Increased Transnational Sea Ice Transport Between Neighboring Arctic States in the 21st Century

The Arctic is undergoing a rapid transition toward a seasonal ice regime, with widespread implications for the polar ecosystem, human activities, as well as the global climate. Here we focus on how the changing ice cover impacts transborder exchange of sea ice between the exclusive economic zones of the Arctic states. We use the Sea Ice Tracking Utility, which follows ice floes from formation to melt, in conjunction with output diagnostics from two ensembles of the Community Earth System Model that follow different future emissions scenarios. The Community Earth System Model projects that by midcentury, transnational ice exchange will more than triple, with the largest increase in the amount of transnational ice originating from Russia and the Central Arctic. However, long‐distance ice transport pathways are predicted to diminish in favor of ice exchanged between neighboring countries. By the end of the 21st century, we see a large difference between the two future emissions scenarios considered: Consistent nearly ice‐free summers under the high emissions scenario act to reduce the total fraction of transnational ice exchange compared to midcentury, whereas the low emissions scenario continues to see an increase in the proportion of transnational ice. Under both scenarios, transit times are predicted to decrease to less than 2 yr by 2100, compared to a maximum of 6 yr under present‐day conditions and 2.5 yr by midcentury. These significant changes in ice exchange and transit time raise important concerns regarding risks associated with ice‐rafted contaminants.</p

Caractéristiques de l'accroissement de la résistance de la souris contre <i>Pseudomonas aeruginosa</i> provoqué par <i>Staphylococcus aureus</i>

Mice were protected against a lethal dose of Pseudomonas aeruginosa by a previous sublethal infection with Staphylococcus aureus. Under similar conditions, Staphylococcus epidermidis afforded only slight protection.The following characteristics of this increased resistance that we have observed are (1) survival of mice, and decrease of the number of viable units of P. aeruginosa in the peritoneal cavity of the same mice infected with S. aureus coagulase-positive strains, either from our laboratory collection or from hospital cases, when the time interval between the injection with staphylococci and that of P. aeruginosa was between 4 and 96 h; (2) absence of a net inhibitory effect in vitro on P. aeruginosa with serum from mice infected with a sublethal dose of coagulase-positive S. aureus; (3) changes in the appearance of peritoneal exudate cells after infection with a sublethal dose of S. aureus; P. aeruginosa injected afterwards in the peritoneal cavity of mice was eliminated; when P. aeruginosa was injected alone, "activated macrophages" were not observed and bacterial cells were present in large numbers in the exudate. The immunostimulation induced by a previous sublethal injection of S. aureus coagulase-positive strains seemed to be inhibited by the immunosuppressive drug cyclophosphamide, since mice were no longer protected against a lethal dose of P. aeruginosa. Cell immunity may intervene in such infections with opportunistic species and check the invasiveness of a gram-negative bacterium superinfecting a host already exposed to coagulase-positive S. aureus. </jats:p

Increase in the in vitro susceptibility of <i>Staphylococcus aureus</i> to antimicrobial agents in the presence of <i>Candida albicans</i>

In experiments with mixed cultures of Staphylococcus aureus and Candida albicans both in the absence and in the presence of 5-fluorocytosine (5-FC), we have observed that (1) there is an inhibition of S. aureus growth in mixed cultures with C. albicans in media supplemented with 1 μg/mL of 5-FC and that 5-FC has no effect on staphylococci in pure cultures; (2) this inhibition occurred with clinically isolated and laboratory strains and could be reversed by specific metabolites; (3) Staphylococcus aureus was inhibited by filtrates of C. albicans cultures treated with 5-FC and this seemed to be favored by some C. albicans filterable product which can affect the cell wall and the permeability of the staphylococcal cells since they become sensitive to 5-FC; (4) nine other commonly used antimicrobials showed an increased inhibitory activity against S. aureus in mixed cultures with C. albicans; and (5) there is a decrease in the number of precipitating antigens of S. aureus and of the activity of alpha toxin when this species was grown with both C. albicans and 5-FC. Our results indicate that the susceptibility of some species to antimicrobials could be significantly modified in the presence of other species. One cannot exclude that a similar phenomenon could happen in hosts under treatment with antibiotics against infection. </jats:p

Accroissement par <i>Staphylococcus aureus</i> de la résistance de la souris envers l'infection par <i>Pseudomonas aeruginosa</i>

In our study of opportunistic pathogens, we have some indication that Staphylococcus aureus can increase resistance in mice against Pseudomonas aeruginosa. Intraperitoneal injections of sublethal doses of S. aureus had a protective effect in mice against lethal doses of P. aeruginosa, more so if living and coagulase-positive S. aureus strains were injected. This protective effect was obtained both with laboratory and freshly isolated hospital strains. The interval between these infections can be extended from 2 h up to 1 week and it is still possible to observe the resistance phenomenon. The increased resistance was accompanied by a decrease in viable units of P. aeruginosa in the peritoneal cavity of mice 6 h after the injection of this species. There was no protection by S. aureus against Candida albicans in similar experimental conditions. These observations indicate that intermicrobial ecology, understood here as the previous presence of another species in a host, may be a significant factor in the resistance to infection with opportunistic pathogens such as P. aeruginosa. </jats:p

