Pycnocline Layer Research Articles

A new method of estimating carbon sequestration and its efficiency in coastal waters

The biological pump (BP) in oceans refers to the fraction of phytoplankton organic matter sinking out of the euphotic zone (surface layer) into below the pycnocline layer (bottom layer) in the water column. Currently, sediment traps are commonly used to estimate organic settlement and carbon sequestration in open oceans, but the installation of the sediment traps in the ocean requires special efforts, let alone the temporal and spatial discordance of particle sinking trajectory from the surface to the bottom. Net community production is used only for the euphotic zone. Thus, there has been a lack of a simple method to estimate the export flux of organic carbon from the surface to bottom layer and to quantify BP efficiency in the coastal areas. In this study, we develop a conceptual model to illustrate carbon sequestration processes from the surface to the pycnocline layer and the bottom layer. The idea is to examine an increase (the release) in dissolved inorganic carbon (DIC) and organic carbon (DOC) in the bottom layer. Based on this model, a new method was developed to estimate carbon sequestration (CS) and carbon sequestration efficiency (CSE). Two cruises in May and August in 2016 were conducted to establish a three-end-member mixing model of θ-S which is used to estimate biologically mediated DIC (ΔDIC = DICin-situ-DICmixed) in relation to the conservative mixing of DIC. Based on the density gradient threshold of 0.03 kg m-3m-1, the water column is separated into the surface mixed layer, the pycnocline layer and bottom layer and integrated ΔDIC (IntΔDIC) in the three layers are estimated. The same approach is applied to dissolved organic carbon (DOC) data which are used to make the same calculation with the mixing model to obtain the sequestrated DOC mass in the bottom layer. Carbon uptake and carbon sequestration (CS) can be calculated as the integrated ΔDIC in the surface mixed layer and bottom layers, respectively. Carbon sequestration efficiency (CSE), which is defined as sum of bottom layer Int ΔDIC + Int ΔDOC divided by the whole water column integrated ΔDIC can also be calculated. The results showed that during algal blooms driven by abundant nutrients from the Pearl River Estuarine water in May, little sinking carbon was observed due to the absence of the bottom layer, resulting in low CSE. In contrast, in August, even no significant algal bloom occurred, the strengthened water stratification, lead to a substantial increase in the CS(449.49 ± 366.14 mmol C m-2), leading to an increased CSE to a range of 0 ∼ 92.79 % (average 60.55 ± 25.07 %). The carbon sequestration rate was 55.61 ± 45.30 mg C m-2 d-1. The new method, based on vertical changes of DIC and DOC due to biological uptake or release in relation to the conservative mixing of water masses, provides an easy and direct tool to estimate carbon sequestration and carbon sequestration efficiency in the stratified water column in coastal waters.

Observations of Near-Inertial Internal Waves over the Continental Slope in the Northeastern Black Sea

The article presents observations of near-inertial internal waves (NIWs) in the slope waters of the Black Sea in winter and summer. Rotary spectral analysis of a time series of sea current velocity measurements revealed the prevailing anticyclonic component of the motions near the local inertial frequency f. The clockwise rotation of the velocity vector with depth implies that the NIWs propagate downwards. The amplitude of NIWs usually was 0.1–0.2 m s−1. NIWs were observed in the layer of the permanent pycnocline and the seasonal pycnocline, which attenuate below depths of 160 m and 80 m in winter and summer, respectively. The amplitude of the near-inertial kinetic energy (NIKE) showed a close relationship with vertical stratification. During winter, NIKE exhibited maximum values in the layer of the permanent pycnocline, whereas, in summer, it was primarily observed in the seasonal pycnocline layer. The near-inertial oscillations were generally more energetic in winter.

