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

A novel deep-sea in-situ anion analyzer (DIAA) is proposed and developed for long-term and continuous observation of marine biogeochemistry and ecology. The DIAA is designed to analyze the concentrations of various anions in seawater, such as F⁻, Cl⁻, Br⁻, NO₃⁻, SO₄²⁻, and PO₄³⁻, based on ion chromatography (IC) technology. The DIAA consists of a control circuit module, a conductivity signal acquisition module, and a flow analysis module. The control circuit module is installed in a sealed pressure-resistant vessel, while the conductivity signal acquisition module and the flow analysis module are housed in a sealed pressure-balanced vessel. The two vessels are capable of functioning at a water depth of up to 4000 m. A seawater in-situ dilution device is designed to solve the issue that the concentrations of Cl⁻ and SO₄²⁻ in seawater exceeds the IC detection limit. Moreover, an in-situ calibration device enables the DIAA to operate subsea for a long time without recovery. In addition, the DIAA can diagnose and isolate faults automatically. The operation status can be monitored remotely on the shore, and the scientific data can be acquired in real-time. During the sea trial, the DIAA was connected to Monterey Accelerated Research System (MARS) seafloor observatory at a water depth of approximately 900m and operated for six months successfully. The measurement accuracy and the long-term stability of the instrumentation have been verified.

Rapid rise of salinity is observed in the Black Sea in recent years, with the largest positive trend (0.07 psμ per 10 years) detected in the pycnocline. We use long-term hydrological measurements for 1985–2019 to show that salinity of pycnocline has intense seasonal and interannual variability modulated by the mechanical and convective mixing. In the warm period of a year, shear turbulence driven by strong winds and intense geostrophic currents causes the penetration of warm waters into the lower density layers. This is accompanied by the rise in their salinity, the source of which is the deep saline waters situated below the halocline. This process is most intense in the areas of downwelling and intensifies in the autumn period, when thermal stratification is relatively weak. Another important reason is the entrainment of salty Mediterranean waters in the upper part of the Black Sea halocline, which is modulated by the deepening of the seasonal thermocline near the Bosphorus strait and mechanical mixing.

The increase of salinity is compensated during cold winters, when convective mixing transports fresher water influenced by river discharge into lower density layers of the basin and causes a decrease in pycnocline salinity. This process is most intense in the center of the cyclonic gyres, where pycnocline is located closer to the surface and winter temperature reaches minimal values.

Due to the long-term warming of the Black Sea, the process of freshening of deep layers now is observed only in rare cold years. At the same time, an intensification of wind speed, vorticity, and geostrophic circulation processes promote the blurring of the halocline and the rise of the salinity of the Black Sea upper layers. Such rise begins after 2007 in the upper part of Black Sea halocline (depth 50–100 m) and is traced down to 250 m by 2020.

The occurrence of cold-water coral (CWC) reefs off Northwest Africa that has a broad oxygen minimum zone (OMZ) is poorly studied. A 400 km long almost continuous coral mound chain off Mauritania that was investigated by earlier expeditions revealed mainly dead corals. In 2021, the EAF-Nansen Programme conducted a survey at the border between Mauritania and Senegal with the main objective to map CWCs. Acoustic mapping with multibeam echosounder was used to target mounds at 450–650 m depth and 14 video lines were conducted using a remotely operated vehicle (ROV). The occurrence and health status of CWC reefs along video transects were annotated using the software “CampodLogger”, oceanographic variables were measured using a CTD sonde, and terrain and backscatter analysis were conducted.

Here we present the environment and health status of 13 Lophelia reefs established in the study area, six of them were large and healthy reefs with areas having 15–50% cover of live colonies. Oxygen concentrations were measured to be as low as 1 ml L⁻¹ and temperature ranged from 8.8 to 11.6° C. We compare reef health with the environmental variables: temp, salinity, oxygen, and particle load. A GIS based model was developed to predict the occurrence of live reefs in the study area based on the observed average range of a set of terrain descriptors measured where live Lophelia reefs occurred.

Our findings of healthy Lophelia reefs are unexpected and further north in the OMZ reefs have been described as dormant. There is an urgent need for visual seafloor mapping to aid the development of spatial management plans in these understudied waters.

