Hasil untuk "Oceanography"

C. Bacon, D. Silvestro, C. Jaramillo et al.

Significance The formation of the Isthmus of Panama, which linked North and South America, is key to understanding the biodiversity, oceanography, atmosphere, and climate in the region. Despite its importance across multiple disciplines, the timing of formation and emergence of the Isthmus and the biological patterns it created have been controversial. Here, we analyze molecular and fossil data, including terrestrial and marine organisms, to show that biotic migrations across the Isthmus of Panama began several million years earlier than commonly assumed. An earlier evolution of the Isthmus has broad implications for the mechanisms driving global climate (e.g., Pleistocene glaciations, thermohaline circulation) as well as the rich biodiversity of the Americas. The linking of North and South America by the Isthmus of Panama had major impacts on global climate, oceanic and atmospheric currents, and biodiversity, yet the timing of this critical event remains contentious. The Isthmus is traditionally understood to have fully closed by ca. 3.5 million years ago (Ma), and this date has been used as a benchmark for oceanographic, climatic, and evolutionary research, but recent evidence suggests a more complex geological formation. Here, we analyze both molecular and fossil data to evaluate the tempo of biotic exchange across the Americas in light of geological evidence. We demonstrate significant waves of dispersal of terrestrial organisms at approximately ca. 20 and 6 Ma and corresponding events separating marine organisms in the Atlantic and Pacific oceans at ca. 23 and 7 Ma. The direction of dispersal and their rates were symmetrical until the last ca. 6 Ma, when northern migration of South American lineages increased significantly. Variability among taxa in their timing of dispersal or vicariance across the Isthmus is not explained by the ecological factors tested in these analyses, including biome type, dispersal ability, and elevation preference. Migration was therefore not generally regulated by intrinsic traits but more likely reflects the presence of emergent terrain several millions of years earlier than commonly assumed. These results indicate that the dramatic biotic turnover associated with the Great American Biotic Interchange was a long and complex process that began as early as the Oligocene–Miocene transition.

Jeffrey van der Voort, Martin Verlaan, Hanne Kekkonen

Currently, more and more machine learning (ML) surrogates are being developed for computationally expensive physical models. In this work we investigate the use of a Multi-Fidelity Ensemble Kalman Filter (MF-EnKF) in which the low-fidelity model is such a machine learning surrogate model, instead of a traditional low-resolution or reduced-order model. The idea behind this is to use an ensemble of a few expensive full model runs, together with an ensemble of many cheap but less accurate ML model runs. In this way we hope to reach increased accuracy within the same computational budget. We investigate the performance by testing the approach on two common test problems, namely the Lorenz-2005 model and the Quasi-Geostrophic model. By keeping the original physical model in place, we obtain a higher accuracy than when we completely replace it by the ML model. Furthermore, the MF-EnKF reaches improved accuracy within the same computational budget. The ML surrogate has similar or improved accuracy compared to the low-resolution one, but it can provide a larger speed-up. Our method contributes to increasing the effective ensemble size in the EnKF, which improves the estimation of the initial condition and hence accuracy of the predictions in fields such as meteorology and oceanography.

Agissilaos Athanassoulis, Fotini Karakatsani, Irene Kyza

The von Neumann equation with delta self-interaction kernel serves as a statistical model for nonlinear waves, and it exhibits a bifurcation between stable and unstable regimes. In oceanography it is known as the Alber equation, and its bifurcation is important for understanding rogue waves, a key problem in marine safety. Despite its significance, only one first-order-in-time numerical method exists in the literature. In this paper, we propose a structure-preserving, linearly implicit, second-order-in-time scheme for its numerical solution. We employ fourth-order finite differences for the spatial discretization. As an illustrative example, we explore the onset of modulation instability. We verify that the linear stability analysis accurately predicts the initial growth phase, but fails to forecast the maximum amplitude, the formation of a coherent structure in the nonlinear regime, or the relevant timescales. Monte Carlo simulations with Gaussian background spectra reveal that the maximum amplitude depends mainly on the homogeneous background rather than the initial inhomogeneity. For weak instabilities, the inhomogeneity grows substantially from its initial condition, but remains small compared to the background. On the other hand, strong instability leads to recurrent hotspots of increased variance. This provides a possible explanation of how modulation instability makes rogue waves more likely in unidirectional sea states.