Effects of water masses on the zooplankton community structure in the northern East China Sea during the East Asian Summer Monsoon in 2020

The prolonged rainy season in 2020 was classified as the second-largest rainfall event since 1961. In this study, we conducted a survey to assess fluctuations in the zooplankton community structure of the northern East China Sea (nECS) after the rainy season in August 2020. We examined 24 stations and observed several environmental factors, including water temperature, salinity, chlorophyll-a concentration, suspended particulate matter (SPM), and phytoplankton density. Zooplankton samples were collected from 12 stations using MOCNESS to target the surface mixed layer (SML), pycnocline layer (PNC), and lower layer (LL). In regions with low water temperatures, the Yellow Sea and northern East China Sea shelf mixed water community in each layer exhibited a decrease in the relative abundance of Calanus sinicus, whereas the incidence of Paracalanus parvus s. l. showed an increasing trend. Similarly, in areas with low salinity, the CDW and northern East China Sea shelf mixed water community in SML and PNC displayed comparable distributions, with a tendency for the relative abundance of Acartia pacifica and Paracalanus parvus s. l. to show a replacement pattern. Moreover, the Tsushima Warm Current (TWC) community in each layer, characterized by high water temperature and salinity, showed a high relative abundance of Oncaea spp. and a diverse species distribution, mainly in the eastern part of the study area. Our study identified multiple vertically distributed communities, providing detailed information on water mass structures through cluster analysis. This approach enhanced previous studies by offering novel insights into the vertical structure of water masses and their association with zooplankton communities in the nECS.

Subsurface oxygen minima regulated by remineralization and bottom flushing along 123°E in the inner East China Sea

The summer hypoxia off the Changjiang Estuary is one of the largest coastal hypoxic systems in the world and has displayed spatial heterogeneity in recent years. Based on observation data in the summer of 2014, hypoxia was identified both in the bottom and mid-layers. Except for the typical bottom hypoxia in the submarine canyon, the subsurface oxygen minima (SOM) were captured in the mid-layer of 10~15 m, with lower dissolved oxygen in the mid-layer than at the bottom (30–50 m). This SOM phenomenon was located in the lower boundary of the pycnocline and above the Taiwan warm current (TWC) and Kuroshio subsurface water (KSSW). Due to the southern expansion of Changjiang diluted water (CDW), a high phytoplankton biomass (the maximum chlorophyll a of 25 μg L−1, pH of 8.6, and DO of 11 mg L−1) band occupied the surface area along 123°E. By analyzing the 24-h continuous observation and high-resolution profile data, we revealed that the subsurface oxygen minima were predominantly controlled by remineralization and bottom-flushing effects. Fast local consumption occurred near the pycnocline layer, while the lateral transport of oxygen-rich ambient water replenished the bottom oxygen deficit from south to north. We summarize and contextualize three hot spots of hypoxia into a conceptual diagram and emphasize the influences of advection, mixing, and respiration on their location and severity. Overall, compared with the discussion about the low DO background of TWC/KSSW, this research highlights the flushing effects of TWC/KSSW that will reshape the hypoxia structure and alleviate the hypoxia severity in the south hypoxia area off the Changjiang Estuary.

Internal Solitary Waves in the White Sea: Hot-Spots, Structure, and Kinematics from Multi-Sensor Observations

A detailed picture of internal solitary waves (ISWs) in the White Sea is presented based on an analysis of historical spaceborne synthetic aperture radar (SAR) data and field measurements. The major hot-spot of ISW generation locates in the southwestern (SW) Gorlo Strait (GS), characterized by the presence of strong tides, complex topography, and two distinct fronts. Here, pronounced high-frequency isopycnal depressions of 5–8 m were regularly observed during flood and flood/ebb slackening. Other regions of pronounced ISW activity are found near Solovetsky Islands and in the northwestern Onega Bay. The spatial and kinematic properties of the observed ISWs are linked to water depth, with larger wave trains and higher propagation speeds being observed over the deep regions. Direct estimates of ISW propagation speeds from sequential and single SAR images agree well, while theoretical ones obtained using a two-layer model overestimate the observed values by 2–3 times. This is explained by the effective modulation of ISW propagation speed during the tidal cycle by background currents that are not accounted for in the model. Enhanced values of diapycnic diffusion coefficient in the pycnocline layer were registered near the frontal zones, where intense 14–17 m high ISWs were regularly observed.

