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WACCM 기후모델을 이용한 극지역 고층대기 흐름의 수치모의에 대한 연구계획 및 초기 결과 발표
Water stable isotope composition of precipitation has been used to understand the global and regional water cycles. To investgate the regional water cycle, previous studies have relied mostly on changes in daily- to monthly-averaged isotope composition of precipitation. Figure 1 displays an isotopic scheme during evaporation and precipitation. In the figure, however, the exact numbers can vary depending on meteorological factors such as temperature and precipitation rate, even within a single rainfall event. In this study, we monitored the changes in water isotope composition over the course of rainfall events. The results showed that the δD and δ18O values varied widely from -11.94‰ to -2.18？‰ and from -91.44‰ to -14.40？‰, respectively. The δD-δ18O slope for entire samples was 8.18, but those for single events were 6.51, 7.43 and 9.93. Our study stresses the need for high-resolution sampling of precipitation to better understand the regional water cycle.
We analyzed the temperature data obtained from Aura/MLS and the polar cap index (PCI) of MERRA re-analysis data during the period of 2004 through 2013, in order to statistically investigate the variations of the stratospheric and mesospheric temperatures during northern sudden stratospheric warming (SSW) event. In this study, we investigated the height profiles of the correlation coefficients between MERRA daily PCI anomalies at 10hPa and MLS daily temperatures of 55 height levels in the range of 1 km to 100 km during northern winter seasons. Our results showed that there is a weak and broad negative correlation between PCI and temperature anomalies in entire mesospheric region during the period without SSW. Furthermore, our results indicate that there is a strong positive correlation between the PCI anomalies and upper mesospheric temperatures during major SSWs, whereas a strong negative correlation appears in lower mesosphere region. This is good agreement with the result of Siskind et al. (2005) which studied the correlation coefficients derived from TIMED/SABER temperatures for three SSW events. In this study, we also present the comparison of our results from observation and re-analysis data with those from WACCM simulation and the discussions about the difference will be addressed.
We conducted the scientific ice coring project led by PNRA and KOPRI during the 2013/2014 Italian-Korean Antarctic Expedition in the framework of International Partnerships in Ice Core Science (IPICS) to understand the climatic variability in the last 2000 years. In the part of project, we collected a 3.0 m-depth snow pit at the site of GV7 (S 70°41'17.1", E 158°51'48.9", 1950 m a.s.l.), Antarctica. Here, we present the results obtained from the analysis of the water isotope compositions, the major ion concentrations, and the mineral dust concentrations from the snow pit. Snow densities and temperatures also measured in the field. At KOPRI, the samples were melted, then the stable water isotopes, major ions, and particle size distribution were analyzed with the cavity ring-down spectrometers (L1102-i, Piccaro), ion chromatography (ICS-2100, Thermo), and coulter counter (Multisizer 3, Beckman Coulter), respectively. The <sup>18</sup>O varies between -38.3 and -24.1‰ with a mean value of -31.0‰. The δD ranges between -331 and -186‰ with a mean value of -243‰. Among the ion concentrations (Na+, Ca2+, Mg2+, Cl-, SO42-, MSA) from the snow pit, MSA concentrations show a clear seasonal variation. The mineral dust in the pit characterized with the differences of the concentration and the particle size distribution by the seasonality. These data allow us to assume about 4.5 years of snow deposition covered from 2009 to 2013 by these oscillations of the isotopes and geochemical characteristics.
We determined the complete chloroplast DNA sequence of an extremophile plant, Colobanthus quitensis (Antarctic pearlwort), by de novo assembly based on the sequencing results from Illumina MiSeq platform (Illumina Inc., San Diego, CA). The chloroplast genome of C. quitensis (NCBI accession no. KT737383) is a sequence of 151 276 bp long with a typical quadripartite structure composed of a large single copy region, a small single copy region and a pair of inverted repeats. The overall GC content of C. quitensis genome is 36.7% and it has 66 simple sequence repeats. It contains a total 112 genes including 78 protein coding genes, 30 tRNA genes, and four rRNA genes.
We determined the mitogenome sequence of Munida gregaria (Fabricius 1793) (Anomura, Galatheoidea,
Munididae), which is the first complete mitogenome sequence in the family Munididae Ahyong et al.,
2010. The mitogenome of M. gregaria is 16 326 bp in length and contains 13 protein-coding genes
(PCGs), 22 transfer RNAs (tRNAs), two ribosomal RNAs (rRNAs) and two control regions (CRs).
