha -1 ) and lowest in tropical forest (21.64 Mg ha -1 ) up to the depth of 1m. The rates of carbon sequestration was in the order of the tropical>temperate> sub- tropical forest and the rate of soil CO 2 flux was estimated to be highest in tropical and lowest in temperate forest. Regression analysis shows that annual soil CO 2 flux was highly influenced by soil moisture, soil temperature and soil organic carbon as well as by C stocks in aboveground biomass. The annual carbon budget of the tropical, sub-tropical and temperate forest shows that 11.41 Mg C ha -1 ,9.84 Mg C ha -1 and 10.34 Mg C ha -1 was captured by the vegetation through photosynthesis, while 10.36 Mg C ha -1 ,5.84 Mg C ha -1 and 8.07 Mg C ha -1 was released into the atmosphere through CO 2 emissions from soil due to root and microbial respiration thereby a net balance of 1.05 Mg C ha -1 yr -1 ,1.77 Mg C ha -1 yr -1 and 2.27 not ( 4.50) Mg C ha -1 yr -1 was being retained in the forest ecosystems. Thus our study indicates that these forests have a huge potential in the reduction of carbon dioxide levels in the atmosphere and could be used as C-sinks in the Northeast India depending upon the level of protection.

Trends and potential human health risk of trace elements accumulated in transplanted blue mussels during restoration activities of Flekkefjord fjord (Southern Norway)

The monitoring of contaminants represents a priority to preserve the integrity of marine ecosystems, as well as to plan and to manage restoration activities in order to protect environmental and human health. In the present study, a 6-months active biomonitoring was performed to explore the levels of eighteen trace and toxic elements, including heavy metals (TEs; i.e. Al, As, Ca, Cd, Cr, Cu, Fe, Hg, K, Mg, Mn, Na, Ni, P, Pb, Sr, Ti, and Zn), accumulated in soft tissues of blue mussel (Mytilus edulis Linnaeus, 1758) individuals transplanted at different depths (5- and 15-m depth) in five locations within the Flekkefjord fjord (Southern Norway). As this area suffered a long-lasting contamination due to both organic and inorganic contaminants, a series of restoration activities were activated to tackle and to prevent potential risks for ecosystem and local population. Our results demonstrated that the levels of TEs accumulated in edible tissues of transplanted mussels in the Flekkefjord fjord were generally low before the beginning of the restoration activities. However, location- and time-specific differences in the accumulation of TEs were noted after the implementation of such activities. Interestingly, the levels of Fe and Mn significantly increased after the beginning of the restoration activities, likely because the release of these TEs from the slag used in such operations and/or resuspension of contaminated sediments. However, assuming that native mussels can accumulate the same TEs at levels measured in transplanted individuals, our results suggest a substantial safety for human consumption of native mussels from the Flekkefjord fjord, regardless of restoration activities.

A Four-Dimensional Survey of the Almeria–Oran Front by Underwater Gliders: Tracers and Circulation

Abstract A four-dimensional survey by a fleet of seven underwater gliders was used to identify pathways of subduction at the Almeria–Oran Front in the western Mediterranean Sea. The combined glider fleet covered nearly 9000 km over ground while doing over 2500 dives to as deep as 700 m. The gliders had sensors to measure temperature, salinity, velocity, chlorophyll fluorescence, and acoustic backscatter. Data from the gliders were analyzed through objective maps that were functions of across-front distance, alongfront distance, and time on vertical levels separated by 10 m. Geostrophic velocity was inferred using a variational approach, and the quasigeostrophic omega equation was solved for vertical and ageostrophic horizontal velocities. Peak downward vertical velocities were near 25 m day−1 in an event that propagated in the direction of the frontal jet. An examination of an isopycnal surface that outcropped as the front formed showed consistency between the movement of the tracers and the inferred vertical velocity. The vertical velocity tended to be downward on the dense side of the front and upward on the light side so as to flatten the front in the manner of a baroclinic instability. The resulting heat flux approached 80 W m−2 near 100-m depth with a structure that would cause restratification of the front. One glider was used to track an isotherm over a day for a direct measure of vertical velocity as large as 50 m day−1, with a net downward displacement of 15 m over the day.

