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Reactive halogens play various key roles in the global environment. In particular, the presence of gaseous halogens in the polar and marine boundary layers is of great interest as these highly reactive species can affect the oxidative capacity of Earth’s atmosphere. The sources and impacts of iodine in polar atmospheric chemistry are much less understood in comparison with chlorine and bromine. Although the active iodine compound in the polar regions have been observed by ground and satellite based techniques, the sources and mechanisms of this large iodine burden are still being debated. Especially, abiotic sources of atmospheric iodine in Antarctic is less understood compared to biological iodine sources from micro- or macro algae. In this investigation, we shows that the production of triiodide (I3-) via iodide (photo-)oxidation, which is negligible in aqueous solution, is significantly accelerated in frozen solution - both in the presence and absence of solar irradiation. Outdoor experiments carried out in the Antarctic region (King George Island, 62°13′S 58°47′W) also showed that the production of triiodide via solar photooxidation is accelerated when iodide contained solution is solidified. We used CRDS(Cavity Ring Down Spectroscopy) for measurement of gaseous I2 emission upon thawing the irradiated frozen solution of iodide. A modeling study was also carried out to reproduce the experimental results. The enhanced (photo)oxidation of iodide and the subsequent formation of triiodide and I2 in ice are ascribed to the freeze concentration phenomenon of iodide and dissolved O2 trapped in the ice crystal grain boundaries. These findings propose that an enhanced abiotic transformation of iodide to I3- and gaseous I2 in ice media provides a previously unknown generation mechanism of active iodine compounds in the polar atmosphere.
Recent findings report that wild animals can recognize individual humans. To explain how the animals distinguish humans, two hypotheses are proposed. The high cognitive abilities hypothesis implies that pre-existing high intelligence enabled animals to acquire such abilities. The pre-exposure to stimuli hypothesis suggests that frequent encounters with humans promote the acquisition of discriminatory abilities in these species. Here, we examine individual human recognition abilities in a wild Antarctic species, the brown skua (Stercorarius antarcticus), which lives away from typical human settlements and was only recently exposed to humans due to activities at Antarctic stations. We found that, as nest visits were repeated, the skua parents responded at further distances and were more likely to attack the nest intruder. Also, we demonstrated that seven out of seven breeding pairs of skuas selectively responded to a human nest intruder with aggression and ignored a neutral human who had not previously approached the nest. The results indicate that Antarctic skuas, a species that typically inhabited in human-free areas, are able to recognize individual humans who disturbed their nests. Our findings generally support the high cognitive abilities hypothesis, but this ability can be acquired during a relatively short period in the life of an individual as a result of interactions between individual birds and humans.
Recent global warming caused the shrinkage of summer sea ice in the Arctic. The distribution of the sea ice reflects ice drift pattern mainly controlled by the Beaufort Gyre circulation, Transpolar Drift, and Bering Strait inflow. Understanding the ocean circulation in climate regimes different from today is thus helpful to predict the future condition of Arctic sea ice. In this study, we investigated mineral compositions, grain size distribution, ice-rafted debris (IRD) content, glycerol dialkyl glycerol tetraethers (GDGTs), total organic matter (TOC) and total sulfur (TS) in five sediment cores retrieved in the western Arctic Ocean during RV “Araon” ARA02B (August 2011) and ARA03B (August-September 2012) expeditions to reconstruct changes in ice drift pattern in the western Arctic Ocean during the last 70 ka.
IRD-, quartz-, and dolomite-rich layers were found in the last glacial sediments in the Chukchi Sea and Chukchi Borderland areas and they are useful to correlate cores. Based on the distribution of minerals in the surface sediments and geological information, we suppose that dolomite grains were delivered by icebergs discharge from the Canadian Arctic Archipelago. Kaolinite-rich layers were found in the LGM or deglaciation intervals in the restricted area near the Chukchi Plateau. They show high concentration of branched GDGTs and the high C/S ratio. The molecular distribution of the branched GDGTs is typical in those on the shelf sediments in the western Arctic (Park et al., 2014 Marine Chemistry). This suggests that the kaolinite-rich grains were delivered from the nearly continental shelf by sea ice or icebergs. The quartz/feldspar ratio is much lower in the Holocene brown layer B1 than the glacial brown layers B2 and B3, suggesting that the former was delivered from the Siberian margin, whereas the latter from the Alaskan margin. These results indicate a drastic changes in ice drift pattern during the last 70 ka.
Recent research results concerning frequency domain reverse time migration based on the adjoint-state of the acoustic wave equation have highlighted several limitations imposed by the use of an acoustic-based algorithm. In marine seismic exploration, targeted areas are located within elastic media. Elastic wave components, such as S-waves, surface waves and mode converted waves can remain obscured by reverse time migration based on the acoustic wave equation in the targeted media. Several research papers addressing the topic of acoustic-elastic coupled media with full waveform inversion have shown that this method can generate more accurate inversion results for P-wave velocity models than acoustic-based algorithms. This paper formulates the frequency domain reverse time migration for acoustic-elastic coupled media based on the adjoint-state of the wave equation. It goes on to adopt the wavefield separation method to reduce the effects of crosstalk artifacts on migrated images. The validity of the proposed algorithm is demonstrated using a synthetic dataset generated by elastic staggered grid time modeling. The image of the frequency domain reverse time migration for acoustic-elastic coupled media calculated using the wavefield separation method is then compared to the results of the acoustic reverse time migration and reverse time migration for acoustic-elastic coupled media using a conventional zero-lag cross-correlation approach. Comparison of the migration images revealed that the images of acoustic-elastic coupled media from the wavefield separation method resolved geological structures with greater accuracy and exhibited fewer noise-contaminated components than those obtained from the acoustic and conventional acoustic-elastic coupled media imaging methods. We also analyze the reverse time migration method’s sensitivity to correct P- and S-wave inputs and density model assumptions.
