Structure and grazing impact of the mesozooplankton community during late summer 1994 near South Georgia, Antarctica

first_imgMesozooplankton abundance, community structure and grazing impact were determined during late austral summer (February/March) 1994 at eight oceanic stations near South Georgia using samples collected with a Bongo and WP-2 nets in the upper 200-m and 100-m layer, respectively. The zooplankton abundance was generally dominated by copepodite stages C3–C5 of six copepod species: Rhincalanus gigas, Calanus simillimus, Calanoides acutus, Metridia spp., Clausocalanus laticeps and Ctenocalanus vanus. Most copepods had large lipid sacs. All copepods accounted for 41–98% of total zooplankton abundance. Juvenile euphausiids were the second most important component contributing between 1 and 20% of total abundance. Pteropods, mainly Limacina inflata, were important members of the pelagic community at two sites, accounting for 44 and 53% of total abundance. Average mesozooplankton biomass in the upper 200 m was 8.0 g dry weight m−2, ranging from 4.3 to 11.5 g dry weight m−2. With the exception of Calanussimillimus, gut pigment contents and feeding activity of copepod species were low, suggesting that some species, after having stored large lipid reserves, had probably started undergoing developmental arrest. Daily mesozooplankton grazing impact, measured using in situ gut fluorescence techniques and in vitro incubations, varied widely from <1 to 8% (mean 3.5%) of phytoplankton standing stock, and from 5 to 102% (mean 36%) of primary production. The highest grazing impact was found northeast of the island co-incident with the lowest phytoplankton biomass and primary production levels.last_img read more

Meesia uliginosa Hedw. (Musci, Meesiaceae) in Antarctica

first_imgMeesia uliginosa Hedw. and the family Meesiaceae are recorded for the first time in the Antarctic. The species is occasional on Joinville and James Ross Islands near the Trinity Peninsula, on Signy Island in the South Orkney Islands and on Livingston and Robert Islands in the South Shetland Islands, whereas on King George Island, in the latter archipelago, it is locally frequent. The Antarctic plants are briefly described and illustrated and the local distribution of the species on King George Island and in the maritime Antarctic is mapped. The ecological requirements of M. uliginosa in Antarctica are described in detail and the global geographical distribution of the species is reviewed. Ceratodon kinggeorgicus Kanda, a species originally described from King George Island, is considered to be conspecific with M. uliginosa.last_img read more

A pilot study for predicting ozone amounts for the general public in southern Chile

first_imgDuring 1994/95 a UK Overseas Development Administration (now Department for International Development – DFID) funded project was undertaken to predict ozone amount over Punta Arenas in southern Chile. A low-cost satellite receiver was installed to receive the digital data stream from the NOAA series of weather satellites. The ozone channel of the TIROS Operational Vertical Sounder instrument on the NOAA satellites was used to obtain maps of stratospheric ozone for the area around Punta Arenas in near real time. Also, a simple model was developed to predict the amount of column ozone from the forecast 100 hPa temperatures obtained from the UK Meteorological Office. These techniques used together made it possible to issue timely warnings to the general public of Punta Arenas before the Antarctic ozone hole moved across southern South America during the Austral spring.last_img read more

Cretaceous (Late Albian) coniferales of Alexander Island, Antarctica. 2. Leaves, reproductive structures and roots

first_imgConiferous foliage from the Albian of AlexanderIsland, Antarctica, is assigned to the Araucariaceae, Podocarpaceae, and Taxodiaceae based on attached or associated fertile remains. Araucarian foliage represented by Araucaria alexandrensis sp. nov. and A. chambersii sp. nov. is associated with ovulate cone scales described as Araucarites wollemiaformis sp. nov. and A. citadelbastionensis sp. nov., respectively. The Podocarpaceae is represented by Bellingshausium willeyii sp. nov. and the Taxodiaceae by Athrotaxites ungeri, both with attached cones. Sterile foliage is widespread belonging to the form genera Podozamites, Elatocladus, Brachyphyllum and Pagiophyllum. The conifers in this Albian southern high-latitude flora make up ca. 15% of the species diversity. Evidence from leaf litter distribution on palaeosols and leaf morphology suggest that the majority of conifers were large canopy-forming trees, although a few were probably small understorey shrubs.last_img read more

