Benthic foraminiferal distributions in Chilean fjords: 47°S to 54°S

Surface sediment samples collected from the fjord region of southern Chile (47° to 54° South) were analyzed for benthic foraminifera. A total of 175 species were identified including agglutinated and calcareous benthic taxa. Hierarchical cluster analysis of the foraminiferal data resulted in the recognition of three distinct biofacies: inner-fjord, intermediate fjord and channel, and oceanic biofacies, geographically controlled by relative position between the Pacific Ocean and fjord heads. Similarity percentage (SIMPER) analysis identified key taxa in the definition of the biofacies that include Globocassidulina rossensis, Cassidulina laevigata and Bulimina notovata. Principal components analysis resulted in two principal components representing sediment size, and bottom water temperature and salinity.Regional distributions are strongly controlled by the oceanographic conditions influenced from the Pacific in the west and the glacial/freshwater input from the east. Localized distributions of foraminifera are controlled by conditions influenced by the physiography of the individual fjords and channels. The distribution of Chilean fjord foraminifera and their environmental associations are consistent with results from other temperate to high latitude fjord foraminiferal studies.     

Exploring nursery sites for oviparous chondrichthyans in the Southwest Atlantic (36°S–41°S)

The aim of this paper was to explore egg-laying areas of oviparous chondrichthyans occurring in the northern part of the Southwest Atlantic Ocean (36°S–41°S) at between 50 and 200 metres depth and the Mar del Plata Canyon (from 200 to 3447?m). A total of 515 capsules were collected corresponding to 10 species. Four species accounted for 87.6% of the total catch: Psammobatis normani, Bathyraja macloviana, Amblyraja doellojuradoi and Bathyraja brachyurops. The remaining corresponded to Schroederichthys bivius, Psammobatis rudis, Zearaja chilensis, Bathyraja albomaculata, Psammobatis lentiginosa and Bathyraja sp. Most hauls were monospecific and relatively few hauls contained four or five species (southern part of the area, in sites located at 75 and 94–105?m depth). No egg capsules were recorded between 1712?m and 3447?m. Highest densities (>3000 capsules/km²) were mainly found between 39°46.2′ and 40°29.9′S from 85 to 105?m and they were also recorded near the Mar del Plata Canyon at 37°59.7′S and at 852?m. The highest value recorded was 12,326 capsules/km² (located at 40°18.9′S and 85.4?m). The highest densities for each of the most abundant species are discussed. The finding of high densities of egg cases near the Argentine shelf-break front indicates that many skate species use this area as a nursery site. The egg-laying areas explored here are the first reported sites of this kind in the Southwest Atlantic Ocean. Recognizing and protecting egg-laying habitats may be important steps to a long-term conservation of oviparous chondrichthyan populations.     

Reproductive biology of Rioraja agassizi from the coastal southwestern Atlantic ecosystem between northern Uruguay (34°S) and northern Argentina (42°S)

A total of 552 individuals of Rioraja agassizi (257 females and 295 males) were collected by bottom-trawl during research cruises. Sexual dimorphism was observed with females are heavier than males for a given total length (TL). Using logistic regression, it was determined that TL at 50% maturity of males was 475 mm TL and of females 520 mm TL. This estimation agrees with the morphological parameters measured. Although not statistically significant, a peak in reproductive activity was observed in males during late spring and summer. The monthly variation in the gonadosomatic index and oviducal gland width, together with the largest diameter of ovarian follicles, suggests that R. agassizi females have a partially defined annual reproductive cycle with two peaks, one from November (spring) to February (summer) and another in July (winter).     