Recent studies have shown that photosynthetic eukaryotes are an active and often dominant component of Arctic phytoplankton assemblages. In order to investigate the structure of phytoplankton communities, this study was carried out at 18 stations from July 29 to August 20, 2011 in the Chukchi Sea and Canadian Basin. Concentrations of total microphytoplankton, and nano-picophytoplankton chlorophyll a were higher at southwest area than northern area in the study area due to Bering shelf Anadyr Water current from Bering Strait. On the Melting ponds in Canadian Basin, phytoplankton communities were composed of 31 taxa representing Bacillariophyceae, Chrysophyceae, Dictyochophyceae, Prasinophyceae and unidentified phytoplankton(< 20㎛). The most abundant species were Pyramimonas sp. and Thalassiosira sp. except nano-pico sized phytoplankton in Melting pond.
Recent studies suggest that bacterial communities in lichens contribute structurally and ecologically, but their biological activities are not fully investigated. In this study, we explored biological potential of microorganisms that are isolated from Antarctic lichen Psoroma sp. Using their bacterial cell culture extracts, we evaluated antibacterial and antioxidant properties. Among 20 bacterial species that were isolated from Antarctic lichen Psoroma sp., PAMC 26508 (Streptomyces sp., similarity: 100%) showed antibacterial activities against all target bacteria with inhibition zone diameter of 7 to 9. PAMC 26537 (Burkholderia sordidicola, similarity: 98.828%) exhibited higher antioxidant potential with an inhibition rate of 60.12% in 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 58.69% in 2,2'-azino-bis[3-ethyl benzothiazoline-6-sulphonic acid] (ABTS) assay than control ascorbic acid (29.31%). Our results indicated that they have potential to be used as novel source of antibacterial and antioxidant agents.
Recent succession of soil microorganisms and vegetation has occurred in the glacier foreland, because of
glacier thawing. In this study, whole microbial communities, including bacteria, archaea, and eukaryotes,
from the glacier foreland of Midtre Lov？nbreen in Svalbard were analyzed by metagenome sequencing,
using the Ion Torrent Personal Genome Machine (PGM) platform. Soil samples were collected from two
research sites (ML4 and ML7), with different exposure times, from the ice. A total of 2,798,108 and 1,691,859
reads were utilized for microbial community analysis based on the metagenomic sequences of ML4 and
ML7, respectively. The relative abundance of microbial communities at the domain level showed a high
proportion of bacteria (about 86？87%), whereas archaeal and eukaryotic communities were poorly represented
by less than 1%. The remaining 12% of the sequences were found to be unclassified. Predominant
bacterial groups included Proteobacteria (40.3% from ML4 and 43.3% from ML7) and Actinobacteria (22.9%
and 24.9%). Major groups of Archaea included Euryarchaeota (84.4% and 81.1%), followed by Crenarchaeota
(10.6% and 13.1%). In the case of eukaryotes, both ML4 and ML7 samples showed Ascomycota (33.8% and
45.0%) as the major group. These findings suggest that metagenome analysis using the Ion Torrent PGM
platform could be suitably applied to analyze whole microbial community structures, providing a basis for
assessing the relative importance of predominant groups of bacterial, archaeal, and eukaryotic microbial
communities in the Arctic glacier foreland of Midtre Lov？nbreen, with high resolution.
Recent time series of satellite-observed ocean colour data (Moderate Resolution Imaging Spectroradiometer; MODIS) were examined to understand the dominant temporal and spatial patterns of chlorophyll-a concentration in the Arctic Ocean. Total twelve years (2003-2014) 8-days mean level-3 data (spatially, approximate 4.5 km resolution) were used for analysis. Though this was our preliminary study for Arctic Ocean using remote sensing data, we tried to provide some fundamental informations for oceanographer and ecologist who is studying Arctic Ocean. Our major objectives were as follows: (1) utilize satellite chlorophyll data to classify biological domain over an extended Arctic region which include Bering Sea; (2) evaluate spatial patterns and seasonal-to-interannual variability of chlorophyll of the study area; and (3) identify possible mechanisms that could control the phytoplankton dynamics at each classified region. We investigated not only the intensity of seasonality of phytoplankton bloom but also peak timing of the bloom. Possible implications of these results will be discussed.
