Research

Open AccessArticle

Recent Changes in Composition and Distribution Patterns of Summer Mesozooplankton off the Western Antarctic Peninsula

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Water 2023, 15(10), 1948; https://doi.org/10.3390/w15101948 - 21 May 2023

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The Southern Ocean has undergone significant climate-related changes in recent decades. As a result, pelagic communities inhabiting these waters, particularly mesozooplankton, have adapted to new conditions. The present study considers the patterns of horizontal and vertical (up to 1000 m) distribution, the composition, [...] Read more.

The Southern Ocean has undergone significant climate-related changes in recent decades. As a result, pelagic communities inhabiting these waters, particularly mesozooplankton, have adapted to new conditions. The present study considers the patterns of horizontal and vertical (up to 1000 m) distribution, the composition, abundance, and biomass of mesozooplankton, and the relationships of these parameters to the extreme environmental conditions off the western Antarctic Peninsula throughout the record-warm austral summer season of 2022. Sampling was conducted using the opening/closing Multinet system (0.25 m² aperture) equipped with five 150-μm mesh nets and a WP-2 net. The mesozooplankton was represented by the three most abundant groups: eggs and larvae of euphausiids such as Euphausia superba, small copepods such as Oithona similis, and large calanoid copepods such as Calanoides acutus, Calanus propinquus, Metridia gerlachei, and Rhincalanus gigas. The composition and quantitative distribution of the mesozooplankton significantly varied: the copepods were abundant in the west, off the Antarctic Peninsula, while eggs and larvae of euphausiids were abundant in the east, off the South Orkney Islands. Most mesozooplankton occurred in the upper 200 m layer, and each taxon showed characteristic depth preference: small copepods, euphausiids larvae, and cirripeds cypris larvae were abundant in the epipelagic layer, while large calanoid copepods, euphausiids eggs, amphipods, pelagic polychaetes, and ostracods were found mostly in the mesopelagic layer. The composition and quantitative distribution of mesozooplankton had clear relationships with environmental factors, particularly with a combination of variables such as water salinity, temperature, and chlorophyll a concentration. Full article

(This article belongs to the Special Issue Physical and Biological Properties of Waters in the Region of the Antarctic Peninsula and Adjacent Basins of the South Atlantic)

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Open AccessArticle

Distribution and Phylogenetic Position of the Antarctic Ribbon Worm Heteronemertes longifissa (Nemertea, Pilidiophora)

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Alexei V. Chernyshev

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Neonila E. Polyakova

Water 2023, 15(4), 809; https://doi.org/10.3390/w15040809 - 19 Feb 2023

Viewed by 870

Abstract

To date, a total of 23 valid species of heteronemerteans belonging to 15 genera have been recorded in Antarctic and Subantarctic waters. The ribbon worm Heteronemertes longifissa (Hubrecht, 1887) is the only heteronemertean species reported to have bipolar distribution, but this statement is [...] Read more.

To date, a total of 23 valid species of heteronemerteans belonging to 15 genera have been recorded in Antarctic and Subantarctic waters. The ribbon worm Heteronemertes longifissa (Hubrecht, 1887) is the only heteronemertean species reported to have bipolar distribution, but this statement is doubtful. The phylogenetic relationships of H. longifissa to other heteronemerteans remain uncertain. A genetic analysis of specimens from Antarctica has shown that the name H. longifissa refers to two sibling species with an uncorrected p-distance of 5.3% in COI. These species differ in body color: one is whitish, and the other is grayish-pink. The species with the whitish body has been reliably identified from off the Norway coast (as Cerebratulus sp. NemBar1383 (BOLD: ACM5920)), i.e., it has a bipolar distribution. A molecular phylogenetic analysis of Lineidae based on five gene markers (COI, 16S, 18S, 28S, and histone H3) has shown the genus Heteronemertes to belong to Lineage D of Clade 2 sensu Kajihara et al., 2022 (crown Lineidae). The phylogenetic positions of four more species of unidentified lineids are currently under discussion. Full article

(This article belongs to the Special Issue Physical and Biological Properties of Waters in the Region of the Antarctic Peninsula and Adjacent Basins of the South Atlantic)

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Open AccessArticle

Current Assessment of Water Quality and Biota Characteristics of the Pelagic Ecosystem of the Atlantic Sector of Antarctica: The Multidisciplinary Studies by the Institute of Biology of the Southern Seas

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Olga Chuzhikova-Proskurnina

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Water 2022, 14(24), 4103; https://doi.org/10.3390/w14244103 - 16 Dec 2022

Viewed by 971

Abstract

Comprehensive studies of the ecosystem of the Atlantic sector of the Antarctic were carried out in the period between 2020 and 2022, during the 79th and 87th sea expeditions on the R/V “Akademik Mstislav Keldysh”. Concentrations of soluble forms of 15 trace elements, [...] Read more.

