Entire Margin Research Articles

STUDIES ON LEAF VENATION IN SELECTED CLIMBERS

In this paper studies on leaf venation characterized for four species of climbers namely, Clitoria ternatea Linn, Daemia extensa R. Br., Aristolochia bracteata Retz, and Gloriosa superba Linn. To morphotype leaves, these were sorted out on the basis of serrated versus entire margins, primary and secondary vein patterns, etc. With some exceptions, these characters are usually stable within morphotypes. The leaf size and shape are the least reliable characters in identifying leaves. After the leaves are sorted into these broad categories, one can further divide them by looking at higher order venation patterns and tooth type. This paper illustrated with line drawings of prepared stained leaves, provides a framework of the leaves. This study will be very useful to a broad range of people who work with plants.

Populus luzae (Salicaceae), a new species of white poplar endemic to the western Transmexican Volcanic Belt, in Zapopan, Jalisco, Mexico

Populus luzae, a new species of white poplar from the western Transmexican Volcanic Belt, Zapopan, Jalisco, Mexico, is described and illustrated. Populus luzae belongs to section Populus and is morphologically close to P. guzmanantlensis, but it differs from the latter in having smaller size and soboliferous habit, narrower twigs and petioles, ovate to ovate-deltoid and chartaceous leaf blades, adaxial leaf surface with less depressed veins, abaxial surface puberulent, thrice smaller ovate male bracteoles with entire margin, twice longer female bracteoles sparsely denticulate but none lobed, smaller number of pistillate flowers, capsules pubescent, twice longer mature male inflorescence, and a lax and longer infrutescence.

Nelumbo jiayinensis sp. nov. from the Upper Cretaceous Yong'ancun Formation in Jiayin, Heilongjiang, Northeast China

Fossil leaves of Nelumbo jiayinensis sp. nov. are described from the Yong'ancun Formation (Santonian) in Jiayin, Heilongjiang, Northeast China. This is the first report on fossil Nelumbo from the Upper Cretaceous of China. The leaves are simple with entire margins, orbicular or sub-orbicular in shape, with a peltate and symmetric lamina. The venation is actinodromous with 20–25 primary veins, the secondary and tertiary veins are poorly developed and interweave into meshes. The areoles are irregularly polygonal in shape and well developed both in upper and lower surfaces. Combined with data derived from associated fossil mega-plants, spores and pollen, bivalves and dinosaur footprints, the aquatic angiosperm Nelumbo existed in a fluviolacustrine environment under a warm but seasonal temperate climate.

Optical coherence tomography for margin definition of basal cell carcinoma before micrographic surgery-recommendations regarding the marking and scanning technique.

Mohs Micrographic Surgery (MMS) is the preferred therapeutic treatment for high-risk basal cell carcinoma (BCC). Optical Coherence Tomography (OCT) is a non-invasive imaging technique that enables the diagnosis of BCC. We thought to determine the margins of BCCs with OCT, prior to MMS, to reduce the number of surgical steps. Different permanent markers were tested on the skin regarding line width, resistance against disinfection and brightness in the OCT image. The visible tumor margins of BCCs were defined by dermoscopy, adding a safety margin of 2mm and labeled using the selected pen, causing a signal shadow in OCT. Scans of the center and of entire margin were performed. If parts of the BCC were visible outside the margin, another 2mm were added and the scan was repeated until the tissue outside the labeling looked tumor free. Eight out of ten BCCs were totally excised in a single stage when margin delineation was done by OCT. Macroscopic margins were enlarged after OCT scanning in four patients, saving further stages of MMS. OCT may help to better define the microscopic dimensions of BCCs and therefore reduce the number of stages of MMS.

Evaluating feasibility of an automated 3-dimensional scanner using Raman spectroscopy for intraoperative breast margin assessment

Breast conserving surgery is the preferred treatment for women diagnosed with early stage invasive breast cancer. To ensure successful breast conserving surgeries, efficient tumour margin resection is required for minimizing tumour recurrence. Currently surgeons rely on touch preparation cytology or frozen section analysis to assess tumour margin status intraoperatively. These techniques have suboptimal accuracy and are time-consuming. Tumour margin status is eventually confirmed using postoperative histopathology that takes several days. Thus, there is a need for a real-time, accurate, automated guidance tool that can be used during tumour resection intraoperatively to assure complete tumour removal in a single procedure. In this paper, we evaluate feasibility of a 3-dimensional scanner that relies on Raman Spectroscopy to assess the entire margins of a resected specimen within clinically feasible time. We initially tested this device on a phantom sample that simulated positive tumour margins. This device first scans the margins of the sample and then depicts the margin status in relation to an automatically reconstructed image of the phantom sample. The device was further investigated on breast tissues excised from prophylactic mastectomy specimens. Our findings demonstrate immense potential of this device for automated breast tumour margin assessment to minimise repeat invasive surgeries.