Recently, Psychrobacter sp. ArcL13 strain showing the extracellular lipase activity was isolated from the Chuckchi
Sea of the Arctic Ocean. However, due to the low expression levels of the enzyme in the natural strain, the production of
recombinant lipase is crucial for various applications. Identification of the gene for the enzyme is prerequisite for the production
of the recombinant protein. Therefore, in the present study, a novel lipase gene (ArcL13-Lip) was isolated from Psychrobacter
sp. ArcL13 strain by gene prospecting using PCR, and its complete nucleotide sequence was determined. Sequence analysis showed that
ArcL13-Lip has high amino acid sequence similarity to lipases from bacteria of some Psychrobacter genus (84？90%) despite low
nucleotide sequence similarity. The lipase gene was cloned into the bacterial expression plasmid and expressed in E. coli. SDS-PAGE
analysis of the cells showed that ArcL13-Lip was expressed as inclusion bodies with a molecular mass of about 35 kDa. Refolding was
achieved by diluting the unfolded protein into refolding buffers containing various additives, and the highest refolding efficiency was seen
in the glucose-containing buffer. Refolded ArcL13-Lip showed high hydrolytic activity toward p-nitrophenyl caprylate and p-nitrophenyl
decanoate among different p-nitrophenyl esters. Recombinant ArcL13-Lip displayed maximal activity at 40°C and pH 8.0 with
p-nitrophenyl caprylate as a substrate. Activity assays performed at various temperatures showed that ArcL13-Lip is a cold-active lipase
with about 40% and 73% of enzymatic activity at 10°C and 20°C, respectively, compared to its maximal activity at 40°C.
Recently, the areal extent of melt ponds within sea ice has rapidly increased during the Arctic Ocean summer. However, the biological impacts of melt ponds on the Arctic marine
ecosystem have rarely been studied. Carbon and nitrogen uptake rates of phytoplankton were measured at 26 different melt ponds in 2005 and 2008, using a <sup>13</sup>C-<sup>15</sup>N dual stable
isotope tracer technique. Generally, the open ponds had relatively higher nutrients than closed ponds, but the nutrient concentrations in the open ponds were within a range similar
to those in surrounding surface seawaters. Chlorophyll a (Chl a) concentrations in melt ponds ranged from 0.1 to 2.9 mg Chl a m<sup>-3</sup> with a mean of 0.6 mg Chl a m<sup>-3</sup> (SD = 0.8 mg Chl a m<sup>-3</sup>) in the Canada Basin in 2005, whereas the range of the Chl a concentrations was from 0.1 to 0.3 mg Chl a m<sup>-3</sup> with a mean of 0.2 mg Chl a m<sup>-3</sup>
(SD = 0.1 mg Chl a m<sup>-3</sup>) in the central Arctic Ocean in 2008. The average annual carbon production in sea ice melt ponds was 0.67 g C m<sup>-3</sup> (SD = 1.03 g C m<sup>-3</sup>) in the Arctic Ocean. Based on this study, recent annual carbon production of all melt ponds was roughly estimated to be approximately 2.6 Tg C, which is less than 1% of the total production in the Arctic Ocean.
Reefs dominated by the anthaspidellid sponge Rankenella zhangxianensis, the calcimicrobe Epiphyton and
the stem-group cnidarian Cambroctoconus orientalis, together with encrusting microstromatolites occur
early in the middle Cambrian (Series 3, late Stage 5) of Shandong, eastern China. In the Zhangxia Formation,
these in situ components created a tight framework, with centimeter-scale growth cavities mainly filled by
fine-grained matrix. Among them, R. zhangxianensis and C. orientalis mutually attached and locally formed
metazoan-dominated frameworks. These metazoan-microbial reefs form thin lenses b2m wide within microbial
mounds, and probably developed at least a fewcentimeters of synoptic relief above these surrounding structures.
With an age of N505 Ma, these Rankenella reefs indicate recovery of framework-buildingmetazoans within
~5 million years of the archaeocyath reef decline. In structure, they resemble archaeocyath reefs as well as Early
Ordovician lithistid sponge-microbial reefs, having conjoined conical macroskeletons thickly veneered by
calcimicrobes and microbial carbonate with largely matrix-filled intervening cavities. In combination with
other sponge-microbial reefs reported from Australia, Iran, Korea and the USA, they demonstrate that an
anthaspidellid sponge-microbial reef consortium was widespread throughout the mid-late Cambrian.
Remote sensing approaches based on satellite observations have been widely conducted to investigate the retreat of Antarctic ice sheets. However, most of the satellite-based studies have following limitations; i) they cannot capture the short-term variability of basal melting rate due to the relatively lower temporal resolutions from several years to decades, and ii) they cannot give an insights to pathways or distributions of glacial meltwater (GMW) in the water columns. Recently, Kim et al. (2016) presented the distributions of GMW in the water column of Amundsen Sea revealed by light noble gas tracers, helium (He) and neon (Ne). The study shows that there were significant spatio-temporal variations between each ice shelves and (inter-annual) sampling periods. However, the conventional method to determine noble gases is dependent on shore-based mass spectrometric system and very time-consuming processes. Thus, the main objective of this study is i) to make on-board measurements of 5 noble gases (4He, 22Ne, 38Ar, 84Kr, and 132,136Xe) in seawater, for the first time, ii) to get a broader understandings of GMW distribution in the Amundsen Sea. Recently, Visser et al. (2013) developed a quicker and more efficient noble gas analysis for laboratory experiments using a membrane inlet mass spectrometer (MIMS) with a semi permeable membrane and simplified gas extraction line. Based on this method, we conducted a intensive noble gas observation covering entire Amundsen Sea region, (Jan.～Feb. 2016) on the Korean icebreaker R/V Araon. Here, we will present the detailed method and preliminary results as a beginning of our effort to observe GMW distributions with a larger spatial coverage of polar oceans in future.
