The role of rare rainstorms in the formation of calcic soil horizons on alluvial surfaces in extreme deserts     

Rivka Amit  Yehouda Enzel  Naomi Porat 《Quaternary Research》2010,74(2):177-187

Soils in similar geomorphic settings in hyperarid deserts (< 50 mm yr⁻¹) should have similar characteristics because a negative moisture balance controls their development. However, Reg soils in the hyperarid southern Negev and Namib deserts are distinctly different. Soils developed on stable alluvial surfaces with only direct input of rainfall and dust depend heavily on rainfall characteristics. Annual rainfall amount can be similar (15-30 mm), but storm duration can drastically alter Reg soil properties in deserts. The cooler fall/winter and dry hot summers of the southern Negev Desert with a predominance brief (≤ 1 day) rainstorms result in gypsic-saline soils without any calcic soil horizon. Although the Namib Desert receives only 50-60% of the southern Negev annual rainfall, its rainstorm duration is commonly 2-4 days. This improves leaching of the top soil under even lower annual rainfall amount and results in weeks-long grass cover. The long-term cumulative effect of these rare rain-grass relationships produces a calcic-gypsic-saline soil. The development of these different kinds of desert soils highlights the importance of daily to seasonal rainfall characteristics in influencing soil-moisture regime in deserts, and has important implications for the use of key desert soil properties as proxies in paleoclimatology.  相似文献   

Climate change mitigation: trade-offs between delay and strength of action required     

Naomi E. Vaughan  Timothy M. Lenton  John G. Shepherd 《Climatic change》2009,96(1-2):29-43

Climate change mitigation via a reduction in the anthropogenic emissions of carbon dioxide (CO₂) is the principle requirement for reducing global warming, its impacts, and the degree of adaptation required. We present a simple conceptual model of anthropogenic CO₂ emissions to highlight the trade off between delay in commencing mitigation, and the strength of mitigation then required to meet specific atmospheric CO₂ stabilization targets. We calculate the effects of alternative emission profiles on atmospheric CO₂ and global temperature change over a millennial timescale using a simple coupled carbon cycle-climate model. For example, if it takes 50 years to transform the energy sector and the maximum rate at which emissions can be reduced is ?2.5% $\text{year}^{-1}$ , delaying action until 2020 would lead to stabilization at 540 ppm. A further 20 year delay would result in a stabilization level of 730 ppm, and a delay until 2060 would mean stabilising at over 1,000 ppm. If stabilization targets are met through delayed action, combined with strong rates of mitigation, the emissions profiles result in transient peaks of atmospheric CO₂ (and potentially temperature) that exceed the stabilization targets. Stabilization at 450 ppm requires maximum mitigation rates of ?3% to ?5% $\text{year}^{-1}$ , and when delay exceeds 2020, transient peaks in excess of 550 ppm occur. Consequently tipping points for certain Earth system components may be transgressed. Avoiding dangerous climate change is more easily achievable if global mitigation action commences as soon as possible. Starting mitigation earlier is also more effective than acting more aggressively once mitigation has begun.  相似文献   

Removal of trace metals from seawater during a phytoplankton bloom as studied with sediment traps in Funka Bay,Japan     