Partial nephrectomy margin imaging using structured illumination microscopy.

Partial nephrectomy (PN) is the recommended procedure over radical nephrectomy (RN) for patients with renal masses less than 4 cm in diameter (Stage T1a). Patients with less than 4 cm renal masses can also be treated with PN, but have a higher risk for positive surgical margins (PSM). PSM, when present, are indicative of poor clinical outcomes. The current gold-standard histopathology method is not well-suited for the identification of PSM intraoperatively due to processing time and destructive nature. Here, video-rate structured illumination microscopy (VR-SIM) was investigated as a potential tool for PSM detection during PN. A clinical image atlas assembled from ex vivo renal biopsies provided diagnostically useful images of benign and malignant kidney, similar to permanent histopathology. VR-SIM was then used to image entire parenchymal margins of tumor resection covering up to >1800× more margin surface area than standard histology. Aided by the image atlas, the study pathologist correctly classified all parenchymal margins as negative for PSM with VR-SIM, compared to standard postoperative pathology. The ability to evaluate large surgical margins in a short time frame with VR-SIM may allow it to be used intraoperatively as a "safety net" for PSM detection, allowing more patients to undergo PN over RN.

New Records of Intertidal Marine Algae from Korea

Bryopsis africana and Pyropia kinositae are reported for the first time on the list of Korean marine algal flora based on integrated morphological-molecular study. Bryopsis africana from Korea is recognized with distinct main axes, robust thalli, pinnately and radially branched above, and basally denuded. Phylogenetic analyses revealed that B. africana was placed within a clade of Bryopsis. Bryopsis africana differs from B. corymbosa by 2.7% gene sequence divergence. Pyropia kinositae is characterized by oblong to lanceolate thalli, entire margin, purplish red in color, twice as long as broad cells in transversal section view. Phylogenetic analyses revealed that P. kinositae was placed within a clade of Pyropia. Pyropia kinositae differs from P. tenera by 1.5-1.8%, P. ishigecola by 1.2-1.3%, and P. yezoensis by 1.5-1.8% gene sequence divergence respectively.

Towards a Better Understanding of the Tribe Aniseieae: Revisiting Aniseia and Iseia (Convolvulaceae)

Abstract In this paper we propose a new circumscription of Aniseia that includes Iseia and reduces Aniseia martinicensis var. ambigua and A. cernua to the synonymy of A. martinicensis. The new combination Aniseia luxurians is made. The three species of Aniseia recognized herein are characterized by simple trichomes; simple leaves with entire margin, mucronate apex and eucamptodromous venation; axillary cymose inflorescences, or solitary flowers; unequal to subequal sepals; campanulate corolla; single style; glandular trichomes at bases of filaments, sagittate anthers, and 2-globose and papillose stigma. Furthermore, twelve new synonyms and eleven lectotypifications are proposed herein. We provide an identification key, illustrations, comments on geographical distribution, and specimen-based distribution maps, as well as taxonomic and nomenclatural information.

A taxonomic revision of the Pteronia camphorata group (Astereae, Asteraceae)

As a first step towards a comprehensive revision of Pteronia (Asteraceae, Astereae), we present here a taxonomic treatment of the Pteronia camphorata group, in which we recognise three species. The group includes the type species P. camphorata (an important medicinal plant) and is easily distinguished from the rest of the genus by the glabrous rather than glandular or variously pilose cypselas. The lectotype of P. camphorata has involucral bracts with entire margins and long acuminate apices, both diagnostic characters for P. stricta. As such P. stricta is here reduced into synonymy with P. camphorata and the next available name, P. aspera Thunb, reinstated to accommodate the species heretofore treated as P. camphorata. Three varieties within Pteronia camphorata had been previously recognised (var. armata, var. laevigata and var. longifolia). The characters distinguishing var. armata were found to be continuous with the variation observed within var. longifolia. The third infraspecific taxon, var. laevigata, was however found to be distinct and is therefore recognised here as a new species, P. cederbergensis Bello, Magee & Boatwr. It is readily distinguished by the glabrous branches, opposite to sub-opposite somewhat succulent leaves, the 2-seriate pappus and larger, obclavate cypselas. Transverse sections of the leaves and cypselas were also examined and provide additional differences between the three recognised species.