The effects of global climate variability in pup production of Antarctic fur seals

first_imgClimate variability has strong effects on marine ecosystems, with repercussions that range in scale from those that impact individuals to those that impact the entire food web. Climate-induced changes in the abundance of species in lower trophic levels can cascade up to apex predators by depressing vital rates. However, the characteristics and predictability of predator demographic responses remain largely unexplored. We investigated the detectability, limits, and nonlinearity of changes in Antarctic fur seal pup production at South Georgia over a 20-year period in response to environmental autocorrelation created by global climate perturbations; these were identified in time series of monthly averaged sea surface temperature (SST). Environmental autocorrelation at South Georgia was evident with frequent SST anomalies between 1990 and 1999, during a decade of warm background (time-averaged) conditions. SST anomalies were preceded by, and cross-correlated with, frequent El Niño-La Niña events between 1987 and 1998, which was also a decade of warm background conditions in the tropical Pacific Ocean. Nonlinear mixed-effects models indicated that positive anomalies at South Georgia explained extreme reductions in Antarctic fur seal pup production over 20 years of study. Simulated environmental time series suggested that the effect of anomalies on Antarctic fur seals was only detectable within a narrow range of positive SST, regardless of the distribution, variance, and autocorrelation structure in SST; this explained the observed nonlinearity in responses in pup production, which were observed only under persistent high SST levels. Such anomalies at South Georgia were likely associated with low availability of prey, largely krill, which affected Antarctic fur seal females over time scales longer than their breeding cycle. Reductions in Antarctic fur seal pup production could thus be predicted in advance by the detection of large-scale anomalies, which appeared to be driven by trends in global climate perturbation.last_img read more

Total ozone dependence of the difference between the empirically corrected EP-TOMS and high-latitude station datasets

first_imgA comparison was made of the ground-based and satellite total ozone content (TOC) measurements in the atmosphere over the Antarctic stations Vernadsky, Halley and Amundsen–Scott and the Arctic station Barrow. A similar discrepancy analysis was performed using the global network of ground-based ozonometric stations from the beginning of regular satellite observations in 1978. Slowing of the long-term global ozone losses has been observed during the past decade and a recovery of the ozone layer is forecast for the coming decades. Therefore, the accuracy requirements for ozone measurements are increasing, which, in turn, requires corresponding analysis of the measurement errors. In this work, the Earth Probe Total Ozone Mapping Spectrometer (EP-TOMS) satellite data from 1996 to 2005 were used. Satellite daily TOC values were taken using version 8 of the algorithm introduced in 2004 and empirically corrected in 2007. The most persistent features of the relative EP-TOMS–Dobson difference are: (1) a significant increase in dispersion during the period of the spring Antarctic ozone hole and (2) a differing dependence on total ozone in the trend tendency and significance for EP-TOMS and Dobson datasets. The results indicate the influence of the specific conditions during the Antarctic ozone hole on the possible precision that could be achieved in assessments of Montreal Protocol effects in the ozone layer over this region.last_img read more

Seasonal inflow of warm water onto the southern Weddell Sea continental shelf, Antarctica

first_imgTo capture the austral summer to winter transition in water mass properties over the southern Weddell Sea continental shelf and slope region, 19 Weddell seals were tagged with miniaturized conductivity–temperature–depth sensors in February 2011. During the following 8 months the instruments yielded about 9000 temperature–salinity profiles from a previously undersampled area. This allows, for the first time, a description of the seasonality of warm water intrusions onto the shelf, as well as its southward extent towards the Filchner Ice Shelf. A temperature section across the Filchner Depression and eastern shelf shows a pronounced decrease in warm water inflow from summer to winter, further supported by an almost 3–year long time series from a shelf–break mooring. The seasonal variability is related to the surface wind stress and an associated deepening of the off-shelf core of Warm Deep Water.last_img read more

Early spawning of Antarctic krill in the Scotia Sea is fuelled by “superfluous” feeding on non-ice associated phytoplankton blooms

