Weddell Sea Area Research Articles

Biologging of emperor penguins-Attachment techniques and associated deployment performance.

An increasing number of marine animals are equipped with biologgers, to study their physiology, behaviour and ecology, often for conservation purposes. To minimise the impacts of biologgers on the animals’ welfare, the Refinement principle from the Three Rs framework (Replacement, Reduction, Refinement) urges to continuously test and evaluate new and updated biologging protocols. Here, we propose alternative and promising techniques for emperor penguin (Aptenodytes forsteri) capture and on-site logger deployment that aim to mitigate the potential negative impacts of logger deployment on these birds. We equipped adult emperor penguins for short-term (GPS, Time-Depth Recorder (TDR)) and long-term (i.e. planned for one year) deployments (ARGOS platforms, TDR), as well as juvenile emperor penguins for long-term deployments (ARGOS platforms) in the Weddell Sea area where they had not yet been studied. We describe and qualitatively evaluate our protocols for the attachment of biologgers on-site at the colony, the capture of the animals and the recovery of the devices after deployment. We report unprecedented recaptures of long-term equipped adult emperor penguins (50% of equipped individuals recaptured after 290 days). Our data demonstrate that the traditional technique of long-term attachment by gluing the biologgers directly to the back feathers causes excessive feather breakage and the loss of the devices after a few months. We therefore propose an alternative method of attachment for back-mounted devices. This technique led to successful year-round deployments on 37.5% of the equipped juveniles. Finally, we also disclose the first deployments of leg-bracelet mounted TDRs on emperor penguins. Our findings highlight the importance of monitoring potential impacts of biologger deployments on the animals and the need to continue to improve methods to minimize disturbance and enhance performance and results.

Metals and metalloids in Antarctic krill and water in deep Weddell Sea areas

The study on the concentration of trace elements in Antarctic krill and in water in the deep areas of the Atlantic sector of the Antarctic was performed. Concentrations of 22 trace elements were studied to determine their spatial distribution in krill, and to assess the accumulation ability of the krill against 8 of them. The trace elements concentration in krill diminished in the following order: Fe > Cu > Zn > Bа > B > Se > As > Cr > Ni > Ag > Li > Mn > V > Mo > Cd > Co > Hg > Be. Concentrations of Pb, Ti, Tl, Sb were below their detection limits. Concentration factors of trace elements by krill varied from n × 102 to n × 104. The Cu and As concentrations in dry krill exceeded their MPC. Concentrations of all trace elements in wet mass of krill were not exceeded established regulative values.

Field studies of bioluminescence in the Antarctic sector of the Atlantic Ocean in 2002 and 2020.

In this work, IBSS materials on seawater bioluminescence intensity changes in the Atlantic sector of the Antarctic Ocean (the Weddell Sea area) with an interval of almost 20 years are presented. Data were obtained using a single instrument, the hydrobiophysical system Salpa-M, in the area of 50-63°S, 62-49°W in March 2002 (183 soundings at 45 stations during cruise 7 on RV Gorizont) and in February 2020 (122 soundings at 18 stations during cruise 79 on RV Academic Mstislav Keldysh). The bioluminescence studies were coupled with the simultaneous measurement of temperature, electrical conductivity, and photosynthetically active radiation, and they were compared with the data from processing plankton samples. Over the past 20 years, as a consequence of the appearance of a large number of gelatinous organisms and the resulting changes in the structure of the plankton community, the bioluminescence of Antarctic waters in the euphotic layer of this region has decreased almost two-fold, currently being in the range 8.4 × 10-12 to 104.42 × 10-12 W·cm-2 ·L-1 .

Spatial and Temporal Variations of Polar Ionospheric Total Electron Content over Nearly Thirteen Years.