Discovery of new hydrothermal activity and chemosynthetic fauna on the Central Indian Ridge at 18°-20° S

Indian Ocean hydrothermal vents are believed to represent a novel biogeographic province, and are host to many novel genera and families of animals, potentially indigenous to Indian Ocean hydrothermal systems. In particular, since its discovery in 2001, much attention has been paid to a so-called 'scaly-foot' gastropod because of its unique iron-sulfide-coated dermal sclerites and the chemosynthetic symbioses in its various tissues. Despite increasing interest in the faunal assemblages at Indian Ocean hydrothermal vents, only two hydrothermal vent fields have been investigated in the Indian Ocean. Here we report two newly discovered hydrothermal vent fields, the Dodo and Solitaire fields, which are located in the Central Indian Ridge (CIR) segments 16 and 15, respectively. Chemosynthetic faunal communities at the Dodo field are emaciated in size and composition. In contrast, at the Solitaire field, we observed faunal communities that potentially contained almost all genera found at CIR hydrothermal environments to date, and even identified previously unreported taxa. Moreover, a new morphotype of 'scaly-foot' gastropod has been found at the Solitaire field. The newly discovered 'scaly-foot' gastropod has similar morphological and anatomical features to the previously reported type that inhabits the Kairei field, and both types of 'scaly-foot' gastropods genetically belong to the same species according to analyses of their COI gene and nuclear SSU rRNA gene sequences. However, the new morphotype completely lacks an iron-sulfide coating on the sclerites, which had been believed to be a novel feature restricted to 'scaly-foot' gastropods. Our new findings at the two newly discovered hydrothermal vent sites provide important insights into the biodiversity and biogeography of vent-endemic ecosystems in the Indian Ocean.     

Planktic foraminifera from the southwestern Atlantic (30 °–60 °S): species-specific patterns in the upper 50 m

Planktic foraminifers were studied in 96 samples collected in the southwestern Atlantic (30 °–60 °S, along 53 °W) in November 1993, mainly from depths between 0 and 50 m. Very high proportions of juveniles (unidentified) were present throughout the area, especially north of 37 °S, where they accounted for up to 70–80% of all shells recorded. For most species no clear vertical specific stratification was detected in the 0–50 m layer. Zoogeographic grouping of the 18 species identified allowed the defining of 5 distinct zones along the transect: Subtropical (north of 31 °S, 80% warm water individuals); Warm-Transitional (34 °–37 °S, 35% warm water); Transitional (37 °–49 °S, 99% cold water); Subantarctic (49–55 °S, 100% cold water); and Antarctic (south of 56 °S, 100% cold water). Boundaries between foraminiferal assemblage zones are in good agreement with hydrological fronts described for the area. Comparison of the present data with planktic collections from the North Atlantic show large differences in the proportions of various taxa. In the 14–24 °C range, G. bulloides is much more abundant in the northern hemisphere than in the southern one, whereas G. quinqueloba G. inflata and G. rubescens show the opposite trend. On the other hand, temperature-related percentage contributions within the 14 °–24 °C range indicate that the preferred thermic régimes of the 9 species considered are remarkably similar in the North and South Atlantic collections compared. The southernmost planktic distributional ranges of selected warm water taxa are roughly coincident with those established previously on the basis of surface sediments, disagreements being chiefly attributable to selective dissolution on the bottom. In contrast, at the bottom percentages of cold water foraminifers (G. bulloides G. pachyderma) are significantly enhanced with respect to their planktic populations, and their sedimentary northward limits extend well beyond their maximum ranges in the upper-layer plankton. It is suggested that submergence of these cold water species and northward displacement at subsurface depths is chiefly responsible for the mismatching patterns observed. Dissimilar species proportions in both hemispheres and plankton-sediment uncoupling can conceivably engender erroneous conclusions when distributional data are used for paleoecologic reconstructions with the aid of numerical analyses such as the Imbrie-Kipp transfer-function technique.     

