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Male sperm whales (Physeter macrocephalus) are known to interact with and depredate from commercial longline fishing vessels targeting sablefish (Anoplopoma fimbria) in the Gulf of Alaska (GOA). This study aims to better understand their movement patterns and diving behavior in this region, and in relation to depredation behavior. Between 2007 and 2016 a total of 33 satellite tags were deployed on sperm whales interacting with fishing vessels in the eastern GOA. A subset of these tags also collected dive characteristics. We used state space models to interpolate hourly positions from tags and estimate behavioral state from 29 usable tag records, 14 of which had associated dive information. Whales exhibited slower horizontal movement (1.4 km/hr) within GOA waters compared to south of the GOA (5.5 km/hr), indicating tagged whales sped up when they left the region. Behavioral states indicated primarily foraging behavior (82% of locations) in the GOA and primarily transiting behavior (74% of locations) when whales left the GOA. Dive data showed average (± Standard Deviation) maximum dive depths of 396 m (± 166), and dive durations of 32 min (± 9). Generalized additive models indicated that dives were significantly deeper and longer during the daytime than dawn, dusk, or nighttime, and dives were significantly deeper and shorter during quarter moons, when tidal currents are weakest. Maximum dive depth decreased in areas of higher sablefish CPUE, suggesting a potential link between the sablefish fishery and depredation behavior. As seafloor depth increased, up to 800 m, dives became deeper, indicating that whales were likely targeting both bathypelagic and mesopelagic prey. This highlights the importance of the GOA continental slope as a foraging ground for male sperm whales. This enhanced understanding of sperm whale foraging ecology informs management and conservation efforts in high latitude foraging grounds. [ABSTRACT FROM AUTHOR]

Wave- and current-supported fluid mud on gently sloped continental shelves represents a type of sediment gravity flow capable of rapidly transporting substantial sediment over short periods, significantly contributing to coastal geomorphic evolution. To investigate the dynamics of intertidal fluid mud events, in-situ observations were conducted from May 9 to May 18, 2017, using a seabed tripod system at the lower intertidal flat of the central Jiangsu coast, China. Fluid mud was observed following a medium wind-wave event, with a maximum significant wave height of 0.42 m. The liquefied seabed, loosened by liquefaction, facilitated bed erosion and sediment resuspension. Fluid mud layers, with mean suspended sediment concentrations (SSCs) exceeding 10 g/L, periodically formed during high slack tide, early flood, and late ebb phases. These layers varied in thickness from 4 cm to 20 cm and exhibited strong stratification caused by suspended sediment. Fluid mud disappeared when the bottom turbulence kinetic energy exceeded a threshold of 0.00045 m2/s2 due to an increase in current velocity. The downslope movement of intertidal fluid mud was estimated using a theoretical buoyancy-friction model and validated by observed offshore-directed velocity jets at 0.1 m above the seabed during high slack tide phases. Additionally, onshore winds favored fluid mud formation during early flood phases, while offshore winds favored it during late ebb phases. These observations suggest that fluid mud can form on intertidal flats under conditions where tidal flows and winds align, contributing to a deeper understanding of the formation mechanisms of shallow gravity flows and the improvement of sediment transport models. [ABSTRACT FROM AUTHOR]

The solution from linear theory for the barotropic-to-baroclinic tidal energy conversion into vertical modes is validated with numerical simulations and analytical results. The main result is the translation of the traditional critical slope condition into a modewise condition on the topographic height only. Our findings are then used for estimates of the global M2 tidal conversion into the first 10 vertical modes in the open ocean (excluding the continental shelves and slopes). We observe a rapid increase with mode number of the fraction of the World Ocean where linear theory is invalid. In terms of conversion, which is highly variable in space, this corresponds to an even more rapid increase with mode number of the fraction of the converted energy that is strongly affected by nonlinear effects. Out of the 373.6 GW of the globally integrated conversion into modes 1–10, only 241.7 GW occur in locations where linear theory is valid. While it represents 95% for mode 1, this fraction rapidly drops with mode number to reach 27% for mode 10. Moreover, for the conversion into a single mode, we show that capping the linear solution at supercritical topography is inappropriate. Hence, linear theory appears unfit to directly quantify the role played by high-mode internal tides in the internal wave energy budget. [ABSTRACT FROM AUTHOR]

The 2016 Mw 7.8 Kaikōura Earthquake triggered simultaneous turbidity currents down ten submarine canyons along a 200 km stretch of the continental slope, east of New Zealand. Some discharged into the Hikurangi Channel which flows >1500 km northwards along the abyssal trench floor. To better understand provenance continuity in deep-sea sedimentary records, foraminiferal samples from the 2016 turbidites from 17 canyon and channel cores were used to investigate the source histories of these submarine gravity flows. Cluster analyses suggest the canyon provenances for most 2016 turbidite faunas should be determinable using a combination of the relative abundance of key benthic genera, planktic foraminiferal index (dissolution), absolute test abundance and planktic % of the foraminiferal faunas. Two ordinations (PCA, PCO) based on these parameters were used to infer provenance and flow history. One hundred kilometres down the Hikurangi Channel, faunas in the 2016 turbidite confirm a Kaikōura Canyon source. Further downstream, 200–500 km north of the confluence with Campbell, Cook and Opouawe canyons, faunas indicate that the 2016 turbidite in the northern Hikurangi Channel is a composite deposit, from an initial Opouawe-Cook canyon-sourced turbidity current over-ridden and partly mixed with, a Kaikōura Canyon-sourced flow that arrived sometime later. [ABSTRACT FROM AUTHOR]

Glacio-eustatic cycles lead to changes in sedimentation on all types of continental margins. There is, however, a paucity of sedimentation rate data over eustatic sea-level cycles in active subduction zones. During International Ocean Discovery Program Expedition 375, coring of the upper ∼110 m of the northern Hikurangi Trough Site U1520 recovered a turbidite-dominated succession deposited during the last ∼45 kyrs (Marine Isotope Stages (MIS) 1–3). We present an age model integrating radiocarbon dates, tephrochronology, and δ18O stratigraphy, to evaluate the bed recurrence interval (RI) and sediment accumulation rate (SAR). Our analyses indicate mean bed RI varies from ∼322 yrs in MIS1, ∼49 yrs in MIS2, and ∼231 yrs in MIS3. Large (6-fold) and abrupt variations in SAR are recorded across MIS transitions, with rates of up to ∼10 m/kyr occurring during the Last Glacial Maximum (LGM), and <1 m/kyr during MIS1 and 3. The pronounced variability in SAR, with extremely high rates during the LGM, even for a subduction zone, are the result of changes in regional sediment supply associated with climate-driven changes in terrestrial catchment erosion, and critical thresholds of eustatic sea-level change altering the degree of sediment bypassing the continental shelf and slope via submarine canyon systems. [ABSTRACT FROM AUTHOR]

The southeastern Australian margin hosts a series of submarine canyons. Although the origin and evolution of canyons within the northwestern segment of the margin is relatively well studied, their quantitative morphology, interaction with longshore drift currents and slope failure remain poorly understood in the southeastern region. In this study, high-resolution bathymetry and 3D seismic reflection datasets revealed five main submarine canyons present in the central offshore Otway Basin. The canyons have V-shaped, evolving to U-shaped morphology downslope with sedimentary infill characterized by medium–high amplitudes, recognizable stratal pattern and localized chaotic seismic reflections. Analysis reveals these canyons were initiated by retrogressive slope failure on the continental slope, that once the shelf edge was reached and subsequently incised, development of the canyon heads was influenced by the shelf parallel Zeehan Current, active on the continental shelf of the region. The heads of the shelf-incised canyons preferentially migrate northwestward and were infilled by laterally accreting sedimentary packages characterized by southeast dipping seismic reflections. These indicate an early erosive phase followed by a period of deposition, a result of the prevalent eastward flowing Zeehan Current. These results have important implications for understanding of the mechanisms that control initiation and development of submarine canyons, and their morphology, both offshore southeastern Australia, and similar settings on continental margins worldwide. [ABSTRACT FROM AUTHOR]

The Gulf Stream, a major ocean current in the North Atlantic ocean is a key component in the global redistribution of heat and is important for marine ecosystems. Based on 27 years (1993–2019) of wind reanalysis and satellite altimetry measurements, we present observational evidence that the path of this freely meandering jet after its separation from the continental slope at Cape Hatteras, aligns with the region of maximum cyclonic vorticity of the wind stress field known as the positive vorticity pool. This synchronicity between the wind stress curl maximum region and the Gulf Stream path is observed at multiple time-scales ranging from months to decades, spanning a distance of 1500 km between 70 and 55W. The wind stress curl in the positive vorticity pool is estimated to drive persistent upward vertical velocities ranging from 5 to 17 cm day−1 over its ~ 400,000 km2 area; this upwelling may supply a steady source of deep nutrients to the Slope Sea region, and can explain as much as a quarter of estimated primary productivity there. [ABSTRACT FROM AUTHOR]