It is of great significance for the global navigation satellite system (GNSS) service to detect the polar ionospheric total electron content (TEC) and its variations, particularly under disturbed ionosphere conditions, including different phases of solar activity, the polar day and night alternation, the Weddell Sea anomaly (WSA) as well as geomagnetic storms. In this paper, four different models are utilized to map the ionospheric TEC over the Arctic and Antarctic for about one solar cycle: the polynomial (POLY) model, the generalized trigonometric series function (GTSF) model, the spherical harmonic (SH) model, and the spherical cap harmonic (SCH) model. Compared to other models, the SCH model has the best performance with ±0.8 TECU of residual mean value and 1.5–3.5 TECU of root mean square error. The spatiotemporal distributions and variations of the polar ionospheric TEC are investigated and compared under different ionosphere conditions in the Arctic and Antarctic. The results show that the solar activity significantly affects the TEC variations. During polar days, the ionospheric TEC is more active than it is during polar nights. In polar days over the Antarctic, the maximum value of TEC always appears at night in the Antarctic Peninsula and Weddell Sea area affected by the WSA. In the same year, the ionospheric TEC of the Antarctic has a larger amplitude of annual variation than that of the TEC in the Arctic. In addition, the evolution of the ionization patch during a geomagnetic storm over the Antarctic can be clearly tracked employing the SCH model, which appears to be adequate for mapping the polar TEC, and provides a sound basis for further automatic identification of ionization patches.

Состав популяции и транспорт молоди антарктического криля в районе бассейна Пауэлла (северо-западная часть моря Уэдделла) в январе 2020 г.

This paper presents the data on distribution and size composition of the Antarctic krill (Euphausia superba) population in the northwestern Weddell Sea (Powell Basin) and adjacent areas in summer 2020. Juvenile krill dominated in the western Powell basin and the eastern Bransfield Strait as a result of transport with the advected Weddell Sea water and drifting sea ice. Using a distribution mixture analysis made possible to identify up to 9–10 size groups of krill. Groups 1–4 corresponds to juveniles (average size about 22, 25, 27–28 and 32 mm respectively). They may reflect the transport of different “waves” of recruitment of the Atlantic sector krill population with the waters of the western branch of Weddell Gyre as well as the presence of juvenile krill of local origin. Groups 5–7 are intermediate in size (average length within 38–43 mm) and include mostly immature specimens. Larger groups 8–10 comprise of mostly mature females and mature and immature males. The maximum average size of the largest group reaches about 53 mm. the Wedell Front zone in the north of Powell Basin plays an in important role for retention and growth of krill, originating from different sources: western Weddell Sea, Bransfield Strait and the zone of the southern branch of Antarctic Circumpolar Current.

A new species of Austrorhynchus (Platyhelminthes: Kalyptorhynchia) from King George Island (Maritime Antarctic)

ABSTRACTA new species of the turbellarian genus Austrorhynchus (Kalyptorhynchia: Polycystididae) was found in King George Island (South Shetland Islands, Maritime Antarctic). The new species has eyes and white to greyish parenchyma. The type II prostate stylet has a funnel and a slightly bent tube with an inner stylet extending throughout its length; a strongly bent hook of about the same size as the tube is present. The type III prostate stylet has a foot and a style connected by a bridge, defining a broad window; the style expands to a comb-bearing plate with large teeth; the foot continues into a narrow flagellum with a distal expansion and a row of fine teeth. The species is oviparous. It can be distinguished from the other known Austrorhynchus species by the shape and size of the type II and type III prostate stylets. Out of the five known species of Austrorhynchus presenting a window in the type III stylet, the four more similar ones are found in the northern arm of the Scotia Arc and the Weddell Sea area. This is the first report of Kalyptorhynchia from the Antarctic portion of the Scotia Sea, and it confirms previous observations that the true number of Austrorhynchus species in the area must be higher than what is currently known.http://www.zoobank.org/urn:lsid:zoobank.org:pub:098ADF23-763B-41F6-A2F5-54F6AA8620E8

