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81.
Locally enhanced turbulent mixing over rough bottom bathymetry is one of the candidates that might make up for the lack of
diapycnal diffusivity in maintaining the global overturning circulation. In the present study, using a two-dimensional vertical
numerical model for the Brazil Basin, we numerically examine the intensity and vertical structure of tide-induced mixing over
multi-beam bottom bathymetry via the comparison with those over somewhat smoothed bottom bathymetry. Note that even this smoothed
bottom bathymetry is finer than in commonly used datasets. In comparison to the response over the smoothed bottom bathymetry,
energy dissipation rates are enhanced within a few hundred meters over the multi-beam bottom bathymetry. In spite of several
limitations of the two-dimensional vertical numerical model, the magnitude and vertical distribution of the calculated dissipation
rates agree well with those from microstructure measurements. We find that tidal interaction with fine-scale (≤2 km) bottom
bathymetry efficiently generates high wavenumber internal waves, which are subject to local energy dissipation and hence strongly
control the abyssal mixing; the most important finding is that the intensity and vertical decay scale of abyssal mixing are
in a trade-off relationship with each other, which is not taken into account in the existing parameterizations. 相似文献
82.
Tong Lee Toshiyuki Awaji Magdalena Balmaseda Nicolas Ferry Yosuke Fujii Ichiro Fukumori Benjamin Giese Patrick Heimbach Armin Köhl Simona Masina Elisabeth Remy Anthony Rosati Michael Schodlok Detlef Stammer Anthony Weaver 《Dynamics of Atmospheres and Oceans》2010
Monthly averaged total volume transport of the Indonesian throughflow (ITF) estimated by 14 global ocean data assimilation (ODA) products that are decade to multi-decade long are compared among themselves and with observations from the INSTANT Program (2004–2006). The main goals of the comparisons are to examine the consistency and evaluate the skill of different ODA products in simulating ITF transport. The ensemble averaged, time-mean value of ODA estimates is 13.6 Sv (1 Sv = 106 m3/s) for the common 1993–2001 period and 13.9 Sv for the 2004–2006 INSTANT Program period. These values are close to the 15-Sv estimate derived from INSTANT observations. All but one ODA time-mean estimate fall within the range of uncertainty of the INSTANT estimate. In terms of temporal variability, the scatter among different ODA estimates averaged over time is 1.7 Sv, which is substantially smaller than the magnitude of the temporal variability simulated by the ODA systems. Therefore, the overall “signal-to-noise” ratio for the ensemble estimates is larger than one. The best consistency among the products occurs on seasonal-to-interannual time scales, with generally stronger (weaker) ITF during boreal summer (winter) and during La Nina (El Nino) events. The scatter among different products for seasonal-to-interannual time scales is approximately 1 Sv. Despite the good consistency, systematic difference is found between most ODA products and the INSTANT observations. All but the highest-resolution (18 km) ODA product show a dominant annual cycle while the INSTANT estimate and the 18-km product exhibit a strong semi-annual signal. The coarse resolution is an important factor that limits the level of agreement between ODA and INSTANT estimates. Decadal signals with periods of 10–15 years are seen. The most conspicuous and consistent decadal change is a relatively sharp increase in ITF transport during 1993–2000 associated with the strengthening tropical Pacific trade wind. Most products do not show a weakening ITF after the mid-1970s’ associated with the weakened Pacific trade wind. The scatter of ODA estimates is smaller after than before 1980, reflecting the impact of the enhanced observations after the 1980s. To assess the representativeness of using the average over a three-year period (e.g., the span of the INSTANT Program) to describe longer-term mean, we investigate the temporal variations of the three-year low-pass ODA estimates. The average variation is about 3.6 Sv, which is largely due to the increase of ITF transport from 1993 to 2000. However, the three-year average during the 2004–2006 INSTANT Program period is within 0.5 Sv of the long-term mean for the past few decades. 相似文献
83.
84.
85.
86.
The origin of Zn isotope fractionation in sulfides 总被引:2,自引:0,他引:2
Toshiyuki Fujii Frédéric Moynier Francis Albarède 《Geochimica et cosmochimica acta》2011,75(23):7632-7643
Isotope fractionation of Zn between aqueous sulfide, chloride, and carbonate species (Zn2+, Zn(HS)2, , , ZnS(HS)−, ZnCl+, ZnCl2, , and ZnCO3) was investigated using ab initio methods. Only little fractionation is found between the sulfide species, whereas carbonates are up to 1‰ heavier than the parent solution. At pH > 3 and under atmospheric-like CO2 pressures, isotope fractionation of Zn sulfides precipitated from sulfidic solutions is affected by aqueous sulfide species and the δ66Zn of sulfides reflect these in the parent solutions. Under high PCO2 conditions, carbonate species become abundant. In high PCO2 conditions of hydrothermal solutions, Zn precipitated as sulfides is isotopically nearly unfractionated with respect to a low-pH parent fluid. In contrast, negative δ66Zn down to at least −0.6‰ can be expected in sulfides precipitated from solutions with pH > 9. Zinc isotopes in sulfides and rocks therefore represent a potential indicator of mid to high pH in ancient hydrothermal fluids. 相似文献
87.
