Hyoun Soo Lim

Vegetation and climate changes during the Late Pleistocene to Holocene inferred from pollen record in Jinju area, South Korea

The pollen record from paleo-swamp deposits spanning the last ca. 26,000 yr reveals a detailed history of vegetation and climate changes of the Jinju area, South Korea. From ca. 26.2 to 23.9 cal. kyr BP, xerophyticArtemisia-dominated grassland and mixed subalpine coniferous and deciduous broadleaved forests occupied the study area, indicating a cool and dry condition during interstadial stage of the last glacial period. The period between ca. 23.9 and 14.7 cal. kyr BP exhibits the expansion of grassland and subalpine coniferous forest and the retreat of deciduous broadleaved forest, reflecting a cold and dry condition during the Last Glacial Maximum (LGM). During the period of ca. 14.7–11.2 cal. kyr BP, climatic amelioration comparable to the Boelling-Alleroed Event induced an enlargement of temperate deciduous broadleaved forest and a shrink of subalpine coniferous forest and grassland. Vegetation changes controlled by human impact occurred from ca. 4.7 to 0.7 cal. kyr BP, as indicated by an increase inPinus and Gramineae pollen.

Mid-latitude interhemispheric hydrologic seesaw over the past 550,000 years

An interhemispheric hydrologic seesaw—in which latitudinal migrations of the Intertropical Convergence Zone (ITCZ) produce simultaneous wetting (increased precipitation) in one hemisphere and drying in the other—has been discovered in some tropical and subtropical regions. For instance, Chinese and Brazilian subtropical speleothem (cave formations such as stalactites and stalagmites) records show opposite trends in time series of oxygen isotopes (a proxy for precipitation variability) at millennial to orbital timescales, suggesting that hydrologic cycles were antiphased in the northerly versus southerly subtropics. This tropical to subtropical hydrologic phenomenon is likely to be an initial and important climatic response to orbital forcing. The impacts of such an interhemispheric hydrologic seesaw on higher-latitude regions and the global climate system, however, are unknown. Here we show that the antiphasing seen in the tropical records is also present in both hemispheres of the mid-latitude western Pacific Ocean. Our results are based on a new 550,000-year record of the growth frequency of speleothems from the Korean peninsula, which we compare to Southern Hemisphere equivalents. The Korean data are discontinuous and derived from 24 separate speleothems, but still allow the identification of periods of peak speleothem growth and, thus, precipitation. The clear hemispheric antiphasing indicates that the sphere of influence of the interhemispheric hydrologic seesaw over the past 550,000 years extended at least to the mid-latitudes, such as northeast Asia, and that orbital-timescale ITCZ shifts can have serious effects on temperate climate systems. Furthermore, our result implies that insolation-driven ITCZ dynamics may provoke water vapour and vegetation feedbacks in northern mid-latitude regions and could have regulated global climate conditions throughout the late Quaternary ice age cycles.

Polychlorinated biphenyl congeners in soils and lichens from King George Island, South Shetland Islands, Antarctica

Abstract The levels and distribution of polychlorinated biphenyl (PCB) congeners were analysed in fourteen soil and eight lichen (Usnea aurantiaco-atra) samples from King George Island, West Antarctica. A total of 32 PCB congeners were found in five soil samples collected in 2006, and the mean concentration of total PCBs was 20.4 pg g-1 dry weight (range, 8.0−33.8 pg g-1 dry weight). The most abundant PCB isomers in soil samples were di-, tri-, and penta-CBs, which accounted for more than 75% of the total residues. Twelve dioxin-like PCBs were also detected in nine soil and eight lichen samples, and the levels of dioxin-like PCBs were 5-fold higher in lichens than in soil. PCBs were detected at very low levels in most soil and lichen samples. The highest congener concentrations were found for PCB 118 (6.63 and 21.93 pg g-1 in soil and lichen, respectively) among dioxin-like PCBs. PCB levels in air samples were highly correlated with those in soil and lichen samples, as were PCB levels in soil and lichen samples collected at the same site. Long-range atmospheric transport is thought to be the main source of PCBs on King George Island. However, PCB levels in soil and lichen samples were also apparently influenced by local sources of PCBs.