Chemical and biological screening of deep-water sponges from Antarctic regions

The majority of marine natural products (MNPs) originate from tropical and temperate shallow water invertebrates, such as sponges [1]. Recent studies indicate the presence of great genetic diversity in deep-waters that may be linked to unprecedented chemistry due to evolution/adaptation to extremely harsh environmental conditions. However, only less than 2% of MNPs derive from the deep-sea organisms [2]. Antarctic ecosystems are rich in biodiversity [3] and exposed to unique environmental characteristics resulting in communities structured both by biotic interactions (e.g. predation, competition) and abiotic factors (e.g. seasonality, ice-scouring) [4], suggesting a high chemical diversity. In this work, we investigated 39 deep-water sponges collected from the Antarctic Weddell Sea and adjacent areas (depths -100 – 600 m). The freeze-dried sponge samples were extracted with water, followed by MeOH and CH2Cl2 separately. The combined organic extracts were tested for activity against cancer cells [HepG2 (liver) and HT29 (bowel) cancer cell lines], bacteria [ESKAPE panel: Enterococcus faecalis, Staphylococcus aureus (MRSA), Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Escherichia coli) and fungi (yeasts Candida albicans, Cryptococcus neoformans). Several Latrunculia sponge extracts displayed high anticancer activity against both cell lines (IC50 values 0.50 – 3.16 µg/ml). The organic extract of the glass sponge Rossella cf. antarctica showed moderate antibiotic activity towards MRSA and E. faecalis with IC50 values of 96 and 213 µg/ml, respectively. All extracts have undergone chemical profiling/dereplication studies by HPLC-DAD-MS and 1H NMR spectroscopy. The results of chemical and biological screening will assist in selection and activity-guided isolation of Antarctic deep-water sponge metabolites.

Sea ice concentration variability over the Southern Ocean and its impact on precipitation in southeastern South America

ABSTRACTThis article quantifies the relationship between sea ice cover (SIC) on the Southern Ocean and precipitation and river discharges over southeastern and eastern South America. The period of analysis covers from 1981 to 2008 and includes monthly mean data of SIC over the Ross, Amundsen–Bellingshausen and Weddell Seas, as well as atmospheric variables and discharges of selected rivers in eastern South America. To isolate the effect of known modes of climate variability on SIC, the signals of El Niño‐Southern Oscillation and the Southern Annual Mode are removed from all time series through regression analysis. Composites of precipitation differences over South America reveal a pattern of enhanced rainfall activity over the South Atlantic Convergence Zone (SACZ) in summer (JFM) when SIC is above average particularly over the Weddell Sea area, while winter (ASO) SIC anomalies show negative and significant correlations with rainfall over much of South America. Moisture fluxes patterns in summer reveal increased moisture transport towards the SACZ region and decreased low‐level jet activity (and precipitation) over northern Argentina. In particular a large dry bias over southeastern South America associated to positive SIC anomalies on the Weddell Sea in September is shown to impact the discharges of the Uruguay and Iguazú Rivers, with the largest effects found two months after the SIC anomaly (November). Although less robust, a relationship with the Paraná River is also found. These results suggest that increased SIC over the Weddell Sea during September can help to forecast drier conditions particularly on the Uruguay basin and somewhat wetter conditions in the SACZ region within the following season.

Responses of Antarctic pack-ice seals to environmental change and increasing krill fishing

The compound effects of changing habitats, ecosystem interactions, and fishing practices have implications for the management of Antarctic krill and conservation of its predators. For Antarctic pack-ice seals, an important group of krill predators, we estimate the density and krill consumption in the West Antarctic Peninsula (WAP)–Western Weddell Sea area, the main fishery region; and we consider long-term changes in suitable pack-ice habitat, increased fishing pressure and potential krill declines based upon predictions from declines in sea ice cover. More than 3 million crabeater seals consumed over 12 million tonnes of krill each year. This was approximately 17% of the krill standing stock. The highest densities of pack ice seals where found in the WAP, including in its small-scale fishery management areas, where apparently suitable seal habitat has declined by 21–28% over a 30year period, where krill density is likely to have declined, and fishing has increased. The highest seal density was found in the Marguerite Bay area which is a source of krill for the Antarctic Peninsula and elsewhere. Significant sea-ice loss since 1979 has already occurred, leading to open water and possible expansion for the fishery in the future. These factors may combine to potentially reduce food for pack ice seals. Therefore, high uncertainty in krill and seal stock trends and in their environmental drivers call for a precautionary management of the krill fishery, in the absence of survey data to support management based on specific conservation objectives for pack-ice seals.

