Intermediate Depths Research Articles

Nutriclines and nutrient stoichiometry in the eastern Arabian Sea: Intra-annual variations and controlling mechanisms

Repeat measurements (nine times) of nutrients at seven to ten coast-offshore transects along the eastern Arabian Sea (EAS) in 2018–19 revealed nitrogen as the major limiting nutrient controlling the primary production. The summer monsoon upwelling at varying extents along the EAS and the winter convection in the north EAS primarily controlled the depth of nitracline (DNO3 = depth of ≥ 3 µM NO3–). DNO3 was found positively aligned with the upper boundary of thermocline (depth of 26 °C isotherm or D26), with the strongest relationship in the south EAS (R2 = 0.96) due to its relatively stratified and stable conditions during most of the year compared to the north EAS (R2 = 0.71) which is unstable during winter convection. Mixed layer nutrient availability varied with DNO3/D26 and relatively faster nitrogen exhaustion than phosphorus during the nutrient enrichment events viz. upwelling and convective mixing yielded low N/P ratios. The N/P ratios of nutricline waters upwelled/entrained to the mixed layers were found significantly low (6–14), especially at the north EAS where perennial denitrifying zone persisted in the intermediate depths. With continued uptake of nutrients by the plankton following the Redfield ratio, the system during oligotrophic inter-monsoons became nitrogen-limited with surplus (excess) phosphate (P*), resulting in the lowest N/P ratios (1.5 ± 0.7) in the mixed layer. This stoichiometrically excess phosphate (P*) in the mixed layer waters was highest during nutrient enrichment events of both the summer and winter monsoons. The reduction in P* along with high cyanobacterial abundance (evident by increased zeaxanthin pigment concentrations) towards the late phase of summer monsoon and fall inter-monsoon indicates the dominance of diazotrophy. This diazotrophy after the nutrient enrichment seasons reduced the P* to almost half (0.22 ± 0.12 µM) which counter balance the N-limiting conditions to some extent in the EAS surface waters. The N-limiting condition can be severe in a global warming scenario, so more observations and extensive experiments are needed to ascertain the capability of diazotrophs to counteract the N-limiting situations by utilising the excess phosphate. The findings of this study are highly beneficial, as such an extensive year-long information on large spatio-temporal variability and their cause factors is available for the first time from the EAS basin, especially to improve the validation and forecasting of biogeochemical models under changing climate conditions. Comparison of present nutrient data with climatology data of World Ocean Atlas showed complete disagreement of silicate, which is an issue of major concern.

HyWaves: Hybrid downscaling of multimodal wave spectra to nearshore areas

Long-term and accurate wave hindcast databases are often required in different coastal engineering projects. The assessment of the nearshore wave climate is often accomplished by using downscaling techniques to translate offshore waves to coastal areas. However, dynamical downscaling approaches may incur huge computational cost. Additionally, the common use of bulk parameterizations are often not accurate for multidimensional waves. To overcome these limitations, we present a hybrid downscaling approach that combines mathematical algorithms (statistical downscaling) and numerical modeling (dynamical downscaling) over the individual spectral partitions. Every wave partition is downscaled and aggregated afterward by using principles of wave linear theory. By assuming linearity in the propagation of the wave celerity, the application of the method is limited from offshore to intermediate water depths. In addition, the method proposed uses a technique to simplify the spectral boundary conditions in complex domains. The methodology has been applied and validated in the island states of Samoa, American Samoa, Majuro, and Kwajalein, showing good skill at reproducing the spectral hourly time series of significant wave height, peak period, and peak direction. Moreover, an accurate representation of the observed energy spectrum was achieved. This study provides insight into the numerical approximation of the combined sea-swell states while improving the quality of fast spectral forecasting and early warning systems.

