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Raymond J.A.,University of Nevada, Las Vegas | Kim H.J.,Korea Polar Research Institute | Kim H.J.,Korean University of Science and Technology
PLoS ONE | Year: 2012

Diatoms and other algae not only survive, but thrive in sea ice. Among sea ice diatoms, all species examined so far produce ice-binding proteins (IBPs), whereas no such proteins are found in non-ice-associated diatoms, which strongly suggests that IBPs are essential for survival in ice. The restricted occurrence also raises the question of how the IBP genes were acquired. Proteins with similar sequences and ice-binding activities are produced by ice-associated bacteria, and so it has previously been speculated that the genes were acquired by horizontal transfer (HGT) from bacteria. Here we report several new IBP sequences from three types of ice algae, which together with previously determined sequences reveal a phylogeny that is completely incongruent with algal phylogeny, and that can be most easily explained by HGT. HGT is also supported by the finding that the closest matches to the algal IBP genes are all bacterial genes and that the algal IBP genes lack introns. We also describe a highly freeze-tolerant bacterium from the bottom layer of Antarctic sea ice that produces an IBP with 47% amino acid identity to a diatom IBP from the same layer, demonstrating at least an opportunity for gene transfer. Together, these results suggest that the success of diatoms and other algae in sea ice can be at least partly attributed to their acquisition of prokaryotic IBP genes. © 2012 Raymond, Kim.

Kim Y.,Seoul National University | Kim K.-Y.,Seoul National University | Kim B.-M.,Korea Polar Research Institute
Climate Dynamics | Year: 2013

Annual snow cover in the Northern Hemisphere has decreased in the past two decades, an effect associated with global warming. The regional scale changes of snow cover during winter, however, vary significantly from one region to another. In the present study, snow cover variability over Europe and its connection to other atmospheric variables was investigated using Cyclostationary Empirical Orthogonal Function (CSEOF) analysis. The evolution of atmospheric variables related to each CSEOF mode of snow cover variability was derived via regression analysis in CSEOF space. CSEOF analysis clearly shows that the North Atlantic Oscillation (NAO) is related to European snow cover, particularly in January and February. A negative NAO phase tends to result in a snow cover increases, whereas a positive NAO phase results in snow cover decreases. The temporal changes in the connection between the NAO and European snow cover are explained by time-dependent NAO-related temperature anomalies. If the NAO phase is negative, the temperature is lower in Europe and snow cover increases; by contrast, when the NAO phase is positive, the temperature is higher and snow cover decreases. Temperature and snow cover variations in Europe are associated with the thermal advection by anomalous wind by NAO. CSEOF analysis also shows an abrupt increase of snow cover in December and January and a decrease in February and March since the year 2000, approximately. This abrupt change is associated with sub-seasonal variations of atmospheric circulation in the study region. © 2012 Springer-Verlag.

Yang E.J.,Korea Polar Research Institute | Ha H.K.,Inha University | Kang S.-H.,Korea Polar Research Institute
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2015

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. © 2014 Elsevier Ltd.

News Article | March 26, 2016

The Antarctica seabirds, the brown skuas (Stercorarius Antarcticus) seem to have the ability to recognize humans after brief interactions, claim a group of researchers from South Korea. Birds that live among human habitation such as crows, parrots, magpies and mockingbirds have been known to display traits of recognizing humans. But in the case of skua birds, they live remotely in Antarctica with hardly any contact with humans, and hence it makes it an amazing fete. "It is amazing that brown skuas, which evolved and lived in human-free habitats, recognized individual humans just after 3 or 4 visits. It seems that they have very high levels of cognitive abilities," exclaimed Won Young Lee, one of the senior study researchers. Researchers from the Korea Polar Research Institute, South Korea, ventured into Antarctica to essentially study the breeding behavior of brown skuas. For this purpose, researchers had to physically examine the nests and eggs. In the process, they began to realize that these seabirds could actually recognize those researchers who got too close to their nests or eggs. Following which, the birds would display aggressive behavior and try to carry out focused attacks aimed at the "intruders". The researchers who did not disturb their nest were left alone. "I had to defend myself against the skuas' attack," said Yeong-Deok Han, a Ph.D. student at Inha University. "When I was with other researchers, the birds flew over me and tried to hit me. Even when I changed my field clothes, they followed me. The birds seemed to know me no matter what I wear." There are predominantly two hypotheses that have been arrived at by the researchers in their study towards determining how animals in the wild distinguish humans. One hypothesis is that they possess pre-existing intelligence that helps them distinguish and the other is that they acquire this ability through periodic exposure to humans. The interesting details of the study have been published in the journal Animal Cognition dated March 3.

