Factors affecting the breeding performance of Antarctic blue-eyed shags Phalacrocorax atriceps

first_imgThe breeding performance of Blue-eyed shags of known age (up to 12 yr old) was studied on Signy Island, South Orkney Islands for three seasons. Mate change between seasons was high (77.3%), was unaffected by the age of either partner, and was unrelated to prior or subsequent breeding success. Pairs nesting in the centre of the colony experienced greater social contact, poorer access to their nests, but less exposure to wind and high seas. The degree of social contact with neighbouring nests increased with the age of the male. Average clutch sizes were of 2.31-2.84 eggs, and in one season declined with laying date. The proportion of eggs which hatched also declined with laying date, by 1.5% wk-1. Chick survival (to fledging) was higher in broods hatched in the first third of the season (88.2%) than in the last third (75.2%), and late-laying females fledged 0.64-0.66 fewer chicks on average. Some 19% of the variation in laying dates could be explained by individual consistency between seasons. In contrast to many long-lived species, there was no relationship between female age and laying date. Average clutch sizes increased after 10 yr. Eggs laid by 10-12 yr olds were 15% smaller than those of 4-9 yr olds, as were chick hatching-weights. The mean number of chicks hatched and fledged per pair increased between three and five years of age, but showed no significant change thereafter.last_img read more

Whistler observations of the plasmasphere/plasmapause from stations of the British Antarctic Survey

first_imgVLF whistler observations from Eights Station, Antarctica were crucial to the discovery and exploration of the plasmapause (”Carpenter’s knee”) by Don Carpenter in the mid-1960s. The Weddell Sea sector of Antarctica is particularly well suited to such work because of the high whistler rate (conjugate to thunderstorm regions), proximity to the ground footprint of the average plasmapause, low electromagnetic noise levels (far from power lines, etc.), low ionospheric absorption (in winter), and wave amplification due to the South Atlantic Geomagnetic Anomaly. VLF recordings have been made at Halley, Antarctica, (76oS,27oW,L~4.3) since 1967; the station is located on a similar L-shell to Eights and its successor Siple, but eastward in longitude by about 2 h in magnetic local time. In this paper, we review some of the research on the structure and dynamics of the plasmasphere/plasmapause which has been based on whistler data from Halley. In particular, the use of Halley and Siple as a station pair corotating with the Earth through the Sun-Earth frame has enabled the complex dynamics of the duskside bulge region to be better understood. For example, features consistent with narrow dense sunward-pointing plasma tails, have been delineated. Whistler data from Halley have also provided much information on fine structure within the plasmasphere. The paper discusses some important results of inner plasmaspheric probing using fixed-frequency (~20kHz) whistler data from the lower latitude Faraday station (65oS,64oW,L~2.3), including annual density variations and magnetic storm effects, and concludes by indicating some directions for the future.last_img read more

Origin, sequence stratigraphy and depositional environment of an upper Ordovician (Hirnantian) deglacial black shale, Jordan

first_imgThe upper Ordovician succession of Jordan was located ~60°S, less than 100 km from the Hirnantian ice sheet margin. New graptolite dates indicate glaciation ended in Jordan in the late Hirnantian (persculptus Biozone). The succession records two glacial advances within the Ammar Formation and the subsequent deglaciations. Organic-rich black shales (Batra Formation) form part of the final deglacial transgressive succession that in-filled an existing low stand glacial continental shelf topography. The base of the black shale is coincident with the maximum flooding surface. During transgression, interfluves and sub-basin margins were breached and black shale deposition expanded rapidly across the region. The top of the black shales coincides with peak highstand. The “expanding puddle model” (sensu Wignall) for black shale deposition, adapted for the peri-glacial setting, provides the best explanation for this sequence of events. We propose a hypothesis in which anoxic conditions were initiated beneath the halocline in a salinity stratified water column; a fresher surface layer resulted from ice meltwater generated during early deglaciation. During the initial stages of marine incursion, nutrients in the monimolimnion were isolated from the euphotic zone by the halocline. Increasing total organic carbon (TOC) and δ13Corg up section indicates the organic carbon content of the shales was controlled mainly by increasing bioproductivity in the mixolimnion (the Strakhov model). Mixolimnion nutrient levels were sustained by a continual and increasing supply of meltwater-derived nutrients, modulated by obliquity changes in high latitude insolation. Anoxia was sustained over tens to hundreds of thousands of years. The formation of black shales on the north Gondwana shelf was little different to those observed in modern black shale environments, suggesting that it was the nature of the Ordovician seas that pre-disposed them to anoxia.last_img read more