Oxygen and hydrogen isotopic evidence that Kamaʻehuakanaloa (Lōʻihi) Seamount hydrothermal systems are recharged by deep Pacific seawater

We observed negative and positive δ18O and δ2H deviations from fluids collected at Kamaʻehuakanaloa (previously known as Lōʻihi) seamount relative to Pacific seawater from the same depth. Hydrothermal vents on the crater floor of Pele's Pit at Kamaʻehuakanaloa, at a depth of 1320 m, had δ18O and δ2H values as low as −0.19‰ and −0.3‰, respectively. Seawater collected within the caldera, within a zone 45 m above the crater floor, had δ18O and δ2H values as high as 1.15‰ and 6.5‰, respectively. In comparison, Pacific seawater at 1200 m and 1400 m at nearby station ALOHA exhibit intermediate δ18O and δ2H values of 0.2‰ and 0.34‰. The high δ18O and δ2H values observed in the caldera water-column may be explained by isotopic modification processes, including water-rock reactions. However, we did not observe a vent source with similar isotopic composition; this suggests that substantial hydrothermal flow is entering the caldera through unidentified sources, potentially individually small but collectively important. Further, the low δ18O and δ2H values of the crater floor vents cannot be readily explained by isotopic modification processes alone. We conclude the crater floor vents predominantly reflect the isotopic composition of the Pacific seawater entrained into the hydrothermal system. Our observations suggest recharging seawater is entrained from below >4500 m, in the zone of Pacific Bottom Water. These findings illustrate the heterogeneity of hydrothermal transport processes at a volcanic seamount and how seamount hydrothermal convection can provide a mechanism that may contribute to vertical ocean mixing by transporting deep bottom waters to intermediate ocean depths.

Maximizing sampling efficiency to detect differences in fish community composition using environmental DNA metabarcoding in subarctic fjords

AbstractEnvironmental DNA (eDNA) has gained popularity as a tool for ecosystem biomonitoring and biodiversity assessment. Although much progress has been made regarding laboratory and fieldwork protocols, the issue of sampling efficiency requires further investigation, particularly in three‐dimensional marine systems. This study focuses on fish community composition in marine ecosystems and aims to analyze the efficiency of sampling design given the sampling effort for distinguishing between different communities. We sampled three fjords in Northern Norway, taking samples along fjord transects and at three different depths, and amplified a fragment of the mitochondrial 12S rRNA gene of bony fishes using the MiFish primers. We evaluated the effect of (i) the number of sampling stations, (ii) samples' spatial distribution, and (iii) the data treatment approach (presence/absence versus semiquantitative) for maximizing the efficiency of eDNA metabarcoding sampling when inferring differences of fish community compositions between fjords. We found that the manner of data treatment strongly affected the minimum number of sampling stations required to detect differences among communities; because the semiquantitative approach retained some information about abundance of the underlying reads, it was the most efficient. Furthermore, we found little‐to‐no difference of fish communities in samples from intermediate depths when comparing vertical fish communities. Lastly, we found that the differences between fish communities at the surface were the highest across the horizontal distance and overall, samples ~30 km apart showed the highest variation in the horizontal distribution. Boosting sampling efficiency (reducing sampling effort without compromising ecological inferences) can significantly contribute to enhanced biodiversity management and efficient biomonitoring plans.

Horizontal and Vertical Distribution of Perfluoroalkyl Acids (PFAAs) in the Water Column of the Atlantic Ocean.

Perfluoroalkyl acids (PFAAs) are widely distributed in the oceans which are their largest global reservoir, but knowledge is limited about their vertical distribution and fate. This study measured the concentrations of PFAAs (perfluoroalkyl carboxylic acids (PFCAs) with 6 to 11 carbons and perfluoroalkanesulfonic acids (PFSAs) with 6 and 8 carbons) in the surface and deep ocean. Seawater depth profiles from the surface to a 5000 m depth at 28 sampling stations were collected in the Atlantic Ocean from ∼50° N to ∼50° S. The results demonstrated PFAA input from the Mediterranean Sea and the English Channel. Elevated PFAA concentrations were observed at the eastern edge of the Northern Atlantic Subtropical Gyre, suggesting that persistent contaminants may accumulate in ocean gyres. The median ΣPFAA surface concentration in the Northern Hemisphere (n = 17) was 105 pg L-1, while for the Southern Hemisphere (n = 11) it was 28 pg L-1. Generally, PFAA concentrations decreased with increasing distance to the coast and increasing depth. The C6-C9 PFCAs and C6 and C8 PFSAs dominated in surface waters, while longer-chain PFAAs (C10-C11 PFCAs) peaked at intermediate depths (500-1500 m). This profile may be explained by stronger sedimentation of longer-chain PFAAs, as they sorb more strongly to particulate organic matter.

