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Hyeong, Kiseong,Lee, Jongmin,Seo, Inah,Lee, Mi Jung,Yoo, Chan Min,Khim, Boo-Keun Geological Society of America 2014 Geology Vol.42 No.8
<P>The Mi-1 glaciation (ca. 23 Ma), which marks the Oligocene-Miocene boundary, was an aberrant cooling event that led to a build-up of the Antarctic ice sheet, which reached the near-modern volume (or greater) from its ephemeral or partial existence. An increase of ∼1‰ in the δ<SUP>18</SUP>O of benthic foraminifera during this interval has been attributed to the development of Antarctic ice sheets and deep-water cooling. Without definitive evidence, Northern Hemisphere (NH) glaciation has not been a material consideration for the δ<SUP>18</SUP>O increase. Here we investigate the interhemispheric temperature contrast during Mi-1, with the movement of the Intertropical Convergence Zone (ITCZ) at a site (10°31′N) in the East Pacific (Integrated Ocean Drilling Program Site U1333), to understand NH cooling and the possibility of NH glaciation. The measured <SUP>143</SUP>Nd/<SUP>144</SUP>Nd, <SUP>87</SUP>Sr/<SUP>86</SUP>Sr, and clay mineral compositions of eolian dust fractions indicate unequivocally the deposition of Asian dust during Mi-1, and of Central American and South American dust before and after Mi-1. This is attributed to the southward displacement of the ITCZ over Site U1333 during Mi-1. The ITCZ shifts toward the warmer hemisphere. Thus our results suggest that the cooling during Mi-1 was more significant in the NH than in the Southern Hemisphere, which underwent a sudden expansion of continental ice sheets. Our data call for a forcing mechanism to drive significant NH cooling during this episode. Based on the available data, we propose that the widespread growth of NH ice sheets and/or changes in the production of North Atlantic–origin deep water could be possible causes of the NH cooling at that time.</P>
Hyeong, Kiseong,Seo, Inah,Lee, Hyun-Bok,Yoo, Chan Min,Chi, Sang-Bum,Um, In Kwon Korean Ocean Research & Development Institute and 2018 OCEAN SCIENCE JOURNAL Vol.53 No.2
Radionuclide activities of <TEX>$^{210}Pb$</TEX> and <TEX>$^{226}Ra$</TEX> were measured to determine bioturbation coefficients (<TEX>$D_b$</TEX>) in seven sediment cores from the Korean licensed block for polymetallic nodules in the Clarion-Clipperton Fracture Zone. Variability in <TEX>$D_b$</TEX> is considered in the context of the sedimentological, geochemical, and geotechnical properties of the sediments. <TEX>$D_b$</TEX> values in the studied cores were estimated using a steady-state diffusion model and varied over a wide range from 1.1 to <TEX>$293cm^2/yr$</TEX> with corresponding mixing depths (L) of 26 to 144 cm. When excepting for spurious results obtained from cores where diffusive mixing does not apply, <TEX>$D_b$</TEX> values range from 1.1 to <TEX>$9.0cm^2/yr$</TEX> with corresponding mixing depths (L) of 26 to 63 cm. Such wide variability in <TEX>$D_b$</TEX> and L values is exceptional in sites with water depths of ~5000 m and is attributed in this study to an uneven distribution of sediment layers with different shear strengths and total organic carbon (TOC) contents, caused by erosion events. The studied cores can be grouped into two categories based on lithologic associations: layers with high maximum shear strength (MSS) and low TOC content, showing a narrow range of <TEX>$D_b$</TEX> values (<TEX>$1.1-9.0cm^2/yr$</TEX>); and layers with low MSS and high TOC content, yielding much higher <TEX>$D_b$</TEX> values of over <TEX>$30cm^2/yr$</TEX>. The distribution of different lithologies, and the resultant spatial variability in MSS and labile organic matter content, controls the presence and maximum burrowing depth of infauna by affecting their mobility and the availability of food. This study provides a unique case showing that shear strength, which relates to the degree of sediment consolidation, might be an important factor in controlling rates of bioturbation and sediment mixing depths.
Kiseong Hyeong,James R. Lawrence 한국지질과학협의회 2003 Geosciences Journal Vol.7 No.1
A hydrological study using oxygen isotopic ratiosand salinities was carried out in the San Bernard-Brazos RiverEstuaries, Brazoria County, Texas, USA, to understand the influ-ence of 4 fresh water sources draining into the area, Brazos River,San Bernard River, Oyster Creek, and Jones Creek, on variousparts of the Gulf Intra-Coastal Waterway (GIW) that transectsthese rivers half to 1 mile inland of the Gulf of Mexico. The mea-sured oxygen isotopic ratios and salinities of GIW waters areexplained with simple mixing between one of the 4 fresh watersources with marine water and made it possible to identify 3 sub-areas of the GIW, each of which is influenced by different fresh-water source. These sub-areas locate on the western part of theBrazos River, between the Brazos and Old Brazos River, and onthe eastern part of the Old Brazos River, and have their freshwa-ter source from the San Bernard River, Brazos River, and OysterCreek, respectively. An interesting result was found in the GIWbetwen the San Bernard and Brazos Rivers, where fresh water ismainly sourced from the San Bernard River although its dis-charge rate is 40 to 100 times less than that of the Brazos River.This westerly flow of the San Bernard River toward the largerBrazos River is due to shallowing of the San Bernard River at theriver mouth, which restricts free discharge of river water to opensea and diverts the flow toward the GIW on both sides of the river.The influence of the other two creeks, Oyster and Jones, wasminor and limited near the confluence with the GIW due to minorinfluxes. The generalized flow pattern derived in this study isessential for the construction of contingency plan against toxiccontaminations, which wil minimize environmental impact onnumerous organisms living in the GIW. The results of this studyare also useful for tracing of contaminants in the studied GIW.