News Article | March 25, 2016

Scientists in South Korea studied brown skuas living in Antarctica and reported that these birds too recognize people who had previously accessed the nests to measure their eggs and nestlings. "I had to defend myself against the skuas' attack," says Yeong-Deok Han, a PhD student at Inha University. "When I was with other researchers, the birds flew over me and tried to hit me. Even when I changed my field clothes, they followed me. The birds seemed to know me no matter what I wear." The research team performed a series of experiments. The researchers checked the nests once a week to monitor the breeding status, and the skuas attacked at closer distances with repeated visits of the researchers. To test if the birds specifically distinguish the researchers who visited the nests from those who did not, a pair of humans consisting of nest intruder (who accessed the nests) and neutral human (who never accessed the nests before) approached to the nests and walked towards the opposite directions. All seven skua pairs followed and tried to attack the nest intruder but never followed the neutral human. "It is amazing that brown skuas, which evolved and lived in human-free habitats, recognized individual humans just after 3 or 4 visits. It seems that they have very high levels of cognitive abilities." says Dr. Won Young Lee, a Senior Researcher from Korea Polar Research Institute who led the research. The cognitive abilities of Antarctic animals have not been well studied before. Brown skuas have been recorded to steal food from other birds or even steal breast milk of nursing elephant seals. According to the researchers, this opportunistic feeding habits may make them cleverer with time. Dr. Lee commented: "Since this area has been inhabited by humans only after the Antarctic research stations were installed, we think that the skuas could acquire the discriminatory abilities during a short-term period of living near humans." These findings are published in the journal Animal Cognition. Check out the video to see how the birds reacted to the nest intruder in the discriminatory experiment. Explore further: I know you, bad guy! Magpies recognize humans

Do H.,Korea Polar Research Institute | Do H.,Korean University of Science and Technology | Kim S.-J.,Mokpo National University | Kim H.J.,Pukyong National University | And 2 more authors.
Acta Crystallographica Section D: Biological Crystallography | Year: 2014

Ice-binding proteins (IBPs) inhibit ice growth through direct interaction with ice crystals to permit the survival of polar organisms in extremely cold environments. FfIBP is an ice-binding protein encoded by the Antarctic bacterium Flavobacterium frigoris PS1. The X-ray crystal structure of FfIBP was determined to 2.1 Å resolution to gain insight into its ice-binding mechanism. The refined structure of FfIBP shows an intramolecular disulfide bond, and analytical ultracentrifugation and analytical size-exclusion chromatography show that it behaves as a monomer in solution. Sequence alignments and structural comparisons of IBPs allowed two groups of IBPs to be defined, depending on sequence differences between the α2 and α4 loop regions and the presence of the disulfide bond. Although FfIBP closely resembles Leucosporidium (recently re-classified as Glaciozyma) IBP (LeIBP) in its amino-acid sequence, the thermal hysteresis (TH) activity of FfIBP appears to be tenfold higher than that of LeIBP. A comparison of the FfIBP and LeIBP structures reveals that FfIBP has different ice-binding residues as well as a greater surface area in the ice-binding site. Notably, the ice-binding site of FfIBP is composed of a T-A/G-X-T/N motif, which is similar to the ice-binding residues of hyperactive antifreeze proteins. Thus, it is proposed that the difference in TH activity between FfIBP and LeIBP may arise from the amino-acid composition of the ice-binding site, which correlates with differences in affinity and surface complementarity to the ice crystal. In conclusion, this study provides a molecular basis for understanding the antifreeze mechanism of FfIBP and provides new insights into the reasons for the higher TH activity of FfIBP compared with LeIBP. © 2014 International Union of Crystallography.

News Article | August 30, 2016

Historic changes to Antarctic sea ice could be unraveled using a new technique pioneered by scientists at Plymouth University. It could also potentially be used to demonstrate past alterations to glaciers and ice shelves caused by climatic changes, a study published in Nature Communications suggests. The new method builds on an existing technique, also developed by Plymouth University over the last 10 years, which identified a means by which scientists could measure changes to sea ice in the Arctic. That has already led scientists to reveal periods when the Arctic was previously ice free during summers, and when sea ice first expanded to is modern extent. "In addition to allowing us to unlock historical changes to Antarctic sea ice, our new method also has the potential to provide further insights into other critical climatic features that may have changed in the past. Indeed, sea ice around the Antarctic coastline is strongly influenced by nearby glaciers and ice shelves, both of which contribute to increased global sea level when they melt. Therefore, our new approach may also permit a much broader spectrum of climatic changes to be unraveled in the future," said Simon Belt, professor of chemistry at Plymouth University and lead author on the study. The previous technique is based on the presence of IP25 (ice proxy with 25 carbon atoms), a lipid chemical made solely by microalgae that live in the bottom of Arctic sea ice. When the ice melts, the algae and its lipids fall into the sediments that can be recovered, dated and analyzed. IP25 does not exist in the Antarctic, but scientists from Plymouth - working with colleagues from Hanyang University, the Korea Polar Research Institute, the British Antarctic Survey and Isoprime Limited - have discovered a related chemical in the Southern Ocean. Analysis of surface sediments covering different regions of Antarctica - including the Weddell Sea, the Antarctic Peninsula, the Bellingshausen Sea and the Ross Sea - showed the presence of IPSO25 (ice proxy for the Southern Ocean with 25 carbon atoms) in nearly all cases. Its source, Berkeleya adeliensis, is a widespread and commonly occurring constituent of microalgae inhabiting Antarctic sea ice, which explains why IPSO25 is so common in the sediments. "The identification of IPSO25 in the Antarctic sea ice diatom Berkeleya adeliensis likely ensures that future interpretations of the sedimentary occurrence of this sea ice proxy can be made with greater confidence and in more detail. Thus, in addition to representing a qualitative measure of the past occurrence of Antarctic landfast ice during late spring/summer, our findings indicate that variability in sedimentary IPSO25 potentially provides further insights into changes to ice shelf and glacial melt processes in long-term records," the paper concludes.