Comprehensive studies of the ecosystem of the Atlantic sector of the Antarctic were carried out in the period between 2020 and 2022, during the 79th and 87th sea expeditions on the R/V “Akademik Mstislav Keldysh”. Concentrations of soluble forms of 15 trace elements, except Mo, in surface waters of the Southern Ocean were matched the lower limit of their background concentrations in oceanic waters. A high spatial variability of chlorophyll a—an indicator of phytoplankton biomass, which is the main food object of the Antarctic krill—was revealed. In the Bransfield Strait, the abundance of bacterioplankton exhibited a weak relationship with water temperature and a pronounced dependence on chlorophyll fluorescence. It was determined, by using the bioluminescence method, that the largest concentrations of larvae and juveniles of krill were noted in the Bransfield Strait, on the shelf of the Antarctic Peninsula. Against the background of a decline in krill abundance in recent years, there has been an intensive development of Salpa thompsoni, the main food competitor of krill. New data on the distribution of mesoparasitic copepods on endemic fish of the Southern Ocean were also obtained, and their pathogenic effect on the body of fish hosts has been revealed. Full article

(This article belongs to the Special Issue Physical and Biological Properties of Waters in the Region of the Antarctic Peninsula and Adjacent Basins of the South Atlantic)

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Open AccessArticle

Physical and Biological Features of the Waters in the Outer Patagonian Shelf and the Malvinas Current

Water 2022, 14(23), 3879; https://doi.org/10.3390/w14233879 - 28 Nov 2022

Cited by 1 | Viewed by 1514

Abstract

The aim of this study is to trace how the fine-thermohaline and kinematic structure, formed over a section along 45.8° S in the interaction zone of the outer Patagonian Shelf (PS) and Malvinas (Falkland) Current (MC) System waters, affect the spatial distribution of [...] Read more.

The aim of this study is to trace how the fine-thermohaline and kinematic structure, formed over a section along 45.8° S in the interaction zone of the outer Patagonian Shelf (PS) and Malvinas (Falkland) Current (MC) System waters, affect the spatial distribution of bio-optical characteristics, phyto/zooplankton, birds, and marine mammals. For the first time, simultaneous multidisciplinary observations at high spatial resolution (~2.5 km) were performed in this region during the cruise of the R/V “Akademic Mstislav Keldysh” in February 2022. A fine structure of alternating upwelling and downwelling zones over the PS and slope was identified, which resulted from the interaction between the MC inshore branch (MCi), bottom topography, and wind. This interaction significantly affects all the physical, and optical characteristics analyzed in the work, as well as the biota of the region. It was found that the euphotic zone is larger in the downwelling zones than in the upwelling zones, and all spatially local maxima of phytoplankton photosynthetic efficiency are observed in the zones between upwelling and downwelling. Phytoplankton along the section were represented by 43 species. A total of 30 zooplankton species/taxa were identified. Three species of marine mammals and 11 species of birds were recorded in the study site. Most of the phytoplankton species list were formed by dinoflagellates, and picoplankton Prasinoderma colonial quantitatively dominated everywhere. Two floristic and three assemblage groups were distinguished among the analyzed phytoplankton communities. High phytoplankton biodiversity was observed above the PS and low above the PS edge and in the MCi core. Copepods mostly dominated in zooplankton. Subantarctic species/taxa of zooplankton concentrated in the nearshore waters of the PS, while Antarctic species/taxa were most abundant in the zone between the MCi and the MC offshore branch (MCo). The relative abundance of birds in the PS was several times higher than in the MCo. The minimum abundance of birds was in the MCi in the zone of the strongest upwelling identified above the PS edge. Full article

