Periodic motions in Weddell Sea pack ice

first_imgPosition data from an Argos-tracked buoy deployed in the southern Weddell Sea in the austral summer of 1986 are analysed to determine important time-scales of variation of sea-ice motion in the seasonal sea-ice zone. Quality control and pre-processing of raw buoy data are discussed. Processed position data are subjected to time- and frequency-domain analyses. These highlight the importance of diurnal and semi-diurnal periodicities in the buoy motion. These preferred periodicities are associated with tidal forcing rather than wind forcing or inertial oscillations. Periodograms of the longitudinal component of buoy motion indicate that the power of the 24 h tidal component drops dramatically around day 130 in 1986. The possible causes of this are discussed and it is concluded that internal resistance within the sea-ice field may have increased at that time.last_img read more

The epidemiology of cold injury in Antarctica

first_imgMETHOD: A retrospective study was performed of 10 yr of medical records to determine the type, severity, etiological factors and treatment of cold injury experienced by members of the British Antarctic Survey between 1986-95. RESULTS: There were 61 new consultations for cold injury. These comprised 2.5% of all new consultations with an incidence of 65.6 per 1000 per year. Cold injuries seen were frostbite (95%), hypothermia (3%) and trench foot (2%). Superficial frostbite was the most common injury (74% of cases) with the face the most frequently affected area (47% of injuries). No cases of frostbite severe enough to cause permanent tissue loss were seen. The prevalence of cold injury increased with falling temperature to a maximum between -25 and -35 degrees C, despite these temperatures occurring infrequently. The relationship with windchill is not as clear cut with frequency of injury tending to follow the frequency of windchill values except at higher windchill values. Neither temperature nor windchill were found to significantly influence the severity of frostbite. Prior cold injury was shown to be significantly (chi2 p < 0.001) associated with further cold injury. Most injuries (78%) occurred during recreation; skiing and snowmobile driving were often implicated. CONCLUSIONS: Cold injury is uncommon in Antarctica. Despite this, it warrants a continued high profile as under most circumstances it may be regarded as an entirely preventable occurrence.last_img read more

Modeling entrainment of sedimentary particles by wind and water: A generalized approach

first_imgFor long-standing theoretical reasons, it is often asserted that the threshold shear stress for entrainment of sedimentary particles (τ*t = ρfu*2t, made dimensionless as A = ρfu*2t/((ρp − ρf)gd)) has a universal relationship with the particle Reynolds number (Re*t = u*t d/ν), where u*t is the threshold friction velocity, ρf is the fluid density, ρp is the density of the particles, d is the particle diameter, g is the gravitational acceleration and ν is the kinematic viscosity of the fluid. However, experimental plots of A(Re*t) for sediment entrainment in air and water show two major differences: (1) For large Re*t, the values of A in water are, in general, a few times larger than those in air, and (2) when Re*t <1, A increases more rapidly in air than in water as Re*t decreases. This paper derives a new, general theory for A, which incorporates the effects of fluid turbulence, particle cohesion and probabilistic aspects of grain entrainment. It is found that difference (1) is explained by differences in the probability distribution of streamwise velocity fluctuations for typical situations in air and water, which follow from basic scaling laws for velocity variances in turbulent flow. Difference (2) is explained by the different behaviors of interparticle cohesion forces in air and water. The resulting expression is shown to compare well with experimental data.last_img read more

Impact of instantaneous sea ice removal in a coupled general circulation model

first_img1] The impact of extreme sea ice initial conditions on modelled climate is analysed for a fully coupled atmosphere ocean sea ice general circulation model, the Hadley Centre climate model HadCM3. A control run is chosen as reference experiment with greenhouse gas concentration fixed at preindustrial conditions. Sensitivity experiments show an almost complete recovery from total removal or strong increase of sea ice after four years. Thus, uncertainties in initial sea ice conditions seem to be unimportant for climate modelling on decadal or longer time scales. When the initial conditions of the ocean mixed layer were adjusted to ice- free conditions, a few substantial differences remained for more than 15 model years. But these differences are clearly smaller than the uncertainty of the HadCM3 run and all the other 19 IPCC fourth assessment report climate model preindustrial runs. It is an important task to improve climate models in simulating the past sea ice variability to enable them to make reliable projections for the 21st century.last_img read more

Climate change selects for heterozygosity in a declining fur seal population

first_imgGlobal environmental change is expected to alter selection pressures in many biological systems, but the long-term molecular and life history data required to quantify changes in selection are rare. An unusual opportunity is afforded by three decades of individual-based data collected from a declining population of Antarctic fur seals in the South Atlantic. Here, climate change has reduced prey availability and caused a significant decline in seal birth weight. However, the mean age and size of females recruiting into the breeding population are increasing. We show that such females have significantly higher heterozygosity (a measure of within-individual genetic variation) than their non-recruiting siblings and their own mothers. Thus, breeding female heterozygosity has increased by 8.5% per generation over the last two decades. Nonetheless, as heterozygosity is not inherited from mothers to daughters, substantial heterozygote advantage is not transmitted from one generation to the next and the decreasing viability of homozygous individuals causes the population to decline. Our results provide compelling evidence that selection due to climate change is intensifying, with far-reaching consequences for demography as well as phenotypic and genetic variation.last_img read more

