Deep-Sea Research Part I-Oceanographic Research Papers最新文献

An intermediate nepheloid layer (INL) serves as an important conduit for the cross-slope transport of particulate matter, including organic carbon, biological nutrients and other lithogenic minerals. Despite extensive reports on the substantial sediment influx from the Ayeyarwady River into the northern continental slope of the Andaman Sea (AS), the transport route and fate of these river-borne sediments remain poorly understood, due to lack of in situ observations of turbid INL over the slope. In this study, we present direct evidence of an INL over the northern continental slope of the AS during the winter of 2019/2020, accompanied by enhanced mid-water turbulent mixing. Mooring measurements reveal energetic internal tides with high-mode vertical structure in the study region; and beam-like structures of internal tides are observed, which could be responsible for the enhanced mid-water turbulent mixing coinciding with the INL. Moreover, available microstructure profiles reveal energetic turbulent mixing with bottom-intensified turbulent diffusivity over the study area. Numerical experiments suggest that inhomogeneous distribution of turbulent mixing over the continental slope could induce local convergence of the upwelling transport in the upslope direction, resulting in an intrusion from the boundary to the interior and consequently promoting the INL formation. The discovery of the INL and its mixing-driven generation mechanism provide new insights into sediment transport dynamics over the northern continental slope of the AS.

The Gulf of Mexico (GoM) is a unique ecosystem due to its physical characteristics, being influenced by the Mississippi River in the north and the Loop Current from the south, resulting in a gradient of organic to carbonate sediment composition from north to south. The continental slope of the northern and southwestern portions of the GoM are generally well studied; however, less is known about the southeastern GoM along the slope of Cuba. To fill this knowledge gap, sediment cores were collected in 2017 at nine stations (974–1580 m depth) to determine abiotic controls on the deep-sea benthic macrofauna community. Oceanographic data indicated a stratified water column typical of an oligotrophic ocean and no evidence of hypoxia. Sediment texture and composition indicated a west-east gradient likely determined by downslope transport of terrigenous material in the eastern part with a high proportion of carbonate in the west. Heavy metals (Cu, Hg, Pb, and Zn) at concentrations known to cause adverse benthic effects were present in the east near the city of Havana, with the macrofauna community showing characteristics indicative of environmental stress. Overall, this region supported a diverse community of macrofauna families of low abundance, typically only 1–2 animals, and high variability among replicates within stations. Rarefaction curves revealed higher biodiversity per number of individuals in the samples from Cuba compared to those from the nGoM at similar depths, though more samples would be needed to better reveal the true diversity. The major factors influencing macrofauna communities in the continental slope off northwestern Cuba are most likely the lack of organic-rich sediment and low sediment deposition rates, both of which can be attributed to the strong currents and lack of major terrigenous input, along with the regular natural disturbances which prevents domination.

Recently studies have shown that Rhizaria, a super-group of marine protists, have a large role in pelagic ecosystems. They are unique in that they construct mineral tests out of silica, calcium carbonate, or strontium sulfate. As a consequence, Rhizaria can have large impacts on the ocean’s cycling of carbon and other elements. However, less is known about Rhizaria ecology or their role in the pelagic food-web. Some taxa, like certain Radiolarians, are mixotrophic, hosting algal symbionts. While other taxa are flux-feeders or even predatory carnivores. Some prior research has suggested that Rhizaria will partition vertically in the water column, likely due to different trophic strategies. However, very few studies have investigated their populations over extended periods of time. In this study, we present data investigating Rhizaria abundance and vertical distribution from over a year of monthly cruises in the Sargasso Sea. This study represents the first quantification of Rhizaria throughout the mesopelagic zone in an oligotrophic system for an extended period of time. We use this data to investigate the hypothesis that Rhizaria taxonomic groups will partition due to trophic mode. We also investigate how their abundance varies in accordance with environmental parameters. Rhizaria abundance was quantified using an Underwater Vision Profiler (UVP5), an in-situ imaging device. Ultimately, we show that different Rhizaria taxa will have unique vertical distribution patterns. Models relating their abundance to environmental parameters have mixed results, yet particle concentration is a common predictive variable, supporting the importance of heterotrophy amongst many taxa.

High spatial-resolution satellite images show the presence of numerous eddies in the deep Kuril Basin of the Okhotsk Sea, where in-situ measurements acquired within eddies are relatively rare. We conducted the first altimetry-based systematic census of mesoscale eddies in the Kuril Basin in 1993–2021 using the automatic eddy tracking algorithm AMEDA. The dominance of cyclonic eddies over anticyclonic eddies was observed, which contradicts the common opinion that anticyclonic eddies prevail over cyclonic ones in the Kuril Basin. The paper focuses mainly on the long-lived eddies with the lateral size in the range from several tens of kilometers to some hundreds of kilometers and with the lifetime exceeding 30 days. It was found that these eddies are inhomogeneously distributed over the study area with high values of occurrence frequency in some domains. This is explained by the topographic features and peculiarities of the circulation in the Basin where Soya Warm Current water, Okhotsk Sea water and subarctic Pacific water circulate and mix. The fractions of these water masses and their seasonal and interannual variations within the surface cores of the eddy were estimated using a particle-tracking technique. The kinematic characteristics of these eddies have been computed as well. The vast majority of the anticyclonic and cyclonic eddies have the nonlinearity parameter exceeding one implying that the eddies in the Kuril Basin are coherent features transporting water with its properties. Peculiarities in distribution of formation, occurrence and decay locations have been analyzed. Our results have been compared with shipboard and buoy's observations and numerical simulation of eddies in the Kuril Basin.

