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

Given the go ahead, deep-sea mining operations are likely to continue for decades on a substantial spatial scale and the resulting sediment plumes combined, are likely to extend beyond the licenced mining areas, and could lead to the chronic exposure of deep-sea organisms to a mixture of metals, even mobile species, such as fish, that could conceivably display avoidance behaviour. The metal concentrations, often substantially below lethal doses, mean that individual mortality is too blunt a measure to allow assessment of “serious harm”. Commonly used cellular biomarkers of exposure in ecotoxicology include DNA damage using the Comet assay. True deep-sea ecotoxicological studies with fish are rare and to our knowledge, there are no published data or method optimizations for deep-sea fish. Coryphaenoides ssp. were collected during SMARTEX expedition 1 (Feb/Mar, 2023) to the Clarion Clipperton Zone (CCZ) in the Eastern Pacific Ocean using a baited trap deployed between 4580–4,732m depth for 24–48 h. Blood and gill tissue were removed and processed for the Comet assay. In order to reduce artefactual DNA damage from cryopreservation observed previously, two sets of samples were prepared: a cryopreservative (10% DMSO) was added to one set of samples and stored at −80 °C; the second set was used to perform a Comet assay within hours of collection. A custom-built gimble table enabled horizontal electrophoresis at sea after which Comet assay slides were dried and stored at room temperature until further analysis. The Comet assay was also assessed in freshly sampled and frozen rainbow trout cells as a proxy control in order to evaluate potential artefacts from the collection and sampling procedure of the deep-sea fish. The blood samples processed at sea had a significantly reduced level of DNA damage compared to the frozen samples. There was no significant difference between the fresh deep-sea and rainbow trout samples. However, the freshly prepared gill samples in Coryphaenoides ssp. showed substantial artefacts, possibly as a consequence of barotrauma. These results represent the first effort at establishing baseline DNA damage data for deep-sea fish, an essential component in understating and quantifying the impact of deep-sea mining.

The eddy-mean flow interactions are critical processes in the ocean energy cycle. This study investigated the energetics of eddy-mean flow interactions in the western tropical Pacific Ocean using the multiscale window transform (MWT) and MWT-based canonical transfer theory, based on 16-year numerical outputs from the Ocean General Circulation Model for the Earth Simulator and two mooring measurements. Energy analysis revealed that prominent eddy kinetic energy (EKE) appears in the upper layer of the Sulawesi Sea and the source region of North Equatorial Countercurrent (NECC), and in the subsurface layer along the Philippine coast. The kinetic energy in the upper layer is mainly transferred from the mean flow to the eddy field through barotropic instability. Below the thermocline, the prominent subsurface EKE is not only caused by barotropic conversion, but also by baroclinic one. Subsurface mesoscale eddies east of the Mindanao Island extract energy from mean flow through barotropic instability, and those further north seem to release their kinetic energy to the mean flow of North Equatorial Undercurrent, indicating inverse energy cascades. Our results highlight that the advection effect plays a key role in the horizontal distribution of EKE, which generally shifts the high EKE area a few degrees downstream from the eddy formation region. Particularly, in the source region of NECC, the advection term shifts the EKE center 5° eastward from ∼132°E to ∼137°E.

The potential impact of manganese mining on benthic remineralization in the Pacific Ocean was assessed in this study. We estimated total sediment oxygen uptake rates (TOU) using in situ autonomous benthic chambers at the polymetallic nodule and Co-rich polymetallic crust mining sites of Korea: at the Clarion-Clipperton Fracture Zone (PILOT site) in the eastern Pacific and the open-sea seamounts (OSM) 9-1 and OSM17 in the western Pacific, respectively. The TOU rates in the shallow seamount areas (0.58 ± 0.01–2.22 ± 0.04 mmol O₂ m⁻² d⁻¹) were significantly higher than in the PILOT station (0.21 ± 0.05 mmol O₂ m⁻² d⁻¹), indicating that relatively labile organic matter could be deposited according to the regional oceanographic features and water depth. The highest TOU found among the seamount areas was in the wide summit area at OSM9-1, which may be due to environmental conditions such as seasonal wind-driven mixing, upwelling around the seamount slope, and topography, which can increase productivity seasonally. Our findings suggest that organic carbon quality and hydrodynamics can be closely linked to benthic carbon mineralization in the targeted polymetallic mining areas of the Pacific.

