Colonisation and development in encrusting communities from the Antarctic intertidal and sublittoral

first_imgA total of 985 rocks with a wide range of surface areas were examined from six locations at Signy Island in the maritime Antarctic. The shallowest site was intertidal and the deepest at 42 m. The probability of coralline algae occurring was found to increase with surface area and depth of rocks, implying decreased levels of turnover or physical disturbance with increasing rock size and depth. Percent area colonised, number of animal phyla, bryozoan species and bryozoan colonies all increased both with rock surface area and depth. The largest rocks in the intertidal had broadly similar levels of colonisation and community development as did the smallest at 42 m. Thus, because of depth-dependent ice-scour, community development in the Antarctic sublittoral may be followed along a pseudo-time sequence by using two axes (substratum size and depth) of environmental stability. Frequent disturbance appears to be responsible for maintaining the level of diversity and preventing monopolisation. Bryozoans and polychaetes were the most abundant encrusting animal groups, although tunicates and sponges were the dominant overgrowth competitors. The faunal elements of the colonising biota were almost entirely confined to the undersurfaces of rocks whereas algae dominated upper surfaces. In most bryozoan species the proportion of colonies occurring on the upper surfaces of rocks increased with depth to 34 m and then decreased at 42 m where silt deposition apparently became a major influence. Such a shift in distribution may reflect decreasing current velocities, and therefore reduced disturbance to animal feeding, and/or decreasing growth of coralline algae due to reduced light availability.last_img read more

Climatology of short-period mesospheric gravity waves over Halley, Antarctica (76 S, 27 W)

first_imgWe present a first detailed climatological study of individual quasi-monochromatic mesospheric, shortperiodgravity-wave events observed over Antarctica. The measurements were made using an all-skyairglow imager located at Halley Station (76S, 27W) and encompass the 2000 and 2001 austral winterseasons. Distributions of wave parameters were found to be similar to findings at other latitudes. Thewave headings exhibited unusually strong anisotropy with a dominant preference for motion towardsthe Antarctic continent and a rotation from westward during fall, to poleward in mid-winter, toeastward in spring. This rotation was accompanied by a systematic increase of 50% in the magnitudesof the horizontal wavelengths and observed phase speeds. It is postulated that the observed waveanisotropy was due to a succession of wave sources of different characteristics lying equatorward ofHalley, or a dominant source mechanism evolving with time during the winter months.last_img read more

Impact of anthropogenic transportation to Antarctica on alien seed viability

first_imgAntarctic ecosystems are at risk from the introduction of invasive species. The first step in the process of invasion is the transportation of alien species to Antarctic in a viable state. However, the effect of long-distance human-mediated dispersal, over different timescales, on propagule viability is not well known. We assessed the viability of Poa trivialis seeds transported to Antarctica from the UK, South Africa and Australia by ship or by ship and aircraft. Following transportation to the Antarctic Treaty area, no reduction in seed viability was found, despite journey times lasting up to 284 days and seeds experiencing temperatures as low as -1.5A degrees C. This work confirms that human-mediated transport may overcome the dispersal barrier for some propagules, and highlights the need for effective pre-departure biosecurity measures.last_img read more

Geomagnetic activity related NOx enhancements and polar surface air temperature variability in a chemistry climate model: modulation of the NAM index

first_imgThe atmospheric chemistry general circulation model ECHAM5/MESSy is used to simulate polar surface air temperature effects of geomagnetic activity variations. A transient model simulation was performed for the years 1960-2004 and is shown to develop polar surface air temperature patterns that depend on geomagnetic activity strength, similar to previous studies. In order to eliminate influencing factors such as sea surface temperatures (SST) or UV variations, two nine-year long simulations were carried out, with strong and weak geomagnetic activity, respectively, while all other boundary conditions were held to year 2000 levels. Statistically significant temperature effects that were observed in previous reanalysis and model results are also obtained from this set of simulations, suggesting that such patterns are indeed related to geomagnetic activity. In the model, strong geomagnetic activity and the associated NOx (=NO+NO2) enhancements lead to polar stratospheric ozone loss. Compared with the simulation with weak geomagnetic activity, the ozone loss causes a decrease in ozone radiative cooling and thus a temperature increase in the polar winter mesosphere. Similar to previous studies, a cooling is found below the stratopause, which other authors have attributed to a decrease in the mean meridional circulation. In the polar stratosphere this leads to a more stable vortex. A strong (weak) Northern Hemisphere vortex is known to be associated with a positive (negative) Northern Annular Mode (NAM) index; our simulations exhibit a positive NAM index for strong geomagnetic activity, and a negative NAM for weak geomagnetic activity. Such NAM anomalies have been shown to propagate to the surface, and this is also seen in the model simulations. NAM anomalies are known to lead to specific surface temperature anomalies: a positive NAM is associated with warmer than average northern Eurasia and colder than average eastern North Atlantic. This is also the case in our simulation. Our simulations suggest a link between geomagnetic activity, ozone loss, stratospheric cooling, the NAM, and surface temperature variability. Further work is required to identify the precise cause and effect of the coupling between these regions.last_img read more

