Mass, Heat and Salt Balances in the Eastern Barents Sea Obtained by Inversion of Hydrographic Section Data     

Gleb Panteleev  Motoyoshi Ikeda  Alex Grotov  Dmitri Nechaev  Max Yaremchuk 《Journal of Oceanography》2004,60(3):613-623

Standard hydrological section data, collected in the eastern Barents Sea in September 1997, have been analyzed using a variational data assimilation technique. This method allows us to obtain temperature, salinity and velocity fields that are consistent with observations and dynamically balanced within the framework of a steady-state model describing large-scale nearly geostrophic circulation. Error bars of the optimized fields are computed by explicit inversion of the Hessian matrix. The optimized velocity field is in agreement with independent velocity observations derived from surface drifter trajectories in the southwestern part of the Barents Sea. Optimized fields provide the following estimates of integral characteristics of the circulation in the region: i) the North Cape current transport is 2.12 ± 0.25 Sv; ii) the Karskie Vorota Strait throughflow is 0.7 ± 0.06 Sv; iii) heat flux with Atlantic water is 4.7 ± 0.16⋅10¹¹ W; iv) salt import from the Atlantic Ocean is 7.41 ± 0.46⋅10³ kg/s. The imbalance of the heat budget in the eastern part of the Barents Sea indicates the presence of statistically insignificant surface heat fluxes which are less than 1 W/m². This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Behind every robust result is a robust method: Perspectives from a case study and publication process in hydrological modelling     

Fabrizio Fenicia  Dmitri Kavetski 《水文研究》2021,35(8):e14266

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Skeleton as a probe of the cosmic web: the two-dimensional case     

Dmitri Novikov  Stéphane Colombi  Olivier Doré 《Monthly notices of the Royal Astronomical Society》2006,366(4):1201-1216

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Nonlinear Dynamics of Ionization Fronts in HII Regions     

Akira Mizuta  Jave O. Kane  Marc W. Pound  Bruce A. Remington  Dmitri D. Ryutov  Hideaki Takabe 《Astrophysics and Space Science》2007,307(1-3):183-186

Hydrodynamic instability of an accelerating ionization front (IF) is investigated with 2D hydrodynamic simulations, including absorption of incident photoionizing photons, recombination in the HII region, and radiative molecular cooling. When the amplitude of the perturbation is large enough, nonlinear dynamics of the IF triggered by the separation of the IF from the cloud surface is observed. This causes the second harmonic of the imposed perturbation to appear on the cloud surfaces, whereas the perturbation in density of ablated gas in the HII region remains largely single mode. This mismatch of modes between the IF and the density perturbation in the HII region prevents the strong stabilization effect seen in the linear regime. Large growth of the perturbation caused by Rayleigh-Taylor-like instability is observed late in time.  相似文献   

Sea Ice Dynamics Induced by External Stochastic Fluctuations     

Dmitri V. Alexandrov  Irina A. Bashkirtseva  Alexey P. Malygin  Lev B. Ryashko 《Pure and Applied Geophysics》2013,170(12):2273-2282

The influence of stochastic fluctuations in the atmosphere and in the ocean caused by different occasional phenomena (noises) on dynamic processes of sea ice growth with a mushy layer is studied. It is shown that atmospheric temperature variances substantially increase the sea ice thickness, whereas dispersion variations of turbulent flows in the ocean to a great extent decrease the ice content produced by false bottom evolution.  相似文献   

Practical Use of Computationally Frugal Model Analysis Methods          下载免费PDF全文

Mary C. Hill  Dmitri Kavetski  Martyn Clark  Ming Ye  Mazdak Arabi  Dan Lu  Laura Foglia  Steffen Mehl 《Ground water》2016,54(2):159-170