The Relationship of the Spatial Structure of the Total Suspended Matter Concentration and Hydrological Parameters in the Northern Black Sea According to Contact Measurements

Here we describe the features of the horizontal and vertical distribution of total suspended matter in the northern part of the Black Sea and their relationships with the water temperature, salinity, and density fields measured at the identical grid during hydro-optical surveys from 2016 to 2020. The results show that the primary sources of increased total suspended matter concen trations in the northern part of the Black Sea are low-salinity and turbid waters of the Kerch Strait; runoffs of the Rioni, Enguri, and other rivers in the east of the survey area; together with freshened waters of the Dnieper, Dniester, and Danube runoff from the northwestern shelf. Higher turbidity was observed in the deep-water part of the sea, associated with the cyclonic gyres and meanders of the Rim Current effects. The total suspended matter vertical structure features an upper mixed layer, which usually coincides in thickness with the upper thermohaline upper mixed layer. Significant negative correlations were found for this layer comparing total suspended matter concentration versus temperature and salinity, while the correlation appears positive with density values. Below, a total suspended matter subsurface maximum was observed in the seasonal thermocline and pycnocline layer. The high turbidity layer appeared almost an order of magnitude thinner in the regions of maximum temperature gradients versus the areas where the temperature gradient was weak. A local total suspended matter minimum occurred below the cold intermediate core, corresponding to the main thermocline, halocline, and pycnocline layer. Beneath this minimum, there was a local increase of total suspended matter coinciding with the upper boundary of the hydrogen sulfide zone.

Shelf Seas Baroclinic Energy Loss: Pycnocline Mixing and Bottom Boundary Layer Dissipation

AbstractObservations of turbulent kinetic energy dissipation rate () from a range of historical shelf seas data sets are viewed from the perspective of their forcing and dissipation mechanisms: barotropic to baroclinic tidal energy conversion, and pycnocline and bottom boundary layer (BBL) dissipation. The observations are placed in their geographical context using a high resolution numerical model (NEMO AMM60) in order to compute relevant maps of the forcing (conversion). We analyze, in total, 18 shear microstructure surveys undertaken over a 17 year period from 1996 to 2013 on the North West European shelf, consisting of 3,717 vertical profiles of shear microstructure: 2,013 from free falling profilers and 1,704 from underwater gliders. A robust positive relationship is found between model‐derived barotropic to baroclinic conversion, and observed pycnocline integrated . A fitted power law relationship of approximately one‐third is found, giving a simple new parameterization. We discuss reasons for this apparent power law and where the “missing” dissipation may be occurring. We conclude that internal wave related dissipation in the bottom boundary layer provides a robust explanation and is consistent with a commonly used fine‐scale pycnocline dissipation parameterization.

Clarifying Water Column Respiration and Sedimentary Oxygen Respiration Under Oxygen Depletion Off the Changjiang Estuary and Adjacent East China Sea

The Changjiang Estuary and its adjacent East China Sea are among the largest coastal hypoxic sites in the world. The oxygen depletion in the near-bottom waters (e.g., meters above the seabed) off the Changjiang Estuary is caused by water column respiration (WCR) and sedimentary oxygen respiration (SOR). It is essential to quantify the contributions of WCR and SOR to total apparent oxygen utilization (AOU) to understand the occurrence of hypoxia off the Changjiang Estuary. In this work, we analyzed the δ18O and O2/Ar values of marine dissolved gas samples collected during a field investigation in July 2018. We observed that the δ18O values of dissolved oxygen in near-bottom waters ranged from 1.039 to 8.457‰ (vs. air), generally higher than those of surface waters (−5.366 to 2.336‰). For all the sub-pycnocline samples, the δ18O values were negatively related to O2 concentrations (r2 = 0.97), indicating apparent fractionation of δ18O during oxygen depletion in the water column. Based on two independent isotope fractionation models that quantified the isotopic distillation of dissolved oxygen concentration and its δ18O, the mean contributions of WCR and SOR to total near-bottom AOU were calculated as 53 and 47%, respectively. Beneath the pycnocline, the WCR contribution to the total AOU varied from 24 to 69%, and the SOR contribution varied from 31 to 76%. The pooled samples beneath both the pycnocline and upper mixed layer indicated that WCR contributions (%) to total AOU increased with increasing AOU (μmol/L), whereas SOR% – AOU had the reverse trend. We propose that the WCR% and SOR% contributions to the total AOU of the sub-pycnocline waters are dynamic, not stationary, with changes in ambient environmental factors. Under hypoxic conditions, we observed that up to 70% of the total AOU was contributed by WCR, indicating that WCR is the major oxygen consumption mechanism under hypoxia; that is, WCR plays a vital role in driving the dissolved oxygen to become hypoxic off the Changjiang Estuary.