first_imgThe spawning success of Antarctic krill (Euphausia superba) is generally assumed to depend on substantial winter sea ice extent, as ice biota can serve as a food source during winter/spring and the seasonal ice melt conditions the upper water column for extensive phytoplankton blooms. However, direct observations during spring are rare. Here we studied krill body condition and maturity stage in relation to feeding (i.e. stomach fullness, diet, absorption of individual fatty acids and defecation rate) across the Scotia Sea in November 2006. The phytoplankton concentrations were low at the marginal ice zone (MIZ) in the southern Scotia Sea (Stn. 1, 2, and 3), high in open waters of the Southern Antarctic Circumpolar Current Front (SACCF) in the central Scotia Sea (Stn. 5), and moderate further north (Stn. 6 and 7). Krill had low lipid reserves (∼6.5% of dry mass, DM), low mass:length ratios (∼1.7 mg DM mm−1), and small digestive glands (∼7% of total DM) near the ice edge. The stomachs contained lithogenic particles, diatom debris, and bacterial fatty acids, but low proportions of diatom-indicating fatty acids, which suggest that these krill were feeding on detritus rather than on fresh ice algae. In the SACCF, krill had higher lipid reserves (∼10% of DM), high mass:length ratios (∼2.2 mg DM mm−1), and large digestive glands (∼16% of total DM). Stomach content and tissue composition indicate feeding on diatoms. In the north, moderate food concentrations co-occurred with low lipid reserves in krill, and moderate mass:length ratios and digestive gland sizes. Only in the phytoplankton bloom in the SACCF had the mating season already started and some females were about to spawn. Based on the way krill processed their food at the different stations, we indicate two mechanisms that can lead to fast regeneration of body reserves and oocyte maturation in E. superba. One is “superfluous” feeding at high food concentrations, which maximises the overall nutrient gain. The other is a preferential absorption of crucial fatty acids: 20:5(n−3) and 22:6(n−3) when regaining body condition after the winter, and 14:0 and 16:1(n−7) during accumulation of oocyte yolk. Multi-year time series of phytoplankton distribution show that an early spring bloom, as found in 2006, is not unusual for the central Scotia Sea and coincides with high krill larval concentrations in this area. In conclusion, the Scotia Sea is a main spawning ground of Antarctic krill and this is linked to phytoplankton blooms in open waters of the SACCF rather than to ice edge blooms.last_img read more

Climate variability features of the last interglacial in the East Antarctic EPICA Dome C ice core

first_imgWhereas millennial to sub-millennial climate variability has been identified during the current interglacial period, past interglacial variability features remain poorly explored because of lacking data at sufficient temporal resolutions. Here, we present new deuterium data from the EPICA Dome C ice core, documenting at decadal resolution temperature changes occurring over the East Antarctic plateau during the warmer-than-today last interglacial. Expanding previous evidence of instabilities during the last interglacial, multi-centennial sub-events are identified and labelled for the first time in a past interglacial context. A variance analysis further reveals two major climatic features. First, an increase in variability is detected prior to the glacial inception, as already observed at the end of Marine Isotopic Stage 11 in the same core. Second, the overall variance level is systematically higher during the last interglacial than during the current one, suggesting that a warmer East Antarctic climate may also be more variable.last_img read more

Can bottom ice algae tolerate radiative and temperature changes?

first_imgSea ice algae are significant primary producers of the ice-covered marine environment, growing under typically cold, dim conditions. During ice break-up they are released to the water column, where temperatures can be several degrees higher and irradiance can increase by orders of magnitude. To determine how sea ice algae respond to such rapid changes, we carried out incubations to examine their tolerance to environmentally realistic levels of change in temperature and PAR, as expressed by photosynthetic response and production of mycosporine-like amino acids (MAAs). The algae were also exposed to a broader range of temperatures, to evaluate their potential to function in warmer seas in the event, for instance, of anthropogenic transfer to locations further north. When subjected to PAR (0–100 μmol m− 2 s− 1) at ecologically relevant temperatures (− 1 °C, 2 °C, 5 °C), the algae showed tolerance, indicated by a lack of decline in the quantum efficiency of photosystem II (PSII). The data show that bottom ice algae can tolerate increasing temperature and PAR comparable to the changes experienced during and after sea ice melt. MAA production increased at higher PAR and temperature. At ambient PAR levels, increased temperatures resulted in lower ϕPSII. However, as PAR levels were increased, higher temperature reduced the level of stress as indicated by higher ϕPSII values. This result suggests, for the first time in sea ice algal studies, that higher temperatures can ameliorate the negative effects of increased PAR. Exposure to much higher temperatures suggested that the algae were capable of retaining some photosynthetic function at water temperatures well above those currently experienced in some of their Antarctic habitats. However, when temperature was gradually increased past 14 °C, the photosystems started to become inactivated as indicated by a decrease in quantum yield, suggesting that the algae would not be viable if transferred to lower latitude cold temperate areas.last_img read more