Influence of trace element fluxes from submarine groundwater discharge (SGD) on their inventories in coastal waters off volcanic island,Jeju, Korea

The concentrations of trace elements in groundwater and seawater were measured in a coastal embayment (Bangdu Bay) of a volcanic island (Jeju) off the southernmost coast of Korea in August and December of 2009. The concentrations of trace elements (Al, Mn, Fe, Co, Ni, and Cu) in the groundwater in summer were approximately 20-fold higher than those in winter, with good correlation to each other. Overall, the concentrations of most of the trace elements in the groundwater were 3- to 70-fold higher than those in the seawater of this Bay. Simple budget calculations showed that large fluxes of submarine groundwater discharge (SGD)-driven trace elements were responsible for the unusually enhanced concentrations of trace elements (particularly for Al, Fe and Co) in the summer seawater. The results imply that the temporal changes in SGD-driven trace element fluxes are large and may contribute considerably to the budget of trace elements in the coastal ocean, particularly off a highly permeable volcanic island.     

Spatial and seasonal variations in the water quality of Jinhae Bay,Korea

The chemical and biological characteristics of surface waters in Jinhae Bay were investigated over four seasons to understand water quality in light of the growing industrialisation occurring within this area. Jinhae Bay includes four smaller bays: Masan; Hangam; Jindong; and Gohyun. The water quality in Jinhae Bay varied spatially and seasonally. The water quality of both Hangam Bay and Masan Bay was highly degraded, demonstrating high concentrations of ammonia, nitrate, chlorophyll a and particulate organic carbon. Contamination from sewage was the dominant cause of the water quality deterioration in these bays. Conversely, the water quality in Jindong Bay and Gohyun Bay was not as severely affected as that of the above two bays. Water quality in Jinhae Bay was particularly poor in summer when nutrient loading was highest due to the run-off associated with high precipitation. Principal component analysis indicated that nitrogen contamination was a major factor influencing the water quality of Jinhae Bay. The effective reduction in high-nitrogen discharges is essential to improve water quality in Jinghae Bay.     

Morphology and molecular characterization of the epiphytic dinoflagellate Prorocentrum cf. rhathymum in temperate waters off Jeju Island, Korea

Prorocentrum spp. are planktonic and/or benthic species. Benthic Prorocentrum species are of primary concern to scientists and the public because some of them are toxic. We established clonal cultures of 3 strains of Prorocentrum species that were collected from the thalli of a macroalga in the coastal waters off Jeju Island, located at the southern end of Korea. The Korean strains of P. cf. rhathymum, which are morphologically almost identical to the Virgin Island strain of P. rhathymum, were different from P. mexicanum because the former dinoflagellate has one simple collar-like spine in the periflagellar area, while the latter dinoflagellate has a 2- or 3-horned spine. In addition, the sequences of the small subunit (SSU) rDNA of the Korean strains were identical to those of the Malaysian and Floridian strains of P. rhathymum, while the sequences of the large subunit (LSU) rDNA of the Korean strains were 0.1–0.9% different from those of the Iranian and Malaysian strains of P. rhathymum. In phylogenetic trees based on the SSU rDNA sequences, the Korean strains of P. rhathymum formed a clade with the Malaysian and Floridian strains of P. rhathymum and the Vietnamese and Polynesian strains of P. mexicanum. However, in phylogenetic trees based on the LSU rDNA sequences, the Korean strains of P. rhathymum formed a clade with the Iranian strain of P. rhathymum and the Spanish and Mexican strains of P. mexicanum. Therefore, the molecular characterization of the Korean strains does not allow us to clearly classify them as P. rhathymum, nor P. mexicanum, although their morphology has so far been reported to be closer to that of P. rhathymum than P. mexicanum and thus we designated them as P. cf. rhathymum.     

The potential of vegetation feedback to alleviate climate aridity over the United States associated with a 2×CO2 climate condition

This study examines the potential impact of vegetation feedback on changes in summer climate aridity over the contiguous United States (US) due to the doubling of atmospheric CO₂ concentration using a set of 100-year-long climate simulations made by a global climate model interactively coupled with a dynamic vegetation model. The Thornthwaite moisture index (I _m ), which quantifies climate aridity on the basis of atmospheric water supply (i.e., precipitation) and atmospheric water demand (i.e., potential evapotranspiration, PET), is used to measure climate aridity. Warmer atmosphere and drier surface resulting from increased CO₂ concentration increase climate aridity over most of the contiguous US. This phenomenon is due to larger increments in PET than in precipitation, regardless of the presence or absence of vegetation feedback. Compared to simulations without active dynamic vegetation feedback, the presence of vegetation feedback significantly alleviates the increase in aridity. This vegetation-feedback effect is most noticeable in the subhumid regions such as southern, midwestern and northwestern US, primarily by the increasing vegetation greenness. In these regions, the greening in response to warmer temperatures enhances moisture transfer from soil to atmosphere by evapotranspiration (ET). The increased ET and subsequent moistening over land areas result in weaker surface warming (1–2?K) and PET (3–10?mm?month^?1), and greater precipitation (4–10?mm?month^?1). Collectively, they result in moderate increases in I _m . Our results suggest that moistening by enhanced vegetation feedback may prevent aridification under climatic warming especially in areas vulnerable to climate change, with consequent implications for mitigation strategies.     