Wenli Guo, Xiaoli Lei, Chen Liang et al.

Mayorella marianaensis (Amoebozoa: Discosea) was the only Mayorella species isolated from deep sea (over 3000 m-depth). We firstly present a transcriptomic analysis of the non-model amoeba species collected from the Mariana Trench area. Illumina sequencing platform was used to generate data which including raw data, cleaned reads, de novo assembly, and functional annotation. After assembly, the final transcriptome consists of 57,459,544 transcripts with a mean length of 1646 and N50 length of 1170. The transcriptome has a completeness of 67.4 % as assessed by BUSCO. Functional annotation pathways related to signal transduction, transport and catabolism, and translation are the most annotated in the transcriptome.

Xuran Men, Jinlong He, Bo Jiao et al.

With the rapid development and accelerated utilization of marine resources, multi-body floating systems have become extensively used in practical applications. This study examines the coupled motions of a side-by-side anchoring system for five fishing vessels in a harbor using ANSYS-AQWA. The system is connected by hawsers and equipped with fenders to reduce collisions between the vessels. It is designed to operate in the sheltered wind-wave combined environment within Ningbo Zhoushan Port, China. Considering the diverse types and quantities of fishing vessels in the anchorage area, this paper proposes a mixed arrangement of three large-scale fishing vessels in the middle and two small-scale vessels on both sides. The time-domain analysis is performed on this system under the combined effects of wind and waves, calculating the motion responses of the five fishing vessels along with the mechanical loads at the hawsers, fenders, and moorings. The results indicate that the maximum loads on these mechanical components remain well within the safe working limits, ensuring reliable operation. In addition, the impact of varying wind-wave angles on the coupled motions of the fishing vessel system are studied. As the wind-wave angle increases, the surge motion of the fishing vessels gradually decreases, while the sway motion intensifies. The forces on the hawsers, fenders, and mooring system exhibit distinct characteristics at different angles.

J. Xavier Prochaska, Daniel Rudnick

Dissolved oxygen (DO) is a non-conservative tracer of interactions at the air-sea interface, respiration and photosynthesis, and advection. In this manuscript, we study extremes in the degree of oxygen saturation (SO), the ratio of DO to the maximum concentration given the water's temperature, salinity, and depth with SO=1 critically saturated. We perform the analysis with the California Underwater Glider Network (CUGN), which operates gliders on four lines that extend from the California coast to several hundred kilometers offshore, profiling to 500m depth every 3km. Since ~2017, the gliders have been equipped with a Sea-Bird 63 optode sensor to measure the DO content. We find that parcels with SO>1.1, hyperoxic extrema, occur primarily near-shore in the upper 50m of the water column and during non-winter months. Along Line 90 which originates in San Diego, these hyperoxic events occur primarily in stratified waters with shallow mixed layers. We hypothesize that photosynthesis elevates DO in sub-surface water that can not rapidly ventilate with the surface. Along the three other lines, hyperoxic extrema occur almost exclusively at the surface and are correlated with elevated Chl-a fluorescence suggesting they are primarily driven by blooms of photosynthesis. We also examine hypoxic extrema, finding that parcels with SO<0.9 and z<50m occur most frequently along the northernmost line where upwelling has greatest impact.

Onay Hatice, Kurtul Irmak, Kaya Cüneyt et al.

