Seasonality and interannual variability of freshwater inflow to a large oligohaline estuary in the Northern Gulf of Mexico     

Y. Jun Xu  Kangsheng Wu 《Estuarine, Coastal and Shelf Science》2006,68(3-4):619

Quantity, timing, duration, and fluctuation of freshwater inflow are important factors affecting the development and health of aquatic and adjacent wetland ecosystems in coastal estuaries. This study assessed six decades of freshwater inflow from the Amite River, Tickfaw River, and Tangipahoa River watersheds to Lake Pontchartrain, a large oligohaline estuary in the Northern Gulf of Mexico, whose flood waters caused recent damage to the city of New Orleans in the aftermath of Hurricane Katrina. By utilizing the long-term (1940–2002) river discharge and climatic data from the three major tributary watersheds, monthly and annual freshwater inflows have been quantified and their spatial and temporal variations have been analyzed. On average, the three rivers discharged (±standard error) 0.27 ± 0.04 km³ freshwater monthly and 3.29 ± 0.15 km³ freshwater annually into the lake estuarine system, with the highest inflow from the Amite River (0.16 ± 0.03 m³ mon⁻¹, and 1.91 ± 0.09 km³ yr⁻¹) and the lowest inflow from the Tickfaw River (0.03 ± 0.00 km³ mon⁻¹, and 0.34 ± 0.02 km³ yr⁻¹). A distinct seasonality was evident with over 69% of the total annual inflow occurring during December and May (wet months) and with a low flow period from August to November (dry months). The monthly inflow during the wet months was positively correlated with the monthly precipitation (r² = 0.64), while the monthly inflow during the dry months was subject to evapotranspiration. Furthermore, the study found a 20-year low flow period from 1954–1973 (2.76 ± 0.24 km³ yr⁻¹) and a 24-year high flow period from 1975–1998 (3.84 ± 0.24 km³ yr⁻¹), coinciding with both the climate variation and population growth in the watersheds.  相似文献   

Geophysical and geochemical observations on actively seeping hydrocarbon gases on the south-eastern Yellow Sea continental shelf   总被引：2，自引：0，他引：2  

K.?S.?JeongEmail author  J.?H.?Cho  S.?R.?Kim  S.?Hyun  U.?Tsunogai 《Geo-Marine Letters》2004,24(1):53-62

In the southeastern Yellow Sea, active seepage of hydrocarbon gases has been observed by high-resolution (3.5 kHz) seismic profiling both in 1987 and 2001, occurring through a large number of plumes from the topmost pre-Holocene sedimentary layer. It is strong enough to compensate for current speed, extending vertically up to the sea surface. The gas seepage often appears to be explosive to form craters and diapirs, although pockmarks are rare due to the redistribution of mobile palimpsest sands. In core-top seawater and sediments, the gases are characterized by high amounts of C₂, homogenous ¹³C₁ values and a large difference (19.7 on average) between ¹³C₁ (–55.2 to –53.6 PDB) and ¹³C₂ (–36.8 to –32.5 PDB) values. The gases are considered to be generated with a smaller amount of C₁ at the early thermal cracking stage of labile source materials, after which the C₂ gas is enriched in ¹³C by diffusion or biological alternation at the generation or accumulation site. The homogenous ¹³C₁ values may be one of the geochemical characteristics of gases acquired at depth which are less altered in the case of rapid diffusive gas migration to the seafloor.  相似文献   

A densely sampled core and climate variable aliasing     

C.?WunschEmail author  D.?E.?Gunn 《Geo-Marine Letters》2003,23(1):64-71

Undersampled records are susceptible to aliasing, in which a high frequency appears incorrectly as a lower one. We study the sampling requirements in a core taken from Rockall Trough using bulk density, P-wave velocity, and magnetic susceptibility as measured on an automated system. At 2-cm spacing (approximately 33 years in this core), all variables show a characteristic red-noise behavior, but with a spectral slope that is sufficiently weak so that significant aliasing appears to be present. P-wave velocity shows the largest potential corruption, probably owing to the weaker spatial averaging present in the sensor. Approximately 50% of the apparent low-frequency energy is aliased in all variables at some frequencies in both quiet and active regions of the record. In this core, a sampling interval of 0.2 cm appears to be "safe" in both active and quiet portions of the core, aliasing little or no energy, except in the P-wave record. For cores of different duration, sampling interval, and measurement type, the considerations will be identical, the importance of the problem depending directly upon the shape of the overall spectrum describing the entire frequency (wavenumber) range of physical variability.  相似文献   