An unusual new species of Oenonidae (Polychaeta, Eunicida) from the North Atlantic Ocean

A new species of Tainokia (family Oenonidae) is described from the Gulf of Cadiz (NE Atlantic). Tainokia logachevae sp. nov. was retrieved from a dredge sample across the crater of Mercator mud volcano at 375–397 m depths. It is characterized by having H-shaped mandibulae with distal bidentate accessory pieces, maxillae I and II dentate along the entire margin and greatly asymmetric, with 6 or 10 teeth, and maxillae III, IV, and V with 5/6, 4/5, and 1 teeth, respectively. DNA fragments from the mitochondrial genes COI and 16S rDNA, and the nuclear genes 18S rDNA and 28S rDNA are given, providing a molecular tag for future reference of this species. This is the first report of the genus for both the deep sea and for the Atlantic Ocean.

Possible threshold controls on sediment grain properties of Peruvian coastal river basins

Abstract. To determine possible controls on sediment grain properties, 21 coastal rivers located along the entire western Peruvian margin were analysed. This represents one of the largest grain size dataset that has been collected over a large area. Modern gravel beds were sampled along a north–south transect on the western side of the Peruvian Andes where the rivers cross the tip of the mountain range, and at each site the long a axis and the intermediate b axis of about 500 pebbles were measured. Morphometric properties of each drainage basin, sediment and water discharge, together with flow shear stresses, were determined and compared against measured grain properties. Pebble size data show that the values for the D50 are nearly constant and range between 2 and 3 cm, while the values of the D96 range between 6 and 12 cm. The ratios between the intermediate and the long axis range from 0.67 to 0.74. Linear correlations between all grain size percentiles and water shear stresses, mean basin denudation rates, mean basin slopes and basin sizes are small to non-existent. However, exceptionally large D50 values of 4–6 cm were measured for basins situated between 11–12 and 16–17° S latitude where hillslope gradients are steeper than on average or where mean annual stream flows exceed the average values of the western Peruvian streams by a factor of 2. We suggest that the generally uniform grain size pattern has been perturbed where either mean basin slopes or water fluxes exceed threshold conditions.

Kushneria konosiri sp. nov., isolated from the Korean salt-fermented seafood Daemi-jeot.

A halophilic bacterial strain, X49T, was isolated from the Korean traditional salt-fermented seafood Daemi-jeot. X49T was an obligately aerobic, Gram-stain-negative, motile, oval or rod-shaped (0.5-1.0×1.2-3.2 µm) bacterium. After 2 days of growth, colonies on Marine agar medium were orange and circular with entire margins. X49T growth was detected at 10-37 °C and pH 4.5-8.5 in the presence of 0-26 % (w/v) NaCl. The 16S rRNA gene sequence of strain X49T was most similar to that of the type strain of Kushneria marisflavi SW32T and shared a sequence similarity of 94.7-98.6 % with type strains of species of the genus Kushneria. The predominant fatty acids were C16 : 0, C18 : 1ω7c and C12 : 0 3OH. The major isoprenoid quinone was Q9 (93 %), and minor quinones were Q8 (4 %) and Q10 (3 %). The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and phosphatidylserine, two unidentified aminolipids, two unidentified phospholipids and two unidentified lipids. The genomic DNA G+C content was 59.1 mol%. The level of the ANI value between strain X49T and K. marisflavi SW32T, the most closely related species of the genus Kushneria, was 89.32 %. Based on the low ANI value, strain X49T and its reference strains represent genotypically distinct species. Based on this polyphasic taxonomic analysis, strain X49T represents a novel species of the genus Kushneria. The name Kushneria konosiri sp. nov. is proposed and the type strain is X49T (=KACC 14623T=JCM 16805T).