This study analyzed the length–weight relations and condition factors of 13 species belonging to three highly endemic genera: Oxynoemacheilus (6), Seminemacheilus (2) and Cobitis (5). Fish were sampled in several streams and lakes using a backpack electroshocker. Analyses were based on a total number of individuals, which was n = 304. A linear regression model was applied to determine the relationship between fish length and weight. The coefficient of determination (R2) ranged from 0.950 to 0.980 for all populations (p < 0.05). Allometric coefficient ‘b’ values ranged from 2.498 to 3.201 for Oxynoemacheilus, from 2.970 to 2.127 for Seminemacheilus, and from 2.111 to 3.076 for Cobitis populations. Fulton’s condition factor for Oxynoemacheilus, Seminemacheilus and Cobitis ranged from 0.391 to 3.080. This study addresses gaps in LWR and CF information for a number of ecologically important freshwater fish species. It is expected that the results of this research provide baseline data for further fisheries management studies and may support conservation studies of related species.

V. I. Ostrovsky

Methods for forecasting the stocks of pacific salmon in Khabarovsk Region are considered. Errors of the forecasts based on theoretical parent-offspring models are associated with variability in weather conditions on the spawning grounds. The progeny dynamics is modeled much better when weather factors are assimilated into the single- factor models. The errors reduction would be expected for multifactor models, assuming that they will be based on reliable data on the number of parents and offspring, though this condition seems questionable in the face of a growing shortage of qualified observers and modelers.

Sofiia Drozd, Nataliia Kussul

The Green Deal strategic plan for the development of renewable energy until 2030 is of particular importance in the context of the restoration of Ukraine’s post-war energy infrastructure. One of the key topics is the analysis of the possibilities of installing large solar power plants in Ukraine. In this article, a multi-criteria analysis of the suitability of the territory of Ukraine is carried out on the basis of climatic, topographic and land use criteria. To assess land suitability, criteria standardized using fuzzy logic with weights determined by experts through the method of pairwise comparisons were combined using a weighted sum model. Upon completing the study, a suitability map was generated, depicting zones with varying levels of suitability (ranging from 0 to 1) for solar power plant placement. It was found that more than 35.68% of the country has average values of the suitability index (0.65–0.7), and approximately 18.82% show high indicators (<0.7). Conditions are especially favorable in the south of Ukraine.

Chung Hyeon Lee, Young Kyun Lim, Mungi Kim et al.

The seasonal dynamics of phytoplankton communities in Korean coastal waters (KCWs) are influenced by complex interactions between ocean currents and nearshore human activities. Despite these influences, the understanding of seasonal phytoplankton changes and their environmental relationships in KCWs remains limited. We investigate the influence of the distinct characteristics of the three seas surrounding the KCWs (the Yellow Sea, the South Sea, and the East Sea) on seasonal phytoplankton communities based on field surveys conducted at 23 stations between 2020 and 2021. The East Sea exhibited higher winter temperatures due to the Jeju and Tsushima warm currents, while summer temperatures were lower compared to the other regions, highlighting the role of currents and deeper oceanic waters. The Yellow Sea showed significant freshwater influence with low salinity levels from major rivers, contrasting with the higher salinity in the East Sea. These differences led to a disparity in the productivity of the two regions: the highest value of Chl. <i>a</i> was observed to be 6.05 µg L⁻¹ in the Yellow Sea in summer. Diatoms dominated in nutrient-rich conditions, particularly in the Yellow Sea, where they comprised up to 80–100% of the phytoplankton community in summer, winter, and spring. PCA analysis revealed positive correlations between diatoms and Chl. <i>a</i>, while cryptophytes, which thrive in the absence of diatom proliferation, showed no such correlation, indicating their opportunistic growth in nutrient-limited conditions. This study highlights the significant impact of region-specific hydrographic factors on phytoplankton communities in KCWs, with diatoms dominating in summer and cryptophytes and dinoflagellates showing seasonal and regional variations. Understanding these dynamics is crucial for predicting phytoplankton bloom dynamics and their ecological implications in coastal ecosystems.

Anand Gnanadesikan, Gianluca Fabiani, Jingwen Liu et al.

