Th isotopes in the Santa Monica basin: Temporal variation,long-term mass balance and model rate constants     

Huh  Chih-An 《Journal of Oceanography》1995,51(3):363-373

Distribution and flux of²³⁴Th,²³²Th and²³⁰Th in the water column of central Santa Monica basin observed over a period of seven years show seasonal and interannual variabilities. A steady-state model is applied to the integrated data to calculate long term average flux and model rate constants of Th isotopes. Mass balance calculations show that the basin acts like a closed system for short-lived²³⁴Th, but not for the long-lived isotopes²³⁰Th and²³²Th. Most²³⁰Th in the basin is transported from elsewhere. Of the incoming Th, 40–55% of the²³⁰Th and 14–26% of the²³²Th enter the surface water in dissolved form. In the upper 100 m, the residence time of dissolved Th with respect to adsorption onto suspended particulates, 70–80 days, is about one order of magnitude higher than the residence time of suspended particles with respect to aggregation into sinking particles, 7–10 days.  相似文献   

Radiochemical observations on manganese nodules from three sedimentary environments in the north Pacific     

Hun Chih-An  Ku Teh-Lung 《Geochimica et cosmochimica acta》1984,48(5):951-963

Decay-series isotopes were measured on manganese nodules from three sedimentary environments, characterized by substrates of red clay (R), siliceous ooze (S) and hemipelagic clay (H). Growth rates of nodules are shown to be site dependent: 1–2 mm/Myr at site R, 3–8 mm/Myr at sites S, and 20–50 mm/ Myr at site H. Correlation between growth rate and the parameter Mn/Fe² suggests that regional diagenetic variations control the compositions and growth rates of the nodules. The frequency of nodule turnover and the period of their growth are assessed from the “top” vs. “bottom” distributions of several nuclides. Based on the ²³⁰Th, ²³¹Pa and ²²⁶Ra data, turnover times of 10³ to 10⁵ years are estimated and they vary with relative size and shape of the specimens at a given site. The presence of unsupported ²¹⁰Pb and ²²⁸Th in the top surfaces but not in the bottom surfaces of the surface nodules suggests active growth during the last decades or years, despite their old ages. The data also indicate that turnover rates are not more frequent than once every several years or decades.The ²³⁰Th-²²⁶Ra, ²²⁶Ra-²¹⁰Pb and ²³²Th-²²⁸Th disequilibrium relationships in the nodules allow the migratory behavior of ²²⁶Ra, ²²²Rn and ²²⁸Ra and their fluxes to be deduced: thus radium leaves the top sides but enters the bottom sides of the surface nodules at sites R and S. At site R there is a net loss of radium to the sea; the opposite is true at site S. Surface nodules at site H trap radium from both sides, probably due to more intense diagenetic input of radium from sediment pore water. The effective diffusivities of ²²⁶Ra in nodules vary from $\text{3 × 10}{}^{\mathrm{?12}}$ to $\text{8 × 10}{}^{\mathrm{?14}}$ cm²/s, dependent on the textural variation of the nodule material, which crudely reflects the growth rate and hence sedimentary environment. ²²²Rn diffuses out of nodules from all sides, with an effective diffusivity of ca. $\text{(2–6) × 10}{}^{\mathrm{?8}}\text{cm}{}^2\text{/s}$. At all sites nodules serve as a more effective source of ²²²Rn to sea water than their adjacent sediments. The outward flux of ²²²Rn from nodules relative to that from adjacent sediments tends to be higher in more reduced environments, an effect caused by the fact that Mn-rich nodules from more reduced environment act as a more efficient trap for ²²⁶Ra.  相似文献   

Fluid seepage along the San Clemente Fault scarp: basin-wide impact on barium cycling     

Marta E. Torres  James McManus  Chih-An Huh 《Earth and Planetary Science Letters》2002,203(1):181-194

Material fluxes associated with fluid expulsion at cold seeps and their contribution to oceanographic budgets have not been accurately constrained. Here we present evidence that the barium released at cold seeps along the San Clemente Fault zone may significantly impact the geochemical budget of barium within the basin. Barium fluxes at seep localities on the fault scarp, measured with benthic chambers, reach values as high as 5 mmol m⁻² day⁻¹. This is the largest dissolved barium flux measured to date at a cold seep. The discharge of barium-rich fluids results in formation of massive barite deposits along the escarpment wall. The deposits are young (approximately 8 yr) and appear to grow at a minimum rate of 0.2 cm yr⁻¹. This rapid growth rate requires a barium efflux rate that is about two orders of magnitude higher than the measured dissolved flux. We believe that the discrepancy reflects a highly localized seepage system and that chambers positioned as close as possible to the growing chimneys did not sample the foci of fluid discharge. Transport of fine barite particles from the seeps may be responsible for excess rates of barium accumulation throughout the San Clemente Basin, relative to other basins in the California Margin. Based on a preliminary budget, we estimate that cold-seep barite is accumulating at the basin floor in San Clemente at a rate of 2 μmol m⁻² day⁻¹, a value that is comparable to the total barium accumulation rates driven by detrital and biogenic components in neighboring basins. Remobilization of cold-seep barite on the basin floor adds to that driven by the biogenic barium flux and results in benthic barium recycling rates (effluxes) within the San Clemente Basin that are as much as seven times higher than the effluxes from surrounding borderland basins. Our estimates imply that processes associated with fluid seepage along the San Clemente Fault significantly contribute to the basin’s barium cycle. The strontium isotopic composition of the seep barite is significantly different from marine ‘biogenic’ barite, which is known to accurately record seawater composition. In addition, the seep deposits are depleted in ²²⁶Ra relative to their modern biogenic counterparts, and are likely to be a source of radium-depleted particulate barium to the basin. Thus the impact of barite transport from seeps on the San Clemente escarpment to the basin floor might also have implications for the geochemistry of elements other than barium.  相似文献   

