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Characterizing the diel variability of acoustic scattering layers near the Okinawa Islands using cyclostationary empirical orthogonal function
No full textThe behavior of marine organisms is part of the oceanic carbon cycle and closely linked to climate change. To investigate biological behaviors such as vertical migration and aggregation layers near the Okinawa Islands, a year-long mooring observation was conducted from June 2015 to July 2016 using acoustic Doppler current profilers at the Okinawa Trough (KCM1) and the North Pacific side of the Okinawa Islands (RCM1). Acoustic backscattering intensity (Sv) served as an indicator of diel vertical migration (DVM) and aggregation layers. At both stations, nocturnal DVM was consistently observed between ∼100–400 m, including a shallow scattering layer (SSL: 100–200 m) and a deep scattering layer (DSL: 300–400 m). Vertical migration speed was higher at KCM1 (3.6–5.6 cm s⁻¹) than at RCM1 (2.2–3.2 cm s⁻¹), likely reflecting differences in water masses. Using the cyclostationary empirical orthogonal function (CSEOF), 24-hour Sv cycles were decomposed into three principal modes and corresponding amplitude time series, primarily representing DVM, DSL, and SSL. DVM intensity increased with temperature above the SSL and showed a one-month lag with surface net solar radiation (SSR), suggesting surface warming as a potential driver. DSL depth was negatively correlated with surface temperature (0–30 m), while SSL showed a longer lag. During summer, therefore, enhanced SSR and warming could intensify DVM and deepen the scattering layers, potentially enhancing the biological carbon cycle. These results highlight the relationship of biological behaviors to surface warming and their role in carbon export near the Okinawa Islands.11Nsciescopu
Dissolved organic matter dynamics in a whale-dominated coastal system: Insights from Península Valdés, Argentina
No full textDissolved organic matter (DOM) is increasingly being recognized as critical components of the global carbon cycle. Sheltered coastal areas that host high densities of large marine mammals may play a particularly important role in coastal carbon fluxes, but spatial and temporal changes in dissolved organic carbon (DOC) and nitrogen (DON) dynamics in coastal ecosystems remain largely unexplored. Here, we provide the first quantitative data on DOC and DON dynamics and sources in Golfo Nuevo, a protected gulf in the Península Valdés (Argentina) known as one of the most important calving grounds for the southwestern Atlantic population of the southern right whale (Eubalaena australis). Specifically, we show that Golfo Nuevo is a highly productive system that acts as a major source of DOM to the South Atlantic shelf. We also found that DOC and DON concentrations increased by 1.37- and 1.41-fold, respectively, during the whale calving season. The δ13C isotopic signal of this DOC indicated that it was predominantly whale- and phytoplankton-derived, suggesting a potential ‘whale pump’. In addition, microbial carbon overconsumption during the whale calving season increased the DOC:DON ratio, indicating increased DOC refractoriness. Bioavailable DOC accounted for 18.6 %–52.7 % of the DOC pool, whereas the average recalcitrant DOC concentrations were 200 ± 19 μM and 180 ± 7 μM in the non-whale and whale seasons, respectively. Overall, our results highlight how large marine mammals can act as a vector for both, labile and recalcitrant DOC and thereby modulate DOM dynamics in coastal habitats.11Nsciescopu
Joint receiver deghosting and streamer depth inversion without prior depth information
No full textReceiver-side ghost reflections in marine seismic data cause destructive interference that degrades vertical resolution and limits usable bandwidth, particularly in shallow water environments. While dual-sensor and variable-depth streamer systems can mitigate these effects, their effectiveness relies on accurate depth measurements, which are typically available but may be compromised in legacy data sets or in the presence of equipment malfunctions. Processing-based deghosting methods typically assume static and known receiver depths, limiting their effectiveness when depth variations are unmeasured or dynamic. This study introduces a joint inversion framework for simultaneous receiver deghosting and streamer depth estimation without prior depth information. The method operates in the tau-p domain and combines sparse inversion via iterative shrinkage-thresholding algorithm with depth optimization through gradient descent. Initial depth estimates are obtained from autocorrelation-derived ghost delay analysis. Numerical experiments on synthetic and field data sets demonstrate that the method effectively suppresses ghost artefacts, broadens spectral bandwidth and enhances reflector continuity. The estimated depth profiles reflect realistic streamer behaviour, including sag, and converge towards effective values that best explain the ghost interference under a least-squares criterion. These results confirm the robustness and practical value of the approach for marine seismic processing, particularly in reprocessing legacy data or handling surveys with incomplete acquisition metadata. The framework offers a data-driven alternative to hardware-dependent deghosting solutions.11Ysciescopu
