Conductivity , Temperature And Depth Research Articles

Reinterpretation of the Thorpe Length Scale

Abstract In 1977, S. A. Thorpe proposed a method to estimate the dissipation rate ε of turbulence kinetic energy (TKE) in an overturning turbulent layer in a lake, by sorting the observed (unstable) density profile to render it stable and thus deriving a length scale LT named after him, from the resulting vertical displacements of water parcels. By further proposing that this purely empirical scale (with no a priori physical basis, unlike many other turbulence length scales) is proportional to the Ozmidov scale LO, definable only for stably (not unstably or neutrally) stratified flows, he was able to extract ε. The simplicity of the approach that requires nothing but CTD (Conductivity, Temperature and Depth) casts in water bodies, including lakes and oceans, made it attractive, until microstructure profilers were developed and perfected in later decades to actually make in-situ measurements of ε. Since equivalent microstructure devices are not available for the atmosphere, Thorpe technique has been resurrected in recent years for application to the atmosphere, using potential temperature profiles obtained from high vertical resolution radiosondes. Its popularity and utility have increased lately, in spite of unresolved issues related to the validity of assuming LT is proportional to LO. In this study, we touch upon these issues and offer an alternative interpretation of the Thorpe length scale as indicative of the turbulence velocity scale σK, which allows Thorpe sorting technique to be applied to all turbulent flows, including those generated by convection.

Best practices for Core Argo floats - part 1: getting started and data considerations

Argo floats have been deployed in the global ocean for over 20 years. The Core mission of the Argo program (Core Argo) has contributed well over 2 million profiles of salinity and temperature of the upper 2000 m of the water column for a variety of operational and scientific applications. Core Argo floats have evolved such that the program currently consists of more than eight types of Core Argo float, some of which belong to second or third generation developments, three unique satellite communication systems (Argos, Iridium and Beidou) and two types of Conductivity, Temperature and Depth (CTD) sensor systems (Seabird and RBR). This, together with a well-established data management system, delayed mode data quality control, FAIR and open data access, make the program a very successful ocean observing network. Here we present Part 1 of the Best Practices for Core Argo floats in terms of how users can get started in the program, recommended metadata parameters and the data management system. The objective is to encourage new and developing scientists, research teams and institutions to contribute to the OneArgo Program, specifically to the Core Argo mission. Only by leveraging sustained contributions from current Core Argo float groups with new and emerging Argo teams and users who are eager to get involved and are actively encouraged to do so, can the OneArgo initiative be realized. This paper presents a list of best practices to get started in the program, set up the recommended metadata, implement the data management system with the aim to encourage new scientists, countries and research teams to contribute to the OneArgo Program.

The Brazil current cyclonic meandering and shelf-slope water exchanges at 27°S–31°S

The Brazil Current (BC) experiences intense mesoscale activity from its origin on the northeastern Brazilian coast till it reaches the Brazil-Malvinas Confluence. The BC meandering behavior near the Cape Santa Marta (27°S – 31°S), has not been well described in the literature. In this study, in situ observations and satellite images are used to describe the BC meanders and cyclonic eddies near the cape. The results obtained from two Lowered Acoustic Doppler Current Profilers (LADCP) sections show that these structures are surface intensified but extend through the whole water column. Conductivity Temperature and Depth (CTD) profiles show evidence of coastal water trapping inside an eddy. Altimeter data show two hot spots of cyclones, one at 28.5°S and the other at 30.5°S, with an average of ∼5 and 7 eddies per year, respectively. The eddies generated on both sites have a mean lifetime of 37 days, and no significant differences were found between their surface properties. Satellite images of chlorophyll show that coastal water horizontal advection is a recurrent phenomenon in these eddies, imprinting an eddy stirring signal into their average composites. Furthermore, using Empirical Orthogonal Functions to analyze the BC flow in a mooring line, we observed that the mesoscales meanders are responsible for explaining at least 1/3 of the flow variability in this area.