Influence of lithosphere and basement properties on the stretching factor and development of extensional faults across the Otway Basin, southeast Australia

The NW-SE striking Otway Basin in southeastern Australia is part of the continental rift system that formed during the separation of Australia from Antarctica. The development of this sedimentary basin occurred in two phases of Late Jurassic-Early Cretaceous and Late Cretaceous rifting. The evolution of this basin is mainly associated with extensional processes that took place in a pre-existing basement of Archean, Proterozoic to Paleozoic age. In this study, the total amounts of extension and stretching factor (β factor) have been measured for six transects across the entire passive margin of the Otway Basin region. The results show significant variation in extensional stretching along the basin, with the smallest stretching factors in the easternmost (β = 1.73, 1.9) and westernmost part of the basin (β = 2.09), and the largest stretching factors in the central part (β = 2.14 to 2.44). The domain with the lowest β factor is underlain mostly by thicker lithosphere of the Delamerian Orogen and older crustal fragments of the Selwyn Block. In contrast, the region with the largest β factor and amount of extension is related to younger and thinner lithosphere of the Lachlan Orogen. The main basement structures have been mapped throughout eastern South Australia and Victoria to examine the possible relationships between the younger pattern of extensional faults and the older basement fabrics. The pattern of normal faults varies considerably along onshore and offshore components of the Otway Basin from west to east. It appears that the orientation of pre-existing structures in the basement has some control on the geometry of the younger normal faults across the Otway Basin, but only in a limited number of places. In most areas the basement fabric has no control on the younger faulting pattern. Basement structure such as the north-south Coorong Shear Zone seems to affect the geometry of normal faults by changing their strike from E-W to NW-SE and also, in the easternmost part of the basin, the Bambra Fault changes the strike of normal faults from NW-SE to the NE-SW. Our results imply that the properties of the continental lithosphere exert a major influence on the β factor and amount of crustal extension but only a minor influence on the geometry of extensional faults.

Echinicola sediminis sp. nov., a marine bacterium isolated from coastal sediment.

A novel Gram-stain-negative, rod-shaped, gliding bacterium, designated strain 001-Na2T, was isolated from coastal sediment of the Yellow Sea in Sindu-ri, Republic of Korea. Cells were aerobic, oxidase-positive and catalase-positive. Colonies were dark salmon-coloured, circular, and pulvinate with entire margins. 16S rRNA gene sequence analysis revealed that strain 001-Na2T belonged to the genus Echinicola and these species formed a distinct lineage within the family Cyclobacteriaceae. The closest phylogenetic neighbours were 'Echinicola shivajiensis' AK12T (98.1 % 16S rRNA gene sequence similarity), Echinicola vietnamensis LMG 23754T (96.4 %), Echinicola jeungdonensis HMD 3054T (96.0 %), Echinicola pacifica KMM 6172T (96.0 %) and Echinicola rosea JL 3085T (95.8 %). The predominant respiratory quinone was menaquinone MK-7. The major fatty acids were iso-C15 : 0, summed feature 3 (comprising C16 : 1ω7c and/or C16 : 1ω6c), C17 : 1ω6c and summed feature 9 (comprising iso-C17 : 1ω9c and/or 10-methyl C16 : 0). The polar lipids were phosphatidylethanolamine, one unidentified aminophospholipid, one unidentified phospholipid and three unidentified lipids. The DNA G+C content was 44.6 mol%. DNA-DNA relatedness between strain 001-Na2T and 'E. shivajiensis' JCM 17847T was 20.8-21.1 %. On the basis of the phenotypic features, and phylogenetic and DNA-DNA hybridization analyses presented, strain 001-Na2T (=KCTC 52495T=JCM 31786T=DSM 103729T) is the type strain of a novel species of the genus Echinicola, for which the name Echinicola sediminis sp. nov. is proposed.

Oceanospirillum sanctuarii sp. nov., isolated from a sediment sample.