Spatial-temporal variability of ultraplankton vertical distribution in the Antarctic frontal zones within 60–66°E, 43–46°S

The vertical distribution of heterotrophic bacteria and four ultraphytoplanktonic (<10 µm) groups (Prochlorococcus, Synechococcus, pico- and nanoeukaryotes) was investigated by flow cytometry at three process stations located in three different sub-systems belonging to the Antarctic Circumpolar Current frontal zone and to the Southern Indian Ocean (60–66°E, 43–46°S; ANTARES 4 cruise, January-February 1999): the Subtropical Zone (STZ), the Convergence Zone and the Polar Frontal Zone (PFZ). In each sub-system, short-term variability of cell abundance and flow cytometric parameters (right-angle light scatter and chlorophyll autofluorescence) was assessed through a times series of up to 24 h with a 2 h sampling frequency. The ultraphytoplankton vertical distribution exhibited a high spatial variability, with dominance of Prochlorococcus in the STZ (mean: 762.85×10¹⁰ cells m^–2), whereas picoeukaryotes (<3 µm) were dominant in the PFZ (55.46×10¹⁰ cells m^–2), a typically high-nutrient low-chlorophyll zone. Heterotrophic bacteria abundance was maximum (9.84×10¹³ cells m^–2) in the frontal zone, between the Agulhas Front and the Subtropical Front. Nanoeukaryotes showed the largest (up to 80%) variations between two consecutive sampling periods (2 h). Abundance variations could not be assigned to the same water mass during the time series due to the highly variable hydrodynamics of the study area. Trends of short-term abundance variations were opposite between the PFZ (lowest at night) and north of the Subtropical Front (highest at night). The observed spatial and short-term variations illustrate the complexity of the water masses in the Indian sector of the Southern Ocean, and highlight the challenge of extrapolating discrete measurements over space and time for use in evaluating carbon budgets in such dynamic areas.     

Climatic dependency of soil organic carbon isotopic composition along the S–N Transect from 34°N to 52°N in central-east Asia

We explored the relationships between surface-soil (1–20 cm) organic carbon isotopic signatures and associated climatic factors in central-east Asia in an attempt to develop transfer functions that can be used to retrieve the paleoclimatic information stored in the thick eolian–paleosol sequences within the area. Our analysis shows that the negative correlation between the surface-soil organic δ¹³C values and the mean annual precipitation is robust (R² = 0.453; n = 196; p < 0.05) and the negative correlation with the growing-season (April–September) precipitation is more significant (R² = 0.4966; n = 196; p < 0.05). Our study further shows that the positive correlation between the surface-soil organic δ¹³C values and mean growing-season aridity is most significant (R² = 0.5805; n = 196; p < 0.05). We have smoothed both the organic δ¹³C values and the mean growing-season aridity values using a 3-point moving-window average-filter method in an attempt to remove some of random errors and found that the positive correlation between the two is further increased (R² =  0.7784; n =  192; p < 0.05). These robust linear relationships demonstrate their value in reconstructing paleoclimate changes in the study area. The documented climatic dependency of the surface-soil carbon isotopic composition in the study area might have resulted both from the humidity-related isotopic enrichment processes of the dominant C₃ plants (stomatal conductance and photosynthetic discrimination) and from the aridity-related abundance of C₄ plants (mainly Chenopodiaceae species) along the S–N bioclimatic gradient.     

Einfluß der Fixierung und der Säurekonzentration auf die Feulgen-Hydrolyse bei 28° C

