Rb-Sr geochronology of Graham Land, Antarctica

first_imgThirty-five new Rb-Sr whole-rock and mineral isochrons are reported for igneous rocks from Graham Land. Magmatism was essentially continuous but peaks of activity occurred in early Jurassic, early Cretaceous, late Cretaceous and Eocene times. The oldest dated granite is Triassic (209 ± 3 Ma). Volcanic rocks were erupted throughout this history and some previously supposed Upper Jurassic volcanic rocks must be mid-Cretaceous or younger. A change in magma type, from uniformly acid to predominantly basic or intermediate, combined with westward migration of the arc, may be partly responsible for previously reported transverse geochemical variations. There is a marked trend of decreasing initial 87Sr/86Sr ratio of the plutonic rocks with time, from c. 0.707 to 0.704, although volcanic rocks tend to have higher values. This trend is ascribed to the waning influence of an, as yet unidentified, pre-magmatic crustal basement, due to increasing depth of magma generation. Close parallels to the observed age pattern imply continuity of the Andean belt through southern South America into Graham Land back to early Mesozoic times and are not compatible with reconstructions of Gondwana in which the Antarctic Peninsula is located W of South America.last_img read more

A new mechanism for polar patch formation

first_imgPolar patches are regions within the polar cap where the F-region electron concentration and airglow emission at 630 nm are enhanced above a background level. Previous observations have demonstrated that polar patches can be readily identified in Polar Anglo-American Conjugate Experiment (PACE) data. Here PACE data and those from complementary instruments are used to show that some polar patches form in the dayside cusp within a few minutes of the simultaneous occurrence of a flow channel event (short-lived plasma jets ∼2 km s−1) and azimuthal flow changes in the ionospheric convection pattern. The latter are caused by variations of the y-component of the interplanetary magnetic field. The physical processes by which these phenomena cause plasma enhancements and depletions in the vicinity of the dayside cusp and cleft are discussed. Subsequently, these features are transported into the polar cap where they continue to evolve. The spatial scale of patches when formed is usually 200-1000 km in longitude and 2°-3° wide in latitude. Their motion after formation and the velocity of the plasma within the patches are the same, indicating that they are drifting under the action of an electric field. Occasionally, patches are observed to occur simultaneously in geomagnetic conjugate regions. Since some of these observations are incompatible with the presently-accepted model for patch formation involving the expansion of the high latitude convection pattern entraining solar-produced plasma, further modeling of the effects of energetic particle precipitation in the cusp, the consequences of flow channel events on the plasma concentrations, and the time dependence of plasma convection as a result of interplanetary magnetic field By changes is strongly recommended. Such studies could be used to determine the relative importance of this new mechanism compared with the existing theory for patch formation as a function of universal time and season.last_img read more

Stochastic perturbation of divide position

first_imgPerturbation of divide position is considered by a linearization about the Vialov-Nye solution and also about related solutions with 0(1) relief. Relaxation times of one-sixteenth the fundamental thickness/accumulation-rate time-scale are found for the Vialov-Nye configuration, while substantial basal topography can halve the rate of relaxation. Steady divide position is most sensitive to anti-symmetric accumulation-rate distributions near the divide, but transient divide motion is most strongly excited by anti-symmetric accumulation rate variations halfway between the margin and the divide. Relaxation times for the Antarctic Peninsula divide position are estimated to be around 200 years, while the larger Greenland ice sheet has a divide-position relaxation time of around 600 years. Modelling accumulation rate as a white-noise process permits analysis of divide perturbation as a (stochastic) Ornstein-Uhlenbeck process, where the standard deviation of the response is proportional to the standard deviation of the forcing. If observed accumulation-rate variability in the Antarctic Peninsula were antisymmetric about the divide, it would be sufficient to force the divide position to fluctuate with standard deviation 10-20 times the depth of the ice sheet. There appears to be sufficient noise to cause Raymond bumps to be spread significantly. More data on the statistical variation of accumulation with position are needed. Random forcing will increase the complexity of any fold structures created in the divide region and in particular the number of such structures intersecting any borehole.last_img read more

