In certain regions of the Southern Ocean, tidal energy is believed to foster the mixing of different water masses, which eventually contribute to the formation of deep and bottom waters. The Ross Sea is one of the major ventilation sites of the global ocean abyss and a region of sparse tidal observations. We investigated M2 tidal dynamics in the Ross Sea using a three-dimensional sigma coordinate model, the Regional Ocean Model System (ROMS). Realistic topography and hydrography from existing observational data were used with a single tidal constituent, the semi-diurnal M2. The model fields faithfully reproduced the major features of the tidal circulation and had reasonable agreement with ten existing tidal elevation observations and forty-two existing tidal current measurements. The differences were attributed primarily to topographic errors. Internal tides were generated at the continental shelf/slope break and other areas of steep topography. Strong vertical shears in the horizontal velocities occurred under and at the edges of the Ross Ice Shelf and along the continental shelf/slope break. Estimates of lead formation based on divergence of baroclinic velocities were significantly higher than those based on barotrophic velocities, reaching over 10% at the continental shelf/slope break.

An ecomorphological study was performed on ten species of the family Artedidraconidae, the most benthic of the suborder Notothenioidei. These species are sympatric on the shelf of the Weddell Sea. The results show that the four genera comprising the family (Artedidraco, Dolloidraco, Histiodraco and Pogonophryne) can be differentiated by just a few morphometric features of their sensory organs and mouth. The genera were also clearly defined by the composition of their diet (benthic and epibenthic), the size of their prey, and their bathymetric distribution. Comparison of the morphological and ecological data shows a very close connection between sensory organs development, the mouth and bathymetric distribution. The morphological and ecological divergence observed can be explained as the result of the rapid adaptive radiation of the artedidraconids. The results confirm that characteristics of the sensory organs and alimentary structures are very suitable for the ecomorphological study of fishes.

Annual land-fast ice, particularly an unconsolidated layer or “platelet ice-like” layer (PLI), was sampled in spring 1995 to study the spatial and short-term variations of ice-associated diatoms. Under-ice water, a lead and small polynyas were also sampled. Along a 7 km seaward transect a geographical gradient was evident, with some rare diatom species present only in the offshore PLI, whereas others (mainly pennate diatoms) were ubiquitous. The dense microphytic PLI community as well as the phytoplankton was diatom-dominated, but, within these two communities, marked differences appeared. First, the sea-ice communities (PLI and solid bottom ice) were moderately diverse (36 species), mostly composed of pennate diatoms, of which many were chain forming or tube-dwelling. Dominant taxa were Navicula glaciei, Berkeleya adeliensis, Nitzschia stellata, Amphiprora kufferathii and Nitzschia lecointei. Some differences in the distribution of the most dominant species appeared within the bottom ice and the PLI, attesting to differences in the origin or/and growing capability of these diatoms in these two ice compartments. Under-ice water species composition was mixed with sea-ice communities only on the most coastal sites and during ice melt. Maximum cell numbers were mostly noticed in the PLI, reaching up to 1010 cells l−1 and very high Chl a concentrations (exceptionally up to 9.8 mg Chl a l−1 or 1.9 g Chl a m−2, from a 10 to 20 cm thick PLI layer, close to the continent). Secondly, the phytoplankton in the lead and small polynyas had a low diversity, very low standing stocks (on an average 0.69 μg Chl a l−1) and cell densities (2 × 104 cells l−1). Some species from the polynyas were similar to those of the PLI, such as Navicula glaciei, but others were typically planktonic, such as Chaetoceros cf. neglectus. The presence of encysted cells (Chaetoceros and Chrysophytes) was also noticeable in the polynya water. In early spring no seeding process was obvious from the PLI to polynya water. A comparison with similar fast-ice diatom communities in other parts of coastal Antarctica, is presented.

