https://repository.kopri.re.kr/handle/201206/5508 2026-04-06T10:05:36Z https://repository.kopri.re.kr/handle/201206/6129 Title: Milankovitch cycles and paleoceanographic evolution within sediments from ODP Sites 980 and 983 of the North Atlantic Ocean Authors: Naokaze Ahagon; Hyun, Sangmin; Yoon, Ho Il Abstract: Sediments from Ocean Drilling Program (ODP) Sites 980 and 983 in the North Atlantic Ocean were analyzed to obtain evidence of long-range Milankovitch cycles and to examine the cycles' effect on the paleoceanographic evolution of the North Atlantic Ocean. Wide cyclic variations in total organic carbon and biogenic carbonate occur throughout the columns at both sites and provide distinctive characteristics of both sediment groups. Spectral modeling of these variations shows typical 100-ka cyclic variations in both the total organic carbon (TOC) and carbonate records at Site 980, although this 100-ka Milankovitch frequency occurs only in the upper, similar to 472.5 ka, section of the core. In Site 983, only 400-ka cycle in carbonate is observed but the 100-ka cycle in TOC and carbonate is absent. The terrigenous content, expressed in terms of K, Al, Ti, and Th, also shows strong 100-ka and 400-ka cyclic variations at Site 983. The earth's eccentricity as expressed 100-ka and 400-ka cycles, and no appearance of obliquity (41-ka) and precession (23-ka) are important characteristics of North Atlantic Ocean sediments. Milankovitch pulse differences in carbonate, TOC at the two sites likely arise from the evolution of paleoceanography. The dilution of carbonate fractions by terrigenous materials (indicated by the cyclical behavior of trace elements) at Site 983 is one of plausible explanation. Climatic warming over the last 600 ka probably caused the differences in the sedimentary cycles at the two sites;induced meltwater discharge is recorded in the terrigenous record, and changes in the oceanic circulation system are related to major glacial-interglacial climatic episodes that probably underlie the differences in the cyclical records. 2005-01-01T00:00:00Z https://repository.kopri.re.kr/handle/201206/6589 Title: First Cenozoic glaciers in West Antarctica Authors: Andrzei Gazdzicki; Andrzei Solecki; Krzysztof Birkenmajer; Ho Il Yoon; Andrzej Tatur; Andrzei Przybycin; Krzysztof Krajewski Abstract: One of the most significant global climatic events in the Cenozoic was the transition from greenhouse to icehouse conditions in Antarctica. Tectonic evolution of the region and gradual cooling at the end of Eocene led to the first appearance of ice sheets at the Eocene/Oligocene boundary (ca. 34 Ma). Here we report geological record of mountain glaciers that preceded major ice sheet formation in Antarctica. A terrestrial, valley-type tillite up to 65 metres thick was revealed between two basaltic lava sequences in the Eocene-Oligocene Point Thomas Formation at Herv？ Cove - Breccia Crag in Admiralty Bay, King George Island, South Shetland Islands. K-Ar dating of the lavas suggests the age of the glaciation at 45-41 Ma (Middle Eocene). It is the oldest Cenozoic record of alpine glaciers in West Antarctica, providing insight into the onset of glaciation of the Antarctic Peninsula and South Shetland Islands. 2005-01-01T00:00:00Z https://repository.kopri.re.kr/handle/201206/6631 Title: Climatic Characteristics Related with Sedimentary Process in Bransfield Strait, Antarctica Authors: Lee, Bang Yong; Lee, Jeong Soon; 윤영준; Yoon, Ho Il; 권태영 Abstract: This study examines the relationships among sea ice concentration, surface air temperature, surfacewind, and SST (Sea Surface Temperature) in Bransfield Strait to understand the climatic characteristicsand its related sedimentary process there. In analyses of the monthly data, during the austral autumn(Mar., Apr., and May), the frequency of southeasterlies is correlated positively with the sea ice concentrationand negatively with the surface air temperature, whereas that of northwesterlies is reverse. Theserelationships are explained by the process that the southeasterlies of the cold air from the AntarcticContinent affect the ocean current around Bransfield Strait. And then the ocean current makes thesea ice generated in the Weddell Sea drift into the strait. During the spring (Sep., Oct., and Nov.),sea ice concentration and surface air temperature are closely correlated with the frequency ofnorthwesterlies with warm air mass. In the some parts of the northern boundary region, the sea iceconcentration in Bransfield Strait is positively correlated with the SST during the autumn and spring.Such relationship may rather propel the sea ice melting in proportion to the sea ice concentrationduring the autumn. 2005-01-01T00:00:00Z https://repository.kopri.re.kr/handle/201206/5581 Title: Geochemical characteristics and the provenance of sediments in the Bransfield Strait, West Antarctica Authors: Park, Byoung-Kwon; Kim, Yeadong; Jwa, Young-Joo; Lee, Jae Il; Yoo, Kyu-Cheul; Yoon, Ho Il Abstract: The Bransfield Basin is a Quaternary marginal basin separating the South Shetland Islands from the Antarctic Peninsula. We analyzed major, trace, and rare earth element chemistries, and the Nd, Sr, and Pb isotopic compositions for six piston core sediments from the western and eastern Bransfield basins to determine the sediment provenance and factors controlling the composition of the sediments. The Bransfield sediments have chemical characteristics similar to sediments deposited in a tectonically active setting where the source rocks are predominated by igneous rocks of intermediate to mafic composition: low K and high CN in the A-CN-K diagram, low La/Sc, low Th/Sc, and lower LREE/HREE than average shale. The low chemical alteration index of the sediments, about 45 on average, suggests the effect of weathering on the sediment composition was minimal. The source rocks of the Bransfield sediments are mostly composed of Mesozoic to Tertiary arc volcanic and plutonic rocks in the Antarctic Peninsula and the South Shetland Islands. Meanwhile, contributions from other rock types in the northern Antarctic Peninsula region, such as the Trinity Peninsula Group or Scotia Metamorphic Complex, seem to be negligible. The Bransfield sediments can be divided into three distinct compositional groups. Group I sediments have a lower La/Yb and a less prominent negative Eu anomaly than Group II sediments. They are also characterized by negative Ce anomalies. Group I sediments have been derived mainly from the South Shetland Islands, whereas Group II sediments, which are more widespread than Group I sediments in the Bransfield Strait, have been derived mainly from the Antarctic Peninsula. Group III sediments, which are very low in La/Yb with the lowest Sr-87/Sr-86 and the highest Nd-143/Nd-144 values, have been derived from Deception Island. The composition of the Bransfield sediments is largely controlled by the composition of nearby source rocks;the distribution of sediments is further modified by the current and topography of the basin. (c) 2005 Elsevier B.V. All rights reserved. 2005-01-01T00:00:00Z