Prediction of Dominant Ocean Parameters for Sustainable Marine Environment

Prediction of ocean parameters is the rising interest in ocean-related fields to perceive variations in climatic conditions. Most of the existing methods reveal that predictions involve a single parameter, namely Sea Surface Temperature (SST). This paper proposed a deep learning technique of Multi-Layer Perceptron (MLP) with Multi-Variant Convolutional (MVC) High Speed (HS) Long and short-Term Memory (HM-LSTM) model to predict the four essential parameters - temperature, pressure, salinity and density at three different Oceans -the Bay of Bengal, Arctic Ocean, and the Indian Ocean. The traditional method is limited to time sequence prediction without considering its spatial linkage. The horizontal and vertical parametric variations with spatial and temporal dependencies at 2000 m below the ocean is the observation considerations for the proposed prediction model. The ARGO provides the thermocline, pycnocline, and halocline layers data to perform the parameter prediction. Its results demonstrate the excellent overall accuracy, low Root Mean Square Error (RMSE), and low Mean Absolute Error (MAE) without any overfitting or underfitting compared to the current State-of-the-art. The forecasting of ocean weather helps conserve the ocean environment for human life in food security, developing the global economy, biomedical exploration, medicines, treatments, diagnostic analysis, and producing a significant passenger transport and tourism source.

Study of the formation of the Black Sea haline stratification from the numerical simulations

The excess of river runoff and precipitation over evaporation (positive freshwater balance) and the supply of the Marmara Sea highly saline waters through the Bosphorus is the cause of the sharp halocline in the 100-300 m layer and low vertical mixing in the permanent pycnocline layer, where the contribution salinity to the seawater density prevails compared to temperature. Such features of the Black Sea waters make the description of the process of formation of the haline stratification an actual and inexhausted problem. Investigating the patterns of the formation of the haline stratification in the Black Sea, a laboratory model of a rotating cylindrical cavity and a numerical model are proposed. Laboratory studies have shown that in a simple configuration, the buoyancy flux across the basin boundaries leads to the formation of a sharp pycnocline and the formation of a three-layer vertical structure of horizontal currents. Numerical experiments demonstrate that halocline is formed at a depth of 10-40 m. The haline stratification has been established with a pronounced halocline for about hundred years which later slowly evolved.

Regional'nye osobennosti raspredeleniya chastoty Vyaysyalya – Brenta v moryakh Laptevykh i Vostochno-Sibirskom

Purpose. The aim of the paper is to study buoyancy frequency in the Laptev and East Siberian seas and to assess correlation relations between the intra-year variability of the Vaisal – Brent frequency maximum and the climatic indices reflecting the atmosphere and hydrosphere state. Methods and Results. Based on the World Ocean Atlas 2013 for 1955–2012, the features of spatial and temporal variability of the buoyancy frequency distribution and its maximum depth in the Laptev and East Siberian seas are considered. It is found that the highest values of the Vaisal – Brent frequency are observed in the estuaries of the rivers Lena, Khatanga, Kolyma and Indigirka in summer where they attain 70–86 cycle/hour. In the deep-water northern areas of the seas under study, the majority of the water area is covered with ice throughout the whole year. As a consequence the surface layer of water is heated slightly and stability of stratification is much lower. The buoyancy frequency values in the seasonal pycnocline attain 24–46 cycle/hour. As a result of advection of the transformed Pacific waters in the northern and southeastern regions of the East Siberian Sea, on the depths 25–55 m observed is the layer of constant pycnocline where the Vaisal – Brent frequency values can mount to 21 cycles/hour. Correlation analysis is performed for the relations between the intra-annual variability of the Vaisal – Brent frequency maximum and the climatic indices (North Atlantic Oscillation, Arctic Oscillation, Pacific Decadal Oscillation, Gulf Stream North Wall) reflecting the atmosphere and hydrosphere state. It is shown that relationship between the buoyancy frequency maximum and the two latter indices is the most pronounced. Conclusions. The results of the carried out investigations show that the features of spatial-temporal variability of the buoyancy frequency distribution and its maximum depth in the Laptev and East Siberian seas are conditioned by the river discharge and also by advection in the Arctic region of the Atlantic and transformed Pacific waters inflowing from the adjacent basins.