Assesment of the risk of degazation of the Black Sea: type of limnological disaster on lake Nyos reconsidered

The possibility of a repetition of the limnological catastrophe in the Black Sea is considered. It is shown that, in contrast to the volcanic lakes of Africa Nyos and Manun, where limnological catastrophes occurred in the 1980s, the concentration of dissolved gases in deep waters is significantly less than the saturation value. This eliminates the mechanism of so called “eruption” of carbon dioxide such as gas lift. However, on a smaller scale, significant methane releases are possible during strong eruptions of underwater mud volcanoes. The mechanism for the release of carbon dioxide from the lake into the atmosphere is so similar to a volcanic eruption that mathematical models developed for ordinary volcanoes are used to describe it. In both cases, the rise of erupted masses occurs due to an increase in the buoyancy of the gas-liquid mixture, which carries with it particles of the environment. The formation and growth of gas bubbles at intermediate depths occurs provided that the total partial pressure of all gases inside the bubble exceeds the hydrostatic pressure at a given depth. The article shows that the concentration of dissolved methane in the Black Sea is much less than the saturation level. Due to the relatively low solubility of methane in water, methane bubbles are able to overcome a significant depth range. And as additional components of the gas mixture, together with methane, carbon dioxide and hydrogen sulfide can thus enter the atmosphere. It was concluded that as the water temperature in the Black Sea increases due to climate change, the reserves of methane gas hydrate at the bottom of the sea will begin to decompose, which will also be accompanied by jet gas release. At the same time, methane can escape to the surface from depths of no more than 900 m.

Exploring the Geological Formation and Sub-Surface Lithology Modelling of Hadejia, Jigawa State Nigeria

This research aims to explore the geological formation and sub-surface lithology modelling of Hadejia, Jigawa State using the VES (vertical electrical sounding) method. The VES method is a geophysical technique that measures the electrical resistivity of the subsurface, which is related to the lithology of the rock units. The study area is located in the north-western part of Nigeria, on latitudes 12025’23.73‘‘N and longitudes 10°04’06.74‘‘E, and is characterized by a chad formation geological setting with a variety of rock units, including sandstones, shales, and limestone. The research was conducted using a total of 50 VES stations, which were distributed over the study area in a grid pattern. The data collected from the VES stations were analyzed using the IPI2WIN software. The results were used to create a subsurface electrical resistivity model, which was then used to infer the lithology units present in the subsurface. The results showed that the study area is characterized by a complex subsurface structure, with several rock units present, including sandstones, silt, and clay. The subsurface electrical resistivity model revealed that the sandstone units are located at shallow depths, while the silt units are found at deeper depths. The clay is present at intermediate depths and is interbedded with sandstones and clay. The results provide valuable information for hydro-geological and mineral exploration in the area.

A novel tool for predicting the dose distribution of non-sealed 188 Re (Rhenium) resin in non-melanoma skin cancers (NMSC) patients.

High-dose rate brachytherapy using a non-sealed 188 Rhenium resin (188 Re) is a recently approved treatment option for non-melanoma skin cancer (NMSC). The treatment goal is to deliver a personalized absorbed dose to the deepest point of neoplastic infiltration corresponding to the minimal target dose. The treatment consists of the application of a 188 Re-based resin over a plastic foil placed on the target skin surface. However, there is no treatment planning tool to assess the 188 Re activity needed for a personalized treatment. The paper aims to present a novel Monte Carlo (MC)-based tool for 188 Re-based resin activity and dose calculation, experimentally validated using Gafchromic EBT3 films. MC simulations were carried out using FLUKA modeling density and composition of 188 Re resin. The MC-based look up table (LUT) was incorporated in an ad hoc developed tool. The proposed tool allows the personalized calculation of treatment parameters (i.e., activity to be dispensed, the treatment duration, and dose volume histograms), according to the target dimension. The proposed tool was compared using Bland-Altman analysis to the previous calculation approaches conducted using VARSKIN in a retrospective cohort of 76 patients. The tool was validated in ad hoc experimental set ups using a stack of calibrated Gafchromic EBT3 films covered by a plastic film and exposed using a homogenous activity distribution of 188 Re eluate and a heterogeneous activity distribution of 188 Re resin mimic the patient treatment. The agreement between the proposed tool and VARSKIN was evaluated on the investigated cohort with median range of target area, target depth, and treatment time equal to 4.8 [1.0-60.1]cm2 , 1.1 [0.2-3.0]mm, and 70 [21-285]min, with a median range of target dose (Gy) of 23.5 [10-54.9]. The calculated minimal target doses, ranged from 1% to 10% for intermediate target depths (1.2±0.7mm), while showing significant differences in the estimation of superficial (maximal) target doses. The agreement between MC calculation and measurements at different plans in a stack of Gafchromic EBT3 films was within 10% for both the homogenous and heterogeneous activity distribution of 188 Re. Worst agreements were observed for absorbed doses lower than 0.3Gy. Our results support the implementation of our MC-based tool in the practical routine for calculating the 188 Re resin activity and treatment parameters necessary for obtaining the prescribed minimal target dose.

