Journal of Geophysical Research-Oceans最新文献

The Gulf of St. Lawrence has been nearly free of sea ice in the winter six times in its recorded history, four of which have occurred since 2010. This study examines the inter-annual variability of sea ice cover characteristics (1969–2024) and winter mixed layer heat content (1996–2024), their sensitivity to fall oceanic conditions (since fall of 1995) and to winter air temperatures. The study finds no relationship between fall oceanic conditions with either the first occurrence of sea ice, maximum seasonal estimated volume or winter mixed layer heat content. However, it shows that the first occurrence of sea ice in the northwestern Gulf is related to the timing of sea surface temperature crossing the 1°C threshold with a lag time of 30–37 days, and with air temperature dropping below −2°C with a lag of 37–44 days; longer lags have weak correlations. The seasonal maximum conditions in area or estimated volume can be estimated by the preceding measurements of the same metrics with a lead time of only 29 days for volume and 36 days for area. The average air temperature over the Gulf between December and February or March is highly correlated to seasonal maximum sea ice area and estimated volume, as well as ice season duration. The six nearly ice-free winters correspond to the warmest December to February (or December to March) average air temperatures over the Gulf. A warming of >1.9°C–2.4°C (DJFM) or >2.2°C–2.9°C (DJF) above the 1991–2020 climatology leads to nearly ice-free conditions.

Submarine canyons are hot spots for topography-internal wave interactions, with elevated mixing contributing to regional water mass transport and productivity. Two velocity time series compare and contrast internal waves deep inside Barkley Canyon to a nearby site on the shelf-break slope of the Vancouver Island Continental Shelf. Elevation of internal wave energy occurs near topography, up to a factor of 10 above the slope and 100 in the canyon. All frequency bands display strong seasonal variability but weak interannual variability. Diurnal (K₁) energy is sub-inertial, trapped along topography, and forced locally through barotropic motions. Both sites have high near-inertial (NI) energy linked to wind events, though fewer events are observed deep inside the canyon. At the slope site, near-inertial energy is attenuated with depth, while in the canyon it is amplified near the bottom. Freely propagating semidiurnal (M₂) energy appears focused near critical shelf-break and canyon floor topography, due to local and remote baroclinic forcing. The high-frequency internal wave continuum has enhanced near-bottom energy at both sites (up to 7 × the Garrett-Munk spectrum), and inferred dissipation rates, ɛ, reaching 10⁻⁷ W kg⁻¹ near topography. Dissipation is most strongly correlated with semidiurnal energy variability at both sites, with secondary contributors that are site dependent. Forcing power law fits are $��\epsilon �\sim �M_2^{0.8}�+�$ $��{\text{Sub}}_{K_1}^{0.6}�$ on the slope, and $��\epsilon �\sim �M_2^{1.5}�+�$ NI^0.2 in the canyon. There is also a

Floating marine litter is transported by several mechanisms, including surface waves. In studies of marine litter transport, the wave-induced drift is set to be equal to the Stokes drift, corresponding to the Lagrangian-mean wave-induced drift of an infinitesimally small tracer. Large-scale experiments are used to show how the wave-induced drift of objects of finite size depends on their size, density, and shape. We observe increases in drift of 95% compared to Stokes drift for discs with diameters of 13% of the wavelength, up to 23% for spheres with diameters of 3% of the wavelength, whereas drift is reduced for objects that become submerged such as nets. We investigate what these findings may imply for the transport of plastic pollution in realistic wave conditions and we predict an increase in wave-induced drift for (very) large plastic pollution objects. The different extrapolation techniques we explore to make this prediction exhibit a large range of uncertainty.

Small-scale turbulent mixing supplies potential energy for the upwelling of deep waters in the abyssal ocean, a key component of the global overturning circulation. This process is particularly significant in critical regions such as the Northwestern Pacific where the upwelling structure of deep waters remains poorly understood due to limited knowledge of deep ocean mixing. Here, we investigate the full-depth spatiotemporal variability of turbulent mixing in the deep Northwestern Pacific based on hydrographic data collected over repeated surveys. Nineteen-year-average diapycnal diffusivity of 1.42 × 10⁻⁴ m² s⁻¹ is reveled in the deep Philippine Sea, indicating significantly stronger mixing compared to the stratified ocean interior. Spatially, turbulent mixing strengthens toward the bottom and intensifies westward from the open Pacific to the Philippine Sea due to rough topography. At certain mixing hotspots, enhanced mixing can penetrate up to 2,500 m above the bottom, suggesting a substantial potential for upwelling. Below 2,000 m, turbulent mixing exhibits pronounced seasonal variation that deep mixing is more intense in summer (winter) than in winter (summer) in the West Caroline Basin (the Parece Vela Basin). This spatially varying seasonality may be attributed to the inhomogeneous internal tidal energy dissipation in the Northwestern Pacific. Our study will serve to clarify the modulation of turbulent mixing to deep-water mass transformation and circulation in the Northwestern Pacific.

