Journal of Geophysical Research-Oceans最新文献

Carbon monoxide (CO) could be used as an energy source for marine microbes, while the biogeochemical cycling of CO remains largely unexplored in marine sediments. We integrated biogeochemical analysis, thermodynamic calculations, and incubation experiments to constrain the production and consumption potential of CO in the coastal sediments of the East China Sea. The concentrations of CO ranged from 98.3 to 333.7 nM and generally increased with depth along the 4.5-m sediment core. Significant correlations were observed between CO and  DIC, DOC, or sulfate, suggesting the control of CO production from organic matter degradation. The calculations of free energy yield indicated that CO oxidation-coupled microbial processes such as sulfate reduction, metal reduction, acetogenesis, and methanogenesis were thermodynamically feasible under in situ conditions. Incubation experiments demonstrated that trace CO could be produced from the addition of organic compounds such as glucose, glycerol, and methanol. In sediment slurries, amended CO were rapidly metabolized. The addition of electron acceptors or inhibitors suggested a large fraction of CO was consumed by sulfate reducers, and to a lesser extent, by methanogens. Collectively, these results revealed the potential of carboxydotrophy as a metabolic mode for diverse microbes living in marine sediments that were previously ignored.

The St. Anna Trough (SAT) plays a critical role in Arctic Ocean circulation by facilitating heat and water mass exchange, influencing sea-ice melt and thermohaline dynamics. However, ocean circulation in this key region remains understudied compared to other parts of the Arctic. To better understand water mass pathways, origins, and mixing processes in the SAT, this study analyzes anthropogenic radionuclides iodine-129 (¹²⁹I) and uranium-236 (²³⁶U), alongside neodymium isotopes (εNd). Seawater samples were primarily collected from the SAT and Kara Sea during the 2021 Arctic Century Expedition, with complementary data sets from independent sampling campaigns in the Fram Strait (2021) and Barents Sea (2018) providing broader regional context. Distinct ¹²⁹I signatures reveal the mixing of Atlantic Waters with Arctic shelf-formed waters, contributing to the formation of Cold Deep Water, which integrates into the intermediate and deep Arctic Ocean. Elevated ²³⁶U concentrations in mid-depth samples indicate the intrusion of Arctic-Atlantic Waters into the SAT, underscoring the region's role in Arctic water recirculation and mixing complexity. The εNd data indicate a strong riverine signal from the Ob and Yenisei rivers in the southern Kara Sea and Voronin Trough, whereas SAT surface waters show greater influence from Barents Sea Atlantic Waters. Elevated surface radionuclide concentrations above the Voronin Trough highlight this area as a primary gateway for radionuclides entering the central Arctic. These findings provide new insights into Arctic Ocean circulation and demonstrate the complementary strengths of radionuclides and εNd in resolving water mass transformations and pathways.

Over the past decade, the international GEOTRACES program has greatly expanded the coverage of dissolved lead (dPb) observations in the western Arctic Ocean including the Canada Basin and the Canadian Arctic Archipelago. However, it is difficult to quantify the drivers of the spatial distribution and seasonal variability of dPb concentrations using observations alone. Here, we present a three-dimensional model of dPb concentrations in the western Arctic Ocean with experiments from 2002 to 2021 to assess our current understanding of dPb cycling. The dPb model illustrates the impact of current and historical anthropogenic pollution on dPb concentrations in the Arctic Ocean, which accounts for at least 28% of dPb addition to the region, through aerosol deposition and net transport from other ocean basins. Advected water masses from the Pacific and North Atlantic Oceans convey elevated pollution-derived dPb concentrations to the Arctic and play a key role, contributing 43% to the annual dPb budget. The Labrador Sea is a net source of dPb to Baffin Bay via the West Greenland Current. Within Baffin Bay, simulated dPb concentrations track the seasonal extension of warm Atlantic Water along the West Greenland shelf and occasional dense overflows of Atlantic Water into the deep Baffin Bay interior. While dPb concentrations in the western Arctic Ocean are low, the dPb model simulations presented here show that anthropogenic pollution continues to impact the Pb budget in this region, consistent with recent observational work, and demonstrate the use of dPb as a tracer of Atlantic and Pacific Water masses.