Differences in the timing and extent of annual moult of black-browed albatrosses Thalassarche melanophris living in contrasting environments

first_imgMoult entails costs related to the acquisition of energy and nutrients necessary for feather synthesis, as well as the impact of reduced flight performance induced by gaps in the wing plumage. Variation in moult strategies within and between populations may convey valuable information on energetic trade-offs and other responses to differing environmental constraints. We studied the moult strategies of two populations of a pelagic seabird, the black-browed albatross Thalassarche melanophris, nesting in contrasting environments. According to conventional wisdom, it is exceptional for albatrosses (Diomedeidae) to moult while breeding. Here we show that black-browed albatrosses breeding on the Falklands regularly moult primaries, tail and body feathers during chick-rearing, and the majority of those at South Georgia show some body feather moult in late chick-rearing. The greater moult-breeding overlap at the Falklands allows the birds to annually renew more primary feathers than their counterparts at South Georgia. The results of the present paper, pooled with other evidence, suggest that black-browed albatrosses from South Georgia face a more challenging environment during reproduction. They also serve to warn against the uncritical acceptance of conventional ideas about moult patterns when using feathers to study the ecology of seabirds and other migrants for which there is scant information at particular stages of the annual cycle.last_img read more

The Amundsen Sea Low: Variability, change and impact on Antarctic climate

first_imgThe Amundsen Sea Low (ASL) is a climatological low pressure center that exerts considerable influence on the climate of West Antarctica. Its potential to explain important recent changes in Antarctic climate, for example in temperature and sea ice extent, means that it has become the focus of an increasing number of studies. Here, we summarize current understanding of the ASL, using reanalysis datasets to analyze recent variability and trends, and ice-core chemistry and climate model projections to examine past and future changes in the ASL, respectively. The ASL has deepened in recent decades, affecting the climate through its influence on the regional meridional wind field, which controls the advection of moisture and heat into the continent. Deepening of the ASL in spring is consistent with observed West Antarctic warming and greater sea ice extent in the Ross Sea. Climate model simulations for recent decades indicate that this deepening is mediated by tropical variability while climate model projections through the 21st century suggest that the ASL will deepen in some seasons in response to greenhouse gas concentration increases.last_img read more

Sensitivity of Pine Island Glacier to observed ocean forcing

first_imgWe present subannual observations (2009–2014) of a major West Antarctic glacier (Pine Island Glacier) and the neighboring ocean. Ongoing glacier retreat and accelerated ice flow were likely triggered a few decades ago by increased ocean-induced thinning, which may have initiated marine ice-sheet instability. Following a subsequent 60% drop in ocean heat content from early 2012 to late 2013, ice flow slowed, but by < 4%, with flow recovering as the ocean warmed to prior temperatures. During this cold-ocean period, the evolving glacier-bed/ice-shelf system was also in a geometry favorable to stabilization. However, despite a minor, temporary decrease in ice discharge, the basin-wide thinning signal did not change. Thus, as predicted by theory, once marine ice-sheet instability is underway, a single transient high-amplitude ocean cooling has only a relatively minor effect on ice flow. The long-term effects of ocean-temperature variability on ice flow, however, are not yet known.last_img read more

A previously undescribed Helotialean fungus that is superabundant in soil under maritime Antarctic higher plant

first_imgWe report a previously undescribed member of the Helotiales that is superabundant in soils at two maritime Antarctic islands under Antarctic Hairgrass (Deschampsia antarctica Desv.). High throughput sequencing showed that up to 92% of DNA reads, and 68% of RNA reads, in soils from the islands were accounted for by the fungus. Sequencing of the large subunit region of ribosomal (r)DNA places the fungus close to the Pezizellaceae, Porodiplodiaceae, and Sclerotiniaceae, with analyses of internal transcribed spacer regions of rDNA indicating that it has affinities to previously unnamed soil and root fungi from alpine, cool temperate and Low Arctic regions. The fungus was found to be most frequent in soils containing C aged to 1,000–1,200 years before present. The relative abundances of its DNA and RNA reads were positively associated with soil carbon and nitrogen concentrations and δ13C values, with the relative abundance of its DNA being negatively associated with soil pH value. An isolate of the fungus produces flask-shaped phialides with a pronounced venter bearing masses of conidia measuring 4.5–6(7) × 1.8–2.5 μm, suggestive of anamorphic Chalara. Enzymatic studies indicate that the isolate strongly synthesizes the extracellular enzyme acid phosphatase, and also exhibits alkaline phosphatase and naphthol-AS-BI-phosphohydrolase activities. Ecophysiological measurements indicate optimal hyphal growth of the isolate at a pH of 4.2–4.5 and a water potential of −0.66 MPa. The isolate is a psychrotroph, exhibiting measureable hyphal growth at −2°C, optimal hyphal extension rate at 15°C and negligible growth at 25°C. It is proposed that the rising temperatures that are predicted to occur in maritime Antarctica later this century will increase the growth rate of the fungus, with the potential loss of ancient C from soils. Analyses using the GlobalFungi Database indicate that the fungus is present in cold, acidic soils on all continents. We advocate further studies to identify whether it is superabundant in soils under D. antarctica elsewhere in maritime Antarctica, and for further isolates to be obtained so that the species can be formally described.last_img read more