Three challenges compromise the utility of mathematical models of groundwater and other environmental systems: (1) a dizzying array of model analysis methods and metrics make it difficult to compare evaluations of model adequacy, sensitivity, and uncertainty; (2) the high computational demands of many popular model analysis methods (requiring 1000's, 10,000 s, or more model runs) make them difficult to apply to complex models; and (3) many models are plagued by unrealistic nonlinearities arising from the numerical model formulation and implementation. This study proposes a strategy to address these challenges through a careful combination of model analysis and implementation methods. In this strategy, computationally frugal model analysis methods (often requiring a few dozen parallelizable model runs) play a major role, and computationally demanding methods are used for problems where (relatively) inexpensive diagnostics suggest the frugal methods are unreliable. We also argue in favor of detecting and, where possible, eliminating unrealistic model nonlinearities—this increases the realism of the model itself and facilitates the application of frugal methods. Literature examples are used to demonstrate the use of frugal methods and associated diagnostics. We suggest that the strategy proposed in this paper would allow the environmental sciences community to achieve greater transparency and falsifiability of environmental models, and obtain greater scientific insight from ongoing and future modeling efforts.  相似文献   

Detection of ammonia-oxidizing Bacteria and Archaea within coral reef cyanobacterial mats     

Dmitri Sobolev  Matthew R. Boyett  Edwin Cruz-Rivera 《Journal of Oceanography》2013,69(5):591-600

Coral-reef filamentous cyanobacterial mats are complex communities of microbes. We used DGGE and eubacterial and archaeal 16S rRNA and amoA ammonium monooxygenase subunit A primer sets to explore the presence of genes mediating nitrogen conversion within cyanobacterial mats from Hawaii. DGGE band analysis revealed the presence of halophiles such as Halococcus salifodinae and of Nitrosopumilus-like organisms. Twenty seven out of 31 clone sequences exhibited a 95 % or greater 16S rRNA gene identity with known archaeal ammonia oxidizers such as Nitrosopumilus maritimus. The presence of Archaea within those mats, as well as the co-occurrence of both ammonia-oxidizing Archaea and ammonia-oxidizing Bacteria suggests importance of the former in the cyanobacterial mat community, and suggests greater than anticipated diversity of nitrogen conversion processes and organisms in those systems.  相似文献   

Late Holocene climatic changes in Tierra del Fuego based on multiproxy analyses of peat deposits     

Dmitri Mauquoy  Maarten Blaauw  Ana Borromei  Frank M. Chambers 《Quaternary Research》2004,61(2):148-158

A ca. 1400-yr record from a raised bog in Isla Grande, Tierra del Fuego, Argentina, registers climate fluctuations, including a Medieval Warm Period, although evidence for the ‘Little Ice Age’ is less clear. Changes in temperature and/or precipitation were inferred from plant macrofossils, pollen, fungal spores, testate amebae, and peat humification. The chronology was established using a ¹⁴C wiggle-matching technique that provides improved age control for at least part of the record compared to other sites. These new data are presented and compared with other lines of evidence from the Southern and Northern Hemispheres. A period of low local water tables occurred in the bog between A.D. 960-1020, which may correspond to the Medieval Warm Period date range of A.D. 950-1045 generated from Northern Hemisphere tree-ring data. A period of cooler and/or wetter conditions was detected between ca. A.D. 1030 and 1100 and a later period of cooler/wetter conditions estimated at ca. cal A.D. 1800-1930, which may correspond to a cooling episode inferred from Law Dome, Antarctica.  相似文献   

Hf isotope compositions and HREE variations in off-craton garnet and spinel peridotite xenoliths from central Asia   总被引：1，自引：0，他引：1  

Dmitri A. Ionov  Janne Blichert-Toft 《Geochimica et cosmochimica acta》2005,69(9):2399-2418

