Core-based reconstruction of paleoenvironmental conditions in the southern Drake Passage (West Antarctica) over the last 150 ka

A deep-sea sediment core (GC98-06) from the southernmost Drake Passage, West Antarctica, shows late Quaternary depositional environments distinctly different from sedimentary drifts commonly found along the southwestern Pacific margin of the Drake Passage. The chronology of the core has been inferred using geochemical tracers of paleoproductivity and diatom biostratigraphy, and represents the paleoceanographic conditions in a continental rise setting during the last 150,000 years. Three dominant sediment types associated with distinct sedimentary processes have been identified using textural/compositional analyses: (1) hemipelagic mud (interglacial sediments) deposited from pelagic settling of bioclasts, meltwater plumes, and ice-rafted detritus; (2) terrigenous mud (glacial sediments) delivered by turbid meltwater plumes; and (3) massive muds marking the boundaries from interglacial to glacial periods. The succession of the sedimentary facies in core GC98-06 is interpreted to reflect temporal changes in environmental conditions prevailing on the continental rise of the southern Drake Passage in the course of successive climatic stages over the last 150 ka: from the bottom upward, these are glacial, interglacial, glaciation, glacial, and interglacial episodes. Variability in sediment flux and diatom abundance seem to have been related to changes in glacial advance, sea-ice extent, and specific sedimentary environments, collectively influenced by mid- to late Quaternary climatic changes.     

Climate forcings and climate sensitivities diagnosed from atmospheric global circulation models

Understanding the historical and future response of the global climate system to anthropogenic emissions of radiatively active atmospheric constituents has become a timely and compelling concern. At present, however, there are uncertainties in: the total radiative forcing associated with changes in the chemical composition of the atmosphere; the effective forcing applied to the climate system resulting from a (temporary) reduction via ocean-heat uptake; and the strength of the climate feedbacks that subsequently modify this forcing. Here a set of analyses derived from atmospheric general circulation model simulations are used to estimate the effective and total radiative forcing of the observed climate system due to anthropogenic emissions over the last 50 years of the twentieth century. They are also used to estimate the sensitivity of the observed climate system to these emissions, as well as the expected change in global surface temperatures once the climate system returns to radiative equilibrium. Results indicate that estimates of the effective radiative forcing and total radiative forcing associated with historical anthropogenic emissions differ across models. In addition estimates of the historical sensitivity of the climate to these emissions differ across models. However, results suggest that the variations in climate sensitivity and total climate forcing are not independent, and that the two vary inversely with respect to one another. As such, expected equilibrium temperature changes, which are given by the product of the total radiative forcing and the climate sensitivity, are relatively constant between models, particularly in comparison to results in which the total radiative forcing is assumed constant. Implications of these results for projected future climate forcings and subsequent responses are also discussed.     

Regional-scale relationships between aerosol and summer monsoon circulation, and precipitation over northeast Asia

We investigated the regional-scale relationships between columnar aerosol loads and summer monsoon circulation, and also the precipitation over northeast Asia using aerosol optical depth (AOD) data obtained from the 8-year MODIS, AERONET Sun/sky radiometer, and precipitation data acquired under the Global Precipitation Climatology Project (GPCP). These high-quality data revealed the regional-scale link between AOD and summer monsoon circulation, precipitation in July over northeast Asian countries, and their distinct spatial and annual variabilities. Compared to the mean AOD for the entire period of 2001–2008, the increase of almost 40–50% in the AOD value in July 2005 and July 2007 was found over the downwind regions of China (Yellow Sea, Korean peninsula, and East Sea), with negative precipitation anomalies. This can be attributable to the strong westerly confluent flows, between cyclone flows by continental thermal low centered over the northern China and anticyclonic flows by the western North Pacific High, which transport anthropogenic pollution aerosols emitted from east China to aforementioned downwind high AOD regions along the rim of the Pacific marine airmass. In July 2002, however, the easterly flows transported anthropogenic aerosols from east China to the southwestern part of China in July 2002. As a result, the AOD off the coast of China was dramatically reduced in spite of decreasing rainfall. From the calculation of the cross-correlation coefficient between MODIS-derived AOD anomalies and GPCP precipitation anomalies in July over the period 2001–2008, we found negative correlations over the areas encompassed by 105–115°E and 30–35°N and by 120–140°E and 35–40°N (Yellow Sea, Korean peninsula, and East Sea). This suggests that aerosol loads over these regions are easily influenced by the Asian monsoon flow system and associated precipitation.     