The Cape Purvis volcano, Dundee Island (northern Antarctic Peninsula): late Pleistocene age, eruptive processes and implications for a glacial palaeoenvironment

first_imgCape Purvis is a conspicuous promontory on southern Dundee Island. It forms a prominent mesa that contrasts with the smooth, shield-like (snow-covered) topography of the remainder of the island. The promontory is composed of fresh alkaline basaltic (hawaiite) volcanic rocks compositionally similar to younger lavas on Paulet Island 5 km to the east. The outcrop is one of the youngest and northernmost satellite centres of the James Ross Island Volcanic Group. 40Ar/39Ar isotopic dating indicates that the Cape Purvis volcano is 132 ± 19 ka in age. The examined sequence probably formed as a lava-fed delta during a subglacial eruption late in the glacial period corresponding to Isotope Stage 6, when the ice sheet surface elevation was 300–400 m higher than at present. A remarkable unidirectional age progression is now evident, from volcanic centres in Prince Gustav Channel (c. 2.0–1.6 Ma), through Tabarin Peninsula (1.69–c. 1 Ma) to Cape Purvis and Paulet islands (132–few ka). The age variations are tentatively ascribed to construction of progressively younger volcanic centres at the leading edge of an easterly-opening deep fault system, although the origins of the postulated fault system are unclear.last_img read more

Influence of sea surface winds on shearwater migration detours

first_imgTo test the potential effects of winds on the migratory detours of shearwaters, transequatorial migrations of 3 shearwaters, the Manx Puffin us puffinus, the Cory’s Calonectris diomedea, and the Cape Verde C. edwardsii shearwaters were tracked using geolocators. Concurrent data on the direction and strength of winds were obtained from the NASA SeaWinds scatterometer to calculate daily impedance models reflecting the resistance of sea surface winds to the shearwater movements. From these models we estimated relative wind-mediated costs for the observed synthesis pathway obtained from tracked birds, for the shortest distance pathway and for other simulated alternative pathways for every day of the migration period. We also estimated daily trajectories of the minimum cost pathway and compared distance and relative costs of all pathways. Shearwaters followed 26 to 52% longer pathways than the shortest distance path. In general, estimated wind-mediated costs of both observed synthesis and simulated alternative pathways were strongly dependent on the date of departure. Costs of observed synthesis pathways were about 15% greater than the synthesis pathway with the minimum cost, but, in the Cory’s and the Cape Verde shearwaters, these pathways were on average 15 to 20% shorter in distance, suggesting the extra costs of the observed pathways are compensated by saving about 2 travelling days. In Manx shearwaters, however, the distance of the observed synthesis pathway was 25% longer than that of the lowest cost synthesis pathway, probably because birds avoided shorter but potentially more turbulent pathways. Our results suggest that winds are a major determinant of the migratory routes of seabirds.last_img read more

Intercomparison of slant column measurements of NO2 and O4 by MAX-DOAS and zenith-sky UV and visible spectrometers

first_imgIn June 2009, 22 spectrometers from 14 institutes measured tropospheric and stratospheric NO2 from the ground for more than 11 days during the Cabauw Intercomparison Campaign of Nitrogen Dioxide measuring Instruments (CINDI), at Cabauw, NL (51.97 degrees N, 4.93 degrees E). All visible instruments used a common wavelength range and set of cross sections for the spectral analysis. Most of the instruments were of the multi-axis design with analysis by differential spectroscopy software (MAX-DOAS), whose non-zenith slant columns were compared by examining slopes of their least-squares straight line fits to mean values of a selection of instruments, after taking 30-min averages. Zenith slant columns near twilight were compared by fits to interpolated values of a reference instrument, then normalised by the mean of the slopes of the best instruments. For visible MAX-DOAS instruments, the means of the fitted slopes for NO2 and O-4 of all except one instrument were within 10% of unity at almost all non-zenith elevations, and most were within 5%. Values for UV MAX-DOAS instruments were almost as good, being 12% and 7%, respectively. For visible instruments at zenith near twilight, the means of the fitted slopes of all instruments were within 5% of unity. This level of agreement is as good as that of previous intercomparisons, despite the site not being ideal for zenith twilight measurements. It bodes well for the future of measurements of tropospheric NO2, as previous intercomparisons were only for zenith instruments focussing on stratospheric NO2, with their longer heritage.last_img read more