KOMPOSISI JENIS DAN TUTUPAN TERUMBU KARANG DI PANTAI SAMUH, NUSA DUA, BALI

Coral reefs are known as very complex and productive ecosystems with a diversity of biota such as mollusks, crustaceans and reef fish. Coral biodiversity, high ecological and economic functions are also accompanied by high threats from various human activities. This study aims to determine the species composition and cover of coral reefs. The research used purposive random sampling method. Data collection at 2 stations with 3 different depths of 3m, 7m, and 10m was carried out using the 1x1 m2 quadrant transect method. The study found 15 types of coral reefs at Samuh Beach including Acropora Baranching (ACB), Acropora Encrusting (ACB), Acropora Submassive (ACS), Acropora Digitate (ACD), Acropora tabulate (ACT), Non-Acropora Baranching (CB), Non-Acropora Acropora Encrusting (CE), Non-Acropora Foliose (CF), Non-Acropora Massive (CM), Non-Acropora Sub Massive (CS), Non-Acropora Mushroom (CMR), Non-Acropora Millepora (CME), Non-Acropora Helliopora (CHL), Soft Coral (SC), Sponge (SP), Zoanthida (ZO), Other (OT). The percentage of Acropora cover was higher than other corals. The highest percentage of coral reef cover is at a depth of 10 m as much as 94.75%, the lowest is at a depth of 3 m as much as 80.66%. Based on the results of the analysis, it was found that the condition of coral reef cover in Samuh Beach was generally classified in the very good and well maintained category.

A Case Study of Cloud-Top Kelvin–Helmholtz Instability Waves near the Dendritic Growth Zone

Abstract Kelvin–Helmholtz instability (KH) waves have been broadly shown to affect the growth of hydrometeors within a region of falling precipitation, but formation and growth from KH waves at cloud top needs further attention. Here, we present detailed observations of cloud-top KH waves that produced a snow plume that extended to the surface. Airborne transects of cloud radar aligned with range height indicator scans from ground-based precipitation radar track the progression and intensity of the KH wave kinetics and precipitation. In situ cloud probes and surface disdrometer measurements are used to quantify the impact of the snow plume on the composition of an underlying supercooled liquid water (SLW) cloud and the snowfall observed at the surface. KH wavelengths of 1.5 km consisted of ∼750-m-wide up- and downdrafts. A distinct fluctus region appeared as a wave-breaking cloud top where the fastest updraft was observed to exceed 5 m s−1. Relatively weaker updrafts of 0.5–1.5 m s−1 beneath the fluctus and partially overlapping the dendritic growth zone were associated with steep gradients in reflectivity of −5 to 20 dBZe in as little as 500-m depths due to rapid growth of pristine planar ice crystals. The falling snow removed ∼80% of the SLW content from the underlying cloud and led to a twofold increase in surface liquid equivalent snowfall rate from 0.6 to 1.3 mm h−1. This paper presents the first known study of cloud-top KH waves producing snowfall with observations of increased snowfall rates at the surface.

Water Temperature at Different Depths Affects the Distribution of Neon Flying Squid (Ommastrephes bartramii) in the Northwest Pacific Ocean

Ommastrephes bartramii can vertically swim during its life, and previous studies have suggested the need to account for preferred habitat distribution influenced by water temperatures at different depths. To explore the impacts of deep-water temperature on O. bartramii spatial distribution, we constructed generalized additive models (GAMs) based on the Chinese squid-jigging fishery data and the Argo deep water temperature data during 2005–2018 in the Northwest Pacific Ocean to analyze the relationships between the local abundance of O. bartramii and deep-water temperatures. The results showed that the variables including surface water temperature (T0), water temperature at 30- and 100-m depths (T30 and T100), and water differences between T0 and T30 (D0–30) significantly affected the spatial distribution of O. bartramii. The suitable ranges of each variable are different, > 15.5°C for T0, 11–18°C for T30, < 6°C for T100, and 4–4.5°C for D0–30. The areas occupied by the suitable T30 seemed to reflect the outline of fishing ground, whereas the areas with suitable T100 were to indicate the high density of O. bartramii. The predicted suitable habitat area and high-density area for O. bartramii are also regulated by El Niño–Southern Oscillation (ENSO) events. We demonstrated how the estimates of O. bartramii spatial distribution would vary influenced by deep-water temperatures in the Northwest Pacific Ocean. This information may help develop an appropriate method for investigating the effects of deep-water temperature on species with vertical migration.

Global longitudinal strain assessment of cardiac function and extravascular lung water formation after diving using semi-closed circuit rebreather.