Mitogenome analysis of M. gregaria showed an extra copy of the CR and rearrangements of two PCGs
(nad2 and nad3) compared to the arthropod ground pattern. Additionally, it contains a tRNA (trnY) inversion
and rearrangements of two PCGs (nad1 and nad3) when compared with that of Neopetrolisthes
maculatus and Shinkaia crosnieri, respectively. The phylogenetic tree confirmed that M. gregaria belongs
to the superfamily Galatheoidea within Anomura. Our results will be useful for the detailed study of
mitogenome evolution and the phylogenetic relationships among the superfamily in the infraorder
We determined δ<sup>18</sup>O<sub>Cib</sub> values of live (Rose Bengal stained) and dead epibenthic foraminifera Cibicidoides wuellerstorfi, Cibicides lobatulus, and Cibicides refulgens in surface sediment samples from the Arctic Ocean and the Greenland, Iceland, and Norwegian seas (Nordic Sea). This is the first time that a comprehensive δ<sup>18</sup>O<sub>Cib</sub> data set is generated and compiled from the Arctic Ocean. For comparison, we defined Atlantic Water (AW), upper Arctic Bottom Water (uABW), and ABW by their temperature/salinity characteristics and calculated mean equilibrium calcite δ<sup>18</sup>O<sub>equ</sub> from summer sea-water δ<sup>18</sup>O<sub>w</sub> and in situ temperatures accordingly. As a result, in the Arctic environment we compensate for Cibicidoides- and Cibicides-specific offsets from equilibrium calcite of -0.35 and -0.55 ‰, respectively. After this taxon-specific adjustment, mean δ<sup>18</sup>O<sub>Cib</sub> values plausibly reflect the density stratification of principle water masses in the Nordic Sea and Arctic Ocean. In addition, mean δ<sup>18</sup>O<sub>Cib</sub> from AW not only significantly differs from mean δ<sup>18</sup>O<sub>Cib</sub> from ABW, but also δ<sup>18</sup>O<sub>Cib</sub> from within AW differentiates between provenience and water mass age. Furthermore, in shallow waters brine-derived low δ<sup>18</sup>O<sub>w</sub> can significantly lower the δ<sup>18</sup>O<sub>Cib</sub> of Cibicides spp. and thus δ<sup>18</sup>O<sub>Cib</sub> may serve as a paleobrine indicator. There is no statistically significant difference, however, between deeper water masses mean δ<sup>18</sup>O<sub>Cib</sub> of the Nordic Sea, and the Eurasian and Amerasian basins, and no influence of low-δ<sup>18</sup>O<sub>w</sub> brines is recorded in Recent uABW and ABW δ<sup>18</sup>O<sub>Cib</sub> of C. wuellerstorfi. This may be due to dilution of a low-δ<sup>18</sup>O<sub>w</sub> brine signal in the deep sea, and/or to preferential incorporation of high-δ<sup>18</sup>O<sub>w</sub> brines from high-salinity shelves. Although our data encompass environments with seasonal sea-ice and brine formation supposed to ultimately ventilate the deep Arctic Ocean, δ<sup>18</sup>O<sub>Cib</sub> from uABW and ABW do not indicate negative excursions. This may challenge hypotheses that call for enhanced Arctic brine release to explain negative benthic δ<sup>18</sup>O spikes in deep-sea sediments from the late Pleistocene North Atlantic Ocean.
We established the first complete ice core processing method and analytical procedures for
fundamental proxies, using a 40.2 m long ice core drilled on the Mt. Tsambagarav glacier in the Mongolian
Altai mountains in July 2008. The whole core was first divided into two sub ice core sections and the
measurements of the visual stratigraphy and electrical conductivity were performed on the surface of these
sub core sections. A continuous sequence of samples was then prepared for chemical analyses (stable
isotope ratios of oxygen (<sup>18</sup>O/<sup>16</sup>O) and hydrogen (<sup>2</sup>H/<sup>1</sup>H), soluble ions and trace elements). A total of 29
insoluble dust layers were identified from the measurement of visual stratigraphy. The electrical
conductivity measurement (ECM) shows 11 peaks with the current more than 0.8 μA. Comparing the
profiles of SO<sub>4</sub><sup>2-</sup> and Cl<sup>-</sup> concentrations to correlate with known volcanic eruptions, the first two ECM
peaks appear to be linked to the eruptions (January and June 2007) of Kliuchevskoi volcano on the
Kamchatka Peninsula of Russia, which supports the reliability of our ECM data. Finally, the composition of
stable isotopes (δ<sup>18</sup>O and δD) shows a well-defined seasonal variation, suggesting that various chemical
proxies may have been well preserved in the successive ice layers of Tsambagarav ice core. Our ice core
processing method and analytical procedures for fundamental proxies are expected to be used for
paleoclimate and paleoenvironmental studies from polar and alpine ice cores.