Reports of ‘Psoroma sphinctrinum’ from Palaeotropical areas are shown to represent instead
species of the genus Gibbosporina, which is described here as new to science. This genus is superficially
similar to tripartite, austral Pannaria species, such as the species now referred to as Pannaria sphinctrina
(Mont.) Tuck. ex Hue. A phylogrambased on an analysis of the nuclear large subunit rDNA (LSU) locus
shows that Gibbosporina is instead a clade in a Pannariaceae branch referred to as the ‘Physma group’, amost
unexpected addition to Pannariaceae dealt with by several previous studies. Genera assigned to this group
have very contrasting general appearances. However, this diverse group shares distinctly ring-like thalline
excipular margins; strongly amyloid internal ascus structures; well-developed perispores which have
irregular gibbae and/or nodulose or acuminate apical extensions, but not verrucae; lacks TLC-detectable
secondary compounds and have tropical distributions. Gibbosporina is the only tripartite genus in the
group, with distinct, nodulose, placodioid, mini-fruticose to mini-foliose cephalodia with a high diversity
of Nostoc cyanobionts. The cyanomorphs can apparently exist independently in some cases, although
the apothecia on such cephalodia on a specimen from R？union were unexpectedly found to belong to
the chloromorph. The genus and related genera forming the ‘Physma group’ are probably evolutionarily
old, and their weak affinity to the remaining part of Pannariaceae, concentrated in the Southern
Hemisphere, is discussed. The genus includes 13 known species, and the generitype is Gibbosporina
boninensis from the Japanese Ogasawara Islands, originally described as Psoroma boninense and recombined
here. The following 12 species are described here as new to science, seven of them with molecular
support in an LSU and ITS-based phylogram: Gibbosporina acuminata (Australia, the Philippines),
G. amphorella (New Caledonia), G. bifrons (Malaysia, New Caledonia, the Philippines, Solomon
Islands), G. didyma (Mauritius, R？union), G. elixii (Australia), G. leptospora (Australia, Papua
New Guinea), G. nitida (Australia, Papua New Guinea, the Philippines), G. mascarena (Mauritius,
R？union, Sri Lanka), G. papillospora (the Philippines), G. phyllidiata (Solomon Islands), G. sphaerospora
(Australia, Indonesia,Malaysia, the Philippines, Samoa, and with Psoroma sphinctrinum var. endoxanthellum
as a new synonym), and G. thamnophora (Australia and the Philippines). Except for the phyllidiate
G. phyllidiata and for G. thamnophora which has cephalodia adapted for vegetative propagation, the species
are all primarily fertile. A key for determining the species is provided.
Research background and objectives
The light noble gases, helium (He) and neon (Ne), dissolved in seawater, can be useful tracers of freshwater input from glacial melting because the dissolution of air bubbles trapped in glacial ice results in an approximately ten-fold supersaturation. However, the conventional method to determine noble gases is dependent on shore-based mass spectrometric system and very time-consuming processes. The other volatile trace gas, Dimethyl sulfide (DMS), as important precursor of cloud condensation nuclei (CCN), directly affects the radioactive budget and resultant climate change. The oceanic emission is a main natural source of atmospheric DMS. Antarctic polynya, especially, can be a key source region of DMS due to high productivity. However, its observations are evidently lacked due to the limited accessibility of polar ocean.
Membrane inlet mass spectrometry (MIMS) technique directly samples analyte gases from the aqueous phase gases in seawater through a semi-permeable membrane. Since this method does not require headspace equilibration, MIMS enables us to make a near-real time, high frequency continuous observation of dissolved gases. During the Southern Ocean cruise (Jan. ~ Feb. 2016), we applied the MIMS for onboard measurements of various dissolved gases in Antarctic seawater on the Korean icebreaker R/V Araon. We have attempted i) to make onboard analysis of 5 noble gases (4He, 22Ne, 38Ar, 84Kr, and 132,136Xe) in seawater, for the first time, to get a broader understandings of glacial meltwater distribution in the Southern Ocean. With discrete measurements of noble gases, we have also made ii) continuous DMS observations. Here, we will present the detailed methods and preliminary results of noble gases and DMS measurments as a beginning of our effort to understand the climate-related glacial melting and environment changes in polar oceans.
Method in brief
The details of noble gas analysis method are as follows: we made the quicker and more efficient noble gas extraction system. This, so-called noble gas MIMS (NG-MIMS) system has a simplified version of traditional gas extraction lines. This system consists of a membrane inlet (0.2 mm silicon wall), water vapor trap immersed into cooled MeOH (~ -65 oC), CO2 trap (Carbosorb), 400 oC of hot getter (Zr-alloy), and 250 oC of Sorb AC. Two syringe pumps were used to deliver samples and standards. The high vacuum of the whole line (~10-7 torr) allows the dissolved gases to pass through the membrane from the water.
To test the linearity of this method, we prepared a range of binary mixtures of air-equilibrated seawater (AEW) and degassed (boiled) water by changing the each flow rates. The AEW was prepared by gently bubbling of ambient air through seawater kept in a water bath at 2 oC. The 2 end-members (degassed water and AEW) and their mixtures showed good linearity (n=7 trials) with R2 value of 0.97 ？ 0.99 for 4He, 38Ar, and 132Kr.