The phenology of six Antarctic red macroalgae, Delesseria salicifolia Reinsch, Gymnogongrus antarcticus Skottsberg, Gymnogongrus turquetii Hariot, Hymenocladiopsis crustigena Moe, Kallymenia antarctica Hariot and Phyllophora ahnfeltioides Skottsberg, was investigated in a two-year culture study under fluctuating daylengths imitating the conditions of King George Island, South Shetland Islands. The algae were cultured at 0°C in filtered, nutrient enriched seawater under photon fluence rates of 3, 10, 25, 50 μmol photons m−2 s−1. All species are classified as season anticipators, starting growth in late winter–spring and stopping growth before the summer solstice. Formation of new blades was observed from January/February onwards in most of the species. Carpospore formation was observed in K. antarctica in early summer. Growth was light saturated at photon fluence rates of 3 μmol photons m−2 s−1 in D. salicifolia and at 10 μmol photons m−2 s−1 in the other species, corresponding to an annual light dose of 31.4 and 157 mol photons m−2. The results show that this type of life strategy is typical for species from the Antarctic and give further evidence on the high degree of shade adaptation of Antarctic algae and predict a lower distribution limit for these species at 37 ± 15 m and 23 ± 10 m, respectively.

An index of integrated food preferences (IFA) of Notothenia coriiceps Richardson at two sites in Admiralty Bay (Ipanema and Smok Point), calculated for two sequential summers, showed that during 1998/99, the most important food item was Euphausia superba (krill) at both Ipanema (IFA = 0.83) and Smok Point (IFA = 0.75), while the sum of all other food items was significantly smaller (IFA respectively 0.21 and 0.26). Macroalgae, gammarid amphipods and gastropods dominated the diet in the summer 1999/00 (IFA respectively 0.32, 0.32 and 0.21), at Ipanema, while macroalgae were dominant at Smok (IFA = 0.67), where krill and amphipods were secondary prey (IFA respectively 0.12 and 0.14) and gastropods were absent. Thus, the diet composition of N. coriiceps can possibly be used as an indicator of the presence of pelagic krill swarms.

Geochemical and magnetic data from glacigenic sediments can be useful indicators of past environments and climate. In this paper, the results of X-ray fluorescence (XRF) and rock magnetic analyses are presented for samples from the Pagodroma Group, an assemblage of pre-Quaternary glacimarine sediments preserved as remnants along the raised flanks of the Lambert Graben, Prince Charles Mountains, East Antarctica. Samples were obtained from four formations: Mount Johnston, Battye Glacier, Fisher Bench and Bardin Bluffs, which range in age from late Oligocene or early Miocene through to Pliocene or early Pleistocene. Principal component analysis of the XRF data indicates the occurrence of two main element assemblages, which we infer are determined by the presence in the Bardin Bluffs formation of a significant component derived from Permo–Triassic sedimentary rocks of the Amery Group. Calculation of chemical indices of alteration suggests that the values reflect provenance differences rather than the syndepositional weathering environment. Multidomain ferrimagnetic grains mainly dominate the magnetic mineral assemblages of the samples, probably magnetite, with varying concentrations of high coercivity material, probably hematite.

Among the benthic lithological samples collected during the Spanish Antarctic survey GEBRAP 1996–97 in the Bransfield Strait, two new oweniid (Annelida, Polychaeta, Oweniidae) species were collected: Myriochele riojai n. sp. and Myriochele robusta n. sp. Myriochele riojai is closely related to M. heeri Malmgren, 1867 but differs in body size, number and distribution of the notosetae and in the position of elongated abdominal body segments. Myriochele robusta differs from all known species of the genus owing to its possession of a biramous setiger between two uniramous setigers in the anterior (thoracic) body region. A key to oweniid species recorded in Antarctic waters is provided.

Ship-based observations of sea ice thickness using the Antarctic Sea Ice Processes and Climate (ASPeCt) protocol provide information on ice thickness distribution at relatively low cost. This protocol uses a simple formula to calculate the mass of ice in ridges based on surface observations. We present two new formulae and compare these with results from the “Original” formula using data obtained in the Ross Sea in autumn and winter. The new “r-star” formula uses a more realistic ratio of sail and keel areas to transform dimensions of sails to estimates of mean keel areas. As a result, estimates of “equivalent thickness” (i.e. mean thickness of ice in ridged areas) increased by over 200%. The new “Probability” formula goes one step further, by incorporating the probability that a sail is associated with a keel underwater, and the probability that keels may be found under level surfaces. This resulted in estimates of equivalent thickness comparable with the Original formula. Estimates of equivalent thickness at one or two degree latitude resolution are sufficiently accurate for validating sea ice models. Although ridges are small features in the Ross Sea, we have shown that they constitute a significant fraction of the total ice mass.