We evaluated a 10 year time series of δ<sup>18</sup>O and δ<sup>13</sup>C records from three planktic foraminifers (Neogloboquadrina pachyderma, Globigerina umbilicata, and Globigerinita glutinata) in the Bering Sea and
central subarctic Pacific with a focus on their responses to environmental changes. Foraminiferal δ<sup>18</sup>O followed the equilibriumequation for inorganic calcite, with species-specific equilibriumoffsets ranging fromnearly zero
( 0.02‰for N. pachyderma and 0.01‰ for G.umbilicata) to 0.16‰(G. glutinata). Equilibrium offsets in our sediment trap sampleswere smaller than those fromplankton tow studies, implying that foraminiferal δ<sup>18</sup>Owas
modified by encrustation during settling. Habitat/calcification depths varied from 35-55m (N. pachyderma and G.umbilicata) or 25-45m (G. glutinata) duringwarm, stratified seasons to around 100m during winter,
when the mixed layer depth increases. Unlike δ<sup>18</sup>O, foraminiferal δ<sup>13</sup>C showed species-specific responses to environmental changes. We found a dependency of δ<sup>13</sup>C in G.umbilicata on CO<sub>3</sub><sup>-2</sup> concentrations in ambient seawater that agreed reasonably well with published laboratory results, suggesting that δ<sup>13</sup>C of G.umbilicata is subject to vital effects. In contrast, δ<sup>13</sup>C of N. pachyderma and G. glutinata are likely affected by other species-specific biological activities. Seasonal flux patterns reveal that fossil records of N. pachyderma and G. glutinata represent annual mean conditions, whereas that of G.umbilicata most likely indicates those of a
specific season. Because none of these three taxawas abundant from December to February, their fossil records likely do not reflect isotope signals from cold seasons.
We examined microzooplankton abundance, community structure, and grazing impact on phytoplankton in the Amundsen Sea, Western Antarctica, during the early austral summer from December 2010 to
January 2011. Our study area was divided into three regions based on topography, hydrographic prop-erties, and trophic conditions: (1) the Oceanic Zone (OZ), with free sea ice and low phytoplankton
biomass dominated by diatoms; (2) the Sea Ice Zone (SIZ), covered by heavy sea ice with colder water,lower salinity, and dominated by diatoms; and (3) the Amundsen Sea Polynya (ASP), with high phyto-
plankton biomass dominated by Phaeocystis antarctica. Microzooplankton biomass and communities associated with phytoplankton biomass and composition varied among regions. Heterotrophic dino-
flagellates (HDF) were the most significant grazers in the ASP and OZ, whereas ciliates co-dominated with HDF in the SIZ. Microzooplankton grazing impact is significant in our study area, particularly in the
ASP, and consumed 55.4-107.6% of phytoplankton production (average 77.3%), with grazing impact increasing with prey and grazer biomass. This result implies that a signi？cant proportion of the phyto-
plankton production is not removed by sinking or other grazers but grazed by microzooplankton. Compared with diatom-based systems, Phaeocystis-based production would be largely remineralized
and/or channeled through the microbial food web through microzooplankton grazing. In these waters the major herbivorous fate of phytoplankton is likely mediated by the microzooplankton population. Our
study confirms the importance of herbivorous protists in the planktonic ecosystems of high latitudes. In conclusion, microzooplankton herbivory may be a driving force controlling phytoplankton growth in
early summer in the Amundsen Sea, particularly in the ASP.
We examined microzooplankton abundance, community structure, and grazing impact on phytoplankton in the Amundsen Sea, Western Antarctica, during the early austral summer from December 2010 to January 2011. Our study area was divided into three regions based on topography, hydrographic properties, and trophic conditions: (1) the Oceanic Zone (OZ), with free sea ice and low phytoplankton biomass dominated by diatoms; (2) the Sea Ice Zone (SIZ), covered by heavy sea ice with colder water, lower salinity, and dominated by diatoms; and (3) the Amundsen Sea Polynya (ASP), with high phytoplankton biomass dominated by Phaeocystis antarctica. Microzooplankton biomass and communities associated with phytoplankton biomass and composition varied among regions. Heterotrophic dinoflagellates (HDF) were the most significant grazers in the ASP and OZ, whereas ciliates co-dominated with HDF in the SIZ. Microzooplankton grazing impact is significant in our study area, particularly in the ASP, and consumed 55.4 - 107.6% of phytoplankton production (average 77.3%), with grazing impact increasing with prey and grazer biomass. This result implies that a significant proportion of the phytoplankton production is not removed by sinking or other grazers but grazed by microzooplankton. Compared with diatom-based systems, Phaeocystis-based production would be largely remineralized and/or channeled through the microbial food web through microzooplankton grazing. In these waters the major herbivorous fate of phytoplankton is likely mediated by the microzooplankton population. Our study confirms the importance of herbivorous protists in the planktonic ecosystems of high latitudes. In conclusion, microzooplankton herbivory may be a driving force controlling phytoplankton growth in early summer in the Amundsen Sea, particularly in the ASP.