Zusammenfassung Es wurde eine für Routinezwecke geeignete Feulgenreaktion für die cytophotometrische DNS-Bestimmung ausgearbeitet, die gegen geringe Schwankungen der Temperatur, der Säurekonzentration und der Zeitdauer der HCl-Hydrolyse weniger empfindlich ist als die 60°-Standardhydrolyse. Dazu wurden die Feulgen-Hydrolysekurven von alkohol-, formalin- und methanol-formalin-eisessigfixierten Hühnererythrocyten nach Behandlung mit 5 N, 4 N und 2 N HCl bei 28° C, bzw. mit 1 N HCl bei 60° C geprüft und miteinander verglichen. Als besonders brauchbar erwies sich die Fixierung mit 70%igem Isopropylalkohol (20 min Hydrolyse in 5 N HCl oder 45 min in 4 N HCl) und die MethanolFormalin-Eisessig-Fixierung (105 min Hydrolyse in 4 N HCl). Reine Formalinfixierung erwies sich als ungeeignet, da eine starke Kernschrumpfung mit Extinktionen größer als 0,75 beobachtet wurden.An alkoholfixierten Leberzellausstrichen wurde ein gleichartiger Verlauf der Hydrolysekurven von di-, tetra- und oktoploiden Leberzellkernen festgestellt. Die relativen Farbstoffmengen (AE-Werte) dieser Kerne verhielten sich bei allen geprüften Hydrolysezeiten wie 124.

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Influence of fixation and add concentration on the Feulgen hydrolysis at 28° C

Summary A routine Feulgen procedure for quantitative cytophotometric absorption measurements of DNA at the integrating microdensitometer should be established, which is less alterable by minor deviations in temperature, acid concentration and in duration of hydrolysis than is the 60° C standard treatment. Feulgen hydrolysis curves of alcohol-, formalin- and methanol-formalin-glacialacidicacid-fixed fowl erythrocytes have been examined after hydrolysis in 5 N, 4 N and 2 N HCl at 28° C, as well as in 1 N HCl at 60° C. Fixation in 70% isopropylalcohol and hydrolysis in 5 N HCl for 20 minutes or in 4 N HCl for 45 minutes proved to be particularly useful. Fixation in a mixture of 85% methanol, 10% formalin and 5% glacialacidicacid gave good results, too, but hydrolysis time had to be chosen considerably longer for maximum staining (105 minutes in 4 N HCl). Formalin fixation proved not to be suitable because of a considerable shrinkage of the nuclei resulting in extinctions well above 0.75.Identical hydrolysis curves have been obtained for di-, tetra- and octoploid liver cell nuclei from alcohol-fixed liver smears. The relative dye contents (AE-values) of these nuclei were in the ratio 124 at all hydrolysis times examined.

     

Human exposure to ultraviolet radiation at the Antipodes – a comparison between an Antarctic (67°S) and Arctic (75°N) location

. We used ultraviolet radiation dosimeters to investigate human exposure at two polar latitudes with a 24-h photoperiod: at Rothera Station (UK) (67°S) and at a field camp in the Haughton impact structure in the Canadian High Arctic (75°N). Mean personal UV radiation exposure in the Antarctic location was 4.3 times greater than that in the Arctic location, even in the absence of ozone depletion. More than zenith angle accounted for the higher UV exposure. Widespread snow and ice covers, and probably less atmospheric pollution, caused higher personal exposures. Although the mean exposures were higher in the Antarctic location, the mean exposure ratio in the Antarctic (0.20ǂ.09) was similar to the value measured in the Arctic (0.27ǂ.09) on clear days. We use the Antarctic ratio to provide quantitative estimates of UV-radiation exposure for workers at the Geographical South Pole for the winter solstice under a constant 24-h photoperiod. Exposure ratios can be used to translate measurements of UV radiation by horizontally fixed spectroradiometers into estimates of the mean exposures expected in populations at polar latitudes, although variations between individuals are large. The data have implications for determining the UV exposures of indigenous high-latitude populations.     