Divergence in Climate Model Projections of Future Arctic Atlantification

Abstract The Arctic Ocean is strongly stratified by salinity in the uppermost layers. This stratification is a key attribute of the region as it acts as an effective barrier for the vertical exchanges of Atlantic Water heat, nutrients, and CO2 between intermediate depths and the surface of the Eurasian and Amerasian basins (EB and AB, respectively). Observations show that from 1970 to 2017, the stratification in the AB has strengthened, whereas, in parts of the EB, the stratification has weakened. The strengthening in the AB is linked to freshening and deepening of the halocline. In the EB, the weakened stratification is associated with salinification and shoaling of the halocline (Atlantification). Simulations from a suite of CMIP6 models project that, under a strong greenhouse gas forcing scenario (ssp585), the overall surface freshening and warming continue in both basins, but there is a divergence in hydrographic trends in certain regions. Within the AB, there is agreement among the models that the upper layers will become more stratified. However, within the EB, models diverge regarding future stratification. This is due to different balances between trends at the surface and trends at depth, related to Fram Strait fluxes. The divergence affects projections of the future state of Arctic sea ice, as models with the strongest Atlantification project the strongest decline in sea ice volume in the EB. From these simulations, one could conclude that Atlantification will not spread eastward into the AB; however, models must be improved to simulate changes in a more intricately stratified EB correctly.

Enlarged rete pegs with excessive accumulation of melanosomes leading to darker aging spots revealed by histomorphological measurements of internal structures of the epidermis.

Various histological studies of facial pigmented spot sites such as solar lentigo have been reported, but few studies have used quantitative indices by histomorphometric analysis of the internal structure of pigmented spot sites using non-invasive methods. In the present study, to quantitatively elucidate morphological changes in the epidermis in male, darker-pigmented spots and female, light-pigmented spots, indices that characterize the internal structure of the epidermis in pigmented spot sites were measured using in vivo confocal laser scanning microscopy (CLSM). The darkness of pigmented spots on the cheeks of 69 women and 43 men was analysed using image analysis software. The L* value was calculated from RGB values obtained from facial images. The internal structures of pigmented spots on the cheeks of 13 subjects were observed by CLSM. Various parameters were measured using CLSM images from the surface of the stratum corneum to the bottom of the dermal papillae, including the thickness of the epidermis, melanosome content, and shape of the dermal papillae. Mean ΔL* values between pigmented spots and non-pigmented areas of male subjects were significantly increased in the 40s and 50s compared with those of female subjects. Conspicuous pigmented spots increased in the 40s in male subjects and the 50s in female subjects. In CLSM observations, significant increases in the thickness of the epidermis and melanosome content were confirmed in pigmented spots compared with surrounding non-pigmented areas. In particular, melanosome content in the male subject group with dark-coloured pigmented spots increased significantly to about eight times that of non-pigmented areas, and more than double that of the male subject group with light-coloured pigmented spots. From the measurements of quantitative parameters, morphological changes in the epidermis were clearly related to the surface colour tone of pigmented spots. Darker pigmented spot sites tended to show longer rete pegs in the epidermis. Accumulation of melanosomes in epidermal basal cells could be considered to increase with the degree of elongation of rete pegs at pigmented spot sites and, thus, induce darker pigmented spots.