Caribbean ocean environments house several large deep-sea basins that remain poorly surveyed. Here we report observations of benthic faunal communities attracted to remote, deep-sea video landers deployed at depths between 262 and 1100 m in two deep basins in The Bahamas, the Tongue of the Ocean (n = 18 deployments) and Exuma Sound (n = 11 deployments). The video comprises >8000 min of survey data across five years of sampling (2018–2022). We estimated regional deep-sea particulate organic carbon (POC) flux using satellite-derived observations and a model of POC decay with depth to assess potential food availability to benthic communities living deeper than 800 m in these basins. The benthic POC flux helped to contextualize potential drivers of faunal biodiversity and abundances estimated from the lander measurements. Throughout twilight zone depths of The Bahamas (defined here as approximately 200–1000 m) we identified taxa from 22 families across invertebrates, teleost fishes, and elasmobranchs. Faunal communities were largely dominated by giant isopods (Bathynomus sp.), gulper sharks (Centrophorus sp.), and swimming sea cucumbers (Enypniastes eximia). Despite sampling biases toward larger individuals, our findings suggest that Bahamian twilight zone communities comprise a diversity of large predator species that are potentially sustained through high energetic connectivity with shallow neritic sources of organic carbon. Our findings suggest that the Central and Southern Tongue of the Ocean should be the focus of future sampling efforts given a lack of historical sampling combined with high export productivity to depth. This study provides new insight into community composition, assemblage structure, and POC flux in Caribbean deep-sea ecosystems, shedding light on previously unrecognized patterns of biodiversity.

Marine systems are active regions for producing and emitting nitrous oxide (N₂O), a potent greenhouse gas. In October 2018, samples were collected in the western tropical North Pacific (WTNP) to study the distributions, emissions, and influencing factors of N₂O. The N₂O concentrations in surface seawater showed little variation, ranging from 6.2 to 7.9 nmol L⁻¹ (corresponding to N₂O saturation range of 104–125%), with an average of 6.7 ± 0.6 nmol L⁻¹. The vertical N₂O distribution is a mirror image of dissolved oxygen (DO), increasing with depth from the surface to a maximum in the vicinity of the DO minimum. The sea-to-air fluxes of N₂O ranged from 0.1 to 7.5 μmol m⁻² d⁻¹, with an average of 1.7 ± 2.2 μmol m⁻² d⁻¹, indicating that the WTNP was a net source of N₂O to the atmosphere. Nitrification is the main process for N₂O production. The presence of the Mindanao Eddy noticeably changes the vertical profiles of N₂O in the water column, allowing the N₂O-rich deep water to reach the subsurface layers, but has little effect on the surface N₂O concentration. After Typhoon “Yutu” passed through, N₂O concentrations in surface and subsurface water increased dramatically. The surface concentration increased by about 20%, and the sea-to-air flux of N₂O increased by about 56%. Despite the short duration of the typhoon, its effect on N₂O distribution and sea-to-air flux was more pronounced than that of eddies.

Thermohaline staircases play a crucial role in the vertical transport of heat and salt in the thermocline. However, there are few in-situ observations of internal waves within thermohaline staircases. The seismic method offers high horizontal resolution and full ocean depth images over large volumes of the ocean, which can enable the visualization of internal waves within the thermohaline staircase region. In this paper, we characterize and analyze internal waves within thermohaline staircases in the Caribbean Sea using two-dimensional seismic data. Snapshots of fine structure displacements caused by internal waves are captured. We calculate the horizontal wavenumber spectra of the vertical displacement of internal waves, which closely align with the Garrett-Munk tow spectrum, indicating features of background internal wave field. We employed the Empirical Mode Decomposition (EMD) method to analyze vertical displacement data of internal waves derived from seismic data and obtained new results. The internal waves within thermohaline staircases consist of some dominant wavelength components of around 0.34 km, 0.83 km, 1.8 km, 6.25 km, 12.5 km, and 25 km. Wavelengths of approximately 0.34 km, 0.83 km, 1.8 km, and 6.25 km are coupled between the upper and lower sections, indicating the vertical transmission of the energy of high-wavenumber internal waves. By applying the prestack migration method, we observed that internal waves within thermohaline staircases display a staggered pattern. Except for the fractured strip structure, other reflectors show subtle alterations, suggesting that the thermohaline staircase stays stable during the acquisition period. Seismic oceanography emerges as a reliable method for studying internal wave characteristics within thermohaline staircases. It has the capacity to facilitate research on the complex dynamics of the ocean at multiple scales.

