Journal of Geophysical Research-Oceans最新文献

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.

The biological carbon pump (BCP) transfers CO₂ from the surface ocean to depth, helping regulate atmospheric CO₂ and accounting for roughly one-third of glacial–interglacial CO₂ changes. Its strength is widely estimated from satellite-based relationships between net primary production (NPP) and export efficiency, but these approaches cannot distinguish organic matter rapidly recycled near the surface from that exported to depth. This ambiguity inflates export estimates and obscures BCP variability. Here, using a tracer-constrained inverse biogeochemical model, we explicitly quantify the “rapid recycling” fraction of NPP that does not contribute to deep-ocean sequestration. We find that ∼48%–60% of satellite-measured NPP is respired within the euphotic zone within hours to days, leaving a climatological mean carbon export of 13.72–15.55 Pg C yr⁻¹—consistent across multiple satellite NPP products. Export fluxes derived from our inverse model agree more closely with sediment trap and ²³⁴Th observations than those from empirical NPP–export relationships or Earth system models. Of course, the inverse model's steady-state assumption and dependence on a low-resolution climatological circulation field prevent future predictions and limit its accuracy in coastal and polar regions. These results still show that deep-ocean tracer constraints yield robust BCP estimates despite large surface productivity uncertainties, and they provide the first global-scale quantification of rapid surface recycling as a major limitation of satellite-based export assessments.

The spatial evolution of sedimentary organic carbon (OC) along transport pathways reflects burial and remineralization processes, traditionally attributed to hydrodynamic transport. However, direct evidence verifying the mechanism or examining whether the evolution pattern can be disrupted particularly by the input of marine OC from anthropogenic sources remains limited. This study integrates sediment resuspension experiment with sediment and OC characteristics analyses to elucidate hydrodynamic regulation on OC and additional mariculture-induced variability. Hydrodynamic resuspension regulates OC content through grain-size and mineral sorting but does not directly alter its thermochemical properties, regardless of hydrodynamic intensity. In comparison, mariculture directly modulates OC content and properties by the input of labile OC. We address a previously overlooked aspect of the thermochemical properties of mariculture-derived OC and underscore the importance of comprehensively evaluating the impacts of mariculture activities on OC, particularly regarding their long-term biogeochemical consequences.

The eastern equatorial Pacific Ocean (EEP) plays a critical role in the global climate system through widespread CO₂ outgassing and cool sea surface temperatures (SST) that occur due to persistent Ekman suction (upwelling). The Galápagos Islands—situated on the equator in the EEP—disrupt the Equatorial Undercurrent (EUC), causing strong upwelling on its western boundary and an SST minimum referred to as the Galápagos Cold Pool (GCP). This study analyzes the ocean mixed layer heat budget of the GCP relative to an open-ocean region in the EEP using a 140-year present day simulation of a high-resolution (0.1° ocean) version of the Community Earth System Model (CESM), version 1.2.2. We diagnose the contributions of each heat budget term with emphasis on vertical advection and eddy diffusion—hypothesized to be important near the Galápagos. Our results distinguish the seasonal heat balance in the GCP from the open ocean in the EEP. The net surface heat flux in the cold tongue is balanced primarily by vertical mixing, vertical advection dominates in the GCP. A variety of processes that vary throughout El Niño-Southern Oscillation (ENSO) phases are also important within the GCP, including changes to vertical and horizontal advection and vertical mixing, leading to associated SST anomalies. A thorough understanding of these processes and their contribution to the surface heat balance is essential in understanding the formation of the GCP, its interaction with the atmosphere, and its potential response to climate change with implications for this climatically and ecologically vital region.

Subduction and obduction are water mass exchanges between the ocean mixed layer (ML) and the permanent pycnocline. Knowledge of how they change in a warming climate is of great importance to anticipating how warming will affect material circulation and biogeochemistry. We investigated interannual variations of annual subduction and obduction rates (S_ann and O_ann) over the North Pacific Ocean using an eddy-resolving ocean reanalysis. Both S_ann and O_ann integrated over the basin increased during the last few decades. The volumes of subducted and obducted water parcels increased in most of the potential density range, and the regions where the volumes were large shifted northward after 2004. These increases of S_ann and O_ann were especially large north of the Kuroshio Extension (KE), despite a decrease of the potential density of the winter ML. The failure of the trends of either S_ann or O_ann to increase when mesoscale spatial variations were filtered out was consistent with calculations using a gridded product based on in situ observations, implying that eddy activity was responsible for the trends. The variations of S_ann and O_ann corresponded closely with that of eddy kinetic energy (EKE) north of the KE. This implies that northward migration of the KE increased available potential energy, thereby elevating EKE through baroclinic conversion. Warm eddies especially enhanced subduction and obduction. These results suggest that these processes activated vertical exchanges of water masses and materials, thereby surpassing enhanced stratification due to warming of the upper ocean.

Utilizing 250-m resolution sea surface height anomaly (SSHA) data from the Surface Water and Ocean Topography (SWOT) satellite in combination with mooring measurements, this research investigates the three-dimensional evolution of internal solitary waves (ISWs) in the northern South China Sea (nSCS). A novel inversion method based on the horizontal momentum equation was developed to retrieve ISW amplitudes from SSHA data, yielding a mean absolute deviation of 16% relative to mooring measurements. Application of this method to ISW SSHA (5–60 cm) in the nSCS revealed ISW amplitude distributions spanning 10–250 m. A stratification-modulated quasi-linear correlation between amplitude and SSHA was identified in waters deeper than 1,000 m, with slope coefficients ranging from ∼350 (July–September) to ∼530 (January–March), enabling fast amplitude estimation from SWOT observations. SWOT's orbital configurations allow tracking of ISW evolution in the nSCS at daily intervals, revealing three key features of ISW evolution: (a) the total energy integrated along the ISW crest typically decreased, and the south-strong–north-weak asymmetry of the ISW crest generally reversed during the basin-to-slope propagation; (b) in addition to distorting the wave crest, mesoscale eddies are linked to ISW amplitude increases of up to 34% in energy convergence portions and decreases of up to 49% in energy divergence portions; (c) oblique interactions between ISWs generated near the Batan and Babuyan Islands notably enhanced the ISW amplitude. This research underscores the potential of combining SWOT and mooring data to better monitor ISW structure and understand their interactions with mesoscale features.