Satellite and High-Spatio-Temporal Resolution Data Collected by Southern Elephant Seals Allow an Unprecedented 3D View of the Argentine Continental Shelf

High spatial and temporal resolution hydrographic data collected by Southern Elephant Seals (Mirounga leonina, SESs) and satellite remote sensing data allow a detailed oceanographic description of the Argentine Continental Shelf (ACS). In-situ data were obtained from the CTD (Conductivity, Temperature, and Depth), accelerometer, and hydrophone sensors attached to five SESs that crossed the ACS between the 17th and 31st of October 2019. The analysis of the temperature (T) and salinity (S) along the trajectories allowed us to identify two different regions: north and south of 42°S. Satellite Sea Surface Temperature (SST) data suggests that north of 42°S, warm waters are coming from the San Matias Gulf (SMG). The high spatio-temporal resolution of the in-situ data shows regions with intense gradients along the T and S sections that were associated with a seasonal front that develops north of Península Valdés in winter due to the entrance of cold and fresh water to the SMG. The speed of the SESs is correlated with tidal currents in the coastal portion of the northern region, which is in good agreement with the macrotidal regime observed. A large number of Prey Catch Attempts (PCA), a measure obtained from the accelerometer sensor, indicates that SESs also feed in this region, contradicting suggestions from previous works. The analysis of wind intensity estimated from acoustic sensors allowed us to rule out the local wind as the cause of fast thermocline breakups observed along the SESs trajectories. Finally, we show that the maximum depth reached by the elephant seals can be used to detect errors in the bathymetry charts.

Upwelling characteristics in the Gulf of Riga (Baltic Sea): multiple data source approach

Upwellings are characteristic for the Baltic Sea region including the Gulf of Riga, although the current knowledge is rather limited with only few research conducted in the Gulf itself. Upwelling events in the Gulf of Riga in 2010–2022 were studied by analyzing sea surface temperature time series from coastal stations and SmartBuoy, together with satellite data, model data, and CTD (conductivity, temperature, and depth) surveys. The starting/end point, active, and relaxation phases were defined in each event to describe the characteristics and length of each phase. Upwellings were less frequent (41%) on the eastern coast but lasted longer and had higher temperature drops than on the western coast. On the western coast, a variety of upwelling characteristics between stations only 30 km apart were found with the likely reason being the different orientations of the coastline with respect to the wind direction. Satellite data revealed that on the western coast of the Gulf, rather small upwelling events form along specific sections of the coastline. Of all upwelling events, 30% were characterized by an immediate temperature increase after reaching the minimum temperature, and we suggest that this is related to a distinct change in wind direction. The results from the simulations indicated smaller lateral density and salinity gradients in the sea surface than in larger Baltic Sea gulfs. It signals that conditions for the occurrence of baroclinic instabilities are rather small; thus, we suggest that weaker gradients could explain quite fast upwelling relaxation in the basin if compared to, e.g., the Gulf of Finland.

