Seasonal and interannual variability of oceanic carbon cycling in the western and central tropical-subtropical pacific: A physical-biogeochemical modeling study

The oceanic carbon cycle in the tropical-subtropical Pacific is strongly affected by various physical processes with different temporal and spatial scales, yet the mechanisms that regulate air-sea CO₂ flux are not fully understood due to the paucity of both measurement and modeling. Using a 3-D physical-biogeochemical model, we simulate the partial pressure of CO₂ in surface water (pCO_2sea) and air-sea CO₂ flux in the tropical and subtropical regions from 1990 to 2004. The model reproduces well the observed spatial differences in physical and biogeochemical processes, such as: (1) relatively higher sea surface temperature (SST), and lower dissolved inorganic carbon (DIC) and pCO_2sea in the western than in the central tropical-subtropical Pacific, and (2) predominantly seasonal and interannual variations in the subtropical and tropical Pacific, respectively. Our model results suggest a non-negligible contribution of the wind variability to that of the air-sea CO₂ flux in the central tropical Pacific, but the modeled contribution of 7% is much less than that from a previous modeling study (30%; McKinley et al., 2004). While DIC increases in the entire region SST increases in the subtropical and western tropical Pacific but decreases in the central tropical Pacific from 1990 to 2004. As a result, the interannual pCO_2sea variability is different in different regions. The pCO_2sea temporal variation is found to be primarily controlled by SST and DIC, although the role of salinity and total alkalinity, both of which also control pCO_2sea, need to be elucidated by long-term observations and eddy-permitting models for better estimation of the interannual variability of air-sea CO₂ flux.     

Uptake mechanism of anthropogenic CO<Subscript>2</Subscript> in the Kuroshio Extension region in an ocean general circulation model

The uptake mechanism of anthropogenic CO₂ in the Kuroshio Extension is examined by a Lagrangian approach using a biogeochemical model embedded in an ocean general circulation model. It is found that the uptake of anthropogenic CO₂ is caused mainly by the increase of pCO₂ dependency of seawater on temperature, which is caused by greater dissolved inorganic carbon concentration in the modern state than in the pre-industrial state. In contrast with the view of previous studies, the effect of the vertical entrainment, which brings waters that last contacted the atmosphere with the past lower CO₂ concentration, is comparatively small. Winter uptake of anthropogenic CO₂ increases with the rise of the atmospheric CO₂ level, while summer uptake is relatively stable, resulting in a larger seasonal cycle of the uptake. This increase is significant, especially in the Kuroshio Extension region. It is newly suggested that this increase in the Kuroshio Extension region is largely caused by the combined effects of the increased pCO₂ dependency of the sea water on the temperature and the seasonal difference in cooling.     

Bedrock structure in Adapazari, Turkey—a possible cause of severe damage by the 1999 Kociaeli earthquake

The 1999 Kocaeli earthquake brought serious damage to downtown of Adapazari. To study why strong motions were generated at the town, a bedrock structure was investigated on the basis of Bouguer gravity anomaly, and SPAC and H/V analyses of microseisms. It was revealed that, the basin consists of three narrow depressions of bedrock with very steep edges, extending in E–W or NE–SW directions along the North Anatolia faults, and the depth to bedrock reaches 1000 m or more. Downtown of Adapazari is located 1–2 km apart from the basin-edge. It is considered that, the specific configuration of bedrock amplifies ground motions at the downtown area by focusing of seismic waves and/or interference between incident S-waves and surface-waves secondarily generated at the basin-edge. Studying 3D bedrock structure is an urgent issue for microzoning an urban area in a sedimentary basin.     

Projected climate change scenario over California by a regional ocean–atmosphere coupled model system

This study examines a future climate change scenario over California in a 10-km coupled regional downscaling system of the Regional Spectral Model for the atmosphere and the Regional Ocean Modeling System for the ocean forced by the global Community Climate System Model version 3.0 (CCSM3). In summer, the coupled and uncoupled downscaled experiments capture the warming trend of surface air temperature, consistent with the driving CCSM3 forcing. However, the surface warming change along the California coast is weaker in the coupled downscaled experiment than it is in the uncoupled downscaling. Atmospheric cooling due to upwelling along the coast commonly appears in both the present and future climates, but the effect of upwelling is not fully compensated for by the projected large-scale warming in the coupled downscaling experiment. The projected change of extreme warm events is quite different between the coupled and uncoupled downscaling experiments, with the former projecting a more moderate change. The projected future change in precipitation is not significantly different between coupled and uncoupled downscaling. Both the coupled and uncoupled downscaling integrations predict increased onshore sea breeze change in summer daytime and reduced offshore land breeze change in summer nighttime along the coast from the Bay area to Point Conception. Compared to the simulation of present climate, the coupled and uncoupled downscaling experiments predict 17.5 % and 27.5 % fewer Catalina eddy hours in future climate respectively.     