Temporal Variability of the Labrador Current Pathways Around the Tail of the Grand Banks at Intermediate Depths in a High‐Resolution Ocean Circulation Model

AbstractThe Northwest Atlantic Shelf and Slope have warmed dramatically in the past decade, changing marine life and challenging fisheries management. A rapid warming event in 2009/2010, linked to a reduced supply of cold water from the Labrador Sea, pushed this region to a new state of unprecedentedly high temperatures that persists today. However, a mechanistic understanding of how the Labrador Current connectivity is reduced at the Tail of the Grand Banks of Newfoundland has been lacking. Here, we present the results of a 25‐year (1993–2017) Lagrangian analysis using the HYbrid Coordinate Ocean Model. Synthetic particles were released in the vicinity of the Labrador Current upstream of the Grand Banks and tracked in a 2‐D velocity field. We found that the Labrador Current can be completely blocked by Gulf Stream eddies and meanders that impinge on the shelf break along the Grand Banks. This blocking can occur in many different locations at, upstream, or downstream of the Tail of the Grand Banks, since the Labrador Current needs a clear passage over a long distance to continue its path. In the simulation, the Labrador Current has been blocked more often since 2008, which led to the warming of the Northwest Atlantic Shelf and Slope. These results, which are consistent with satellite observations, can provide predictability for the New England and Nova Scotia shelf environments potentially helpful for ecosystem management.

Column-based cortical depth analysis of the diffusion anisotropy and radiality in submillimeter whole-brain diffusion tensor imaging of the human cortical gray matter in vivo

High-resolution diffusion tensor imaging (DTI) can noninvasively probe the microstructure of cortical gray matter in vivo. In this study, 0.9-mm isotropic whole-brain DTI data were acquired in healthy subjects with an efficient multi-band multi-shot echo-planar imaging sequence. A column-based analysis that samples the fractional anisotropy (FA) and radiality index (RI) along radially oriented cortical columns was then performed to quantitatively analyze the FA and RI dependence on the cortical depth, cortical region, cortical curvature, and cortical thickness across the whole brain, which has not been simultaneously and systematically investigated in previous studies. The results showed characteristic FA and RI vs. cortical depth profiles, with an FA local maximum and minimum (or two inflection points) and a single RI maximum at intermediate cortical depths in most cortical regions, except for the postcentral gyrus where no FA peaks and a lower RI were observed. These results were consistent between repeated scans from the same subjects and across different subjects. They were also dependent on the cortical curvature and cortical thickness in that the characteristic FA and RI peaks were more pronounced i) at the banks than at the crown of gyri or at the fundus of sulci and ii) as the cortical thickness increases. This methodology can help characterize variations in microstructure along the cortical depth and across the whole brain in vivo, potentially providing quantitative biomarkers for neurological disorders.

The 2013 Slab‐Wide Kamchatka Earthquake Sequence

AbstractStudies of initiation of large earthquakes are usually focused on frictional instabilities occurring in the near vicinity of the future rupture. Possible contributions of long‐distance interactions with large‐scale tectonic instabilities remain unknown. Here we analyze seismic catalogs and geodetic time series during a few months preceding the 2013 M = 8.3 deep‐focus Okhotsk earthquake. This deep‐focus event is preceded by four intense seismic clusters in the seismogenic zone. GNSS time series in Kamchatka revealed a transient landward motion episode 1 month prior to the mainshock, consistent with an increase of seismogenic zone loading. This transient loading episode is accompanied by a doubling of the intermediate depth seismicity rate suggesting a transient slab pull as the origin. These observations question the constant subducting velocity hypotheses and may have implications in the understanding of the long‐distance along‐slab stress interactions and in their contribution to initiation of large deep‐focus earthquakes.

Beyond Stevin’s law: the Janssen effect

We give a detailed derivation of the equation describing the height distribution of the vertical pressure in both cylindrical and conical vessels filled with granular material. It is surprising that for a convergent hopper, the vertical pressure can reach a maximum at some intermediate depth (the enhanced Janssen effect). The consideration of this problem will be useful for undergraduates, who study the statics of heterogeneous media.