In this study, the air-sea carbon dioxide flux (FCO₂) in the subarctic North Pacific is investigated using three data products from 1985 to 2016. Extreme CO₂ release occurred during the winters of 1999–2001 with an average FCO₂ anomaly of 1.09 mol C m⁻² y⁻¹ across the three data products, which is remarkably higher than that in other years (−0.11 mol C m⁻² y⁻¹). Empirical analysis reveals that this event is primarily driven by increased carbon dioxide partial pressure (ΔpCO₂), whose contribution to the event is greater than the wind speed at 10 m, followed by sea surface temperature (SST) and salinity impacts. Specifically, the intensification of pCO_2sea (which contributes 58% of the FCO₂ anomaly) is induced by the upwelling of dissolved inorganic carbon (DIC) due to the increase in Ekman pumping caused by the positive anomaly of wind stress curl associated with the Victoria mode of the SST. Moreover, the weakening of pCO_2atm is induced by the negative anomaly of sea level pressure (contributing 9% to the FCO₂ anomaly), which is also related to the mode and the reduction in the mole fraction of CO₂ (contributing 11% to the FCO₂ anomaly), which is related to fossil fuel emissions. Ultimately, the sea surface pCO₂ is significantly oversaturated relative to the atmosphere, triggering extreme CO₂ release in the subarctic North Pacific. This study enhances our understanding of the natural variability of carbon fluxes in the North Pacific.

Environmental DNA (eDNA) analysis is a technique for detecting organisms based on genetic material in environments such as air, water, or soil. Observed eDNA concentrations vary in space and time due to biological and environmental processes. Here, we investigate variability in eDNA production and loss by sampling water adjacent to a managed population of non-native cetaceans on a near-hourly timescale for 48 hr. We used diverse sampling approaches and modeling methods to describe time variability in observed eDNA concentrations and then compare the magnitude of production and loss mechanisms. We parsed production and loss in a conceptual box model and compared biological and physical loss rates using a decay experiment and a physical transport-and-diffusion tracer model. We then evaluated eDNA concentrations along a transect away from the animal enclosure in light of model parameter estimates. We conclude that eDNA production is best conceptualized using a time-varying mixed-state model, and biological losses are small relative to physical losses in the marine environment. Because physical loss is unsteady and nonlinear, tracer models are especially helpful tools to estimate it accurately.

It is well known that the motion of flexible vegetation leads to drag reduction in comparison to rigid vegetation. In this study, we use a numerical model to investigate how the detailed motion of giant kelp fronds in response to forcing by surface gravity waves can impact the drag exerted by the kelp on waves. We find that this motion can be characterized in terms of three dimensionless numbers: (a) The ratio of hydrodynamic drag to buoyancy, (b) the ratio of blade length to wave excursion, and (c) the Keulegan-Carpenter number, which measures the ratio of drag to inertial forces. We quantify drag reduction, and find that inertial forces can significantly impact the amplitude of kelp motion and amount of kelp drag reduction. For longer plants in waves of shorter periods, inertial forces can cause kelp fronds to accelerate more quickly relative to the wave, which can lead to increased drag reduction and reduced wave energy dissipation. In the most extreme cases, frond motion leads to drag augmentation in comparison to rigid fronds.

The presence of radium activity variation within the lower intertidal aquifer introduces substantial uncertainties in the estimation of submarine groundwater discharge (SGD) and associated chemical fluxes. This study presents findings on the seasonal variation of radium isotopes in a two-dimensional cross-section of an intertidal aquifer. The research demonstrates that the variability in vertical and temporal dimensions is considerably greater than lateral variation, which is due to different flow regimes and mixing with different water sources. Numerical modeling demonstrates that groundwater dynamics strongly influence the seasonal variation of radium isotopes by controlling the groundwater residence time and amount of mixing with infiltrated seawater from the beach boundary. Hydrochemical properties such as salinity and pH play a minor role in the seasonal variation of radium isotopes in the lower intertidal zone. This study provides valuable insights into the seasonal fluctuations of radium isotopes and emphasizes the importance of accounting for variations in multiple dimensions when analyzing SGD in different timescales.