Ontogenetic changes in stable isotope (δ13C and δ15N) values in squid Gonatus fabricii (Cephalopoda) reveal its important ecological role in the Arctic

first_imgGonatus fabricii is the most abundant cephalopod species in Arctic waters, and the only squid that completes its entire life cycle there. In order to understand its ecological role in the Arctic, we conducted stable isotope analyses of beaks from all ontogenetic groups from west and east Greenland waters and the Barents Sea, complemented with morphological data. The values of both delta C-13 and delta N-15 of G. fabricii were not related to sex. Values of delta C-13 showed a small ontogenetic increase, and these values were geographically distinct, with highest levels found in the western part of the study area. Values of delta N-15 showed a dramatic ontogenetic increase (i.e. 10.0 parts per thousand delta N-15; 2.6 trophic levels), from epipelagic juvenile forms to large bathypelagic adults, without significant geographical variation. The observed maximum value of delta N-15 (14.9 parts per thousand) is the highest ever recorded in cephalopod beaks. The estimated trophic level (up to 5.1) compares only to top vertebrate predators in the Arctic: large piscivorous fishes, seals and toothed whales or large benthic scavenging fishes. Thus, G. fabricii is a top invertebrate predator in the Arctic, with the widest isotopic niche observed to date for any species there. Among cephalopods its trophic level is only exceeded by its Antarctic congener, G. antarcticus, and by the Antarctic colossal squid Mesonychoteuthis hamiltoni. Thus, polar squids occupy higher trophic positions than do squids living in warmer regions. Finally, our study shows that G. fabricii descends to bathypelagic layers during ontogenesis, continuously increasing its trophic level by changing prey types and sizes, and avoiding predation pressure.last_img read more

On the annual variability of Antarctic aerosol size distributions at Halley research station

first_imgThe Southern Ocean and Antarctic region currently best represent one of the few places left on our planet with conditions similar to the preindustrial age. Currently, climate models have low ability to simulate conditions forming the aerosol baseline; a major uncertainty comes from the lack of understanding of aerosol size distributions and their dynamics. Contrasting studies stress that primary sea-salt aerosol can contribute significantly to the aerosol population, challenging the concept of climate biogenic regulation by new particle formation (NPF) from dimethyl sulphide marine emissions. We present a statistical cluster analysis of the physical characteristics of particle size distributions (PSD) collected at Halley (Antarctica) for the year 2015 (89 % data coverage). By applying the Hartigan-Wong k-Means method we find 8 clusters describing the entire aerosol population. Three clusters show pristine average low particle number concentrations (< 121–179 cm−3) with three main modes (30 nm, 75–95 nm, 135–160 nm) and represent 57 % of the annual PSD (up to 89–100 % during winter, 34–65 % during summer based upon monthly averages). Nucleation and Aitken mode PSD clusters dominate summer months (Sep–Jan, 59–90 %), whereas a clear bimodal distribution (43 and 134 nm, respectively, min Hoppel mode 75 nm) is seen only during the Dec–Apr period (6–21 %). Major findings of the current work include: (1) NPF and growth events originate from both the sea ice marginal zone and the Antarctic plateau, strongly suggesting multiple vertical origins, including marine boundary layer and free troposphere; (2) very low particle number concentrations are detected for a substantial part of the year (57 %), including summer (34–65 %), suggesting that the strong annual aerosol concentration cycle is driven by a short temporal interval of strong NPF events; (3) a unique pristine aerosol cluster is seen with a bimodal size distribution (75 nm and 160 nm, respectively), strongly correlating with wind speed and possibly associated with blowing snow and sea spray sea salt, dominating the winter aerosol population (34–54 %). A brief comparison with two other stations (Dome C Concordia and King Sejong Station) during the year 2015 (240 days overlap) shows that the dynamics of aerosol number concentrations and distributions are more complex than the simple sulphate-sea spray binary combination, and it is likely that an array of additional chemical components and processes drive the aerosol population. A conceptual illustration is proposed indicating the various atmospheric processes related to the Antarctic aerosols, with particular emphasis on the origin of new particle formation and growth.last_img read more