A random forest-based method for reconstructing pressure fields in tropical cyclones from wind data
No full textTropical cyclones (TCs) are among the most destructive weather phenomena, causing severe social and economic damage through extreme rainfall, strong winds, and storm surges. Wind and pressure fields, which define TCs’ structure and impact, are spatial variables whose accurate estimation is essential for improved analysis and prediction. However, high-precision observations are limited by cost and coverage, and numerical or reanalysis models are computationally intensive. Parametric models based on radial symmetry also struggle to represent the asymmetry and diversity of real TCs. This study proposes a random forest model that estimates TC pressure fields by learning the nonlinear relationship between wind and pressure. Trained on ERA5 reanalysis data, the model captures spatial patterns such as pressure asymmetry, land–sea contrasts, and shows high explanatory power and low error, especially for intense TCs and within the gale-force wind radius. Comparison with parametric and other data-driven models confirms its superior spatial accuracy. An experiment using satellite-based two-dimensional wind data demonstrates the model’s ability to estimate pressure fields from real time inputs, supporting its use in disaster response and early warning.11Nsciescopu
Molecular-level composition and sources of airborne organic matter deposited into the Yellow Sea
No full textUsing Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), we analyzed the molecular composition of airborne organic matter (OM) deposited to the inshore and offshore regions of the Yellow Sea. The airborne OM deposited to offshore had the largest proportion of recalcitrant lignin/tannin compounds derived from Asian dust, riverine runoff, and biomass burning. The second largest proportion of airborne OM was labile protein/carbohydrate-like compounds produced by marine phytoplankton via sea spray aerosols during air-sea transport. However, in the inshore site, recalcitrant and labile OMs made up airborne OMs in similar proportion, respectively. The remaining airborne OM at both regions was composed of condensed aromatic/unsaturated hydrocarbon-like OM derived from anthropogenic sources. These results implied that airborne OM deposited inshore may be less degraded and more likely to remain in water column, whereas airborne OMs deposited offshore is more readily available to microbes and primary producers. Thus, this study demonstrated the complex composition of airborne OM from a mixture of terrestrial and marine sources at the molecular level, and showed that differences in airborne OM between regions can influence the oceanic C cycle and long-term C dynamics in marginal seas. © 2025 Elsevier B.V., All rights reserved.11Nsciescopu
Marine Macrobenthos Diversity of Chuuk Atoll in the Federated States of Micronesia, Western Tropical Pacific
No full textThe Federated States of Micronesia (FSM), located in the Western Tropical Pacific on the periphery of the Indo-Pacific Coral Triangle, which constitutes the epicenter of marine biodiversity since the early Miocene (about 25 MA), are recognized as a hotspot of terrestrial biodiversity. However, scientific data on the status of FSM’s marine ecosystems remain limited, hindering formal classification for purposes of conservation. Here, we present the taxonomic outcomes of a marine macrobenthos survey conducted in Chuuk Atoll between 2011 and 2014. Our inventory documents high species richness, particularly among cnidarians, followed by echinoderms, arthropods, mollusks, plathelminthes, annelids, nemerteans, sipunculans, and invertebrate chordates. These findings are discussed in comparison with marine biodiversity records from the Eastern Tropical Pacific (ETP), where climate models project a narrowing of differences in sea surface temperature (SST) relative to the Western Tropical Pacific (WTP). Such shifts could alter current biogeographic and diversity patterns across the Pacific basin. This study provides a baseline for assessing the impacts of ocean warming, anthropogenic pressures, and variability in natural climate, such as the El Niño-Southern Oscillation, on tropical macrobenthic communities. Our results not only help advance the understanding of regional marine biodiversity, but also support the inclusion of FSM’s marine environments in future biodiversity hotspot designations.11Nsciescopuskc
The relationships between fish length and otolith size of the striped snakehead, Channa striata (Bloch, 1793), collected from the River Ganga and its two tributaries in India
No full textThe relationship between the total length of fish and the morphometric characteristics of their otoliths (length, width, and weight) was examined in striped snakehead (Channa striata, Bloch, 1793) specimens collected from the River Ganga and its two tributaries in India. Channa striata, a commercially valuable species in India, was the focus of this study, which aimed to analyse the statistical correlations between the fish's total and standard lengths and their corresponding otolith measurements, with the expectation that the data will contribute to future research on the species' biology, particularly its age, and growth patterns. Both linear and non-linear regression models were applied, and the regression equations varied significantly between the three collection sites. These findings represent the first investigation into the relationship between otolith morphology and total fish length for striped snakehead from the River Ganga and its tributaries in India.11Nsciescopu