Growth rates of cold-water bamboo corals are of crucial importance for establishing high-resolution chronology and reconstructing the development of these corals. However, due to the difficulty of sampling, their ages and growth rates as well as ecological indications are still fragmentary. In this study, radiocarbon analysis was performed on live-collected bamboo corals from the South China Sea (SCS) to investigate their growth and the controlling environmental factors. The obtained bomb ¹⁴C curve of organic nodes, which is formed by corals via consuming the surface-sourced sinking particulate organic material suggest that the organic nodes can document the upper ocean environmental conditions. The corals with ages up to 829 years have radial growth rates (RGRs) of 7.4–60.0 μm/year (average: 22.9 μm/year). These RGRs are among the lowest values of all the published RGRs of bamboo corals, representing the slow growth of corals in the SCS, and probably results from the low surface productivity. On the other hand, the relatively high coral RGRs at water depths of ∼1000 m and ∼2000 m probably results from the enhanced food availability caused by the strong bottom current at the water mass boundaries in the intermediate and deep waters. Although no significant correlation between the coral RGRs and the ambient environmental conditions were found, the relatively low RGRs of bamboo corals in the SCS clearly imply rather low ability to recover after damage. Further investigation of the environmental conditions controlling the growth of bamboo corals is needed.

The reproductive aspects of all Plesionika species are relatively well known worldwide, except for the deepest species of the genus, Plesionika williamsi, for which little information is available throughout its range. The ovarian maturity, sex ratio, brood size, and size-depth distribution of the deep-sea shrimp Plesionika williamsi (Pandalidae) in the Canary Islands (eastern-central Atlantic) were analysed. Ovigerous females were observed all year round, with the highest number of ovigerous females recorded between July and October. The presence of a greater number of ovigerous females during the summer may reflect a high local availability of food or the optimal abiotic conditions, which are factors with a strong influence on reproduction. The presence of non-ovigerous mature females throughout the year indicates that their resting period in the reproductive cycle occurs asynchronously. The physiological size at first sexual maturity was 19.24 mm in carapace length (CL) and the length at first sexual maturity was estimated at 23.15 mm CL. Estimates of size at first sexual maturity based on ovigerous females describe the result of the reproduction process, whereas size at first sexual maturity based on ovarian maturity deals with physiological preparation for reproduction. The modal size class of egg production was 24–30 mm CL, which yielded 83.22% of the population egg production. Plesionika williamsi is an iteroparous species that can produce small eggs during egg extrusion. The mean number of external embryos carried by females was 3048 and can be considered a true approximation of the number of larvae released in each batch, which depend on the conditions existing in each system. The shallower individuals are associated with a depth stratum that represents the boundary between two water masses present in the Canary Islands. The increase in size with depth is related to the presence of submarine volcanic canyons, which constitutes a flow channel of surface organic matter to depth.

The Southwestern Atlantic (SWA) is characterized by its large Eddy Kinetic Energy as the result of the confluence of two major western boundary currents, the northward flowing Malvinas Current (MC) and the southward flowing Brazil Current. The SWA study was addressed in the literature based on altimetry data, in situ measurements, regional models and ocean reanalysis. The present study constitutes the first effort to sample a portion of the SWA, with a dense drifter array (N = 62) deployment. The drifters, drogued at 15 m depths, were deployed across the MC and the Argentine Continental Shelf along two zonal transects located at 47°S and 47.25°S, between the 8th and the September 9, 2021. Drifters were set to deliver their position every 10 and 60 min, providing accurate Lagrangian trajectories that provide information on a large range of space and time scales of the surface currents. Three regions are clearly identified based on the analysis of the speed of the drifters, of their trajectories and of the spectral density of their velocities: the continental shelf, the slope and the open ocean. The comparison of the trajectories of the drifters with satellite altimetry images shows that, in general, drifters follow mesoscale features that are detectable in satellite altimetry maps. The analysis of the drifter trajectories also allowed us the study of submesoscale features of the flow (1–10 km) that are not observable in satellite altimetry data. Comparison with cloud-free, high-resolution color images, shows that drifter trajectories organized by the mesoscale flow might also locally follow sub-mesoscale features. In frontal regions it was found that drifter velocities double satellite altimetry geostrophic velocities, which suggests that the dynamics at those regions is largely dominated by ageostrophic components. The ageostrophic Ekman component might explain the direction of the drifters when strong winds from a given direction prevail for several days and the drifters are not in a region with large sea surface height (SSH) gradients. The joint analysis of drifters’ trajectory and SSH clearly depicts that mesoscale features on the open ocean region control the cross-shelf exchanges between the MC and open ocean regions as well as the strength and width of the MC. Finally, the spatial density distribution of the drifters during the first hours after deployment and within a small eddy also allowed us to characterize the flow in terms of its divergence, vorticity and strain, indicating that the MC is geostrophic and has a jet-like behavior while the eddy is largely ageostrophic and has a dominant vorticity component over strain. We conclude observing that the analysis of a dense array of drifters provides valuable information of the flow that cannot be attained solely based on satellite data.