Challenging Vertical Turbulence Mixing Schemes in a Tidally Energetic Environment: 1. 3‐D Shelf‐Sea Model Assessment

AbstractMixing in the ocean and shelf seas is critical for the vertical distribution of dynamically active properties, such as density and biogeochemical tracers. Eight different decadal simulations are used to assess the skill of vertical turbulent mixing schemes (TMS) in a 3‐D regional model of tidally active shelf seas. The TMS differ in the type of stability functions used and in the Ozmidov/Deardorff/Galperin limiter of the turbulence length scales. We review the dependence of the critical Richardson and Prandtl numbers to define the “diffusiveness” of the TMS. The skill in representing bias and variability of stratification profiles is assessed with five different metrics: surface and bottom temperatures and pycnocline depth, thickness, and strength. The assessment is made against hydrography from three data sets (28,000 profiles in total). Bottom and surface temperatures are found to be as sensitive to TMS choice as to horizontal resolution or heat flux formulation, as reported in other studies. All TMS underrepresent the pycnocline depth and benthic temperatures. This suggests physical processes are missing from the model, and these are discussed. Different TMSs show the best results for different metrics, and there is no outright winner. Simulations coupled with an ecosystem model show the choice of TMS strongly affects the ecosystem behavior: shifting the timing of peak chlorophyll by 1 month, showing regional chlorophyll differences of order 100%, and redistributing the production of chorophyll between the pycnocline and mixed layer.

Diagnosing the development of seasonal stratification using the potential energy anomaly in the North Pacific

Upper-ocean seasonal stratification (seasonal pycnocline and/or transition layer) is a ubiquitous feature and its vertical structure has large spatial variability. The density stratification regulates the stability of the upper ocean and thus can affect the oceanic response to atmospheric forcing and biogeochemical processes by modulating vertical mixing. In this study, we described the development of the seasonal stratification in terms of the stability of the water column, using the potential energy anomaly (PEA) as a metric based on Argo profiles. PEA budget analysis reveals that over most of the North Pacific, seasonal stratification develops under a vertical one-dimensional energy balance between an increase in PEA (i.e., a strengthening of the stratification) driven by atmospheric buoyancy forcing and a decrease in PEA associated with vertical mixing within the water column. Horizontal advection of PEA plays a significant role in the seasonal development of the stratification only in the regions of the western boundary current and equatorial current system south of 10°N. We find that, in addition to the total magnitude of the oceanic buoyancy gain, the balance between compositions of the atmospheric forcing (non-penetrating surface buoyancy forcing and penetrating radiative heating) is also important in explaining regional differences in the development of the seasonal stratification. The vertical diffusivity in the seasonal stratification estimated from the residual of the PEA budget is in the range from 5 × 10−5 m2 s−1 to 5 × 10−4 m2 s−1 and shows spatial and seasonal variability associated with local wind forcing.

Diel Vertical Variability of the Concentration of Chlorophyll a and Colored Dissolved Organic Matter in Possjet Bay, Sea of Japan

The vertical distribution of the concentration of chlorophyll a (Chl) and colored dissolved organic matter (CDOM), temperature (T), and salinity (S) were studied at two diel stations located at close coordinates and performed at a weekly interval and seven stations spaced 1 mi apart on hydrological section in the shelf zone of Possjet Bay (Sea of Japan) in the autumn of 2014. The Chl concentration was estimated from fluorescence intensity (FChl). In the surface layer of the diel stations, the Chl concentration varied within ± 10% of the mean value. In the water column, a negative correlation of FChl with T and a positive relationship of S with CDOM were established at both stations. At all stations, the maximum Chl concentration occurred under the seasonal pycnocline layer.