Nepheloid layer dynamics overview of the Portuguese continental shelf

As part of project AQUIMAR, intensive CTD (conductivity, temperature and depth), and turbidity/particulate matter concentration (PMC) data were collected in four cruises along the Portuguese continental shelf, over three consecutive years under contrasting seasonal scenarios. Two of the cruises were carried out during Fall (5-26 October 2018 and 10 - 31 October 2019), one in Spring (18 April to 12 May 2019), and another under Winter conditions (24 February to 19 March 2020). Water samples were collected at the surface nepheloid layer (SNL) and bottom nepheloid layer (BNL) for evaluation particulate matter concentration (PMC) and composition. Differences found between the 5 sampled areas (Viana do Castelo-Porto; Aveiro-Figueira da Foz; Peniche-Santa Cruz; Setúbal-Sines; Sagres-Tavira), are well visible in T-S (temperature vs. salinity) diagrams based on CTD casts. PMC found in the study samples for all cruises was in the range of 0.1-10.2 g/m3. Turbidity meter data, calibrated and converted into inferred PMC values, showed that the study areas were generally characterized by low values, with the exception of some sporadic maxima found during Winter in the northern areas (between Minho River and the Cape Mondego). Particulate matter sample composition, obtained via X-ray diffraction, identified illite > chlorite > kaolinite > calcite > quartz > feldspars as major minerals, with clay minerals dominating and taking up more than 83% in average of the total identified mineral content. This analysis revealed that, for the Fall and Spring cruises, particles in the SNL were mainly biogenic, and for the BNL, the lithogenic material (average mica content of 71%) and biogenic calcite (average content of 10%) were dominant in all cruises. Cruise data also indicate that upwelling/downwelling and internal waves affected and promoted a higher level of turbulence in the water column, resulting in generally higher turbidity values, found in both the SNL and BNL.

Deep-water hydrodynamic observations of two moorings sites on the continental slope of the southern Adriatic Sea (Mediterranean Sea)

Abstract. This work presents an 8-years-long dataset of monitoring activities conducted on the western margin of the southern Adriatic Sea where two moorings have been placed since 2012 in sites that are representative of different morpho-dynamic conditions of the continental slope (open slope vs. submarine canyon). The dataset includes measurements conducted with both current meters and conductivity, temperature and depth (CTD) probes, and it provides information about the hydrodynamics and thermohaline properties of the last 100 m of the water column. The hydrodynamics in both sites are dominated by weak currents (< 0.1 m s−1) which undergo yearly to episodic pulsation able to exceed intensity greater than 0.5 m s−1, which are linked to the passage of dense waters. The 8-years records presented here represent a starting point for the continuous observation activity set up on occasion of the “Operation Dense Water” in 2012 focussed on the southern Adriatic deep-water dynamics. Since then, the observatory has been ongoing since 2012 and the database is regularly updated. All the data described here are made publicly available from https://doi.org/10.5281/zenodo.6770201 (Paladini de Mendoza et al., 2022) and are compliant with the FAIR principles (findable, accessible, interoperable and reusable).

Lightweight drone-deployed autonomous ocean profiler for repeated measurements in hazardous areas – Example from glacier fronts in NE Greenland

Accelerated melting of ice in Polar Regions due to global warming increases freshwater input to coastal waters from marine terminating glaciers. Lack of measurements near the glacier terminus limits our knowledge of the mixing processes between freshwater and the underlying ocean.We present a low-cost (< € 3200) and lightweight (2.6 kg) drone-deployed, retrievable conductivity, temperature and depth (CTD) instrument for remote controlled (1 km) autonomous profiling in highly hazardous and remote areas. The instrument was deployed with a drone taking off from land and marine vessels to perform measurements near tidewater glaciers termini of the Greenland ice sheet.The free-flowing profiler is reusable due to a compact ballast based single-shot buoyancy engine and post-profiling pickup by drone. It can reach a depth of up to 250 m, and is equipped with low-cost sensors for conductivity, temperature, and depth measurements.During decent the profiler reaches a velocity of about 0.48 m/s, resulting in about 3.5 data points pr. m depth, but is designed to easily vary the velocity by changing buoyancy setup before deployment.Successful tests were conducted at marine terminating glaciers in Northeast Greenland in August 2021.