S Noriki  N Ishimori  K Harada  S Tsunogai 《Marine Chemistry》1985,17(1):75-89

To study biological effects on the particulate removal of chemical elements from seawater, sediment trap experiments were carried out successively ten times throughout the spring phytoplankton bloom in Funka Bay. Sediment traps were deployed every one to two weeks at 1, 40 and 80 m depths. The settling particles obtained were analyzed for trace metals, phosphate and silicate. The propagation of diatoms in spring results in larger particulate fluxes than that of dinoflagellates. The biogenic silicate concentration is higher in the earlier period, when diatoms are predominant, than in the subsequent period, when dinoflagellates are predominant. The concentrations of aluminum, iron, manganese and cobalt in the settling particles comprising largely biogenic particles are lower during phytoplankton bloom. The concentration of copper is not reduced by the addition of biogenic particles, and its vertical flux is approximately proportional to the total flux, indicating that its concentration in the biogenic particles is nearly equal to that in the non-biogenic particles. The results for nickel and lead show the same tendency as for copper. Cadmium is more concentrated in biogenic particles than in non-biogenic particles, and the concentration of cadmium in the settling particles decreases with depth, similarly to phosphate and organic matter. Thus, metals in seawater are segregated by biological affinities, and the degree of incorporation into biogenic particles is in the order Cd > Pb, Ni, Cu > Co > Mn, Fe, Al. Biogenic particles are the most important agent controlling the vertical distribution of metals in the ocean. They remove the metals from the surface water, transport them through the water column, and regenerate them in the deep.  相似文献   

Different partitioning among thorium isotopes in seawater of the Northern North pacific     

Shizuo Tsunogai  Mitsuhiro Kawasaki  Koh Harada 《Journal of Oceanography》1994,50(2):197-207

Each about 400 l of seawater sample was collected in the northern North Pacific and filtered through a membrane filter. Four radioisotopes of thorium,²³²Th,²³⁰Th,²²⁸Th and²³⁴Th, were determined for the two FractionsF (filtrate) andP (particles on the filter). In the percentages of FractionP in the subsurface water,²³⁰Th was significantly larger than other 3 isotopes, and²³²Th was significantly smaller than other 3 isotopes. The former finding can be explained by the slower rates in the reversible change between the FractionsF andP. The latter one, however, cannot be explained if thorium isotopes in the FractionF are truly dissolved with the same chemical form. This suggests that major part of the FractionF of²³²Th is not identical with those of other radiogenic thorium isotopes, and it should not be composed of simple dissolved ions. The removal of radiogenic²³⁴Th was related to the biological activity, but there was a deviation, between the FractionP and radioactivity deficiency of²³⁴Th in their vertical profiles. The deviation was similar to that between the chlorophylla and phaeo-pigments contents including their maximum depths.  相似文献   

A practical method for the simultaneous determination of234Th,226Ra,210Pb and210Po in seawater     

Koh Harada  Shizuo Tsunogai 《Journal of Oceanography》1985,41(2):98-104

A practical method has been developed for the simultaneous determination of²²⁶Ra,²³⁴Th,²¹⁰Pb and²¹⁰Po in seawater. In the method, the samples are spiked with²²⁸Ra,²³⁰Th,²⁰⁸Po and common lead to determine chemical yield. These nuclides are coprecipitated with calcium carbonate and ferric hydroxide from 20 to 50 l of seawater and separated from one another by using coprecipitation and ion exchange techniques. Counting sources of Ra and the other nuclides are prepared by electrodeposition onto silver discs. Their radioactivities are counted with an-spectrometer and a low background-counter. This method gives a standard deviation of about 5% for replicate determination of²²⁶Ra and the other nuclides.  相似文献   

Development of new drain method for protection of existing pile foundations from liquefaction effects   总被引：1，自引：0，他引：1  

Naoyuki Harada  Ikuo Towhata  Tadashi Takatsu  Shinsuke Tsunoda  Vlatko Sesov 《Soil Dynamics and Earthquake Engineering》2006,26(2-4):297-312

Pile foundation as well as other underground structures could be seriously affected by soil liquefaction during strong earthquakes. Damages on pile foundation due to liquefaction can be reduced by implementation of some soil improvement method. Main objective of present study is developing of drain method that can improve the soil in order to mitigate the destructiveness of liquefaction on superstructure supported by pile foundation. Series of shaking table tests were conducted on 2×2 pile foundation and soil model was improved by drains. Configurations of drains around piles, intensity of shaking were one of the parameters that were changing during the tests in order to investigate the response of pile foundation in improved soil condition.Shaking table tests and performed On-site experiment showed the following effects of the new drain method. (1) When the intensity of earthquake motion is 200 gal or less, generation of excess pore water pressure is reduced and the pile bending moment is decreased, (2) when the intensity of earthquake motion is stronger (300 gal or more), drainage effect prevents disappearance of subgrade reaction, and (3) proposed new type of drain can control excess pore water pressure without clogging.  相似文献   

