The effects of light and temperature on photosynthate partitioning in Antarctic freshwater phytoplankton

first_imgThe effects of temperature and radiation flux on the partitioning of photosynthetically fixed carbon into four intracellulai metabolic pools was investigated for natural phytoplankton assemblages from an Antarctic freshwater lake. At ambient temperature, protein synthesis was saturated at low photon flux densities (30–40 μmol m −2 s −1 ) and above this flux fixed carbon was increasingly stored as lipid and polysaccharide. Increasing temperature raised both the saturated rate of protein synthesis and the photon flux at which saturation occurred. There was a corresponding decline in the accumulation of reserve products, particularly at low radiation fluxes. The consequences of this pattern of uptake for the phytoplankton is discussed.last_img read more

A study of the thermospheric forces at a high latitude site on two days of differing geomagnetic activity

first_imgData from the Fabry-Perot Interferometer and Dynasonde at Halley (75.5°S, 26.6°W, L ∼ 4.2), Antarctica, have been used to calculate the forces acting on the high latitude thermosphere. Two case studies of the forces have been undertaken to study why the thermospheric zonal wind speeds are typically so different on nights with different geomagnetic activity. One case study analyses the forces on a geomagnetically active night and the other analyses them on a geomagnetically quiet night. Even on the geomagnetically active night, it is found that the ion drag force is not necessarily the largest force at any one time. Simple comparison of the magnitudes of the forces does not make it very clear which ones dominate in controlling the motion of the thermosphere. This can be seen more clearly by rewriting the momentum equation so that the neutral velocity is expressed in terms of the ion velocity, and the other forces normalized by the ion density. It then becomes clear that, in the evening, the differences in the neutral velocity are due to increases in both ion density and ion velocity, while in the morning, only changes in ion density are important. Thus, although the ion drag force is often not the largest force, it appears that changes in it can account for the variations in neutral velocity between the two nights that were studied. It has also been shown as part of the analysis that whether or not the viscosity needs to be considered when calculating the ion drag force at an altitude of 240 km depends on the ion density profile. If the profile has a single peak then it is only necessary to consider the ion density at 240 km. It is, however, possible that just considering the ion density at this altitude may lead to an underestimate of the effective ion drag force if more than one peak is present.last_img read more

Analysis of haul data from the South Georgia krill fishery

first_imgData from individual hauls carried out by vessels operating in the South Georgia krill fishery between 1994 and 1996 were examined and a range of descriptive measurements reflecting the fishery operation were produced. The measurements emphasise that the krill fishery at South Georgia was geographically focused, operating in a limited area along the shelf edge on the northern coast of the island. Each day several hauls were undertaken by each vessel (average 7.9 in 1993,9.9 in 1995, and 7.0 in 1996), with hauls producing higher catch rates during the middle of the day. Individual hauls were examined to establish the time required for each phase of the fishing operation. The times associated with shooting and hauling the net were usually short and showed little variation, whereas the time associated with the actual fishing period was longer and more variable. The time between consecutive hauls was almost as long as the fishing period and showed similar levels of variability. Distances moved between consecutive hauls were generally small, suggesting that little effort was spent searching for fishable swarms beyond the near neighbourhood. The range of measurements describing the fishery indicates that differences existed between years, with 1995 being a better season than either 1994 or 1996. Aspects of mesoscale variability are discussed in relation to previous attempts to model fisheries data and to derive suitable abundance indices that are sensitive to changes in biomass. The focused nature of the fishery at South Georgia suggests that fisheries-based indices may be of value for management purposes, consequently further detailed analysis would be useful.last_img read more

Modeling of subionospheric VLF signal perturbations associated with earthquakes

first_imgIt has been reported that propagation of very low frequency (VLF) waves in the Earthionosphere waveguide might provide an indication of imminent earthquakes [Hayakawa et al., 1996; Molchanov et al., 1998]. Narrow-band data from Inubo, Japan, suggested that transmissions from Omega Japan, 1000 km away, might be influenced by pre-earthquake processes. The terminator time (TT) was defined as the time where a minimum occurred in the received phase (or amplitude) during sunrise and sunset. A few days before an earthquake the TT was observed to deviate significantly from the monthly averages, producing a longer “VLF day.” The TT effect has been explained through some rather simple modeling by a 1–2 km drop in the VLF reflection height at the lower ionospheric boundary. In this study we apply more realistic propagation models to show that the changes in VLF reflection height associated with earthquakes would have to be considerably larger (∼4–11 km) than those suggested previously in order to produce the reported effect. If the reported TT changes were caused by alterations in the VLF reflection height associated in some manner with an imminent earthquake, these effects would be commensurate with the effects of a solar flare. However, this would lead to changes in received amplitude (or phase) that would be significant at all times, and not just during the day/night transition. Hence it is not at all clear that a simple height-lowering explanation for the TT effect is correct.last_img read more

A coordinated ground-based and IMAGE satellite study of quiet-time plasmaspheric density profiles

first_imgCold plasma mass density profiles in the plasmasphere have been determined for the geomagnetically quiet day of 19th August 2000 using the cross-phase technique applied to ground-based magnetometer data from the SAMNET, IMAGE and BGS magnetometer arrays. Cross-phase derived mass densities have been compared to electron densities derived from both ground-based VLF receiver measurements, and the IMAGE satellite RPI. The cross-phase results are in excellent agreement with both the VLF and IMAGE observational results, thus validating the cross-phase technique during quiet times. This is the first such coordinated multi-instrument study, and has enabled very few heavy ions to be inferred in the plasmasphere for L > 3.45 on this day. The observational results were compared to plasma mass densities from the SUPIM model and were found to be in excellent agreement. IMAGE EUV data also verified the existence of azimuthal structure in the outer quiet-time plasmasphere.last_img read more