Late Holocene seasonal temperature variability of the western Scottish shelf (St Kilda) recorded in fossil shells of the bivalve Glycymeris glycymeris

first_imgThe North Atlantic Ocean and adjacent shelf seas play a crucial role in global climate. To better constrain long-term natural variability and marine-terrestrial linkages in this region, a network of highly resolved marine archives from the open ocean and continental shelves is needed. In recent decades, bivalve sclerochronology has emerged as a field providing such records from the mid- to high latitudes. In May 2014, dead valves and young live specimens of the bivalve Glycymeris glycymeris were collected at St Kilda, Scotland. A floating chronology spanning 187 years was constructed with fossil shells and radiocarbon dated to 3910–3340 cal yr before present (BP), with a probability density cluster at ca. 3700–3500 cal yr BP. Sub-annual δ18O data were obtained from five fossil and three modern specimens and showed a strong seasonal signal in both time intervals. The growth season of G. glycymeris at this location today lasts from May to October, with most growth occurring before the temperature peak in August. Thus, the modern specimens and the fossil chronology represent late-spring and summer sea surface temperatures (SST). The annual temperature range was 4.4 °C in the fossil shells, which is similar to the range observed today (3.8 °C). Average SSTs reconstructed from the fossil shells were 1 °C cooler than in 2003–2013 CE and similar to the early 20th century CE. The radiocarbon age of the floating chronology coincides with a climatic shift to wetter conditions on the British Isles and with a cold interval observed in palaeoceanographic records from south of Iceland. However, our data do not provide evidence of a cold interval on the Scottish shelf. The similarity in growth season and temperature range between the fossil and modern specimens are attributed to similar boundary conditions in the fourth millennium BP compared to today.last_img read more

UVU Men’s Basketball Hosts Texas-Rio Grande Valley Thursday

first_img FacebookTwitterLinkedInEmailOREM, Utah-Thursday, Utah Valley University men’s basketball hosts Texas-Rio Grande Valley as they ensue in their WAC schedule at the UCCU Center. The Vaqueros come into Orem with a record of 9-10 and 1-2 in conference play. January 16, 2019 /Sports News – Local UVU Men’s Basketball Hosts Texas-Rio Grande Valley Thursday Written by The Wolverines are winners of 11 of their last 15 games and six of their last eight games. Redshirt junior guard Jake Toolson leads the Wolverines with 15.7 points per game and senior guard Conner Toolson remains close behind at 13.2 points per contest. Jake Toolson also leads the WAC in free throw percentage at 88.3 percent. Additionally, Jake Toolson is 44th in NCAA Division I by shooting 57.4 percent from the field. They are also 12-1 all-time against the Vaqueros at home. The Wolverines rank in the Top 50 nationally in field goal percentage (42nd, 48.1 percent), 43rd in free throws made (278), 46th in defensive rebounds per game (27.78 rebounds) and 48th in free throws attempted (385). UTRGV scores 68.6 points per game and surrenders 70.8 points per contest. The Vaqueros are led by senior forward Terry Winn III (12.5 points, 5.1 rebounds per game) and junior forward Lesley Varner II (11.9 points, 5.7 rebounds per game). Utah Valley currently has the second-longest home-winning streak in Division I as the Wolverines have won their last 21 games at the UCCU Center. The 12-6 Wolverines are currently 1-2 in WAC play as they prepare to host the Vaqueros. Brad James The Wolverines have traditionally dominated UTRGV (once known as Texas-Pan American) as they lead the all-time series 22-3. Tags: Conner Toolson/Jake Toolson/Lesley Varner II/Terry Winn III/Texas-Rio Grande Valley Vaqueros/UCCU Center/UVU Men’s Basketballlast_img read more