The hERG K(+) channel S4 domain L532P mutation: characterization at 37°C

hERG (human Ether-à-go-go Related Gene) is responsible for ion channels mediating rapid delayed rectifier potassium current, I(Kr), which is key to cardiac action potential repolarization. Gain-of-function hERG mutations give rise to the SQT1 variant of the Short QT Syndrome (SQTS). Reggae mutant zebrafish, with a S4 zERG mutation (Leucine499Proline; L499P), display arrhythmic features analogous to those seen in the SQTS. The affected S4 domain ERG residue is highly conserved. This study was executed to determine how the homologous hERG mutation (L532P) influences channel function at 37°C. Whole-cell measurements of current (I(hERG)) were made from HEK 293 cells expressing WT or L532P hERG. The half maximal activation voltage (V(0.5)) of L532P I(hERG) was positively shifted by ~+36mV compared to WT I(hERG); however at negative voltages a pronounced L532P I(hERG) was observed. Both activation and deactivation time-courses were accelerated for L532P I(hERG). The inactivation V(0.5) for L532P I(hERG) was shifted by ~+32mV. Under action potential (AP) voltage-clamp, L532P I(hERG) exhibited a dome-shaped current peaking at ~+16mV, compared to ~-31mV for WT-I(hERG). The L532P mutation produced an ~5-fold increase in the IC(50) for dronedarone inhibition of I(hERG). Homology modeling indicated that the L532 residue within the S4 helix lies closely apposed to the S5 region of an adjacent hERG subunit. Alterations to the S4 domain structure and, potentially, to interactions between adjacent hERG subunits are likely to account for the functional effects of this mutation.     

Metabolic differences inBacillus stearothermophilus grown at 55°C and 37°C

Summary Bacillus stearothermophilus was adapted to grow at 55°C and 37°C in a complex medium with almost equivalent yields in cell mass. In both temperature ranges the maximum specific growth rates (μ_max) were identical. Cellular extracts of this bacterium showed remarkable differences in the activity levels of several enzymes, depending on the respective growth temperature. High activities of glyceraldehyde-3-phosphate dehydrogenase and alcohol dehydrogenase were observed in bacteria from thermophilic cultures (55°C) and the respiratory quotient exceeded 1.0. Under anaerobic conditions at 55°C μ_max was the same as in aerobic cultures. No alcohol dehydrogenase was detected in cells from mesophilic cultures (37°C), however, and the level of glyceraldehyde-3-phosphate dehydrogenase was also extremely low under mesophilic conditions. Succinate dehydrogenase and isocitrate dehydrogenase activity appeared to be higher in bacteria grown at 37°C; the resspiratory quotient was always lower than 1.0. At 37°C, acetoin formation was observed regularly, a fermentation product which was never detected in 55°C-cultures. Under anaerobic conditions at 37°C a very low growth rate was found. When adapted to grow at 37°C or 55°C,B. stearothermophilus is apparently able to use different catabolic systems.     

Eating catch of the day: the diet of porbeagle shark Lamna nasus (Bonnaterre 1788) based on stomach content analysis,and the interaction with trawl fisheries in the south-western Atlantic (52° S–56° S)

This work examined the diet of the porbeagle shark Lamna nasus in the south-west Atlantic Ocean (SWAO, Argentina, 52° S–56° S) by analysing the stomach content information obtained by scientific observers who sampled specimens captured as by-catch on-board commercial fishing vessels from 2010 to 2020. A total of 148 fishing sites were analysed, in which the estimated catch was composed mainly of hoki Macruronus magellanicus (56.00%) and southern blue whiting Micromesistius australis (33.13%). From 413 porbeagle sharks sampled (292 females and 121 males) ranging from 71 to 241 cm total length (L_T) (mean: 179.76 ± 26.74 cm), 310 (75.06%) contained food in the stomachs. The forage fish were mainly hoki M. magellanicus (23.53%) and southern blue whiting M. australis (19.05%), followed by the Patagonian sprat Sprattus fuegensis (4.48%) and nototheniids (1.4%). Cephalopods and crustaceans accounted for 10% of the diet. The estimated trophic level was 4.35. Generalized linear models revealed that the consumption of hoki M. magellanicus and southern blue whiting M. australis increased with the L_T of the porbeagle shark. Moreover, smaller porbeagle sharks preyed upon both small and large teleost fish, whereas larger porbeagle sharks predated exclusively upon large fish. The diet of porbeagle shark involved interactions with fisheries as it fed upon the fish species that constituted the main catch in the analysed fishing sites, as well as the main catches of the austral trawl fisheries. The ecological role of porbeagle shark observed in the SWAO exposed implications for fisheries management from a multispecies perspective.     