Estimation of baroclinic tide energy available for deep ocean mixing based on three-dimensional global numerical simulations 总被引:1,自引:0,他引:1
The global distributions of the major semidiurnal (M2 and S2) and diurnal (K1 and O1) baroclinic tide energy are investigated using a hydrostatic sigma-coordinate numerical model. A series of numerical simulations
using various horizontal grid spacings of 1/15–1/5° shows that generation of energetic baroclinic tides is restricted over
representative prominent topographic features. For example, nearly half of the diurnal (K1 and O1) baroclinic tide energy is excited along the western boundary of the North Pacific from the Aleutian Islands down to the
Indonesian Archipelago. It is also found that the rate of energy conversion from the barotropic to baroclinic tides is very
sensitive to the horizontal grid spacing as well as the resolution of the model bottom topography; the conversion rate integrated
over the global ocean increases exponentially as the model grid spacing is reduced. Extrapolating the calculated results in
the limit of zero grid spacing yields the estimate of the global conversion rate to be 1105 GW (821, 145, 102, 53 GW for M2, S2, K1, and O1 tidal constituents, respectively). The amount of baroclinic tide energy dissipated in the open ocean below a depth of 1000 m,
in particular, is estimated to be 500–600 GW, which is comparable to the mixing energy estimated by Webb and Suginohara (Nature
409:37, 2001) as needed to sustain the global overturning circulation. 相似文献
88.
The potential role of the tide-induced time-mean flow (the tidal residual current) in determining transport through the Tsugaru
Strait (located between the East/Japan Sea and the North Pacific) is investigated using a high-resolution numerical barotropic
model. The calculated K1, O1, M2, and S2 tidal fields agree well with available observational records derived from both tide gauge and current meter measurements
in the strait and the adjacent seas. The tidal residual current speed reaches 0.3 ms−1 in two narrow “neck” areas where topographic sills are located. This result suggests that tides should be taken into account
in estimating the long-term water mass and nutrient transport through narrow regions between the East/Japan Sea and the North
Pacific. An interesting aspect of the tidal residual current field is the prediction of several active eddy zones in which
sequences of eddy triplets develop in the vicinity of capes. Our vorticity analysis reveals that the interplay of topographic
effects arising from both the headland and the sill around capes plays a critical role in the formation of these triple eddy
patterns. 相似文献
89.
M. Tajuddin Sikder Yusuke Kihara Masaomi Yasuda Yustiawati Yoshihiro Mihara Shunitz Tanaka Dalkhjav Odgerel Badamtsetseg Mijiddorj Suhaemi M. Syawal Toshiyuki Hosokawa Takeshi Saito Masaaki Kurasaki 《洁净——土壤、空气、水》2013,41(1):60-68
To compare water quality in rivers of developed and developing countries, a study based on physicochemical parameters and dissolved metals levels was conducted. Water samples were collected from selected sites in Dhaka, Bangladesh; Hokkaido and Osaka, Japan; Erdenet, Mongolia and West Java, Indonesia. Analysis of least significant differences revealed that most water quality parameters were within comparable low levels in both developed and developing countries. The dissolved metals concentrations were found to be similar and below those of water standards except for manganese and cadmium at every sampling point, and lead in Erdenet, Mongolia. Some metals showed high enrichment factors in the rivers of Osaka, Japan and Erdenet, Mongolia, indicating accumulation possibility of metals in the river‐bed sediments. High concentrations of dissolved organic carbon, Escherichia coli and dissolved metals suggested greater water pollution in some rivers of developing countries than in the rivers of Japan. Principal component analysis showed strong correlations between “dissolved organic carbon and chemical oxygen demand” and “conductivity and total dissolved solids” at each sampling point, and E. coli, nitrate (NO), nitrite (NO), and pH levels were found to be higher in the rivers of Dhaka and Erdenet. In addition, there were high levels of Al and Zn in West Java, Pb in Erdenet, and Mn, Fe, and Cr in the rivers of Dhaka and Japan. Based on pressures and impacts, it is evident that dissolved metal, organic, and fecal pollution in the rivers of developing countries are in somewhat dreadful condition in comparison with the rivers of developed country. 相似文献
90.
Daiki Nomura Toru Takatsuka Masao Ishikawa Toshiyuki Kawamura Kunio Shirasawa Hisayuki Yoshikawa-Inoue 《Estuarine, Coastal and Shelf Science》2009
Physico-chemical properties in the brine and under-ice water were measured in Saroma-ko Lagoon on the northeastern coast of Hokkaido, Japan, which is connected to the Sea of Okhotsk, during the period from mid-February through mid-March 2006. The brine within brine channels of the sea ice was collected with a new sampling method examined in this study. Salinity, dissolved inorganic carbon (DIC), total alkalinity (TA), dissolved oxygen (DO), nutrients and oxygen isotopic ratio (δ18O) contained in the brine within brine channels of the sea ice and in the under-ice water varied largely in both time and space during the ice melt period, when discharge from Saromabetsu River located on the southeast of the lagoon increased markedly due to the onset of snow melting. The under-ice plume expands as far as 4.5 km from the river mouth at mid-March 2006, transporting chemical components supplied from the river into the lagoon. The under-ice river water was likely transported into the sea ice through well-developed brine channels in the sea ice due to upward flushing of water through brine channels occurred by loading of snowfalls deposited over the sea ice. These results suggest that the river water plume plays an important role in supplying chemical components into the sea ice, which may be a key process influencing the biogeochemical cycle in the seasonally ice-covered Saroma-ko Lagoon. 相似文献