Tundra plants protect the soil surface from UV

first_imgIn the Arctic, seasonal ozone depletion is resulting in periods of enhanced UV-B radiation at ground level while regional climate change is associated with increasing temperatures. These changes are likely to alter plant distribution, biodiversity and morphology, which may have knock-on effects for microbially driven biogeochemical cycling and other soil processes. Our study examined the transmission of solar UV radiation through arctic tundra plants using a portable UV radiometer and the DLR-biofilm biological UV dosimeter. A strong negative correlation was found between vegetation cover and UV transmission to the soil surface. Penetration of UV to the soil beneath tundra plants varied depending upon plant morphology, being greater through low creeping plants than cushion plants, grasses or mosses. UV transmission to the soil surface beyond the foliage edge also varied with plant morphology and the presence of flowers.last_img read more

A three-dimensional calving model: numerical experiments on Johnsons Glacier, Livingston Island, Antarctica

first_imgCalving from tidewater glaciers and ice shelves accounts for around half the mass loss from both polar ice sheets, yet the process is not well represented in prognostic models of ice dynamics. Benn and others proposed a calving criterion appropriate for both grounded and floating glacier tongues or ice shelves, based on the penetration depth of transverse crevasses near the calving front, computed using Nye’s formula. The criterion is readily incorporated into glacier and ice-sheet models, but has not been fully validated with observations. We apply a three-dimensional extension of Benn and others’ criterion, incorporated into a full-Stokes model of glacier dynamics, to estimate the current position of the calving front of Johnsons Glacier, Antarctica. We find that two improvements to the original model are necessary to accurately reproduce the observed calving front: (1) computation of the tensile deviatoric stress opening the crevasse using the full-stress solution and (2) consideration of such a tensile stress as a function of depth. Our modelling results also suggest that Johnsons Glacier has a polythermal structure, rather than the temperate structure suggested by earlier studies.last_img read more

Extraction and characterization of collagen from Antarctic and Sub-Antarctic squid and its potential application in hybrid scaffolds for tissue engineering

first_imgCollagen is the most abundant protein found in mammals and it exhibits a low immunogenicity, high biocompatibility and biodegradability when compared with others natural polymers. For this reason, it has been explored for the development of biologically instructive biomaterials with applications for tissue substitution and regeneration. Marine origin collagen has been pursued as an alternative to the more common bovine and porcine origins. This study focused on squid (Teuthoidea: Cephalopoda), particularly the Antarctic squid Kondakovia longimana and the Sub-Antarctic squid Illex argentinus as potential collagen sources. In this study, collagen has been isolated from the skins of the squids using acid-based and pepsin-based protocols, with the higher yield being obtained from I. argentinus in the presence of pepsin. The produced collagen has been characterized in terms of physicochemical properties, evidencing an amino acid profile similar to the one of calf collagen, but exhibiting a less preserved structure, with hydrolyzed portions and a lower melting temperature. Pepsin-soluble collagen isolated from I. argentinus was selected for further evaluation of biomedical potential, exploring its incorporation on poly-ε-caprolactone (PCL) 3D printed scaffolds for the development of hybrid scaffolds for tissue engineering, exhibiting hierarchical featureslast_img read more

USU Track & Field Athlete Takes Part in NCAA Career Sports Forum

first_img Brad James FacebookTwitterLinkedInEmailINDIANAPOLIS-Last week, a Utah State track and field athlete was given the chance to participate in the 2018 NCAA Career in Sports Forum at the NCAA’s headquarters in Indianapolis.The program ran from May 31-June 3 and Aggies junior thrower Michala Zilkey was granted the opportunity to attend by virtue of the selection of a committee within the NCAA membership.Participants were selected based on their interest in pursuing a career in sports and who are viewed as campus leaders as well as by receiving a nomination from athletics administration at their respective schools.Zilkey, a native of Gig Harbor, Wash., said she found the late Tennessee women’s basketball coach Pat Summitt’s room was “especially impact-ful” to her.In her junior season, Zilkey placed sixth in the discus with a career-best toss of 159-6 and 11th in the hammer throw with a mark of 161-11 at the Mountain West track and field championships last month.Zilkey stated her ambition is to “help develop female leadership in sports” and hopes to work with high school or collegiate female athletes on developing leadership style through sport and character education. June 6, 2018 /Sports News – Local USU Track & Field Athlete Takes Part in NCAA Career Sports Forum Tags: Michala Zilkey/NCAA/Student Leadership/USU Track and Field Written bylast_img read more

Scoreboard roundup — 2/17/19

first_imgFebruary 18, 2019 /Sports News – National Scoreboard roundup — 2/17/19 Beau Lund Written bycenter_img FacebookTwitterLinkedInEmailiStock(NEW YORK) — Here are the scores from Sunday’s sports events:NATIONAL BASKETBALL ASSOCIATIONTeam LeBron West 178, Team Giannis East 164NATIONAL HOCKEY LEAGUEPittsburgh 6, NY Rangers 5St. Louis 4, Minnesota 0New Jersey 4, Buffalo 1Philadelphia 3, Detroit 1Florida 6, Montreal 3Anaheim 5, Washington 2TOP-25 COLLEGE BASKETBALL(9) Houston 85, Tulane 50(11) Michigan St. 62, Ohio St. 44St. John’s 71, (13) Villanova 65Copyright © 2019, ABC Radio. All rights reserved.last_img read more