Formation of Distinct Granitic Magma Batches by Partial Melting of Hybrid Lower Crust in the Izu Arc Collision Zone, Central Japan

The Miocene Kofu Granitic Complex (KGC) occurs in the Izu CollisionZone where the Izu–Bonin–Mariana (IBM) arc has beencolliding with the Honshu arc since the middle Miocene. TheKGC includes rocks ranging in compositions from biotite-bearinggranite (the Shosenkyo and Mizugaki plutons), and hornblende–biotite-bearinggranodiorite, tonalite, quartz-diorite, and granite (the Shiodaira,Sanpo, Hirose and Sasago plutons), to hornblende-bearing tonaliteand trondhjemite (the Ashigawa–Tonogi pluton), indicatingthat it was constructed from multiple intrusions of magma withdifferent bulk chemistry. The Sr-isotopic compositions correctedto sensitive high-resolution ion microprobe (SHRIMP) zirconages (SrI) suggest that the primary magmas of each pluton wereformed by anatexis of mixed lower crustal sources involvingboth juvenile basalt of the IBM arc and Shimanto sedimentaryrocks of the Honshu arc. After the primary magmas had formed,the individual plutons evolved by crystal fractionation processeswithout significant crustal assimilation or additional mantlecontribution. SHRIMP zircon U–Pb ages in the KGC rangefrom 16·8 to 10·6 Ma and overlap the resumptionof magmatic activity in the IBM and Honshu arcs at c. 17 Maand the onset of IBM arc–Honshu arc collision at c. 15Ma. The age of the granite plutons is closely related to theepisodic activity of arc magmatism and distinct granitic magmabatches could be formed by lower crustal anatexis induced byintrusion of underplated mantle-derived arc magmas. Based onpressures determined with the Al-in-hornblende geobarometer,the KGC magmas intruded into the middle crust. Thus, the KGCcould represent an example of the middle-crust layer indicatedthroughout the IBM arc by 6·0–6·5 km/s seismicvelocities. This granitic middle-crust layer acted buoyantlyduring the IBM arc–Honshu arc collision, leading to accretionof buoyant IBM arc middle crust to the Honshu arc. KEY WORDS: arc–arc collision; crustal anatexis; granite; Izu–Bonin–Mariana (IBM) arc; Izu Collision Zone     

Internal architecture and mobility of tidal sand ridges in the East China Sea

On the basis of bathymetric and seismic data and data from piston cores collected by the Chinese–French marine geology and geophysics investigation of 1996, we discuss the internal architecture and mobility of tidal sand ridges in the East China Sea (ECS). We characterized the sand ridges on the middle to outer shelf of the ECS as tide-dominated sand ridges with southwest dipping beds, indicating that the regional net sediment transport is toward the southwest. As the sand ridges gradually migrate toward the southwest, new sand ridges are continually replacing old ones, and several generations of sand ridges have developed in the study area.     

Long-term high-frequency measurements of dibromomethane in the atmosphere at algae-rich and algae-poor coastal sites

Dibromomethane (CH₂Br₂), a natural stratospheric ozone depleting substance, is mostly emitted from the ocean, but the relative importance of coastal (or macroalgae) and open ocean emissions is unknown. We made long-term high-frequency measurements of CH₂Br₂ concentrations at two remote coastal sites in Japan, on the subtropical Hateruma Island (poor in macroalgae) and at Cape Ochiishi (rich in macroalgae). CH₂Br₂ concentrations at Hateruma showed prominent seasonal variation, being lower in summer (around 0.94 ppt) than in winter (around 1.23 ppt). In contrast, CH₂Br₂ concentrations at Ochiishi were highly variable, often exceeding 2 ppt in the summer but with minimum baseline concentrations close to those from Hateruma; in the winter the concentrations were almost constant at about 1.3 ppt. Analysis of the data suggested that (1) emissions from macroalgae were not likely to extend offshore, but instead were localized near the shore, (2) strong macroalgal emissions of CH₂Br₂ were almost limited to the summer, but it was not reflected in the seasonality of the baseline concentrations of CH₂Br₂ in the atmosphere, and therefore (3) macroalgal or coastal emissions of CH₂Br₂ in the temperate zone might have a rather limited contribution to the global CH₂Br₂ sources. These findings are especially important for the understanding of the tropospheric and stratospheric bromine budget.     

Light utilization efficiency of phytoplankton in the Western Subarctic Gyre of the North Pacific during summer

We investigated the water-column light utilization efficiency (Ψ) of phytoplankton photosynthesis in the Western Subarctic Gyre (WSG) of the North Pacific during summer 2008. The Ψ values (0.64–1.86 g C [g Chl a]^?1 [mol photon]^?1 m²) obtained were observed to increase significantly with decreasing daily photosynthetic available radiation (PAR) and were generally higher than those of previous studies, not only from the subarctic Pacific but also from the world’s oceans. To examine the effect of iron availability on Ψ in the WSG, Ψ values were estimated from the data of two in situ iron fertilization experiments: the Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study I (SEEDS-I) and II (SEEDS-II). We found that iron availability did not affect Ψ values. Overall, this study revealed that Ψ values changed remarkably in the WSG during the summer, and that higher values were found at the stations where moderate PAR levels (ca. 10–30 mol photons m^?2 day^?1) were observed and where autotrophic flagellates predominated in the phytoplankton assemblages.     