Research on warming in West Antarctica is important to understand and predict mass balance change of the ice sheet over the region, which is directly connected to global sea level. Air temperature over West Antarctica is known to have increased moderately over past decades [e.g., Steig et al., 2009; Schneider et al., 2011; Ding et al., 2011; Bromwich et al., 2013]. However, it seems rather complicated to identify the dominant and direct cause for the warming. In addition, a lack of ground based measurements of meteorology across West Antarctica have limited better understanding of how the large area has been influenced by the warming through atmospheric processes and how fast the warming has progressed on the region. Some AWSs on West Antarctica have been operated long time and used to identify vast warming but their location is biased inland [e.g., Reusch and Alley, 2004; Bromwich et al., 2013]. Meteorology at coastal area should be different from that inland. Therefore, to better understand the processes of West Antarctica warming, climate at coastal area is required. In addition, meteorology at coastal area is also important in polyna, sea ice melting/formation and air-sea interaction nearWest Antarctica.
An automatic weather station was setup at the Lindsey Island, Amundsen Sea close to the coastal area of West Antarctica in 2008 and has been operated for about seven years. Here, we present meteorological characteristics at the coastal area in Amundsen Sea through analyzing measured data at the site together with those from three AWSs at coastal area and two inland. To extend its characteristic over limited period, we compare them with reanalysis data to investigate long term change . Amundsen sea low indies are used to explain atmospheric variability at that region.
Rhodococcus sp. strain DK17 is capable of utilizing various derivatives of benzene and bicyclics containing both aromatic and alicyclic moieties as sole carbon and energy sources. Here, we present the 9,107,362-bp draft genome sequence of DK17 and its genomic analysis in comparison with other members of the genus Rhodococcus.
Ross Sea Polynya (RSP), the largest polynya around Antarctica, is the regions with the highest primary productivity (annual production of 150 to 200 g C m- 2) in the Southern Ocean. It is also traditionally known for taxonomically distinct regimes: the south-central areas are dominated by Phaeocystis Antarctica and to the west diatoms are abundant. Such distributions are mainly influenced by the various environmental forcings such as irradiance, temperature, and wind systems. We analyzed the spatial pattern of phenology in the RSP using weekly mean MODIS 9-km chlorophyll data for last several years. In this process, feature extractions of the phenology were conducted using the shifted Gaussian filter and then we conducted the parameterization about the phytoplankton bloom with respect to growth rate, initial and terminative timings, peak intensities and periods of bloom. Additionally, this study was performed to understand what physical drivers mainly affect on the phytoplankton assemblage in terms of the relevant parameters.
RV., Polarstern“ cruise ARK-XIII/3 (2008) and RV "Araon" cruise ARA03B (2012) investigated an area in the Arctic Ocean located between the Chukchi Borderland and the East Siberian Sea (between 165 W and 170 E).
Based on swath bathymetry, sediment echosounding, seismic profiling and sediment coring we present evidence that the western Arctic Ocean had a glaciated continental margin during several glacial periods of the Pleistocene
(Niessen et al. 2013). At the southern end of the Mendeleev Ridge and on the Chukchi and East Siberian continental slopes ice sheets and ice shelves grounded in up to 1200 m present water depth. We found mega-scale glacial lineations (MSGL) associated with deposition of glaciogenic wedges and debris-flow deposits indicative of sub-glacial erosion and deposition close to the former grounding lines. Glacially lineated areas are associated with large-scale
erosion, capped with diamicton and draped by, in places, several metres of pelagic sediments. On the Arlis Plateau, a detailed bathymetric map exhibits several generations of MSGL, which we interpret as relicts of different
Pleistocene glaciations. Traces of former grounding line positions suggest that an ice shelf of approximately 900 m in thickness has spread across the Southern Mendeleev Ridge in a north-easterly direction. According to our
results, ice sheets of more than one km in thickness continued onto, and likely centered over, the East Siberian Shelf.
A preliminary age model suggests that the youngest and shallowest grounding event of an ice sheet should be within Marine Isotope Stage (MIS) 3 and clearly predates the Last Glacial Maximum. The oldest and deepest
event predates MIS 6. The youngest grounding event on the Arlis Plateau is tentatively dated to have occurred during MIS 4. These results have important implication for the former distribution of thick ice masses in the Arctic
Ocean during the Pleistocene. They are relevant for albedo, ocean-atmosphere heat exchange, moisture supply to and freshwater export from the Arctic Ocean and the formation of submarine permafrost on the East Siberian Shelf.
Satellite altimeters have been used to monitor Arctic sea ice thickness since the early 2000s. In order to estimate sea ice thickness from satellite altimeter data, leads (i.e., cracks between ice floes) should first be identified for the calculation of sea ice freeboard. In this study, we proposed novel approaches for lead detection using two machine learning algorithms: decision trees and random forest. CryoSat-2 satellite data collected in March and April of 2011？2014 over the Arctic region were used to extract waveform parameters that show the characteristics of leads, ice floes and ocean, including stack standard deviation, stack skewness, stack kurtosis, pulse peakiness and backscatter sigma-0. The parameters were used to identify leads in the machine learning models. Results show that the proposed approaches, with overall accuracy >90%, produced much better performance than existing lead detection methods based on simple thresholding approaches. Sea ice thickness estimated based on the machine learning-detected leads was compared to the averaged Airborne Electromagnetic (AEM)-bird data collected over two days during the CryoSat Validation experiment (CryoVex) field campaign in April 2011. This comparison showed that the proposed machine learning methods had better performance (up to r = 0.83 and Root Mean Square Error (RMSE) = 0.29 m) compared to thickness estimation based on existing lead detection methods (RMSE = 0.86？0.93 m). Sea ice thickness based on the machine learning approaches showed a consistent decline from 2011？2013 and rebounded in 2014.