Distribution of physical and chemical variables in the water column and characterization of the bottom sediment in a macrotidal estuary on the Amazon coast of the state of Maranhão, Brazil

The objective of this research was to characterize the distribution of dissolved nutrients at six sampling stations in the estuary of the Anil River (ARE) and characterize the bottom sediment. The study area is influenced by a tropical climate and semidiurnal macrotidal regime. Sampling of the surface water and sediment was performed in the main channel at six sampling stations distributed along the estuary in the rainy period (May 9th) and dry period (October 5th) during the spring. Physical variables were collected with the aid of a HANNA HI-8424 multi-parameter probe (water temperature, salinity, pH, dissolved oxygen, and turbidity) and YSI CTD (conductivity, temperature, and depth) probe. A van Veen dredge was used for the collection of bottom sediment from the main channel. The sedimentological results were heterogeneous. Grain size ranged from very fine to medium sand. Dissolved nutrients in the ARE had different sources depending on the season. Continental and fluvial inputs, evidenced by salinity values, governed the distribution of nutrients in the rainy period (January to June), whereas nutrient concentrations were related to the recycling of organic material in the estuary in the dry season (July to December). The considerable presence of sand in the main channel indicates that the sediments available in ARE are exposed to intense hydrodynamics. The distribution of nutrients and the grain size revealed the occurrence of different sources in the estuary according to the rainfall regime and the intense hydrodynamics of tidal currents (semidiurnal macrotidal).&#x0D; Keywords: dissolved nutrients, estuarine environment, sedimentology.

Distribution and diversity of Meiobenthos in southern Caspian Sea (Mazandaran-Iran)

Biodiversity and distribution of benthic Meiobenthos in the sediments of the Southern Caspian Sea were studied in order to introduce and determine their relationship with the environmental factors. From 12 stations (ranging in depths from 5, 10, 20 and 50 meters), sediment samples were gathered for four seasons (2012). Temperature, salinity, dissolved Oxygen and pH were measured during sampling with CTD (conductivity, temperature and Depth). Percentage grain size and total organic matter and calcium carbonate were measured. The average water temperature ranged from 9.52 to 23.93 ͦC, dissolved Oxygen from 7.71 to 10.53 mg/L, salinity from 10.57±0.07 to 10.75±0.04 ppt., pH from 7.44±0.29 to 7.41±0.22, EC from 17.97±0.12 to 18.30±0.04 μs/cm2, TDS from 8.92±0.04 to 9.14±0.02 mg/L, total organic matter from 5.83±1.43 to 6.25±0.97% and calcium carbonate fluctuated from 2.36±0.36 to 1.68±0.19%. From the 4 groups of animals (Foraminifera, Crustacea, Worms and Mollusca), 40 species belonging to 29 genera of 25 families were identified Ammonia beccarii caspica, was the common species in all sampling stations. Depth was an important factor in the distribution of meiobenthos. Mean of maximum and minimum Shannon index were measured at depth of 5m and 50 m and were in the order of 0.93 and 0.43, respectively. Account of Shannon and Peilou's index showed that this area is under pressure and is not steady.

Quantifying Patterns in Fish Assemblages and Habitat Use Along a Deep Submarine Canyon-Valley Feature Using a Remotely Operated Vehicle

The aim of this study was to document the composition and distribution of deep-water fishes associated with a submarine canyon-valley feature. A work-class Remotely Operated Vehicle (ROV) fitted with stereo-video cameras was used to record fish abundance and assemblage composition along transects at water depths between 300 and 900 metres. Three areas (A, B, C) were sampled along a submarine canyon-valley feature on the continental slope of tropical north-western Australia. Water conductivity/salinity, temperature, and depth were also collected using an ROV mounted Conductivity Temperature and Depth (CTD) instrument. Multivariate analyses were used to investigate fish assemblage composition, and species distribution models were fitted using boosted regression trees. These models were used to generate predictive maps of the occurrence of four abundant taxa over the survey areas. CTD data identified three water masses, tropical surface water, South Indian Central Water (centred ∼200 m depth), and a lower salinity Antarctic Intermediate Water (AAIW) ∼550 m depth. Distinct fish assemblages were found among areas and between canyon-valley and non-canyon habitats. The canyon-valley habitats supported more fish and taxa than non-canyon habitats. The fish assemblages of the deeper location (∼700–900 m, Area A) were different to that of the shallower locations (∼400–700 m, Areas B and C). Deep-water habitats were characterised by a Paraliparis (snail fish) species, while shallower habitats were characterised by the family Macrouridae (rat tails). Species distribution models highlighted the fine-scale environmental niche associations of the four most abundant taxa. The survey area had a high diversity of fish taxa and was dominated by the family Macrouridae. The deepest habitat had a different fish fauna to the shallower areas. This faunal break can be attributed to the influence of AAIW. ROVs provide a platform on which multiple instruments can be mounted and complementary streams of data collected simultaneously. By surveying fish in situ along transects of defined dimensions it is possible to produce species distribution models that will facilitate a greater insight into the ecology of deep-water marine systems.