Diving behaviour of the grey-headed albatross

first_imgForaging grey-headed albatrosses spent 86% of the night but only 20% of the day sitting on the sea; most diving activity occurred during daylight. During the broad-guard period of nesting, peaks of diving activity occurred at midday and dusk. During the subsequent chick-rearing period, however, diving was mainly at dawn and dusk. Of 485 dives measured, the depth averaged 0.74 m, with maximum depth at 6.5 m. On average grey-headed albatrosses dived 24 times during a five day foraging trip. Dive depths increased towards midday, probably as a function of the birds’ visual acuity rather than due to vertical migration of their prey. We estimate that grey-headed albatrosses may obtain 30–45% of their daily food requirements by diving.last_img read more

Determining the size of lightning-induced electron precipitation patches

first_img[1] We analyze Trimpi signatures during 23 and 24 April 1994 at four sites on or near the Antarctic Peninsula (Palmer, Faraday, Rothera, and Halley) on subionospheric VLF signals received from four U. S. naval transmitters (NAA, NSS, NLK, and NPM). Electron precipitation patches are found to be large, i.e., similar to1500 km x 600 km, with the longer axis orientated east-west. Calculations using a three-dimensional Born scattering model, where patch densities are 1.5 electrons cm(-3) above ambient at the center at similar to84 km altitude, provides results that are consistent with this picture. A high proportion (38%) of the Trimpi events were associated with strong lightning flashes in eastern United States. When lightning discharges had currents >65 kA (positive or negative), there was a >80% chance of seeing an associated Trimpi event. The chance of seeing any Trimpi events fell to near zero for discharges of <45 kA. The largest Trimpi perturbations occur when the center of the precipitation patch is 700-800 km from the receivers. This result is consistent with the modeling calculations for large patches. The equatorward edge of the precipitation patch was estimated to be at &SIM;60&DEG;S, close to the magnetic conjugate of the lightning. The close association of the equatorward edge of the precipitation patch with the conjugate location of the causative lightning is consistent with a quasi-ducted whistler-induced precipitation mechanism. Nonducted whistler-induced precipitation mechanisms would predict a 5&DEG;-10&DEG; latitudinal gap between the lightning and the equatorward edge of the patch. However, the lack of observed whistlers at the time of the Trimpi events is consistent with the nonducted whistler mechanism and is not consistent with the quasi-ducted mechanism, although the distances from duct exit point to receiver may have been too large (&SIM;700-1000 km) for the signals to be detectable. Using the significantly larger patch dimensions determined in this study, it is estimated that lightning may well be 10-100 times more effective at depleting the radiation belts than hiss.last_img read more

Antarctica and the global jigsaw – a centennial perspective

first_imgHistorical perspectives have shown how several scientific disciplines have developed their Antarctic component over the last century. Antarctic science has changed from a secondary activity of privately organised expeditions by a few countries to a major international activity supported by over 30 countries and and making a major contribution to Earth System Science and the improvement of global climate models. What was once a backwater of science is now in the main stream and the seminal contributions of the Discovery expedition and others from the “Heroic Age” of exploration are now becoming clear.last_img read more

A general criterion for the release of background potential energy through double diffusion

first_imgDouble diffusion occurs when the fluid density depends on two components that diffuse at different rates (e.g. heat and salt in the ocean). Double diffusion can lead to an up-gradient buoyancy flux and drive motion at the expense of potential energy. Here, we follow the work of Lorenz (Tellus, vol. 7 (no. 2), 1955, pp. 157–167) and Winters et al. (J. Fluid Mech., vol. 289, 1995, pp. 115–128) for a single-component fluid and define the background potential energy (BPE) as the energy associated with an adiabatically sorted density field and derive its budget for a double-diffusive fluid. We find that double diffusion can convert BPE into available potential energy (APE), unlike in a single-component fluid, where the transfer of APE to BPE is irreversible. We also derive an evolution equation for the sorted buoyancy in a double-diffusive fluid, extending the work of Winters & D’Asaro (J. Fluid Mech., vol. 317, 1996, pp. 179–193) and Nakamura (J. Atmos. Sci., vol. 53 (no. 11), 1996, pp. 1524–1537). The criterion we develop for a release of BPE can be used to analyse the energetics of mixing and double diffusion in the ocean and other multiple-component fluids, and we illustrate its application using two-dimensional simulations of salt fingering.last_img read more

