Stratigraphy of the upper Jurassic-lower cretaceous Nordenskjöld Formation of eastern Graham Land, Antarctica

first_imgThe Nordenskjöld Formation is a sequence of thinly interbedded ash beds and black, radiolarian-rich mudstones which is exposed on the eastern coast of the Antarctic Peninsula. As a result of recent field work, the Nordenskjöld Formation has been re-examined and redefined with three new members recognized — the Longing, Ameghino, and Larsen members. The age of the formation, based on its macrofossil content, is Kimmeridgian to Berriasian, although reworked clasts from James Ross Island suggest it might range down into the Oxfordian.last_img read more

Seasonal variation in vitamin D metabolites in southern elephant seal (Mirounga leonina) females at south Georgia

first_imgSouthern elephant seals spend two periods on land each year, during breeding and moult, exposed to intensive UV radiation. The time between periods on land are spent at sea, with little exposure to the sun. A study of serum 25-OH-D3 and 1,25(OH)2-D3 on southern elephant seals was carried out at South Georgia. Samples were collected on four different occasions: early and late breeding, and early and late moult. The levels of 25-OH-D3 increased when seals were on land, and decreased when at sea. Two annual peaks of 25-OH-D3 were found, both of which immediately followed periods of intensive exposure of UV radiation. 1,25(OH)2-D3 levels showed a seasonal variation, but no significant changes while being on land were detected. The diving behaviour at sea for southern elephant seals and no detectable change in 25-OH-D3 indicates that the seals feed on prey containing vitamin D.last_img read more

Observations of a noctilucent cloud above Logan, Utah (41.7oN, 111.8oW) in 1995

first_imgA Rayleigh-scatter lidar has been operated at the Atmospheric Lidar Observatory (ALO) on the Utah State University (USU) campus (41.7°N, 111.8°W) since August 1993. During the morning of 22 June 1995, lidar returns from a noctilucent cloud (NLC) were observed for approximately 1 hr, well away from the twilight periods when NLCs are visible. This detection of an NLC at this latitude shows that the first reported sighting, in 1999 (Wickwar et al., 2002), was not a unique occurrence. This 1995 observation differs from the 1999 one in that temperatures could be deduced. Near the 83-km NLC altitude the temperatures were found to be up to ∼23 K cooler than the 11-year June climatology for ALO. This analysis shows that these cool temperatures arose, not because the whole profile was cooler, but because of a major temperature oscillation or wave with a 22-km vertical wavelength and a ∼0.9 km/hr downward phase speed. This large-amplitude wave has many of the characteristics of the diurnal tide. However, the amplitude would have to be enhanced considerably. These lidar observations were supplemented by OH rotational temperature observations from approximately 87 km. These NLC observations equatorward of 50° have been suggested to be significant harbingers of global change. However, if that were the case, the mechanism is more complicated than a simple overall cooling or an increase in water vapor. Accordingly, we propose enhanced generation of gravity waves that would interact with the diurnal tide to produce a large-amplitude wave, the cold phase of which would give rise to low enough temperatures to produce the NLC. The gravity wave source might be orographic in the Mountain West or convective far to the east or south.last_img read more

Surface circulation at the tip of the Antarctic Peninsula from drifters

first_imgAn array of 40 surface drifters, drogued at 15-m depth, was deployed in February 2007 to the east of the tip of the Antarctic Peninsula as part of the Antarctic Drifter Experiment: Links to Isobaths and Ecosystems (ADELIE) project. Data obtained from these drifters and from a select number of local historical drifters provide the most detailed observations to date of the surface circulation in the northwestern Weddell Sea. The Antarctic Slope Front (ASF), characterized by a similar to 20 cm s(-1) current following the 1000-m isobath, is the dominant feature east of the peninsula. The slope front bifurcates when it encounters the South Scotia Ridge with the drifters following one of three paths. Drifters (i) are carried westward into Bransfield Strait; (ii) follow the 1000-m isobath to the east along the southern edge of the South Scotia Ridge; or (iii) become entrained in a large-standing eddy over the South Scotia Ridge. Drifters are strongly steered by contours of f/h (Coriolis frequency/depth) as shown by calculations of the first two moments of displacement in both geographic coordinates and coordinates locally aligned with contours of f/h. An eddy-mean decomposition of the drifter velocities indicates that shear in the mean flow makes the dominant contribution to dispersion in the along-f/h direction, but eddy processes are more important in dispersing particles across contours of f/h. The results of the ADELIE study suggest that the circulation near the tip of the Antarctic Peninsula may influence ecosystem dynamics in the Southern Ocean through Antarctic krill transport and the export of nutrients.last_img read more

Variation in size of living articulated brachiopods with latitude and depth

first_imgGeographical variations in animal characters are one of the main subjects for study in macroecology. Variation with latitude has received special interest. Articulated brachiopods are possibly the commonest macrofossil with large variations in size of taxa through the fossil record. Here, we investigate trends in size of the 3 main orders of articulated brachiopod with latitude and depth. Data were insufficient to identify patterns in Thecideida (a micromorph taxon only recorded from low latitudes). Rhynchonellida had no clear trends in size with latitude or depth. Terebratulida exhibited hemispheric differences in size relations, with increasing length of species towards the pole in the south and no significant trend in the north. Tropical species were small (< 20 mm length between 10A degrees N and 10A degrees S), and the largest species were found between 30A degrees and 60A degrees latitude in both hemispheres. There were no articulated brachiopods recorded from the high arctic, and support for a continuous trend in size with latitude was small or absent. In Terebratulida, there was a significant decrease in species length with depth of 1.7 mm per 100 m depth increase. These trends could be explained by competition for space and reduced availability of habitat with progressive depth beyond the continental shelf.last_img read more

