Search Results (6)

A supplemental description of Lamproglena barbicola Fryer, 1961 is provided based on specimens collected from the gills of Labeobarbus altianalis (Boulenger, 1900) from the Nyando River, Lake Victoria Basin, Kenya, using an integrated approach of scanning electron microscopy (SEM) and molecular analysis (18S, 28S rDNA, and cox1 gene regions). Morphologically, the specimens conform to L. barbicola and closely resemble Lamproglena hoi Dippenaar, Luus-Powell & Roux, 2001; however, SEM revealed a previously undescribed feature on the uniramous antennule in L. barbicola, namely indistinctly three-segmented, tapering from a broad base to the apex, basal segment much longer than distal, comprising 14 setae of varying sizes, ventral laterally, absence of distinctive anterior fringe of setae on the antennule, as well as several characters that differentiate L. barbicola from L. hoi, including 5 setae at the basal endopod of leg one, five cuticular protuberances in the oral region, 19 setae on the basal antennular segment, and 10 setae on the distal segment, with 1 seta on each ramus. The phylogenetic analysis confirms L. barbicola as a sister taxon of L. hoi, supporting their close relationship. The genetic divergence presented as the uncorrected genetic p-distances between L. barbicola and L. hoi are 23.1% and 0.45% for cox1 and 28S rDNA regions, respectively, with observed nucleotide differences of 145 and 3 bp between the sequences, respectively. There was no interspecific variability detected in the 18S rDNA sequences. This study provides novel molecular sequences and the first high-resolution SEM images, which reveal additional taxonomic features for L. barbicola, establishing a robust reference for future identification. Full article

Powell Basin is an ocean basin formed as a result of the Scotia Sea evolution. The existing tectonic models propose a variety of starting and ending ages for the spreading of the basin based on seafloor magnetic anomalies. Here, we use recent magnetic field data obtained from eight magnetic profiles in Powell Basin to provide insights into the oceanic spreading evolution. The differences found between the number of anomalies on both sides of the axis and the asymmetry in the spreading rates suggest different opening models for different parts of the basin. We propose a spreading model starting in the late Eocene (38.08 Ma) and ending in the early Miocene (21.8 Ma) for the northern part of Powell Basin. For the southern part, the opening started in the late Eocene (38.08 Ma) and ended in the middle Paleogene (25.2 Ma). The magnetic data have been combined with gravity and sediment thickness data to better constrain the age models. The gravity and sediment thickness information allow us to more accurately locate the position of the extinct spreading axis. Geothermal heat flow measurements are used to understand the relationship between the low amplitudes of the magnetic anomalies and the heat beneath them. Our proposed oceanic spreading models suggest that the initial incursions of the Pacific mantle outflow into the Powell Basin occurred in the Oligocene, and the initial incursions of oceanic currents from the Weddell Sea occurred in the Eocene. Full article

The carbon dioxide concentration in the atmosphere has progressively risen since pre-industrial times. About one-third of the anthropogenically generated CO₂ is absorbed by the waters of the World Ocean, whereas the waters of the Southern Ocean take up about 40% of this CO₂. The concentrations of oxygen and carbon dioxide dissolved in seawater are sensitive to climate changes, transferring anthropogenic pressures with consequences for the biogeochemical cycles in the World Ocean. The Southern Ocean is a key region for the exchange of oxygen and carbon between the surface water and the atmosphere and for their transfer with cold water masses to the deep layers of the Ocean. In this paper, we discuss the dynamics of the carbon dioxide partial pressure (pCO₂) and dissolved oxygen (O₂) in the surface waters of the Atlantic Southern Ocean based on data collected during the 87th cruise of the R/V “Academik Mstislav Keldysh”. The study area includes the Bransfield Strait, Antarctic Sound, the Powell Basin, the Weddell, and Scotia Seas. We have analyzed the spatial distribution of pCO₂ and oxygen for the areas of transformation of water masses and changes in biogeochemical processes. In the zone of Scotia and Weddell Seas, we have observed an increase in pCO₂ and a decrease in oxygen concentrations at the transect from the Weddell Sea at 56° W to the Powell Basin. From the Antarctic Sound to the Bransfield Strait, a decrease in oxygen saturation and an increase in pCO₂ has been traced. The surface waters of the Bransfield Strait have revealed the greatest variability of hydrochemical characteristics due to a complex structure of currents and intrusions of different water masses. In general, this area has been characterized by the maximum pCO₂, while the surface waters are undersaturated with oxygen. The variability of the AOU/ΔpCO₂ (w-a) ratio has revealed a pCO₂ oversaturation and an O₂ undersaturation in the waters of the Bransfield Strait. It is evidence of active organic carbon decomposition as the major controlling process. Yet, photosynthesis is the major biogeochemical process in the studied areas of the Weddell and Scotia seas, and their waters have been undersaturated with pCO₂ and oversaturated with O₂. As it comes from the analysis of the distribution and correlation coefficients of AOU and the sea-air gradient of pCO₂ with other physical and biogeochemical properties, the predominance of the biotic processes to the dynamics of O₂ and pCO₂ in the surface water layer has been demonstrated for the studied areas. Yet, there is evidence of additional sources of CO₂ not associated with the production and destruction processes of organic matter. Full article