Sea ice concentration (SIC) data acquired by passive microwave sensors at daily temporal frequencies over extended areas provide seasonal characteristics of sea ice dynamics and play a key role as an indicator of global climate trends; however, it is typically challenging to study long-term time series. Of the various advanced remote sensing techniques that address this issue, temporal mixture analysis (TMA) methods are often used to investigate the temporal characteristics of environmental factors, including SICs in the case of the present study. This study aims to forecast daily SICs for one year using a combination of TMA and time series modeling in two stages. First, we identify temporally meaningful sea ice signatures, referred to as temporal endmembers, using machine learning algorithms, and then we decompose each pixel into a linear combination of temporal endmembers. Using these corresponding fractional abundances of endmembers, we apply a autoregressive model that generally fits all Antarctic SIC data for 1979 to 2013 to forecast SIC values for 2014. We compare our results using the proposed approach based on daily SIC data reconstructed from real fractional abundances derived from a pixel unmixing method and temporal endmember signatures. The proposed method successfully forecasts new fractional abundance values, and the resulting images are qualitatively and quantitatively similar to the reference data.
Sea ice in the Arctic and Antarctic Ocean plays a role of an indicator of climate changes. Since 1970s, passive microwave sensors have been widely used to study the Arctic and Antarctic sea ice because they have observed the whole polar oceans at least once in every two days, regardless of weather conditions and sun altitudes. The Special Sensor Microwave Imager/Sounder (SSMIS) and the Advanced Microwave Scanning Radiometer 2 (AMSR2), the successor to the Special Sensor Microwave Imager (SSM/I) and the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E), respectively, are the representative passive microwave sensors, producing sea ice concentration since 2008 and 2012, respectively. As sea ice concentration products derived from SSMIS and AMSR2 are universally used in various research fields, it is very important to evaluate accuracies of the products, especially in sea ice melting season. Synthetic Aperture Radar (SAR) is very useful tool for observing sea ice because it is all-weather and day-and-night imaging system. In this study, SSMIS and AMSR2 sea ice concentration was evaluated by using Korea Multi-Purpose SATellte-5 (KOMPSAT-5) SAR, South Korea’s first satellite SAR, images obtained in the Amundsen Sea in the West Antarctica during January-February 2016. All KOMPSAT-5 SAR images were obtained in HH-polarization at Enhanced Wide (EW) swath mode with spatial resolution of 6.25 m. Sea ice, icebergs and open water were classified from the SAR images based on Random Forest, a rule-based machine learning approach, in which texture features derived from gray level co-occurrence matrix were used as input variables. Then sea ice concentration was computed from the SAR images and compared with the passive microwave sea ice concentration. The comparisons showed that both SSMIS and AMSR2 sea ice concentrations were underestimated. This would be probably caused by melting of ice surface which is regarded as open water in sea ice algorithms of the passive microwave sensors. Particularly, SSMIS and AMSR2 sea ice concentration were very low over icebergs due to different microwave radiation characteristics between sea ice and glacial ice.
Sea ice motion from low-resolution satellite sensors with feature tracking methods, e.g. maximum cross-correlation, has been widely used to monitor changes in sea ice covers. This study presents measuring arctic sea ice motion using high-resolution optical satellite images acquired on August 2014. The high-resolution optical images were obtained from Korea Multi-Purpose Satellite-2 and Korea Multi-Purpose Satellite-3 with the spatial resolutions of 1 m panchromatic (PAN) band and 4 m multi-spectral (MS) bands and 0.7 m PAN band and 4 m MS bands, respectively. The sea ice motion was retrieved using sub-pixel correlation strategy, and the measuring results were represented as N/S and E/W displacements. In addition, individual ice floe was able to be delineated using the combinations of the spectral characteristics and the shape metrics, e.g. area, perimeter and length of the ice floe, from the advantages of the high-resolution images. The sea ice motion was also analyzed using the delineated ice floes and shape based matching method. The measurement results were compared with drifting buoy data. The results are applicable to fill the gaps between sparce buoy data and the motions from low-resolution satellite data.
