Abundance and biomass of heterotrophic microbes in the Kongsfjorden, Svalbard

Abundance and biomass of heterotrophic microbes were investigated usingepifluorescense microscopy in August 2004 along a transect in the Kongsfjorden, a glacial fjord inthe high arctic, located in the north-western part of Svalbard. A bacterial abundance was low atouter fjord stations (on average 2.29 x 10~8 ind./dm^3) and was higher at inner fjord stations (onaverage 3.52 x 10~8 ind./dm^3).The biomass of bacteria ranged from 3.69 to 8.01 mg/m^3.The abundanceof bacteria was low at the surface of water(0 m), whereas the higher abundances often occurred atdepths of 30～50 m.The abundance of heterotrophic flagellates varied from 2.785 to 8.891 x 10~4 ind./dm^3. The assemblage was numerically dominated by less than 5 μm heterotrophic flagellates(78.67%～94.80%).The biomass of heterotrophic flagellates varied from 0.37 to 2.30 mg/m^3.The meanbiomass distribution for all stations was 4.91% for less than 5 μm heterotrophic flagellates,86.74% for 6～20 μm flagellates and 8.35% for greater than 20 μm sized flagellates.The low biomassof heterotrophic flagellates often occurred at the surface of water (0 m),while the maximum valueof biomass occurred at different depths. The biomass of total heterotrophic microbial communityranged from 4.20 to 10.03 mg/m^3.The mean biomass distribution for all stations was 82.58% forbacteria, 15.77% for flagellates and 1.66% for ciliates.

Molecular genetic diversity of bacteria in the bottom section of arctic sea ice from the Canada Basin

PCR-DGGE approach was used to analyze bacterial diversity in the bottomsection of seven arctic sea ice samples colleted from the Canada Basin. Thirty-two 16S rDNAsequences were obtained from prominent DGGE bands. The closest relatives of these sequences arefound to be those of cultivated or uncultured bacteria from antarctic or arctic sea ice.Phylogenetic analysis clustered these sequences or phylotypes within α- proteobacteria,γ-proteobacteria and CFB (cytophaga-flexibacter-bacteroides) group. Sequences belonging toγ-proteobacteria were dominant and members of the CFB group were highly abundant. It was suggestedthat the CFB group was the representative of the bottom section of sea ice samples.

Isolation and phylogenetic assignation of actinomycetes in the marine sediments from the Arctic Ocean

Actinomycetes in five marine sediments collected from the Arctic Ocean atdepths of 43 to 3 050 m were cultivated using a variety of media. A total of 61 actinomycetecolonies with substrate mycelia only were observed, and no colonies with aerial mycelia wereobserved under aerobic conditions at 15℃. From these colonies, 28 were selected to representdifferent morphological types. Denaturing gradient gel electrophoresis (DGGE) was used to check thepurity of isolates and select representatives for subsequent sequencing. Phylogentic analyses basedon nearly full-length 16S ribosomal RNA gene (rDNA) sequences indicated that the actinomycetesisolated were accommodated within genus Rhodococcus of family Nocardiaceae, genus Dietzia of familyDietziaceae, genera Janibacter and Terrabacter of family Instrasporangiaceae and genera Kocuria andA nhrobacter of family Micrococcaceae. One of the strains (P27-24) from the deep-sea sediment atdepth of 3 050 m was found to be identical in 16S rDNA sequence(1474/1474) with theradiation-resistant Kocuria rosea ATCC 187~T isolated from air. More than half of the isolatesshowed the similarities ranging from 99.5% to 99.9% in 16S rDNA sequence to dibenzofran-degrading,butyl 2-ethylhexanoate-hydrolysising and nitrile-metabolizing actinomycetes. All the strainsisolated were psychrotolerant bacteria and grew better on the media prepared with natural seawaterthan on the media prepared with deionized water. Three of them (Dietzia sp. P27-10, Rhodococcus sp.S11-3 and Rhodococcus sp.P11-5) had an obligate growth requirement for salt, confirming that thesestrains are indigenous marine actinomycetes.

Factors dominating bacterioplankton abundance and production in the Nordic seas and the Chukchi Sea in summer 2012

Abundance and production of bacterioplankton were measured in the Nordic seas and Chukchi Sea during the 5th Chinese Arctic Research Expedition in summer 2012. The results showed that average bacterial abundances ranged from 3.31×10^11 cells/m^3 to 2.25× 10^11 cells/m^3, and average bacterial productions （calculated by carbon） were 0.46 mg/（m^3·d） and 0.54 mg/（m^3·d） in the Nordic seas and Chukchi Sea, respectively. T-test result showed that bacterial abundances were significantly different between the Nordic seas and Chukchi Sea, however, no significant difference was observed regarding bacterial productions. Based on the slope of lg bacterial biomass versus lg bacterial production, bacterial communities in the Nordic seas and Chukchi Sea were moderately dominated by bottom-up control. Both Pearson correlation analysis and multivariable linear regression indicated that temperature had significant positive correlation with bacterial abundance in the Chukchi Sea, while no correlations with productions in both areas. Meanwhile, Chl a had positive correlations with both bacterial abundance and production in these two regions. As the temperature and Chl a keep changing in the future, we suggest that both bacterial abundance and production been hanced in the Chukchi Sea but weaken in the Nordic seas, though the enhancement will not be dramatic as a result of higher pressure of predation and viral lysis.