A floristic and taxonomic survey was made of the diatom communities of sediments and microbial mats in 66 freshwater and saline lakes and pools in the Larsemann Hills, Rauer Islands and Bølingen Islands (continental eastern Antarctica). A total of 31 taxa were distinguished, 10 of which could not be identified to species (nine) or even generic (one) level, either because they have most probably not yet been described or because they belong to species complexes that are in need of revision. Four new combinations are proposed; three species are reported for the first time from continental Antarctica, while another three are confirmed for eastern Antarctica for the first time. Analysis of literature data on Antarctic lacustrine diatoms shows that taxonomic practice has a profound influence on the assessment of distribution patterns. Force-fitting of European and North American names to Antarctic taxa and erroneous identifications have contributed to an underestimation of endemism in the diatom flora of Antarctic inland waters. In addition, changing concepts on species boundaries during the last decade influence the interpretation of biogeographic patterns. The application of a more fine grained taxonomy will almost certainly reveal a higher degree of endemism in Antarctica, and especially continental Antarctica. The present case study shows that in the Larsemann Hills Antarctic endemics account for about 40% of all freshwater and brackish taxa, while the biogeographic distribution of about 26% is unknown, mainly due to their uncertain taxonomic identity. This contradicts the view that cosmopolitanism prevails in Antarctic diatoms.

Two species of euphausiids (Thysanoessa macrura Sars and Euphausia vallentini Stebbing) from the Southern Indian Ocean were analysed for their lipid content, fatty acid and fatty alcohol composition, in relation to developmental stage (T.m) and sex (E.v). Lipid composition showed wax esters and triacylglycerols as main neutral lipids for T. macrura and E. vallentini respectively. Allometric relationships between lipid class and total lipids indicated that changes in total lipids were size dependent and mainly related to wax esters in T. macrura and polar lipids (both phosphatidylcholine or PC and phosphatidylethanolamine or PE) in E. vallentini. No difference in lipid composition could be shown for male and female E. vallentini, while sampling location, developmental stage and sex were significantly influential in T. macrura. In this latter species wax esters displayed relatively similar fatty acid and alcohol composition in both juvenile and female stages, whereas a striking difference could be seen between females and juveniles in terms of polar lipids with a very low PE content in females. Male and female E. vallentini showed little differences in fatty acid structure with the exception of PC in females, which were low in 22:6n-3. The trophic status of these two species was established using multivariate discriminant analysis, which indicated for E. vallentini a degree of omnivory similar to E. superba, while these T. macrura appeared more omnivorous than individuals collected in other areas of the Southern Ocean. Clustering of polar lipid composition suggested a link between differences in PC fatty acid and the post-spawn stage of the female of E. vallentini collected. The same probably applies for the changes in PE recorded for T. macrura females.

Two groups of geochemical different dykes have been identified in the Grenville-aged basement of Heimefrontfjella. The first group comprises dykes of continental tholeiite composition which probably intruded during the final stage of indentation of the Kaapvaal—Grunehogna Craton into Laurentia. One dyke of this group yielded an U—Pb zircon SHRIMP age of 1033 ± 7 Ma. The second group has an E-type MORB composition and may be related to ocean floor basalts of the Mozambique Ocean between East and West Gondwana. A preliminary U—Pb SHRIMP age of 586 ± 7 Ma for a single zircon crystal was obtained from a dyke of the second group. During the Pan-African orogeny both dyke groups underwent metamorphism and tectonism at different grades: up to amphibolite-facies in the eastern and southern Heimefrontfjella, and at greenschist-facies in the western and northern Heimefrontfjella. The older dykes may be correlated with the Equeefa suite of southern Natal whereas the younger dyke group is not correlatable with any known mafic intrusions or lava flows in adjacent regions.