Sea-ice is an essential component of the global climate system and, especially, the Polar Oceans. An alarming decrease in term of sea-ice concentration, thickness and duration, has been observed in the Arctic Ocean and its
marginal seas over the last 30 years. Thus, understanding the processes controlling modern sea-ice variability and reconstructing paleo-sea-ice extent and variability in polar regions have become of great interest for the
international scientific community during the last years. Here, we present new proxy records determined in sediment cores from the East Siberian Sea (RV Polarstern Expedition ARK-XXIII/3 in 2008; Core PS72/350)
and from the Chukchi Sea (RV Araon Expedition ARA2B in 2011; Core ARA2B-1A, -1B). These records, including organic-geochemical bulk parameters, specific biomarkers (IP25 and sterols; PIP25; for recent reviews
see Stein et al., 2012; Belt and Muller, 2013), biogenic opal, mineralogical data as well as high-resolution XRF scanning data, give new insight into the short-term (decadal-, centennial- to millennial-scale) variability
in sea-ice, primary productivity and Pacific-Water inflow during Holocene times. Maximum concentrations of phytoplankton biomarkers and biogenic opal were determined between 8.5 and 4 kyrs. BP, suggesting enhanced
primary productivity triggered by increased inflow of nutrient-rich Pacific Water (and/or an increased nutrient input due to an ice-edge position). Short-lived peak values in productivity might be related to strong pulses of
Pacific-Water input during this time period (cf., Ortiz et al., 2009). A seasonal sea-ice cover was present in the Chukchi Sea throughout the last 10 kyrs. During the last 3-4 kyrs. BP, the sea-ice cover significantly extended.
Seawater samples were collected over the Chukchi and Beaufort Seas during the ARA04B (25 August？1 September 2013) and ARA04C (7 September？28 September 2013) cruises aboard Korean icebreaker R/V Araon, and analyzed for nutrients, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON). Nutrients (nitrate, phosphate, silicate) were depleted at the surface. The nutrients concentrations increased with increasing depth, with maxima centered at ~150 m depth within the halocline layer, then decreased with increasing depth below the maxima, indicating that the modified Pacific Waters dominate the upper halocline layer. The ratio of nitrate to phosphate in the Chukchi and Beaufort Seas showed that water of Pacific origin is depleted in nitrate with respect to phosphate. In addition, N* values, which reflect only the net impact of N2 fixation, denitrification, and any other process that adds or remove nitrate with a N:P stoichiometry different than 16:1, showed negative values in upper halocline layer, whereas the N* values in lower halocline layer was close to zero. These results suggest that the North Atlantic Ocean acts as a net source of fixed nitrogen while the North Pacific Ocean acts as a net sink, and that the Arctic Ocean plays a key role in balancing the global nitrogen cycle. Concentrations of DOC and DON ranged from 45？125 μM and 3？17 μM, respectively. The highest DOC and DON concentrations were observed in polar surface layer, suggesting that the large contribution of terrigenous dissolved organic matter (DOM) from Arctic rivers is responsible for the elevated concentrations of DOC and DON in this layer. While DOC showed a significant inverse relationship with salinity, a negative correlation between DON and salinity was weak, probably due to biological influence on DON.
Selenium (Se) is an essential element for health of human and animal, but Se in excess is toxic. Studies of the occurrence of Se in successively dated polar snow and ice are of great interest, because the data can allow us to decipher the large-scale changes in the atmospheric Se cycle. However, the measurement of Se in polar snow and ice remains still a great challenge, because of the extremely low concentrations down to the low picogram per gram (10-12g/g) level. In addition, various interferences make the analysis more difficult. We present here the first results of the direct determination of Se in Greenland snow samples using ICP-SF-MS with Apex-ACM sample introduction system. The use of Apex-ACM sample introduction system was observed to effectively reduce spectral interferences in the Se measurement. The detection limit of Se was 6.9 pg/g, which is 10 times lower than that of commercial ICP-MS. The Se concentration of NIST SRM 1643e diluted to the concentration level in Greenland snow samples was repeatedly measured in order to evaluate the precision and accuracy of the Se data. The measured Se concentration (11.17±1.01 ng/g) showed very good agreement with the certified value (11.68±0.13 ng/g).
Selenium (Se) is an essential element for human and animal heath and plant growth. Atmospheric Se is well known to play an important role in global biogeochemical cycle of Se. Recently, it was reported that Se in Greenland snow samples originated mainly from coal combustion in Asian countries. However, the natural biogeochemical cycle of atmospheric Se is required to understand to what extent human activities have perturbed the atmospheric Se cycle. In this research, we present the first record of past natural change in the occurrence of Se in Greenland ice core covering the past 30,000 years. Se was directly measured by ICP-SF-MS. Out data show a strong variability in concentrations with lower values during the Last Glacial Maximum (LGM) and much higher values during warm Holocene period. This pattern is opposite to any known climatic variations in dust-derived trace elements in polar regions, indicating that there exists different natural sources other than crustal dust for atmospheric Se. The variations in Se concentrations during the last 100 years is shown to be similar to those in chlorophyll concentrations in the North Atlantic. This indicates that an important natural source of atmospheric Se could be marine biogenic activities.
Selenium concentrations were determined in a continuous series of 70 snow samples
collected from a 3.2 m snow pit at northwestern Greenland together with soluble ions such as
sodium (Na<sup>+</sup>), calcium (Ca<sup>2+</sup>), methanesulfonic acid (MSA), sulfate (SOsub>4</sub><sup>2-</sup>
) and oxygen isotope ratio
(δ<sup>18</sup>O). The Se concentrations in the snow samples at the low pg/g level were successfully
determined using the inductively coupled plasma sector field mass Spectrometry (ICP-SF-MS) with
an APEX high-sensitivity inlet system and ACM membrane desolvation module. The well defined
depth profiles of δ<sup>18</sup>O, Na+ and Ca<sup>2+</sup> indicated that the snow pit samples covered the time period
from spring 2003 to summer 2009.