(This article belongs to the Special Issue Physical and Biological Properties of Waters in the Region of the Antarctic Peninsula and Adjacent Basins of the South Atlantic)

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Open AccessArticle

Distribution and Demography of Antarctic Krill and Salps in the Atlantic Sector of the Southern Ocean during Austral Summer 2021–2022

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Dmitrii G. Bitiutskii

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Ernest Z. Samyshev

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Natalia I. Minkina

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Victor V. Melnikov

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Elena S. Chudinovskih

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Sergei I. Usachev

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Pavel A. Salyuk

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Alexander N. Serebrennikov

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Oleg A. Zuev

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Alexei M. Orlov

Water 2022, 14(23), 3812; https://doi.org/10.3390/w14233812 - 23 Nov 2022

Cited by 3 | Viewed by 1449

Abstract

The study aimed to investigate krill (Euphausia superba) and salp (Salpa thompsoni) populations in the Atlantic sector of the Southern Ocean in January and February 2022. Samples were obtained to measure the abundance, biomass and distribution patterns of krill [...] Read more.

The study aimed to investigate krill (Euphausia superba) and salp (Salpa thompsoni) populations in the Atlantic sector of the Southern Ocean in January and February 2022. Samples were obtained to measure the abundance, biomass and distribution patterns of krill and salp. Sex differences and feeding habits of the Antarctic krill were determined. The dependence of the physiological state of the studied aquatic organisms on changes in environmental parameters was analyzed. Current data on the association of the dynamics of hydrometeorological parameters and processes with the distribution of chlorophyll a, krill, and salp were obtained. It was established that, at numerous stations, the biomass of salps prevailed over krill. The result indicates the replacement of the Antarctic krill populations by gelatinous zooplankton. The obtained results allow assessment of the biological resource potential in the studied region based on the analysis of the samples collected. Full article

(This article belongs to the Special Issue Physical and Biological Properties of Waters in the Region of the Antarctic Peninsula and Adjacent Basins of the South Atlantic)

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Open AccessArticle

Antarctic Bottom Water Jets Flowing from the Vema Channel

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Water 2022, 14(21), 3438; https://doi.org/10.3390/w14213438 - 28 Oct 2022

Viewed by 786

Abstract

Properties of the abyssal current of Antarctic Bottom Water (AABW) from the Vema Channel are studied based on temperature, salinity, and velocity profiler (CTD/LADCP) data. Previous studies over a period of almost 30 years revealed that very intense current of AABW exists in [...] Read more.

Properties of the abyssal current of Antarctic Bottom Water (AABW) from the Vema Channel are studied based on temperature, salinity, and velocity profiler (CTD/LADCP) data. Previous studies over a period of almost 30 years revealed that very intense current of AABW exists in the Vema Channel. Later, it was found that this current consists of two branches. One branch spreads over the bottom of the channel; the other branch is elevated over the western wall of the channel. The deepest branch decays after it passes approximately 100 km while the upper one continues further to the North Atlantic and is the source of abyssal waters in the Canary and Cabo Verde basins of the North Atlantic. Data analysis suggested that the upper jet splits into two. One of these descends down a canyon at 24°30′ S, while the other (the third one) remains on the continental slope, and indications of its existence are also found at 24°00′ S. This research analyzes the existence and pathway of this third branch that can be traced up to latitude 24° S. Velocity measurements in 2022 allowed us to confirm the existence of this third branch. Full article

(This article belongs to the Special Issue Physical and Biological Properties of Waters in the Region of the Antarctic Peninsula and Adjacent Basins of the South Atlantic)

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Open AccessFeature PaperArticle

Influence of Hydrological Factors on the Distribution of Methane Fields in the Water Column of the Bransfield Strait: Cruise 87 of the R/V “Academik Mstislav Keldysh”, 7 December 2021–5 April 2022

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Andrei Kholmogorov

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Nadezhda Syrbu

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Renat Shakirov

Water 2022, 14(20), 3311; https://doi.org/10.3390/w14203311 - 20 Oct 2022

Cited by 1 | Viewed by 912

Abstract

Within the framework of the expedition research “Complex studies of the Antarctic marine ecosystem in the areas of the transport and interaction of water masses in the Atlantic sector of Antarctica, the Scotia Sea and the Drake Strait” (cruise 87 of the R/V [...] Read more.