Upper vertical structures and mixed layer depth in the shelf of the northern South China Sea

Vertical structures of the water column, especially the surface mixed layer and the pycnocline layer, are important in the mediation of vertical transportation of oceanic matter, momentum, heat and salt. Field observations were conducted to investigate vertical structures and mixed layer depth (MLD) in the shelf sea of the northern South China Sea, where the Pearl River plume enters with distinct extents in different seasons. A total of six cruises were performed in spring, summer and autumn from 2006 to 2016. Four different types of vertical structures, A-α, A-β, B and C types, were identified in the upper water layer. The A-α type was characterized by a gradual increase in density with depth, while the A-β type was characterized by an increase in density in a very thin surface layer (<10 m) with a sub-layer of density uniformity. The B type was defined as an almost uniform layer over the surface water column. The C type was defined as an entirely uniform layer throughout the whole water column. Both the A-α and A-β types occurred in spring and summer. The B type appeared in all three seasons, and the C type mostly appeared in spring and autumn. The MLD was shallower in summer and deeper in autumn. The A-α type could change to the B type under strong wind energy. Two 24-h mooring surveys, one within the Pearl River plume and the other beyond the plume zone, were conducted to examine the MLD temporal variations. The A-α and B types prevailed in and beyond the plume zone, respectively. The A-α type resulted from the strong stratification formed by freshwater and sea water, while the B type was mainly induced by air-sea interface buoyancy fluxes. We proposed that the A-α type should be considered in studies of the mixing and transporting of matter, salt, heat and energy in all the global costal seas.

Vertical turbulent exchange features in the layer of seasonal pycnocline in the northwestern part of the Black Sea

On the basis of experimental physical field’s microstructure data in the upper stratified layers of the Black Sea, the annual variability of the vertical turbulent exchange coefficient in the seasonal thermocline is investigated. The data were collected during eight expedition periods in 2007 – 2017, and they cover the north-western part of the Black Sea. The studies were conducted in different hydrological seasons from April to November. The measurements were carried out by the probing complex “Sigma-1”, the evaluation of turbulence energy dissipation was made by velocity pulsation gradients. The desired coefficient of vertical turbulent diffusion was calculated on the basis of the obtained experimental estimates of energy dissipation by known Osborn’s relationship. The analysis of these measurements makes it possible to calculate and use the vertical turbulent diffusion coefficient dependence on stratification to evaluate the vertical fluxes of heat, salt and other dissolved chemical and biological substances in the studied Black Sea region.

Influence of a Vertical Shift in the Current Velocity during Propagation of Contaminated Water from an Underwater Outfall under Stratified Conditions

The features of the spatial structure of coastal water caused by the impact of a nonstationary deep source of waste under stratified conditions is studied using a numerical hydrothermal model. The task is solved for the case of contaminated water outfall in Golubaya Bay of the city of Sevastopol. It is found that the activity of the source is accompanied by a jet and a stream of contaminated water. The pycnocline layer is mostly polluted with the contaminated area reaching 0.3–0.5 km2. The increase in the vertical shift of the velocity of background current leads to the increase in the existing period of contaminated zones and displacement of the stream of waste water toward the free surface (the stream becomes more localized vertically). The fields of contamination, temperature, and salinity of water have a complex spatial structure.

