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

Using a total of ∼7000 accumulated beaks sorted from 92 food samples, the cephalopod diet of sooty albatross Phoebetria fusca was determined for the first time at the subtropical Amsterdam Island (3898 beaks from 53 food samples), and it was compared with prey eaten at the subantarctic Crozet Islands (3085 beaks from 39 samples). At Amsterdam Island, sooty albatross fed on 42 cephalopod taxa that included the dominant Histioteuthis atlantica (34.7% by number of beaks) and juvenile Ommastrephes cylindraceus/Todarodes filippovae (10.1%). They preyed primarily upon cephalopods that have a wide latitudinal distribution (55.1%), with subtropical species ranking second (25.8%), and Southern Ocean endemics third (19.1%). By contrast, birds from Crozet Islands fed primarily on Southern Ocean endemics (80.7%), followed by subtropical species (14.8%), and taxa with a wide distribution (4.5%). There, the main prey were adult Histioteuthis eltaninae (24.6%), Batoteuthis skolops (27.2%) and Galiteuthis glacialis (16.2%). Sympatric sooty and light-mantled sooty P. palpebrata albatrosses from Crozet Islands segregated by feeding on different prey indicating different foraging grounds north and south of the archipelago, respectively. Light-mantled sooty albatross fed almost exclusively on Southern Ocean endemics (98.2%), such as G. glacialis (44.4%), Psychroteuthis glacialis (21.4%), H. eltaninae (13.4%) and Moroteuthopsis longimana (10.2%). Including cephalopod prey of sooty albatross to the previous investigations on teuthofauna from the southern Indian Ocean added southern subtropical species to Southern Ocean taxa. Overall, teuthofauna of this vast oceanic zone hosts at least 71 cephalopod species, including two bathyteuthids, 56 oegopsids, two sepiolids, three cirrate and seven incirrate octopods, and the vampyroteuthid Vampyroteuthis infernalis.

Understanding the biodiversity of an ecosystem is crucial to determine its structure and resistance to climate change. The South Sandwich Islands (SSI) are located in the Scotia Sea (Southern Ocean), within the South Georgia and the South Sandwich Islands Marine Protected Area. However, the biodiversity of the archipelago remains poorly studied, whilst climate change has the potential for wide-ranging impacts in the Antarctic and Subantarctic regions. Here we used predators as biological samplers to study the bathyal communities of SSI. A total of 61 species including fish, cephalopods and crustaceans, were identified from the diet of 13 predatory taxa (11 fish and two cephalopod). Common Subantarctic and Antarctic species were found, with Moroteuthopsis longimana being the species with the highest density (1.74 individuals per stomach at Montagu Island). Eleven fish and one cephalopod species were recorded for the first time at the archipelago. Furthermore, 16 fish species had their bathymetric range increased. Fifteen fish and one crustacean appear to have SSI as the northern or southern limit of their distribution. Community analysis found two major groups at SSI, one in the north and one in the south, with the southern group subdivided into two groups. This separation is related to the environmental conditions at the archipelago that abruptly change at Saunders Islands. Latitude (correlated with sea surface temperature) and sea surface height (proxy for upwelling) both correlated with the dissimilarity between communities. These results suggest that climate change may affect the biodiversity at SSI in the future as warming waters of the Scotia Sea and changes in the upwelling system may favour range extensions of more northerly species into the archipelago. Furthermore, it could lead to local extinctions of some species exclusively found in the southernmost areas of the archipelago.

An improved off-line separation method of vanadium redox species V(V) and V(IV) in seawater using a solid phase extraction with chelating resin Chelex-100 was developed. Column shape, eluting solution, elution volume, pH of sample, and flow rate were tested and optimized to establish a simple offline separation method. Analyses with inductively coupled plasma mass spectrometry (ICP-MS) combining with a Kinetic Energy Discrimination mode (KED) using helium gas achieved precise determination of vanadium redox species in saline matrix solutions. Average recovery of solutions doped with both V(V) and V(IV) was 92% for V(V) and 96% for V(IV). The method detection limit was 0.87 nmol/kg for V(V) and 0.47 nmol/kg for V(IV) obtained from 0.6 mol/kg NaCl solution. Stability tests of redox species V(IV) in seawater with/without an aerobic chamber revealed that V(IV) species were preserved in seawater for over 24 h and possibly further 14 days in normal oxidizing atmosphere. We developed a method that does not require pH adjustment of sample solution, which reduces the risk of changing the natural fractions of both redox species. The proposed method was applied to selected samples from open ocean and coastal seawater collected in the South-East Atlantic Ocean during GEOTRACES research cruise GA08. Concentrations of 29–37 nmol/kg of V(V) and 1.5–2.2 nmol/kg of V(IV) in samples off-shore the Namibian coast (43–2997 m water depth) were found. Higher concentrations of V(IV) were detected in near-shore coastal seawater characterized by very low oxygen content (2.4 nmol/kg at 200 m water depth) relative to those from off-shore seawater. The newly obtained results suggest that not only dissolved oxygen concentration but also biogeochemical parameters (e.g. biological activity) may play an important role to explain the distribution of redox species of V in seawater.