Impact of combining GRACE and GOCE gravity data on ocean circulation estimates

Abstract. With the focus on the Southern Ocean circulation, results of assimilation of multi-mission-altimeter data and the GRACE/GOCE gravity data into the finite element ocean model (FEOM) are investigated. We use the geodetic method to obtain the dynamical ocean topography (DOT). This method combines the multi-mission-altimeter sea surface height and the GRACE/GOCE gravity field. Using the profile approach, the spectral consistency of both fields is achieved by filtering the sea surface height and the geoid. By combining the GRACE and GOCE data, a considerably shorter filter length can be used, which results in more DOT details. We show that this increase in resolution of measured DOT carries onto the results of data assimilation for the surface data. By assimilating only absolute dynamical topography data using the ensemble Kalman filter, we were able to improve modeled fields. Results are closer to observations which were not used for assimilation and lie outside the area covered by altimetry in the Southern Ocean (e.g. temperature of surface drifters or deep temperatures in the Weddell Sea area at 800 m depth derived from Argo composite.)

Biodiversity and distribution of the genus Gromia (Protista, Rhizaria) in the deep Weddell Sea (Southern Ocean)

We present a survey of morphospecies of Gromia, a genus of testate protists, from bathyal and abyssal depths in the Weddell Sea and adjacent areas of the Southern Ocean. This material represents the most extensive and diverse available collection of deep-sea gromiids so far recorded. The twelve species, nine of which are undescribed, are recognized on the basis of morphological criteria, including the test size and shape, the appearance and structure of the oral capsule, and the characteristics of the test wall. Most species have a single oral capsule, which is circular in plan view with a conical nipple-like shape in lateral view. One morphospecies has three oral capsules. The appearance and structure of the wall displays great variability among Gromia species, ranging from very delicate and transparent with highly reflective highlights to relatively thick with distinct patterns of ridges covering the surface. More often, however, differences in wall structure are more subtle. Most morphospecies were distributed at bathyal depths along the continental margin, but one was sampled at ~4,800 m, representing the first record of an abyssal gromiid. Concurrent with findings from other regions of the World’s oceans, the Weddell Sea gromiids were mostly found in surficial sediments in areas of elevated organic input, suggesting that deep-sea gromiids are likely to play an important role in carbon cycling in bathyal eutrophic regions through the ingestion and degradation of fresh organic matter.

New and little-known Komokiacea (Foraminifera) from the bathyal and abyssal Weddell Sea and adjacent areas

Based on samples from the south-east Atlantic and Southern Ocean collected during the ANDEEP III campaign we describe three new species, Ipoa pennata sp. nov., Septuma stellata sp. nov. and Skeletonia variabilis gen. et sp. nov., of the enigmatic deep-sea foraminiferan superfamily Komokiacea. A further six species, Ipoa fragila Tendal & Hessler, 1977, Komokia multiramosa Tendal & Hessler, 1977, Normanina conferta (Norman, 1878), Septuma ocotillo Tendal & Hessler, 1977, S. brachyramosa Kamenskaya, 1993, and S. komokiformis Kamenskaya 1993, are redescribed. Together, these nine species occurred at 14 stations across the depth range 1549–4935 m. Normanina conferta was found at 11 stations (1579–4935 m); S. ocotillo (4526–4935 m), S. brachyramosa (1819–4730 m) and S. stellata (2603–4934 m) at six stations each; I. fragila (4649–4934 m) at five stations; K. multiramosa (4700–4935) and S. variabilis (4696–4932 m) at four stations each; I. pennata (4803–4934 m) at three stations and S. komokiformis (3103–4526 m) at two stations. Five species occur in both the North Atlantic Ocean and the Southern Ocean, suggesting that close faunal links exist between these areas. Three were first described from the North Pacific Ocean while others, including the three new species, are so far known only from the Southern Ocean.