Hydrodynamic responses of a reversed L type floating breakwater integrated with a wave energy converter impacted by extreme waves

This research studies the hydrodynamic responses of a reversed L type floating breakwater integrated with a wave energy converter moored by a vertical pile in extreme sea states and intermediate water depth in a numerical wave tank based Navier-Stokes equations. Three wave-type representations (solitary, regular, and focus waves) of the same wave state are considered. The surface wave elevation, heave motion, wave force, impulse, wave moment on the mooring pile, moment of impulse, pressure distribution and flow field are investigated and compared. The comparison shows that different waves yield to diverse peak hydrodynamic responses. Largest wave force and moment are found in the regular wave condition, while largest heave motion, impulse and moment of impulse are obtained for the solitary wave. The pressure distribution on the bottom of the floater under the solitary wave shows a distinct character from the two others. The effect of the PTO damping parameter with the focus on the maximum wave force and moment is discussed and it is revealed that there exists an optimal PTO damping force for which the minimum wave force on the floater is obtained. This study therefore gains an insight into the hydrodynamic responses under different extreme waves.

Shear wave velocity estimation in the Bengal Basin, Bangladesh by HVSR analysis: implications for engineering bedrock depth

The S-wave velocity (VS) in the Bengal Basin, Bangladesh has not been resolved from the ground surface to an intermediate depth in a regional context despite its importance for seismic hazard and risk evaluation. For this reason, we estimated VS profiles beneath 19 seismic stations in Bangladesh to a depth approximately 2800 m by employing full horizontal to vertical spectral ratio (HVSR) curve inversion under the diffuse field theory for the noise wavefield. The seismic stations are concentrated in three tectonic zones within the basin: the Surma basin (SB, Zone 1), Bengal Foredeep (BF, Zone 2), and Chittagong Tripura Fold Belt (CTFB, Zone 3). Full HVSR analysis (from 0.2 to 10 Hz) allowed us to obtain deep profiles with combined insights from shallow geotechnical boreholes and deep P-wave velocity (VP) information from active seismic surveys. From the resultant VS profiles, engineering bedrock (VS > 760 m/s) depths were also identified throughout the study area for the first time. The VS profiles within the Holocene to Miocene sedimentary sequences showed rapid variations from location to location. This is due to the highly variable near-surface geology caused by the dense and complex river network and tectonic deformation in Bangladesh. Except for three stations, the engineering bedrock depth exceeded 30 m at all stations. These results indicate the existence of deep soft soil in the study area, where VS30 based site characterization is inappropriate. Furthermore, seismic site response was estimated at a station (DHAK) by simulating a subduction zone earthquake. The resulting response spectrum (RS) exhibited ground motion amplification over a longer period, suggesting that multistory buildings at the site may be at risk if subjected to large earthquakes. The outcomes of this study can serve as useful guidelines for seismic risk reduction planning in Bangladesh.

Advances in the modeling of the Iberian thermal lithosphere and perspectives on deep geothermal studies

Renewable energy sources are key to achieve the transition toward clean energy system. Among them, the geothermal energy has a production whose effectiveness requires sufficient understanding of the temperature distribution and fluid circulation at depth, as well as of the lithological and petrophysical properties of the crust. The focus of this paper is twofold: first, we summarize the main advances in the development of new methodologies and numerical codes to characterize the properties of the thermal lithosphere in terms of its, temperature, density and composition; second, based on the compilation of available thermal modelling results, we present the depth of the thermal Lithosphere–Asthenosphere Boundary (LAB) of the Iberian Peninsula and the temperature distribution at crustal depths of 5, 10, and 20 km, in addition to at Moho level. At 5 km depth, the temperature is above 110 °C with local anomalies (> 130 °C) located in the Iberian Massif and Cenozoic volcanic provinces. A similar pattern is observed at 10 and 20 km depth, where temperatures are above 190 °C and 350 °C, respectively. At 20 km depth, anomalies above > 500 °C, delineate the SE and NE Cenozoic volcanic provinces. At Moho depths, temperature ranges from 450 to 800 °C with hot regions mainly located along the Iberian Massif and the SE and NE volcanic provinces. The compiled results do not show any lithospheric anomaly that could give rise to high temperatures at shallow depths, but they do show an acceptable exploitation potential at intermediate depths. With regard to the direct use of district and greenhouse heating and for industrial processes, the potential is great throughout the Peninsula, the main challenges being the availability of groundwater and drilling costs.