The family Polymixiidae is an ancient group of acanthomorph fish, often regarded as living fossils. Currently, there are 11 valid species allocated in the genus Polymixia, and commonly known as beardfish. All species are benthopelagic and can be found at depths between 80 and 800 meters, in the Atlantic, Indian, and Pacific oceans. Traditionally, only two species had been assigned to the Atlantic Ocean, P. lowei, in the western Atlantic, and P. nobilis, in the North Atlantic, including northern South America and Saint Peter and Saint Paul Archipelago; however, recent studies revealed a cryptic species from the Bermudas, described as P. hollisterae, and a yet undescribed species from the Caribbean Sea. Herein, we describe a new species of Polymixia from the western South Atlantic, which was previously confused with P. lowei. The new species is supported by both morphological and molecular evidence and can be distinguished among its congeners by a combination of characters, including counts of gill rakers, pyloric caeca, and dorsal-fin rays, arrangement of scales spines, and the shape of preopercle. The new species is distributed on the upper continental slope in Brazil, from Bahia to Rio Grande do Sul, and Uruguay, between 160 and 600 meters deep.

The impact of hydrothermal systems on surrounding sedimentary microbial communities is not well understood and previous work has been limited to high temperature vent sites at slow or ultraslow spreading oceanic centres. To build on the current understanding of hydrothermal systems, we explore for the first time the organic geochemistry of the only known back-arc basin hydrothermal system outside the Pacific Ocean: the East Scotia Ridge (ESR), which belongs to the South Georgia and South Sandwich Islands Marine Protected Area. Lipid biomarkers contained in sediments and hydrothermal sulphides along two hydrothermal vent fields north and south of the ESR, respectively, revealed the impact of hydrothermal activity, including both high temperature and low temperature diffusive venting, on sedimentary microbial communities. In the vent field north of the ESR, elevated ring indices of glycerol dialkyl glycerol tetraethers (GDGTs) and proportions of monoalkyl glycerol tetraethers (GMGTs), and a high ratio of total fatty acids (FAs; free plus polar lipids) to putative phytoplankton biomarkers in sediments suggest that high-temperature hydrothermalism has a local impact on surrounding sediments through the input of plume dwelling archaea and bacteria. This impact seems to be restricted to the periphery of the vent source, in agreement with the limited dataset available from slow or ultraslow spreading centres. Likewise, elevated FA to phytoplankton biomarker ratios within a diffusive hydrothermal field south of the ESR suggest an additional input of bacterial biomass relative to background sediments. Our results indicate that low temperature diffusive venting might have a higher impact than previously thought, being locally important in supporting the food chain in deep-sea environments. The distribution of tetraether lipids suggests that a higher proportion of thermophilic archaea thrive in the interior of sulphide chimneys, whereas total FA concentrations and distributions suggest that most bacteria inhabit the exterior chimney layers, where temperature is cooler than the innermost layer in contact with the hydrothermal fluid. Furthermore, differences in total FA concentrations suggest that chimney wall thickness is a control on bacterial abundance through the availability of a higher or lower diversity (and volume) of microhabitats. Our results also indicate that bacteria adapt to increasing temperatures by decreasing their degree of unsaturation. By comparison to GDGT data from other settings, it seems that overall ring indices in hydrothermal deposits are governed by growth temperature, although they might also reflect ecological factors. Our results suggest that hydrothermalism shapes microbial communities within chimneys and surrounding sediments following broadly similar patterns regardless of the type of spreading centre they are located at.

The density of ice krill (Euphausia crystallorophias), a species of key ecological value, and related environmental factors were observed along two transects in the Amundsen Sea Coastal Polynya (ASCP) in Antarctica. The distribution of ice krill was processed using two-frequency acoustic backscatter data identification, and the target strength of ice krill was calculated via stochastic distorted-wave born approximation based on the ice krill sample. The ice krill density ranged from 0.96 to 11.01 g m⁻² for each transect (mean value was 5.77 g m⁻² for the entire survey). These results were of a lower order of magnitude than those of a previous study in the same waters, although the ice krill was still the dominant krill specie in this polynya. We contend that the extent of the phytoplankton bloom might be the factor behind this difference, while other hydrographic parameters such as surface temperature and salinity would have some effect on the spatial distribution of ice krill abundance. Meanwhile, the density and height of ice krill abundance suggested that the diurnal effect on the ice krill was almost negligible. According to the fitted results of regression model, the abundance of ice krill in ASCP in 2022 summer was estimated approximately 175,000 tons.

