Direct measurements of diapycnal mixing in a fjord reach—Puget Sound's Main Basin     

J. B. Mickett  M. C. Gregg  H. E. Seim   《Estuarine, Coastal and Shelf Science》2004,59(4):539

In the spring of 1988, time series of microstructure and ADCP current profiles were collected at four locations in the North Main Basin of Puget Sound, Washington. Depth and time averages of diapycnal diffusivity at the four stations (1.8−67.0×10⁻⁴ m² s⁻¹) were one to three decades above typical open-ocean thermocline levels. The buoyancy frequency-squared N² was near open-ocean levels, but unlike the open-ocean where N²S², finescale shear-squared S² was three to six times N² over significant portions of the water column at two of the stations. The time and space mean of all measurements ( ) is close to inferred vertical eddy diffusivity from a primitive equation model for Puget Sound (K_z=3×10⁻³ m² s⁻¹) (J. Geophys. Res. 96 (1991) 16779). Large time and space variability of K_ρ was found, with differences of inter-station, depth–time means over one decade. A simple scaling argument using the observed K_ρ suggests significant exchange of mass between the layers of the subtidal flow over the basin's residence time. Additionally, measurements show that local mixing may be comparable to volume-weighted sill mixing in modifying the Main Basin's stratification. Both are contrary to the “advective reach” simplification of fjord dynamics. The mixing levels were dominated by the passage of a mid-depth, southward-flowing density intrusion and what we interpret as a strongly advected, non-linear internal tide. These mechanisms elevated profile-averaged K_ρ by more than 10 times background levels, with sustained patches of K_ρ≥1×10⁻² m² s⁻¹. Critical 8-m gradient Richardson numbers (Ri₈<0.25) matching regions of overturns (>20 m) and strong turbulence suggest that shear instabilities dominated the turbulence production, though there was support for double-diffusive convection in the warm core of the density intrusion.  相似文献   

界面附近目标对柱面波的声散射     

徐海亭 《海洋与湖沼》1996,27(6):612-618

运用表面ｈｅｌｍｈｏｌｔｚ积分公式研究柱目标位于不同阻抗界面附近的声散射。根据Ｇｒｅｅ函数的定义，在两维空间中，应用Ｆｏｕｒｉｅｒ变换方法，将柱面波展开成平面波的迭加，并用越过法求解柱面波在界面上的声反射；同时定义扩展反射系数描述柱面波在平面上的反射小大，从而获得二维半无限空间Ｇｒｅｅｎ函数的表达式。  相似文献   

Temporal variations in the concentration and settling flux of carbon and phytoplankton pigments in a deep fjordlike estuary     

Edward T. Baker  Richard A. Feely  Michael R. Landry  Marilyn Lamb 《Estuarine, Coastal and Shelf Science》1985,21(6):859-877

The weekly mass flux of C and phytoplankton pigments at five depths in the main basin of Puget Sound, a deep (200 m) fjordlike estuary, was sampled for a year with moored sequentially-sampling sediment traps. Flux measurements were compared with weekly samples of suspended pigments in the euphotic zone and bi-monthly samples of total suspended matter and particulate C throughout the water column at the mooring site.Seasonal changes in the total mass flux at all depths were small; instead, physical (river runoff, bottom resuspension) and biological (phytoplankton blooms) events caused occasional sharp increases on a weekly scale. The dry weight concentration of pigments in the trap samples mirrored the concentration of pigments in the euphotic zone suspended matter, increasing from 0·01% in winter to a maximum of 0·65% in late summer. Bloom-induced changes in the pigment concentration were observed almost simultaneously in the euphotic zone and in the traps to a depth of 160 m, indicating a rapid vertical transfer of surface-originating particles by organic aggregates. In contrast to the strong seasonal signal in the pigment concentration, C concentration varied by only a factor of three during the year.The seasonal trend of C/pigment ratios in the C flux arises from at least two sources: (1) a balance between terrestrial sources of C during the high-runoff winter season and in-situ primary production in spring and summer, and (2) cycling of C through the zooplankton population. Budget calculations suggest that the loss of primary-produced C and pigment from the euphotic zone by settling is 5% regardless of season. On an annual basis, this C flux (16 g m⁻²) is sufficient to support previously measured values of benthic aerobic respiration at the mooring site. To account for other C sinks such as burial, predation and chemical oxidation, however, terrestrial C sources and alternate transport pathways, such as vertical advection and sediment movement down the steep basin walls, are necessary.  相似文献   

Optimal localization of a seafloor transponder in shallow water using acoustic ranging and GPS observations   总被引：2，自引：0，他引：2  

Hsin-Hung Chen  Chau-Chang Wang 《Ocean Engineering》2007,34(17-18):2385-2399

This study utilized circular and straight-line survey patterns for acoustic ranging to determine the position of a seafloor transponder and mean sound speed of the water column. To reduce the considerable computational burden and eliminate the risk of arriving at a local minimum on least-squares inversion, the position of a seafloor transponder was estimated by utilizing optimization approaches. Based on the implicit function theorem, the Jacobian for this inverse problem was derived to investigate the constraints of employing circular and straight-line survey patterns to estimate the position of a transponder. Both cases, with and without knowledge of the vertical sound speed profile, were considered. A transponder positioning experiment was conducted at sea to collect acoustic and GPS observations. With significant uncertainties inherent in GPS measurements and the use of a commercial acoustic transponder not designed for precise ranging, experimental results indicate that the transponder position can be estimated accurately on the order of decimeters. Moreover, the mean sound speed of the water column estimated by the proposed optimization scheme is in agreement with that derived from conductivity, temperature, and density (CTD) measurements.  相似文献   