Eruption and emplacement of a laterally extensive, crystal-rich, and pumice-free ignimbrite (the Cretaceous Kusandong Tuff, Korea)

The Cretaceous Kusandong Tuff, Korea, is a thin (1–5 m thick) but laterally extensive (~ 200 km) silicic ignimbrite emplaced in a fluviolacustrine basin adjacent to a continental volcanic arc. The tuff has been used as an excellent key bed because of its great lateral continuity and unique lithology, characterized by the virtual absence of juvenile clasts and an abundance of quartz and feldspar crystals (up to 55–73 vol.%). The tuff is mostly massive and ungraded and locally shows crude internal layering, basal inverse grading and near-top normal grading of crystals, either erosional or non-erosional lower surfaces, and flat-lying to imbricated grain fabrics. Fragile intraformational clasts of mudstone and tuff are also included. These features provide only ambiguous information on the properties of the responsible pyroclastic density currents: i.e. whether they were dense and laminar or dilute and turbulent. The overall lateral continuity and sheet-like geometry of the tuff suggests, however, that the transport system of the currents was highly expanded, dilute, and turbulent. A plug-flow or slab-flow model cannot explain the origin of crude internal layering, imbricated grain fabrics, and the high crystal content, which is most likely the result of vigorous sorting processes within a dilute and turbulent current. Features indicative of deposition from a dense and laminar transporting medium are locally present, suggesting that a dense and laminar depositional system could develop locally at the base of the dilute and turbulent transport system. The virtual absence of juvenile clasts in the tuff is interpreted to be due to rapid ascent, sudden decompression, and full fragmentation of silicic magma into fine glass shards and crystals. Scarcity of basement-derived accidental components together with the absence of pumiceous fallout deposits beneath the tuff is interpreted to be due to shallow-level fragmentation of magma followed by immediate generation of pyroclastic density currents from shallow-level blasts at the onset of eruption. The eruption occurred through multiple vent sites in a short period of time, producing a seemingly single but actually composite ignimbrite unit. Such an eruption was probably possible because of a regional tectonic event within the basin or in its vicinity. It is proposed that a composite ignimbrite with the characteristics of the Kusandong Tuff can be an exemplary product of syntectonic volcanism that can provide an insight into the interpretation of structural and stratigraphic evolution of a sedimentary basin.     

Hydrothermal fluid-controlled remagnetization of sedimentary rocks in Korea: Tectonic importance of pervasive Tertiary remagnetization

In order to better understand the tectonic environment of the Korean Peninsula since Cretaceous, a paleomagnetic study was carried out on the Jinan Basin located in southwestern Korea. From the demagnetization of 597 samples, we found that remanence is carried by pyrrhotite and/or magnetite (black siltstone) and hematite (red siltstone), which is a common magnetic mineral assemblage of the rocks remagnetized in Early Tertiary in Korea. All the rock units recorded identical ancient geomagnetic field directions. In particular, paleodirections were better clustered in geographic coordinates, indicating a secondary origin. The presence of abundant silicates as inclusions within Fe-oxides and Fe-sulfides confirms the authigenic origin of the magnetic carriers, precipitated by fluid mediated chemical processes. Compilation of the Korean Cretaceous and Tertiary poles indicates that the Jinan Basin was remagnetized in the Early Tertiary age. In addition, comparison of the Korean Cretaceous and Tertiary poles with those from adjacent major terrains including China and Siberia reveals that a dominant feature of tectonic motions in Korea was a vertical-axis rotation. Sense of vertical-axis rotation was time-dependent, with clear distinction between clockwise rotation in Cretaceous and counter-clockwise rotation in Early Tertiary. Such differences in the mode of vertical axis rotation might be caused by the activities of basin-bounding strike–slip faults in Korea, possibly driven by the changes of subduction regime of the Kula-Pacific plate in Early Tertiary.     

Load–settlement behavior of rock-socketed drilled shafts using Osterberg-Cell tests

Osterberg-Cell (O-Cell) tests are widely used to predict the load–settlement behavior of large-diameter drilled shafts socketed in rock. The loading direction of O-Cell tests for shaft resistance is opposite to that of conventional downward load tests, meaning that the equivalent top load–settlement curve determined by the summation of the mobilized shaft resistance and end bearing at the same deflection neglects the pile-toe settlement caused by the load transmitted along the pile shaft. The emphasis is on quantifying the effect of coupled shaft resistance, which is closely related to the ratios of pile diameter to soil modulus (D/E_s) and total shaft resistance to total applied load (R_s/Q) in rock-socketed drilled shafts, using the coupled load-transfer method. The proposed analytical method, which takes into account the effect of coupled shaft resistance, was developed using a modified Mindlin’s point load solution. Through comparisons with field case studies, it was found that the proposed method reasonably estimated the load-transfer behavior of piles and coupling effects due to the transfer of shaft shear loading. These results represent a significant improvement in the prediction of load–settlement behaviors of drilled shafts subjected to bi-directional loading from the O-Cell test.