Journal of Geophysical Research-Oceans最新文献

As a crucial component of ecosystems, the distribution of zooplankton is closely related to environmental conditions and ocean currents. Despite its unique role in global circulation, zooplankton data for the Eastern Indian Ocean (EIO) remain scarce. To better characterize zooplankton composition and distribution in EIO, we conducted a survey in the region between 5°S and 14°N and 80°−93°E from March–May 2022. To our knowledge, this is among the first applications of ecological models to reveal the preliminary characteristics of zooplankton community assembly mechanisms in EIO. Through microscopic examination, we identified 427 species of adult zooplankton and 24 zooplankton larvae taxa. The zooplankton abundance in the surveyed ranged from 137 to 1,326 ind./m³. Among them, copepods, particularly small-bodied species, were the dominant components, contributing most significantly to the abundance and species richness of EIO zooplankton. Redundancy Analysis (RDA) and Random Forest (RF) results indicated that Dissolved oxygen (DO), temperature, and chlorophyll a were the primary factors influencing the abundance and diversity of EIO zooplankton. According to cluster analysis, the EIO zooplankton could categorized into three ecological groups: Group A (GA), Group B (GB) and Group C (GC). The results of Neutral Community Model revealed that the community assembly of EIO zooplankton was primarily influenced by stochastic processes. However, certain deterministic factors still influence the community assembly mechanisms of GA and GB. Correlation analyses between environmental factors and characteristic species in each group showed that deterministic assembly in GA is mainly driven by interspecific interactions, whereas in GB it is primarily driven by environmental selection.

Atlantic Water (AW) inflow plays a central role in Arctic Ocean warming and Atlantification, yet its transport into the Amerasian Basin remains poorly constrained. Using four ocean–sea ice reanalyses, including the new SODA4, we assess the structure, long-term trends, and variability of AW transport. While three of the reanalyses are consistent with prior transport estimates upstream of the Lomonosov Ridge, only SODA4 realistically captures the observed transports into the Amerasian Basin across the Lomonosov Ridge. One of the reanalyses, GLORYS12, significantly underestimates the heat content of Atlantic Water upstream of the Lomonosov Ridge as a result of anomalously high heat loss in the Barents Sea and excess cooling in the Barents Sea. We derive the first 40-year time series of heat transport into the Amerasian Basin. The ensemble mean of this time series shows that AW heat transport has increased by 0.36 TW/year (1984–2016) yielding a 5 ZJ increase in Amerasian Basin heat content. Interannual and interdecadal modes strongly modulate AW heat transport across the Lomonosov Ridge over the 40-year period. The leading mode of variability is associated with the phases of the Arctic Dipole anomaly, an atmospheric climate pattern which modulates the strength of the Siberian and Beaufort high-pressure systems. These results suggest that accurately resolving Atlantic Water structure and transport across the Lomonosov Ridge and in the Barents Sea is essential for accurately characterizing ocean-driven Arctic warming as far east as the Amerasian Basin and Beaufort Gyre.

This study investigates the long-term salinity dynamics of the partially mixed Ems Estuary, focusing on the influence of brine inflow on salt intrusion. Salinity time series from eight monitoring sites (2000–2023) were analyzed to assess variations due to river discharge and brine inflow from two injection sites. Tidally-averaged salinity was evaluated by tracking the positions of the 2 and 13 g$��·�$kg⁻¹ isohalines. Brine effects were identified by separating the data set into four subsets: two no-brine, one low-brine, and one high-brine period. For each, we computed temporal averages, absolute and relative salinity changes, and horizontal salinity gradients. Salinity showed strong seasonal variation driven by river discharge, both with and without additional salt input. The effect of brine inflow was superimposed on river discharge-related variability and depended on prevailing and previous discharge conditions. Although brine volumes were, on average, five orders of magnitude smaller than flood tidal volumes, they increased salt intrusion during low discharge conditions. Compared to no-brine scenarios, salt intrusion shifted up to 10 km further upstream during the high-brine period. Estuarine transport processes caused the salinity to increase 15–35 km upstream (exceeding the tidal excursion) of the brine inflow sites. The longitudinal location of the brine release affected salt dispersion, as demonstrated by a movement of the maximum salinity gradient. These findings emphasize the sensitivity of estuarine systems to small but persistent salt sources, with implications for estuarine ecosystems and management globally under increasing salinity stress from freshwater scarcity, land-use pressure, and climate change.