A strong variability in Se concentrations, ranging from 7.2 to 45.1 pg/g, are observed with
generally higher values during winter and spring and lower values during summer and fall.
Concentrations of Se showed rather significant correlations with Ca<sup>2+</sup> (r=0.400) and non-sea salt
(r=0.447), indicating that significant anthropogenic Se input to the snow is likely controlled by
the seasonality of transport efficiency of anthropogenic Se from the source regions of Asia. The
high Se/MSA ratios and crustal enrichment factors are generally coincident with relatively high Se
concentrations. This supports that a significant part of Se present in the snow layers is primarily
attributed to anthropogenic inputs.
Selenium is one of the trace elements which are essential for human and animals health. Previously, numbers of researches have been carried out with various environmental samples, and it has been known that atmospheric transport of selenium plays important role in its bio-geochemical cycle (Wen and Carignan, 2007). Most of previous researches focused on spatial distribution and/or changes over short period less than one year (Ellis et al., 1993; Kagawa et al., 2003; Ranville et al., 2010). Only one record showing long-term changes in atmospheric selenium was reported 40 years ago from Greenland ice core (Weiss et al., 1971). This study, however, did not follow clean protocols essential for analysis for trace metals in ice core, and thus the reliability of data was not confirmed.
In This research, past changes in atmospheric selenium during 1900-1970s are recovered from the Greenland NEEM ice core. The selenium concentrations increases from 1900 to 1940, and then decreased until 1970s. The largest natural and anthropogenic sources for atmospheric selenium are marine bioactivity and coal combustion, respectively. The selenium record of Greenland NEEM ice core is rather similar to that of chlorophyll concentration in North Atlantic, while global coal consumption record did not show decrease (Boyce et al., 2010; Roser, 2015). Therefore, it can be inferred that the input of atmospheric selenium during the 20th century was controlled by the marine bio-activity in North Atlantic.
Seven gravity cores (2.5~8-m long) from southern Drake Passage were analyzed for magnetic susceptibility, grain size distribution, total organic carbon, and total inorganic carbon content to reconstruct paleoceanographic changes in late Quaternary. Glacial sediments from southern Drake Passage are distinguished from interglacial sediments by their higher magnetic susceptibility and lower total organic carbon, due to the increased influx of magnetic minerals from nearby source areas (South Shetland Islands and northern Antarctic Peninsula) during glacial periods and increased marine productivity during interglacial periods. Correlation among the cores based on magnetic susceptibility indicates that sedimentation rates are higher in northeastern cores than in southwestern cores. Northeastern cores record paleoceanographic changes since the last glacial period, whereas a southwestern core of the lowest sedimentation rate show records of last ~900 thousand years. Carbonate content is higher in interglacial sediments than in glacial sediments prior to mid-Pleistocene transition (MPT), reflecting higher productivity during interglacial periods. Since the MPT carbonate dissolution occurs widely, and carbonates are preserved only in some glacial sediment. Absence of carbonate in post-MPT interglacial sediments suggests an invasion of corrosive deep water, possibly from Weddell Sea, since the MPT. Influence of Weddell Deep Water decreased during glacial periods due to extensive ice sheets and weakened current from the Weddell Sea, and carbonates are preserved in some post-MPT glacial sediment.
Several primary and reworked tephra layers are present in core sediments collected from Limnopolar Lake on Livingston Island, maritime sub-Antarctica (Fig. 1). Some of these tephra layers were used as
a stratigraphic marker to construct the composite core (2.34 m long) by correlating overlapping two cores (Toro et al., 2013). This study intends to test the values of those tephra layers for establishing
regional tephrochronology for the lake in ice-covered landscape in the vicinity of volcano. This study uses volcanic glass samples from nine tephra layers of Limnopolar Lake. By visual observation using
optical microscope, two distinct types of tephra are identified on the basis of color, vesicularity and morphology. Most common are brown, vesicular and bubble-wall fragments of andesitic clasts. Some
microcrystals, mainly lath-shaped plagioclases as well as euhedral opaque minerals, are present and common in the brown glass shards (Figure 2). The second type consists of black blocky shards. Both
types of glasses are isotropic under cross-polarized light. Major element analyses of glass shards reveal that the majority of glass fragments belong to basic glass (< 60 wt.% of SiO2), compositionally
ranging from basalt to andesite, probably sourced from both Deception and King George islands. This result agrees with the previous studies that show Deception Island to be the major source of
Quaternary tephra horizons in the northern Anatarctic Peninsula region. However, it may suggest that they were the mixture of reworked tephras from eruption events of Deception and King George
Islands (Figure 3). Based on geochemical similarity results, most tephra samples in two overlapping cores of Limnopolar Lake are not similar enough to be correlated each other. Therefore, most tephra
layers of Limnopolar Lake are interpreted not ashfall deposits but reworked and redeposited pyroclasts. They are probably derived from the catchment transported by surface runoff during snow
pack melt and the permafrost thaw periods. In this case, reworked tephras from the catchment and primary ashfall deposited on the lake ice cover would be trapped together in different ratios in the
same horizon of lake sediments. The result of this study implies that geochemical study in addition to sedimentological information is necessary to study tephrochronology and regional correlation and to
understand paleoenvironmental changes using tephra in lacustrine environment in Antarctica.