An overview of decadal climate predictability in a multi-model ensemble by climate model MIROC

Decadal climate predictability is examined in hindcast experiments by a multi-model ensemble using three versions of the coupled atmosphere-ocean model MIROC. In these hindcast experiments, initial conditions are obtained from an anomaly assimilation procedure using the observed oceanic temperature and salinity with prescribed natural and anthropogenic forcings on the basis of the historical data and future emission scenarios in the Intergovernmental Panel of Climate Change. Results of the multi-model ensemble in our hindcast experiments show that predictability of surface air temperature (SAT) anomalies on decadal timescales mostly originates from externally forced variability. Although the predictable component of internally generated variability has considerably smaller SAT variance than that of externally forced variability, ocean subsurface temperature variability has predictive skills over almost a decade, particularly in the North Pacific and the North Atlantic where dominant signals associated with Pacific decadal oscillation (PDO) and the Atlantic multidecadal oscillation (AMO) are observed. Initialization enhances the predictive skills of AMO and PDO indices and slightly improves those of global mean temperature anomalies. Improvement of these predictive skills in the multi-model ensemble is higher than that in a single-model ensemble.     

Clashing strategic cultures and climate policy

Abstract

Kagan (2002) argues that the different responses of Europeans and Americans to major strategic and international challenges is not simply due to differences in the current administrations, but rather results from (i) a power gap and (ii) differing ideologies. This article applies Kagan's theory to climate policy, employing terrorism policy as a point of comparison. We argue that the power gap between Europe and America is unable to explain the differences in climate policy. In contrast, the ideology gap may indeed have some explanatory value. Furthermore, we argue that one additional feature is critical—the costs and benefits imposed by climate change and terrorism prevention, and the process by which such costs and benefits are evaluated, differ between America and Europe.     

Assessing land-use and carbon stock in slash-and-burn ecosystems in tropical mountain of Laos based on time-series satellite images

In the tropical mountains of Southeast Asia, slash-and-burn (S/B) agriculture is a widely practiced and important food production system. The ecosystem carbon stock in this land-use is linked not only to the carbon exchange with the atmosphere but also with food and resource security. The objective of this study was to provide quantitative information on the land-use and ecosystem carbon stock in the region as well as to infer the impacts of alternative land-use and ecosystem management scenarios on the carbon sequestration potential at a regional scale. The study area was selected in a typical slash-and-burn region in the northern part of Laos. The chrono-sequential changes of land-use such as the relative areas of community age and cropping (C) + fallow (F) patterns were derived from the analysis of time-series satellite images. The chrono-sequential analysis showed that a consistent increase of S/B area during the past three decades and a rapid increase after 1990. Approximately 37% of the whole area was with the community age of 1–5 years, whereas 10% for 6–10 years in 2004. The ecosystem carbon stock at a regional scale was estimated by synthesizing the land-use patterns and semi-empirical carbon stock model derived from in situ measurements where the community age was used as a clue to the linkage. The ecosystem carbon stock in the region was strongly affected by the land-use patterns; the temporal average of carbon stock in 1C + 10F cycles, for example, was greater by 33 MgC ha⁻¹ compared to that in 1C + 2F land-use pattern. The amount of carbon lost from the regional ecosystems during 1990–2004 periods was estimated to be 42 MgC ha⁻¹. The study approach proved to be useful especially in such regions with low data-availability and accessibility. This study revealed the dynamic change of land-use and ecosystem carbon stock in the tropical mountain of Laos as affected by land-use. Results suggest the significant potential of carbon sequestration through changing land-use and ecosystem management scenarios. These quantitative estimates would be useful to better understand and manage the land-use and ecosystem carbon stock towards higher sustainability and food security in similar ecosystems.     

Palynological evidence for late Holocene environmental change on the Gimhae fluvial plain,Southern Korean peninsula: Reconstructing the rise and fall of Golden Crown Gaya State

This paper presents the results of detailed studies of palynomorphs recovered from two cores collected near the Yeanri burial mound on the Gimhae fluvial plain. Two local pollen zones were recognized on the basis of variations in the palynofloral assemblage: a lower Pollen Zone I, dominated by a Pinus‐Quercus assemblage, and an upper Pollen Zone II, dominated by a Pinus‐Quercus‐Gramineae assemblage. The palynological and molluscan analyses indicate that the depositional environments changed from a lower intertidal flat of a shallow bay environment to an upper intertidal flat in a shallow bay (before 1280 ± 110 ¹⁴C yr B.P.), and finally to a fluvial plain similar to that of today. This environmental change may have resulted from uplift along the Yangsan Fault. Afterward, the exposed area was modified by human activities, as indicated by a sudden increase in grassland herbaceous pollen grains. The loss of this bay likely had a dramatic effect on the Golden Crown Gaya State (3rd–7th centuries A.D.), which used it as a major port for regional trade, and may explain why it eventually merged with the Shilla State. © 2003 Wiley Periodicals, Inc.