Gondwana breakup via double-saloon-door rifting and seafloor spreading in a backarc basin during subduction rollback

A model has been developed where two arc-parallel rifts propagate in opposite directions from an initial central location during backarc seafloor spreading and subduction rollback. The resultant geometry causes pairs of terranes to simultaneously rotate clockwise and counterclockwise like the motion of double-saloon-doors about their hinges. As movement proceeds and the two terranes rotate, a gap begins to extend between them, where a third rift initiates and propagates in the opposite direction to subduction rollback. Observations from the Oligocene to Recent Western Mediterranean, the Miocene to Recent Carpathians, the Miocene to Recent Aegean and the Oligocene to Recent Caribbean point to a two-stage process. Initially, pairs of terranes comprising a pre-existing retro-arc fold thrust belt and magmatic arc rotate about poles and accrete to adjacent continents. Terrane docking reduces the width of the subduction zone, leading to a second phase during which subduction to strike-slip transitions initiate. The clockwise rotated terrane is caught up in a dextral strike-slip zone, whereas the counterclockwise rotated terrane is entrained in a sinistral strike-slip fault system. The likely driving force is a pair of rotational torques caused by slab sinking and rollback of a curved subduction hingeline. By analogy with the above model, a revised five-stage Early Jurassic to Early Cretaceous Gondwana dispersal model is proposed in which three plates always separate about a single triple rift or triple junction in the Weddell Sea area. Seven features are considered diagnostic of double-saloon-door rifting and seafloor spreading: i) earliest movement involves clockwise and counterclockwise rotations of the Falkland Islands Block and the Ellsworth Whitmore Terrane respectively; ii) terranes comprise areas of a pre-existing retro-arc fold thrust belt (the Permo-Triassic Gondwanide Orogeny) attached to an accretionary wedge/magmatic arc; the Falklands Islands Block is initially attached to Southern Patagonia/West Antarctic Peninsula, while the Ellsworth Whitmore Terrane is combined with the Thurston Island Block; iii) paleogeographies demonstrate rifting and extension in a backarc environment relative to a Pacific margin subduction zone/accretionary wedge where simultaneous crustal shortening occurs; iv) a ridge jump towards the subduction zone from east of the Falkland Islands to the Rocas Verdes Basin evinces subduction rollback; v) this ridge jump combined with backarc extension isolated an area of thicker continental crust — The Falkland Islands Block; vi) well-documented EW oriented seafloor spreading anomalies in the Weddell Sea are perpendicular to the subduction zone and propagate in the opposite direction to rollback; vii) the dextral strike-slip Gastre and sub-parallel faults form one boundary of the Gondwana subduction rollback, whereas the other boundary may be formed by inferred sinistral strike-slip motion between a combined Thurston Island/Ellsworth Whitmore Terrane and Marie Byrd Land/East Antarctica.

Diversity and distribution of Porifera in the bathyal and abyssal Weddell Sea and adjacent areas

Abstract During the ANDEEP I–III expeditions, we obtained a rich and highly diverse sponge collection from the deep Weddell Sea. All the three Poriferan classes, Calcarea, Demospongiae and Hexactinellida, were well represented. Among this material, we have identified a total of 76 species from 47 genera and 30 families. Of these, 17 species (22%) are new to science and 37 (49%) new for the Southern Ocean. Particularly remarkable is the considerable depth of the boundary between bathyal and abyssal sponge faunas. Both Demospongiae and Hexactinellida show a strong shift in their taxonomic composition from a typical shelf assemblage to a more cosmopolitan deep-sea fauna at around 2500 m. Within the Demospongiae, the families Polymastiidae and Cladorhizidae (carnivorous sponges) are particularly abundant and very diverse. The Calcarea are recorded for the first time from the Antarctic deep sea. The type of sampling gear used, especially the epibenthic sledge, was an important factor for the successful collection of deep-sea sponges during the ANDEEP campaigns.