In this study we introduce one new genus and five new species of cheilostome bryozoans based on material collected mainly at bathyal depths in the Subantarctic Southwest Atlantic by the vessels ARA Bahía Blanca, BO Puerto Deseado and RV Meteor. Bathyanasca incubatrix gen. nov., sp. nov., Chondriovelum perforatum sp. nov., Aspidostoma adeoniforme sp. nov., Talivittaticella bathyalis sp. nov. and Turritigera formidabilis sp. nov. are described and illustrated. Bathyanasca incubatrix, characterized by the lack of ovicells and the incubation of embryos within the autozooidal cavity, is tentatively classified in the family Calloporidae. Present results contribute to support the hypothesis of close faunal affinities between Antarctica and relatively deep areas around southern South America.

The enhancement of particulate organic carbon transfer to the deep sea by zooplankton fecal pellets constitutes a crucial component of the marine biological carbon pump. Here, we investigated time-series variations in characteristic and flux of zooplankton fecal pellets at different water depths of two sediment-trap mooring stations from May 2021 to May 2022 in the western South China Sea. The results show that numerical fluxes of fecal pellets were 0.75 ± 0.60 × 10⁴, 0.63 ± 0.63 × 10⁴, and 0.38 ± 0.29 × 10⁴ pellets m⁻² d⁻¹ at 500 m, 1170 m, and 1380 m water depth, respectively, corresponding to their carbon fluxes of 0.10 ± 0.06, 0.09 ± 0.04, and 0.10 ± 0.04 mg C m⁻² d⁻¹. Both numerical and carbon fluxes of fecal pellets exhibited clear seasonal variations, with two peaks occurred in August and early November at all water depths. The fecal pellets have distinct morphological types (spherical, cylindrical, and ellipsoidal) and their contributions to the numerical and carbon fluxes were different. At all water depths, ellipsoidal and spherical pellets accounted for 96.0% of the numerical flux and 72.1% of the carbon flux. Cylindrical pellets were rare in quantity, accounting for 4.0% of numerical flux, but their carbon contribution accounted for 27.9% of the total fecal pellet carbon flux. The proportional fractions of zooplankton fecal pellets contributed to the overall particulate organic carbon from 0.7% to 28.2% in the western South China Sea, and fell in a reasonable range around the world. Multiple mechanisms, including East Asian monsoon climate and zooplankton community structure may be responsible for the production and fate of fecal pellets as well as their contribution to the settling particulate organic carbon.

This study focused on the chemistry of sedimentary pore fluids to clarify hydrothermal fluid migrating within sediments at the Geolin Mounds (GLM) and Mienhua Volcano (MHV) hydrothermal fields, southernmost Okinawa Trough, where are characterized by covering of thick sediment. The significant downward decrease in Mg²⁺ (low to 23.3 mmol L⁻¹) and concurrent increase in Li⁺ (up to 2,269 μmol L⁻¹) in sedimentary pore fluids implied a substantial influence of hydrothermal fluid, which might be associated with high-temperature (>350 °C) rock/sediment-fluid interaction. The best fitting of the 1-D advection-diffusion equation to pore-fluid Cl⁻, Mg²⁺, and Li⁺ concentrations further evidenced the upward hydrothermal through sediments with rates of 0.13 ∼ 124 cm yr⁻¹. The apparently Cl-depleted and slightly Cl-enriched pore fluids in the GLM and MHV hydrothermal fields supported the occurrence of subseafloor phase separation and classified their hydrothermal fluids into vapor-rich and brine-rich phases, respectively. The low pH values (pH = 5.67 ∼ 6.21) with downward increasing trends of pore-fluid dissolved inorganic carbon (DIC, up to 60 mmol L⁻¹) and its heavy isotopic compositions (δ¹³C_DIC = +2.5 ∼ +7.0 ‰) inferred in-situ liquid CO₂-impregnated sedimentary circumstance in the GLM and MHV hydrothermal fields. This sedimentary environment, as demonstrated, enhanced the chemical weathering of silicate and carbonate minerals, resulting in the elevated concentrations of Ca²⁺ and K⁺ in pore fluids. It highlights the impact of acidic and in-situ CO₂-saturated fluids within sediments on geochemical alterations of bulk solids/sediments and interstitial fluids.