Characteristics of alkenones synthesized by a bloom of emiliania huxleyi in the Bering Sea     

Naomi Harada  Kyung Hoon Shin  Masao Uchida 《Geochimica et cosmochimica acta》2003,67(8):1507-1519

We investigated the characteristics of the alkenones produced by a bloom of Emiliania huxleyi in the eastern Bering Sea in 2000. Alkenones were detected in surface waters between 57°N and 63°N, where phosphate concentrations were low and the ammonium/nitrate ratio was high. The total alkenone content (C_37:2, C_37:3, and C_37:4) ranged from 22.0 to 349 μg g⁻¹ in suspended particles and from 0.109 to 1.42 μg g⁻¹ in surface sediments. This suggests that a large proportion of the particulate alkenones synthesized in the surface water rapidly degraded within the water column and/or at the water-sediment interface of the Bering Shelf. The change in the stable carbon isotopic composition (δ¹³C) of C_37:3 alkenone could not be explained only by variation in [CO₂(aq)] in the surface water but also depended on the growth rate of E. huxleyi. The alkenone unsaturation index (U^K′₃₇) was converted into an alkenone “temperature” with three equations [Prahl et al 1988], [Sikes et al 1997] and [Müller et al 1998]; Sikes et al.’s (1997) equation gave the best correlation with the observed sea surface temperature (SST) in the eastern Bering Sea. However, some temperatures estimated by Sikes et al.’s (1997) equation from the U^K′₃₇ varied from the observed SST, possibly because of the rapidly changing rate of alkenone synthesis in the logarithmic growth stage or the low rate of alkenone synthesis when nutrients were limiting. Temperatures estimated from U^K′₃₇ in the surface sediments (6.8-8.2°C) matched the observed SST in September (7-8°C) but differed from the annual average SST of 4 to 5°C, suggesting that most of the alkenone in the eastern Bering Sea was synthesized during limited periods, for instance, in September. The relative amounts of C_37:4 alkenone as proportions of the total alkenones (referred to as C_37:4%) were high, ranging from 18.3 to 41.4%. Low-salinity water (<32 psu) within the study area would have contributed to the high C_37:4% because a negative linear relationship between C_37:4% and salinity was found in this study.  相似文献   

Ba, Si, U, Al, Sc, La, Th, C and C/C in a sediment core in the western subarctic Pacific as proxies of past biological production     

Masahito Shigemitsu  Hisashi Narita  Yutaka W. Watanabe  Naomi Harada  Shizuo Tsunogai 《Marine Chemistry》2007,106(3-4):442-455

A sediment core covering the last 145 kyrs was collected in the western subarctic Pacific (WSAP), and analyzed for Ba, U, Al, Sc, La, Yb, Th, biogenic opal (Opal) and organic carbon (C_org) as well as its isotopic ratio (δ¹³C). This study examined the change of past biological production in WSAP with multiple proxies, together with understanding the relation between Loess from the Asian continent and the biological production. The Loess content was estimated from the metal components, Al, Sc, La, Yb and Th. In this high latitude core (50°N), the Loess content was generally high during the glacial periods, but it was also high even in some interglacial periods. The excess amount of Ba relative to the detrital material composition, Ba_ex, showed the best correlation with the Vostok δD (r = 0.72, p < 0.001), indicating that the biological production was lower in the glacial periods than in the interglacials. This corroborates the pervasive correlation between Ba_ex in the polar region, WSAP and the Antarctic Sea, and Antarctic temperature, combined with previous research. This correlation might be explained by the stratification caused by cooling. In addition, the time variations of Ba_ex in WSAP were similar to those of Ba_ex in the Okhotsk Sea and of other proxies (C_org and Opal) in both the Okhotsk and the Bering Sea, indicating the spatial homogeneity of Ba_ex in WSAP including proximal marginal seas. The Opal content was more weakly correlated with the Vostok δD (r = 0.46, p < 0.001) than Ba_ex, reflecting that Opal in WSAP including proximal marginal seas was spatially heterogeneous compared to Ba_ex. While both the C_org content and U_ex, the excess amount of U relative to the detritus composition, were not positively correlated with the Vostok δD, they behaved similarly in the sediments. The positive correlation between δ¹³C and the Vostok δD (r = 0.42, p < 0.001), between δ¹³C and Ba_ex (r = 0.60, p < 0.001) and between δ¹³C and Opal (r = 0.36, p < 0.01) indicates that δ¹³C in WSAP may give some information on the phytoplankton growth rate. There was not a significant correlation between the spatially homogeneous Ba_ex in WSAP and Loess (r = − 0.16, p > 0.01), suggesting that the increase of biological production with the increase of Loess supply during the glacial periods did not occur.  相似文献   