α°- and β°- Thalassemia in a Thai family: unusually mild homozygous β°-thalassemia without α-globin gene deletion

Summary Alpha-globin genes were analyzed by the direct method of DNA mapping using - and -globin specific probes in a Thai family in which the proposita was an unusually mild °-thalessemia homozygote. °-Thalessemia was found to be segregating in the family, inherited from the proposita's father by one of her younger sisters. However, °-thatlessemia was not detected by this DNA mapping in the proposita. The mild homozygous °-thalessemia in this family may result from interactions of a non-deletion -thalassemia, a gene responsible for high proteolytic activity permitting more balanced globin-chain levels, or from an unusually active hemoglobin F production in the proposita.     

Low cyanobacterial diversity in biotopes of the Transantarctic Mountains and Shackleton Range (80-82°S), Antarctica

The evolutionary history and geographical isolation of the Antarctic continent have produced a unique environment rich in endemic organisms. In many regions of Antarctica, cyanobacteria are the dominant phototrophs in both aquatic and terrestrial ecosystems. We have used microscopic and molecular approaches to examine the cyanobacterial diversity of biotopes at two inland continental Antarctic sites (80-82°S). These are among the most southerly locations where freshwater-related ecosystems are present. The results showed a low cyanobacterial diversity, with only 3-7 operational taxonomic units (OTUs) per sample obtained by a combination of strain isolations, clone libraries and denaturing gradient gel electrophoresis based on 16S rRNA genes. One OTU was potentially endemic to Antarctica and is present in several regions of the continent. Four OTUs were shared by the samples from Forlidas Pond and the surrounding terrestrial mats. Only one OTU, but no internal transcribed spacer (ITS) sequences, was common to Forlidas Pond and Lundstr?m Lake. The ITS sequences were shown to further discriminate different genotypes within the OTUs. ITS sequences from Antarctic locations appear to be more closely related to each other than to non-Antarctic sequences. Future research in inland continental Antarctica will shed more light on the geographical distribution and evolutionary isolation of cyanobacteria in these extreme habitats.     

Biases in determining the diet of jumbo squid <Emphasis Type="Italic">Dosidicus gigas</Emphasis> (D’ Orbigny 1835) (Cephalopoda: Ommastrephidae) off southern-central Chile (34°S–40°S)

The diet of jumbo squid (Dosidicus gigas) off southern-central Chile is described to examine potential biases in the determination of their main prey. Specimens were collected from catches using different fishing gear (jigging, trawl and purse-seine), from July 2003 to January 2004, and from December 2005 to October 2006. The stomach contents were analyzed in terms of frequency of occurrence, number, and weight of prey items and the diet composition was analyzed using Detrended Correspondence Analysis. In the industrial purse-seine fleet for jack mackerel (Trachurus murphyi), the dominant prey of D. gigas was T. murphyi. In the industrial mid-trawl fishery for Patagonian grenadier (Macruronus magellanicus), the dominant species in the diet of D. gigas was M. magellanicus. Similarly, Chilean hake (Merluccius gayi) was the main prey in the diet of D. gigas obtained in the industrial trawl fishery for Chilean hake; and, in both artisanal fisheries (purse-seine for small pelagics and jigging), small pelagic fish and D. gigas were the main prey in the stomach contents of D. gigas. Cannibalism in D. gigas varied between different fleets and probably is related to stress behavior during fishing. The Detrended Correspondence Analysis ordination showed that the main prey in the diet of D. gigas is associated with the target species of the respective fishery. Consequently, biases are associated with fishing gear, leading to an overestimate in the occurrence of the target species in the diet. We recommend analyzing samples from jigging taken at the same time and place where the trawl and purse-seine fleets are operating to avoid this problem, and the application of new tools like stable isotope, heavy metal, and fatty acid signature analyses.     

