Journal of Geophysical Research-Oceans最新文献

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.

This study investigates the influence of tropical Atlantic sea surface temperature (SST) variability on boreal autumn (August–September–October, ASO) sea ice concentration (SIC) in the Beaufort Sea. Although Arctic warming and sea ice retreat have been well-documented, the influence of tropical Atlantic SST on Arctic sea ice remains understudied. Using reanalysis data sets and model simulations, we demonstrate that tropical Atlantic warming significantly reduces Beaufort Sea SIC. This warming triggers a Rossby wave train that propagates northeastward, altering the high-latitude atmospheric circulation and inducing southerly flow anomalies. These anomalies enhance moisture transport, increase cloud cover, and amplify downward longwave radiation accelerating sea ice melt. Our findings, supported by Community Atmosphere Model version 5 and Community Earth System Model simulations, highlight the crucial role of tropical-Arctic teleconnections in Arctic sea ice variability.

Previous studies of air-sea interactions over sharp oceanic fronts have suggested that it is the ocean that drives the atmosphere across sub-mesoscale ocean fronts, but it is the atmosphere that drives the ocean at synoptic scales; the responsible mechanism, however, is still a matter of debate. This paper examines direct sea surface temperature (SST) measurements of the skin (SST_skin) and near-surface SST (SST_depth), and wind speeds measured during the Sub-Mesoscale Ocean Dynamics Experiment (S-MODE) along with derived bulk fluxes. We evaluate the modulation of the net heat flux, wind speed, and skin cooling across SST fronts and the ability of the COARE bulk flux algorithm to reproduce this variability. Bulk flux computations can be performed directly from a radiometric SST_skin, or more commonly, from the SST_depth provided that the depth of the SST measurement is corrected for cool skin and diurnal warming effects. Both types of SST were measured during S-MODE allowing for (a) an assessment of the importance of having a SST_skin for a direct flux evaluation in frontal regions, and (b) an evaluation of the accuracy of the cool skin and diurnal warming corrections within COARE for the indirect bulk flux computation. The ocean-atmosphere feedback over the sampled S-MODE submesoscale front suggested that the ocean was indeed forcing the atmosphere, mainly through the surface net heat losses, while the wind response to changes in SST_skin was irregular. Testing of the COARE algorithm suggested that indirect bulk fluxes had sufficient accuracy to close the heat budget over the front.

Uncertainty related to biogeochemical model structure—the equations, parameters, and variables used to simulate lower trophic level dynamics—can contribute significantly to overall uncertainty of regional model predictions of living marine resources metrics such as primary production. This may be particularly true in shallow coastal regions, where there is growing interest in using these types of regional models to inform ecosystem management. Here, we use a biogeochemical model intercomparison to analyze the divergence of ecosystem metrics across models for the eastern Bering Sea shelf region, and identify the biogeochemical processes that may lead to this spread. We run three biogeochemical models with varying complexity coupled to the same regional ocean model and run 30-year hindcast simulations spanning 1990–2020. We find that the models differ widely in their spatial and temporal patterns of simulated primary production, and that these differences propagate to most of the higher trophic level metrics examined. We highlight structural elements that lead to these differences, including (a) representation of benthic processes and their role in retaining nitrogen on the shelf, (b) the role of grazing control on spring bloom timing, and (c) the role of zooplankton groups in supporting regenerated production through the summer months. Overall, we conclude that the potential uncertainty associated with even well-established biogeochemical models may be high, particularly when these models are pushed beyond the original contexts under which they were developed. End users should strive to acknowledge and communicate this, particularly when using biogeochemical model output in management contexts.