Photodegradation of PET plastics produces persistent compounds that accumulate in sediments
No full textPolyethylene terephthalate (PET) is one of the most widely used plastics, particularly in packaging and textiles. Although PET is widely used in consumer products, only 10–28 % is recycled. Most PET waste is not properly managed. It is often landfilled, burned, or simply discarded, eventually making its way into rivers and drainage systems and accumulating in marine ecosystems. In addition to hydrolytic degradation, PET is particularly susceptible to photodegradation, as its UV-absorbing aromatic rings facilitate backbone cleavage and the formation of lower-molecular-weight compounds. While microplastic formation has been widely studied, far less attention has been given to the polar, water-soluble degradation products—despite their potential for high mobility and bioavailability. In this study, PET photodegradation was simulated under controlled marine-like conditions. Using ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry, 17 degradation products were identified, five of which confirmed with authentic standards. Laboratory-based simulations indicated that the global annual release of these compounds could range from 1 to 5.5 tons, suggesting potential environmental accumulation. To verify this, targeted environmental analyses were conducted, detecting PET-derived degradation products in marine sediments collected from Ganggu Port, South Korea. This study reveals overlooked polar byproducts of PET photodegradation and highlights their relevance in assessing plastic pollution in marine environments.11Nsciescopu
Spatiotemporal variations of dissolved organic matter in coastal groundwater and controlling biogeochemical factors in tidal flats of Incheon, on the west coast of Korea
No full textTo investigate the spatiotemporal variability of dissolved organic matter (DOM) in coastal groundwater as influenced by aquifer type, we analyzed dissolved organic carbon (DOC) along with the optical properties of colored DOM (CDOM) and fluorescent DOM (FDOM) in a mud flat (Sohwangsando) and a sand flat (Seonnyeobawi) on the west coast of Korea (Incheon) from 2022 to 2023. DOC and FDOM concentrations in coastal groundwater were consistently higher in the mud flat, with pronounced increases during the summer. Across all seasons, groundwater exhibited higher concentrations of DOC, humic-like FDOM (FDOMH), and specific ultraviolet absorbance at 254 nm (SUVA254) than coastal seawater, indicating a significant groundwater contribution of humic substances to the coastal ocean. SUVA254 values were particularly elevated in the mud flat, suggesting greater DOM aromaticity, whereas the biological index (BIX) was higher in the sand flat, reflecting fresher and more bioavailable DOM. These results demonstrate distinct DOM signatures governed by aquifer type, with preferential accumulation of refractory DOM in muddy systems and enhanced contributions of labile, marine-derived DOM in permeable sandy environments. This study provides the first comparative insight into DOM dynamics across contrasting tidal aquifers in Korea, highlighting the overlooked role of submarine groundwater discharge (SGD) in regulating coastal carbon fluxes under monsoonal influence. Our results advance the understanding of how aquifer properties regulate the sources, composition, and fate of DOM within the coastal carbon cycle.11Nsciescopu
Characterizing the diel variability of acoustic scattering layers near the Okinawa Islands using cyclostationary empirical orthogonal function
No full textThe behavior of marine organisms is part of the oceanic carbon cycle and closely linked to climate change. To investigate biological behaviors such as vertical migration and aggregation layers near the Okinawa Islands, a year-long mooring observation was conducted from June 2015 to July 2016 using acoustic Doppler current profilers at the Okinawa Trough (KCM1) and the North Pacific side of the Okinawa Islands (RCM1). Acoustic backscattering intensity (Sv) served as an indicator of diel vertical migration (DVM) and aggregation layers. At both stations, nocturnal DVM was consistently observed between ∼100–400 m, including a shallow scattering layer (SSL: 100–200 m) and a deep scattering layer (DSL: 300–400 m). Vertical migration speed was higher at KCM1 (3.6–5.6 cm s⁻¹) than at RCM1 (2.2–3.2 cm s⁻¹), likely reflecting differences in water masses. Using the cyclostationary empirical orthogonal function (CSEOF), 24-hour Sv cycles were decomposed into three principal modes and corresponding amplitude time series, primarily representing DVM, DSL, and SSL. DVM intensity increased with temperature above the SSL and showed a one-month lag with surface net solar radiation (SSR), suggesting surface warming as a potential driver. DSL depth was negatively correlated with surface temperature (0–30 m), while SSL showed a longer lag. During summer, therefore, enhanced SSR and warming could intensify DVM and deepen the scattering layers, potentially enhancing the biological carbon cycle. These results highlight the relationship of biological behaviors to surface warming and their role in carbon export near the Okinawa Islands.11Nsciescopu