Freshwater content variability in the Arctic Ocean

Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): C03051, doi:10.1029/2003JC001940.Arctic Ocean model simulations have revealed that the Arctic Ocean has a basin-wide oscillation with cyclonic and anticyclonic circulation anomalies (Arctic Ocean Oscillation (AOO)) that has a prominent decadal variability [Proshutinsky and Johnson, 1997]. This study explores how the simulated AOO affects the Arctic Ocean stratification and its relationship to the sea ice cover variations. The simulation uses the Princeton Ocean Model coupled to sea ice [Häkkinen and Mellor, 1992; Häkkinen, 1999]. The surface forcing is based on National Centers for Environmental Prediction/National Center for Atmospheric Research Reanalysis and its climatology, of which the latter is used to force the model spin-up phase. Our focus is to investigate the competition between ocean dynamics and ice formation/melt on the Arctic basin-wide freshwater balance. We find that changes in the Atlantic water inflow can explain almost all of the simulated freshwater anomalies in the main Arctic basin. The Atlantic water inflow anomalies are an essential part of AOO, which is the wind driven barotropic response to the Arctic Oscillation (AO). The baroclinic response to AO, such as Ekman pumping in the Beaufort Gyre, and ice melt/freeze anomalies in response to AO are less significant considering the whole Arctic freshwater balance.We gratefully acknowledge the support from National Science Foundation under Grant No OPP-0230184 (AP) and from NASA Headquarters (SH)

Theoretical and Experimental Investigation of Random Gust Loads Part I : Aerodynamic Transfer Function of a Simple Wing Configuration in Incompressible Flow

Sinusoidally oscillating downwash and lift produced on a simple rigid airfoil were measured and compared with calculated values. Statistically stationary random downwash and the corresponding lift on a simple rigid airfoil were also measured and the transfer functions between their power spectra determined. The random experimental values are compared with theoretically approximated values. Limitations of the experimental technique and the need for more extensive experimental data are discussed

Severe Outbreak of Sorbitol-Fermenting Escherichia coli O157 via Unpasteurized Milk and Farm Visits, Finland 2012

Shiga toxin-producing, sorbitol-fermenting Escherichia coli O157 (SF O157) has emerged as a cause of severe human illness. Despite frequent human findings, its transmission routes and reservoirs remain largely unknown. Foodborne transmission and reservoir in cattle have been suspected, but with limited supporting evidence. This study describes the outbreak of SF O157 that occurred in Finland in 2012. The outbreak originated from a recreational farm selling unpasteurized milk, as revealed by epidemiologic and microbiological investigations, and involved six hospitalized children and two asymptomatic adults with culture-confirmed infection. An identical strain of SF O157 was isolated from patients, cattle and the farm environment, and epidemiologic analysis suggested unpasteurized milk as the vehicle of transmission. This study reports the first milkborne outbreak of SF O157, provides supporting evidence of cattle as a reservoir and highlights the health risks related to the consumption of unpasteurized milk

Molecular dynamics study of melting of a bcc metal-vanadium II : thermodynamic melting

We present molecular dynamics simulations of the thermodynamic melting transition of a bcc metal, vanadium using the Finnis-Sinclair potential. We studied the structural, transport and energetic properties of slabs made of 27 atomic layers with a free surface. We investigated premelting phenomena at the low-index surfaces of vanadium; V(111), V(001), and V(011), finding that as the temperature increases, the V(111) surface disorders first, then the V(100) surface, while the V(110) surface remains stable up to the melting temperature. Also, as the temperature increases, the disorder spreads from the surface layer into the bulk, establishing a thin quasiliquid film in the surface region. We conclude that the hierarchy of premelting phenomena is inversely proportional to the surface atomic density, being most pronounced for the V(111) surface which has the lowest surface density

Polar mesoscale cyclones in the northeast Atlantic: Comparing climatologies from ERA-40 and satellite imagery

Polar mesoscale cyclones over the subarctic are thought to be an important component of the coupled atmosphere–ocean climate system. However, the relatively small scale of these features presents some concern as to their representation in the meteorological reanalysis datasets that are commonly used to drive ocean models. Here polar mesocyclones are detected in the 40-Year European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis dataset (ERA-40) in mean sea level pressure and 500-hPa geopotential height, using an automated cyclone detection algorithm. The results are compared to polar mesocyclones detected in satellite imagery over the northeast Atlantic, for the period October 1993–September 1995. Similar trends in monthly cyclone numbers and a similar spatial distribution are found. However, there is a bias in the size of cyclones detected in the reanalysis. Up to 80% of cyclones larger than 500 km are detected in MSL pressure, but this hit rate decreases, approximately linearly, to ∼40% for 250-km-scale cyclones and to ∼20% for 100-km-scale cyclones. Consequently a substantial component of the associated air–sea fluxes may be missing from the reanalysis, presenting a serious shortcoming when using such reanalysis data for ocean modeling simulations. Eight maxima in cyclone density are apparent in the mean sea level pressure, clustered around synoptic observing stations in the northeast Atlantic. They are likely spurious, and a result of unidentified shortcomings in the ERA-40 data assimilation procedure

A review of recent perspectives on biomechanical risk factors associated with anterior cruciate ligament injury

