Qualitative assessment of gas hydrate and gas concentrations from the AVO characteristics of the BSR in the Ulleung Basin, East Sea (Japan Sea)

The presence of gas hydrate in the Ulleung Basin, East Sea (Japan Sea), inferred by various seismic indicators, including the widespread bottom-simulating reflector (BSR), has been confirmed by coring and drilling. We applied the standard AVO technique to the BSRs in turbidite/hemipelagic sediments crosscutting the dipping beds and those in debris-flow deposits to qualitatively assess the gas hydrate and gas concentrations. These BSRs are not likely to be affected by thin-bed tuning which can significantly alter the AVO response of the BSR. The BSRs crosscutting the dipping beds in turbidite/hemipelagic sediments are of low-seismic amplitude and characterized by a small positive gradient, indicating a decrease in Poisson’s ratio in the gas-hydrate stability zone (GHSZ), which, in turn, suggests the presence of gas hydrate. The BSRs in debris-flow deposits are characterized by a negative gradient, indicating decreased Poisson’s ratio below the GHSZ, which is likely due to a few percent or greater gas saturations. The increase in the steepness of the AVO gradient and the magnitude of the intercept of the BSRs in debris-flow deposits with increasing seismic amplitude of the BSRs is probably due to an increase in gas saturations, as predicted by AVO model studies based on rock physics. The reflection strength of the BSRs in debris-flow deposits, therefore, can be a qualitative measure of gas saturations below the GHSZ.     

Molecular and isotopic signatures in sediments and gas hydrate of the central/southwestern Ulleung Basin: high alkalinity escape fuelled by biogenically sourced methane

Natural marine gas hydrate was discovered in Korean territorial waters during a 2007 KIGAM cruise to the central/southwestern Ulleung Basin, East Sea. The first data on the geochemical characterization of hydrate-bound water and gas are presented here for cold seep site 07GHP-10 in the central basin sector, together with analogous data for four sites (07GHP-01, 07GHP-02, 07GHP-03, and 07GHP-14) where no hydrates were detected in other cores from the central/southwestern sectors. Hydrate-bound water displayed very low concentrations of major ions (Cl⁻, SO₄²⁻, Na⁺, Mg²⁺, K⁺, and Ca²⁺), and more positive δD (15.5‰) and δ¹⁸O (2.3‰) signatures compared to seawater. Cl^– freshening and more positive isotopic values were also observed in the pore water at gas hydrate site 07GHP-10. The inferred sulfate–methane interface (SMI) was very shallow (<5 mbsf) at least at four sites, suggesting the widespread occurrence of anaerobic oxidation of methane (AOM) at shallow sediment depths, and possibly high methane flux. Around the SMI, pore water alkalinity was very high (>40 mM), but the carbon isotopic ratios of dissolved inorganic carbon (δ¹³C_DIC) did not show minimum values typical of AOM. Moreover, macroscopic authigenic carbonates were not observed at any of the core sites. This can plausibly be explained by carbon with high δ¹³C values diffusing upward from below the SMI, increasing alkalinity via deep methanogenesis and eventually escaping as alkalinity into the water column, with minor precipitation as solid phase. This contrasts, but is not inconsistent with recent reports of methane-fuelled carbonate formation at other sites in the southwestern basin sector. Methane was the main hydrocarbon component (>99.85%) of headspace, void, and hydrate-bound gases, C₁/C₂₊ ratios were at least 1,000, and δ¹³C_CH4 and δD_CH4 values were in the typical range of methane generated by microbial reduction of CO₂. This is supported by the δ¹³C_C2H6 signatures of void and hydrate-bound gases, and helps clarify some contradictory interpretations existing for the Ulleung Basin as a whole. In combination, these findings suggest that deep biogenic gas and pore waters migrate upward through pathways such as hydrofractures, and measurably influence the shallow carbon cycle. As a result, cation-adjusted alkalinity/removed sulfate diagrams cannot always serve to estimate the degree of alkalinity produced by sulfate reduction and AOM in high methane flux areas.     