Coastal upwelling along the west coast of Sabah and its impact on coastal aquaculture management

The aquaculture industry in Malaysia is currently growing at nearly 9 percent per year and is generating more than 250,000 tons of production per annum. However, little commercial scale aquaculture is present along the west coast of the state of Sabah. Few if any studies have been conducted to investigate aquaculture site suitability along the west coast of Sabah and the wider west coast of Borneo from an environmental or coastal management perspective. To determine the site suitability for marine aquaculture and other coastal resource users there needs to be an improved understanding of the physical, chemical, and biological characteristics of the coastal environment. One year of data collection including the long-term deployment of Conductivity, Temperature and Depth (CTD) sensors, and bi-monthly water column and seabed sediment sampling was undertaken to provide an indication if the coastal waters between Kota Belud and Kudat are suitable for marine aquaculture purposes. The site provided an analogy for much of the west coast of Borneo, especially the west coast of Sabah, due to similar oceanographic drivers in the region. Results indicated that during the NE monsoon period there is dramatic decrease in water temperature due to the upwelling of cold dense nutrient rich water onto the west coast of Sabah's continental shelf from deeper offshore areas of the South China Sea. This large change in temperature will likely rule out the potential commercial marine grow out of such species as Asian Seabass and perhaps Tropical Spiny Lobsters. Other species such as Cobia, Grouper and Snapper which have a wider tolerance for temperature change will likely be suitable but at times will be stressed due to magnitude of the observed changes. Such observations have ramifications in regard to site suitability for future resource consent applications for open ocean and coastal aquaculture along the west coast of Borneo. In summary the study highlights how physical processes can impact on resource use and development in a coastal setting.

High‐resolution multibeam sonar bathymetry of the deepest place in each ocean

AbstractOver the course of 10 months, the global Five Deeps Expedition (2018–2019) mapped ~550,000 km2 of seafloor of which 61% comprised new coverage over areas never before surveyed and ~30% was acquired from some of the ocean's deepest trenches and fracture zones. The deepest points of each ocean were mapped using a latest‐generation, full‐ocean depth Kongsberg EM 124 multibeam echosounder. These extreme depths were corrected using Conductivity, Temperature and Depth (CTD) data from sea surface to full ocean depth. The deepest place in each ocean were identified as the Brownson Deep, Puerto Rico Trench in the Atlantic Ocean (8,378 ± 5 m), an unnamed deep within the South Sandwich Trench in the Southern Ocean (7,432 ± 13 m), an unnamed deep within the Java Trench in the Indian Ocean (7,187 ± 13 m), Challenger Deep within the Mariana Trench in the Pacific Ocean (10,924 ± 15 m), and the Molloy Hole in the Arctic Ocean (5,551 ± 14 m). As part of the overarching mission of the Five Deeps Expedition, and to clarify beyond doubt the deepest point in the Indian, Pacific and Southern oceans, other sites were visited that had been postulated as potential deepest locations. This study has confirmed that the Horizon Deep within the Tonga Trench is the second deepest point in the Pacific Ocean (10,816 ± 16 m), the Dordrecht Deep within the Diamantina Fracture Zone is not the deepest point in the Indian Ocean (7,019 ± 17 m) and that in accordance with the guidelines of the Antarctic Treaty and International Hydrographic Organisation, although the Meteor Deep is the deepest point in the South Sandwich Trench (8,265 ± 13 m) it is located within the waters of the Atlantic Ocean and not the Southern Ocean.