Anthropogenic perturbations from fossil fuel burning, nuclear bomb testing, and chlorofluorocarbon (CFC) use have created useful transient tracers of ocean circulation. The atmospheric ¹⁴C/C ratio (∆¹⁴C) peaked in the early 1960s and has decreased now to pre-industrial levels, while atmospheric CFC-11 and CFC-12 concentrations peaked in the early 1990s and early 2000s, respectively, and have now decreased by 10%–20%. We present the first analysis of a decade of new observations (2007 to 2018–2019) and give a comprehensive overview of the changes in ocean ∆¹⁴C and CFC concentration since the WOCE surveys in the 1990s. Surface ocean ∆¹⁴C decreased at a nearly constant rate from the 1990–2010s (20‰/decade). In most of the surface ocean ∆¹⁴C is higher than in atmospheric CO₂ while in the interior ocean, only a few places are found to have increases in ∆¹⁴C, indicating that globally, oceanic bomb ¹⁴C uptake has stopped and reversed. Decreases in surface ocean CFC-11 started between the 1990 and 2000s, and CFC-12 between the 2000–2010s. Strong coherence in model biases of decadal changes in all tracers in the Southern Ocean suggest ventilation of Antarctic Intermediate Water was enhanced from the 1990 to the 2000s, whereas ventilation of Subantarctic Mode Water was enhanced from the 2000 to the 2010s. The decrease in surface tracers globally between the 2000 and 2010s is consistently stronger in observations than in models, indicating a reduction in vertical transport and mixing due to stratification.

In this work, the seasonal variations of the carbonate system and air-sea CO₂ fluxes were investigated by two cruises in the southern Yellow Sea (SYS) and the East China Sea (ECS), which were significantly influenced by the Changjiang riverine inputs across seasons. Biological-mediated change of dissolved inorganic carbon (DIC) was first quantitated through a three end-member mixing model from winter to spring. Our modeling results suggested that DIC addition through biological remineralization persisted in the SYS during winter and spring, while DIC removal was evident in the Changjiang River Plume and the offshore ECS triggered by river inputs in spring. Horizontal and vertical mixing together constituted the largest contribution to the interseasonal variability of partial pressure of CO₂ (pCO₂) in the SYS (−69.5%), the river plume (−59.3%), and the ECS offshore (−43.8%), followed by temperature effects in the plume area (29.4%), and biological processes in the ECS offshore (24.1%) and the SYS (−7.7%), with air-sea CO₂ exchange contributing the least in both three subregions. The SYS, the river plume, and the ECS offshore all acted as atmospheric CO₂ sinks in both winter and spring. Furthermore, their ability to absorb atmospheric CO₂ increased from winter to spring, as reflected in a ∼1.8-fold increase in the overall spring air-sea CO₂ flux compared to winter estimation.

Benthic storms are episodes of intensified near-bottom currents capable of sediment resuspension in the deep ocean. They typically occur under regions of high surface eddy kinetic energy (EKE), such as the Gulf Stream. Although they have long been observed, the mechanism(s) responsible for their formation and their relationships with salient features of the deep ocean, such as bottom mixed layers (BMLs) and benthic nepheloid layers (BNLs), remain poorly understood. Here we conduct idealized experiments with a primitive-equation model to explore the impacts of the unforced instability of a surface-intensified jet on near-bottom flows of a deep zonal channel. Vertical resolution is increased near the bottom to represent the bottom boundary layer. We find that the unstable near-surface jet develops meanders and evolves into alternating, deep-reaching cyclones and anticyclones. Simultaneously, EKE increases near the bottom due to the convergence of vertical eddy pressure fluxes, leading to near-bottom currents comparable to those observed during benthic storms. These currents in turn form BMLs with thickness of O(100 m) from enhanced velocity shears and turbulence production near the bottom. The deep cyclonic eddies transport fluid particles both laterally and vertically, from near the bottom through the entire BML and may contribute to the formation of the lower part of BNLs. A sloping bottom reduces both the intensity of the near-bottom currents and the extent of vertical transport. Overall, our study highlights a significant response of the abyssal environment to near-surface current instability, with potential implications for sediment transport in the deep ocean.