Increased precipitation during the Little Ice Age in northern Taiwan inferred from diatoms and geochemistry in a sediment core from a subalpine lake   总被引：3，自引：0，他引：3  

Liang-Chi Wang  Hermann Behling  Teh-Quei Lee  Hong-Chun Li  Chih-An Huh  Liang-Jian Shiau  Su-Hwa Chen  Jiunn-Tzong Wu 《Journal of Paleolimnology》2013,49(4):619-631

We studied diatoms in a 55.5-cm-long sediment core from a subalpine lake in northern Taiwan, Tsuifong Lake (TFL), to investigate environmental changes from AD 490 to present. Diatom assemblages of the last century were dominated by acidophilous species, whereas alkaliphilous taxa dominated the record between AD 1480 and 1910. Over the studied time frame, four decadal periods with high precipitation were inferred from evidence of elevated soil input from the watershed, supported by the stable isotope signatures (δ¹⁵N, δ¹³C) of organic matter and magnetic susceptibility of the sediments. We compared the inferred changes in pH of TFL to values obtained from three other Taiwanese subalpine lakes. The present study revealed that elevated precipitation was associated with increased solar irradiance over the last five centuries, with a stable dry period between AD 490 and 1450. Acidification of TFL in the last ~100 years was a consequence of deforestation and acid rain.  相似文献   

Neutron activation analysis(NAA) and geochemical studies of 38 elements in surface sediments from lower reach and estuary of Huanghe(Yellow) River     

Li Peiquan  Chih-An Huh  Zhihxin Zhang  Weizhi Tian  Lu Guanshan 《海洋学报(英文版)》1990,9(2):227-246

Using a neutron activation analysis technique, which involves gamma-spectrometry with a Ge(Li) detector coupled to a S40 multichannel analyzer and interfaced to a PDP-11 computer, we determined thirty-eight elements in sediments from the lower reach (downstream from Jinan) and estuary of Huanghe. The results are discussed in this paper.From inter-elemental correlations, it ts found that a large number of metals (Mn.As, Co, Cr.Cs, Rb, Sc, Ti, Ta, V and Zn) correlate positively with Fe. Ba and Ca correlate positively with Al. Whereas some elements (e. g. , Ti and lanthanides) show no correlation with either Fe or Al. On the other hand, Hf and Zr show a negative correlation with Fe. Elements which tend to be scavenged by Fe and Al colloids or suspended particles are enriched in sediments at the Huanghe Estuary relative to its lower reach. On the other hand, the contents of some elements (e. g. , Zr,Hf,U, Ba, etc. )are higher in sediments from the lower reach of Huanghe than in the estuarine sediments,which  相似文献   

Modern (<100 years) sedimentation in the Taiwan Strait: Rates and source-to-sink pathways elucidated from radionuclides and particle size distribution   总被引：1，自引：0，他引：1  

Chih-An Huh  Weifang Chen 《Continental Shelf Research》2011,31(1):47-63

A large number of sediment cores collected during 2005-2010 from the Taiwan Strait were analyzed for radionuclides (²¹⁰Pb, ¹³⁷Cs and ⁷Be) to elucidate sedimentation dynamics in this all-important gateway linking two largest marginal seas in the western Pacific (namely, the South China Sea and the East China Sea). Apparent sediment accumulation rates derived from ²¹⁰Pb and ¹³⁷Cs profiles vary from <0.1 to >2 cm/yr, averaging ∼0.4 cm/yr and showing a spatial pattern closely related to hydrodynamics and sediment source-to-sink pathways. Spatial-temporal variation of ⁷Be activity in surface sediments off Taiwan’s west coast indicates episodic deposition of flood layers and their mobility from river estuaries toward the north. In conjunction with particle size distribution in surface sediments and the structure of sediment strata revealed by sub-bottom echo images; the radionuclide data can be used to outline three different sediment source-to-sink dispersal systems. Based on sediment loads of surrounding rivers and the distribution of sediment accumulation rates, lateral transport is required to account for the budget and size distribution of sediments in the strait.  相似文献   

Distribution and accumulation of heavy metals in carbonate and reducible fractions of marine sediment from offshore mid-western Taiwan     

Hou-Chun Liu  Chen-Feng You  Bor-Jiun Huang  Chih-An Huh 《Marine pollution bulletin》2013

Two marine sediment cores from offshore mid-western Taiwan were subsampled and pre-treated using a sequential extraction procedure to separate carbonate and reducible fractions. Aliquots of these extracts were analyzed to determine their chemical composition to evaluate the geochemical processes responsible for heavy metal distribution and accumulation in the coastal environment. Our data demonstrate that sedimentation rates derived from excess ²¹⁰Pb associated with metal fluxes show large increases circa A.D. 1990. A well-synchronized increase in metal flux in both geochemical fractions was found and validated by Pearson’s correlation. Principal component analysis revealed the heavy metal fluxes to be highly correlated with the sediment deposition rate, with metal contamination potentially driven by a sole contributor. This study emphasizes the changes in sedimentation rate is potentially caused by activities associated with the inland economic development during this time, rather than by raising heavy metal pollution dominated the accumulation offshore mid-western Taiwan.  相似文献