The “tipping” temperature within Subglacial Lake Ellsworth, West Antarctica and its implications for lake access.

first_imgWe present results from new geophysical data allowing modelling of the water flow within Subglacial Lake Ellsworth (SLE), West Antarctica. Our simulations indicate that this lake has a novel temperature distribution due to significantly thinner ice than other surveyed subglacial lakes. The critical pressure boundary (tipping depth), established from the semi-empirical Equation of State, defines whether the lake’s flow regime is convective or stratified. It passes through SLE and separates different temperature (and flow) regimes on either side of the lake. Our results have implications for the location of proposed access holes into SLE, the choice of which will depend on scientific or operational priorities. If an understanding of subglacial lake water properties and dynamics is the priority, holes are required in a basal freezing area at the North end of the lake. This would be the preferred priority suggested by this paper, requiring temperature and salinity profiles in the water column. A location near the Southern end, where bottom currents are lowest, is optimum for detecting the record of life in the bed sediments; to minimise operational risk and maximise the time span of a bed sediment core, a location close to the middle of the lake, where the basal interface is melting and the lake bed is at its deepest, remains the best choice. Considering potential lake-water salinity and ice-density variations, we estimate the critical tipping depth, separating different temperature regimes within subglacial lakes, to be in about 2900 to 3045 m depth.last_img read more

Schmidt Hammer studies in the maritime Antarctic: Application to dating Holocene deglaciation and estimating the effects of macrolichens on rock weathering

first_imgIn order to contribute to the reconstruction of the deglaciation history of the Marguerite Bay area (~ 68°S, Maritime Antarctic) and to estimate the rock weathering rate in this Antarctic sector, 28 sites (7 on Rothera Point and 21 on Anchorage Island) were characterised using Schmidt Hammer values. The weathering effect of two of the most widespread species of macrolichens in this area (Usnea sphacelata and Umbilicaria decussata) was tested at 5 different sites on Rothera Point. Schmidt Hammer data, in conjunction with recent 14C age, suggest a deglaciation age for the Marguerite Bay area of around 12 ka, and an average uplift rate of 5.4 mm year− 1 on Anchorage Island for the period between 3.3 and 5.2 ka. The weathering rates are extremely slow (e.g. three times slower than reported in Norway). Our data confirm that lichens exert a strong impact on weathering, decreasing the Schmidt Hammer R-values on lichenised surfaces by a factor of 3–4 compared to bare rock surfaces. The effect of lichens on weathering is mainly due to edaphic conditions and the type of the lichen involved rather the period of exposure.last_img read more

Biological invasions in terrestrial Antarctica: what is the current status and can we respond?

first_imgUntil recently the Antarctic continent and Peninsula have been little impacted by non-native species, compared to other regions of the Earth. However, reports of species introductions are increasing as awareness of biological invasions as a major conservation threat, within the context of increased human activities and climate change scenarios, has grown within the Antarctic community. Given the recent increase in documented reports, here we provide an up-to-date inventory of known terrestrial non-native species introductions, including those subsequently removed since the 1990s, within the Antarctic Treaty area. This builds on earlier syntheses of records published in the mid-2000s, which focused largely on the sub-Antarctic islands, given the dearth of literature available at that time from the continental and maritime Antarctic regions. Reports of non-native species established in the natural environment (i.e. non-synanthropic) are mainly located within the Antarctic Peninsula region and Scotia Arc, with Deception Island, South Shetland Islands, the most impacted area. Non-native plants have generally been removed from sites of introduction, but no established invertebrates have yet been subject to any eradication attempt, despite a recent increase in reports. Legislation within the Protocol on Environmental Protection to the Antarctic Treaty has not kept pace with environmental best practice, potentially presenting difficulties for the practical aspects of non-native species control and eradication. The success of any eradication attempt may be affected by management practices and the biology of the target species under polar conditions. Practical management action is only likely to succeed with greater co-operation and improved communication and engagement by nations and industries operating in the region.last_img read more

Inbreeding depresses altruism in a cooperative society

first_imgIn some animal species, individuals regularly breed with relatives, including siblings and parents. Given the high fitness costs of inbreeding, evolutionary biologists have found it challenging to understand the persistence of these inbred societies in nature. One appealing but untested explanation is that early life care may create a benign environment that offsets inbreeding depression, allowing inbred societies to evolve. We test this possibility using 21 years of data from a wild cooperatively breeding mammal, the banded mongoose, a species where almost one in ten young result from close inbreeding. We show that care provided by parents and alloparents mitigates inbreeding depression for early survival. However, as adults, inbred individuals provide less care, reducing the amount of help available to the next generation. Our results suggest that inbred cooperative societies are rare in nature partly because the protective care that enables elevated levels of inbreeding can be reduced by inbreeding depression.last_img read more

How climate change is affecting sea levels

first_imgSea level rise increases the frequency and severity of storm surges and coastal flooding, causing serious damage to critical infrastructure and leading to the displacement of coastal communities around the world. Globally, more than 600 million people live in low‐lying coastal areas at less than 10m elevation, and the population of these regions is expected to exceed 1 billion by 2050 (Neumann et al., 2015). In the United Kingdom, current annual damages from coastal flooding are estimated at over £500 million per year (Edwards, 2017), and costs of damage are likely to increase under projections of future sea level rise.last_img read more