Introduction: Methane seeps influence surrounding benthic communities in different ways from slight changes in benthic abundance and biomass to major altering the species composition. Materials and Methods: We studied benthic communities of 14 methane seep flares in Laptev and East Siberian seas with comparative analysis of species composition and abiotic parameters at the nearby areas not affected by methane seeps. The species diversity was comparable at seep and non-seep sites varying from 3.9 to 39.6 taxa per 100 individuals and from 4.5 to 34.8 taxa per 100 individuals, correspondingly. Results: The Laptev Slope community corresponds with the Polychaeta-community, encircling the upper continental slope area of the entire Siberian Arctic. The Lower Shelf community described in this study apparently corresponds with the Ophiocten sericeum community identified in the shelf areas of the Kara, Laptev and East Siberian seas. The Upper Shelf community is mostly inhabited by the bivalves species such as Portlandia arctica, Ennucula tenuis and Astarte montagui communities. The Estuarine community, which is the poorest by diversity but has high values of abundance and biomass is directly influenced by the Lena River runoff in terms of lower salinities and higher sedimentation rates. Discussion: Throughout the study area, the differences between the Estuarine, Upper Shelf Lower Shelf and Laptev Slope communities exceeded the differences between the seep and background non-seep areas. Several taxa demonstrated correlations with different environmental factors, including the latitude, depth, temperature, salinity, pH and methane content, not depending on the revealed benthic community. Eight taxa demonstrated correlations with the methane content measured at different sediment depths. Two siboglinids taxa demonstrated high abundances at stations with highest methane content deep in the sediment. At the Siberian shelf, our geochemical data for siboglinid habitats are the first to be published so far. [ABSTRACT FROM AUTHOR]

The article presents the species diversity, abundance, and distribution features of ichthyoplankton and fodder zooplankton in the northern Black Sea in summer 2021. The intensification of cyclonic activity over the Black Sea in June–July slowed the formation of summer-type thermal stratification in the studied water area. At the beginning of July, only 13 species of eggs and fish larvae were observed in ichthyoplankton of the Crimean Peninsula, and their average abundance was 29 and 2 ind./m2, respectively. At the beginning of August, summer-type vertical thermal stratification off the coast of the Caucasus had already formed. The number of ichthyoplankton species increased to 20. Activation of atmospheric processes in June–July intensified the intraseasonal wind "pumping" of the upper layer of the sea. The Black Sea Rim Current transformed into a pronounced jet over the continental slope, oriented alongshore, partially extending to the shelf. This did not affect the spawning activity of mass fish species. The average abundance of eggs in the shelf and deep-water zone was about 160 ind./m2, and the average abundance of larvae on the shelf was almost five times higher, 452 ind./m2. [ABSTRACT FROM AUTHOR]

Two moorings deployed for 75 days in 2019 and long‐term satellite altimetry data reveal a spatially complex and temporally variable internal tidal field at the Surface Water and Ocean Topography (SWOT) Cal/Val site off central California due to the interference of multiple seasonally‐variable sources. These two data sets offer complementary insights into the variability of internal tides in various time scales. The in situ measurements capture variations occurring from days to months, revealing ∼45% coherent tides. The north mooring displays stronger mode‐1 M2 with an amplitude of ∼5.1 mm and exhibits distinct time‐varying energy and modal partitioning compared to the south mooring, which is only 30‐km away. The 27‐year altimetry data unveils the mean and seasonal variations of internal tides. The results indicate that the complex internal tidal field is attributed to multiple sources and seasonality. Mode‐1 tides primarily originate from the Mendocino Ridge and the 36.5–37.5°N California continental slope, while mode‐2 tides are generated by local seamounts and Monterey Bay. Seasonality is evident for mode‐1 waves from three directions. The highest variability of energy flux is found in the westward waves (±22%), while the lowest is in the southward waves (±13%). The large variability observed from the moorings cannot be solely explained by seasonality; additional factors like mesoscale eddies also play a role. This study emphasizes the importance of incorporating the seasonality and spatial variability of internal tides for the SWOT internal tidal correction, particularly in regions characterized by multiple tidal sources. Plain Language Summary: This study explores the variations of internal tides, which are waves at tidal frequencies beneath the ocean surface. They play a crucial role in deep‐ocean mixing, ocean circulation, and the overall climate system by transporting nutrients, heat, and carbon within the ocean. Our research area is off central California. We use both in situ measurement and satellite observation to understand how internal tides change over time and space. Our discoveries suggest that four main sources, changing ocean currents, and seasonal variations of internal tides, contribute to these tidal changes and create the complicated tidal field off central California. Key Points: Temporal and spatial variations of semidiurnal internal tides are observed using in situ moorings and satellite altimetryComplex internal tide field is caused by multiple generation sources, seasonal stratification, and likely mesoscale eddiesThe three generation sources of mode‐1 M2 internal tides are subject to strong but different seasonalities [ABSTRACT FROM AUTHOR]

We study the impacts of a continental slope on instability and mesoscale eddy fluxes in idealized 3‐layer numerical model simulations. The simulations are inspired by and mimic the situation in the Arctic Ocean's Beaufort Gyre, where anti‐cyclonic winds drive anti‐cyclonic currents that are guided by the continental slope. The forcing and currents are retrograde with respect to topographic Rossby waves. The focus of the analysis is on eddy potential vorticity (PV) fluxes and eddy‐mean flow interactions under the Transformed Eulerian Mean framework. Eddy lateral vorticity fluxes dominate over the continental slope where eddy form stress, that is, vertical momentum flux, is suppressed due to the topographic PV gradient. The diagnosis also shows that while eddy momentum fluxes are up‐gradient over parts of the slope, the total quasi‐geostrophic PV flux is down‐gradient everywhere. We then calculate the linearly unstable modes of the time‐mean state and find that the most unstable mode contains several key features of the observed finite‐amplitude fluxes over the slope, including down‐gradient PV fluxes. When accounting for additional unstable modes, more qualitative features of the observed eddy fluxes in the numerical model are reproduced. Plain Language Summary: The ocean circulation in the Arctic is heavily influenced by the bottom bathymetry. Essentially, currents are steered to follow continental slopes and submarine ridges. This topographic steering makes transfer of properties by ocean currents across continental slopes difficult, and the result is that the deep basins are partially isolated from the continental shelves. Large‐scale oceanic turbulence, or "mesoscale eddies," are able to cross bottom bathymetry, but transport by such eddies is also hampered. In this study, a simplified numerical model is used to learn about how bottom bathymetry impacts eddy transport in and out of the Beaufort Gyre, a wind‐driven large‐scale gyre in the Arctic Ocean's Canada Basin. The gyre is the largest reservoir of fresh waters in the Arctic, and understanding how topography controls the export of this freshwater is thought to be of crucial importance if climate models are to properly simulate a future Arctic Ocean. The study shines light on some key aspects that the models need to capture to get transport across the continental slope right. Key Points: A numerical 3‐layer model is used to study instability and eddy dynamics over the continental slope in an idealized wind‐driven ocean gyreEddy fluxes of potential vorticity are down‐gradient in all three layersLinearized stability calculations are able to reproduce the qualitative features of PV fluxes near the slope [ABSTRACT FROM AUTHOR]

This study focuses on the acoustic classification of delphinid species at the southern continental slope of Brazil. Recordings were collected between 2013 and 2015 using towed arrays and were processed using a classifier to identify the species in the recordings. Using Raven Pro 1.6 software (Cornell Laboratory of Ornithology, Ithaca, NY), we analyzed whistles for species identification. The random forest algorithm in R facilitates classification analysis based on acoustic parameters, including low, high, delta, center, beginning, and ending frequencies, and duration. Evaluation metrics, such as correct and incorrect classification percentages, global accuracy, balanced accuracy, and p-values, were employed. Receiver operating characteristic curves and area-under-the-curve (AUC) values demonstrated well-fitting models (AUC ≥ 0.7) for species definition. Duration and delta frequency emerged as crucial parameters for classification, as indicated by the decrease in mean accuracy. Multivariate dispersion plots visualized the proximity between acoustic and visual match data and exclusively acoustic encounter (EAE) data. The EAE results classified as Delphinus delphis (n = 6), Stenella frontalis (n = 3), and Stenella longirostris (n = 2) provide valuable insights into the presence of these species between approximately 23° and 34° S in Brazil. This study demonstrates the effectiveness of acousting classification in discriminating delphinids through whistle parameters. [ABSTRACT FROM AUTHOR]

In the North West Shelf region of Australia is a surface current (Holloway Current), which flows southwestward along the shelf break. This paper describes a seasonal undercurrent below the Holloway Current. A 5-day climatology is constructed from the output of an eddy-resolving oceanic general circulation model (OGCM). A seasonal northeastward-flowing undercurrent is found on the upper continental slope during the climatological April-May. This undercurrent reverses during February-March. During its annual cycle, the phase of the undercurrent tends to propagate southwestward and upward. The annual frequency dominates, but the positive and negative phases of the undercurrent are not symmetric in the yearly cycle because of the contributions from the semi-annual and 1/3-annual components. We propose a hypothesis that this undercurrent is a beam of coastal trapped wave (CTW). As an initial attempt to assess the plausibility of this hypothesis, we construct an idealized linear coastal-trapped wave (CTW) solution driven by an idealized harmonic meridional winds at the annual frequency. The solution takes the form of a beam originating from the forcing region on the continental shelf and propagating offshore and southward. When it emerges on to the continental slope, it takes the form of an undercurrent. This idealized solution shares several properties with the undercurrent in the OGCM despite several discrepancies. [ABSTRACT FROM AUTHOR]