2500年来艾比湖的环境演变信息

通过对艾比湖缘1，8m浅孔的沉积相和孢粉组合，结合14C测年资料分析。指出近2500年来艾比湖的沉积环境总体是比较稳定的，但由于气候波动引起艾比湖水位曾发生较明显的变化。约在公元前300～400年，是艾比湖面积缩小时期；约公元前300—公元300年，即东周末至西晋，是艾比湖水位较高时期；约公元300—1400年，即东晋至15世纪初，是艾比湖的高水位时期；约15世纪初至17世纪中是艾比湖的水位下降期，但水位比现代仍然高；约17世纪中至19世纪初的小冰期是艾比湖的水位上升期。研究还提供了历史时期湖泊的盐度变化和湖周发生大火的信息。     

Hydrographic structure in association with deep boundary current in the north of the Shikoku Basin

High quality CTD data were collected in the north of the Shikoku Basin where an abyssal boundary current has been observed through direct current measurements. Analyses of hydrographic data showed:

1. Colder and saltier water (heavier water) compared to surrounding waters is found above the continental shelf-toe and the eastern flank of the Kyushu-Palau Ridge where the existence of the abyssal boundary current has been expected. The heavier water has a horizontal extent of about 50 km.
2. The heavier water has the vertical scale of 2000 m from the sea bottom, and is associated with a thermal wind shear which enhances a component of the flow toward a direction looking the Nankai Trough (a trough located along the northern end of the Shikoku Basin) to the left in the abyss. The assumed “level of no motion” at about 2500 m depth gives the geostrophically estimated current in a good agreement with the directly measured current.

A volume transport associated with the colder and higher salinity water is estimated to be about 2 Sv off Cape Shiono-misaki which may include a recirculation above the Nankai Trough. This is about twice of the transport estimated in the interior of the Shikoku Basin through a vorticity balance between the stretching term and latitudinal variation of the planetary vorticity.     

Phase diagrams describing solid-gas equilibria in the system Fe-Mg-Si-O-C-H,and its bearing on redox states of chondrites

Abstract— Phase diagrams describing solid-gas equilibria in the system Fe-Mg-Si-O-C-H under H-rich conditions (～700–2000 K and 10^?2–10^?20 atm of Ph ₂), including solar nebula conditions, were constructed based on thermochemical calculations. Boundaries of vaporous phases, which are the first phases to condense from a gas, can be obtained without calculating condensation temperatures of individual gas compositions because the numbers of major gaseous species are the same as those of components in the concerned systems. Fractionations by condensation and/or evaporation can be discussed easily in such phase diagrams. A thermal divide, which is a barrier that vapors cannot cross by a single cooling process, was recognized in the phase diagrams. This is present on the Fe-MgO-SiO₂-CO-H plane at high temperatures (≥500–700 K) and plays an important role in fractionations. Oxidizing states of ordinary chondrites and carbonaceous chondrites before aqueous alteration are located at the O-rich side of the thermal divide. Such oxidizing states can be formed from the solar gas by fractionation in the primordial solar nebula because the solar composition is located on the O-rich side. On the other hand, the reducing states of enstatite chondrites, located at the O-poor side, cannot be formed as long as the thermal divide is present. The reducing states can be obtained by CO to CH₄ molecular reaction at low temperatures (≤500–700 K), where the high-temperature thermal divide is absent. Addition of H₂O-rich and CH₄-rich ice can explain establishment of the redox states of ordinary and enstatite chondrites, respectively.     

A Preliminary Study of Oceanic Bomb Radiocarbon Inventory in the North Pacific during the Last Two Decades

Radiocarbon and total carbonate data were obtained near the 1973 GEOSECS stations in the North Pacific along 30°N and along 175°E between 1993 and 1994. In these stations, we estimated radiocarbon originating from atomic bomb tests using tritium, trichlorofluoromethane and silicate contents. The average penetration depth of bomb radiocarbon during the two decades has deepened from 900 m to 1300 m. Bomb radiocarbon inventories above the average value for the whole North Pacific were found widely in the western subtropical region around 30°N both in the 1970s and 1990s, and its area in the 1990s was broader than that in the 1970s. In most of the North Pacific, while the bomb radiocarbon has decreased above 25.4, the bomb radiocarbon flux below 25.4 was over 1 × 10¹² atom m^-2yr^-1 in the subtropical region around 30°N. In the tropical area south of 20°N, the bomb radiocarbon inventory below 25.4 increased from zero to over 10 × 10¹² atom m^-2 during the last three decades. These distributions suggest that the bomb radiocarbon removed from the surface is currently accumulated with bomb ¹⁴C flux of over 1 × 10¹² atom m^-2yr^-1 below 25.4 in the subtropical region, mainly by advection from the higher latitude, and that part of the accumulated bomb ¹⁴C gradually spread southward with about 30 years.     

Experimental study on the bidirectional inelastic deformation capacity of U‐shaped steel dampers for seismic isolated buildings

Hysteretic dampers are used to dissipate earthquake‐induced energy in base‐isolated structures by acquiring inelastic deformations, rendering their hysteretic behavior of vital importance. The present paper focuses on investigating the behavior of U‐shaped steel dampers under bidirectional loading; this is significantly different from their corresponding uniaxial behavior. Two main sets of loading tests on full‐scale specimens are conducted in this regard: (i) quasi‐static tests with simple histories and (ii) dynamic tests with realistic loading histories. Based on the results obtained in the quasi‐static tests, an interaction curve that accounts for the reduction of the cyclic deformation capacity is proposed. However, the fidelity of this relation must be assessed under loading conditions similar to those of a seismically isolated structure subjected to an earthquake, which represents the goal of the second set of tests. The results of the dynamic tests validate the proposed interaction curve for estimating the deformation capacity of U‐shaped steel dampers under bidirectional loading. Copyright © 2015 John Wiley & Sons, Ltd.