First insights into the biodiversity and biogeography of the Southern Ocean deep sea

Shallow marine benthic communities around Antarctica show high levels of endemism, gigantism, slow growth, longevity and late maturity, as well as adaptive radiations that have generated considerable biodiversity in some taxa. The deeper parts of the Southern Ocean exhibit some unique environmental features, including a very deep continental shelf and a weakly stratified water column, and are the source for much of the deep water in the world ocean. These features suggest that deep-sea faunas around the Antarctic may be related both to adjacent shelf communities and to those in other oceans. Unlike shallow-water Antarctic benthic communities, however, little is known about life in this vast deep-sea region. Here, we report new data from recent sampling expeditions in the deep Weddell Sea and adjacent areas (748-6,348 m water depth) that reveal high levels of new biodiversity; for example, 674 isopods species, of which 585 were new to science. Bathymetric and biogeographic trends varied between taxa. In groups such as the isopods and polychaetes, slope assemblages included species that have invaded from the shelf. In other taxa, the shelf and slope assemblages were more distinct. Abyssal faunas tended to have stronger links to other oceans, particularly the Atlantic, but mainly in taxa with good dispersal capabilities, such as the Foraminifera. The isopods, ostracods and nematodes, which are poor dispersers, include many species currently known only from the Southern Ocean. Our findings challenge suggestions that deep-sea diversity is depressed in the Southern Ocean and provide a basis for exploring the evolutionary significance of the varied biogeographic patterns observed in this remote environment.

A new stratigraphy for the Latady Basin, Antarctic Peninsula: Part 2, Latady Group and basin evolution

Recent detailed mapping, section logging and an improved understanding of the geological evolution of the Antarctic Peninsula provide a robust framework for an improved lithostratigraphic subdivision of the Latady Basin, eastern Ellsworth Land. Within the Latady Basin we recognize two main groups: Ellsworth Land Volcanic Group and Latady Group. The focus of this paper is the Latady Group, which is formally subdivided into five formations: Anderson Formation, Witte Formation, Hauberg Mountains Formation, Cape Zumberge Formation and Nordsim Formation. Middle Jurassic, shallow marine deposits of the Anderson Formation are overlain by quiet anoxic deposits assigned to the Witte Formation. The start of the Late Jurassic is marked by the deposition of higher energy deposits of the Hauberg Mountains Formation, subdivided into three members (Long Ridge, Mount Hirman and Novocin members) that reflect varying lithological and environmental characteristics. Thermal subsidence during the latest Jurassic led to deposition of the basinal Cape Zumberge Formation, while uplift of an active continental arc along the Antarctic Peninsula led to deposition of the terrestrial Nordsim Formation in the latest Jurassic to earliest Cretaceous. The evolution of the Latady Basin reflects early extension during Gondwana break-up, from the Early Jurassic to earliest Cretaceous, and is consistent with a shift in the underlying forces driving extension in the Weddell Sea area from intracontinental rifting related to a mantle plume, to active margin forces in response to subduction.

Distribution patterns and biodiversity in polychaete communities of the Weddell Sea and Antarctic Peninsula area (Southern Ocean)

During the expedition EASIZ II with RV ‘POLARSTERN’ in 1998 a multibox corer yielded 151 quantitative samples from 26 stations between 120 and 2415 m water depth for benthic community analysis. From this material a total of 235 polychaete species out of 37 families was determined. Forty-seven species are new to science. The polychaete fraction contributed 41.9% to total benthic abundance and 6.5% to total benthic biomass at these stations. Overall mean polychaete abundance (ind m−2) and biomass (g wet weight m−2) at the stations were 1617 and 49, respectively.Multidimensional scaling procedure clearly grouped the stations into south-eastern Weddell Sea shelf stations, deep-water stations, and stations mostly around the Antarctic Peninsula. Differences between these groups existed in terms of polychaete abundance and biomass as well as species composition, diversity, and evenness.