Antarctic Bottom Water has been warming in recent decades throughout most of the oceans and freshening in regions close to its Indian and Pacific sector sources. We assess warming rates on isobars in the eastern Pacific sector of the Southern Ocean using CTD data collected from shipboard surveys from the early 1990s through the late 2010s together with CTD data collected from Deep Argo floats deployed in the region in January 2023. We show cooling and freshening in the temperature‐salinity relation for water colder than ∼0.4°C. We further find a recent acceleration in the regional bottom water warming rate vertically averaged for pressures exceeding 3,700 dbar, with the 2017/18 to 2023/24 trend of 7.5 (±0.9) m°C yr−1 nearly triple the 1992/95 to 2023/24 trend of 2.8 (±0.2) m°C yr−1. The 0.2°C isotherm descent rate for these same time periods nearly quadruples from 7.8 to 28 m yr−1. Plain Language Summary: Cold winds blowing over polynyas (areas of ice‐free water) on the Antarctic continental shelf create sea ice, forming very cold and somewhat salty, hence very dense, waters. These dense shelf waters descend the continental slope to the abyss, mixing with adjacent waters to form Antarctic Bottom Water (AABW). AABW spreads northward from there, filling much of the global abyssal ocean as it mixes with warmer, lighter waters above. AABW has been warming on pressure surfaces, freshening and cooling on density surfaces, and reducing in volume (contracting). These changes are likely a result of melting Antarctic ice sheets, which freshen the shelf waters, making them less dense, hence less able to sink to the bottom. We compare profiles of ocean temperature and salinity in the eastern Pacific sector of the Southern Ocean collected in 2023 and 2024 by robotic freely drifting profilers to data collected from ships from the early 1990s to the late 2010s. We find all of the above listed changes, but also acceleration of the warming, with the rate from 2017/18 to 2023/24 being nearly triple the rate from 1992/95 to 2023/24. The contraction rate has nearly quadrupled. This acceleration has been predicted by high‐resolution climate model simulations. Key Points: Antarctic Bottom Water (AABW) changes in the east Pacific sector of the Southern Ocean are assessed using Deep Argo and ship‐based CTD profilesBottom water warming rates from 2017/18 to 2023/24 nearly triple compared to 1992/95 to 2023/24 rates, contraction rates nearly quadrupleAABW cooling and freshening on isopycnals is also observed in the region, relative to older Circumpolar Deep Water [ABSTRACT FROM AUTHOR]

The interannual variability of the physical properties of the shelf waters in Sardinia, western Mediterranean Sea, is studied by using hydrological data gathered during three oceanographic cruises: two in late summer of 2019 and 2021 respectively and another one in early autumn of 2020. The data consist of vertical profiles of salinity and potential temperature acquired by a multiparametric probe for a total of 171 casts performed along a set of transects extending from the nearshore to the continental slope, up to the depth of 200 m. Satellite remote sensing and numerical modelling oceanographic products support the phenomenological analysis. Atlantic Water, characterised by low salinity signatures (S<37.0), is detected in the surface waters of the southwestern shelf areas, induced by the Algerian Eddies, and with differences between years. It is also observed on the southern-eastern and north-eastern shelf areas of Sardinia, mainly driven by the interaction with large-scale circulation features like the southeast Sardinia Gyre and the Bonifacio Gyre. An upwelling phenomenology is identified as one of the major features of the coastal circulation on the western shelf area. The study provides the first assessment of the thermohaline features on the Sardinian shelf; an enhanced contribution to the current knowledge of the coastal sea phenomena, and contributes to numerical modelling applications and implementations for ecosystem services. [ABSTRACT FROM AUTHOR]

Growing evidence suggests that complex spatial structure occurs within the Scotian Shelf and southern Grand Banks (SSGB) Atlantic halibut stock, yet large knowledge gaps remain about diversity of migratory and spawning behaviors. Here, 71 pop-up satellite archival tags were deployed on large Atlantic halibut (FL: 87–166 cm) between 2012 and 2020. Migration tracks were successfully reconstructed for 43 fish using a hidden Markov geolocation model, and temperature and depth time series were available for an additional nine fish (total n = 52). Five migratory behavior categories were identified: shelf residency, slope residency, shelf-channel migration, shelf-slope migration, and dispersal. High-resolution data for four of 20 physically recovered tags provided evidence of putative spawning behavior in deep channels on the continental shelf and along the continental slope between January and February. Additionally, four halibut displayed previously undocumented periods of sustained, oscillatory vertical movements along the continental slope between November and February. The high migratory diversity observed in this study provides support for the existence of multiple resident and migratory contingents in the SSGB stock in the apparent absence of significant genetic structure. [ABSTRACT FROM AUTHOR]

Life history characteristics of Watases lanternfish Diaphus watasei from a deep sea fishing ground of the East China Sea were studied. Overall, 452 adult individuals with standard length ranging from 91 to 147 mm were collected in the continental slope during 3 years. The growth pattern and hatching date were inferred from otolith microstructure analysis, and the stomach contents were examined to clarify feeding ecology. Three distinct zones of the otolith microstructure were depicted, the numbers of increments in the central and middle zones of the D. watasei otolith are in the lowest level in myctophid species studied. The maximum number of growth increments indicated a short lifespan of 2 years. The spawning time almost lasted throughout the year, and then two cohorts were separated according to the estimated hatching time. The length–weight relationship revealed a negative allometric pattern and significant difference between the two cohorts, and a significant seasonal difference was also detected in somatic growth pattern. A piscivorous habit dominated by Maurolicus muelleri was revealed across sampling seasons and standard length groups. Overall, D. watasei show distinct life history characteristics compared to coinhabiting myctophids, and such characteristics could reduce interspecific competition. [ABSTRACT FROM AUTHOR]

Submarine canyons are hot spots for topography‐internal wave interactions, with elevated mixing contributing to regional water mass transport and productivity. Two velocity time series compare and contrast internal waves deep inside Barkley Canyon to a nearby site on the shelf‐break slope of the Vancouver Island Continental Shelf. Elevation of internal wave energy occurs near topography, up to a factor of 10 above the slope and 100 in the canyon. All frequency bands display strong seasonal variability but weak interannual variability. Diurnal (K1) energy is sub‐inertial, trapped along topography, and forced locally through barotropic motions. Both sites have high near‐inertial (NI) energy linked to wind events, though fewer events are observed deep inside the canyon. At the slope site, near‐inertial energy is attenuated with depth, while in the canyon it is amplified near the bottom. Freely propagating semidiurnal (M2) energy appears focused near critical shelf‐break and canyon floor topography, due to local and remote baroclinic forcing. The high‐frequency internal wave continuum has enhanced near‐bottom energy at both sites (up to 7 × the Garrett‐Munk spectrum), and inferred dissipation rates, ɛ, reaching 10−7 W kg−1 near topography. Dissipation is most strongly correlated with semidiurnal energy variability at both sites, with secondary contributors that are site dependent. Forcing power law fits are ε∼M20.8+ $\varepsilon \sim {M}_{2}^{0.8}+$SubK10.6 ${\text{Sub}}_{{K}_{1}}^{0.6}$ on the slope, and ε∼M21.5+ $\varepsilon \sim {M}_{2}^{1.5}+$ NI0.2 in the canyon. There is also a build‐up of "shoulder" energy (PSh) near the buoyancy frequency, with a power law fit to dissipation of PSh ∼ ɛ0.3 at both sites. Plain Language Summary: Internal waves are sub‐surface waves that can mix ocean water, particularly over rough topography such as that found on continental slopes or in submarine canyons. Mixing is important for understanding ocean circulation, climate, and biological productivity. At Barkley Canyon on Canada's west coast, 4 years of current observations are used to study internal waves at both slope and canyon sites. These long‐term data allow for analysis of seasonal and year‐to‐year trends. The currents follow topography, and near‐bottom internal wave energy is generally increased. The observed seasonal patterns change little year‐to‐year. Internal waves occurring once‐a‐day or less are trapped along the slope, and result from once‐a‐day surface tides. Internal waves associated with the Earth's rotation are driven by wind—with only some events reaching the deep canyon. Internal waves occurring twice‐a‐day may be amplified by topography, and result from twice‐a‐day surface tides and internal waves from other underwater sites. Seasonal trends indicate that larger internal waves transfer energy to smaller, turbulent motions near topography, elevating mixing. There is evidence that this transfer of energy may continue to smaller scales than is typically observed. These findings can support models of mixing near topography and improve understanding of internal wave processes. Key Points: Analysis of 4 years of acoustic Doppler current profiler horizontal velocity data from Barkley Canyon and nearby slopeElevated internal wave energy and mixing near topography, with power law relationships to semidiurnal and site‐dependent secondary forcingBuild‐up of energy near the local buoyancy frequency with a power law relationship to dissipation [ABSTRACT FROM AUTHOR]