Sedimentology of a subtidal,tide-dominated sand body in the Yellow Sea,southwest Korea     

George DeVries Klein  Y.A. Park  J.H. Chang  C.S. Kim 《Marine Geology》1982,50(3):221-240

Odanam Satoe, a subtidal, tide-dominated sand body in the Yellow Sea, Korea, is linear in plan and asymmetrical in cross-section. It consists of fine- to medium-grained, well-sorted subangular sand. Bedforms consist of high-amplitude (1–2 m) sandwaves on the lower flanks of the gentler-sloping bar surface, and medium-amplitude (0.5-1 m) sandwaves on the sand body trough adjoining the steeper face, the bar crest and shallower parts of the gently sloping bar surface. Bedforms are absent on the relatively steeper bar surface, which is characterized by 2° slopes. Bedform orientation on the gentler slope is oblique by 30° to the bar crest, parallel to the sand-body crest on the crest itself, and opposite to the steeper sand-body face in the trough below the steeper slope of the bar.Bottom current velocity data show that tidal currents are semi-rotary with a flood time—velocity asymmetry over the gentler slope, and ebb time—velocity asymmetry over the steeper slope during most of the tidal cycle. Tidal-current flow parallels bar elongation over the steeper slope, whereas over the gentler slope, tidal-current flow is directed at 30° to the bar crest and changes to normal to the crest one hour prior to low tide. Bedform orientation mapped with side-scan sonar shows agreement with these flow directions.Sand dispersal around the sand body is controlled by time—velocity asymmetry and partial rotary flow directions of tidal currents. This circulation causes not only a trapezoidal mode of grain dispersal, but also westerly migration of the sand body documented from comparative bathymetric surveys in 1964 and 1980.  相似文献   

Wind-induced eddy motion in the lower St. Lawrence Estuary     

G. Mertz  V.G. Koutitonsky  Y. Gratton  M.I. El-Sabh 《Estuarine, Coastal and Shelf Science》1992,34(6)

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Algorithm for non-hydrostatic dynamics in the Regional Oceanic Modeling System     

Y. Kanarska  A. Shchepetkin  J.C. McWilliams 《Ocean Modelling》2007,18(3-4):143-174

A non-hydrostatic algorithm for the Regional Oceanic Modeling System (ROMS) is proposed. It is based on a decomposition technique for hydrostatic and non-hydrostatic pressure. The algorithm has a pressure-correction scheme with split-explicit time-stepping for baroclinic and barotropic vertical modes with a free surface. The algorithm implementation requires solving a Poisson equation for a non-hydrostatic pressure that has a non-symmetric matrix in discrete form. The efficiency of a different class of solvers and preconditioners were tested. The algorithm is successfully implemented with several examples where non-hydrostatic effects are important. These include standing external gravity waves; strongly nonlinear internal wave generation and transformation; stratified shear instability and its associated mixing; and nonlinear internal tidal generation over a ridge. The corresponding changes in the pre-processing and post-processing infrastructure in the existing hydrostatic ROMS code were performed to implement parallel elliptic solvers and a new set of dynamical equations.  相似文献   

Processes Causing the Temporal Changes in Si/N Ratios of Nutrient Consumptions and Export Flux during the Spring Diatom Bloom     

Naoki?YoshieEmail author  Yasuhiro?Yamanaka 《Journal of Oceanography》2005,61(6):1059-1073