The circulation and water properties of Cape Darnley Bottom Water (CDBW), which is a component of Antarctic Bottom Water (AABW) produced in the Cape Darnley polynya, were investigated using results of mooring measurements and hydrographic data collected by a ship-based conductivity-temperature-depth (CTD) profiler and instrumented elephant seals. CDBW was transported northwestward on the western flank of a gully located in Wild Canyon. As CDBW descended down the slope, its thickness increased from $\sim$100 m to $\sim$600 m. The basic properties of CDBW were determined near the Antarctic Slope Front (ASF), where modified shelf water (mSW) intrudes below the dense part of Circumpolar Deep Water (CDW) and mixes with the overlying CDW to produce CDBW. mSW is shown to be the mixture of 40–45 % CDW, 30–40 % winter water (WW), and 20–25 % shelf water (SW) produced in the Cape Darnley polynya. Compared with CDBW produced in 2008, CDBW produced in 2018 and 2019 was colder and less saline. The enhanced influence of dense WW, which is locally produced on the shelf, is suggested to drive the year-to-year variability of CDBW’s salinity, at least in these three years. Water properties indicate that CDBW basically corresponds to a water mass in a transition layer between mSW and CDW. The annual mean transport of mSW contained in CDBW was estimated to be 0.26–$1.2\times 10^6$ m${}^3$ s⁻¹

Chemosynthetic ecosystems host unique geological, biogeochemical, microbial and faunistic settings, which provide key ecosystem services for human wellbeing. In the Argentine continental margin, the existence of chemosynthetic ecosystems is still unknown. We present the first finding of chemosynthetic ecosystems in the Argentine deep sea. We assessed and compared biological and geological settings for cold seeps at Malvinas Basin and Colorado Basin and a control site (no gas) at Colorado Basin. We found two cold seeps with crater-like geomorphic features (pockmarks) of 500-m and 1000-m diameter at depths of ⁓500 m. Both cold seeps exhibited methane gas bubbles trapped at the surface of the seafloor, one exhibited seepage into the water column. Cold seeps hosted dense benthic macroinvertebrates (≥300 μm) assemblages consisting mainly of polychaetes, peracarid crustaceans and mollusks. The fauna from Argentinean seeps exhibited δ¹³C and δ¹⁵N stable isotope signatures indicative of multiple trophic levels, supported by both chemosynthetic and photosynthetic sources of energy. The difference in bubbling to the water column was not associated with different trophic input of chemosynthetically-derived sources of energy, suggesting that gas input is mediated by the bubbles trapped in the seafloor sediments. The presence of gas bubbles trapped in the surface sediments of the ocean floor allowed the detection of ecological and trophic characteristics of active chemosynthetic ecosystems. Integration of the sub-bottom dimension can help improve our understanding of the interactions of chemosynthetic ecosystems with seafloor fluid flow in a more reliable manner than the gas plumes. These cold seeps host significant biodiversity and ecosystem functions of the deep ocean. They fall within areas tendered for oil and gas industry development, but have not been a focus of conservation efforts to date. Information provided here can inform effective conservation actions and improve our understanding of the distribution of chemosynthetic ecosystems worldwide.

Relative to a single typhoon, the ocean response and feedback mechanisms during sequential super typhoon process have yet to be fully understood. The upper ocean responses to super typhoons Trami and Kong-Rey that occurred sequentially in autumn 2018 over the northwestern Pacific (NWP) Ocean were investigated using multi satellite and Argo float data. As a slow-moving typhoon, the location of maximum sea surface temperature (SST) cooling induced by Trami was determined by the typhoon's translation speed and the preexisting cyclonic eddy (CE). The most significant SST cooling was observed near the abrupt turning point, where Trami nearly stalled over the ocean, rather than in the CE region, although the CE could enhance the SST cooling. For the subsequent, fast-moving typhoon Kong-Rey, the most significant SST cooling was observed in the CE region. Two different mechanisms (i.e., slow translation and cyclonic eddy) for the enhancement of SST cooling, salinity and chlorophyll-a were also compared. For salinity and chlorophyll-a concentration, slow translation speed plays a more important role than the preexisting cold eddy. Additionally, both typhoons experienced rapid weakening, suggesting that typhoon-induced negative feedback affects not only the intensification of the typhoon itself but also the subsequent typhoon. An analysis of data from Argo floats demonstrated that weak mixing and upwelling contributed to a three-layer structure in the upper ocean temperature on the left side of the typhoon track; strong upwelling played a more important role in the cooling of the whole upper ocean near the typhoon track center; and strong vertical mixing was the dominant factor for the two-layer temperature structure on the right side.