Understanding patterns of species abundance is essential for planning landscape‐level conservation. The complex hierarchies of dendritic ecosystems result in different levels of heterogeneity at distinct geographic scales. Species responses to dynamic environmental drivers may also vary spatially depending on their interactions with landscape features. Monitoring abundance by explicitly quantifying their spatial and temporal variation is important for strategic management.We analysed brook trout (Salvelinus fontinalis) count data collected from 173 sites in western North Carolina between 1989 and 2015. We developed a Bayesian hierarchical model that used single‐ and multi‐pass electro‐fishing data and characterized their respective capture probabilities. We quantified spatial variation using a multi‐scale process model representative of the nested stream habitats, and we investigated differences in population temporal trends and responses to seasonal weather patterns by space and life stage.Trout abundance was lower on the Atlantic slope of the Eastern Continental Divide than in the interior, on average, and the Atlantic slope juveniles were more adversely affected by high winter flows. However, Atlantic slope populations of both lifestages demonstrated positive temporal trends, whereas Interior juveniles demonstrated a negative trend. We found higher spatial variation than temporal variation in abundance when conditioned on the covariates, where the primary source of spatial heterogeneity was revealed at the segment level, compared to watershed or network levels.Our multi‐scale spatial model outperformed simpler models in abundance estimation and out‐of‐sample prediction. The inferred per‐pass capture probabilities indicated that single‐pass surveys were as efficient as multi‐pass surveys.Synthesis and applications. Our study suggested conservation priority should involve multiple criteria, including present‐day abundance, temporal trend and sensitivity to environmental drivers. Based on the inferred scale‐specific variations in trout abundance, we recommend that future surveys strategically combine single‐pass surveys with multi‐pass surveys to optimize abundance estimation. Our approach is widely applicable to other species and ecosystems occupying dendritic habitats. [ABSTRACT FROM AUTHOR]

Meltwater from the Greenland Ice Sheet can alter the continental shelf/slope circulation and cross-shelf freshwater fluxes and limit deep convection in adjacent basins through surface freshening. We explore the impacts on the West Greenland Current and eastern Labrador Sea with different vertical distributions of the meltwater forcing. In this study, we present the results from global coupled ocean/sea ice simulations, forced with atmospheric reanalysis, that are mesoscale eddy-active (∼2–3-km horizontal spacing) and eddy-permitting (∼6–7-km horizontal spacing) in the study region. We compare the West Greenland Current in mesoscale eddy-active and eddy-permitting without meltwater to highlight the role of small-scale features. The mesoscale eddy-active configuration is then used to assess the change in the eastern Labrador Sea when meltwater is added to the surface or vertically distributed to account for mixing within fjords. In both simulations with meltwater, the West Greenland and West Greenland Coastal Currents are faster than in the simulation with no meltwater; their mean surface speeds are the highest in the vertical distribution case. In the latter case, there is enhanced baroclinic conversion at the shelf break compared to the simulation with no meltwater. When meltwater is vertically distributed, there is an increase in baroclinic conversion at the shelf break associated with increased eddy kinetic energy. In addition, in the eastern Labrador Sea, the salinity is lower and the meltwater volume is greater when meltwater is vertically distributed. Therefore, the West Greenland Current is sensitive to how meltwater is added to the ocean with implications for the freshening of the Labrador Sea. Significance Statement: Our goal is to understand how the flux of freshwater across the West Greenland continental slope into the Labrador Sea is modified by meltwater from the Greenland Ice Sheet. We compare the simulations of the ocean that capture key dynamics along the West Greenland continental slope that have no meltwater, meltwater added to the ocean surface, and meltwater distributed vertically to represent the mixing within fjords. When meltwater is added, the currents along the continental slope are faster, with the greatest increase when meltwater is vertically distributed. In that case, there is enhanced freshening of the Labrador Sea because modified density gradients generate more eddies. Proper representation of the vertical structure of meltwater is important for projecting the impact of freshwater on the subpolar North Atlantic. [ABSTRACT FROM AUTHOR]

The shelf‐margin deltas are the primary 'sources' of interest in siliceous submarine fan source‐to‐sink systems. However, less has yet to be discovered about the roles and effects of the shallow water platform situated on continental slopes. Using the Miocene sediments of the Ledong‐Lingshui Sag in the western part of the Qiongdongnan Basin (QDNB), this paper studies the YC35 coarse‐grained submarine fan that developed in the Meishan Formation (Fm.). The material sources, depositional characteristics, and developmental mechanisms of this fan were investigated. The restored palaeogeomorphology, based on high‐resolution 3D seismic data, shows that a shallow water platform exists. According to geochemical palaeoenvironmental data, the shallow water platform was ideal for forming carbonate deposits in the Meishan Fm., owing to the warm and humid palaeoclimate and the shifting trend in palaeowater depth. Based on the combined source tracing of heavy minerals, coherence slices, and seismic profiles, the shallow water platform and the Ningyuan River source on Hainan Island contributed to the YC35 coarse‐grained submarine fan. Compared to submarine fans formed during different periods, coarse‐grained fan stands out due to its distinct sedimentary structure, rock composition, and microlithological characteristics. Aside from not following the usual Bowmar sequence, there is an excess of gravel and no clear bedding or lamination. A large number of rock fragments, mostly granite and sedimentary rock (carbonatite), make up the rock composition. According to these results, the shallow water platform significantly affects submarine fan material composition. In addition, the attribute slice based on the root mean square reveals that shallow water platforms moderate peripheral deposition. We attribute the development and proximal supply of the shallow water platform to diapirism and forced regression. Our research provides novel insights and comprehension into the investigation of submarine fan sedimentary systems. [ABSTRACT FROM AUTHOR]

Large and diverse Eocene otolith assemblages have been described from the US Gulf and Atlantic coastal plains, various basins in Europe, and New Zealand. Here we described a highly diverse otolith association from the middle Eocene (Lutetian and Bartonian) strata of southern California, San Diego County, which was retrieved from the heritage of John E. Fitch (1918-1982) in the archives of the Ichthyology Department of the Natural History Museum of Los Angeles County, Los Angeles, Califronia. The collection represents the first Eocene otolith assemblage described from the Northeastern Pacific and stems from two localities: the Ardath Shale at Black’s Beach in the Torrey Pines Park just south of Black’s Canyon Road and north of the Salk Fault on the Pacific shore face, and the MissionValley Formation from the west-facing graded hill just east of the Miramar Water Treatment Plant near the southern shore of Miramar Reservoir. The Ardath Shale was deposited on the deep shelf and continental slope while the Mission Valley Formation represent an inland, nearshore environment during times of the maximum transgression. A total of more than15,000 otoliths were found representing 96 species of which 53 are described as new and 12 remain in open nomenclature. The fauna of the Ardath Shale is distinctly richer containing 88 species while the one from the Miramar Reservoir site yielded 38 species. The low diversity at the Miramar Reservoir site is thought to be related to the shallow-water environment in which it was deposited whereas the high diversity at Black’s Beach reflects a mixture of shelf and bathyal fishes. In addition, 24 new otolith-based genera are established, four of which are in the category “incertae sedis”. Furthermore, five new species are described from a comparative otolith collection from the US Gulf Coast Eocene and one new species from a comparative collection from the Lutetian of Balegem in Belgium. The Eocene otolith-based fish fauna from California is assessed for its paleoecological, paleobiogeographic and evolutionary significance. Particular emphasis is directed towards the elucidation of the evolution of the early Ophidiiformes, which during the early Paleogene were predominantly adapted to warm, clastic shallow-water environments and there were competing in abundance and diversity with other percomorphs (e.g., perciforms s.l.). A warm Eocene paleobioprovince is proposed for the Californian fish fauna which is not related to today’s endemic Northwest Pacific fish fauna along the regime of the cold-water California Current. [ABSTRACT FROM AUTHOR]

Myctophids are central in ocean food webs, yet knowledge of the ecology of larval stages is sparse. We investigated if larval feeding ecology is different in continental shelf break waters compared to waters off oceanic islands in the western Tropical Atlantic. The larvae were collected through diurnal and nocturnal oblique hauls using a Bongo net and stomach contents were analyzed. The larvae ranged between 2.27 and 16.5 mm in standard length. Diet composition was different in the slope and islands (Permutational Multivariate Analysis of Variance (PERMANOVA), P  < 0.001). Diatoms (mainly Thalassiosira spp. and fragments of diatoms) were numerically important in the diet at the slope site (69% of relative importance). Copepods were the most relevant prey (71% of relative importance) near the islands. Copepods were the biomass-dominant dietary item at both areas, alongside ostracods near the islands. Smaller prey items were more important for smaller larvae, particularly those measuring up to 4 mm. Larger prey became relatively more important as the larvae grew to at least 8 mm. Larvae fed mostly during the daytime regardless of their size class. [ABSTRACT FROM AUTHOR]

Bottom trawling in submarine canyons can affect their sedimentary dynamics, but studies addressing this topic are still scarce. In the Gulf of Palermo (NW Sicily, SW Mediterranean Sea), bottom trawling occurs on the continental slope, but principally concentrates within Oreto Canyon. Hydrographic profiles and time series data of temperature, turbidity, and currents obtained by a CTD probe and by moored instruments, respectively, revealed increased turbidity values and the presence of bottom and intermediate nepheloid layers coinciding with periods of bottom trawling activity. The delay between the onset of trawling activities along the Oreto canyon axis and the increase in water turbidity at the mooring location indicate that trawling resuspended particles are progressively advected down-canyon by hydrodynamic processes. Topographic waves and near-inertial currents seem to contribute to the sediment transport of resuspended particles as bottom and intermediate nepheloid layers. Results presented in this paper highlight the complex relationship between hydrodynamic processes and sediment resuspension by trawling in submarine canyons. [ABSTRACT FROM AUTHOR]