Biogeographical patterns of meso- and bathypelagic fish along a Northeastern Atlantic transect

Abstract The influence of oceanographic variables on assemblages of meso- and bathypelagic fish was investigated along a Northeastern Atlantic Ocean transect (Cape Verde to the Bay of Biscay) during May 2019. Fish were collected using a mrozooplankton trawl during daylight hours at ten stations. Along the transect, 17 hydrographic stations were also performed with a CTD (Conductivity, Temperature, and Depth). A total of 130 fish taxa were identified. The dominant family was Gonostomatidae, with four species (Cyclothone braueri, Cyclothone microdon, Cyclothone pseudopallida, and Cyclothone pallida) being responsible of more than 78% of the total density. The most frequent species that appeared to be ubiquitous were C. braueri and C. pseudopallida, while Myctophidae was the most diverse family. Multivariate analyses revealed two clusters related with the latitudinal gradient. The fish community in the southern stations (25–37°N) was more diverse than in the northern stations (42–48°N). Temperature from 300 to 700 m depth explained 65% of variation in terms of density and 58% in terms of biomass, both statistically significant. The investigated variation in the deep-pelagic ecosystems on a large spatial scale gives essential information to ecosystem management approhes and marine spatial planning.

Comparison of a Smartfin with an Infrared Sea Surface Temperature Radiometer in the Atlantic Ocean

The accuracy and precision of satellite sea surface temperature (SST) products in nearshore coastal waters are not well known, owing to a lack of in-situ data available for validation. It has been suggested that recreational watersports enthusiasts, who immerse themselves in nearshore coastal waters, be used as a platform to improve sampling and fill this gap. One tool that has been used worldwide by surfers is the Smartfin, which contains a temperature sensor integrated into a surfboard fin. If tools such as the Smartfin are to be considered for satellite validation work, they must be carefully evaluated against state-of-the-art techniques to quantify data quality. In this study, we developed a Simple Oceanographic floating Device (SOD), designed to float on the ocean surface, and deployed it during the 28th Atlantic Meridional Transect (AMT28) research cruise (September and October 2018). We attached a Smartfin to the underside of the SOD, which measured temperature at a depth of ∼0.1 m, in a manner consistent with how it collects data on a surfboard. Additional temperature sensors (an iButton and a TidbiT v2), shaded and positioned a depth of ∼1 m, were also attached to the SOD at some of the stations. Four laboratory comparisons of the SOD sensors (Smartfin, iButton and TidbiT v2) with an accurate temperature probe (±0.0043 K over a range of 273.15 to 323.15 K) were also conducted during the AMT28 voyage, over a temperature range of 290–309 K in a recirculating water bath. Mean differences (δ), referenced to the temperature probe, were removed from the iButton (δ=0.292 K) and a TidbiT v2 sensors (δ=0.089 K), but not from the Smartfin, as it was found to be in excellent agreement with the temperature probe (δ=0.005 K). The SOD was deployed for 20 min periods at 62 stations (predawn and noon) spanning 100 degrees latitude and a gradient in SST of 19 K. Simultaneous measurements of skin SST were collected using an Infrared Sea surface temperature Autonomous Radiometer (ISAR), a state-of-the-art instrument used for satellite validation. Additionally, we extracted simultaneous SST measurements, collected at slightly different depths, from an underway conductivity, temperature and depth (CTD) system. Over all 62 stations, the mean difference (δ) and mean absolute difference (ϵ) between Smartfin and the underway CTD were −0.01 and 0.06 K respectively (similar results obtained from comparisons between Smartfin and iButton and Smartfin and TidbiT v2), and the δ and ϵ between Smartfin and ISAR were 0.09 and 0.12 K respectively. In both comparisons, statistics varied between noon and predawn stations, with differences related to environmental variability (wind speed and sea-air temperature differences) and depth of sampling. Our results add confidence to the use of Smartfin as a citizen science tool for evaluating satellite SST data, and data collected using the SOD and ISAR were shown to be useful for quantifying near-surface temperature gradients.