During summer (2 December 1999–23 January 2000) an Ocean Surface Current Radar (OSCR-II) was used to provide surface current measurements within the Terra Nova Bay polynya, one of the most important coastal polynyas of the Ross Sea. This represents an important step towards a continuous monitoring of the area. Useful information is now available as a basis for future work in this field, although the two radar sites, necessary to calculate the total current vector, did not work together throughout the whole period of the experiment as one of the units was damaged. The results demonstrate the feasibility of this kind of measurement and suggest that very important dynamical characteristics of the polynya could be deduced from long term deployment of such a system.

Although world oceans have been warming over the past 50 years, the impact on biotic components is poorly understood because of the difficulty of obtaining long-term datasets on marine organisms. The Southern Ocean plays a critical role in global climate and there is growing evidence of climate warming. We show that air temperatures measured by meteorological stations have steadily increased over the past 50 years in the southern Indian Ocean, the increase starting in mid 1960s and stabilizing in mid 1980s, being particularly important in the sub-Antarctic sector. At the same time, with a time lag of 2–9 years with temperatures, the population size of most seabirds and seals monitored on several breeding sites have decreased severely, whilst two species have increased at the same time. These changes, together with indications of a simultaneous decrease in secondary production in sub-Antarctic waters and the reduction of sea-ice extent further south, indicate that a major system shift has occurred in the Indian Ocean part of the Southern Ocean. This shift illustrates the high sensitivity of marine ecosystems, and especially upper trophic level predators, to climatic changes.

The validity of the Antarctic species of the “Oikopleura gaussica group” (O. gaussica, O. valdiviae, O. drygalskii, and O. weddelli) is discussed. The characteristics of new material from South Georgia and the Bellingshausen Sea are compared with the original descriptions. We examined 495 specimens at different stages of maturity and concluded that the characters used to differentiate these species of Oikopleura have not enough weight to justify their separation. The morphological variations found were ascribed either to intraspecific variability and/or to the different degree of maturity of the specimens examined of a single species, Oikopleura gaussica. The main taxonomic characters for the identification of this species are: the particular way in which the flat triangular gonads surround the intestinal ball like a sheath, the equal size of the two lobes of the stomach, the oesophagus entering the postero-dorsal edge of the rounded left lobe of the stomach, the presence of oval and some times lobate oral glands, and the variable number of subchordal cells (4 to 14) arranged in a single row on the right (ventral) side of the chorda.

This study looks at the feasibility of using Ocean Acoustic Tomography for long-term monitoring of polynyas using both observations in Terra Nova Bay polynya (Ross Sea) and simulations with a range dependent, multi-layered adiabatic normal mode acoustic propagation model. The summer sound speed profile is characterized by surface values of around 1450 m s−1, a minimum of 1441 m s−1 around 50 m depth and a linear increase with a 0.016 s−1 slope. Thus, the sound propagation is apparently ducted in the near surface layer and is refracted upward below it. During winter, due to water cooling and mixing processes, the subsurface minimum disappears, the surface sound speed is about 1440 m s−1 and no near surface layer ducted propagation occurs. Because of the specificity of the Terra Nova Bay seasonal sound speed profile and to cope with both deep and shelf water applicability, the feasibility study of acoustic inversion was undertaken using normal mode Match Field Tomography instead of the more classical travel-time inversion. The results from simulations demonstrate that ocean acoustic tomography is able to reproduce quite well the vertical sound speed profile, in particular the temporal evolution of summer stratification and winter mixing processes, thus providing information on the upper layer, where direct measurements are not possible.

Large mafic sills in the Ahlmannryggen region of western Dronning Maud Land were intruded into partially lithified sediments of the mid-Proterozoic Ritscherflya Supergroup. Clastic sedimentary dykes intruding the thick mafic sills have been identified, and show evidence for fluidization of the partially lithified sediments. Previous work had demonstrated in situ fluidization and localized anatectic melting. This study demonstrates mobilization of the fluidized sediments, with penetration at least 50 m into the fractured, intruding sill. Physical features within the clastic dykes (e.g. sediment balls, flame structures) suggest that the sediments were largely unconsolidated, or at most only partially lithified. The presence of a thin zone of anatectic melt along the dyke—sill contact suggests that the mafic sill was still hot (c. 700°C) at the time of sedimentary dyke injection.