The results of geochemical and Nd isotopic studies of rocks and U–Th–Pb (LA-ICP-MS) geochronological and Hf isotopic studies of detrital zircon from metaterrigenous rocks of the Kodar Group of the Udokan Complex (Aldan Shield) are presented. It is established that the age of rocks of the Kodar Group is 1.99–1.91 Ga, whereas the age of rocks of the Chinei and Kemen groups of the Udokan Complex is 1.90–1.87 Ga (Kovach et al., 2018, 2023a). This allows us to raise the issue of recognition of the Kodar Group as an independent stratigraphic subdivision. The terrigenous rocks of the group were sourced from the Archean igneous and metamorphic rock of the Chara–Olekma Geoblock and probably the Kalar and Kurulta blocks of the Stanovoi suture zone, as well as the Paleoproterozoic (2.04–1.99, 2.08, 2.20, and 2.30 Ga) complexes of active continental margins or ensialic island arcs in the western–northwestern and southern (in the present-day coordinates) frame of the Chara–Olekma Geoblock, which are unidentified in the region at the current erosion level. Erosion of rocks of magmatic arcs and the continental slope led to the deposition of rocks of the Kodar Group in a retroarc foreland basin, whereas further collapse of the orogen and the formation of an intracontinental extension basin were responsible for the deposition of terrigenous rocks of the Chinei and Kemen groups. The obtained data indicate widespread previously unidentified Paleoproterozoic continental crust formation at about 2.04–1.97 Ga in the western part of the Aldan Shield. [ABSTRACT FROM AUTHOR]

Climate change and anthropogenic stressors affect the distribution, abundance, and diversity of fish communities across the world. To understand rapidly changing biotic communities, resource managers need a method to quickly and efficiently document temporal and spatial changes in community assemblages across various spatial scales. In this study, we describe the use of new video lander tools to survey fish communities in rocky marine habitats on the continental shelf and slope in California, USA. We evaluate how fish diversity metrics determined by video surveys vary among geographically distinct areas. Our results demonstrate that species diversity, evenness, and richness vary spatially across the coast. Furthermore, community assemblages differ at both broad and fine spatial scales because of differences among habitats. Length frequencies and densities of species in this study were similar to those reported in previous studies. As community assemblages and biodiversity metrics shift in response to changing stressors, it is increasingly important to develop tools and methodologies to detect and rapidly monitor these changes. [ABSTRACT FROM AUTHOR]

This article, published in the Journal of Bryology, presents new national and regional records of bryophytes. The records include the discovery of various plant species in different regions, such as liverworts and mosses. The article provides detailed descriptions of each species, including their characteristics and habitats. These findings contribute to our understanding of the distribution and diversity of bryophytes in these regions. The authors acknowledge the support and funding they received for their research. [Extracted from the article]

The east coast of India is highly prone to devastating winds, torrential rainfall, and storm surges caused by tropical cyclones. The storm surge is affected by ocean basin characteristics involving the width and slope of the continental shelf. The bed roughness plays a major role in surge formation. The east coast of India is characterized by a broader shelf in the north and a narrow shelf in the south. This paper uses a hybrid Finite Volume Method–Finite Element Method based Shallow water equation (SWE) solver to predict the storm surges during different cyclone events, and the roughness parameter Manning's n is used in bed friction calculations. The bottom friction coefficient parameterization involving bed roughness is used to calibrate the resistance to flow in the numerical model. The calibration exercises are carried out with different values of n for each surge simulations for different cyclones to predict the surface elevation. Different statistical parameters against the measured values are used to analyze the impact of varying n values on predicted surge levels, and the most suitable n value is carefully chosen. The relationship between n and the bed slope is established as an expression, to replace the formulations involving Manning's n, thereby minimizing the usual computational efforts. The performance of the novel bed friction formulation involving the physical parameter in bed slope is demonstrated through statistical evaluations. [ABSTRACT FROM AUTHOR]

A comprehensive analysis of geological and geophysical data characterizing the structure of the eastern continental margin of India and the adjacent part of the bottom of the Bay of Bengal has been carried out. According to the structural and tectonic features, three sectors are distinguished: southern, central, and northern, the natural boundaries between which are the fault zones of the Makhanadi and Godavari–Krishna aulacogens. In the central sector, the pericontinental East Indian Plateau adjoins the continental slope. In 2003, the R/V Mezen acquired deep seismic sounding data on two profiles in this region. These data and their geological interpretation made it possible to identify "reduced" continental crust, characterized by reduced thickness of the upper, middle, and lower layers. A conclusion is drawn about the continental nature of the East Indian Plateau and northern part of the 85° Ridge adjacent to it. The light sialic and effusive rocks that form the top of the ridge give a negative gravimetric anomaly in the free-air reduction, which is its distinguishing feature. [ABSTRACT FROM AUTHOR]

The principal basins on the Mozambique continental margin are the Mozambique and Rovuma, on the passive continental margin with complex tectonic history, following after the East African Rift System in the Triassic. Although the first gas fields in the coastal zone of the Indian Ocean in southeast Mozambique are appeared yet in the 1960s, only in 2010, did Mozambique achieve a new status as a major world hydrocarbon player—with the discovery of a number of large gas fields in the northeast of the country, in deep-water regions of the Indian Ocean, and in the Rovuma Basin. More than 20 recently discovered gas fields are located in deep-water regions and on the continental slope of the Indian Ocean at depths of 468–2610 m. It is noteworthy that the pays of the same age, the deeper they are buried beneath the water column, the greater their volume of hydrocarbon reserves. A similar trend may help in the case of targeted oil and gas exploration. The prospects of liquid hydrocarbon discoveries are possible in the Madagascar channel behind the Davie Ridge and in deep-water parts on the slopes of the Mozambique continental margin. [ABSTRACT FROM AUTHOR]

The anticyclonic eddies (ACEs) shed from the Kuroshio intrusion often interact with internal waves (IWs). Those interactions are complex but play an important role in the biogeochemical effects in the northern South China Sea (SCS). However, previous studies on these interactions have mainly focused on physical processes, while biological responses to their interactions have been unclear. In this study, results of two field cruises with focus on two sets of high-frequency time-series observations over the continental slope of the SCS during the summers of 2016 and 2017 revealed that phytoplankton in the euphotic zone were affected by both IWs and ACEs shed from the Kuroshio Current. Distinct surface distributions of phytoplankton were attributable to different sources of the water, Kuroshio intrusions and the plume from the Pearl River. However, similarities of phytoplankton biomass and community composition in the subsurface chlorophyll maximum layer in both years could be explained by the similar upward transport of nutrients induced by combinations of small-amplitude IWs and mature ACEs in 2016 and large-amplitude IWs in 2017. The distinct vertical distributions of the phytoplankton community in both years were attributable to the different responses of phytoplankton groups to the direct effects of isopycnal uplifting, bottom-up controls, and top-down controls. Our results showed that the ecological effects of the interactions between IWs and ACEs shed from the Kuroshio water were complex, and those complex effects further influenced the structure of this marginal sea ecosystem. [ABSTRACT FROM AUTHOR]

The Antarctic Slope Front and the associated Antarctic Slope Current dynamically regulate the exchanges of heat across the continental shelf break around Antarctica. Where the front is weak, relatively warm deep waters reach the ice shelf cavities, contributing to basal melting and ultimately affecting sea level rise. Here, we present new 2017–2021 records from two moorings deployed on the upper continental slope (530 and 738 m depth) just upstream of the Filchner Trough in the southeastern Weddell Sea. The structure and seasonal variability of the frontal system in this region, central to the inflow of warm water toward the large Filchner‐Ronne Ice Shelf, is previously undescribed. We use the records to describe the mean state and the seasonal variability of the regional hydrography and the southern part of the Antarctic Slope Current. We find that (a) the current is, contrary to previous assumptions, bottom‐enhanced, (b) the isotherms slope upwards toward the shelf break, and more so for warmer isotherms, and (c) the monthly mean thermocline depth is shallowest in February‐March and deepest in May‐June while (d) the current is strongest in April‐June. On monthly timescales, we show that (e) positive temperature anomalies of the de‐seasoned records are associated with weaker‐than‐average currents. We propose that the upward‐sloping isotherms are linked to the local topography and conservation of potential vorticity. Our results contribute to the understanding of how warm ocean waters propagate southward and potentially affect basal melt rates at the Filchner‐Ronne Ice Shelf. Plain Language Summary: Melting at the base of the Filchner‐Ronne Ice Shelf in the southeastern Weddell Sea is predicted to increase dramatically. The melt occurs within the ice shelf cavity filled with seawater, and the heat needed to melt the ice comes from warm water from the deep ocean. The warm water is carried toward the cavities over the relatively shallow continental shelves by ocean currents. The Antarctic Slope Current, a current that flows along the continental slope between cold and warm water masses, limits the amount of warm water that enters the continental shelf. Here, we use new four year‐long mooring records from the upper part of the continental slope north of the Filchner‐Ronne Ice Shelf and just east of the Filchner Trough to describe how the current changes with the season and how its vertical structure evolves throughout the year. We find that the warm water is lifted up toward the shelf break and suggest that this is linked to the presence of the Filchner Trough. An improved understanding of the dynamics of the Antarctic Slope Current in the region will allow us to better evaluate the potential for dramatic changes to the system in the future. Key Points: Four years of observations show that the Antarctic Slope Current north of the Filchner Trough is bottom‐enhanced and strongest during winterThe bottom enhancement is linked to isotherms that slope upward toward the shelf break, facilitating on‐shelf transport of warm waterOn monthly to seasonal time scales, positive temperature anomalies above the slope are associated with weaker‐than‐normal currents and vice versa [ABSTRACT FROM AUTHOR]