In recent decades, the waters off the Antarctic Peninsula and surrounding region have undergone a significant transformation due to global climate change affecting the structure and distribution of pelagic fauna. Here, we present the results of our study on the taxonomic composition and quantitative distribution of plankton communities in Bransfield Strait, Antarctic Sound, the Powell Basin of the Weddell Sea, and the waters off the Antarctic Peninsula and South Orkney Islands during the austral summer of 2022. A slight warming of the Transitional Zonal Water with Weddell Sea influence (TWW) and an increase in its distribution area was detected. Among the pelagic communities, three groups were found to be the most abundant: copepods Calanoides acutus, Metridia gerlachei, and Oithona spp., salpa Salpa thompsoni, and Antarctic krill Euphausia superba. Euphausiids were found in cases of low abundance, species diversity, and biomass. In the studied region, an increase in the amount of the salpa S. thompsoni and the euphausiid Thysanoessa macrura and the expansion of their distribution area were observed. Significant structural shifts in phytoplankton communities manifested themselves in changes in the structure of the Antarctic krill forage base. The composition and distribution of pelagic fauna is affected by a combination of environmental abiotic factors, of which water temperature is the main one. The obtained results have allowed us to assume that a further increase in ocean temperature may lead to a reduction in the number and size of the Antarctic krill population and its successive replacement by salps and other euphausiids that are more resistant to temperature fluctuations and water desalination. Full article

The Antarctic krill, Euphausia superba Dana, 1850, is a species forming high biomass and, therefore, playing a major role in the Antarctic marine food web. The age structure and patterns of spatial distribution of E. superba larvae in the waters of the Bransfield Strait (Antarctic Sound, Powell Basin), and off the South Orkney Islands, were studied based on data collected through a research survey in January and February 2022. Eggs and larvae (naupliar, calyptopis, and furcilia stages) of E. superba were found in these regions. Eggs and nauplii were concentrated in the southern, deep-sea part of the Antarctic Sound and over the northeastern and southwestern slopes of the Powell Basin, while calyptopis and furcilia larvae were concentrated north of the South Orkney Islands. The larvae abundance increased in an easterly direction. Four groups of communities comprising krill larvae at different development stages were identified. These groups were located in two subregions with the border between them running off the South Orkney Islands. The distribution and abundance of E. superba larvae showed a clear relationship with environmental conditions, in particular with a combination of such factors as sea surface temperature and chlorophyll a concentration. Full article

The thermal state of the lithosphere and related geothermal heat flow (GHF) is a crucial parameter to understand a variety of processes related to cryospheric, geospheric, and/or biospheric interactions. Indirect estimates of GHF in polar regions from magnetic, seismological, or petrological data often show large discrepancies when compared to thermal in situ observations. Here, the lack of in situ data represents a fundamental limitation for both investigating thermal processes of the lithosphere and validating indirect heat flow estimates. During RV Polarstern expeditions PS86 and PS118, we obtained in situ thermal measurements and present the derived GHF in key regions, such as the Antarctic Peninsula and the Gakkel Ridge in the Arctic. By comparison with indirect models, our results indicate (1) elevated geothermal heat flow (75 ± 5 mW m⁻² to 139 ± 26 mW m⁻²) to the west of the Antarctic Peninsula, which should be considered for future investigations of ice-sheet dynamics and the visco-elastic behavior of the crust. (2) The thermal signature of the Powell Basin characteristic for oceanic crust of an age between 32 and 18 Ma. Further, we propose (3) that at different heat sources at the slow-spreading Gakkel Ridge in the Aurora Vent Field region might explain the geothermal heat flow distribution. We conclude that in situ observations are urgently required to ground-truth and fine-tune existing models and that a multidisciplinary approach is of high importance for the scientific community’s understanding of this parameter. Full article