Multi-decadal glacier surface lowering in the Antarctic Peninsula

first_imgFrom approximately 400 glaciers of the westernAntarctic Peninsula, no in situ records of mass balance exist and their recent contribution to sea level is consequently poorly constrained. We seek to address this shortcoming by using surface elevations from USGS and BAS airborne(1948–2005) and ASTER spaceborne (2001–2010) stereoimagery, combined by using a rigorous semi-automatedregistration approach, to determine multi-decadal glaciersurface elevation changes in the western Antarctic Peninsulafor 12 glaciers. All observed glaciers show near-frontalsurface lowering and an annual mean lowering rate of0.28 � 0.03 m/yr at the lower portion of the glaciers duringthe �4 decades following the mid-1960s, with higher ratesfor the glaciers in the north-west parts of the AntarcticPeninsula. Increased lowering of up to 0.6 m/yr can beobserved since the 1990s, in close correspondence toincreased atmospheric positive degree days. In all cases,surface lowering reduces to zero within 5 km of the glacierfront at around 400 m altitude. This lowering may havebeen at least partially compensated for by increased highaltitude accumulation.last_img read more

Functional associations and resilience in microbial communities.

first_imgMicrobial communities have inherently high levels of metabolic flexibility and functional redundancy, yet the structure of microbial communities can change rapidly with environmental perturbation. To understand whether such changes observed at the taxonomic level translate into differences at the functional level, we analyzed the structure of taxonomic and functional gene distribution across Arctic and Antarctic locations. Taxonomic diversity (in terms of alpha diversity and species richness) differed significantly with location. However, we found that functional genes distributed evenly across bacterial networks and that this functional distribution was also even across different geographic locations. For example, on average 15% of the functional genes were related to carbon cycling across all bacterial networks, slightly over 21% of the genes were stress-related and only 0.5% of the genes were linked to carbon degradation functions. In such a distribution, each bacterial network includes all of the functional groups distributed following the same proportions. However, the total number of functional genes that is included in each bacterial network differs, with some clusters including many more genes than others. We found that the proportion of times a specific gene must occur to be linked to a specific cluster is 8%, meaning the relationship between the total number of genes in the cluster and the number of genes per function follows a linear pattern: smaller clusters require a gene to appear less frequently to get fixed within the cluster, while larger clusters require higher gene frequencies. We suggest that this mechanism of functional association between equally rare or equally abundant genes could have implications for ecological resilience, as non-dominant genes also associate in fully functioning ecological networks, potentially suggesting that there are always pre-existing functional networks available to exploit new ecological niches (where they can become dominant) as they emerge; for example, in the case of rapid or sudden environmental change. Furthermore, this pattern did not correlate with taxonomic distribution, suggesting that bacteria associate based on functionality and this is independent of its taxonomic position. Our analyses based on ecological networks also showed no clear evidence of recent environmental impact on polar marine microbial communities at the functional level, unless all communities analyzed have changed exactly in the same direction and intensity, which is unlikely given we are comparing areas changing at different rates.last_img read more

Stable isotopes demonstrate intraspecific variation in habitat use and trophic level of non‐breeding albatrosses

first_imgThe non‐breeding period is critical for restoration of body condition and self‐maintenance in albatrosses, yet detailed information on diet and distribution during this stage of the annual cycle is lacking for many species. Here, we use stable isotope values of body feathers (δ13C, δ15N) to infer habitat use and trophic level of non‐breeding adult Grey‐headed Albatrosses Thalassarche chrysostoma (n = 194) from South Georgia. Specifically, we: (1) investigate intrinsic drivers (sex, age, previous breeding outcome) of variation in habitat use and trophic level; (2) quantify variation among feathers of the same birds; and (3) examine potential carry‐over effects of habitat use and trophic level during the non‐breeding period on subsequent breeding outcome. In agreement with previous tracking studies, δ13C values of individual feathers indicate that non‐breeding Grey‐headed Albatrosses from South Georgia foraged across a range of oceanic habitats, but mostly in subantarctic waters, between the Antarctic Polar Front and Subtropical Front. Sex differences were subtle but statistically significant, and overlap in the core isotopic niche areas was high (62%); however, males exhibited slightly lower δ13C and higher δ15N values than females, indicating that males forage at higher latitudes and at a higher trophic level. Neither age nor previous breeding outcome influenced stable isotope values, and we found no evidence of carry‐over effects of non‐breeding habitat use or trophic level on subsequent breeding outcome. Repeatability among feathers of the same individual was moderate in δ13C and low in δ15N. This cross‐sectional study demonstrates high variability in the foraging and migration strategies of this albatross population.last_img read more