Through interactions with the continental margins, incident low‐mode internal tides (ITs) can be reflected, scattered to high modes, transmitted onto the shelf and dissipated. We investigate the fate of remotely generated mode‐1 ITs in the U.S. West Coast (USWC) continental margin using two 4‐km horizontal resolution regional simulations. These 1‐year long simulations have realistic stratification, and atmospheric, tidal, and sub‐tidal forcings. In addition, one of these simulations has remote internal wave (IW) forcing at the open boundaries while the other does not. To compute the IT reflectivity of the USWC margin, we separate the IT energy fluxes into onshore and offshore propagating components using a Discrete Fourier Transform in space and time. Overall, ∼20% of the remote mode‐1 semidiurnal IT energy fluxes reflect off the USWC margin, 40% is scattered to modes 2–5, and 7% is transmitted onto the shelf while the remaining is dissipated on the continental slope. Furthermore, our results reveal that differences in stratification, slope criticality, topographic roughness and angle of incidence cause these fractions to vary spatially and temporally along the USWC margin. However, there is no clear seasonal variability in these estimates. Remote IWs enhance the advection and diffusion of heat in the continental margin, resulting in cooling at the surface and warming at depth, and a reduction in the thermocline stratification. These results suggest that low‐mode ITs can cause water mass transformation in continental margins that are far away from their generation sites. Plain Language Summary: Ocean dynamics that exist over a wide range of spatial scales, such as the internal tides (ITs), are best resolved in numerical simulations with fine grid spacings. To accomplish this, model solutions are downscaled by nesting domains with increasingly higher resolution. However, the long propagation distances of low‐mode ITs away from their generation sites necessitate their inclusion at the open boundaries of regional simulations. Here, we show that these remotely generated ITs, for example, from Hawaii, modulate turbulence in the U.S. West Coast (USWC) continental margin. Approximately 80% of the remote mode‐1 semidiurnal IT energy is available for mixing in the USWC margin. In the absence of an accurate IT forcing at the open boundaries of coastal regional models, IT mixing may be underestimated. Key Points: The bulk of the internal tide (IT) energy approaching the U.S. West Coast comes from far‐field sources, for example, HawaiiOn average, 20% of the remote mode‐1 IT energy is reflected while the remaining energy is scattered to higher modes and dissipatedThe remote ITs advect and diffuse heat in the continental margin, causing surface cooling and subsurface warming [ABSTRACT FROM AUTHOR]

The West Antarctic Ice Sheet is experiencing rapid thinning of its floating ice shelves, largely attributed to oceanic basal melt. Numerical models suggest that the Bellingshausen Sea has a key role in setting water properties in the Amundsen Sea and further downstream. Yet, observations confirming these pathways of volume and tracer exchange between coast and shelf break and their impact on inter‐sea exchange remain sparse. Here we analyze the circulation and distribution of glacial meltwater at the boundary between the Bellingshausen Sea and the Amundsen Sea using a combination of glider observations from January 2020 and hydrographic data from instrumented seals. Meltwater distributions over previously unmapped western regions of the continental shelf and slope reveal two distinct meltwater cores with different optical backscatter properties. At Belgica Trough, a subsurface meltwater peak is linked with hydrographic properties from Venable Ice Shelf. West of Belgica Trough, the vertical structure of meltwater concentration changes, with peak values occurring at greater depths and denser isopycnals. Hydrographic analysis suggests that the western (deep) meltwater core is supplied from the eastern part of Abbot Ice Shelf, and is exported to the shelf break via a previously‐overlooked bathymetric trough (here named Seal Trough). Hydrographic sections constructed from seal data reveal that the Antarctic Coastal Current extends west past Belgica Trough, delivering meltwater to the Amundsen Sea. Each of these circulation elements has distinct dynamical implications for the evolution of ice shelves and water masses both locally and downstream, in the Amundsen Sea and beyond. Plain Language Summary: Floating ice shelves in West Antarctica are thinning, which is largely due to melting of the ice shelf base by the ocean. Here, measurements of ocean temperature, salinity, and dissolved oxygen, collected by a remotely‐controlled underwater vehicle (a glider), are used to estimate the amount of ice shelf meltwater released in the Bellingshausen Sea. Distinct cores of meltwater can be distinguished by the amount of suspended material that is present in the water, which we attribute to meltwater following different circulation pathways after entering the ocean. Historical data from seals equipped with temperature and salinity sensors provide additional information about how the meltwater circulates in the region. The seal data show the presence of a narrow coastal current that brings meltwater from the Bellingshausen Sea into the Amundsen Sea. The pathways of meltwater revealed in this study suggest an important influence of the Bellingshausen Sea on ice shelves throughout West Antarctica. Key Points: Hydrographic observations identify both shelf‐break and coastal meltwater pathways from the western Bellingshausen Sea into the Amundsen SeaDifferences in optical backscatter properties associated with meltwater are related to distinct coast‐to‐shelf break pathwaysThe main pathway to the shelf break is via Seal Trough, identified as the de facto western boundary of the Bellingshausen Sea [ABSTRACT FROM AUTHOR]

Sediment trap data set and 234Th profiles (deep water excesses and deficits) reveal that particulate organic carbon (POC) export at the highly oligotrophic Levantine Sea is dominated by lateral transport from the nearby margin. These intermediate nepheloid layers (INL) operate at multi‐depth, with the silt‐to‐clay size particulate matter (PM) fraction transported at water depths of about 100–500 m, while finer fraction arrives also at deeper depths. The shallow NIL is triggered by winter storms, manipulated by coastal flash floods and shelf resuspension and assisted by cross‐shore currents, which allow the arrival of PM at a distance of 50 km within about 10 days. The deeper INL could be related to sediments initially driven to depth by density currents. Our data show that inter‐annual differences in sediment trap fluxes were related to changes in both the intensity of coastal floods and current velocity. The frequent observation of deep‐water 234Th excesses during a (relatively) low export winter (2018) is related to lessened cleansing of the water column, that is, reduced removal of fine‐grained PM by sinking coarser‐grained material. These observations highlight the importance of winter storm intensity in the POC budget of marginal seas like the Levantine Basin (LB) even in areas with limited river discharge. This further suggests that the anticipated increase in extreme weather events due to the on‐going climate change should have an impact on this coastal‐deep sea conveyor and on POC export in the LB. Plain Language Summary: We present sediment traps and radioisotope results from the DeepLev marine station, the first deep water mooring to be deployed in the highly fragile ecosystem of the Levantine Basin (eastern Mediterranean Sea). Unlike the open ocean, particulate organic carbon export from surface to deep water is controlled by the transport of particulate matter from the nearby coast/continental shelf. We show that this land‐sea conveyor is nurtured by flash floods and shelf sediment resuspension, and is further manipulated by cross‐shore currents. The conveyor operates at multiple depths, with silt and clay transported sub‐horizontally from the shelf, arriving at DeepLev within ca. 10 days at 100–500 m depth (shallow intermediate nepheloid layer, INL), while colloids being carried through the whole water column (deep INL). The latter is probably related to particle‐laden density currents, which flow down submarine canyons, cutting into the nearby continental slope. Inter‐annual changes in winter events and cross‐shore current velocity result in significant changes of POC export intensity. This further implies that the predicted increase in the occurrence of extreme meteorological events could result in an enhanced transport of particular carbon, with important implications to the POC export in this and other marginal basins. Key Points: POC export in the Levantine Basin is controlled by lateral transport of multi‐depths intermediate nepheloid layers (INL)The shallow INL carries silt and clay from the coast and shelf, while the deep INL hauls colloids related to transport through submarine canyonsInter‐annual variability in winter event intensity results in lateral transport and vertical export variability [ABSTRACT FROM AUTHOR]

Submarine geohazards significantly threaten human economic activities and essential infrastructure. Based on multi‐beam data and high‐resolution 2D seismic data, two types of submarine geohazards are identified: direct and indirect geohazards on the northwestern continental slope and the Xisha Uplift of the South China Sea (SCS). Direct geohazards include submarine landslides and active faults, while indirect geohazards include buried channels, submarine canyons, pockmarks, volcanoes and magma diapirs. This study comprehensively analyzes geomorphological features, including their characteristics, genesis and distribution. Statistical analysis reveals that the gradient of the Xisha Uplift slope is steeper than the shelf break, making it a more unstable region. However, assessing disaster potential indicates that submarine geohazards at the shelf break pose a greater threat than those at the Xisha Uplift. Many factors, including tectonic activity, sediment supply and relative sea‐level changes, influence submarine geohazards' formation. These hazards do not occur in isolation but often interact with one another. The research results provide a scientific basis for predicting deep‐sea geohazards near the northern continental margin and Xisha Island in the SCS. [ABSTRACT FROM AUTHOR]