Two processes are generally explained as causes of temporal changes in the stoichiometric silicon/nitrogen (Si/N) ratios of sinking particles and of nutrient consumption in the surface water during the spring diatom bloom: (1) physiological changes of diatom under the stress of photosynthesis of diatom and (2) differences of regeneration between silicon and nitrogen. We investigated which process plays an important role in these changes using a one-dimensional ecosystem model that explicitly represents diatom and the other non-silicious phytoplankton. The model was applied to station A7 (41°30′ N, 145°30′ E) in the western North Pacific, where diatom regularly blooms in spring. Model simulations show that the Si/N ratios of the flux exported by the sinking particles at 100 m depth and of nutrient consumptions in the upper 100 m surface water have their maxima at the end of the spring diatom bloom, the values and timings of which are significantly different from each other. Analyses of the model results show that the differences of regeneration between silicon and nitrogen mainly cause the temporal changes of the Si/N ratios. On the other hand, the physiological changes of diatoms under stress can hardly cause these temporal changes, because the effect of the change in the diatom's uptake ratio of silicon to nitrogen is cancelled by that in its sinking rate.  相似文献   

A Zonal Pathway for NADW in the South Atlantic     

Nelson?G.?HoggEmail author  Andreas?M.?Thurnherr 《Journal of Oceanography》2005,61(3):493-507

Several large deployments of neutrally buoyant floats took place within the Antarctic Intermediate (AAIW), North Atlantic Deep Water (NADW), and the Antarctic Bottom Water (AABW) of the South Atlantic in the 1990s and a number of hydrographic sections were occupied as well. Here we use the spatially and temporally averaged velocities measured by these floats, combined with the hydrographic section data and various estimates of regional current transports from moored current meter arrays, to determine the circulation of the three major subthermocline water masses in a zonal strip across the South Atlantic between the latitudes of 19°S and 30°S. We concentrate on this region because the historical literature suggests that it is where the Deep Western Boundary Current containing NADW bifurcates. In support of this notion, we find that a net of about 5 Sv. of the 15–20 Sv that crosses 19°S does continue zonally eastward at least as far as the Mid-Atlantic Ridge. Once across the ridge it takes a circuit to the north along the ridge flanks before returning to the south in the eastern half of the Angola Basin. The data suggest that the NADW then continues on into the Indian Ocean. This scheme is discussed in the context of distributions of dissolved oxygen, silicate and salinity. In spite of the many float-years of data that were collected in the region a surprising result is that their impact on the computed solutions is quite modest. Although the focus is on the NADW we also discuss the circulation for the AAIW and AABW layers.  相似文献   

Food and feeding ecology of juvenile albacore, Thunnus alalunga, off the Bay of Biscay: a case study     

Pusineri  C.; Vasseur  Y.; Hassani  S.; Meynier  L.; Spitz  J.; Ridoux  V. 《ICES Journal of Marine Science》2005,62(1):116-122

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The fate of dumped sediments monitored by a high-resolution multibeam echosounder system,Weser Estuary,German Bight     

Claudia?WienbergEmail author  Jens?Dannenberg  Dierk?Hebbeln 《Geo-Marine Letters》2004,24(1):22-31

With the development of high-resolution multibeam echosounder systems (MBES) for surveying shallow-water areas a new tool is available to monitor rapid changes in seabed morphology as, e.g., caused by the dumping of dredge spoil in coastal waters. In this study, four data sets of repeated bathymetric surveys with a MBES were processed and analyzed. The data were collected in a 1.94-km² dumping site in the outer Weser Estuary (German Bight). Between June and December 1998, 2.6 million m³ of dredged sediment were deposited there. The bathymetric maps generated in the course of this study reveal features such as subaqueous dunes, scour holes, and mounds of dumped dredge spoil. The mean water depth decreased by about 1 m during the dumping period. Furthermore, difference grids showing changes in sediment volume allowed a calculation of the sediment budget for the monitored area. After a time period of only 5 months, 0.5 million m³ of the originally dumped 2.6 million m³ of dredge spoil had already been removed from the dumping site.  相似文献