Large river-influenced coastal seas serve as critical interfaces for particulate organic matter (POM) dynamics within the global carbon cycle, characterized by intricate hydrodynamics and diverse sources. However, the response patterns of these POM processes to typhoon events remain poorly understood. This study conducted two field cruises in Laizhou Bay (LZB), a semiclosed bay with multiple river inputs, to compare the impacts of riverine pulses on POM dynamics during posttyphoon Lekima and a nontyphoon period. Typhoon-induced heavy rainfall significantly altered POM composition and fluxes. Posttyphoon, particulate organic carbon (POC) and particulate nitrogen fluxes increased to 4.9 × 10¹⁰ mmol d⁻¹ and 4.8 × 10⁹ mmol d⁻¹, respectively, compared to 1.5 × 10¹⁰ mmol d⁻¹ and 2.3 × 10⁹ mmol d⁻¹ during the nontyphoon period. Monte Carlo (MC) simulations quantitatively revealed riverine organic carbon (OC_riverine) dominated POC posttyphoon (44.8%), followed by marine OC (OC_marine) (35.0%), while deltaic organic carbon (OC_deltaic) was least (20.3%) in LZB. Under nontyphoon conditions, OC_deltaic dominated (46.0%) with OC_riverine being minimal (25.0%). Both δ¹³C and C/N ratio analyses showed that posttyphoon POM sources included freshwater algae, soil organic carbon, C3 plants, and marine POC, while nontyphoon POM primarily derived from freshwater algae and marine POC. Molecular indicators suggested that typhoon-driven terrestrial inputs of labile organic matter enhanced POM degradation via the priming effect. Consequently, POM degradation was more extensive posttyphoon, transforming the coastal region from a carbon sink to a carbon source. These disturbances likely reduce carbon burial in marine sediments during extreme weather events.

Large-scale offshore wind farms are expected to influence surface waves by modifying local wind forcing through wake effects. We use regional coupled ocean-atmosphere-wave model simulations to investigate a realistic large-scale offshore wind development scenario in the northeastern U.S. during boreal summer. Near-surface wind speeds are reduced by 10% over lease areas and within downstream wake regions, leading to decreases in significant wave height (3%) and wave-supported momentum flux (30%). This further leads to reductions in surface roughness length (16%) and near-surface ocean turbulent kinetic energy (20%). Spectral analysis shows a clear reduction in wind-sea energy, indicating suppressed local wind-wave growth near the wind farms. Weaker winds favor the development of longer-period waves, increasing dominant wave phase speed by 3% and suggesting a transition to an older sea state. Modern bulk flux algorithms often parameterize surface roughness using inverse wave age and/or wave slope. This raises the question of whether wake-driven reductions in inverse wave age and wave height impact air-sea momentum exchange. To assess this, we compare fully coupled simulations with an atmosphere-only run excluding wave coupling. Results show that about one-third of the reduction in roughness length can be attributed to sea state changes, while two-thirds result from lower friction velocity due to lower wind speeds. However, the impact of sea state on the drag coefficient and momentum flux is negligible ($��\sim �$1%), suggesting that wake-induced wind speed reductions are the primary driver, with sea state changes playing a secondary role.

The Pacific Decadal Oscillation (PDO), a dominant low-frequency climate mode in the North Pacific, modulates sea surface temperature (SST), circulation dynamics, and wind stress, thereby controlling nutrient supply and phytoplankton primary production (PP) in the sunlit ocean layer. However, the mechanisms linking PDO to PP variability remain insufficiently understood, mainly due to limited long-term observational data sets. Using simulations from the Community Earth System Model Large Ensemble Project (CESM-LE), which includes both historical and RCP8.5 scenarios (1920–2100), this study investigates PDO impacts on PP across the Pacific Ocean. The PP response to the PDO exhibits strong latitudinal variability driven by regional limiting factors. In subarctic regions, PP exhibits a tripolar pattern associated with the PDO and is primarily controlled by nutrient availability, particularly iron and nitrate. In the mid-latitude North Pacific, upper-euphotic PP is positively correlated with PDO, largely regulated by lateral nutrient transport within the mixed layer. In contrast, photosynthetically available radiation (PAR) acts as the dominant linkage between PDO and PP in the lower euphotic zone. The PDO's influence also extends to the tropical Pacific, where its positive phases weaken trade winds and equatorial currents, reducing the zonal nitrate supply and leading to significant PP declines in the western and central tropical Pacific. Together, these results illustrate how the PDO orchestrates marine productivity through distinct regional mechanisms.

This study evaluates the response method for predicting tidal currents. We introduce a coupled response model which explicitly accounts for interactions between velocity components. By leveraging non-parametric and data-driven weight estimation, the approach demonstrates superior predictive accuracy compared to classical harmonic analysis (HA), particularly for fast-moving and non-linear tidal currents. Using ADCP data from the world's largest deployment of tidal stream turbines, the coupled model achieves superior accuracy with fewer than 30 days of input measurements compared to HA using over 180 days of data. Accuracy improvements extend to both current predictions and the derived harmonic constituents, obtained through a specialized procedure. The response approach shows greater robustness when applied to extremely sparse data. This is reflected by the pseudo-admittances, which also show the non-parametric approach advanced can effectively capture unsmooth deviations in the admittance. Analysis of 40 active NOAA current stations highlight when the response approach should and should not be used, yielding average reductions in absolute error of 9.6%. The framework offers new opportunities for studying non-tidal forcing and sediment transport and has significant implications for tidal energy site development. The proposed method is implemented in the open-source RTide Python package, providing a practical and accessible tool that reduces the level of expertise required to apply the response method to higher-order nonlinear processes.