Inter-comparisons of thermodynamic sea-ice modeling results using various parameterizations of radiative flux

Radiative fluxes are of primary importance in the energy and mass balance of the sea-ice cover. Various parameterizations of the radiative fluxes are studied in a thermodynamic sea-ice model. Model outputs of the surface radiative and heat fluxes and mass balance are compared with observations. The contribution of short-wave radiation is limited to a long part of winter. Therefore, simple schemes are often sufficient. Errors in estimations of the short-wave radiation are due mainly to cloud effects and occasionally to multi-reflection between surface and ice crystals in the air. The long-wave radiation plays an important role in the ice surface heat and mass balance during most part of a winter. The effect of clouds on the accuracy of the simple radiative schemes is critical, which needs further attention. In general, the accuracy of an ice model depends on that of the radiative fluxes.

Snow and sea ice thermodynamics in the Arctic:Model validation and sensitivity study against SHEBA data

Evolution of the Arctic sea ice and its snow cover during the SHEBA year were simulated by applying a high-resolution thermodynamic snow/ice model （HIGHTSI）. Attention was paid to the impact of albedo on snow and sea ice mass balance, effect of snow on total ice mass balance, and the model vertical resolution. The SHEBA annual simulation was made applying the best possible external forcing data set created by the Sea Ice Model Intercomparison Project. The HIGHTSI control run reasonably reproduced the observed snow and ice thickness. A number of albedo schemes were incorporated into HIGHTSI to study the feedback processes between the albedo and snow and ice thickness. The snow thickness turned out to be an essential variable in the albedo parameterization. Albedo schemes dependent on the surface temperature were liable to excessive positive feedback effects generated by errors in the modelled surface temperature. The superimposed ice formation should be taken into account for the annual Arctic sea ice mass balance.

Diurnal variability of the planetary boundary layer height estimated from radiosonde data

Diurnal variations in the planetary boundary layer height(PBLH)at different latitudes over different surface characteristics are described,based on 45 years(1973−2017)of radiosonde observations.The PBLH is determined from the radiosonde data by the bulk Richardson number(BRN)method and verified by the parcel method and the potential temperature gradient method.In general,the BRN method is able to represent the height of the convective boundary layer(BL)and neutral residual layer cases but has relatively large uncertainty in the stable BL cases.The diurnal cycle of the PBLH over land is quite different from the cycle over ocean,as are their seasonal variations.For stations over land,the PBLH shows an apparent diurnal cycle,with a distinct maximum around 15:00 LT,and seasonal variation,with higher values in summer.Compared with the PBLH over land,over oceans the PBLH diurnal cycles are quite mild,the PBLHs are much lower,and the seasonal changes are less pronounced.The seasonal variations in the median PBLH diurnal cycle are positively correlated with the near-surface temperature and negatively correlated with the near-surface relative humidity.Finally,although at most latitudes the daytime PBLH exhibits,over these 45 years,a statistically significant increasing trend at most hours between 12:00 LT and 18:00 LT over both land and ocean,there is no significant trend over either land or ocean in the nighttime PBLH for almost all the studied latitudes.

基于无线电掩星数据,探空资料以及再分析资料估算大气边界层高度的比较

用11年的全球无线电掩星数据(COSMIC),无线电探空数据(IGRA)以及欧洲中心再分析资料(ERA-Interim)对全球大气边界层高度(PBLH)进行估算比较.结果表明:(1)在1200 UTC和0000 UTC,由ERA-Interim和IGRA数据估算得到的全球PBLH空间分布较为一致,相关性较好,在白天正午时候太阳辐射能力较强,对流活动频繁,估算得到的大气边界层高度较高.(2)由COSMIC掩星数据估算得到的边界层高度比探空数据和再分析数据估算结果整体偏大.(3)COSMIC掩星数据,IGRA探空数据以及ERA-Interim再分析资料估算结果都表明边界层高度在低纬度地区偏大,高纬度地区偏小.(4)分析不同数据估算边界层高度纬向季节性差异表明,IGRA探空数据和COSMIC数据间差异为-1700m至-500m,IGRA与ERA-Interim之间的差异为-500m至250m.此外,对于大多数纬度而言,三个数据集之间的差异在冬季较大,在夏季较小.