Species distribution within the free-living marine nematode genus Dichromadora in the Weddell Sea and adjacent areas

Abstract Studies of Antarctic, free-living, marine nematodes are mostly restricted to genus level. In the current study, the genus Dichromadora (Kreis, H.A., 1929. Capita Zoologica 2(7), 1–98) is analysed to species level. Dichromadora is one of the genera that are frequently present along the continental margin of the eastern Weddell Sea. Samples were retrieved from the 1000–2000 m depth line in the eastern Weddell Sea (Halley Bay, Vestkapp and Kapp Norvegia), South Sandwich Trench and the Drake Passage. Eight species are distinguished within the genus Dichromadora of which seven are new to science. Out of these seven species, five are described taxonomically: Dichromadora weddellensis sp. n. , Dichromadora southernis sp. n. , Dichromadora polarsternis sp. n., Dichromadora parva sp. n., and Dichromadora polaris sp. n. The two other species ( D. spec A, D. spec B) receive, as to the scarcety of available specimens, no scientific name. The distribution of the Dichromadora species from Antarctica are discussed in the context of deep-sea (1000–2000 m) observations in Arctic, Atlantic, Pacific and Indian oceans.

Distribution and Characteristics of Mesoscale Cyclones in the Antarctic: Ross Sea Eastward to the Weddell Sea*

The mesoscale cyclone activity observed in the portion of Antarctica that faces the South Pacific Ocean and Weddell Sea area is summarized from a study of 1991. In general, area-normalized results reveal much greater mesoscale cyclonic activity over the Ross Sea/Ross Ice Shelf and southern Marie Byrd Land than on both sides of the Antarctic Peninsula. More than 50% of the observed mesoscale vortices are of the comma cloud type. The average diameter of mesoscale vortices is approximately 200 km near Terra Nova Bay, 270 km near Byrd Glacier, and 280 km near Siple Coast. Near the Antarctic Peninsula, the average diameter is about 370 km over the Bellingshausen Sea and 380 km on the Weddell Sea side. The largest percentage of deep vortices occurs over the Bellingshausen Sea sector (38% of all cases), where convective instability frequently occurs. Over the Ross Sea/Ross Ice Shelf and Weddell Sea sectors the majority of the mesoscale vortices are low cloud features that probably do not exceed the 700-hPa level due to the prevailing lower-atmospheric stability. The areas identified as sources of mesoscale vortices concur with the locations of enhanced katabatic winds. A synthesis of the available literature leads to some general characteristics of mesoscale cyclone formation and development. Mesoscale cyclogenesis is associated with areas of warm and/or cold air advection, low-level baroclinicity, and cyclonic vorticity resulting from the stretching mechanism. Subsequent intensification depends on the presence of upper-level support. Spatial and temporal variability in mesoscale cyclone formation is often related to the behavior of synoptic-scale cyclone tracks. Mesoscale cyclones can generate precipitation and severe weather conditions and thus present a critical forecasting challenge.

A new magnetic map of the Weddell Sea and the Antarctic Peninsula

As part of the Antarctic Digital Magnetic Mapping Project (ADMAP) workers from VNIIOkeangeologia (Russia), the British Antarctic Survey (UK) and the Naval Research Laboratory (USA) have brought together almost all of the available magnetic data in the area 0–120°W, 60–90°S. The final map covers the whole Weddell Sea and adjacent land areas, the Antarctic Peninsula and the seas to the west, an area comparable in size with that of the USA. This paper describes the methods used during the compilation of the map and reviews briefly some of the main features shown on it. Distinct magnetic provinces are associated with Precambrian rocks of the East Antarctic craton, highly extended continental crust in the Weddell Sea embayment, the arc batholith of the Antarctic Peninsula, and oceanic crust of the northern Weddell Sea, which was created as a direct consequence of South America–Antarctica plate motion and oceanic crust generated at the Pacific–Antarctic ridge. The magnetic anomaly map thus provides an overview of the fragmentation of south-western Gondwana and the tectonic development of the Weddell Sea sector of Antarctica.