Denitrification and the nitrogen gas excess in the eastern tropical South Pacific oxygen deficient zone     

Bonnie X. Chang  Allan H. Devol  Steven R. Emerson 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(9):1092-1101

Recent studies of the nitrogen gas excess produced during water column denitrification have indicated that water column denitrification rates calculated using nitrate deficit-type methods could be a substantial underestimate. Since there are no other significant processes that produce (or consume) N₂ in the oxygen deficient zone (ODZ), its excess above background can be used to estimate the amount of denitrification, avoiding assumptions made in nitrate deficit calculations of the composition of the respired organic matter and also uncertainties in the nitrogen removal pathways. Dissolved N₂, Ar, and nutrient concentrations were measured at 2 stations in the ODZ of the eastern tropical South Pacific (ETSP) in order to compare the nitrogen gas excess with the dissolved inorganic nitrogen (DIN) deficit due to denitrification. In contrast with previous findings in the Arabian Sea ODZ, the shapes of the N₂ excess and DIN deficit profiles were similar in the ETSP ODZ, with maxima at the top of the ODZ. Maximum DIN deficits at each station were 19 and 18 μM N compared to the maximum N₂ excesses of 15 and 20 μM N, respectively. Given the same considerations of the volume and residence time for the oxygen deficient zone waters, denitrification rates for the ETSP estimated from the N₂ excess would be comparable or no greater than 30% larger than the one determined using the DIN deficit. This implies that the source of the DIN removed from the ODZ is either deep sea nitrate or organic matter with an N:P ratio close to Redfield.  相似文献   

Absolute Accuracy and Repeatability of the Rmib Radiometers for Tsi Measurements     

Sabri Mekaoui  Steven Dewitte  Dominique Crommelynck  Andre Chevalier  Christian Conscience  Alexandre Joukoff 《Solar physics》2004,224(1-2):237-246

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Galaxies as complex systems     

Steven N. Shore  Daniele Galli 《Astrophysics and Space Science》2003,284(2):809-818

... all for the want of a nail. English nursery rhyme Feedback is the essential property of multiphase models for the evolution of galaxies. In this review, we stress the generic behavior of toy models to highlight those features that are inevitable consequences of assumptions in the current catalog of galactic evolution calculations. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

¹³C/¹²C ratio double cyclicity in a Miocene browncoal: isotopic signals and orbital forcing     

Timothy P. Jones  Steven M. Fortier  Volker Mosbrugger  Jochen Roessler  Thorsen Utescher  & Abdul R. Ashraf 《地学学报》1997,9(1):19-23

A detailed stable carbon isotopic profile of a late Miocene browncoal seam from the Lower Rhine Embayment, Germany, reveals two clear separate cycles of different frequency: this is the first instance of this type of isotopic signature being recognized within coals. The ratio of the two frequencies suggests this isotopic signal possibly resulted from climatic or vegetational responses to orbital forcing. The cyclicity has been enhanced by the application of conventional filtering methods on the data set. An analysis of the seam's palynology indicates a correlation between heavier isotopic compositions and the presence of Sequoiapollenites polyformosus , whose parent plant is believed to have favoured moist climates and higher groundwater tables.  相似文献   

Coastal inundation under concurrent mean and extreme sea-level rise in Coral Gables,Florida, USA     

Alarcon  Vladimir J.  Linhoss  Anna C.  Kelble  Christopher R.  Mickle  Paul F.  Sanchez-Banda  Gonzalo F.  Mardonez-Meza  Fernando E.  Bishop  Joseph  Ashby  Steven L. 《Natural Hazards》2022,111(3):2933-2962

Natural Hazards - Southeast Florida (SF) is among the most vulnerable regions to sea-level rise in the United States of America. The consequences associated with sea-level rise (SLR) are already...  相似文献   

Identification of fresh submarine groundwater off the coast of San Diego,USA, using electromagnetic methods     

King  Roslynn B.  Danskin  Wesley R.  Constable  Steven  Maloney  Jillian M. 《Hydrogeology Journal》2022,30(3):965-973

Hydrogeology Journal - Climate change has a pronounced effect on water resources in many semiarid climates, causing populated areas such as San Diego County (USA), to become more vulnerable to...  相似文献   

Effects of Small-Scale Armoring and Residential Development on the Salt Marsh-Upland Ecotone     

Alyssa-Lois M. Gehman  Natalie A. McLenaghan  James E. Byers  Clark R. Alexander  Steven C. Pennings  Merryl Alber 《Estuaries and Coasts》2018,41(1):54-67

