Terrestrial ecosystems in the Antarctic

first_imgThe composition of the terrestrial Antarctic flora and fauna and the distribution patterns of a number of species and of the principal vegetation types is now reasonably well established, at least in outline, for the Antarctic Peninsula region and the areas about McMurdo Sound as well as for some areas around the coastal ranges of East Antarctica. Detailed research at Signy Island has provided information concerning the biomass and productivity of certain vegetation types, decomposer organisms, microbivores, and invertebrate herbivores and predators. The main pathways of energy and nutrient within the terrestrial study sites can be regarded as reasonably established. Net annual production locally reaches very high levels (up to 800 g m-2). Only a tiny part of this productivity is consumed by herbivores, the greater part passing to the decomposers or persisting as peat. Most of the animals are microbivores, or graze on fungi, and in turn sustain the small number of invertebrate predators. Analysis of the range of habitats even on Signy Island indicates however that the sites for which detailed ecological information is available represent only a part of the range of environmental and ecological variation. The island is in fact characterized by a very high level of within-site diversity, some of it on a very small scale. Similarly, recent research which permits ecological comparisons with the sub-Antarctic islands of South Georgia and Macquarie, and with the McMurdo area, confirms that Signy Island displays only a small part of the very large range of diversity within the Antarctic regions as a whole. It is a reasonably representative sample of the maritime Antarctic zone in the Antarctic Peninsula region where conditions are particularly favourable for terrestrial life. Its ecological features resemble most closely those of the South Shetland Islands (except over permeable volcanic rocks) and the Palmer Archipelago on the western side of the Antarctic Peninsula. Very different plant and animal communities occur over much of the McMurdo Sound region and in the inland ranges of East Antarctica. Some general statements can now be made about the relationships between terrestrial Antarctic eco-systems and climatic, edaphic and historical factors. There is a clearly marked attenuation of the vegetation and fauna and simplification of the ecological systems as one moves towards cold, arid continental conditions. But the biota of the maritime Antarctic and the sub-Antarctic islands is more impoverished than ecological factors alone would indicate, because of the isolation of these land habitats, many of which have only recently been deglaciated. If present environmental conditions persist, a slow increase in the complexity of these ecological systems is to be expected and in some areas, especially the subantarctic islands, this process is being accelerated by human influence.last_img read more

Effect of temperature change on the metabolic rate of an antarctic mite

first_imgMeasurements of metabolic rate in the terrestrial miteAlaskozetes antarcticus showed that the ability for metabolic temperature compensation is lacking in adults of this species. Animals cultured at 0 and 10°C displayed similar metabolic rates when transferred to 5 or 10°C, and individuals cultured at 0°C and measured at 0, 5 and 10°C showed the same metabolic response as animals cultured and measured at each of these temperatures. These findings, which suggest thatA. antarcticus does not regulate its metabolism in response to changes in temperature, are discussed in the context of the environmental temperature patterns experienced by the animal in the field.last_img read more

Metamorphosed fragments of oceanic crust in the upper Paleozoic Chonos accretionary complex, southern Chile

first_imgA 15 km2 body of metabasite with occasional pillow structures occurs within the Paleozoic accretionary complex in Isla Italia and Isla Dring. Trace elements and REE geochemistry indicate similarities between the metabasites and either plume-related mid-oceannic ridge basalts (P-type MORB) or ocean-island tholeiite basalte. The chemistry of relict clinopyroxenes is also indicative of an ocean-floor basalt protolith. The metabasites exhibit very low-grade metamorphism (pumpellyite-stilpnomelane-actinolite assemblage), comparable to the grade of the sorrounding semi-pelitic mélange as determined by illite crystallinity studies. Isotopic modification of the RbSr system in the metabasites occurred during high fluid-pressure metamorphism, probably by introduction of metamorphic fluids from the sorrounding metapelites. A relatively early tectonic emplacement of the body into the accretionary complex before metamorphism and the generation of the main regional S2 foliation is proposed to explain these characteristics, in contrast to its previous interpretation as a late intrusion into the sorrounding metamorphic rocks.last_img read more

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