Within the framework of the expedition research “Complex studies of the Antarctic marine ecosystem in the areas of the transport and interaction of water masses in the Atlantic sector of Antarctica, the Scotia Sea and the Drake Strait” (cruise 87 of the R/V “Academik Mstislav Keldysh”, 7 December 2021–5 April 2022), the distribution of gas-geochemical fields of methane in the Bransfield Strait was studied in detail for the first time. The connection of the methane distribution in water with the complex hydrological regime of the strait has been revealed. Elevated values of methane concentrations brought to the Bransfield Strait in the warm current flow from the Bellingshausen Sea have been established. Low concentrations of methane also mark the cold waters of the Weddell Sea, which carry out the transit of water masses into the Atlantic Ocean. The research was carried out within the framework of the theme FWMM-2022-033 “Integrated environmental studies of the Southern Ocean” AAAA17-117030110035-4 and international obligations of the Russian Federation as a party to the Antarctic Treaty and the Convention on the Conservation of Antarctic Marine Living Resources. Full article

(This article belongs to the Special Issue Physical and Biological Properties of Waters in the Region of the Antarctic Peninsula and Adjacent Basins of the South Atlantic)

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Open AccessArticle

Age Structure and Spatial Distribution of Euphausia superba Larvae off the Antarctic Peninsula, Southern Ocean

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Valentina V. Kasyan

Water 2022, 14(20), 3196; https://doi.org/10.3390/w14203196 - 11 Oct 2022

Cited by 1 | Viewed by 939

Abstract

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 [...] Read more.

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

(This article belongs to the Special Issue Physical and Biological Properties of Waters in the Region of the Antarctic Peninsula and Adjacent Basins of the South Atlantic)

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Open AccessFeature PaperArticle

Water Exchange between Deep Basins of the Bransfield Strait

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Alexander A. Latushkin

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Olga S. Mekhova

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Rinat Z. Mukhametianov

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Svetlana A. Murzina

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Sofia A. Ostroumova

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Vladimir I. Ponomarev

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Water 2022, 14(20), 3193; https://doi.org/10.3390/w14203193 - 11 Oct 2022

Cited by 3 | Viewed by 931

Abstract

The Bransfield Strait is a relatively deep and narrow channel between the South Shetland Islands and the Antarctic Peninsula contributing to the water transport between the Pacific and Atlantic sectors of the Southern Ocean. The strait can be divided into three deep separate [...] Read more.

The Bransfield Strait is a relatively deep and narrow channel between the South Shetland Islands and the Antarctic Peninsula contributing to the water transport between the Pacific and Atlantic sectors of the Southern Ocean. The strait can be divided into three deep separate basins, namely, the western, central, and eastern basins. The sources of deep waters in the three basins are different, leading to differences in thermohaline properties and water density between the basins. The difference in water density should in turn cause intense deep currents from one basin to another through narrow passages over the sills separating the basins. However, there are still no works dedicated to such possible overflows in the Bransfield Strait. In this study, we report our new CTD and LADCP measurements performed in 2022 over the watersheds between the basins. Quasisimultaneous observations of the main circulation patterns carried out at several sections allowed us to analyze the evolution of thermohaline and kinematic structures along the Bransfield Strait. Volume transports of waters in the strait were estimated on the basis of direct velocity observations. These new data also indicate the existence of intense and variable deep current between the central and eastern basins of the strait. The analysis of historical data shows that the mean flow is directed from the central to the eastern basin. In addition, LADCP data suggest the intensification of the flow in the narrow part of the sill between the basins, and the possible mixing of deep waters at this location. Full article

(This article belongs to the Special Issue Physical and Biological Properties of Waters in the Region of the Antarctic Peninsula and Adjacent Basins of the South Atlantic)

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Open AccessFeature PaperArticle

Hydraulically Controlled Bottom Flow in the Orkney Passage

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Rinat Z. Mukhametianov

Water 2022, 14(19), 3088; https://doi.org/10.3390/w14193088 - 01 Oct 2022

Cited by 1 | Viewed by 949

Abstract

Supercritical hydraulically controlled overflow of Antarctic Bottom Water from the Weddell Sea has been observed in the Orkney Passage during field measurements in February 2022. The Orkney Passage is the main pathway for the densest layer of Antarctic Bottom Water flow from the [...] Read more.