We examined the recent history of sedimentary organic carbon (SOC) accumulation on the western Amundsen Shelf, to help characterize the biological carbon pump in the Amundsen Sea, Antarctica. Vertical sedimentary profiles (in the upper 21-cm) of SOC content, radio- and stable-carbon isotopes were obtained at four locations in the western Amundsen Sea: near the shelf break, inside the polynya near the Dotson Ice Shelf, and at both the periphery and the center of the Amundsen Sea polynya. Profiles were representative not only of various distances from the coast, but also of various summertime sea ice conditions and bottom depths. The SOC content (up to 1.1%) and the radiocarbon content were distinctly higher at the periphery and at the center of the polynya than at the other sites. The SOC and <sup>14</sup>C contents were generally consistent with the spatial distribution of primary productivity in the surface water. A linear SOC accumulation rate of about 1.0 g Cm<sup>-2</sup> yr<sup>-1</sup> was determined from the conventional <sup>14</sup>C ages of bulk SOC below the surface mixed layer at the periphery and at the center of the polynya, for the time period of 3.1 - 4.7 kyr before present (BP). This linear SOC accumulation rate was about 20 times greater than the rates determined at the two other sites for the period of 4.6 - 15.7 kyr BP. Note that all values are for uncorrected 14C ages. At the center of the polynya, a sudden change in SOC accumulation rate was observed at about 16 cm depth, corresponding to 4.7 kyr BP, implying that changes (during this time period) in physical environments greatly affected primary production, SOC burial and/or supply of allochthonous particles to this site. The vertical distribution of <sup>14</sup>C content in the sediments implies that aged organic matter, likely associated with resuspended sediments, was also being deposited inside the polynya, in addition to autochthonous biogenic particles. If our estimation of SOC accumulation is extrapolated to the western Amundsen Shelf between 110°W and 120°W, approximately 3×1010 g C yr<sup>-1</sup> is buried on the shelf, with ~90% of SOC accumulation occurring in the Amundsen Sea polynya
We have conducted intensive Arctic summertime surveys in recent 5 years to examine temporal variations and spatial distributions of the Pacific-origin Summer Water (PSW) in the Chukchi Borderland (CBL), Arctic Ocean. With the Korean icebreaker Araon, these expeditions lasted for 21 days in 2011, 45 days in 2012, 13 days in 2013, and 25 days in 2014, mostly July to August. It is understood that heat transport of the PSW to CBL is one of the key processes to comprehend the rapid sea ice reduction and changes in water column structure in the Pacific sector of the Arctic Ocean. We present recent features of PSW’s variations identified from our Arctic cruise data using CTD/XCTD, LADCP, and other measurements. In 2011 summer, the PSW appeared to exist in the eastern flank of the Chukchi Plateau and its signal diminished gradually toward the west. In 2012 summer, the PSW tended to mainly pass through the vicinity of the Northwind Ridge and extended toward the west. In 2013 summer, the PSW with 0.29° C and 30.68 psu was found in the center of the Chukchi Plateau and its layer deepened slightly toward the east. During the cruises in 2011, 2012, and 2013, the PSW was identified in the west of 175° W where it had never been observed previously. In addition, how the spreading of PSW’s pathway and distribution of temperature maximum layer do have an influence on rapid sea ice retreat will be discussed.
We have conducted three times intensive Antarctic cruises in the Amundsen Sea (west Antarctic) in early (2010/2011 and 2013/2014) and late (2011/2012) austral summertime. These cruises were conducted as a Korea Polar Research Institute (KOPRI) Amundsen project. Amundsen polynya is one of the most productive Antarctic coastal polynya, and high chlorophylls (observed and satellite induced) were concentrated in polynya center rather than in the edge of polynya both in early and late summer. To examine phytoplankton dynamics in severely iron limited environment, the phytoplankton physiological parameters were measured by Fluorescence Induction and Relaxation (FIRe) system. In addition, we carried out iron assimilation experiments on board to demonstrate that iron enrichment responses of natural phytoplankton assemblages. Possible implications of iron limitation and controlling factors of phytoplankton growth in this polynya system will be discussed.
We have conducted three times intensive antarctic cruises in the Amundsen Sea. Amundsen polynya is one of the most productive Antarctic coastal polynya, and high chlorophylls were concentrated in polynya center rather than in the edge of polynya both in early and late summer. To examine phytoplankton dynamics in severely iron limited environment, the phytoplankton physiological parameters were measured by FIRe system.
We have developed a forecast model of solar proton flux profiles (> 10 MeV channel)
for well-connected events. Among 136 solar proton events (SPEs) from 1986 to 2006, we select 49
well-connected ones that are all associated with single X-ray flares stronger than M1 class and start to
increase within 4 h after their X-ray peak times. These events show rapid increments in proton flux. By
comparing several empirical functions, we select a modified Weibull curve function to approximate a SPE
flux profile. The parameters (peak flux, rise time, and decay time) of this function are determined by the
relationship between X-ray flare parameters (peak flux, impulsive time, and emission measure) and SPE
parameters. For 49 well-connected SPEs, the linear correlation coefficient between the predicted and the
observed proton peak fluxes is 0.65 with the RMS error of 0.55 log10(pfu). In addition, we determine another
forecast model based on flare and coronal mass ejection (CME) parameters using 22 SPEs. The used CME
parameters are linear speed and angular width. As a result, we find that the linear correlation coefficient
between the predicted and the observed proton peak fluxes is 0.83 with the RMS error of 0.35 log10(pfu).
From the relationship between error of model and CME acceleration, we find that CME acceleration is an
important factor for predicting proton flux profiles.