A novel Gram-staining-negative, spiral-shaped, pale-yellow, non-sporulating, motile, aerobic bacterium, designated strain AK56T, was isolated from a sediment sample collected at the Coringa Wildlife Sanctuary, India. Colonies on marine agar were circular, pale yellow, shiny, translucent, 1-2 mm in diameter, convex and had an entire margin. The major fatty acids included C16 : 1, C16 : 1ω7c/C16 : 1ω6c and C18 : 1ω7c. Polar lipids included diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, two unidentified aminolipids, one unidentified phospholipid and five unidentified lipids. DNA-DNA hybridization between strain AK56T and Oceanospirillum linum LMG 5214T and 'Oceanospirillum nioense ' NIO-S6 showed relatedness values of 39.91 and 23.62 %, respectively. The DNA G+C content of strain AK56T was found to be 50.3 mol%. A sequence similarity search for the 16S rRNA gene sequence revealed that O. linum and O. nioense were the nearest phylogenetic neighbours, with a pair-wise sequence similarity of 98.9 and 98.2 %, respectively. Phylogenetic analysis also showed the formation of a cluster including strain AK56T with close relative O. linum and O. nioense. Based on the observed phenotypic, chemotaxonomic characteristics and phylogenetic analysis, strain AK56T is described in this study as a novel species in the genus Oceanospirillum, for which the name Oceanospirillum sanctuarii sp. nov. is proposed. The type strain of Oceanospirillumsanctuarii is AK56T (=MTCC 12005T=JCM 19193T=KCTC 52973T).

New Haemoproteus parasite of parrots, with remarks on the virulence of haemoproteids in naive avian hosts

Haemoproteus infections can cause fatal disease in parrots (Psittaciformes), one of the most endangered groups of birds. The great diversity of parrots in tropical and subtropical ecosystems has been markedly understudied in terms of their parasite diversity. Only two psittacine Haemoproteus species have been described. Here we report a new Haemoproteus parasite, H. (Parahaemoproteus) homohandai n. sp. (lineage hARCHL01) found in erythrocytes of a Red-and-green macaw Ara chloropterus. We morphologically and genetically characterize the parasite based on a segment of the mitochondrial cytochrome b gene, which can be used for identification and diagnosis of infection. This is the first Haemoproteus species described from South American parrots and the first genetically characterized psittacine Haemoproteus sp. Haemoproteus homohandai n. sp. can be readily distinguished from other haemoproteids by its growing circumnuclear and close to circumnuclear macrogametocytes, which are strictly associated with erythrocyte nuclei, but do not touch the erythrocyte envelope along their entire margin and do not fill erythrocytes up to their poles. Illustrations of growing and mature gametocytes of the new species are given, and a phylogenetic analysis identifies the position of this parasite lineage in relation to other Haemoproteus parasites. Importantly, H. homohandai n. sp. and all other Haemoproteus lineages reported from parrots cluster with species of the subgenus Parahaemoproteus, indicating the transmission by Culicoides biting midges.

New data on the deep structure of the South Kochkor zone of concentrated deformation

Based on a complex study of the upper crust structure in the southern margin of Kochkor basin (Northern Tien Shan), including study of the structure of the Cenozoic sedimentary cover, the deep geoelectrical structure, the structural unconformities, and occurrences of recent deformations in the basement rocks, new geological–geophysical cross sections are constructed. The cross sections show both fault structures that penetrate the cover from the basement and flat interplate detachments with related fold-overthrust structures. The comparison of the cross sections has established the absence of common planes of fault extensions along the entire margin of the hollow, except for the zone where the margin and the hollow adjoin, which can be caused by the zones of dynamic influence of secondary faults, the zones of fracturing, and the zones of cataclasis of blockwise disintegrated granite massifs.

A new species of Cyclolejeunea (Marchantiophyta: Lejeuneaceae) from the Chocó, Colombia

Cyclolejeunea is a small neotropical genus of six species and a common epiphyllous hepatic in lowland and montane rainforests. We describe the new species Cyclolejeunea glimeana M.E.Reiner & Gradst. from wet lowland rainforest along the Pacific coast of Colombia (Chocó). The new species is characterized by the absence of innovations, entire leaf margins, leaf lobules without any indication of a tooth, and ligulate, thalloid gemmae without rhizoids. The combination of morphological characters seen in C. glimeana sets this species well apart from the remaining members of the genus and warrants its placement in a separate subgenus, C. subg. Chocolejeunea M.E.Reiner & Gradst. subg. nov. Ecologically, the new species stands out by its preference for palm trunks. The new species is a further addition to the unusually rich flora of the Chocó region.

