Records of terrestrial n-alkanes and carbon isotope of organic matter in Hanon-Maar sediment, Jeju Island, Korea: implications of paleovegetation and paleoclimate variations over the last 35 kyr

Carbon isotope of total carbon (&#61540 13CTOC), long-chain n-alkanes and their compound-specific carbon isotope ratios (&#61540 13CALK) were investigated in the Hanon paleo-Maar sediment, Jeju Island of Korea to understand paleovegetationchanges and their paleoclimate linkages. Based on the organic geochemical data (TOC (%), TN(%) and their &#61540 13CTOC and&#61472 &#61540 15NTN ), the core column stratigraphy was divided into three units from bottom to 12.5 ka (UnitI),12.5 ~2.5 ka (Unit II) and 2.5 ka to core tope (Unit III), respectively. In particular, &#61540 13CTOC showed marked fluctuation from -17.31‰ to -28.68‰, suggesting different organic carbon sources.ionchanges and their paleoclimate linkages. Based on the organic geochemical data (TOC (%), TN(%) and their &#61540 13CTOC and&#61472 &#61540 15NTN ), the core column stratigraphy was divided into three units from bottom to 12.5 ka (UnitI),12.5 ~2.5 ka (Unit II) and 2.5 ka to core tope (Unit III), respectively. In particular, &#61540 13CTOC showed marked fluctuation from -17.31‰ to -28.68‰, suggesting different organic carbon sources.1

Occurrence of organic compound (diploptene) in East Sea core sediments and its paleoceanographic implication

Two piston cores (06GHSA P1 and 06GHSA P6) from the Ulleung Basin of the East Sea were examined for the presence of organic compounds (diploptene in particular), and carbon isotopic variations were also analyzed to determine their origins. More than 70 samples from the two cores were analyzed using gas chromatography–mass spectrometry, and 23 samples were selected for carbon isotope analysis based on isotope ratio mass spectrometry. Data from the core records showed that organic compounds occurred in the two cores, showing high vertical fluctuation in the 06GHSA P6 core during the Last Glacial Maximum. The diploptene concentration ranged from 1.7 to 632.1 ng/g (average 87 ng/g) in core 06GHSA P6 and from 1.4 to 42.2 ng/g in core 06GHSA P1 (average 20.1 ng/g). An especially elevated concentration of diploptene was observed in core 06GHSA P6 during glacial periods. Carbon isotope values in the diploptene ranged from –56.33 to –60.23 per mil, suggesting that this diploptene was in part derived from methanotrophic bacteria, which decomposed methane in the water column and sediment. Thus, the occurrence of diploptene derived from bacterial activity and the carbon isotopic values of diploptene may indicate potential methane seepage during the glacial period in core 06GHSA P6. This implies that a potential dissociation of gas hydrate during glacial periods is observed in the foraminiferal isotopic record and methanotrophic processes in the southern part of Ulleung Basin, East Sea.Reasons for the occurrence of diploptene may include paleoceanographic environmental changes such as in sea level during the glacial period. Unlike the Santa Barbara basin in which the episodic light carbon isotopic signals were interpreted as the reason for the warm intermediate water inflow, in the East Sea, the lowered sea level and climatic changes during glacial period may have reduced the stability of the methane hydrate.1

Geochemical character on Hanon Maar sediment: implicaiton on paleoclimate and paleovegetation around Korean peninsula

과거 약 3.5만년 간 한반도 주변지역에 대한 고기후, 식생 변화를 파악하기 위해 한반도 제주도 소재의 하논분화구에서 퇴적물을 채취했다. 약 12.5미터의 주상시료 퇴적물에 대한 방사성 탄소연대를 측정한 결과 주상시료 최하부는 약 3.5만년으로 나타났다. 이 기간 동안 무기원소(주요원소, 미량원소 및 희토류원소) 및 유기원소(탄소, 질소 동위원소), n-alkanes의 거동을 조사한 결과 전 구간 퇴적상은 뚜렷하게 3개의 Unit으로 구별되었다. 특히 15ka는 가장 뚜렷하게 유·무기 지화학원소의 거동이 달라지고있는 것으로 판단되었다 (Fig 1~3). 이 기간 동안 무기원소(주요원소, 미량원소 및 희토류원소) 및 유기원소(탄소, 질소 동위원소), n-alkanes의 거동을 조사한 결과 전 구간 퇴적상은 뚜렷하게 3개의 Unit으로 구별되었다. 특히 15ka는 가장 뚜렷하게 유·무기 지화학원소의 거동이 달라지고있는 것으로 판단되었다 (Fig 1~3).2

Occurrence of diploptene and its carbon isotope value in East Sea sediments: implications for methane release and paleoceanography

Data from the core records showed that organic compounds occurred in the two cores, showing high vertical fluctuation in the 06GHSA P6 core during the Last Glacial Maximum. The diploptene concentration ranged from 1.7 to 632.1 ng/g (average 87 ng/g) in core 06GHSA P6 and from 1.4 to 42.2 ng/g in core 06GHSA P1 (average 20.1 ng/g). An especially elevated concentration of diploptene was observed in core 06GHSA P6 during glacial periods. Carbon isotope values in the diploptene ranged from –56.33 to –60.23 per mil, suggesting that this diploptene was in part derived from methanotrophic bacteria, which decomposed methane in the water column and sediment. Thus, the occurrence of diploptene derived from bacterial activity and the carbon isotopic values of diploptene may indicate potential methane seepage during the glacial period in core 06GHSA P6. This implies that a potential dissociation of gas hydrate during glacial periods is observed in the foraminiferal isotopic record and methanotrophic processes in the southern part of Ulleung Basin, East Sea.1

Widespread anthropogenic nitrogen in the northwestern Pacific Ocean sediment

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Importance of organic matter in mercury spatial distribution into Svalbard fjord sediments

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Morphologic and seismic stratigraphic analysis of Quaternary deposition on the western Arctic continental margin: Insights into the extent and behavior of the East Siberian Ice Sheet

Extensive mapping of the glaciogenic sedimentary and geomorphic features can enhance our understanding of the spatial extent and behavioral nature of the former ice sheets. The subsurface geological conditions of the high-latitude continental margin continue to be affected by the past ice sheets, such as glacial isostatic uplift and eustatic sea level rise, even after the ice sheet disappeared. Therefore, reconstructing ice-sheet history is crucial for identifying areas that may be at risk of slope failure or for understanding the migration and expulsion of fluids in the subsurface strata. Previous studies in the Chukchi-East Siberian margin in the western Arctic Ocean revealed multiple ice sheet expansions during the Quaternary glacial periods. In this study, we extended the previous seismostratigraphic interpretation of the western Chukchi Rise toward the East Siberian margin to compare characteristics of ice masses in two adjacent regions that were likely grounded by the same ice sheet, known as the East Siberian Ice Sheet (ESIS). The acoustically transparent deposits well defined in the seismic data and can be interpreted as glaciogenic debris flows, till sheets, and recessional moraines. The migration of glacial sediment depocenters from the Chukchi Basin through Kucherov Terrace to the upper slope and outer shelf of the East Siberian margin suggests a decrease in sediment transportation into the deeper area by southern-sourced grounded ice over time. This observational result may indicate a change in the glacial regime from a wet-based dynamic to a dry-based polar conditions, a reduction in vertical and lateral extent of the ice sheet, and/or a decrease in the amount of erodible subglacial sedimentary strata. The development of grounded-ice on the East Siberian margin is similar to the glaciations on the western Chukchi Rise, suggesting that ESIS grew significantly with merging and interaction of the expanded ice masses from both regions.2