Quantifying two-way influences between the Arctic and mid-latitudes through regionally increased CO2 concentrations in coupled climate simulations

Climate Dynamics - In which direction is the influence larger: from the Arctic to the mid-latitudes or vice versa? To answer this question, CO2 concentrations have been regionally increased in...     

北半球对流层厚度的时空变化特征

利用1948—2010年NCEP/NCAR逐月位势高度再分析资料、美国国家海洋局提供的1948—2010年逐月海温再分析资料,分别定义了1 000—500 hPa和500—200 hPa厚度,利用EOF、SVD等方法研究了北半球对流层厚度时空演变特征及其与大气环流和海面温度的关系。结果表明,冬季平均厚度EOF第一模态均具有北太平洋及附近高纬度亚洲大陆地区与北美大陆高纬地区反位相变化的特点,而夏季第一模态则是北半球范围内较一致的位相分布;冬、夏季平均厚度EOF第二模态均突出体现了欧亚大陆及附近地区与北半球其他地区反位相变化的特点;冬、夏季厚度场的变化形势与大气环流及海面温度具有密切联系。     

Climate impact of transportation A model comparison

Transportation contributes to a significant and rising share of global energy use and GHG emissions. Therefore modeling future travel demand, its fuel use, and resulting CO₂ emission is highly relevant for climate change mitigation. In this study we compare the baseline projections for global service demand (passenger-kilometers, ton-kilometers), fuel use, and CO₂ emissions of five different global transport models using harmonized input assumptions on income and population. For four models we also evaluate the impact of a carbon tax. All models project a steep increase in service demand over the century. Technology change is important for limiting energy consumption and CO₂ emissions, the study also shows that in order to stabilise or even decrease emissions radical changes would be required. While all models project liquid fossil fuels dominating up to 2050, they differ regarding the use of alternative fuels (natural gas, hydrogen, biofuels, and electricity), because of different fuel price projections. The carbon tax of 200 USD/tCO₂ in 2050 stabilizes or reverses global emission growth in all models. Besides common findings many differences in the model assumptions and projections indicate room for further understanding long-term trends and uncertainty in future transport systems.     

Spatiotemporal distributions of thermal peaks in summer and winter over South Korea

This study investigated the spatial distributions and long-term trends of the annual highest and lowest temperatures (summer peak temperature, SPT; winter peak temperature, WPT) and their timings (summer peak day, SPD; winter peak day, WPD) in South Korea and analyzed their relationship with the general circulation patterns. The two peaks were determined by selecting the highest and the lowest points after extracting temperature variations longer than the seasonal scale (91 days) in the time series of daily mean temperatures. For the long-term trend, we examined data for 100 years (1909–2008) for five stations and data for 35 years (1974–2008) for 61 stations. The SPD in South Korea is August 4 on average. It is earliest (July 31) in the central inland region, the central hilly sections, and the southern inland region and latest (August 10) in the southern coastal region and on Jeju Island (Seogwipo). The WPD in South Korea is January 16 on average. It is earliest (January 13) in the central inland region and southern inland region and latest (January 24) on Jeju Island (Jeju) and in Ulleungdo. The SPT and WPT are highest on Jeju Island (Seogwipo; 27.3 and 6.4 °C, respectively) and lowest in the central hilly sections (Daegwallyeong; 20.2 and ?7.9 °C, respectively). The interannual variations in the WPD and WPT are greater than those in SPD and SPT. A significant increasing trend in the WPT was observed for all of the analyzed stations only for the second half of the 100-year period (1959–2008). In the case of the 35-year period, the SPD did not show any clear changes at all stations, but the WPD tended to occur earlier at three stations in the east coastal area. The WPT showed an increasing trend at 55 stations for 35 years, but the SPT showed an increasing trend only in Seogwipo (0.041 °C/year) and even showed a decreasing trend in Mungyeong (?0.049 °C/year). General circulation patterns were indexed and their correlations with the seasonal peaks were investigated. No correlations were found with the SPD. However, the WPD showed a significant positive correlation with the day of the highest Siberian High Intensity (SHI) and the day of the lowest Arctic Oscillation Index (AOI). Furthermore, the SPT showed negative correlations with the intensities of the Okhotsk High and North Pacific High, whereas the WPT showed a negative correlation with SHI and a positive correlation with AOI and with the intensity of the northerly wind that flows into the Korean Peninsula.     