Marine snow floc refers to coagulation of microbes and marine debris in the upper ocean layers, bound together by bio-polymers such as transparent exopolymer particles (TEP) secreted by microbes. The stickiness of TEP plays a crucial role in determining the rate of marine snow floc formation. Additionally, the effect of TEP on the size distribution of marine snow influences the sinking velocity of the flocs. Using a surrogate material system, we study the kinetics of marine snow using a custom-built experimental setup, which allows direct measurement of floc size, floc number density, and floc sinking velocity as a function of TEP concentration. By comparing the experimental floc size with Smoluchowski coagulation theory, we obtain stickiness index, which increases with TEP concentration first, reaches maximum around 0.3 g/L of TEP and decreases upon further increase in TEP concentration. The experimental sinking velocity scales with floc size as $w_s=a{d}^b$, with $b$ ranging from 0.57 to 0.68. The exponent is slightly higher than that of 0.5 expected in the Stokes limit. This study establishes a clear link between stickiness index, sinking velocity, and polymer concentration, providing valuable insights for modelling of marine snow dynamics in deep ocean conditions. These findings contribute to a better understanding of the kinetics of marine snow formation, essential for predicting carbon sequestration within the biological carbon pump.

The Bransfield Strait connects the Bellingshausen and Weddell seas and is strongly affected by intense inflows of their water masses. In this work we analyzed Shipborne Acoustic Current Doppler Profiler (SADCP) measurements carried out in the Bransfield Strait from 2015 to 2022. The new dataset includes over 100 transects, crossing the main currents in the strait (namely, the Bransfield Current and the Transitional Weddell Water (TWW) flow). Based on these data, we studied spatial variability of water mass transports in the Bransfield Strait during austral summer season. As shown below in this research, the Bransfield Current was observed down to the 600 m depth. By considering deeper layers, we managed obtaining more precise assessments of mean water mass transports of the Bransfield Current. They were estimated at 1.4–2.1 Sv. We found that the transports of the Bransfield Current and TWW flow in the austral summer season (November–March) do not show significant variability. The water mass transport of the Bransfield Current and the TWW flow was stable within the central basin of the Bransfield Strait and differed in its western basin. We also found that in austral summer the heat transport into the Bransfield Strait varied between 0.2 and 0.4 Sv·°C and salinity transport was −0.07 to −0.06 Sv·psu, their sign reflecting a dominant northeastward flow of relatively warm and fresh water. In addition, we compared Lowered Acoustic Current Doppler Profiler (LADCP) and SADCP measurements and proved that the technical limitations of the SADCP do not significantly affect the estimates of the transports in this region.

Natural whale falls and falls of smaller-sized food have been reported for more than 30 years and are known to be important sources of nutrients and organic matter for the seafloor community. However, the associated species composition and ecological processes during such events in the hadal zone were unknown. Therefore, we aimed to determine the impact of depth and predation on the hadal community during the early stages of a food-fall event. This is the first study to investigate the preliminary stages of the two deepest artificial dolphin-fall events in the Philippine Basin (PB) (∼7729 m) and Mariana Trench (MT) (∼8200 m). A total of nine dives were conducted over a period of 86 days (PB) and 50 days (MT) using the deep-sea manned submersible “Fendouzhe.” Our observations in the PB indicated that the first stage (mobile-scavenger) was controlled by the feeding ecology of hadal amphipods and snailfish. In contrast, the absence of predatory snailfish in the MT enhanced the degradation rate of the carcass compared to that in the PB. Most soft tissues were entirely consumed by scavenging amphipods within days of the event in the MT, whereas in the PB, amphipods were observed taking a feeding hiatus on Day 10 to escape snailfish predation. The second stage (enrichment-opportunist), which hosted few grazing faunas, began at different times in each location and overlapped with the mobile-scavenger stage. Dolphin carcasses, being smaller than those of full-grown whales, can only sustain a large community of scavenging amphipods, and indirectly, predatory snailfish. After the first stage, the dispersed organic matter and limited lipid content in dolphin bones were likely insufficient to sustain an active grazing community or the chemosynthetic community that typically follows. We concluded that water depth influences the successional stages and decomposition rate of food falls in the hadal zone by controlling the dynamic relationship between prey and predators. Our study elucidates the ecology of food-fall events in the hadal zone and highlights the key differences in food-fall events at different depths.