Prep Track Roundup: 4/20

first_img Tags: Beaver/Brynnli Nelson/Delta/Juab/Linley White/Wayne Brad James FacebookTwitterLinkedInEmailPRICE, Utah-Friday, numerous Mid-Utah Radio Sports Network schools and athletes competed at the Carbon Invitational.The boys’ championship was won by the Grand Red Devils with 108 points, clearly ahead of second-place Delta with 66.5 points. Juab placed fourth overall with 54 points.For the girls, Juab won the crown with 101 points, outlasting second-place Carbon, who finished with 95 points. Delta placed third overall with 74.2 points.The meet commenced with the girls’ medley relay, which saw Union place first in a time of 4:20.23 with Juab finishing third.Grand’s boys won the medley title, with Juab placing second at a time of 3:50.34.Savannah Nielson of Delta won the girls’ 100-meter hurdles in a time of 16.53 seconds, with her teammate, Delta’s Adi Nielson winning the 300-meter hurdles in a time of 48.78 seconds.Delta’s Jaymen Brough again excelled in numerous events, winning the 110-meter hurdles (16.35 seconds) and high jump (6 feet 1 inch) crowns, while placing second in the 300-meter hurdles to Connor Guerrero of Grand.Derek Smith of Delta also fared well, finishing fourth in the boys’ 100-meter dash, with Madison Norris of Manti finished fifth in the girls’ 1600-meter run.Delta’s girls also did well in the 4 x 100 relay, which saw the Rabbits win the title in 52.73 seconds. This team consisted of Jordyn Nieson, Ashlee Nielson, Adi Nielson and Bridgette Christensen.Gunnison’s Jade Wimmer swept the 400-meter (59.96 seconds) and 200-meter dash (26.31 seconds) titles and Richfield’s Chaz Roberts placed third in the boys’ 800-meter run.In the girls’ 3200-meter run, Juab’s Maura Williams and Whitney Slater finished third and fourth, respectively.Delta’s girls also won the 4 x 400 relay, with the Rabbits posting a time of 4:17.11 as the team consisted of Ashlee Nielson, Adi Nielson, Savannah Nielson and Quincy Allred.The boys’ discus crown was won by Delta’s Chase Fowles with a toss of 121-06.50 feet, as he also won the shot put crown with a toss of 42-10 feet. Meanwhile Wayne’s Brynnli Nelson won the girls’ javelin crown with a toss of 120-02 feet.Juab’s Willow Kay won the girls’ long jump title with a leap of 16-01.25 feet. In the boys’ long jump, Wayne’s Wyatt Van Orden placed third and Trey Brough of Delta finished fourth, while Cole Marshall of Beaver placed sixth.Rhiannon West of Juab won the girls’ high jump with a leap of 5 feet 1 inch, with her teammates Emilia Anderson and Brooklynn Hunter placing fourth and fifth, respectively.Finally, the boys’ javelin title was won by Juab’s Jackson Rowley with a toss of 174-08 feet, with his teammate Bradley Brindley finishing third and Beaver’s Tyler Griffiths placed fifth.PROVO, Utah-Friday, at Brigham Young University’s Robison Track, Beaver represented all small schools in Utah at the BYU High School Multi-Steeple Event. The Beavers fared admirably, all things considered, as they were often paired against Class 6-A Pleasant Grove in many events.The Beavers were able to compete in the 2000-meter steeplechase (an amended version of the conventional collegiate 3000-meter steeplechase) while in this event, Beaver’s Samantha Williams and Sophia Almeida ran 8:03.32 and 10:00.05 respectively.In the boys’ 2000-meter steeplechase, Beaver’s Caysen Crum, Spencer Williams and Rhett Marshall placed fourth through sixth respectively.Beaver’s boys have placed third with 12 points overall in the standings.Meanwhile, Beaver’s girls also competed in the heptathlon, an event primarily reserved for collegiate athletes, but Linley White currently has 1787 points, with her teammate, Kaitlyn Hemond, posting 1191 points thus far.The meet will resume Saturday. April 21, 2018 /Sports News – Local Prep Track Roundup: 4/20 Written bylast_img read more