We have examined the flux, biogenic composition, and isotopic values of sinking particles collected by a time-series sediment trap deployed in the sea ice zone (SIZ) of the Amundsen Sea from January 2011 for one year. The major portion of the particle flux occurred during the austral summer in January and February when sea ice concentration was reduced to <60 %. Biogenic components, dominated by opal (~78 % of the biogenic components), accounted for over 75 % of particle flux during this high flux period. The dominant source of sinking particles shifted from diatoms to soft-tissued organisms, evidenced by high particulate organic carbon (POC) content (>30 %) and low bio-Si/POC ratio (<0.5) during the austral winter. CaCO3 content and its contribution to total particle flux were low (~6 %) throughout the study period. Aged POC likely supplied from sediment resuspension accounted for a considerable fraction only from October to December, which was evidenced by low radiocarbon content and relatively high (30-50 %) content of the non-biogenic component. When compared to POC flux inside the Amundsen Sea polynya obtained by the US Amundsen Sea Polynya International Research Expedition (ASPIRE), the POC flux integrated over the austral summer in the SIZ was virtually identical although maximum POC flux was about half that inside the Amundsen Sea polynya. This comparatively high POC flux integrated over the austral summer in the SIZ may be caused by persistence of phytoplankton bloom for a longer period and more efficient export of organic matter potentially owing to the diatom-dominant plankton community. If this observation is a general phenomenon on the Amundsen Shelf, the role of the SIZ compared to the polynyas need to be examined more carefully when trying to characterize the POC export in this region.
We have statistically studied the relationship between electromagnetic ion cyclotron (EMIC) waves and cold plasmaspheric plasma (Nsp) in the L range of 6-12 using the Time History of Events and Macroscale Interactions during Substorms (THEMIS) data for 2008-2011. The important observational results are as follows: (1) Under quiet geomagnetic conditions (Kp≤ 1), the maximum occurrence rate of the hydrogen (H) band EMIC waves appears in the early morning sector (0600-0900 MLT) at the outermost region (L = 10-12). (2) Under moderate and disturbed conditions (Kp≥ 2), the H-band occurrence rate is higher in the morning-to-early afternoon sector for L> 10. (3) The high occurrence region of helium (He) band waves for Kp≤ 1 varies from L = 7 to 12 in radial distances along the local time (i.e., at L∼ 7 near noon and at L = 8-12 near late afternoon). (4) The He-band waves for Kp≥ 2 are mainly localized between 1200 and 1800 MLT with a peak around 1500-1600 MLT at L = 8-10. (5) Nsp is much higher for the He-band intervals than for the H-band intervals by a factor of 10 or more. The He-band high occurrence appears at a steep Nsp gradient region. (6) The morning-afternoon asymmetry of the normalized frequency seen both in H-band and He-band is similar to the asymmetric distribution of Nsp along the local time. These observations indicate that the cold plasma density plays a significant role in determining the spectral properties of EMIC waves. We discuss whether a morning-afternoon asymmetry of the EMIC wave properties can be explained by the spatial distribution of cold plasmaspheric plasma.
We have studied the spectral properties of quiet-time electromagnetic ion cyclotron (EMIC)waves following a steady quiet condition, which is defined with Kp values ≤1 during 12 h, using GOES 10,11, and 12 magnetometer data for solar minimum years 2007-2008. We identified 6584 steady quiet-timeEMIC wave samples using a semiautomated procedure. Approximately 82% of the samples were observedin the morning-to-early afternoon sector (0700-1500 magnetic local time) with a maximum occurrencenear noon, and their peak frequencies were mostly in the He band. We found that the occurrence rate ofsteady quiet-time EMIC waves is higher than that of EMIC waves for all or quiet geomagnetic conditions(Dst>0 nT or AE < 100 nT) reported in previous studies by a factor of 2 or more. The frequency ratio fpeak(sample’s peak frequenc y)/fH+(the local proton gyrofrequency) of the He-band waves (∼0.11-0.16) understeady quiet conditions is lower than that (∼0.14-0.24) in previous studies. These results may be due tothe fact that the plasmasphere expanded more frequently to the geosynchronous region under extremelyquiet geomagnetic conditions in 2007-2008 than the periods selected in previous studies. The amplitudeand frequency of He-band EMIC waves for nonlinear wave growth are examined as changing cold plasmadensity at geosynchronous orbit. We confirm that the spectral properties of observed EMIC waves are ingood agreement with the nonlinear theory.
We investigate the climatological characteristics of diurnal variations of electron density in middle and high latitude ionospheres during solar maximum (2000-2002) and minimum (2008-2009) periods. For this study, we use the electron density profiles obtained from incoherent scatter radars at Millstone Hill, European Incoherent Scatter UHF radar (EISCAT) in Tromsø, and EISCAT Svalbard radar (ESR). In middle latitude at Millstone Hill, mid-latitude summer evening anomaly (MSEA) appears for both solar activities. Annual anomaly is much stronger during solar maximum. In the auroral region at Tromsø, two density peaks appears for June solstice and strong annual anomaly also occurs during solar maximum. In the polar cap region at Svalbard, nighttime peak appears in addition to the daytime peak only during solar maximum. Electron density for June solstice is greater than the other seasons during solar minimum. There are differences of electron densities between auroral and polar cap regions. Daytime peak in the auroral region occurs at local noon time, but in the polar cap region, it occurs at magnetic local noon time. During solar maximum, the nighttime peaks at magnetic local midnight are much stronger in the polar cap region.