Supercritical hydraulically controlled overflow of Antarctic Bottom Water from the Weddell Sea has been observed in the Orkney Passage during field measurements in February 2022. The Orkney Passage is the main pathway for the densest layer of Antarctic Bottom Water flow from the Weddell Sea to the Scotia Sea. The bottom current overflows the sill across the passage and flows down from the crest of the sill at 3600 m deeper than 4000 m. The descending flow accelerates because of the difference in the height of the sill and its foot. An estimate of the Froude number of this flow was greater than unity. Near the foot of the slope the kinetic energy of the flow becomes insufficient to continue moving in this regime. The flow slows down, and strong mixing and warming of the bottom water occurs due to the exchange with the surrounding waters. This hydrodynamic phenomenon is called supercritical hydraulically controlled flow. However, the flow of bottom water continues further and eventually fills the abyssal depths of the Atlantic. Full article

(This article belongs to the Special Issue Physical and Biological Properties of Waters in the Region of the Antarctic Peninsula and Adjacent Basins of the South Atlantic)

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Open AccessFeature PaperArticle

Multidisciplinary Observations across an Eddy Dipole in the Interaction Zone between Subtropical and Subantarctic Waters in the Southwest Atlantic

Water 2022, 14(17), 2701; https://doi.org/10.3390/w14172701 - 30 Aug 2022

Cited by 3 | Viewed by 1278

Abstract

Seawater properties in two intense rings in the South Atlantic are considered. One ring separated from the Brazil Current and the other from the Malvinas Current. The analysis is based on the CTD casts and SADCP measurements from the onboard velocity profiler. The [...] Read more.

Seawater properties in two intense rings in the South Atlantic are considered. One ring separated from the Brazil Current and the other from the Malvinas Current. The analysis is based on the CTD casts and SADCP measurements from the onboard velocity profiler. The optical properties, chemical parameters, methane concentration, and biological properties such as primary production, plankton, and fish were also analyzed. Analysis of strong differences between the eddies is supplemented by observations of whales and birds in the region. Full article

(This article belongs to the Special Issue Physical and Biological Properties of Waters in the Region of the Antarctic Peninsula and Adjacent Basins of the South Atlantic)

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Open AccessFeature PaperArticle

Cryptophyte and Photosynthetic Picoeukaryote Abundances in the Bransfield Strait during Austral Summer

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Water 2022, 14(2), 185; https://doi.org/10.3390/w14020185 - 10 Jan 2022

Cited by 1 | Viewed by 1209

Abstract

A remarkable shift in the species composition and size distribution of the phytoplankton community have been observed in coastal waters along the Antarctic Peninsula over the last three decades. Smaller photoautotrophs such as cryptophytes are becoming more abundant and important for the regional [...] Read more.

A remarkable shift in the species composition and size distribution of the phytoplankton community have been observed in coastal waters along the Antarctic Peninsula over the last three decades. Smaller photoautotrophs such as cryptophytes are becoming more abundant and important for the regional ecosystems. In this study, flow cytometry was used to quantify the smallest phytoplankton in the central Bransfield Strait and explore their distribution across the strait in relation to physical and chemical properties of the two major water masses: the warmer and less saline Transitional Zonal Water with Bellingshausen Sea influence (TBW), and the cold and salty Transitional Zonal Water with Weddell Sea influence (TWW). Pico- and nano-phytoplankton clusters were distinguished and enumerated in the cytograms: photosynthetic picoeukaryotes, cryptophytes (about 9 µm in size), and smaller (3 µm) nanophytoplankton. It was shown that nanophytoplankton developed higher abundances and biomasses in the warmer and less saline TBW. This biotope was characterized by a more diverse community with a pronounced dominance of Cryptophyta in terms of biomass. The results support the hypothesis that increasing melt-water input can potentially support spatial and temporal extent of cryptophytes. The replacement of large diatoms with small cryptophytes leads to a significant shift in trophic processes in favor of the consumers such as salps, which able to graze on smaller prey. Full article

(This article belongs to the Special Issue Physical and Biological Properties of Waters in the Region of the Antarctic Peninsula and Adjacent Basins of the South Atlantic)

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