Uranium in coastal sediments of Tokyo Bay and Funka Bay   总被引：2，自引：0，他引：2  

Shizuo Tsunogai  Seiya Nagao  Shintaro Watanabe  Yoshiaki Takahashi  Kazunari Suzuki  Masatoshi Yamada  Koh Harada 《Journal of Oceanography》1990,46(5):211-218

The sediment cores from Tokyo Bay and Funka Bay were analyzed for U and its isotopic ratio,²³⁴U/²³⁸U, after dissolving them in 0.1 M HCl, and 30% H₂O₂ in 0.05 M HCl. A small fraction of U in the anoxic sediments was dissolved in 0.1M HCl and even the added yield tracer,²³²U, was lost. The isotopic ratio of H₂O₂ soluble U in the sediments was equal to that of seawater, suggesting that the H₂O₂ soluble U in the sediments is authigenic. The 6M HCl solution dissolved part of the lithogenic U besides the authigenic U. The depth profiles of U from the two bays resembled each other. The authigenic U comprised more than half of the total U even at the surface and increased with depth down to 70 cm, showing small maxima at about 20 cm. The concentration of refractory U was nearly constant with depth and similar to that of the pelagic sediments. The highest U concentration, 6 µg g^–1 which was about 5 times that of the pelagic sediments, was observed in the layer between 70 and 160 cm depth in Tokyo Bay. The annual sedimentation rates of U in the Tokyo Bay sediments were 2.6 tons at the surface and 7.0 tons at the 70–160 cm depth. The increase in U with depth should be due to the deposition of interstitial U either diffusing downward from the surface indicating the trapping of seawater U, or otherwise diffusing upward from the deeper layer indicating the internal cycling of U within the sediments.  相似文献   

Flow conditions of the 2004 Indian Ocean tsunami in Thailand,inferred from capping bedforms and sedimentary structures     

Montri Choowong  Naomi Murakoshi  Ken‐ichiro Hisada  Thasinee Charoentitirat  Punya Charusiri  Sumet Phantuwongraj  Prawpan Wongkok  Alongkorn Choowong  Rittirong Subsayjun  Vichai Chutakositkanon  Kruawan Jankaew  Pitsanupong Kanjanapayont 《地学学报》2008,20(2):141-149

The 2004 Indian Ocean tsunami deposited a sheet of sand with surficial bedforms at the Andaman coast of Thailand. Here we show the recognition of bedforms and the key internal sedimentary structures as criteria of the tsunami supercritical flow condition. The presence of well‐preserved capping bedforms implied a dominant tsunami inflow. Sets of internal sedimentary structures including parallel lamination, seaward and landward inclined‐laminations, and downstream dipping laminae indicated antidune structures that were generated by a supercritical flow current in a depositional stage during the inflow. A set of seaward dipping cross‐laminations containing sand with mud drape on the surface of one depositional layer are a unique indication of an outflow structure. A majority of deposits show normal grading, but in some areas, localized reverse grading was also observed. The recognition of these capping bedforms and determination of the internal sedimentary structures provides new key criteria to help derive a better understanding of tsunami flow conditions.  相似文献