The Sea of Okhotsk is a marginal sea that plays a major role in the ventilation of the North Pacific, being the key location where Dense Shelf Water (DSW) forms at the surface and sinks to the intermediate layer. The Okhotsk Sea Intermediate Water (OSIW) is a key water mass because it includes large amounts of DSW, outflows to the North Pacific, and supplies the ocean with the micronutrient iron. OSIW has been warming over the past few decades, which is attributed to a decreasing trend in DSW production. The acquisition of numerous hydrographic data after 2000 in the Kuril Basin, especially dissolved oxygen from profiling floats, offers an opportunity to better quantify the water mass composition of OSIW, and the changes in OSIW properties and DSW volume. Here, we used all available hydrographic records and a mapping technique specially adapted to polar and sub-polar regions to revisit the Sea of Okhotsk water properties and document their long-term changes. Our analysis revealed that the volume of heavier DSW (potential density above 26.9 kg.m⁻³) has decreased over the past three decades by 3,600 km³, or 15% of the volume present before 1990. This decline is nearly entirely compensated for by an increase in lighter DSW. This shift toward lighter DSW is possibly a sign of the weakening of the intermediate overturning circulation starting in the Okhotsk Sea. Additionally, we found that dense Soya Current Water only accounts for about 1% of OSIW, against the 5% previously estimated.

Idealized models are analyzed to quantify how large-scale river plumes interact with coastal corners with and without wind-driven currents. The configuration has a corner formed by two perpendicular shelves (with constant slope) that are joined with a coastal radius of curvature (r_c). The buoyant plume originates from an upstream point source. The r_c and wind forcing are varied among runs. Steep- and gentle-slope runs are compared for some situations. Without winds, plumes separate from corners with r_c smaller than two inertial radii (r_i); this threshold is twice the r_c < r_i theoretical separation criterion. After separation, no-wind plumes form an anticyclonic bulge, and reattach farther downstream. Offshore excursion increases as r_c decreases. A downwelling-favorable wind component along the upstream coast (τ_sx) favors separation by increasing total plume speed. An upwelling-favorable wind component along the downstream coast (τ_sy) also increases offshore excursion. Winds blowing obliquely offshore with both these wind components advect the plume farther offshore. Wind-driven currents that steer plumes in this situation include a downshelf jet originating on the upstream shelf and continuing around the coastal corner and beyond, offshore and upshelf surface transport downstream of the corner, and surface Ekman transport on the outer shelf. Multiple linear regressions quantify plume position sensitivity to r_c, τ_sx, and τ_sy; results are discussed in a dynamical context. Globally, many river plumes interact with coastal corners under various wind conditions.

The East China Sea (ECS) is one of the largest marginal seas in the world with high primary productivity and a large area of low dissolved oxygen. This study observed the low-oxygen bottom water on the outer-edge shelf of ECS in summer seasons of 2018–2020. The contributions of various water masses to low-oxygen waters were quantified, and the interaction between low-oxygen water and Kuroshio water was validated by a mixing model using heavy rare earth elements (HREEs) together with potential temperature, and salinity. For further reliability verification, tracers such as δ³⁴S and ²²⁶Ra were additionally utilized to avoid the non-conservative processes on the shelf area. The low-oxygen water on the shelf was clarified to be linked to the inner/middle shelf water, and dominated by Kuroshio Subsurface Water (KSSW, 81% ± 3%) and influenced by a non-negligible extent of pore water (3.0% ± 0.5%). Our findings revealed the transport of low-oxygen water from the outer-shelf edge to the Kuroshio area, whose dissolved inorganic nitrogen and dissolved inorganic phosphorus contributions to Kuroshio were 34%–82% and 35%–83%, respectively. The nutrients of low-oxygen water were regulated primarily by the origins of water and secondarily by organic matter remineralization (DIN: ∼17% and DIP: ∼24%). As control factors, the tide, especially spring tide largely enhanced the water contribution of pore water to low-oxygen water by 67%, and the El Niño-Southern Oscillation potentially affected the contributions of KSSW and mid-shelf water to low-oxygen water.