The current configuration of the ocean overturning involves upwelling predominantly in the Southern Ocean and sinking predominantly in the Atlantic basin. The reasons for this remain unclear, as both models and paleoclimatic observations suggest that sinking can sometimes occur in the Pacific. We present a six-box model of the overturning in which temperature, salinity and low-latitude pycnocline depths are allowed to vary prognostically in both the Atlantic and Pacific. The overturning is driven by temperature, winds, and mixing and modulated by the hydrological cycle. In each basin there are three possible flow regimes, depending on whether low-latitude water flowing into northern surface boxes is transformed into dense deep water, somewhat lighter intermediate water, or light water that is returned at the surface. The resulting model combines insights from a number of previous studies and allows for nine possible global flow regimes. For the modern ocean, we find that although the interbasin atmospheric freshwater flux suppresses Pacific sinking, the equator-to-pole flux enhances it. When atmospheric temperatures are held fixed, seven possible flow regimes can be accessed by changing the amplitude and configuration of the modern hydrological cycle . North Pacific overturning can strengthen with either increases or decreases in the hydrological cycle, as well as under reversal of the interbasin freshwater flux. Tipping-point behavior of both transient and equilibrium states is modulated by parameters such as the poorly constrained lateral diffusive mixing. If hydrological cycle amplitude is varied consistently with global temperature, northern polar amplification is necessary for the Atlantic overturning to collapse

Jiangnan Zhang, Hai Wang, Fengjuan Cui et al.

The establishment of ship trajectory prediction is critical in analyzing trajectory data. It serves as a critical reference point for identifying abnormal behavior and potential collision risks for ships. Accurate and real-time ship trajectory prediction is essential during navigation. Since the timing of automatic identification system (AIS) data is irregular, traditional methods usually use time calibration to simulate the data of uniform sequencing before analysis. Inevitably, this increases the chances of error and time delays. To address this issue, we propose a time-aware LSTM (T-LSTM) single-ship trajectory model combined with the generative adversarial network (GAN) to predict multiple ship trajectories. These analysis methods are capable of directly analyzing AIS data and have demonstrated better performance in both single-ship and multi-ship trajectories. Our experimental results show that the proposed method achieves high accuracy and can meet the practical navigation requirements of ships.

Emil Stanev

Yohei Onuki, Sylvain Joubaud, Thierry Dauxois

A gradient-wind balanced flow with an elliptic streamline parametrically excites internal inertia-gravity waves through ageostrophic anticyclonic instability (AAI). This study numerically investigates the breaking of internal waves and the following turbulence generation resulting from the AAI. In our simulation, we periodically distort the calculation domain following the streamlines of an elliptic vortex and integrate the equations of motion using a Fourier spectral method. This technique enables us to exclude the overall structure of the large-scale vortex from the computation and concentrate on resolving the small-scale waves and turbulence. From a series of experiments, we identify two different scenarios of wave breaking conditioned on the magnitude of the instability growth rate scaled by the buoyancy frequency, $λ/N$. First, when $λ/N\gtrsim0.008$, the primary wave amplitude excited by AAI quickly goes far beyond the overturning threshold and directly breaks. The resulting state is thus strongly nonlinear turbulence. Second, if $λ/N\lesssim0.008$, weak wave-wave interactions begin to redistribute energy across frequency space before the primary wave reaches a breaking limit. Then, after a sufficiently long time, the system approaches a Garrett-Munk-like stationary spectrum, in which wave breaking occurs at finer vertical scales. Throughout the experimental conditions, the growth and decay time scales of the primary wave energy are well correlated. However, since the primary wave amplitude reaches a prescribed limit in one scenario but not in the other, the energy dissipation rates exhibit two types of scaling properties. This scaling classification has similarities and differences with D'Asaro and Lien's (2000) wave-turbulence transition model.

Nihar Paul, Jai Sukhatme, Bishakhdatta Gayen et al.