We investigate the diurnal variations of electron density in the middle and high latitude summer ionosphere during the last deep solar minimum period. For this study, we use the electron density profiles obtained from incoherent scatter radars at Millstone Hill, European Incoherent Scatter UHF radar (EISCAT) in Tromsø, and EISCAT Svalbard radar (ESR) and total electron content (TEC) measured by JASON-1 satellite. The data show that there is a density peak in the evening in addition to the daytime peak. This evening peak at mid-latitude is particularly distinctive in summer, even larger than the daytime peak, but disappears in winter. At high latitudes, however, the evening peak becomes moderate and the altitude of the peak is also similar to the daytime peak while it is much higher than the latter at mid-latitude. We also find that the two-peak structure in summer is more distinctive in the polar cap region (e.g., in Svalbard) than in the auroral region (e.g., in Tromsø). In this presentation, we will discuss the possible explanations for the characteristics of the structure.
We investigate the possible impacts of the
Pacific Decadal Oscillation (PDO) on the occurrence of
weak stratospheric polar vortex (WSV) events in the Northern
Hemisphere winter. WSV events, which are defined
when polar-cap geopotential height anomalies at 50 hPa
fall below the 10th percentile in winter, are observed more
frequently during positive PDO phases than during negative
PDO phases. Additionally, tropospheric wave forcings
that drive WSV events are remarkably different between
the two phases of the PDO. During the positive PDO phase,
the vertical propagation of wavenumber-one waves plays
a predominant role with a rather minor contribution of
wavenumber-two waves. This contrasts with the negative
PDO phase when the WSV events are primarily caused by
wavenumber-two waves. This difference is partly related to
the PDO-induced tropospheric circulation anomalies over
the North Pacific whose zonal wavenumber-one component
constructively (destructively) interferes with climatological
planetary-scale waves during positive (negative) PDO
winters. The predominant wavenumber-two wave forcings
during the negative PDO phase are likely related to
the enhanced tropospheric eddy activity over Alaska that
results from the poleward shift of the Pacific jet in response
to the negative PDO.
We investigated 32 net primary productivity (NPP) models by assessing skills to reproduce integrated NPP in the Arctic Ocean. The models were provided with two sources each of surface chlorophyll-a concentration (chlorophyll), photosynthetically available radiation (PAR), sea surface temperature (SST), and mixed-layer depth (MLD). The models were most sensitive to uncertainties in surface chlorophyll, generally performing better with in situ chlorophyll than with satellite-derived values. They were much less sensitive to uncertainties in PAR, SST, and MLD, possibly due to relatively narrow ranges of input data and/or relatively little difference between input data sources. Regardless of type or complexity, most of the models were not able to fully reproduce the variability of in situ NPP, whereas some of them exhibited almost no bias (i.e., reproduced the mean of in situ NPP). The models performed relatively well in low-productivity seasons as well as in sea ice-covered/deep-water regions. Depth-resolved models correlated more with in situ NPP than other model types, but had a greater tendency to overestimate mean NPP whereas absorptionbased models exhibited the lowest bias associated with weaker correlation. The models performed better when a subsurface chlorophyll-a maximum (SCM) was absent. As a group, the models overestimated mean NPP, however this was partly offset by some models underestimating NPP when a SCM was present. Our study suggests that NPP models need to be carefully tuned for the Arctic Ocean because most of the models performing relatively well were those that used Arctic-relevant parameters.
We investigated horizontal and vertical distributions of dimethyl sulfide (DMS) in the upper water column of Amundsen Sea Polynya and Pine Island Polynya in austral summer (Jan. ∼Feb., 2016) using a membrane inlet mass spectrometry (MIMS) on the Korean icebreaker R/V Araon. We conducted the underway measurements of DMS and the surface water concentrations of DMS varied 3 to 400 nM. The highest DMS (up to >300 nM) were observed in the polynya mouth and near Getz ice shelf surface, where the sudden local ice melting provoked the concentrated DMS productions by plankton. The other regions, the horizontal trends of DMS were generally well consistent with chlorophyll and ΔO2/Ar. The large spatial variability of DMS and productivity in the Amundsen Sea surface seems to be attributed to melting conditions of sea ice, competitions in phytoplankton community, and timing differences between bloom and subsequent DMS productions. We also measured the vertical distributions of DMS. In general, the depth profiles of DMS and resultant ΔO2/Ar were consistent with the horizontal surface data, showing noticeable spatial variability. However, despite the large spatial variability, in contrast to the previous result in 2009, DMS concentrations and ΔO2/Ar ratio in surface water were in distinct between the two major domains; sea ice zone and polynya region. The discrepancy can be associated with the inter-annual variations of phytoplankton assemblage superimposed on differences of sea-ice conditions, blooming period, and spatial coverage along the vast surface area of Amundsen Sea.