Operational prediction of acoustic properties in the ocean using multi-model statistics     

M. Rixen  E. Ferreira-Coelho 《Ocean Modelling》2006,11(3-4):428-440

Super-ensemble (SE) multi-model forecasts optimize local combination of individual models which is superior to individual models because they allow for local correction and bias removal. Multi-model statistics are applied to optimize the forecast skills from ocean models with different resolution or configuration, run operationally during the MREA04 field experiment off the West coast of Portugal. The method, based on a training/forecast cycle uses linear regression optimization. The performance and the limitations of the different super-ensemble combinations and the individual models are discussed. The SE method is shown to reduce errors in sound velocity significantly for 24 h forecasts.  相似文献   

A box model of Puget Sound   总被引：1，自引：0，他引：1  

Peter Hamilton  John T. Gunn  Glenn A. Cannon 《Estuarine, Coastal and Shelf Science》1985,20(6):673-692

A classical two-layer box model has been used to calculate volume transports and vertical exchange coefficients for the Main Basin of Puget Sound. High river flow (January–February) and low flow (August–September) calculations, using salinity and runoff observations, show that basically two estuarine types exist within the basin under both flow conditions. Admiralty Inlet, the north entrance to the Main Basin, is similar to a partially mixed estuary with vigorous tidal mixing, so that horizontal and vertical salinity gradients are similar in winter and late summer. Within the deep main basin, two layer transports are proportional to salinity stratification and the vertical exchanges are low. Calculated summer transports are about a factor of two smaller than winter transports for the Main Basin. Model transports agree quite well with daily net transports estimated from current meters. Flushing times calculated by the model also agree with volume replacement times calculated using current meter data and by methods using oxygen deficits in the lower layer.  相似文献   

A coming boom in commercial shipping? The potential for rapid growth of noise from commercial ships by 2030     

《Marine Policy》2016

Ocean noise levels are thought to be increasing as a result of major growth in global shipping activity, but data quantifying those changes are limited in space and time. As an alternative approach, this study examines the current and future maximum noise capacity of three segments of the global commercial shipping fleet: container ships, oil tankers, and bulk carriers. It shows that continued growth in the number of ships, the quantity of goods carried and the distances traveled could increase the maximum noise capacity of the global shipping fleet by up to a factor of 1.9 by 2030, with major growth in particular in the container and bulk carrier segments. Thus, in the absence of operational or manufacturing changes to such ships, the contribution of commercial shipping to ambient ocean noise levels can be expected to dramatically increase.  相似文献   

Perfluorinated compounds in the surface waters of Puget Sound,Washington and Clayoquot and Barkley Sounds,British Columbia     

《Marine pollution bulletin》2014,78(1-2):173-180

Perfluorinated compounds (PFCs) are persistent organic contaminants detected in various environmental matrices including sediment, air, biota, and water. The objectives of this study was to evaluate the occurrence of these contaminants within the surface waters of the Pacific Northwest region and through relative concentrations and ratios, to assess their possible sources. Surface waters were extracted and analyzed by liquid chromatography tandem mass spectrometry (LCMSMS). Perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) were the most commonly detected PFCs. Total PFC concentrations detected ranged from 1.5 to 41 ng L-1. Surprisingly, levels of PFCs in the more urbanized Puget Sound waters were comparable to those measured from the more rural region of Clayoquot and Barkley Sounds in British Columbia. The ratio of PFHpA/PFOA were also similar between the two regions, suggesting that the burden of PFCs throughout the region results from direct input from regional sources.  相似文献   

Marine species mortality in derelict fishing nets in Puget Sound, WA and the cost/benefits of derelict net removal   总被引：1，自引：0，他引：1  

Kirsten V.K. Gilardi  Daphne Carlson-Bremer  Kyle Antonelis  Tom Cowan 《Marine pollution bulletin》2010,60(3):376-382

Derelict fishing gear persists for decades and impacts marine species and underwater habitats. Agencies and organizations are removing significant amounts of derelict gear from marine waters in the United States. Using data collected from repeated survey dives on derelict gillnets in Puget Sound, Washington, we estimated the daily catch rate of a given derelict gillnet, and developed a model to predict expected total mortality caused by a given net based on entanglement data collected upon its removal. We also generated a cost:benefit ratio for derelict gear removal utilizing known true costs compared to known market values of the resources benefiting from derelict gear removal. For one study net, we calculated 4368 crab entangled during the impact lifetime of the net, at a loss of $19,656 of Dungeness crab to the commercial fishery, compared to $1358 in costs to remove a given gillnet, yielding a cost:benefit ratio of 1:14.5.  相似文献   

Derelict fishing nets in Puget Sound and the Northwest Straits: Patterns and threats to marine fauna     

Thomas P. Good  Jeffrey A. June  Ginny Broadhurst 《Marine pollution bulletin》2010,60(1):39-50

Derelict fishing gear remains in the marine environment for years, entangling, and killing marine organisms worldwide. Since 2002, hundreds of derelict nets containing over 32,000 marine animals have been recovered from Washington’s inland waters. Analysis of 870 gillnets found many were derelict for years; most were recovered from northern Puget Sound and high-relief rocky habitats and were relatively small, of recent construction, in good condition, stretched open, and in relatively shallow water. Marine organisms documented in recovered gillnets included 31,278 invertebrates (76 species), 1036 fishes (22 species), 514 birds (16 species), and 23 mammals (4 species); 56% of invertebrates, 93% of fish, and 100% of birds and mammals were dead when recovered. For all taxa, mortality was generally associated with gillnet effectiveness (total area, age and condition, and suspension in the water). Mortality from derelict fishing gear is underestimated at recovery and may be important for species of economic and conservation concern.  相似文献