Interaction between seabed morphology and water mass in the South Eastern Arabian Sea: deductions of water mass flow

Geomorphic analysis utilizing multibeam bathymetry and sediment profiler data along with conductivity, temperature and depth (CTD) measurements was undertaken to investigate morphological aspects of bottom current features that prevail in the area. The aim of the study was to deduce the prevailing water mass in the area and to infer interactions between water mass and seabed of South Eastern Arabian Sea. Morphological and bottom current features were identified and analysed. Based on morphological components and their structural orientation, deduction of flow pattern and direction of current flow in the area were attempted. Deconstructing structural aspects of typical bottom current features such as contourite drifts and scours reveal origin under influence of consistent exogenic bottom current having definitive flow pattern. Sub-surface seismic profiles were analysed to infer the presence of a consistently aggrading seafloor. The aspect distribution computed exhibits a prominent trend ranging between 200° and 275° indicating NNW-SSE orientation of erosive features which is usually synonymous with flow direction in the area. Backscatter intensity analysis undertaken for the area revealed seafloor with patches of loose to compact surface sediment distribution. Variation in reflection intensity level from surface sediments was utilized to demarcate zones that are susceptible in future to consistent turbulence-induced erosion. Temperature salinity (TS) diagram for values from CTD measurements was plotted overlaying isopycnals and the resulting plots tagged for various water masses that prevail in the Arabian Sea. Owing to the depth of the study area (~ 1800 m) and structural orientation of bottom current features, dominant oceanographic agent from TS plot was deduced to be the North Indian Deep Water (NIDW). Surface and sub-surface morphology of existing features were interpreted for influence of bottom current action. Geomorphic analysis of seabed is an efficient method to understand the flow pattern and of prevailing water masses and can be applied as passive indicators of bottom current flow. This approach of deducing flow pattern and intensity of water mass movement by analysing morphology of the undersea features can be effectively used globally especially in areas where adequate data and observations for deep water masses are scarce.

Estimated transport of Equatorial Undercurrent observed at 90°E during the Indonesia Prima 2017 campaign

Equatorial Undercurrent (EUC) plays an important role in the dynamic of the eastern Indian Ocean. EUC supplies water masses with high salinity into Indonesian waters. This article examines the EUC transport volume at 90°E across 2°S - 2°N observed on 1st – 3rd March 2017 during the Initiative on Maritime Observation and Analysis Expedition (Indonesian Prima 2017). The analysis of temperature and salinity obtained from conductivity, temperature and depth (CTD) instruments at five stations (CTD11 - CTD14) and current profiles of Shipboard Acoustic Doppler Current Profiles (SADCP) indicate the presence of high speed water column flowing the Arabian Sea High Salinity Water (ASHSW) as characterised by maximum salinity (35.15 - 35.2 PSU) in the temperature range of 18°C - 23°C. ASHSW carried by EUC from the western Indian Ocean at the upper thermocline layer had a tendency to be asymmetrically stronger to the north of the equator. The analysis shows a maximum EUC current speed of 94 cm/sec. Estimated EUC transport water masses based on the curvature area of salinity contour 35.15 and 35.2 PSU respectively result a ∼3.4 Sv and a ∼1.4 Sv, while at curvature area of salinity 35.00 - 35.10 PSU gave about ∼8.7 Sv. The total estimated EUC mass eastward transport calculated in this study is ∼13.5 Sv.