We investigated paleoclimate and environmental changes using beryllium isotopes from the 39 cm-long box core sediment obtained from the Mendeleev Ridge of the western Arctic Ocean. The age of core PS72/396-3 seems to be back < 100 kyr based on stratigraphy of beryllium isotopes and paleomagnetic data and other isotopic data of this study, AMS <sup>14</sup>C ages and oxygen and carbon isotopes of planktonic foraminifer N. pachyderma sin. The both authigenic <sup>10</sup>Be and <sup>9</sup>Be records show that there are three major cold periods during the last 100 kyr and reveals a much longer warm period after the second cold period based on <sup>9</sup>Be record. The <sup>10</sup>Be stratigraphy also reveals a paleomagetic excursion at ~45 kyr which is comparable with the record of δ<sup>18</sup>O. At depth from 22 to 25 cm, the lowest <sup>10</sup>Be signal may be due to the highest paleomagnetic intensity, which is indicated as an age of 75 kyr elsewhere. However, cold climate signal such as ice coverage could be possible because δ<sup>18</sup>O reveals a cold period. Interestingly, <sup>9</sup>Be data show that constant input of <sup>9</sup>Be to the Mendeleev Ridge is clearly observed for this time period. This could be associated in warmer climate which provided constant <sup>9</sup>Be input to the marine environment from the land. During this time period, TOC (%) values also show a similar pattern. The record of authigenic <sup>9</sup>Be is inversely correlated to that of Ca and proportional to opal production. These observations confirm that <sup>9</sup>Be can be a good proxy for climatic tracer. This study may be a useful approach for understanding Arctic climate change for the Mendeleev Ridge as well as global paleoclimate changes during the late quaternary glacial-interglacial cycles.
We investigated rates of total oxygen uptake (TOU) sulfate reduction (SRR), and benthic nutrient flux (BNF) in sediments of polynya (730-825 m water depth), ice shelf (1064 m water depth), and marginal
sea-ice zone (530 m water depth) to evaluate the role of benthic mineralization in degrading organic material produced by primary production in the Amundsen Sea polynya (ASP), Antarctica. Despite high
primary production (110 mmol C m<sup>-2</sup> d<sup>-1</sup>) in the water column, benthic carbon mineralization in the ASP (average, 2.1±0.3 mmol C m<sup>-2</sup> d<sup>-1</sup>) was strikingly lower than in other less productive polar
regions, accounting for only 1.9% of primary production. Low sediment accumulation rates (0.18-0.20 cm yr<sup>-1</sup>) and sinking fluxes of organic matter likely caused the low oxygen consumption rates
(2.44-3.11 mmol m<sup>-2 </sup>d</sup>1<sup>) and low effluxes of dissolved inorganic nitrogen (0.12-0.13 mmol m<sup>-2</sup> d<sup>-1</sup>) and phosphate (0.017-0.018 mmol m<sup>-2</sup>
d-1) in the ASP. Carbon oxidation by sulfate reduction (0.11-0.19 mmol Cm<sup>-2</sup> d</sup>-1<sup>) comprised only 10% of total benthic mineralization, indicating that anaerobic C
oxidation plays a minor role in total C oxidation. Our results, including low sediment accumulation rates and benthic metabolic rates, suggest that most organic carbon produced by Phaeocystis blooms would be
respired to CO<sub>2</sub> in the water column, and thus the organic carbon reaching the sediment is not adequate to stimulate benthic metabolism in the ASP.
We investigated the biochemical compositions (lipids, proteins, and carbohydrates) of particulate organic matter (POM) as a potential food source in the northern Chukchi Sea. We aimed to understand physiological status of phytoplankton, determine important controlling factors, and estimate the energetic contents of POM. The major inorganic nutrients were generally depleted at upper mixed-layer depth (>20 m). The average chlorophyll a (chl-a) concentration was 31.9 mg m<sup>-2</sup> (S.D.=±31.3 mg m<sup>-2</sup>) in this study, significantly higher than that reported previously in the northern Chukchi Sea. Small phytoplankton (0.7-5μm) accounted for 65.9% of total chl-a concentration. The overall average compositions of lipids, carbohydrates, and proteins were 50% (S.D.=±10.7%), 35% (S.D.=±11.0%), and 15% (S.D.=±11.2%) for POM, respectively. Along with other evidence (e.g., low N:P and protein？carbohydrate ratios), the high lipid and low protein compositions of POM in this study suggests that phytoplankton might have had a nitrogen limitation and/or stationary growth phase in the northern Chukchi Sea during the cruise period, 2011. The overall average calorific content of food material (FM) was 149.2 μg L<sup>-1</sup> (S.D.=±36.5 μg L<sup>-1</sup>) or 1.0 Kcal m<sup>-3</sup> (S.D.=±0.2 Kcal m<sup>-3</sup>). The relatively higher calorific contents in the northern Chukchi Sea were due to high lipid contributions and the considerably high calorific content of FM per POC.