Eddy-freshwater interaction is studied in the north Bay of Bengal (BoB) with a high-resolution simulation using the Regional Ocean Modeling System. Following observations, the model simulates the trapping and homogenization of river water by a cyclonic mesoscale eddy on a sub-monthly time scale from October-November of 2015. As fresh river water is trapped in the eddy, it is characterized by strong vertical and lateral gradients in salinity. Within a few weeks, these gradients relax along with the progressive homogenization of freshwater within the eddy. A mixed layer salinity budget shows the importance of ageostrophic vertical advection in addition to lateral advection during the evolution of salinity within the eddy. An analysis of the eddy kinetic energy (EKE) budget in the upper ocean indicates the development of barotropic and baroclinic instabilities. The vertical profiles of EKE conversion terms reveal that the surface freshwater was involved in the evolution of baroclinic instability within the mixed layer. In addition, an eddy available potential energy (EPE) budget shows that the entrainment of the river water raises the EPE, which is due to an increase in lateral salinity gradients across the eddy during the trapping event. Subsequently, the salinity homogenization leads to a decrease in the EPE, and its rate of decay is modulated by a correlation between surface buoyancy fluxes and density anomalies. Finally, reanalysis data show similar trapping and homogenization events across multiple years, highlighting the importance of this mechanism of subseasonal freshwater evolution in the BoB.

Mona Fairuz Ramli, Ahmad Shabudin Ariffin, Marziah Zahar et al.

Mangrove forests are special type of coastal ecosystem characterized by their adaptations that enable plants to thrive in saline soil. Despite accounting for only about 1% of global forest coverage, mangroves are keystone ecosystems that provide a variety of critical ecological processes and environmental services. In recent years, there has been a considerable increase in interest in mangrove biodiversity. The lack of community-based organizations (CBO) on the awareness of conservation has a direct negative impact on endangered species. The aim of this is to analyze the conservation and preservation for mangrove in north coast area of Malaysia. Qualitative method was used to collect and analyzed the data, and supported with observations. The findings showed that mangrove conservation project in Kilim and Acheh River rivers are participated by the different stakeholders such as local government units (LGU), NGOs (PiFWA and Koperasi Komuniti Kampung Kilim Langkawi Berhad and Koperasi Nelayan Sungai Kubang Badak Langkawi Berhad), as well as a local community composed of fishermen, gleaners and business operator (travel agent). Those stakeholders are playing different role depend on their capacities. This study proves that mangrove forests are important for coastal area in Malaysia, and conservation efforts are needed to protect it. This finding also can be applied in other area. The contribution and participation of all parties also need for any conservation activities. The funding is crucial for supporting the sustainability of conservation program because some parts of conservation need it to be built such infrastructure or material for conservation.

Holly E. Jenkins, Holly E. Jenkins, Florence Atherden et al.

Calanoid copepods comprise around 90% of Arctic zooplankton biomass and are fundamental to the ecological and biogeochemical functioning of high-latitude pelagic ecosystems. They accumulate lipid reserves during the productive months and represent an energy-rich food source for higher trophic levels. Rapidly changing climate in the Arctic may alter the quantity and composition of the food environment for one of the key copepod species, Calanus finmarchicus, with as yet unquantified effects on its production. Here we present rates of feeding and egg production in female C. finmarchicus exposed to the range of feeding conditions encountered across the Fram Strait in May/June 2018. Carbon (C) budgets were constructed and used to examine the relationship between feeding and growth (= egg production) in these animals. C-specific ingestion rates (mean ± standard deviation) were highly variable, ranging from 0.015 ± 0.004 to 0.645 ± 0.017 day-1 (mean = 0.295 ± 0.223 day-1), and were positively correlated with food availability. C-specific egg production rates ranged from 0.00 to 0.049 day-1 (mean = 0.012 ± 0.011) and were not correlated with either food availability or ingestion rate. Calculated gross growth efficiencies (GGE: growth/ingestion) were low, 0.12 ± 0.13 (range = 0.01 to 0.39). The assembled C budgets indicate that the average fraction of ingested food that was surplus to the requirements for egg production, respiration and losses to faecal pellets was 0.17 ± 0.42. We suggest that this excess occurred, at least in part, because many of the incubated females were still undergoing the energetically (C-) expensive process of gonad maturation at the time of sampling, an assertion that is supported by the relatively high C:N (nitrogen) ratios of the incubated females, the typically low egg production rates, and gonad maturation status. Ontogenetic development may thus explain the large variability seen in the relationship between egg production and ingestion. The apparently excessive ingestion rates may additionally indicate that recently moulted females must acquire additional N via ingestion to complete the maturation process and begin spawning. Our results highlight the need for improved fundamental understanding of the physiology of high-latitude copepods and its response to environmental change.

