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

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.

Megafauna, such as cold-water corals, can promote diversity through various processes, such as predation, bioturbation, competition, and facilitation as habitat engineers. Further investigation into their ecology and role in epifaunal community structure in the deep sea is needed. Diversity, abundance, and spatial patterns of epibenthic megafauna (≥2 cm) were quantified at regional-scales (100 s m – 100 s km) using high-resolution imagery from 15 stations in the Laurentian Channel Marine Protected Area, Canada. A patchy community structure was significantly associated with station and benthoscape class, which in turn was based on geological factors. Three types of assemblages included: (1) dominated by corals Pennatula sp. 2 and/or Hexacorallia (SC.) spp. in shallow eastern benthoscape classes with high abundance and low diversity; (2) a diverse mix of taxa (e.g. sea pens Anthoptilum spp. and Kophobelemnon spp., anemones/cerianthids, etc.) in deeper (>400 m) western benthoscape classes, with low abundance and high diversity; and (3) a unique community dominated by sponges. Overall, eight taxa contributed to most dissimilarities between stations, and communities were similar within 10 km but could differ at greater distances. Benthoscape classes captured environmental factors (e.g. depth and substrate) that may be responsible for changes in diversity and abundance, and are used as a proxy for different habitats. Our study advanced the understanding of regional spatial patterns in the abundance, composition, and diversity of epibenthic communities, by identifying spatial patterns particularly in the Laurentian Channel where data were limited, adding to interpretations of spatial ecology in a previous fine-scale study. Additionally, these spatial patterns reflect various underlying ecological processes that are mostly unknown. Our community analysis and observed changes in abundance and diversity have implications that can help inform future monitoring designs to promote representative and meaningful spatial assessments.

In recent years, methane gas released from the seafloor has been considered a sub-oceanic resource, and comprehending the dynamics of methane bubbles in the ocean has garnered increasing attention. Therefore, in this study, we conducted a quantitative analysis of the behavior of ascending methane bubbles with and without a hydrate layer. The bubbles were filmed at two natural gas seep sites and reproduced by numerical simulations using two-dimensional motion analysis software. The simulations were performed with gas bubbles and methane hydrate (MH)¹ bubbles spouting from a nozzle in a computational domain filled with pure water to assess the validity of image analysis for in-situ data, whereas numerical models and physical properties were utilized for the current two-phase (gas-liquid) simulations. The rising velocity, size, circumference, circularity, and maximum diameter of the methane bubbles were examined to understand the effects of the MH layer on the statistical and stochastic features of ascending methane bubbles. Based on the statistics of the above variables, the gas bubbles had a higher rising velocity and smaller circularity than the MH bubbles when the bubble sizes were identical. In addition, stochastic analysis indicated that the circularity of the MH bubble was uniquely determined by their size, due to the more rigid skin of the MH bubbles compared to that of gas bubbles. Consequently, discrepancies in bubble dynamics between methane gas and MH bubbles were clarified in this study.

This paper develops three composite paleomagnetic secular variation (PSV) records (directions and relative paleointensity) for MIS 8–10 (243–375 ka) from IODP Ex. 323 Sites 1343, 1344, and 1345 in the Bering Sea. There are 79 inclination features and 74 declination features in each of these records that can be correlated among them. Oxygen isotope records and correlation of our Bering Sea paleointensity records to the oxygen-isotope dated global PISO-1500 paleointensity record provide a detailed chronostratigraphy for our three sites with an uncertainty of ∼±2000 years. There are two excursions recorded reproducibly in our PSV records, the Portuguese Orphan Excursion (286 ± 2 ka) and the Calabrian Ridge Excursion (326 ± 2 ka). Both of these excursions have only short intervals (less than 500 years) of excursional directions. Both excursions have simple open looping of the directions. The Portuguese Orphan excursion has counter-clockwise (CC) looping, while the Calabrian Ridge Excursion has clockwise (C) looping. Statistical study of the PSV after removal of all excursional directions has been carried in overlapping 3-ky and 9-ky intervals. We have identified two distinctive features of the long-term secular variation. First, the ‘normal’ PSV has coherent long-term variability noted by several successive 9-ky inclination or declination averages distinct from overall averages. These persistent >10⁴ ky variations indicate long-term memory in the regional pattern of dynamo activity. Such memory is not consistent with persistent millennial-scale drift of the Earth's magnetic field. Second, PSV angular dispersion (a measure of directional variability) is quite low (∼15°) for ∼75% of the MIS 8–10 time interval. But angular dispersion more than doubles (∼35°) in three short intervals around 265–272 ka, 283–295 ka, and 307–325 ka. The onset and termination of these three high-angular-dispersion intervals occurs fast (∼10³ yrs). These same three high-angular-dispersion intervals also occur almost synchronously in the North Atlantic Ocean (Lund, 2022). These high-angular-dispersion intervals are also intervals in which excursions occur in both regions and are associated with relatively low paleointensity. We think this constitutes a distinctive bimodal pattern to overall pattern to Global secular variation in the Brunhes Chron.