Deschampsia antarctica is a freezing-tolerant plant and the only native Poaceae that grows in the Maritime Antarctic. During the long days of the growing season this plant accumulates sucrose (Suc) in the leaves to 36% of the dry weight. The mechanism that leads to this high accumulation is unknown. The effect of day length and low temperature on sucrose phosphate synthase (SPS) (EC: 2.4.1.14) activity and sugar accumulation was studied in D. antarctica and compared with other Poaceae. Three different day lengths: short (SD) (8/16 h), medium (MD) (16/8 h) and long (LD) (21/3 h); and two temperatures: 4°C (cold-acclimated) and 15°C (non-acclimated) were tested. The highest contents in total soluble sugars (TSS) and Suc were reached in crowns and leaves, respectively, in cold-acclimated plants under LD. TSS and Suc contents and SPS activity with cold acclimation were higher in D. antarctica than in other agricultural (wheat, oat and barley) and non-agricultural (D. caespitosa and D. beringensis) Poaceae species. Suc/TSS ratio was higher in all Deschampsia species than in agricultural Poaceae species. SPS activity and sucrose content in leaves were positively correlated only in LD cold acclimated plants. This result shows that SPS activity is responsive to day length in D. antarctica.

The Southern Ocean plays an important role in the global carbon cycle and, as a consequence, in the planetary climate equilibrium. The Ross Sea is one of the more productive regions in the Southern Ocean, due to strong phytoplankton blooms occurring during summer. Satellite remote sensing is a powerful tool for investigating such phenomena, especially if the bio-optical algorithms are tuned with in situ data. In this paper, after having compared the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and the ENEA Lidar Fluorosensor (ELF), the SeaWiFS chlorophyll a (Chl a) algorithm is tuned in the Ross Sea by means of the ELF measurements. The Chl a concentrations obtained in this way have been the basis for estimating productivity values and their evolution during summer 1997–98. Three primary production models have been used, providing information on their accuracy and performance in the Antarctic environment. Our investigations suggest that the primary production was lower than usual during the period 3 December 1997–16 January 1998.

Accurate assessment of the abundance of pinnipeds from visual surveys requires estimation of both the available (hauled-out) and unavailable (in-water) components of the population (Eberhardt et al. 1979). Continental estimates of the abundance of the four Antarctic seals are based on limited information on haul-out behaviour. In developing continental estimates, Erickson & Hanson (1990) corrected visual surveys of the hauled-out component of the species' populations using data from observational studies of haulout behaviour by Erickson et al. (1989). Erickson & Hanson (1990) point out that, because the observational studies did not account for an unknown fraction of seals that remained in the water during the peak haul-out period, their abundance estimates are minimum values. Further, Erickson & Hanson (1990) corrected the visual surveys for all four species using haul-out data for the crabeater seal only, as observational data for the other species were not available. This assumes that haul-out patterns are constant across species, which is largely untested. Consequently, there is potential for bias, in both a relative and absolute sense, in the estimated abundance of Antarctic seals.

A mesoscale experiment was conducted in the Ross Sea near the shelf break in summer 1997–98 within the framework of the activities of the CLIMA Project of the Italian National Program for Antarctic Research (PNRA), focus on study the shelf—slope interaction between the shelf waters and the CDW in correspondence of the Antarctic Slope Front. This paper deals with the dissolved oxygen distribution and with the application of conservative tracers NO and PO related to the physical variables, improving understanding of mixing processes study in correspondence of the shelf break. Experimental data showed the presence of both Ice Shelf Water overflowing the shelf and Circumpolar Deep Water intruding onto the shelf. Dissolved Oxygen (DO), NO and PO resulted useful as chemical tracers in outlining the mixing processes and bottom water formation spreading off continental shelf break of the Ross Sea, in which seems to be evidence that ISW plays an important role. In fact, a plume of ISW was observed flowing down the continental slope to the deep ocean. From chemical tracers we estimate its magnitude to be about 0.4 ± 0.2 Sv.