Boise State beats Utah State, gets Mountain West title shot

first_img FacebookTwitterLinkedInEmailBOISE, Idaho (AP) — Brett Rypien threw for 310 yards and a touchdown, Alexander Mattison rushed for 200 yards and three scores, and No. 21 Boise State beat No. 14 Utah State 33-24 on Saturday night.Boise State (10-2, 7-1), which has won seven straight since losing to San Diego State on Oct. 6, will host Fresno State for the Mountain West championship on Saturday in a rematch from last season.Utah State (10-2, 7-1) had its 10-game winning streak snapped as had its hopes dashed of earning a berth to one of the New Year’s Six bowls.The Broncos relied on a bend-but-don’t-break defense as the offense struggled to land a knockout blow in a tight game throughout.In a see-saw affair early, the game seemed to turn in Boise State’s favor after a big gamble by the Aggies.Trailing 10-7 early in the second quarter, Utah State faked a punt on fourth-and-1 from its own 34 on a direct snap to tight end Dax Raymond. But Boise State, which had its defensive unit on the field, stuffed Raymond at the line of scrimmage.Boise State promptly responded with a scoring drive that took seven plays and overcame a pair of personal fouls, culminating on a 1-yard run by Mattison.Despite a 348-yard passing performance by Jordan Love, Utah State never seemed to find a rhythm on offense.The Aggies stayed within striking distance late in the fourth quarter after Gerold Bright took a screen pass from Love and raced 83 yards for the touchdown.But Boise State drove right back down the field, scoring on another 1-yard run by Mattison to ice the victory.THE TAKEAWAYUtah State: The Aggies weren’t consistent on the road this season and it finally caught up with them. However, Love is only a sophomore and the future is bright for Utah State in the Mountain West.Boise State: The Broncos have yet to put together four solid quarters since early in the season, but they continue to find a way to win in close games down the stretch. While this hasn’t been Bryan Harsin’s strongest team, it has been resilient and could be a formidable foe in a New Year’s Six bowl should Central Florida stumble next week and open the door for the Broncos.POLL IMPLICATIONSUtah State: The Aggies will slide but shouldn’t fall all the way out of the rankings after losing a relatively close game to another ranked team.Boise State: The Broncos may move up a couple of notches but there isn’t much room to climb, as most of the teams directly in front of them won over the weekend.UP NEXTUtah State: The Aggies will await the bowl announcements on Dec. 2 to see where they will conclude the season.Boise State: The Broncos will remain at home next week to host Fresno State in a rematch of last season’s Mountain West championship game. Written by Tags: Mountain West/Utah State Aggies Football Associated Press November 25, 2018 /Sports News – Local Boise State beats Utah State, gets Mountain West title shotlast_img read more