The use of 234Th–238U disequilibrium has been widely employed to estimate the sinking flux of particulate organic carbon (POC) from the upper sea and ocean. Here, the deficits of 234Th relative to 238U in the water column and the carbon isotope signature (δ13C) of POC in the East China Sea (ECS) Shelf were measured, which was used to distinguish the fraction of marine and terrestrial POC export fluxes. In the ECS Shelf, very strong deficits of 234Th relative to 238U were observed throughout the water column, with 234Th/238U activity ratios ranging from 0.158 ± 0.045 to 0.904 ± 0.068 (averaging 0.426 ± 0.159). The residence times of particle reactive radionuclide 234Th (τTh–T) in the ECS shelf water varied between 9 and 44 days, which is significantly shorter than that in the continental slope area or the basin area. This phenomenon indicates that there is a more rapid particle scavenging process in the ECS shelf water compared to the continental slope and basin upper water. By applying a two-end-member mixing model based on the δ13C, the fraction of terrestrial POC was estimated to be 0 to 74% (mean: 30 ± 22%) and the fraction of marine POC was in the range of 25% to 100% (mean: 70 ± 22%). Fluxes of marine and terrestrial POC settling to the seafloor exhibited significant spatial differences among different stations, ranging from 11 to 129 mmol C/m2/day and from 2.6 to 38 mmol C/m2/day, respectively. The averaged terrestrial POC fluxes in the southern and northern ECS Shelf were similar (~ 21 to 24 mmol C/m2/day), while the marine POC fluxes in the north (86 ± 37 mmol C/m2/day) were approximately four times higher than those in the south (26 ± 20 mmol C/m2/day). Interestingly, the estimated export flux of both marine and terrestrial POC were approximately one order of magnitude higher than the previously reported burial fluxes of POC (ranging from 1.1 ± 0.1 to 11.4 ± 1.1 mmol C/m2/day) in the underlying bottom sediments, indicating that the majority (> 90%) of both terrestrial and marine POC exported from the upper water column are degraded in the sediments of the ECS Shelf. This "carbon missing" phenomenon can greatly be attributed to rapid decomposition by other processes (including microbial reworking, cross-shelf transport, and possible consumption by benthic organisms). Our findings highlight the dynamic nature of carbon cycling in the continental shelf and the need for further research to understand these processes and improve carbon budget assessments. [ABSTRACT FROM AUTHOR]

Impacts of structuration on the geomorphology and internal architecture of a Pleistocene feeder channel-ponded lobe system, Channel-1B (Ch-1B), on the continental slope of the Niger Delta, Nigeria, has been studied using a combination of 3D seismic stratigraphy and geomorphology methods. Mapping of diagnostic seismic facies, characterization of channel morphology and internal architecture, quantitative analysis, architectural element (AE) delineation, and reservoir modeling were carried out with the view to (1) establish Ch-1B geomorphology, internal architecture, and sediment fills, (2) investigate the influence of structuration on the evolution of internal architecture over time, and (3) assess the impact of the resulting internal architecture variability on reservoir modeling and development strategies. This study established a strong link between structuration and the evolution of feeder channel-ponded lobe systems. Evolution of Ch-1B has been summarized in five phases: (I) channel initiation dominated by sediment bypass and incision into fold-1, (II) major break in slope gradient resulting in deposition of ponded lobe-1, (III) complete fill of accommodation created in the ponded basin between folds 1 and 2, diversion of the channel axis westward by fold-2 and eventual incision into lobe-1 and fold-2 by the feeder channel as it adjusted to a new base level, (IV) deposition of lobe-2 in the footwall of fold-2, and (V) filling of the feeder channel, almost entirely, by turbidite muds thereby creating a channel plug that partitioned lobe-1 into two compartments. Understandings, from this work, of the impacts of structuration on geomorphology and internal architecture have been applied to AE delineation, reservoir modeling, and development strategies in terms of the number and type of wells needed to produce hydrocarbon in lobe-1 efficiently. Given that well costs represent a significant portion of field development costs, this study concludes that adequately delineating and modeling structurally influenced AEs will significantly affect field development economics. [ABSTRACT FROM AUTHOR]

Notacanthid fishes constitute a common part of benthopelagic deep‐sea fish communities on seamounts and continental slopes around the world. However, their highly conserved morphology and the usual lack of information on deep‐water organisms make it difficult to appropriately address their biodiversity. A multidisciplinary approach combining morphological data with a DNA‐based species delimitation analyses was used to explore the taxonomy of Notacanthus species. For this purpose, morphological and molecular data were obtained from 43 individuals, and the resulting information was combined with the available data. The results showed the occurrence of Notacanthus arrontei n. sp. from the Iberian Peninsula and highlighted several taxonomic conundrums regarding the Notacanthus genus. For instance, no significant differences were found between Notacanthus indicus and the recently described Notacanthus laccadiviensis, questioning its taxonomic status. Similarly, the result of the species delimitation molecular analysis coincided with previous DNA barcoding studies supporting the snubnosed spiny eel Notacanthus chemnitzii as a species complex that requires further research. Moreover, two unidentified records from the Indian Ocean were confirmed to belong to an unknown species pending formal description, and barcoding data show for the first time the occurrence of the shortfin spiny eel Notacanthus bonaparte in the Australia‐New Zealand area. This research confirms the existence of important gaps in the knowledge of notacanthid fishes and represents a step forward toward a better understanding of their biological diversity. [ABSTRACT FROM AUTHOR]

In current practices of determining continental shelf area, the measured sediment thickness data do not effectively reflect the distribution of sediments across the area due to its dispersed nature. This issue raises potential limitations in unknown optimal survey line layout strategies for maximizing the posterior determination area. This paper adopts the binary search algorithm, relies on existing sediment thickness grid data, and uses geodetic formulas to build an ellipsoidal surface grid distance calculation model. This model quickly screens potential areas for the 1% sediment thickness line candidate points set. By constraining the azimuth parameter values during the construction process of the ellipsoidal point feature buffer zones, efficiently select the candidate points set for the 1% sediment thickness line. Furthermore, by elucidating the essential meanings of points on the formula limit and combining the candidate points set of the foot of the continental slope (FOS)+60 n mile line, the polygon minimal convex hull construction technique and a baseline points optimization algorithm with a length threshold are used to efficiently select points on formula limit. Experimental results demonstrate that this method can effectively assist coastal states in optimizing the determination of continental shelf area to the fullest extent under the length threshold requirements of the United Nations Convention on the Law of the Sea. Experiments have proven that compared to the traditional intersection method, the method presented in this paper can help coastal countries delineate a larger continental shelf area. In typical application scenarios, the gain in area can reach 77,278,427 m2 accounting for 0.51% of the total area. [ABSTRACT FROM AUTHOR]

Modern cold-water corals (CWCs) occur in a wide range of water depths, with Desmophyllum pertusum being one of the most common species. Pleistocene, Holocene, and modern coral mound formation by living CWC reefs have previously been described in the Porcupine Seabight from water depths greater than 700 m in the vicinity of the transitional zone between the Eastern North Atlantic Water and Mediterranean Outflow Water. Here we document occurrence of fossil corals retrieved from two cores at 370 m depth in the Macnas Mounds, a relatively shallow occurrence for mounds on the Irish shelf-edge. Both cores feature D. pertusum restricted to the upper two metres, immediately overlying an erosive surface and a coeval major down-core change in grain size from sand to mud. Radiocarbon dating of coral specimens indicates the CWC mounds initiated 7.82 Cal ky BP. Our study unequivocally documents the existence of Holocene shelf-edge coral mounds in the eastern Porcupine Seabight and highlights the possibility of other occurrences of CWCs in similar settings elsewhere in the northeast Atlantic. Given that no living CWCs were encountered in the study area, we suggest that the area previously experienced more favourable conditions for CWC mound initiation and development along the shelf-edge margin, possibly due to differing conditions in the European Slope Current which flows northward along the continental slope from south of the Porcupine Bank to the Faroe-Shetland Channel. [ABSTRACT FROM AUTHOR]

The first record of the solitary stony coral Fungiacyathus (Fungiacyathus) fragilis is reported from the southwestern Atlantic Ocean. Specimens were collected at the Mar del Plata submarine canyon in the Argentinian continental slope at 2419–3447 m depth during 2012 and 2013. The four specimens studied through histological sections were gonochoric. A high fecundity was recorded for one female (26,496 oocytes per polyp). The maximum size of oocytes was 786 µm suggesting lecitotrophic development, also no planulae were observed. Both previtellogenic and large vitellogenic oocytes were found in all females. Evidence of asexual reproduction was identified in corallum of a dried specimen. [ABSTRACT FROM AUTHOR]