The aim of the present investigation is to study the relationship of ventricular global longitudinal strain (GLS) and ultrasound lung comets (ULC) formation to establish a link between extravascular pulmonary water formation and cardiac contractile dysfunction. This is a prospective observational study including 14 active military divers. The subjects performed two sea dives of 120min each with a semi-closed SCUBA circuit at 10m depth. Divers were examined at baseline, 15min (D1) and 60min (D2) after diving. The evaluation included pulmonary and cardiac echography (including speckle tracking techniques). Blood samples were drawn at baseline and after diving, assessing hs-TnT and Endothelin-1. ULC were detected in 9 (64.2%) and 8 (57.1%) of the subjects after D1 and D2 respectively. No differences were found in right and left ventricular GLS after both immersions (RV: Baseline: - 17.9 4.9 vs. D1: - 17.2 6.5 and D2: - 16.7 5.8s-1; p = 0.757 and p = 0.529; LV: Baseline: - 17.0 2.3 vs. D1: - 17.4 2.1 and D2: - 16.9 2.2s-1; p = 0.546 and p = 0.783). However, a decrease in atrial longitudinal strain parameters have been detected after diving (RA: Baseline: 35.5 9.2 vs. D1: 30.3 12.8 and D2: 30.7 13.0s-1; p = 0.088 and p = 0.063; LA: Baseline: 39.0 10.0 vs. D1: 31.6 6.1 and D2: 32.4 10.6s-1; p = 0.019 and p = 0.054). In the present study, no ventricular contractile dysfunction was observed. However, increase pulmonary vasoconstriction markers were present after diving.

EFFECT OF COMPACTION AT DIFFERENT ENERGY LEVELS ON THE GEOTECHNICAL PROPERTIES OF STABILIZED SOILS

This study is aimed at evaluating the influence of compaction (at different energy levels) on the geotechnical properties of stabilized soils. To achieve this, four bulk soil samples (BDL1, BDL2 BDL3 & BDT) consisting of termite reworked soils and residual lateritic soils were collected at New Stadium Road, Awo hall, University of Ibadan, Nigeria at a depth of 2m for strength tests and at depths of 1m, 1.5m & 2m for index tests. Geotechnical analysis (index tests and strength tests) and geochemical analysis (X-ray Diffraction) were carried out on the sampled soils. The study revealed that the mineral constituents of the sampled soils are quartz, kaolinite and hematite; with the termite-reworked soil richer in kaolinite content than the quartz schist derived soil with about 125% increase. The values of index tests for both soils met the required Nigeria specification for good soil with termite reworked soil performing better. The values of specific gravity for both soils are close suggesting similar origin. AASHTO classification put termite-reworked soil within the range of A-2-7 (good rating) while most of the residual soil samples fall within A-7-5 to A-7-6 range (fair to poor rating). The stabilisation of residual lateritic soil using termite-reworked soil as stabiliser brought about increase in the values of maximum dry density, uncured unconfined compressive strength as well as the sun-cured unconfined compressive strength of the studied soil. The influence of stabilisation using termite-reworked soil was strongest at the highest level of compaction ((30%) of termite-reworked soil with the weight of residual soil). There also exist a fairly strong positive correlation between the amount of termite reworked soil and energy of compaction and between the uncured and sun-cured unconfined compressive strength was plotted against the number of blows for BDL1, BDL2 and BDL3 respectively. In sum, these stabilised soils are suitable for foundation and landfills materials.

EFFECT OF DRYING TEMPERATURE ON THE ENGINEERING PROPERTIES OF STABILISED AND NATURAL SOILS FOR ROAD CONSTRUCTION

The aim of this investigation is to determine the effect of drying temperature on the geotechnical properties of natural soils and stabilised soils. Soil samples were taken along Supare Akoko- Emure Ekiti road from three locations at the depth of 1m each. Soil sample for location 1 soil was taken from a stable section while soil samples from locations 2 & 3 were taken from the failed portions of the road. The following laboratory analysis were conducted on the soil samples; atterberg limit test, grain size analysis, Linear shrinkage, Specific gravity, Compaction test and California Bearing Ratio test (CBR). The results show that sampled soil from location 1 has better engineering properties than soil samples from Loc. 2 and 3. This is an indication that the soils of locations 2 & 3 contributed to the failing of the failed part. These three soil samples were further tested by adding 6% (of the total weight of the sampled soils) of Saw dust ash (SDA) and Fine Palm kernel shells (FPKSA) to the soil as stabilisers. Both the index and strength properties improved upon the addition of stabilizers with SDA proving to be a better stabiliser. Under varying temperature of pretest drying with stabilisers (SDA and FKPSA) and without stabiliser; the same engineering properties were considered. The results show that temperature plays a major role to better the properties of the soil.