Jiahui Shi, Zhengjiang Liu

The port waterway network plays an important role in the organization and management of port ship traffic. Due to limited ship operations, conflicts, congestion, and safety issues often arise in port waters. Conflicts between ships can be predicted by collision detection between ships. A novel collision detection algorithm for trajectory pairs is proposed by introducing variable time interval variables. In addition, to improve the overall accuracy of trajectory compression and reduce redundant calculation in collision detection, a multi-factor Douglas-Peucker algorithm adapted to ship trajectory compression is proposed with the consideration of speed and turn constraints. The maximum speed difference of the algorithm is increased by 1.5–2.5%, and the average speed difference increased by 2.0–4.5%. Based on the method mentioned above, the risk assessment framework of maritime collision is established and the risk situation of the waters near Ningbo Zhoushan Port is evaluated and analyzed by using ship historical track data.

Amartya Mukherjee, Yusuf Aydogdu, Thambirajah Ravichandran et al.

Growing set of optimization and regression techniques, based upon sparse representations of signals, to build models from data sets has received widespread attention recently with the advent of compressed sensing. This paper deals with the parameterization of the Lorenz-96 model with two time-scales that mimics mid-latitude atmospheric dynamics with microscopic convective processes. Compressed sensing is used to build models (vector fields) to emulate the behavior of the fine-scale process, so that explicit simulations become an online benchmark for parameterization. We apply compressed sensing, where the sparse recovery is achieved by constructing a sensing/dictionary matrix from ergodic samples generated by the Lorenz-96 atmospheric model, to parameterize the unresolved variables in terms of resolved variables. Stochastic parameterization is achieved by auto-regressive modelling of noise. We utilize the ensemble Kalman filter for data assimilation, where observations (direct measurements) are assimilated in the low-dimensional stochastic parameterized model to provide predictions. Finally, we compare the predictions of compressed sensing and Wilk's polynomial regression to demonstrate the potential effectiveness of the proposed methodology.

Carlos Leal-Bastidas, Luis Vargas-Chacoff, Natalia Sandoval et al.

Los ríos de la Patagonia son uno de los ecosistemas acuáticos mejor conservados en América del Sur. Sin embargo, debido al creciente desarrollo económico en la región, numerosos cuerpos de agua se han visto amenazados por actividades humanas. Analizamos la calidad del agua y la estructura del ensamble de macroinvertebrados en ocho estaciones a lo largo del río Palena, en el sector alto de la cuenca con mínima perturbación y sector bajo para aquellas estaciones perturbadas por actividades humanas. El muestreo abarcó cuatro estaciones del año (septiembre 2013 a mayo 2014). La temperatura, conductividad eléctrica, pH, oxígeno disuelto, dureza total, sílice, aluminio y fierro mostraron diferencias significativas (p < 0,05) entre la parte alta y baja de la cuenca y entre estaciones del año. Se registraron 30 familias de macroinvertebrados (90% larvas de insectos), siendo el Orden Diptera el más diverso (8 familias). La familia Leptophlebiidae (Ephemeroptera) fue la más abundante en las cuatro estaciones del año. Diferencias significativas en el ensamble de macroinvertebrados se registraron entre estaciones del año, agrupándose en dos grupos: verano-otoño y invierno-primavera, pero no entre la estructura del ensamble entre la zona alta y baja de la cuenca. Estos resultados indican que la estacionalidad tiene un efecto sobre la composición del ensamble de macroinvertebrados por sobre diferencias espaciales en la cuenca. Por otro lado, la alta diversidad de macroinvertebrados registradas en el río Palena, y buena calidad del agua, indican que las actividades antrópicas aún no son un riesgo para el ecosistema acuático.