Santa Anita to continue racing because reforms are ‘working,’ spokesman says

first_img Beau Lund Written by June 10, 2019 /Sports News – National Santa Anita to continue racing because reforms are ‘working,’ spokesman sayscenter_img FacebookTwitterLinkedInEmailMario Tama/Getty Images)(LOS ANGELES) — Santa Anita Park will not heed the California Horse Racing Board’s recommendation to suspend racing in the wake of two more horse deaths over the weekend because the reforms that were enacted earlier in the year appear to be effective, according to a spokesman. In March, the park announced a series of changes surrounding horse safety, including a “zero tolerance” policy for the use of medication on racing day in the wake of more than two dozen horse deaths since December 2018.The California Horse Racing Board further voted to limit whips on racing day as well, a rule that applies to Santa Anita.After the reforms took place, the park saw up to seven weeks of “clean racing,” Stefan Friedman, spokesman for The Stronach Group, a company that owns the park, told ABC News. In addition, the track has seen 50% fewer catastrophic breakdowns during racing and 84% fewer catastrophic incidents during training, Friedman said.There were no horse fatalities between April 1 to May 18, when the death toll remained at 23, Santa Anita said in a statement last month. But after that time, the number of horses dying began to climb once again.On Sunday, 3-year-old Truffalino collapsed in the final stages of the third race and died of a heart attack, Friedman said. The day before, 4-year-old Formal Dude broke down while nearing the finish line in the 10th race and was euthanized, he said.A total of 29 horses have died at Santa Anita since the start of the racing season.The chairman, vice chairman and executive director of the California Horse Racing Board recommended on Saturday that Santa Anita suspend racing for the seven remaining race days of 2019, which lasts until June 23, but continue training during that time period, according to a statement from Mike Marten, the board’s public information officer.“It is our understanding that Santa Anita management, after consultation with certain other industry stakeholders, believes that for a variety of reasons, the future of California racing is best served by continuing to race,” the California Horse Racing Board said in a statement over the weekend.Under current California law, the board does not have the authority to suspend a race meet or remove race dates without the approval of the race track operator or without holding a public meeting with 10 days’ notice, Marten said. Santa Anita’s decision to stay open was made after and “extensive consultation” among the The Stronach Group, the Thoroughbred Owners of California and California Thoroughbred Trainers, according to a joint statement from those organizations.Friedman described the most recent horse deaths as “really devastating,” adding that the decision to continue racing “was not made lightly.” The park and the California Horse Racing Board have a “really good relationship,” Friedman added.“The reforms that we instituted are working,” Friedman said. “Do we have a lot more work to do? Absolutely. And everyone at this track, whether it’s the Stronach Group or the horsemen or the trainers or the jockeys, are fully on board and committed to the goal of having zero catastrophic breakdowns.”In April, PETA Senior Vice President Kathy Guillermo told ABC News that the animal rights advocacy group supported the new rules that Santa Anita put into place, calling them the “first step in what needs to be an overhaul in racing nationwide.”“The reason that we take that perspective is that the broken bones in California are happening all over the country,” Guillermo said, referring to horse injuries.Friedman argued that if Santa Anita were to shut down the track, it would be a “terrible signal to everyone that these reforms were ineffective, and that’s just not correct.”“Secondly…to shut down racing and essentially shut down training, you’re taking about closing down a facility and the horses,” Friedman said. “There’s no place for them to go in this juncture in California,” he added.Nearly 2,000 horses live on site and hundreds of Santa Anita employees live and work on site as well, Friedman said.Guillermo said in a statement Monday that what’s happening at Santa Anita is a “microcosm of what’s happening in racing nationally: broken bones, death and public outrage.”“Their bodies litter tracks in New York, Kentucky, Florida, Texas and many other states,” she said, adding that PETA recently called for tracks nationwide to suspend racing until they can implement “long-needed and significant changes that will help end the cruelty and protect horses.”Santa Anita Park will host the 2019 Breeders’ Cup world championships on Nov. 1 and 2.Copyright © 2019, ABC Radio. All rights reserved.last_img read more

Garrett Lever Leaves Weber State’s Men’s Basketball Staff

first_img Written by Tags: Big Sky Conference/Garrett Lever/NCAA Tournament/Randy Rahe/Weber State Men’s Basketball FacebookTwitterLinkedInEmailOGDEN, Utah-Tuesday, Weber State men’s basketball assistant Garrett Lever left the program to take a position in business outside of coaching per an announcement from head coach Randy Rahe.Lever had spent the last seven seasons on the Wildcats’ staff. He had also spent two seasons as Weber State’s director of basketball operations and the other five as an assistant.During his tenure with the Wildcats, the squad won a pair of Big Sky Conference championships and made the NCAA Tournament on two occasions. Brad James July 9, 2019 /Sports News – Local Garrett Lever Leaves Weber State’s Men’s Basketball Stafflast_img read more