We investigated the effects of ultraviolet-B
(UV-B) radiation on the natural phytoplankton assemblage
in Marine Cove on King George Island, Antarctica, in
December 2005. The amount of newly synthesized phytoplankton
polyunsaturated fatty acids (PUFAs) was lower
with exposure to full irradiation (PAR+UV-A+UV-B)
than without such exposure (exposed instead to PAR+UV？A
radiation) in an in situ incubation under the light conditions
in two different types of incubation bottles: quartz
bottles transmitting all light wavelengths including UV-B
and polycarbonate bottles with no UV-B transmission and
20 % reduced PAR compared to the quartz bottle. However,
the amount of newly synthesized saturated fatty acids
was greater with than without UV-B radiation. Thus, UV-B
radiation may have a significant influence on fatty acid
synthesis in phytoplankton. In particular, the production of
eicosapentaenoic acid [20:5(n-3)] and docosahexaenoic
acid [22:6(n-3)] was reduced during incubation under the
natural solar radiation including UV-B. To understand the
indirect influence of UV-B on herbivores (the secondary
producer), we conducted feeding experiments with amphipods
fed in situ on the natural phytoplankton assemblage.
The amphipods fed on the phytoplankton with the
low PUFA values also exhibited a low PUFA accumulation
rate, which could negatively affect their growth, development,
and reproduction. Consequently, the diminished rate
of essential fatty acid synthesis [especially 20:5(n-3) and
22:6(n-3)] in primary producers caused by UV-B exposure
could affect the structure and function of the Antarctic
We investigated the heterotrophic bacterial biomass and production in February 2012, in four habitats (a polynya, sea-ice zone, ice shelf, and the open sea) in the Amundsen Sea to determine the spatial distribution, controlling
factors, and ecological role of the bacteria during a late phytoplankton bloom by Phaeocystis antarctica. Bacterial abundance (BA) and production (BP) were highest at the center of the polynya, and both were significantly
correlated with phytoplankton biomass. BP accounted for average 17% of the organic carbon produced by phy-toplankton primary production (PP), which is higher than the average BP:PP ratio reported in most open ocean.
The abundance of heterotrophic nanoflagellates (HNF) was correlated with the BA, and the average bacteria:HNF ratio (260) was lower than the values reported in most marine environments (400-1000), including the Ross Sea
Polynya (800). Evidence for a tight coupling of bacteria and phytoplankton activities on the one hand and intense HNF grazing on bacteria on the other could be found in the high BP:PP and low bacteria:HNF ratios, respectively.
Interestingly, these data were accompanied by low particulate carbon export fluxes measured during the late Phaeocystis bloom. Together, these results indicated that the microbial loop plays a significant role in the bio-
geochemical carbon cycle and food web processes in the Amundsen Sea Polynya.
We investigated the microzooplankton community and its grazing impact on major phytoplankton groups in the Chukchi Sea and in the western Canada Basin during the period July？August 2010. The study area was divided into three regions based on topography, hydrographic properties and trophic conditions: (1) a productive region over the Chukchi Sea shelf (CSS) with high phytoplankton biomass dominated by diatoms, (2) an oligotrophic region over the Northwind Abyssal Plain (NwAP) with low phytoplankton biomass dominated by picophytoplankton, and (3) the Northwind Ridge (NwR), over which waters were dominated by picophytoplankton and diatoms. The spatial distribution of microzooplankton biomass and its composition were related to differences in phytoplankton biomass and assemblage composition in the three water masses. Heterotrophic dinoflagellates (HDF) and ciliates were significant components of microzooplankton populations. Athecate HDF was the most important component in the CSS, where diatoms were dominant. Naked ciliates were dominant microzooplankton in the NwR. Microzooplankton grazing rate varied by the assemblage composition of both phytoplankton and microzooplankton. Microzooplankton was capable of consuming an average of 71.7±17.2% of daily phytoplankton production. Growth rates of smaller phytoplankton (i.e., picophytoplankton and autotrophic nanoflagellates) and grazing rates on them were higher than rates for diatoms. Microzooplankton grazed more on picophytoplankton (PP grazed=89.3±20.5%) and autotrophic nanoflagellates (PP grazed=82.3±22.5%) than on diatoms (PP grazed=62.5±20.5%). The dynamics of predator and prey populations were almost balanced in waters in which smaller phytoplanktons were dominant. Picophytoplankton production was consumed by microzooplankton allowing transfer to larger consumers. On average, microzooplankton grazed 62.5% of the diatom production in the waters we studied, indicating that the classical food chain (with carbon flux from diatoms to copepods) is likely operational and of significance in this region. Overall, microzooplankton grazing was an important process controlling phytoplankton biomass and composition in the Chukchi Sea and the western Canada Basin during early summer.