Rainfall frequency analysis using a mixed GEV distribution: a case study for annual maximum rainfalls in South Korea

Extreme rainfalls in South Korea result mainly from convective storms and typhoon storms during the summer. A proper way for dealing with the extreme rainfalls in hydrologic design is to consider the statistical characteristics of the annual maximum rainfall from two different storms when determining design rainfalls. Therefore, this study introduced a mixed generalized extreme value (GEV) distribution to estimate the rainfall quantile for 57 gauge stations across South Korea and compared the rainfall quantiles with those from conventional rainfall frequency analysis using a single GEV distribution. Overall, these results show that the mixed GEV distribution allows probability behavior to be taken into account during rainfall frequency analysis through the process of parameter estimation. The resulting rainfall quantile estimates were found to be significantly smaller than those determined using a single GEV distribution. The difference of rainfall quantiles was found to be closely correlated with the occurrence probability of typhoon and the distribution parameters.     

Water quality assessment at Jinhae Bay and Gwangyang Bay,South Korea

A new water quality index for evaluating the water quality of Jinhae Bay and Gwangyang Bay was developed. Four water quality parameters were selected as water quality indicators for the water quality index: dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), chlorophyll-a (Chl-a), and dissolved oxygen (DO). Reference levels of DIN, DIP, and Chl-a were determined as 6.22 μmol L^?1, 0.38 μmol L^?1, and 2.32 μmol L^?1, respectively, on the basis of a long-term dataset that was collected monthly in the Korea Strait over a period of seven years (2006–2012). The water quality index established for Jinhae Bay and Gwangyang Bay is (bottom DO grade × 0.33) + (surface Chl-a grade × 0.33) + (surface DIN grade × 0.17) + (surface DIP grade × 0.17). On the basis of a three-year observation, the water quality of Jinhae Bay was classified as “good” in winter and spring, “poor” in summer, and “fair” in autumn and exhibited large spatial variation, with the lowest-quality water observed in Masan Bay. The water quality of Gwangyang Bay was classified as “good” in winter, “fair” in spring, “poor” in summer, and “fair” in autumn. Unlike Jinhae Bay, the water quality of Gwangyang Bay exhibited minimal spatial variation. In both bays, water quality among the four seasons was worse during summer. It is essential that a survey for water quality evaluation be conducted during summer.     

Environmental determinism and geomancy: Two cultures,two concepts

Geomancy and environmental determinism, respectively Eastern and Western concepts which accord “nature” a primary role in shaping human life, show striking similarities and differences. Both incorporate viewpoints on environmental qualities, the dichotomy of man and nature, the application of ideas and the discipline of geography. The differences between these concepts are due largely to differing perspectives on the linkages and characteristics between man and nature.     

Adsorption of organic matter at mineral/water interfaces: I. ATR-FTIR spectroscopic and quantum chemical study of oxalate adsorbed at boehmite/water and corundum/water interfaces