Observed eddy-internal wave interactions in the Southern Ocean

first_imgThe physical mechanisms that remove energy from the Southern Ocean’s vigorous mesoscale eddy field are not well understood. One proposed mechanism is direct energy transfer to the internal wave field in the ocean interior, via eddy-induced straining and shearing of preexisting internal waves. The magnitude, vertical structure, and temporal variability of the rate of energy transfer between eddies and internal waves is quantified from a 14-month deployment of a mooring cluster in the Scotia Sea. Velocity and buoyancy observations are decomposed into wave and eddy components, and the energy transfer is estimated using the Reynolds-averaged energy equation. We find that eddies gain energy from the internal wave field at a rate of −2.2 ± 0.6 mW m−2, integrated from the bottom to 566 m below the surface. This result can be decomposed into a positive (eddy to wave) component, equal to 0.2 ± 0.1 mW m−2, driven by horizontal straining of internal waves, and a negative (wave to eddy) component, equal to −2.5 ± 0.6 mW m−2, driven by vertical shearing of the wave spectrum. Temporal variability of the transfer rate is much greater than the mean value. Close to topography, large energy transfers are associated with low-frequency buoyancy fluxes, the underpinning physics of which do not conform to linear wave dynamics and are thereby in need of further research. Our work suggests that eddy–internal wave interactions may play a significant role in the energy balance of the Southern Ocean mesoscale eddy and internal wave fields.last_img read more

Scoreboard roundup — 3/22/18

first_img FacebookTwitterLinkedInEmailABC News(NEW YORK) — Here are the scores from Thursday’s sports events:INTERLEAGUEMiami 15, Houston 7Detroit 6, Philadelphia 2San Diego 7, Cleveland 6Milwaukee 1, Kansas City 0Colorado 4, Oakland 2Toronto 5, Pittsburgh 4Cincinnati 7, Texas 6Chicago White Sox 3, Arizona 1L.A. Dodgers 4, L.A. Angels 3AMERICAN LEAGUEBaltimore 10, Boston 7N.Y. Yankees 2, Minnesota 1Tampa Bay 5, Toronto 3Seattle 5, Texas 4NATIONAL LEAGUESt. Louis 8, Atlanta 2N.Y. Mets 12, Washington 5San Francisco 4, Chicago Cubs 3NATIONAL BASKETBALL ASSOCIATIONCharlotte 140, Memphis 79Philadelphia 118, Orlando 98New Orleans 128, L.A. Lakers 125Houston 100, Detroit 96Utah 119, Dallas 112Sacramento 105, Atlanta 90NATIONAL HOCKEY LEAGUEPhiladelphia 4, N.Y. Rangers 3Carolina 6, Arizona 5Columbus 4, Florida 0Tampa Bay 7, N.Y. Islanders 6Washington 1, Detroit 0Edmonton 6, Ottawa 2Toronto 5, Nashville 2Vancouver 5, Chicago 2L.A. Kings 7, Colorado 1San Jose 2, Vegas 1TOP 25 COLLEGE BASKETBALL(7) Michigan 99, Texas A&M 72Florida St. 75, (8) Gonzaga 60Kansas St. 61, (18) Kentucky 58Loyola of Chicago 69, (24) Nevada 68Copyright © 2018, ABC Radio. All rights reserved. Beau Lund Written bycenter_img March 23, 2018 /Sports News – National Scoreboard roundup — 3/22/18last_img read more

George scores 36, leads Thunder to 116-108 win over Jazz

first_img Associated Press April 15, 2018 /Sports News – Local George scores 36, leads Thunder to 116-108 win over Jazz FacebookTwitterLinkedInEmailOKLAHOMA CITY (AP) — Paul George scored 36 points to help the Oklahoma City Thunder defeat the Utah Jazz 116-108 in Game 1 of their Western Conference playoff series on Sunday night.George set an Oklahoma City playoff record with eight 3-pointers, blowing past the previous record of five. He made eight of 11 shots from long range, and 13 of 20 shots overall. It was his first playoff game with the Thunder since being acquired in a trade with the Indiana Pacers in the offseason.Russell Westbrook had 29 points, 13 rebounds and eight assists and Carmelo Anthony added 15 points for the Thunder, who will host Game 2 on Wednesday.Jazz rookie Donovan Mitchell had 27 points and 10 rebounds, but he left in the second half with left foot soreness. He returned in the fourth quarter but was noticeably hobbling.Rudy Gobert scored 14 points, and Joe Ingles and Jae Crowder each added 13 for the Jazz.The Thunder recovered from a 16-4 deficit to tie it at 25 at the end of the first quarter. Oklahoma City led 54-48 at halftime behind 20 points from George and 14 from Westbrook.George hit his seventh 3-pointer to push Oklahoma City’s lead to 79-66. George hit a deep 2-pointer to close the quarter and give the Thunder an 81-72 lead.Alex Abrines hit two 3-pointers early in the fourth quarter to give Oklahoma City a 92-80 lead and force Utah to call timeout. The Thunder held off a surge in the final minute.TIP-INSJazz: Mitchell made his first four shots, but just one of six the rest of the first half. … Made just eight of 22 shots in the second quarter.Thunder: G Corey Brewer, who was questionable with a right knee sprain, started. … Anthony scored his 1,700th playoff point. … Oklahoma City made its first 17 free throws and didn’t miss one until the final minute.UP NEXTGame 2 will be Wednesday night in Oklahoma City. Written by Tags: NBA/Oklahoma City Thunder/Playoffs/Utah Jazzlast_img read more