As the interface between seawater and the seabed, superficial sediments on the seabed are an important part of the marine acoustic field environment and are indispensable for marine resource investigations. Studying sediments several meters to hundreds of meters below the seafloor is highly valuable and important. This study processes and analyses the water depth, topography and bottom data and obtains the shallow bottom profile and topographic map of the northern continental slope of the South China Sea (SCS). The study analyzes the influence of physical parameter (including density, porosity, and grain size) on the acoustic velocity in sediments. Single-parameter and dual-parameter models are established to further examine this influence. The results show that porosity and density have greater influences on the acoustic velocity of sediments than does grain size. Finally, the acoustic properties of several typical stations with water depths are tested to analyze the variations in the acoustic properties of the shallow sediments in the northern SCS. The results show that the influence of each parameter on the prediction of the acoustic velocity of the sediment is in the following order: porosity>density>grain size. This study analyses and reveals the reason why the seafloor sediments in the local area cause the acoustic properties to change greatly. It may be caused by changes in the sediment type, lithology along with the depth. And the other reason is the development of interlayer in the land slope of the northern SCS. [ABSTRACT FROM AUTHOR]

Topographic Rossby waves (TRWs) dominate the low-frequency variability of deep ocean currents and play a crucial role in energy exchange and material mixing. On the continental slope of the southwestern South China Sea, a deep-water mooring was deployed to observe TRWs for a period of ~ 40 days. The TRWs, with a wavelength of 109 km, account for 41.3% of the subinertial variations. A ray-tracing model was applied to investigate the propagation and energy source. The results showed that the TRWs propagated from the northeast of the mooring location and were most likely caused by the mesoscale eddy disturbances off the Vietnam coast. This study provides a new perspective on examining the impact of mesoscale eddies off Vietnam on abyssal currents. [ABSTRACT FROM AUTHOR]

The structure of the Antarctic Slope Current at the continental shelf is crucial in governing the poleward transport of warm water. Canyons on the continental slope may provide a pathway for warm water to cross the slope current and intrude onto the continental shelf underneath ice shelves, which can increase rates of ice shelf melting, leading to reduced buttressing of ice shelves, accelerating glacial flow and hence increased sea level rise. Observations and modeling studies of the Antarctic Slope Current and cross-shelf warm water intrusions are limited, particularly in the East Antarctica region. To explore this topic, an idealized configuration of the Antarctic Slope Current is developed, using an eddy-resolving isopycnal model that emulates the dynamics and topography of the East Antarctic sector. Warm water intrusions via canyons are found to occur in discrete episodes of large onshore flow induced by eddies, even in the absence of any temporal variability in external forcings, demonstrating the intrinsic nature of these intrusions to the slope current system. Canyon width is found to play a key role in modulating cross-shelf exchanges; warm water transport through narrower canyons is more irregular than transport through wider canyons. The intrinsically episodic cross-shelf transport is found to be driven by feedbacks between wind energy input and eddy generation in the Antarctic Slope Current. Improved understanding of the intrinsic variability of warm water intrusions can help guide future observational and modeling studies in the analysis of eddy impacts on Antarctic shelf circulation. [ABSTRACT FROM AUTHOR]

Lithogenic materials such as terrigenous lithogenic particles (TLP) can efficiently promote the formation and sinking of mineral‐associated marine organic matter, acting as important ballast and potentially playing an important role in the global carbon cycle. To assess the influence of TLP on fluxes of particulate organic carbon (POC) and other biogeochemical cycles, we construct TLP forcing fields based on global riverine suspended sediment data and then apply them to the Community Earth System Model, version 2 (CESM2) modified with the TLP ballasting effect term. Simulations forced by different concentrations of TLP transported in the surface ocean or along the bottom of continental shelves and slopes are conducted. When the TLP transports seaward along the bottom, simulated POC fluxes at 100 and 2,000 m decrease about 11% and 19%, respectively, for the global ocean, and about 9% and 12%, respectively, for the oceanic regions of continental margins. The initial abiotic ballast processes triggered by TLP input increase POC fluxes, causing additional removal and burial of dissolved iron in continental margins. This further enhances the accumulation of macronutrients in the upwelling regions and their advection transport to neighboring subtropical gyres, thus altering regional productivity when simulations reach quasi‐equilibrium. When consider the impacts of TLP in simulations, the simulated POC flux exhibits an increase in subtropical gyres but a decrease in tropical Pacific and mid‐high latitude regions. The present work highlights the importance of TLP in global biogeochemical cycles, suggesting that the amount of carbon sequestration might be overestimated without TLP in models. Key Points: The ballast effect of terrigenous lithogenic particles has been incorporated into a community earth system modelCarbon sequestration might be overestimated without terrigenous lithogenic particles in the modelWith terrigenous lithogenic ballast, simulated POC flux increases in subtropics but decreases in tropical Pacific and mid‐high latitudes [ABSTRACT FROM AUTHOR]

The larvae of many marine species are pelagic drifters in the vast oceans, yet they are the first and, for sessile species, the only way to connect with other populations. Connectivity is of particular interest in designing and assessing marine protected areas (MPAs), as it is considered a factor of renewal and stability.In this study, we focused on larval mixing between MPAs, investigating mixing rates during and at the end of their pelagic life, and how this is affected by the timing of larval release. We used a particle transport model coupled to the climatological hydrodynamics of the northwestern Mediterranean Sea to simulate the trajectories of Nephrops norvegicus larvae. Larvae were released from four no‐take MPAs, where fishery activity is banned, and started mixing between 7 and 12 days old.At settlement time, larval mixing mainly occurred between two pairs of MPAs labelled AxB (49.4% ± 5.8%) and CxD (23.7% ± 10.7%), respectively, located on the northern and southern sides of a thermal front. Percentages of larval mixing between these pairs changed, and other MPA combinations were formed with delayed larval release times. Mixing of larvae released from the same MPA tended to decrease with increasing delays between release times.This variability in mixing was related to the latitudinal distribution of MPAs along the continental slope and the spatiotemporal dynamics of the regional hydrodynamics, with a strong impact from a thermal front.Larval mixing modelling is a useful measure for understanding connectivity in marine environments and can suggest new conservation decisions. It identifies MPAs that are spatially distributed to facilitate the convergence of larvae from various protected areas. It also underlines that recognizing the significance of hydrodynamic variability when designing MPAs is crucial for promoting efficient connectivity among these areas. [ABSTRACT FROM AUTHOR]

Multiwave interference plays a crucial role in shaping the spatial variations of internal tides. Based on a combination of in situ mooring and altimeter data, interference of semidiurnal internal tides was investigated in the northern South China Sea. Mooring observations indicate the observed kinetic-to-potential energy ratio and group speed are both relatively lower than the theoretical values of mode-1 semidiurnal internal tides, indicating the presence of partly-standing waves. This is consistent with the altimeter result that the mooring was located at the antinode within the interference pattern formed by the superposition of the westward and southward semidiurnal internal tides from the Luzon Strait and the continental slope of the southern Taiwan Strait. However, the kinetic-to-potential energy ratio and group velocity were notably changed when an anticyclonic eddy passed by the mooring. By employing the ray-tracing method, we identified that mesoscale processes may induce a phase difference in the semidiurnal internal tides between the Luzon Strait and the continental slope of the southern Taiwan Strait. This alteration further leads to changes in the positions of nodes and antinodes within the interference pattern of the semidiurnal internal tides. [ABSTRACT FROM AUTHOR]

Picophytoplankton are a ubiquitous component of marine plankton communities and are expected to be favored by global increases in seawater temperature and stratification associated with climate change. Eukaryotic and prokaryotic picophytoplankton have distinct ecology, and global models predict that the two groups will respond differently to future climate scenarios. At a nearshore observatory on the Northeast US Shelf, however, decades of year‐round monitoring have shown these two groups to be highly synchronized in their responses to environmental variability. To reconcile the differences between regional and global predictions for picophytoplankton dynamics, we here investigate the picophytoplankton community across the continental shelf gradient from the nearshore observatory to the continental slope. We analyze flow cytometry data from 22 research cruises, comparing the response of picoeukaryote and Synechococcus communities to environmental variability across time and space. We find that the mechanisms controlling picophytoplankton abundance differ across taxa, season, and distance from shore. Like the prokaryote, Synechococcus, picoeukaryote division rates are limited nearshore by low temperatures in winter and spring, and higher temperatures offshore lead to an earlier spring bloom. Unlike Synechococcus, picoeukaryote concentration in summer decreases dramatically in offshore surface waters and exhibits deeper subsurface maxima. The offshore picoeukaryote community appears to be nutrient limited in the summer and subject to much greater loss rates than Synechococcus. This work both produces and demonstrates the necessity of taxon‐ and site‐specific knowledge for accurately predicting the responses of picophytoplankton to ongoing environmental change. [ABSTRACT FROM AUTHOR]

We discovered seafloor features such as bacterial mats and carbonate crusts typical for active methane seeps on the continental slope southwest of Svalbard. These features are associated with two main northwest-southeast trending morphological structures that are oriented parallel to the regional continental slope. Both structures occur at c. 800 m water depth, at the boundary between the Storfjorden trough mouth fan to the south and the Hornsund trough mouth fan to the north, which suggests a loading related fluid seepage. The main structure displays depressions and ridges forming a crater in its center. Other occurring features include small sediment mounds, domes often covered by bacterial mats, and hummocky seafloor colonized by siboglinid tubeworms. Free gas bubbles were spotted close to the centre and plumes along the rims of the structure. Thick carbonate crusts indicate a long seepage history in the center of the structure and on top of the ridges. The sources of the seeps are likely to be Miocene old organic-rich deposits, or Paleocene hydrocarbon reservoirs. [ABSTRACT FROM AUTHOR]