Biodiversity and phylogenetic analysis of the gut microbiome of Euphausia superba Dana from the Rose Sea of the Antarctic Ocean

Metabolites derived from marine symbiotic microorganisms have great potential as lead compounds for the discovery of novel marine drugs. Euphausia superba Dana, which lives in the Antarctic Ocean, is regarded as a new source of marine microbial natural products. However, no studies have examined the biodiversity of the symbiotic intestinal microbiome of E. superba. To address this issue, the species diversity and abundance of the gut microbiome of E. superba Dana from the Rose Sea of the Antarctic Ocean were analyzed by culture-independent high-throughput sequencing and pure culture methods. A comparison with gene databases revealed that the microbiome contained 61 known microbial species and a plethora of uncultivable microorganisms. Additionally, 7% of the species in the microbiome were currently unknown. The microbes belonged to 56 genera, eight of which, including Arthrobacter, Bacillus, Candidatus, Lactococcus, Lysinibacillus, Leuconostoc, Solibacillus, and Vibrio, were dominant, as were Vibrionaceae spp. Moreover, 81 microbial strains were isolated by the pure culture method, and they belonged to 36 genera, including Mobilicoccus, Rhodococcus, Arthrobacter, and Microbacterium. The results obtained by two different methods demonstrate the richness of the microbial biodiversity of the gut microbiome of E. superba, and it also suggests that they have good potential for the discovery of novel marine microbial species.

Characterization of the summer pack ice biotic community of Canada Basin

Summer pack ice biotic community of the Canada Basin was characterized duringthe Second Chinese National Arctic Research Expedition (CHINARE-2003,20 August—5 September 2003).Bacteria, ice algae (diatoms and autotrophic flagellates) and protozoa (mainly heterotrophicflagellates) were observed throughout the whole ice column. The vertical distribution of biotic taxavaried among sites. The integrated biomass ranged from 48.4 and 58.1 mg/m^2, with an average of55.2 mg/m^2. Bacteria were the dominant of the assemblage in pack ice, accounted for 84.1% of theintegrated, and ice algae, which usually dominate the ice biotic community, constituted only 3.5% ofthe total. Considering the quick environmental changes of the Arctic Ocean in recent years, wesuggested that quick melting of pack ice in summer was suggested, which caused such change of packice biotic community. The low salinity throughout the whole ice column and the continuous melting ofthe pack ice cumbered the formation of ice algae bloom in summer, finally resulting in thedominance of microbial food web with bacteria and heterotrophic flagellates as the most obviouscharacteristics. Considering the high ratio of pack ice primary production to the total found inprevious studies, the quick change of pack ice community structure in summer would deeply influencethe marine ecosystem of the high Arctic Ocean.

Algorithm for the estimation of ionosphere parameters from ground scatter echoes of SuperDARN

The High-frequency over-the-horizon radar ground and sea backscatter echoes can be used to estimate the ionosphere critical frequency, providing the ionosphere states up to thousands of kilometers from the transmitter to receiver location. In this study,using the frequency scanning mode of super dual auroral radar network(SuperDARN), the skip distance of every frequency band can be obtained, then, the variation of maximum usable frequency with range is estimated. With the knowledge of elevation angles or an assigned virtual reflection height in ionosphere, the F-region critical frequency has been estimated. The cross correlation of these two sample populations as a function of the lag is calculated, which shows that the cross-correlation coefficients can be as high as 0.8 in all selected events at 0 lag, thus validating the rationality of the proposed algorithm.Therefore, the algorithm is suitable for application under conditions of abundant ground/sea backscatter echoes.

The variability of surface radiation fluxes over landfast sea ice near Zhongshan station,east Antarctica during austral spring

Surface radiative fluxes over landfast sea ice off Zhongshan station have been measured in austral spring for five springs between 2010 and 2015.Downward and upward solar radiation vary diurnally with maximum amplitudes of 473 and 290 W m^(−2),respectively.The maximum and minimum long-wave radiation values of the mean diurnal cycle are 218 and 210 W m^(−2)for downward radiation,277 and 259 W m^(−2)for upward radiation and 125 and−52 W m^(−2)for net radiation.The albedo has a U-shaped mean diurnal cycle with a minimum of 0.64 at noon.Sea ice thickness is in the growth phase for most spring days,but can be disturbed by synoptic processes.The surface temperature largely determines the occurrence of ice melting.Surface downward and upward long-wave radiation show synoptic oscillations with a 5–8 day period and intraseasonal variability with a 12–45 day period.The amplitudes of the diurnal,synoptic and intraseasonal variability show some differences during the five austral springs considered here.The intraseasonal and synoptic variability of downward and upward long-wave radiation are associated with the variability of cloud cover and surface temperature induced by the atmospheric circulation.