Small-scale armoring placed near the marsh-upland interface to protect single-family homes is widespread but understudied. Using a nested, spatially blocked sampling design on the coast of Georgia, USA, we compared the biota and environmental characteristics of 60 marshes adjacent to either a bulkhead, a residential backyard with no armoring, or an intact forest. We found that marshes adjacent to bulkheads were at lower tidal elevations and had features typical of lower elevation marsh habitats: high coverage of the marsh grass Spartina alterniflora, high density of crab burrows, and muddy sediments. Marshes adjacent to unarmored residential sites had higher soil water content and lower porewater salinities than the armored or forested sites, suggesting that there may be increased freshwater input to the marsh at these sites. Deposition of Spartina wrack on the marsh-upland ecotone was negatively related to elevation at armored sites and positively related at unarmored residential and forested sites. Armored and unarmored residential sites had reduced densities of the high marsh crab Armases cinereum, a species that moves readily across the ecotone at forested sites, using both upland and high marsh habitats. Distance from the upland to the nearest creek was longest at forested sites. The effects observed here were subtle, perhaps because of the small-scale, scattered nature of development. Continued installation of bulkheads in the southeast could lead to greater impacts such as those reported in more densely armored areas like the northeastern USA. Moreover, bulkheads provide a barrier to inland marsh migration in the face of sea level rise. Retaining some forest vegetation at the marsh-upland interface and discouraging armoring except in cases of demonstrated need could minimize these impacts.  相似文献   

The New CLOCIT Irradiation Facility for 40Ar/39Ar Geochronology: Characterisation,Comparison with CLICIT and Implications for High‐Precision Geochronology          下载免费PDF全文

Daniel Rutte  Tim A. Becker  Alan L. Deino  Steven R. Reese  Paul R. Renne  Robert A. Schickler 《Geostandards and Geoanalytical Research》2018,42(3):301-307

The Cadmium‐Lined Outer‐Core Irradiation Tube (CLOCIT) is a new irradiation facility for ⁴⁰Ar/³⁹Ar geochronology at the Oregon State University TRIGA^® reactor. We report fluence (i.e., time‐integrated flux) parameters from the first four CLOCIT irradiations and compare them with the existing Cadmium‐Lined Inner‐Core Irradiation Tube (CLICIT). CLOCIT provides an average neutron flux equivalent of 1.45–1.53 × 10^?4 J h^?1; about 55% of CLICIT. Radial fluence gradients were on the order of 0.2–4.2% cm^?1. A planar fit of J‐values results in residuals in the range of uncertainty in the J‐value, but systematic deviations resolve a non‐planar component of the neutron flux field, which has also been observed in CLICIT. Axial neutron fluence gradients were 0.6–1% cm^?1, compared with 0.7–1.6% cm^?1 for the CLICIT. Production rate ratios of interfering reactions were (⁴⁰Ar/³⁹Ar)_K = (4 ± 6) × 10^?4 and (³⁸Ar/³⁹Ar)_K = (1.208 ± 0.002) × 10^?2, (³⁶Ar/³⁷Ar)_Ca =  (2.649 ± 0.014) × 10^?4, (³⁸Ar/³⁷Ar)_Ca =  (3.33 ± 0.12) × 10^?5 and (³⁹Ar/³⁷Ar)_Ca =  (9.1 ± 0.28) × 10^?4, similar to the CLICIT values.  相似文献   

Numerical modeling of the June 24, 2015, Hongyanzi landslide generated impulse waves in Three Gorges Reservoir,China   总被引：1，自引：0，他引：1  

Lili Xiao  Jiajia Wang  Steven N Ward  Lixia Chen 《Landslides》2018,15(12):2385-2398

Subaerial landslides falling into confined water bodies often generate impulsive waves. Damaging landslide tsunamis in Three Gorges Reservoir, China, have struck several times in the last 15 years. On June 24, 2015, a 23?×?10⁴ m³ slope failure occurred on the east bank of the Daning River opposite Wushan Town. The sliding mass intruded into the Three Gorges Reservoir and initiated a reservoir tsunami that resulted in two deaths and significant damage to shipping facilities. A post-event survey revealed the landslide geometry and wave run-up distribution, while an eyewitness video captured most of the landslide motion. Employing these firm constraints, we applied the Tsunami Squares method to simulate the 2015 Hongyanzi landslide and tsunami. The simulation revealed that the landslide experienced a progressive failure in the first few seconds and impacted the water with a maximum velocity of ~?16 m/s. The initial wave propagated to the opposite shore in an arch shape, and the water surface reached a maximum amplitude of ~?11 m near the landslide. Wave amplitude-time curves at four points on the river cross section show that the initial wave reached Wushan town in about 50 s with an average wave velocity of ~?30 m/s. The maximum wave run-ups on the shoreline opposite the landslide are around 6 m and attenuate to less than 1 m beyond 2-km distance. The landslide simulation matches the observed geological profile and the eyewitness video, and the numerical results coincide with the observed wave run-up heights. Nearly 80% of landslide energy is lost due to frictional resistances, but the remaining fraction imparted to the tsunami carried catastrophic consequences to a large region. The numerical results emphasize the efficiency and accuracy of Tsunami Squares method for a “Quick Look” simulation of a potential landslide.  相似文献   

Reactive transport benchmarks for subsurface environmental simulation     

Carl I. Steefel  Steven B. Yabusaki  K. Ulrich Mayer 《Computational Geosciences》2015,19(3):439-443

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