Impact pressure distribution and characteristics of breaking wave impact on a monopile

A laboratory model study is performed to investigate the characteristics of wave impact pressures on a monopile substructure for offshore wind turbines subjected to breaking waves in intermediate water depth. Laboratory experiments are conducted in a 30m long, 2m wide and 1.8m deep wave flume. Breaking wave was generated by focusing the wave energy from a wave group at a pre-defined time and space in the laboratory flume. High-resolution impact measurements are carried out in a well-controlled wave flume for different wave loading conditions of varying incident wave steepness and wave impact conditions. The evolution of local wave characteristics and geometric properties of breaking waves is investigated along the wave flume. The sensitivity of the vertical distribution and the variation of peak pressures to small changes in time and spatial scale is assessed during the impact. During the breaking wave interaction with a monopile, the wave impact characteristics such as pressure rise time, duration of impact, maximum pressure, and pressure impulse are analyzed. The measured geometric properties and impact characteristics are in good agreement with previous studies. The impact region and its correlation with wave characteristics and geometric properties are evaluated and discussed.

Effectiveness of Venting and Recompression for Increasing Postrelease Survival of Barotraumatized Black Sea Bass across a Range of Depths

AbstractThe effectiveness of venting and recompression for increasing postrelease survival for fish that experience barotrauma has rarely been tested across a range of depths. We conducted a field tag–recapture experiment to test how well venting and recompression each increased postrelease survival of Black Sea Bass Centropristis striata relative to untreated controls at three different depth ranges on the U.S. South Atlantic continental shelf: 24–26, 29–32, and 35–38 m. Venting and recompression were applied by researchers alongside untreated controls at all three depths, and venting by anglers who were inexperienced with this technique was an additional treatment at the intermediate depth. Tests of independence were used to evaluate the association between treatment type (venting versus controls) and postrelease submergence at each depth. Cox proportional hazards models were fit to the tag–recapture data that were collected at each depth to determine whether the experimental treatment influenced postrelease survival. Postrelease submergence was significantly higher in vented fish at the intermediate and deep depths but not at the shallow depth. The hazards rates were not significant for venting and recompression at the shallow and intermediate depths but were at the deepest depth, demonstrating that these techniques practiced at >35 m increased postrelease survival relative to untreated controls. Mean increases in absolute survival at the 35–38 m depth were calculated to be 6.8% and 8.1% relative to controls when using venting and recompression, respectively. The results further suggest that anglers who are unfamiliar with venting do not reduce postrelease survival compared with venting by experienced personnel. These results provide guidance to fishery managers who are tasked with seeking methods to reduce catch‐and‐release mortality for an important reef species. Taken together, the findings from submergence success and survival models suggest that both venting and recompression should be encouraged to increase the postrelease survival of Black Sea Bass that are caught from depths >29 m.

High‐Resolution, Basin‐Scale Simulations Reveal the Impact of Intermediate Zonal Jets on the Atlantic Oxygen Minimum Zones

AbstractEastward zonal jets at intermediate depths of 300–800 m connect the oxygen‐rich western boundary of the Atlantic basin with the oxygen minimum zones (OMZs) on the eastern boundary. They are not well represented in climate models because the low horizontal resolution of these models yields excessive viscosity. We use two physical‐biogeochemical model configurations of the Tropical Atlantic to show that the increase in resolution results in more robust intermediate zonal jets and a better representation of the OMZs. The OMZ structure is distorted at low‐resolution as surface, westward jets advect low‐oxygen waters from the eastern boundary much further west than in the climatology. The emergence of robust eastward jets in the high‐resolution run alleviate this problem and reproduce the Atlantic OMZs more accurately. The asymmetry between westward and eastward jets occurs because the former are associated with homogenous potential vorticity regions originating in the eastern boundary while the latter are associated with potential vorticity gradients. Intermediate, eastward jets constrain the westward expansion of the OMZs by supplying oxygen to their western edge. Within the OMZs, higher resolution allows a better representation of the boundary current system and eddying processes at depth which redistribute of low oxygen values from the productive eastern boundary. Basin‐scale, high‐resolution simulations reproduce more accurately the transfer of energy across scales that results in robust zonal jets as well as their impact on the ocean biogeochemistry. Accurate model predictions provide a pathway to disentangle natural and anthropogenic causes of ocean deoxygenation.