Garnet-facies continental mantle is poorly understood because the vast majority of mantle xenoliths in continental basalts are spinel peridotite. Peridotite xenoliths from Vitim (southern Siberia) and Mongolia provide some of the best samples of garnet and garnet-spinel facies off-craton lithospheric mantle. Garnets in those fertile to moderately depleted lherzolites show a surprisingly broad range of HREE abundances, which poorly correlate with modal and major oxide compositions. Some garnets are zoned and have Lu-rich cores. We argue that these features indicate HREE redistribution after the partial melting, possibly related to spinel-garnet phase transition on isobaric cooling. Most peridotites from Vitim have depleted to ultra-depleted Hf isotope compositions (calculated from mineral analyses: ε_Hf(0) = +17 to +45). HREE-rich garnets have the most radiogenic ε_Hf values and plot above the mantle Hf-Nd isotope array while xenoliths with normal HREE abundances usually fall within or near the depleted end of the MORB field. Model Hf isotope ages for the normal peridotites indicate an origin by ancient partial melt extraction from primitive mantle, most likely in the Proterozoic. By contrast, an HREE-rich peridotite yields a Phanerozoic model age, possibly reflecting overprinting of the ancient partial melting record with that related to a recent enrichment in Lu. Clinopyroxene-garnet Lu-Hf isochron ages (31-84 Ma) are higher than the likely eruption age of the host volcanic rocks (∼16 Ma). Garnet-controlled HREE migration during spinel-garnet and garnet-spinel phase transitions may be one explanation for extremely radiogenic ¹⁷⁶Hf/¹⁷⁷Hf reported for some mantle peridotites; it may also contribute to Hf isotope variations in sub-lithospheric source regions of mantle-derived magmas.  相似文献   

Spinel peridotite xenoliths from the Atsagin-Dush volcano, Dariganga lava plateau, Mongolia: a record of partial melting and cryptic metasomatism in the upper mantle   总被引：14，自引：0，他引：14  

U. Wiechert  Dmitri A. Ionov  Karl Hans Wedepohl 《Contributions to Mineralogy and Petrology》1997,126(4):345-364

Spinel peridotite xenoliths from the Atsagin-Dush volcanic centre, SE Mongolia range from fertile lherzolites to clinopyroxene(cpx)-bearing harzburgites. The cpx-poor peridotites typically contain interstitial fine-grained material and silicate glass and abundant fluid inclusions in minerals, some have large vesicular melt pockets that apparently formed after primary clinopyroxene and spinel. No volatile-bearing minerals (amphibole, phlogopite, apatite, carbonate) have been found in any of the xenoliths. Fifteen peridotite xenoliths have been analysed for major and trace elements; whole-rock Sr isotope compositions and O isotope composition of all minerals were determined for 13 xenoliths. Trace element composition and Sr-Nd isotope compositions were also determined in 11 clinopyroxene and melt pocket separates. Regular variations of major and moderately incompatible trace elements (e.g. heavy-rare-earth elements) in the peridotite series are consistent with its formation as a result of variable degrees of melt extraction from a fertile lherzolite protolith. The Nd isotope compositions of LREE (light-rare-earth elements)-depleted clinopyroxenes indicate an old (≥ 1 billion years) depletion event. Clinopyroxene-rich lherzolites are commonly depleted in LREE and other incompatible trace elements whereas cpx-poor peridotites show metasomatic enrichment that can be related to the abundance of fine-grained interstitial material, glass and fluid inclusions in minerals. The absence of hydrous minerals, ubiquitous CO₂-rich microinclusions in the enriched samples and negative anomalies of Nb, Hf, Zr, and Ti in primitive mantle-normalized trace element patterns of whole rocks and clinopyroxenes indicate that carbonate melts may have been responsible for the metasomatic enrichment. Low Cu and S contents and high δ³⁴S values in whole-rock peridotites could be explained by interaction with oxidized fluids that may have been derived from subducted oceanic crust. The Sr-Nd isotope compositions of LREE-depleted clinopyroxenes plot either in the MORB (mid-ocean-ridge basalt) field or to the right of the mantle array, the latter may be due to enrichment in radiogenic Sr. The LREE-enriched clinopyroxenes and melt pockets plot in the ocean island-basalt field and have Sr-Nd isotope signatures consistent with derivation from a mixture of the DMM (depleted MORB mantle) and EM (enriched mantle) II sources. Received: 18 January 1996 / Accepted: 23 August 1996  相似文献