Estimating subsurface thermohaline structure from concurrent satellite data is a meaningful way to enrich internal oceanic observations. As a powerful tool for data mining, many studies have used machine learning in subsurface reconstruction, but most conventional applications have been purely black-box in nature without further consideration of oceanic characteristics. Instead, proposed here for the first time is a semi-explicit deep network for reconstructing the oceanic interior from surface data. Named EEFFNN, the method embeds empirical orthogonal functions extracted from reanalysis data (the EE part of the name) into the inner framework of a feed-forward neural network (the FFNN part of the name). Comparison with Argo profiles and reanalysis data shows that EEFFNN can significantly outperform conventional machine-learning algorithms in estimating subsurface thermohaline structures and especially subsurface-intensified eddies. Also, EEFFNN can perform thermohaline reconstruction in one pass, making it more lightweight than “shallow” machine-learning algorithms such as random forest. Overall, EEFFNN shows promise for being applied to operational thermohaline reconstruction in the near future.

The evolution of the mixed layer temperature anomalies in the Mozambique Channel is analysed using a mixed layer heat budget covering sub-seasonal to interannual time scales. Sub-seasonal variations in mixed layer temperature are largely dominated by surface heat fluxes, except along the southern coast of Mozambique and Madagascar, where both the advection and the residual terms become significant. The northern Channel is dominated by the mean flow while the southern Channel is modulated by both the mean and eddy terms. Minimum heat gain through advection is observed in the channel during January–February when the Northeast Madagascar current opposes the northwesterly monsoonal winds. During the 1997/98 El Niño/positive Indian Ocean dipole, extreme warming and coral bleaching events were noted in the northern Channel. Such warming was linked with the relaxation of local winds, positive heat gain from the atmosphere and the shedding of large anticyclonic eddies northwest of Madagascar, associated with the arrival of downwelling Rossby waves. By contrast, upwelling Rossby waves and large cyclonic eddies in the Channel occurred during the 1998–2001 protracted La Niña, but only the northern part of the Channel experienced significant negative anomalies in mixed layer temperature. While no coral bleaching hotspots were noted in the northern Channel in summer 1999/2000 due to negative anomalies in advection, marine heatwaves occurred in the southern Channel during that summer. Finally, the protracted 1998–2001 La Niña was the last time that substantial upwelling Rossby wave activity occurred in the tropical South Indian Ocean; recent La Niña events showed muted or weak upwelling Rossby wave activity, including the recent 2020–2022 protracted event. Post-2001 also occurs at the same time as a stronger warming trend in the southwest Indian Ocean region.

Seismic oceanography, characterized by its high horizontal resolution and large imaging coverage, can be used to directly measure the horizontal extension of the thermohaline staircase. This study presents an investigation into the seismic reflection imaging of thermohaline staircases located in the Southeast Caribbean Sea. The findings indicate clear interactions between the staircases and various structures, such as eddies and internal waves. The pre-stack migration method based on common offset gathers is applied to analyze the changes of the thermohaline staircase over different times along line L3. The distributions of dissipation rates within 900 m depth are obtained. The findings indicate the internal wave activity and turbulence in the vicinity of the staircase are locally low. This restraint may support the continuous and enduring presence of the staircase in this region. However, the staircase region away from the eddy has a limited restraining effect on the internal wave, and its intense activity causes intense turbulence, which destroys staircase structure. Our results indicate that the reflection coefficients of the thermohaline staircase and intrusions on the seismic section exhibit opposite polarities. There exists certain intrusion structure within the staircase at the flank of eddy.

Halogenated Organic Compounds (HOCs) are a class of refractory organic compounds produced in large quantities in the ocean, and some compounds can even persist over millions of years. The processes of production, transportation, and burial of HOCs, as well as the transformation and degradation of these compounds by microorganisms, are important parts of the biogeochemical cycling of carbon and halogen in the ocean. Dehalogenation microorganisms and dehalogenation pathways are prevalent in the deep-sea and the subseafloor biosphere, indicating the significance of HOCs metabolism in the ocean and interior of the earth. This paper reviews the current understanding on the generation, distribution, and transport of HOCs, as well as microbial mediated HOC degradation processes in the ocean. The preliminarily model for biogeochemical cycle of marine HOCs is summarized based on the existing knowledge. The research gaps and limitations are identified and future directions are also discussed.