Chronostratigraphy of the sedimentary record of Limnopolar Lake, Byers Peninsula, Livingston Island, Antarctica

Abstract The chronostratigraphy of the sedimentary record of Limnopolar Lake, located on Byers Peninsula (Livingston Island, South Shetland Islands, Maritime Antarctica), is described based on radionuclides and radiocarbon age dating. The oldest moss macrofossil age was 6700±50 yr bp (7510±80 cal yr bp) from which the age/depth model estimates a basal age for the sedimentary record of c. 8300 cal yr bp, suggesting an earlier deglaciation of Byers Peninsula than reported in previous studies. Lithological units and other stratigraphic zones are described throughout the sediment core, showing different mineralogical composition and a fine alternation of clays and silty clays and moss layers of Drepanocladus longifolius. Based on magnetic susceptibility analyses, a number of probable primary and reworked tephra layers were identified, seven of them confirmed by SEM observations, and most of them in agreement with the regional tephrachronology stratigraphy for the north-west Antarctic Peninsula. Sedimentation rates showed no significant changes during the last 5000 years with the exception of an abrupt event that took place around 5400 cal yr bp, which implied the sedimentation of c. 30 cm of clays in a very short time, probably related to a period of glacial re-advance that caused abrupt changes in geomorphological processes in the catchment.

Highly Heterogeneous Soil Bacterial Communities around Terra Nova Bay of Northern Victoria Land, Antarctica

Given the diminished role of biotic interactions in soils of continental Antarctica, abiotic factors are believed to play a dominant role in structuring of microbial communities. However, many ice-free regions remain unexplored, and it is unclear which environmental gradients are primarily responsible for the variations among bacterial communities. In this study, we investigated the soil bacterial community around Terra Nova Bay of Victoria Land by pyrosequencing and determined which environmental variables govern the bacterial community structure at the local scale. Six bacterial phyla, Actinobacteria, Proteobacteria, Acidobacteria, Chloroflexi, Cyanobacteria, and Bacteroidetes, were dominant, but their relative abundance varied greatly across locations. Bacterial community structures were affected little by spatial distance, but structured more strongly by site, which was in accordance with the soil physicochemical compositions. At both the phylum and species levels, bacterial community structure was explained primarily by pH and water content, while certain earth elements and trace metals also played important roles in shaping community variation. The higher heterogeneity of the bacterial community structure found at this site indicates how soil bacterial communities have adapted to different compositions of edaphic variables under extreme environmental conditions. Taken together, these findings greatly advance our understanding of the adaption of soil bacterial populations to this harsh environment.

Late-Holocene palaeoclimatic change at the Dongnimdong archaeological site, Gwangju, SW Korea

A late-Holocene swamp sediment record is presented from the Dongnimdong archaeological site in SW Korea. Pollen analysis, geochemical analyses and radiocarbon dating have been used to reconstruct the vegetation and climatic changes. According to the pollen records, temperate deciduous broadleaved trees combined with herbs predominated in the study area ecology. Reduction of deciduous broadleaved trees with the spread of herbaceous taxa found in the middle part (c. 3300—2600 yr BP) indicates climatic change toward cooler and drier conditions. Significant increase in sand content and concomitant decrease in TOC content may suggest the occurrence of a period of drought. Vegetation changes recorded in the pollen sequence indicate the destruction of lowland deciduous forests and an accompanied expansion of grasses resulting from the climate changes. However, the increase of cultivation-accompanied herbs and excavated wooden tools for agriculture suggest the significant anthropogenic influence on the vegetation changes.

