Journal of Geophysical Research-Oceans最新文献

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.

Greenland's glacial fjords serve as pathways for the transport of heat and freshwater between the continental shelf and the outlet glaciers of the Greenland Ice Sheet. Despite increasing attention from the research community, seasonal studies in Greenland fjords remain scarce. This is especially true for near-surface measurements. Here, we present year-round, near-full water column velocity observations and water mass data in Nuup Kangerlua, a glacial fjord in southwest Greenland. In July, a strong exchange flow is present in the upper 200 m, coinciding with the presence of subglacial discharge waters in the upper 10–50 m. Fjord circulation remains active throughout the year. Net heat transport toward the glaciers is most pronounced in the glacial melt domain (upper 150 m) in summer, while the heat transport occurs mostly in deeper layers in the winter months. Episodic dense coastal inflows renew the deep water in the fjord and can profoundly increase or decrease fjord water temperatures depending on the timing and depth of the inflow. We estimate vertical diffusivity in deeper layers to be around $��{10}^{�-�5�}�$ $��m^2�s^{�-�1�}�$ during stagnant periods (i.e., when no inflows occur). This study underlines the importance of seasonal variations and episodic events in fjord current dynamics and associated heat transport as a potentially important control for the submarine melting of marine-terminating glaciers.

Oligotrophic ocean is generally characterized by lower primary productivity, which has traditionally been considered to result in reduced transport of particulate organic carbon (POC) to the deep ocean compared to high-productivity regions. However, our findings challenge this paradigm based on studying transparent exopolymer particles (TEP) in the western tropical North Pacific (WTNP). This paper systematically examines the formation and distribution of TEP across the 0–2,000 m depth range in the WTNP, analyzes the influence of hydrodynamic factors on TEP dynamics, and investigates the role of Pelagibacter, a dominant bacterium in oligotrophic waters, in facilitating in situ TEP production. Despite low TEP concentrations in the water column (7.53–34.22 μg Xeq/L), the proportion of TEP-C within POC remained stable with increasing depth. Furthermore, the vertical transport efficiency of POC in oligotrophic waters was significantly higher than in high-productivity regions, indicating that TEP plays a crucial yet overlooked role in facilitating the deep transport of POC in oligotrophic environments. Given this unique promotion mechanism, we proposed that the amount of POC transported to the deep oligotrophic ocean has been underestimated by at least fivefold.

This study explores the biases in westerly wind events (WWEs) and their induced oceanic Kelvin waves (OKWs) in seven CMIP6 models from three modeling centers that provide daily thermocline depth output. Among the WWEs and OKWs identified in historical simulations, WWEs are generally weaker than observed for a given OKW response, suggesting that OKWs in models respond too strongly to WWE forcing. The equatorial ocean mixed layers in the models are generally too thin and overly stratified compared to observations. These biases may help inhibit the turbulence-induced mixed layer deepening and trap the WWE-provided momentum within the ocean surface layers. Thus, they support an exaggerated sea surface height buildup and thermocline deepening in OKW initiation regions, which leads to an overly strong OKW response. These biases may be associated with a too-strong net heat flux between the atmosphere and the ocean.

This study evaluates the tsunami generation potential and scaling characteristics of rotational submarine landslides along the eastern margin of the Sea of Japan, where many submarine active faults and fine-grained sediments are distributed. These landslides pose significant tsunami hazards, but their locations and magnitudes are difficult to predict, making them a major source of uncertainty in tsunami hazard assessments. We identified landslide traces using high-resolution bathymetric data, estimated landslide volumes, and applied an established empirical formula to calculate initial tsunami amplitudes. The initial tsunami amplitudes calculated using the empirical formula were validated against numerical simulations using a two-layer model. Several potential tsunami sources were identified with initial amplitudes exceeding 10 m, all located in shallow waters on the continental shelf and characterized by thick landslide deposits. A clear power-law relationship was observed between landslide area and volume, consistent with previous studies of rotational slides. The volume–frequency relationship also followed a power-law, in contrast to the logarithmic trends typically associated with flow-type landslides. Spatial analysis revealed that landslide events with significant tsunami impact often clustered near submarine active faults, suggesting strong ground motion as a primary trigger. The consistency between empirical and numerical estimates supports the validity of the empirical formula for rotational landslide tsunamis. These findings demonstrate the value of failure mode-specific scaling analysis and source characterization for improving quantitative tsunami hazard assessments. The results may contribute to probabilistic hazard analysis, such as Monte Carlo simulations, and support coastal disaster prevention planning.

Nares Strait is an important export pathway of sea ice, where its transport is highly intermittent due to the formation and collapse of sea ice arches. The islands in the strait, especially Hans Island, contribute to heightened collision forces between distinct ice floes and the land. However, since even state-of-the-art large-scale models remain relatively coarse and use continuous sea ice rheology, the complexities of floe-scale sea ice interactions with small islands in the Nares Strait have not been much explored. Here, we use a novel discrete element model, SubZero, to identify the role of small islands in affecting intense summer-time sea ice transport in the Nares Strait. We show that SubZero can reproduce crucial sea ice characteristics, including observed area transport, intermittency of area fluxes, and floe size distribution (FSD) derived from satellite imagery. We find that the intermittency of sea ice fluxes relates to the power-law exponent of the simulated FSD, and matching it to observations implies that the floe strength for fracturing must be inversely proportional to the square root of its length scale. Conducting sensitivity simulations with modified coastlines, we identified several islands as crucial pinning points that suppress sea ice transport and cause jamming, especially during low-to moderate-wind conditions. The momentum budget reveals the islands slow down sea ice through direct normal contact with colliding floes and by increasing tangential drag forces from lateral coastal boundaries. Our study emphasizes floe-scale interactions with islands and other coastlines in large-scale sea ice transport through narrow straits.

Seasonal variability of the magnitude and structure of semidiurnal internal tides radiated from the Mariana Arc was examined based on year-long mooring observations. Internal tidal currents, energy density, and energy flux at the focal point of the Mariana Arc were weakest in summer, but typically comparable in the other three seasons. Mode-1 internal tides dominate over the observed period, except in summer when Mode-2 explains a higher proportion. The coherent variance accounts for about 60% of the total semidiurnal motions, with a reduced proportion in summer and winter, generally consistent with the seasonal trend of the barotropic tides. In contrast, the incoherent internal tides show a close temporal consistency with the low-frequency flows. During summer, the background currents are predominantly influenced by energetic mesoscale eddies, whereas the North Equatorial Current (NEC) system dominates in the other seasons. Internal tides influenced by eddies exhibit more standing wave characteristics, higher modal structures, and more incoherent properties compared to those modulated by the NEC. Internal tides are more progressive and propagate outward more easily when modulated by the NEC, whereas those modulated by eddies are more unstable and prone to nearby dissipation, resulting in a significant summer weakening at the Mariana Arc focus.