Use of rabbit mesentery in the evaluation of adherence of prototrophic and auxotrophic gonococcal strains

Gonococcal strains of different nutritional types did not adhere to the same extent to rabbit mesentery in vitro. Prototrophic strains generally showed much more affinity than strains requiring arginine (or ornithine), hypoxanthine, and uracil (AHU− or OHU−) for growth. Rabbit mesentery may be useful in the comparative study of the adherence properties of prototrophic and AHU− or OHU− auxotrophic strains. </jats:p

Antibiotic susceptibilities and auxotypes of Neisseria gonorrhoeae strains from women with pelvic inflammatory disease or uncomplicated infections

The purpose of the present study was to compare the auxotypes and the minimal inhibitory concentrations of four antibiotics for 50 isolates from women with gonococcal pelvic inflammatory disease with those of 55 isolates from uncomplicated anogenital gonococcal infections. No significant differences in auxotype patterns and susceptibilities were found between isolates from the two groups.</jats:p

Patterns of Sea Ice Retreat in the Transition to a Seasonally Ice-Free Arctic

Abstract The patterns of sea ice retreat in the Arctic Ocean are investigated using two global climate models (GCMs) that have profound differences in their large-scale mean winter atmospheric circulation and sea ice drift patterns. The Community Earth System Model Large Ensemble (CESM-LE) presents a mean sea level pressure pattern that is in general agreement with observations for the late twentieth century. The Community Climate System Model, version 4 (CCSM4), exhibits a low bias in its mean sea level pressure over the Arctic region with a deeper Icelandic low. A dynamical mechanism is presented in which large-scale mean winter atmospheric circulation has significant effect on the following September sea ice extent anomaly by influencing ice divergence in specific areas. A Lagrangian model is used to backtrack the 80°N line from the approximate time of the melt onset to its prior positions throughout the previous winter and quantify the divergence across the Pacific and Eurasian sectors of the Arctic. It is found that CCSM4 simulates more sea ice divergence in the Beaufort and Chukchi Seas and less divergence in the Eurasian seas when compared to CESM-LE, leading to a Pacific-centric sea ice retreat. On the other hand, CESM-LE shows a more symmetrical retreat between the Pacific, Eurasian, and Atlantic sectors of the Arctic. Given that a positive trend in the Arctic Oscillation (AO) index, associated with low sea level pressure anomalies in the Arctic, is a robust feature of GCMs participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5), these results suggest that the sea ice retreat in the Pacific sector could be amplified during the transition to a seasonal ice cover.</jats:p

Is ice-rafted sediment in a North Pole marine record evidence for perennial sea-ice cover?

Ice-rafted sediments of Eurasian and North American origin are found consistently in the upper part (13 Ma BP to present) of the Arctic Coring Expedition (ACEX) ocean core from the Lomonosov Ridge, near the North Pole (≈88° N). Based on modern sea-ice drift trajectories and speeds, this has been taken as evidence of the presence of a perennial sea-ice cover in the Arctic Ocean from the middle Miocene onwards (Krylov et al. 2008 Paleoceanography 23, PA1S06. ( doi:10.1029/2007PA001497 ); Darby 2008 Paleoceanography 23, PA1S07. ( doi:10.1029/2007PA001479 )). However, other high latitude land and marine records indicate a long-term trend towards cooling broken by periods of extensive warming suggestive of a seasonally ice-free Arctic between the Miocene and the present (Polyak et al. 2010 Quaternary Science Reviews 29, 1757–1778. ( doi:10.1016/j.quascirev.2010.02.010 )). We use a coupled sea-ice slab-ocean model including sediment transport tracers to map the spatial distribution of ice-rafted deposits in the Arctic Ocean. We use 6 hourly wind forcing and surface heat fluxes for two different climates: one with a perennial sea-ice cover similar to that of the present day and one with seasonally ice-free conditions, similar to that simulated in future projections. Model results confirm that in the present-day climate, sea ice takes more than 1 year to transport sediment from all its peripheral seas to the North Pole. However, in a warmer climate, sea-ice speeds are significantly faster (for the same wind forcing) and can deposit sediments of Laptev, East Siberian and perhaps also Beaufort Sea origin at the North Pole. This is primarily because of the fact that sea-ice interactions are much weaker with a thinner ice cover and there is less resistance to drift. We conclude that the presence of ice-rafted sediment of Eurasian and North American origin at the North Pole does not imply a perennial sea-ice cover in the Arctic Ocean, reconciling the ACEX ocean core data with other land and marine records. </jats:p