Kim B.-M.,Korea Polar Research Institute | An S.-I.,Yonsei University
Journal of Climate | Year: 2011

The regime behavior of the low-order El Niño-Southern Oscillation (ENSO) model, according to an increase in the radiative-convective equilibrium sea surface temperature (SST; Tr), is studied to provide a possible explanation for the observed increase in ENSO irregularity characterized by decadal modulation. During recent decades, a clear increasing trend of the warm-pool SST has been observed. In this study, the increase in the warm-pool maximum SST is interpreted as an increase in Tr following previous studies. A bifurcation analysis with Tr as a control parameter is conducted to reveal that the degree of ENSO irregularity in the model is effectively controlled by the equilibrium states of the model. At a critical value of Tr, bifurcation analysis reveals that period-doubling bifurcation occurs and an amplitude-modulated ENSO emerges. At this point, a subcycle appears within the preexisting ENSO cycle, which initiates decadal modulation of ENSO. As Tr increases further, nested oscillations are successively generated, illustrating clear decadal modulation of ENSO. The qualitative regime changes revealed in this study are supported by the observation of regime shifts in the 1970s. With increasing Tr, the mean zonal SST gradient increases, and the model adjusts toward a "La Niña-like" mean state. Further constraint with shoaling of the mean thermocline depth and increasing stratification causes ENSO to exhibit stronger amplitude modulation. Furthermore, the timing of the period-doubling bifurcation advances with these two effects. © 2011 American Meteorological Society.

Kim S.-Y.,Korea Polar Research Institute | Lim D.-I.,Korea Advanced Institute of Science and Technology
Progress in Oceanography | Year: 2014

Marine microfossil assemblages in core sediments from the northern East China Sea (ECS) were investigated to understand late Holocene paleoclimatic changes in the northwestern Pacific margin. We find a pronounced alternation of ocean condition during the late Holocene characterized by an abrupt decrease in dinoflagellate cysts and Kuroshio water species of planktonic foraminifera centered at ca. 4000-2500 14C yr BP. Compilation and merger of new and previously published data show that this oceanic event corresponds with terrestrial cooling and dry episodes in the northern China. The synchronicity between marine and terrestrial records is considered to be linked to a weakened Kuroshio influence that is in coupled with intensified winter monsoon, highlighting a significance of oceanic-atmospheric dynamics in determining moisture and heat distribution over both oceanic and terrestrial domains. Superimposed on the late Holocene, the synchronicity between this particular climatic shift in the northwestern Pacific and the Neoglacial cold events in the northern high-latitude regions is tentatively indicative of a global climate signal, possibly associated with dynamics of the North Pacific gyre system and the high latitude North Atlantic thermohaline circulation, and therefore positions of the mean latitude of the Kuroshio extension. © 2014 Elsevier Ltd.

Notothenia coriiceps, a typical Antarctic notothenioid teleost, has evolved to adapt to the extreme Antarctic marine environment. We previously reported an extensive analysis of the Antarctic notothenioid transcriptome. In this study, we focused on a key component of the innate immune system, the Toll-like receptors (TLRs). We cloned the full-length sequence of 12 TLRs of N. coriiceps. The N. coriiceps transcriptome for TLR homologue (ncTLR) genes encode a typical TLR structure, with multiple extracellular leucine-rich regions and an intracellular Toll/IL-1 receptor (TIR) domain. Using phylogenetic analysis, we established that all of the cloned ncTLR genes could be classified into the same orthologous clade with other teleost TLRs. ncTLRs were widely expressed in various organs, with the highest expression levels observed in immune-related tissues, such as the skin, spleen, and kidney. A subset of the ncTLR genes was expressed at higher levels in fish exposed to pathogen-mimicking agonists, heat-killed Escherichia coli, and polyinosinic-polycytidylic acid (poly(I:C)). However, the mechanism involved in the upregulation of TLR expression following pathogen exposure in fish is currently unknown. Further research is required to elucidate these mechanisms and to thereby increase our understanding of vertebrate immune system evolution.

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