Pharmacognostic Evaluation and Analgesic Efficacy of Ethanolic Extract of Euphorbia dracunculoides L.

Background: Euphorbia dracunculoides L is available in market in raw form. It is used by people for the treatment of warts, snake bite and epilepsy. Present study is about Euphorbia dracunculoides L. belonging to the family Euphorbiaceae, comprises pharmacognostic study, physiochemical analysis and their pharmacological efficacy. Materials and Methods: The macroscopic study was carried out through sensory organs like size, shape, texture etc. Physiochemical analysis was carried out through proper procedure from relevant literature, and analgesic activity was done through proper method by following literature. Results: Macroscopic study showed that the plant is an annual herb, stem is branched from the base, yellow green at the bottom and light green at the top, glabrous, smooth, contains white latex, its leaves are sessile, alternate, dark green, simple, stipulated, sub-acute or acute at the apex and entire margin. Root is yellowish in colour, conical in shape, smooth texture, downward in position. Powder drug study which was performed revealed various structures. Phytochemical screening includes both qualitative and quantitative analysis which was carried out indicated the presence of carbohydrates, proteins, saponins, sterols, alkaloids, phenolic compounds, glycosides, flavonoids and tannins. Proximate analysis showed proteins, crude fat, crude fibre, carbohydrates, moisture contents and ash. Elemental analysis revealed the presence of macro and micronutrients i-e Na, Zn, Mg and Fe, Cu, Ag and Au. Analgesic effect was dose dependent. Plant extract showed maximum inhibition of writhing 1.66±0.32 (96.61%) at 300 μg/ml. Conclusion: The pharmacognostic study, physiochemical analysis and their pharmacological efficacy is helpful in the standardization of drug.

Neogene to Quaternary stratigraphic evolution of the Antarctic Peninsula, Pacific Margin offshore of Adelaide Island: Transitions from a non-glacial, through glacially-influenced to a fully glacial state

A detailed morphologic and seismic stratigraphic analysis of the continental margin offshore of Adelaide Island on the Pacific Margin of the Antarctic Peninsula (PMAP) is described based on the study of a regular network of reflection multichannel seismic profiles and swath bathymetry. We present an integrated study of the margin spanning the shelf to the continental rise, establish novel chronologic constraints and offer new interpretations on tectonic evolution and environmental changes affecting the PMAP. The stratigraphic stacking patterns record major shifts in the depositional style of the margin that outline three intervals in its evolution. The first non-glacial interval (Early Cretaceous to middle Miocene) encompasses a transition from an active to a passive margin (early Miocene). The second glacially-influenced interval (middle to late Miocene) is marked by pronounced aggradational sedimentary stacking and subsidence. Ice sheets advanced over the middle shelf of the margin at the end of this second interval, while the outer shelf experienced rare progradational events. The third, fully glaciated interval shows clear evidence of glacially dominated conditions on the margin. This interval divides into three minor stages. During the first stage (late Miocene to the beginning of the Pliocene), frequent grounded ice advances to the shelf break began, depositing an initial progradational unit. A major truncation surface marked the end of this stage, which coincided with extensive mass transport deposits at the base of the slope. During the second progradational glacial margin stage (early Pliocene to middle Pleistocene), stacking patterns record clearly prograding glacial sequences. The beginning of the third aggradational glacial margin stage (middle Pleistocene to present) corresponded to an important shift in global climate during the Mid-Pleistocene Transition. Morphosedimentary characteristics observed along the margin today began to develop during the latest Miocene but did not become fully established until sometime during the interval between the end of the Pliocene and middle Pleistocene. Between these two time intervals, the northeastward lateral migration of the Marguerite Trough also played a critical role in margin evolution, as it controlled ice sheet drainage pathways across the shelf, which in turn influenced development of slope and rise morphologies. Areas offshore from Adelaide Island differ from other areas of the PMAP due to changes in sedimentary processes that resulted from migration of the trough. This study confirms that the PMAP represents an exceptional locality for decoding, reconstructing and linking past tectonic and climatic changes. The study area specifically records not only the most relevant changes in depositional style, but also the relative importance of persistent along- and down-slope sedimentary processes. Our study approach can be extended to other areas and integrated with additional techniques to understand the evolution and the global linkages of the entire Antarctic continental margin and the ice sheets.