Seasonal evolution mechanism of the East Asian winter monsoon and its interannual variability

This study investigates the space–time evolution of the East Asian winter monsoon (EAWM) and its relationship with other climate subsystems. Cyclostationary Empirical Orthogonal Function (CSEOF) analysis and the multiple regression method are used to delineate the detailed evolution of various atmospheric and surface variables in connection with the EAWM. The 120 days of winter (November 17–March 16) per year over 62 years (1948–2010) are analyzed using the NCEP daily reanalysis dataset. The first CSEOF mode of 850-hPa temperatures depicts the seasonal evolution of the EAWM. The contrast in heat capacity between the continent and the northwestern Pacific results in a differential heating in the lower troposphere. Its temporal evolution drives the strengthening and weakening of the Siberian High and the Aleutian Low. The anomalous sea level pressure pattern dictates anomalous circulation, in compliance with the geostrophic relationship. Thermal advection, in addition to net surface radiation, partly contributes to temperature variations in winter. Latent and sensible heat fluxes (thermal forcing from the ocean to the atmosphere) increase with decreased thermal advection. Anomalous upper-level circulation is closely linked to the low-level temperature anomaly in terms of the thermal wind equation. The interannual variability of the seasonal cycle of the EAWM is strongly controlled by the relative strength of the Siberian High to the Aleutian Low. A stronger than normal gradient between the two pressure systems amplifies the seasonal cycle of the EAWM. The EAWM seasonal cycle in the mid-latitude region exhibits a weak negative correlation with the Arctic Oscillation and the East Atlantic/West Russia indices.     

UVES Abundances of Stars in Nearby Dwarf Spheroidal Galaxies

It is a truth universally acknowledged, that a galaxy in possession of a good quantity of gas must want to form stars. It is the details of how and why that baffle us all. The simplest theories either would have this process a carefully self-regulated affair, or one that goes completely out of control and is capable of wrecking the galaxy which hosts it. Of course the majority of galaxies seem to amble along somewhere between these two extremes, and the mean properties tend to favour a quiescent self-regulated evolutionary scenario. But there area variety of observations which require us to invoke transitory ‘bursts’ of star-formation at one time or another in most galaxy types. Several nearby dwarf spheroidal galaxies have clearly determined star-formation histories with apparent periods of zero star formation followed by periods of fairly active star formation. If we are able to understand what separated these bursts we would understand several important phenomena in galaxy evolution. Were these galaxies able to clear out their gas reservoir in a burst of star formation? How did this gas return? or did it? Have these galaxies receieved gas from the IGM instead? Could stars from these types of galaxy contribute significantly to the halo population in our Galaxy? To answer these questions we need to combine accurate stellar photometry and Colour-Magnitude Diagram interpretation with detailed metal abundances to combine a star-formation rate versus time with a range of element abundances with time. Different elements trace different evolutionary process (e.g., relative contributions of type I and II supernovae). We often aren't even sure of the abundance spread in these galaxies. We have collected detailed high resolution UVES spectra of four nearby dwarf spheroidal galaxies (Sculptor, Fornax, Leo I &; Carina) to begin to answer these questions. This is a precursor study to a more complete study with FLAMES. We presented at this meeting the initial results for the Sculptor and Fornax dwarf spheroidal galaxies which have been previously had single element (low resolution) calcium abundance studies (Tolstoy et al., 2001). See Figures 1 and 2.