Analysis of temperature inversion in the Zhujiang River Estuary in July 2015

This study investigates the temperature inversion phenomenon in the Zhujiang (Pearl) River Estuary (ZRE) using hydrological data collected in a summer cruise during July 6–17, 2015. The results suggest that temperature inversion occurred primarily near the salinity front, with an average temperature difference (ΔT) of 0.42°C between the inversion layer and the underlying water. The inversion layer was approximately 4 m thick on average, with an upper boundary at a depth of 1–6 m and a lower boundary at a depth of 3–10 m. Different mechanisms and dynamic processes were responsible for temperature inversion in different parts of the study area. (1) At the salinity front in the west of the ZRE, the measurements collected by CTD (conductivity, temperature, and depth) showed that the low-salinity water mass on the inner side of the front was approximately 2°C cooler than the high-salinity water mass on the outer side. Temperature inversion occurred when the cooler low-salinity water overlapped the warmer high-salinity water near the front due to the driving force of the background flow. (2) Inversion layers occurred at the mouth of the Taiping waterway as a result of varying horizontal flow between two different water masses under the effects of tides and runoff. (3) To the southwest of Hong Kong, temperature inversion occurred due to the interaction of upwelling and the salinity front.

Effect of incorrect sound velocity on synthetic aperture sonar resolution

Synthetic aperture sonar (SAS) is an imaging technique to produce centimeter resolution over hundreds-of-meter range on the sea floor, by constructing a virtual aperture whose length automatically adjusts itself for a given focusing range. SAS is near-field acoustic imaging, and this implies that the sound velocity should be accurately estimated for well focused imaging. Otherwise there will be image quality loss. However, sound velocity in the ocean varies with space and time, and there might also be measuring error of CTD (Conductivity, Temperature, and Depth) sensor, so sound velocity error has become one of the limiting factors to improve SAS resolution further. To characterize the effect of sound velocity error quantificationally, the practice SAS resolution is mode as the convolution of ideal seafloor reflectivity function and a phase error function in frequency domain, where the phase error is caused by incorrect sound velocity. Then the SAS resolution parameterized is calculated as a function of the sound velocity measuring error, or sound velocity gradient. It is shown that SAS azimuthally (along track) resolution loss, caused by sound velocity measurement error, increases linearly with detection range. Meanwhile the loss caused by sound velocity gradient increases squarely. It is simulated by considering the synthetic aperture data collection for a particular pixel, and results show that the point scatter response will defocus when the sound velocity measuring error is up to 1% at 200m range, or the sound velocity changes up to 2% over a typical gradient at 200m range, and be worse at a longer range. Furthermore, we demonstrate the influence of sound velocity errors on SAS imagery using a sea trial data and real CTD measurements at South China Sea. We evaluate the degradation in image quality with respect to sound velocity errors by using two plastic balls and a variable seafloor scene, and results also support the accuracy of theoretical conclusions above.

Seasonally physical characteristics of ROFI zone (Region of Freshwater Influence) in Pelabuhan Ratu Bay

Coastal waters have many oceanographic phenomena are still being studied. One such phenomenon is how the influence of freshwater to the water mass in coastal waters. This study aims to calculate freshwater fraction, volume transport of freshwater and water mass stability. Physical water characteristics were measured by CTD (Conductivity, Temperature and Depth) deployed in 15 locations for temperature, salinity and density. The results of freshwater fraction analysis show that the west season had a greater on water fraction than the east season with value ranging from 0.40 % - 0.70 % with the amount 18.07 %, while the east season had a value of 0.02 % - 0.28 % with the amount is 7.30 %. The transport of freshwater volume in west season is 1.429.244 m3s-1 while in the east season it is 1.066 m3s-1. Water mass stability of water column in the research location has static stability with its average N2 in west and east monsoon are 0.008 cycl/s and 0.7 × 103 cycl/s, respectively. Those analyses above infer that freshwater input hugely influences physical water mass of ROFI zone in research location.