Further evidence of diel vertical migration of copepods under Arctic sea ice during summer

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 592:283-289 (2018) - DOI: https://doi.org/10.3354/meps12484 NOTE Further evidence of diel vertical migration of copepods under Arctic sea ice during summer Hyoung Sul La1,*, Koji Shimada2, Eun Jin Yang1, Kyoung-Ho Cho1, Sun-Yong Ha1, Jinyoung Jung1, Jun-Oh Min3, Sung-Ho Kang1, Ho Kyung Ha4 1Korea Polar Research Institute, Incheon 21990, Korea 2Tokyo University of Marine Science and Technology, Tokyo 108-0075, Japan 3Hanyang University, Ansan 15588, Korea 4Inha University, Incheon 22212, Korea *Corresponding author: hsla@kopri.re.kr ABSTRACT: We examined diel vertical variability of acoustic backscatter under sea ice during the midnight sun season at high latitude in the Canada Basin of the Arctic Ocean. Acoustic backscatter demonstrated that the dominant Arctic copepods (Calanus hyperboreus) consistently performed a distinct diel vertical migration (DVM) synchronized with the solar radiation cycle. DVM was mainly observed between 2 distinctive pycnocline layers at 25 and 45 m above the subsurface chlorophyll maximum (SCM) within Pacific summer water. Picophytoplankton (<2 µm) were mainly distributed within the SCM layer, whereas diatoms (>20 µm) were above the SCM layer. This indicated that light variation is a potential trigger for the DVM of Arctic copepods under sea ice, whereas the vertical depth of occurrence was primarily controlled by water mass stratification and food. This vertical behavior is significant to understanding how Arctic copepods adjust to their habitats relative to sea ice, water masses, and food sources in the dynamic environmental changes in the Arctic Ocean. KEY WORDS: Arctic copepod · Diel vertical migration · Pycnocline · Subsurface chlorophyll maximum · Acoustic Doppler current profiler Full text in pdf format Supplementary material PreviousCite this article as: La HS, Shimada K, Yang EJ, Cho KH and others (2018) Further evidence of diel vertical migration of copepods under Arctic sea ice during summer. Mar Ecol Prog Ser 592:283-289. https://doi.org/10.3354/meps12484 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 592. Online publication date: March 29, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Structure and properties of the egg mass of the ommastrephid squid Todarodes pacificus.

The Japanese flying squid, Todarodes pacificus, is thought to spawn neutrally buoyant egg masses that retain a specific location in the water column by floating at the interface between water layers of slightly different densities. It is important to understand the physical process that determines the vertical distribution of the egg masses to predict their horizontal drift in relation to embryo survival and subsequent recruitment. Here, mesocosm experiments were conducted in a 300 m3 tank by creating a thermally stratified (17–22°C) water column to obtain egg masses. A cage net methodology was developed to sustain egg masses for detailed observation. We measured the density of the egg masses of T. pacificus, and used this information to infer the vertical distribution patterns of the egg masses at the spawning grounds (Tsushima Strait, Japan). When measured separately, the density of the outer jelly of each egg mass was 2.7 σ units higher than that of the surrounding water. The outer jelly and the specific gravity of embedded individual eggs (~1.10) cause the egg masses to have very slight negative buoyancy relative to the water in which they are formed. Analysis of the vertical profile of the spawning ground showed that water density (σθ) increased sharply at ~30 m depth; thus, egg masses might settle above the pycnocline layer. In conclusion, we suggest that T. pacificus egg masses might retain their location in the water column by floating at the interface between water layers of slightly different densities, which happen to be above the pycnocline layer (actual depth varies seasonally/annually) in the Tsushima Strait between Korea and Japan.

Effect of EPS volume fraction in buoyancy characteristics of expanded polystyrene/epoxy sandwich composites

In this study, the buoyancy characteristics of an expanded polystyrene spheres (EPS) embedded epoxy polymer based sandwich composites with aluminium skin are investigated. Composite which float at the pycnocline layers formulated by three fluids namely refined Helianthus annuus (sunflower) oil, brine solution and water are determined. Four composite samples EPS-22, EPS-29, EPS-36 and EPS-43 vol.% of EPS in the epoxy resin matrix core are fabricated by hand lay-up process. It is observed that the density of the composite is decreasing with increasing EPS volume fractions and the buoyant force acting on the samples at pycnocline layers are increased due to the density gradient. Results show that the sandwich composites with greater than EPS-36 and EPS-43 vol.% float in sunflower oil and composites having EPS-29 vol.% floats at the sunflower oil/fresh water pycnocline layer. Further, it is observed that composite with EPS-22 vol.% floats at the fresh/brine water pycnocline layer.