Late Holocene cyclic glaciomarine sedimentation in a subpolar fjord of the South Shetland Islands, Antarctica, and its paleoceanographic significance: Sedimentological, geochemical, and paleontological evidence

The glaciomarine sedimentary record of the fjord head (Collins Harbor) in Maxwell Bay, South Shetland Islands (West Antarctica), a large marine calving embayment, contains repeating couplets of organic-rich massive diamicton and organic-poor stratified diamicton. The massive diamicton is characterized by high total organic carbon (TOC) content and carbon to nitrogen (C/N) ratios and was deposited in a cold climate regime by iceberg-rafted sedimentation from coastal fast ice in which algal plants, as well as gravels, were entrained. The stratified diamicton is characterized by low TOC content and C/N ratios and was formed in a warmer climate regime when the flux of icebergs was suppressed, but turbid meltwater discharge continued to produce lamination. When the meltwater discharge decreased in cold climatic conditions, and resultant phytoplankton productivity was reduced due to the increased sea-ice coverage, ice rafting from shorefast sea ice might have played a major role in entraining benthic algae, as well as loads of sand and gravel, along the coastal area, resulting in an increased C/N ratio and gravel content in the massive diamicton. Accelerator mass spectrometry (AMS) radiocarbon analyses conducted on well-preserved calcite shells were used to construct a chronology for the past 3000 years. Fluctuations in TOC are recorded (approximately four cycles over this time period), with the average duration of a cooling cycle being ∼500 years. These cycles may be correlative with the high-frequency (550 yr) variability in reduced Circumpolar Deep Water (CDW) on the West Antarctic Peninsula shelf, because a decrease in CDW may be related to reduced deep water production in the North Atlantic during colder periods, as demonstrated for glacial intervals throughout the Pleistocene.

Tolerability and single dose pharmacokinetics of a new PDE5 inhibitor, DA‐8159 in healthy male subjects

Clinical Pharmacology & Therapeutics (2003) 73, P20–P20; doi:

Fission-track dating calibration of age standards in a Korean reactor, HANARO

In order to determine the fission-track age calibration constants (ξ-values), both apatite and zircon age standard samples were analyzed using an external detector method, and ξ-values are firstly determined using the NAA-1 facility in HANARO eactor. Two apatite and two zircon age standards recommended by IUGS were used for the zeta calibration. All the analyses for individual standards show high consistency, and sample weighted mean zeta values show a general agreement with each other. The overall weighted mean zeta values (±2σ) determined against a dosimeter glass NIST SRM612 are 337.6±25.4 for apatite, and 346.5±10.4 for zircon, showing no significant difference between the two minerals. These ξ-values are considered to be reasonable ones. The high Cd ratio of the NAA-1 facility in the HANARO reactor indicates that the facility tested in this study, NAA-1 is well-thermalised, and therefore suitable for fission-track dating.

Climate changes in the South Orkney Plateau during the last 8600 years

Climatic and oceanographic changes in the South Orkney Plateau, western Antarctica, during the last 8600 years are reconstructed from a 525 cm long gravity core based on sedimentological, geochemical and diatom analyses. The core sediments are composed mostly of light greyish olive diatomaceous silt and mud with a few diatom ooze laminae in the basal part. The core can be divided at 350 cm into two units (4800 cal. yr BP): the lower unit is characterized by variable total organic carbon (TOC) content and higher CaCO3 content, and the upper unit is characterized by higher TOC and lower CaCO3. The content of biogenic silica varies similar to TOC content in the lower unit but does not increase in the upper unit despite increased TOC. The variations in the organic matter composition and the amount of carbonate suggest that Scotia Sea water had been dominant in the study area prior to 4800 cal. yr BP. Warmer conditions during the middle Holocene are also supported by the fewer sea-ice diatom taxa and a more sub-polar form of Eucampia antarctica in the lower unit. The increased sea ice and decreased influence of Scotia Sea water in the upper unit reflect climate cooling occurred at 4800 cal. yr BP.