The seasonality and generation mechanisms of submesoscale processes (SMPs) in the northern Bay of Bengal (nBoB) are investigated by the outputs of a high-resolution model simulation. The results show that the nBoB has abundant energetic SMPs, with significant seasonal features and geographic variability. The head basin (region A) and central basin (region B) of the nBoB are identified as two typical spots of submesoscale motions. Seasonally, SMPs in region A are strongest in spring and are closely correlated with strong mesoscale strain. By contrast, SMPs in region B are more active in winter and late summer due to the combined effects of deep mixed layer and large mesoscale strain. Energy analysis suggests that baroclinic instability is a dominant generation mechanism for energetic SMPs in region B during winter and summer periods. During spring, the prevalent submesoscale kinetic energy (KE) reservoir in region A is fueled by wind forcing, buoyancy conversion, and the forward KE cascades from mesoscale processes, and mainly balanced by the inverse KE cascades from submesoscale to large-scale processes.

The mesopelagic zooplankton community plays an important role in the cycling and sequestration of carbon via the biological pump. However, little is known about the physiology and ecology of key taxa found within this region, hindering our understanding of their influence on the pathways of energy and organic matter cycling. We sampled the eight most abundant zooplankton (Calanoides acutus, Rhincalanus gigas, Paraeuchaeta spp., Chaetognatha, Euphausia triacantha, Thysanoessa spp., Themisto gaudichaudii and Salpa thompsoni) from within the mesopelagic zone in the Scotia Sea during a sinking diatom bloom and investigated their physiological ecology using lipid biomarkers and stable isotopic signatures of nitrogen. Data suggest that the large calanoid copepods, C. acutus and R. gigas, were in, or emerging from, a period of metabolic inactivity during the study period (November 15th – December 15th^, 2017). Abundant, but decreasing lipid reserves in the predominantly herbivorous calanoid copepods, suggest these animals may have been metabolising previously stored lipids at the time of sampling, rather than deriving energy solely from the diatom bloom. This highlights the importance of understanding the timing of diapause of overwintering species as their feeding is likely to have an impact on the turnover of particulate organic matter (POM) in the upper mesopelagic. The δ¹⁵N signatures of POM became enriched with increasing depth, whereas all species of zooplankton except T. gaudichaudii did not. This suggests that animals were feeding on fresher, surface-derived POM, rather than reworked particles at depth, likely influencing the quantity and quality of organic matter leaving the upper mesopelagic. Our study highlights the complexity of mesopelagic food webs and suggests that the application of broad trophic functional types may lead to an incorrect understanding of ecosystem dynamics.

Understanding the circulation patterns, identifying locations for eddy generation, and monitoring eddy behaviors are all areas of interests for different water bodies. This study focused on submesoscale eddies in the southern Caspian Sea, specifically close to Rudsar and Sefidrud, due to their distinct form and high turbidity. The high-resolution FVCOM model was utilized to identify high turbidity locations for a period from 2010 to 2014. The results of the two selected locations were explored individually using various techniques. Also, the obtained MODIS satellite images were compared to the daily averaged current results. The findings showed distinct turbid current patterns, and most of the eddies were classified as submesoscale. The alterations in shoreline orientation and wind direction were identified as the two most significant factors affecting this highly turbid area, with river discharge having a significant effect on eddy development close to the Sefidrud delta. The detected eddies at Rudsar in 2013 were found to be more diverse than those at the Sefidrud delta. The circulation and eddy patterns of these locations were prepared. The findings really emphasize how crucial it is to look into the small-scale circulations and eddies along the coastal areas of the southern Caspian Sea. These results offer valuable insights into the generation and behavior of these eddies, particularly when influenced by morphological changes, local currents, and various other factors.

The hadal Mariana Trench remains poorly understood. In December 2016, an array of high-resolution temperature loggers, attached to the ocean bottom seismometers (OBSs), was deployed from 1665 to 7520 m for two weeks across the Challenger Deep of the Southern Mariana Trench. The temperature variance spectrum reveals that the bottom water is mildly turbulent and it is mainly modulated by the semidiurnal internal tides. At the second deepest observation station (depth of 7015 m), the viscous subrange is resolved in the high-frequency spectrum. Applying the proposed method with Taylor’s frozen field hypothesis and Kraichnan theoretical spectrum analysis, it is revealed that turbulent dissipation rate $\varepsilon$ is $7.8\times 10^{-10}$ $m^2/s^3$ and flow speed U is 8.9 mm/s. Dissipation rates $\varepsilon$ of all stations vary between $5.9\times 10^{-11}$ and $1.4\times 10^{-9}$ $m^2/s^3$, with the northern region of Challenger Deep experiencing stronger energy dissipation than the southern one. The vertical distribution of dissipation rate $\varepsilon$ shows that it decreases with increasing depth from 1000 to 6000 m, but then increases to around 8000 m, which is consistent with previous observations and numerical simulations. The available turbulent mixing data indicates that the energy dissipation is vertically distributed in a distinct multilayer structure in the deep ocean of Challenger Deep, which is proposed to link to the intrusion of water mass in the deep Mariana trench.