The Southern Ocean upwelling, a crucial component of global upwelling systems, plays a key role in the global-scale redistribution of water, heat, salt, and carbon. This study aims to improve the understanding of this upwelling system by examining its climatology and future trend under a business-as-usual emission scenario, using 25 global climate model data sets. The ensemble mean of the simulated large-scale upwelling pattern in Southern Ocean follows Ekman dynamics, characterized by upwelling south of approximately 50°S and downwelling to the north. Upwelling is generally more pronounced at depths of 200 and 1,000 m (approximately 0.5 m/day) compared to 50 m (approximately 0.2 m/day). Under the high-emission scenario, both large-scale upwelling and downwelling in Southern Ocean are projected to intensify, with the net vertical volume flux expected to decrease by approximately 2 Sv (1 Sv ≡ 10⁶ m³/s) at both 50 and 200 m by the end of the 21st century. The projected changes in zonal wind stress and wind stress curl offer a reasonable mechanism for the projected changes in Southern Ocean upwelling and downwelling, while the enhanced vertical stratification (primarily due to warming) may partially counteract the upwelling and downwelling increase. These findings are essential for understanding the response of Southern Ocean circulations to global climate change.

The ice shelves of the Amundsen Sea are in a phase of rapid melting with intruded Circumpolar Deep Water (CDW) from outside the continental shelf contributing most of the heat. Using a coupled sea ice—ice shelf—ocean general circulation model, the cross-shelf break heat flux and the mechanism of eastward undercurrent deflection are studied. Model results show higher cross-shelf break heat transfer during winter months regulated by both the barotropic and baroclinic geostrophic flow. The vorticity budget along the continental shelf break is examined using the depth-averaged vorticity budget equation based on the model's outputs. Results show that the advection of planetary vorticity (APV) and the joint effect of baroclinicity and relief (JEBAR) dominate the vorticity balance at the CDW intrusion sites on the shelf break, and the JEBAR effect is considered an effective indicator of CDW intrusion. The CDW intrusion is mainly regulated by the southward deflection of the undercurrent on the Amundsen Sea slope. Pre-deflection, the undercurrent's core lies on the southern edge of the shelf break, enabling it to modulate downstream density transport through its vertical distribution variations. Concurrent increases in undercurrent velocities and vertical extent are captured upstream of intrusion sites, supporting more CDW intrusions per unit time and altering the horizontal density gradient, thereby amplifying the JEBAR effect. Additionally, spectral analysis reveals a semiannual cycle in the JEBAR amplitude and heat flux across the Amundsen Sea slope.

Inner shelf circulation studies have focused mainly on alongshore uniform sandy coasts and coral reefs in subtidal and tidal bands, with far less attention given to rocky shores. This study examines depth-averaged circulation at China Rock, a rocky shore on the Monterey Peninsula, CA, with 15 ADCPs deployed for about a month. The bathymetry varies strongly on multiple lengthscales. Large-scale bathymetric features include an embayment and two headlands, whereas smaller-scale features consist of a large variety of rocks extending from the inter-tidal zone to offshore. Circulation variability encompasses subtidal, diurnal, and semidiurnal frequency bands. Velocity principal-axes ellipses decay onshore in all frequency bands indicating strong bottom friction, and have orientation variability attributable to nearby large-scale bathymetric features. Alongshore subtidal currents are reasonably well described by a wind stress and bottom friction balance, with skill similar to previous studies, but with larger linear drag coefficients, particularly in shallower waters. Cross-shore subtidal currents near the embayment are directed offshore as a bathymetrically controlled rip current strengthened by feeder currents from the headlands, with magnitude related to the incident waves. In the diurnal and semidiurnal bands, alongshore currents are attenuated onshore and the tidal phase (relative to an offshore location) decreases onshore both due to enhanced bottom friction. The attenuation is greater than on a comparable sandy shelf or coral reef, with larger phase shifts more resembling the coral reef observations. The increased linear drag friction can be related to directly measured bottom roughness.