Survival of mouse oocytes after being cooled in a vitrification solution to -196°C at 95° to 70,000°C/min and warmed at 610° to 118,000°C/min: A new paradigm for cryopreservation by vitrification

There is great interest in achieving reproducibly high survivals of mammalian oocytes (especially human) after cryopreservation, but the results to date have not matched the interest. A prime cause of cell death is the formation of more than trace amounts of intracellular ice, and one strategy to avoid it is vitrification. In vitrification procedures, cells are loaded with high concentrations of glass-inducing solutes and cooled to −196 °C at rates high enough to presumably induce the glassy state. In the last decade, several devices have been developed to achieve very high cooling rates. Nearly all in the field have assumed that the cooling rate is the critical factor. The purpose of our study was to test that assumption by examining the consequences of cooling mouse oocytes in a vitrification solution at four rates ranging from 95 to 69,250 °C/min to −196 °C and for each cooling rate, subjecting them to five warming rates back above 0 °C at rates ranging from 610 to 118,000 °C/min. In samples warmed at the highest rate (118,000 °C/min), survivals were 70% to 85% regardless of the prior cooling rate. In samples warmed at the lowest rate (610 °C/min), survivals were low regardless of the prior cooling rate, but decreased from 25% to 0% as the cooling rate was increased from 95 to 69,000 °C/min. Intermediate cooling and warming rates gave intermediate survivals. The especially high sensitivity of survival to warming rate suggests that either the crystallization of intracellular glass during warming or the growth by recrystallization of small intracellular ice crystals formed during cooling are responsible for the lethality of slow warming.     

Phospholipid metabolism in Mycobacterium smegmatis ATCC 607 grown at 37° C and 27° C

The rate of synthesis and degradation of phospholipids in Mycobacterium smegmatis ATCC 607, grown at 27° C and 37° C was studied by incorporation of ³²P into phospholipids and chase of radioactivity of the pulse-labelled phospholipids. A relatively low rate of synthesis and degradation of phospholipids in cells growth at 27° C was observed as compared to those grown at 37° C. Phosphatidylethanolamine (PE) had the maximum turnover at 37° C. However, at 27° C, cardiolipin (CL) showed a turnover rate higher than PE. Phosphatidylinositol mannosides (PIMs) were metabolically more active at 37° C than at 27° C. The differences in metabolic activity of the phospholipids at the two temperatures have been discussed.     

Late Pleistocene and Holocene palaeoenvironmental changes in central Tierra del Fuego (~54°S) inferred from pollen analysis

A pollen record was obtained from a coring site at La Correntina mire (54°33′S, 66°59′W, 206 m a.s.l.) to the east of Lago Fagnano, centre of Tierra del Fuego. The results indicate that the valley bottom was free of ice shortly before 15,400 cal bp. Pioneer vegetation included dwarf shrub heaths, grasses and herbs with sparsely distributed Nothofagus trees, indicative of dry conditions. Nothofagus expanded by 10,000 cal bp and the forest-steppe ecotone was established by 9,400 cal bp, implying warm conditions and an increase in available moisture. After ca. 5,000 cal bp, the development of a closed-canopy forest is interpreted as the result of wetter and colder conditions. After 3,000 cal bp, Nothofagus forest became more open, and by about 400 cal bp there was a further decline of the forest. A closed-canopy Nothofagus forest re-established after 400 cal bp.     

O.S.S浅谈

Oncology Support System是荷兰PHI LIPS公司O.S.S的全称。这是一台在Treatment Planning System(T.P.S治疗计划系统)基础上发展而成、辅助CT诊断、设计三维放射治疗的专用计算机系统。我院放射治疗科于84年完成了SL 75—20医用电子直线加速器、模拟定位机、O.S.S等设备的安装