The types and structures of adsorption complexes formed by oxalate at boehmite (γ-AlOOH)/water and corundum (α-Al₂O₃)/water interfaces were determined using in situ attenuated total reflectance fourier transform infrared (ATR-FTIR) spectroscopy and quantum chemical simulation methods. At pH 5.1, at least four different oxalate species were found at or near the boehmite/water interface for oxalate surface coverages (Γ_ox) ranging from 0.25 to 16.44 μmol/m². At relatively low coverages (Γ_ox < 2.47), strongly adsorbed inner-sphere oxalate species (IR peaks at 1286, 1418, 1700, and 1720 cm⁻¹) replace weakly adsorbed carbonate species, and a small proportion of oxalate anions are adsorbed in an outer-sphere mode (IR peaks at 1314 and 1591 cm⁻¹). IR peaks indicative of inner-sphere adsorbed oxalate are also observed for oxalate at the corundum/water interface at Γ_ox = 1.4 μmol/m². With increasing oxalate concentration (Γ_ox > 2.47 μmol/m²), the boehmite surface binding sites for inner-sphere adsorbed oxalate become saturated, and excess oxalate ions are present dominantly as aqueous species (IR peaks at 1309 and 1571 cm⁻¹). In addition to these adsorption processes, oxalate-promoted dissolution of boehmite following inner-sphere oxalate adsorption becomes increasingly pronounced with increasing Γ_ox and results in an aqueous Al(III)-oxalate species, as indicated by shifted IR peaks (1286 → 1297 cm⁻¹ and 1418 → 1408 cm⁻¹). At pH 2.5, no outer-sphere adsorbed oxalate or aqueous oxalate species were observed. The similarity of adsorbed oxalate spectral features at pH 2.5 and 5.1 implies that the adsorption mechanism of aqueous HOx⁻ species involves loss of protons from this species during the ligand-exchange reaction. As a consequence, adsorbed inner-sphere oxalate and aqueous Al(III)-oxalate complexes formed at pH 2.5 have coordination geometries very similar to those formed at pH 5.1.The coordination geometry of inner-sphere adsorbed oxalate species was also predicted using quantum chemical geometry optimization and IR vibrational frequency calculations. Geometry-optimized Al₈O₁₂ and Al₁₄O₂₂ clusters with the reactive surface Al site coordinated by three oxygens were used as model substrates for corundum and boehmite surfaces. Among the models considered, calculated IR frequencies based on a bidentate side-on structure with a 5-membered ring agree best with the observed frequencies for boehmite/oxalate/water samples at Γ_ox = 0.25 to 16.44 μmol/m² and pH 2.5 and 5.1, and for a corundum/oxalate/water sample at Γ_ox = 1.4 μmol/m² and pH 5.1. Based on these results, we suggest that oxalate bonding on boehmite and corundum surfaces results in 5-coordinated rather than 4- or 6-coordinated Al surface sites.     

Assessment of acoustic iterative inverse method for bubble sizing to experimental data

Comparative study was carried out for an acoustic iterative inverse method to estimate bubble size distributions in water. Conventional bubble sizing methods consider only sound attenuation for sizing. Choi and Yoon [IEEE, 26(1), 125–130 (2001)] reported an acoustic iterative inverse method, which extracts the sound speed component from the measured sound attenuation. It can more accurately estimate the bubble size distributions in water than do the conventional methods. The estimation results of acoustic iterative inverse method were compared with other experimental data. The experimental data show good agreement with the estimation from the acoustic iterative inverse method. This iterative technique can be utilized for bubble sizing in the ocean.     

Alkaline phosphatase activity and phosphatase hydrolyzable phosphorus for phytoplankton in hiroshima bay, Japan

We investigated the seasonal variability of free alkaline phosphatase activity in seawater and alkaline phosphatase hydrolysable phosphorus (APHP) at 3 stations in Hiroshima Bay using alkaline phosphatase extracted from the dinoflagellates Alexandrium tamarense and Gymnodinium catenatum. The dissolved inorganic phosphorus (DIP) was lower than 1 μM in all samples; the lowest values were in May. The amount of APHP was high at the surface and bottom waters of all stations in May, showing DIP-depleted conditions. In August and November, the amount of APHP was much less than the amount of APHP in May, indicating that the availability of dissolved organic phosphorus (DOP) for these species was low and/or uptake during the dinoflagellate blooming might have occurred in the area. The results obtained from short-term variations of AP activity might suggest that the growth of dinoflagellates in this season may be partly supported by the AP produced by other diatoms.