There is considerable evidence to support a number of biomechanical risk factors associated with non-contact anterior cruciate ligament (ACL) injury. This paper aimed to review these biomechanical risk factors and highlight future directions relating to them. Current perspectives investigating trunk position and relationships between strength, muscle activity and biomechanics during landing/cutting highlight the importance of increasing hamstring muscle force during dynamic movements through altering strength, muscle activity, muscle length and contraction velocity. In particular, increased trunk flexion during landing/cutting and greater hamstring strength are likely to increase hamstring muscle force during landing and cutting which have been associated with reduced ACL injury risk. Decision making has also been shown to influence landing biomechanics and should be considered when designing tasks to assess landing/cutting biomechanics. Coaches should therefore promote hamstring strength training and active trunk flexion during landing and cutting in an attempt to reduce ACL injury risk.Peer reviewe

Tapering practices of New Zealand's elite raw powerlifters

Pritchard, HJ, Tod, DA, Barnes, MJ, Keogh, JW, and McGuigan, MR. Tapering practices of New Zealand's elite raw powerlifters. J Strength Cond Res 30(7): 1796-1804, 2016-The major aim of this study was to determine tapering strategies of elite powerlifters. Eleven New Zealand powerlifters (28.4 ± 7.0 years, best Wilks score of 431.9 ± 43.9 points) classified as elite were interviewed, using semistructured interviews, about their tapering strategies. Interviews were transcribed verbatim and content analyzed. Total training volume peaked 5.2 ± 1.7 weeks from competition while average training intensity (of 1 repetition maximum) peaked 1.9 ± 0.8 weeks from competition. During tapering, volume was reduced by 58.9 ± 8.4% while intensity was maintained (or slightly reduced) and the final weight training session was performed 3.7 ± 1.6 days out from competition. Participants generally stated that tapering was performed to achieve full recovery; that accessory work was removed around 2 weeks out from competition; and deadlifting takes longer to recover from than other lifts. Typically participants stated that trial and error, and changes based on "feel" were the sources of tapering strategies; equipment used and movements performed during tapering are the same as in competition; nutrition was manipulated during the taper (for weight cutting or performance aims); and poor tapering occurred when too long (1 week or more) was taken off training. These results suggest that athletes may benefit from continuing to strength train before important events with reduced volume and maintained intensity. Only exercises that directly assist sports performance should remain in the strength program during tapering, to assist with reductions in fatigue while maintaining/improving strength expression and performance

The Role of Phytoplankton Dynamics in the Seasonal and Interannual Variability of Carbon in the Subpolar North Atlantic - a Modeling Study

We developed an ecosystem/biogeochemical model system, which includes multiple phytoplankton functional groups and carbon cycle dynamics, and applied it to investigate physical-biological interactions in Icelandic waters. Satellite and in situ data were used to evaluate the model. Surface seasonal cycle amplitudes and biases of key parameters (DIC, TA, pCO2, air-sea CO2 flux, and nutrients) are significantly improved when compared to surface observations by prescribing deep water values and trends, based on available data. The seasonality of the coccolithophore and "other phytoplankton" (diatoms and dinoflagellates) blooms is in general agreement with satellite ocean color products. Nutrient supply, biomass and calcite concentrations are modulated by light and mixed layer depth seasonal cycles. Diatoms are the most abundant phytoplankton, with a large bloom in early spring and a secondary bloom in fall. The diatom bloom is followed by blooms of dinoflagellates and coccolithophores. The effect of biological changes on the seasonal variability of the surface ocean pCO2 is nearly twice the temperature effect, in agreement with previous studies. The inclusion of multiple phytoplankton functional groups in the model played a major role in the accurate representation of CO2 uptake by biology. For instance, at the peak of the bloom, the exclusion of coccolithophores causes an increase in alkalinity of up to 4 mol kg(sup 1) with a corresponding increase in DIC of up to 16 mol kg(sup 1). During the peak of the bloom in summer, the net effect of the absence of the coccolithophores bloom is an increase in pCO2 of more than 20 atm and a reduction of atmospheric CO2 uptake of more than 6 mmolm(sup 2) d(sup 1). On average, the impact of coccolithophores is an increase of air-sea CO2 flux of about 27 %. Considering the areal extent of the bloom from satellite images within the Irminger and Icelandic Basins, this reduction translates into an annual mean of nearly 1500 tonnes C yr(sup 1)

Mechanical properties and formation mechanisms of a wire of single gold atoms

A scanning tunneling microscope (STM) supplemented with a force sensor is used to study the mechanical properties of a novel metallic nanostructure: a freely suspended chain of single gold atoms. We find that the bond strength of the nanowire is about twice that of a bulk metallic bond. We perform ab initio calculations of the force at chain fracture and compare quantitatively with experimental measurements. The observed mechanical failure and nanoelastic processes involved during atomic wire fabrication are investigated using molecular dynamics (MD) simulations, and we find that the total effective stiffness of the nanostructure is strongly affected by the detailed local atomic arrangement at the chain bases.Comment: To be published in Phys. Rev. Lett. 4 pages with 3 figure

Reversed anisotropies and thermal contraction of FCC (110) surfaces

The observed anisotropies of surface vibrations for unreconstructed FCC metal (110) surfaces are often reversed from the "common sense" expectation. The source of these reversals is investigated by performing ab initio density functional theory calculations to obtain the surface force constant tensors for Ag(110), Cu(110) and Al(110). The most striking result is a large enhancement in the coupling between the first and third layers of the relaxed surface, which strongly reduces the amplitude of out-of-plane vibrations of atoms in the first layer. This also provides a simple explanation for the thermal contraction of interlayer distances. Both the anisotropies and the thermal contraction arise primarily as a result of the bond topology, with all three (110) surfaces showing similar behavior.Comment: 13 pages, in revtex format, plus 1 postscript figur