Wave frictional dissipation is a key process in rough seabed’s environments such as coral reefs, expected to significantly reduce incoming wave energy. In phase-averaged models, wave dissipation is typically estimated through a wave friction factor $��f_w�$ which is dependent of the near-bed orbital excursion and the hydraulic length, a proxy for the seabed substrate roughness. A field experiment was conducted in the South-Western coral reef barrier of Mayotte (Indian Ocean) to compute $��f_w�$ through a frequency-integrated wave energy balance. Significant time and space variations of $��f_w�$ have been observed, driven by the evolution of the wavefield and the diversity of coral geometry and scales found along the barrier. The fine reef architecture has been examined thanks to a high-resolution multi-beam echo sounder survey. This study has reassessed the established link between hydraulic roughness length $��k_s�$ and roughness standard deviation; it also indicates that second-order roughness metrics may also significantly explain variations in $��k_s�$. Future challenges remain in the proper definition of the length scales of seabed variability attributed to roughness and to bathymetry.

Typhoons drive sedimentary dynamics and material transport in marginal seas, forming storm deposits that preserve critical information about these extreme disturbance. However, distinguishing typhoon-induced provenance signals from hydrodynamic-driven signals within sedimentary archives remains a major challenge. Taking the northeastern Beibu Gulf, influenced by Typhoon Yagi (2024), as the study area, we systematically collected post-typhoon surface (storm-layer) and subsurface (background-layer) sediments. Grain-size analysis, organic-carbon parameters, and lipid biomarkers were integrated with satellite remote-sensing and environmental data to test the tracing potential of lipid biomarker in storm deposits combining the empirical orthogonal function (EOF) analysis. Results show that Typhoon Yagi emplaced a storm deposit with finer grain-size (74.9% silt), elevated total organic carbon (0.90% vs. 0.30%), and richer lipid biomarkers. Marine biomarkers (brassicasterol, dinosterol, and C₃₇ alkenones) indicate a concurrent phytoplankton bloom triggered by typhoon. Source-specific terrestrial biomarkers reveal that typhoon-driven terrestrial inputs dominate the nearshore zone with high n-C_29+31+33 alkanes, n-C_26+28+30 FAs, and n-C_28+30+32 alkanols, whereas distant-source material, likely derived from the Red and Pearl Rivers, entered prominently along the eastern and western margins. EOF analysis reveals hydrodynamic reworking as an important controlling factor for storm deposit. Thus, typhoon-induced storm deposits preserve a distinct signal of these dynamic reworking processes. This study provides the first systematic validation of source-specific lipid biomarkers as sensitive tracers in storm deposits. Their anomalous concentrations, compositional signatures, and spatial patterns effectively discriminate between typhoon-induced provenance and hydrodynamic transport processes, offering a novel proxy framework and theoretical basis for identifying modern storm deposits and reconstructing paleo-typhoon activity.

Sediments characterized by unsteady dynamics, such as mobile muds (MM), are commonly found in large-river delta-front estuaries (LDEs). These sediments undergo frequent resuspension and intense diagenetic processes. However, the extent and ecological significance of nutrient regeneration in these sediments remain poorly understood. Here, we measured porewater nutrients, total organic carbon (TOC), and total nitrogen (TN) in sediments of the East China Sea Mobile-muds (ECSMM) and the adjacent shelf. An unsteady-state model was developed to simulate the nutrient regeneration under high intensity of reworking. For unsteady stations, promoted benthic nutrient fluxes were −0.11 ± 0.16, 1.30 ± 1.04, 0.04 ± 0.02, and 1.78 ± 0.58 mmol m⁻² d⁻¹ for NO₃⁻ NH₄⁺, PO₄³⁻, and Si(OH)₄, respectively. On average, the DIN and Si(OH)₄ fluxes of unsteady stations are approximately 3 times those at steady stations, while PO₄³⁻ fluxes could reach 8 times. These results revealed that ECSMM is an important nutrient source, and regenerated nutrients could sustain >10% of the local primary production. Furthermore, rapid nutrient regeneration in other major LDEs is estimated through published data. The highest fluxes are found in the Amazon Estuary with the thickest unsteady layer and the most intense reworking. Our work underscores the critical role of unsteady sediment deposition dynamics in global ocean nutrient biogeochemical cycles.