A case study of a modified gravity type cage and mooring system using numerical and physical models

A modified gravity-type cage, developed by SADCO Shelf Ltd., was examined using numerical and physical models to determine if the cage and mooring system is suitable for an exposed site south of the Isles of Shoals, NH. The 3000-m/sup 3/ SADCO Shelf Submersible Fish Cage has angled stays between the upper framework and the ballasted bottom rim (in addition to net) to resist the horizontal shear deformation. The mooring system consists of three legs-each made up of a taut vertical chain and an angled rope, both leading to deadweight anchors. Normalized response amplitudes (response amplitude operators) were found for motion response in heave, surge and pitch, and load response in the anchor and bridle lines, in regular (single frequency) waves. In addition, a stochastic approach was taken to determine the motion and load transfer functions in random waves using a spectrum representative of seas at the selected site. In general, the system motion had a highly damped response, with no resonant peaks within the wave excitation range of 0.05 to 0.45 Hz. The anchor line force response was at all frequencies below 5 kN per meter of wave amplitude. The physical model tests showed consistently more conservative (larger) results compared to those for the numerical model.     

Using ocean ambient noise for array self-localization and self-synchronization

Estimates of the travel times between the elements of a bottom hydrophone array can be extracted from the time-averaged ambient noise cross-correlation function (NCF). This is confirmed using 11-min-long data blocks of ambient noise recordings that were collected in May 1995 near the southern California coast at an average depth of 21 m in the 150-700 Hz frequency range. Coherent horizontal wavefronts emerging from the time derivative of the NCF are obtained across the array's aperture and are related to the direct arrival time of the time-domain Green's function (TDGF). These coherent wavefronts are used for array element self-localization (AESL) and array element self-synchronization (AESS). The estimated array element locations are used to beamform on a towed source.     

Surface circulation of the Levantine Basin: Comparison of model results with observations

The eastern Mediterranean (Levantine Basin) hydrography and circulation are investigated by comparing the results of a high-resolution primitive equation model with observations. After a 10-year integration, the model is able to reproduce the major water masses and the circulation patterns of the eastern Mediterranean. Comparisons with the POEM hydrographical observations show good agreement. The vertical distribution of the water masses matches that of the observations quite well in terms of monthly mean. The model surface circulation is in agreement with circulation schemes derived from recent observations. Some well-known mesoscale features of the upper thermocline circulation are also realistically reproduced. In agreement with satellite observations, the model shows that high-energy mesoscale eddies dominate the upper thermocline circulation in the southern and the central parts of the Levantine Basin. Most of the Atlantic Water follows the north African coast and forms a strong coastal jet near the Libyan coast rather than forming the Mid-Mediterranean Jet described by several authors. The sub-basin circulation shows a strong seasonal signal. A strong and stable current flows along the isobaths in winter, becoming weaker and with more meanders in summer. The mesoscale eddies throughout the whole basin are more energetic in summer than in winter.     

Multi-decadal synthesis of benthic–pelagic coupling in the western arctic: Role of cross-shelf advective processes

Using geographic information systems (GIS) software and geostatistical techniques, we utilized three decades of water-column chlorophyll a data to examine the relative importance of autochthonous versus allochthonous sources of reduced carbon to benthic communities that occur from the northern Bering to the eastern Beaufort Sea shelf. Spatial trend analyses revealed areas of high benthic biomass (>300 g m⁻²) and chlorophyll (>150 mg m⁻²) on both the southern and northern Chukchi shelf; both areas are known as depositional centers for reduced organic matter that originates on the Bering Sea shelf and is advected northward in Anadyr and Bering shelf water masses. We found a significant correlation between biomass and chlorophyll a in the Chukchi Sea, reflective of the strong benthic–pelagic coupling in a system that is utilized heavily by benthic-feeding marine mammals. In contrast, there was no significant correlation between biomass and chlorophyll in the Beaufort Sea, which by comparison, is considerably less productive (biomass and chlorophyll, <75 g m⁻² and <50 mg m⁻², respectively). One notable exception is an area of relatively high biomass (50–100 g m⁻²) and chlorophyll (80 mg m⁻²) near Barter Island in the eastern Beaufort Sea. Compared to other adjacent areas in the Beaufort Sea, the chlorophyll values in the vicinity of Barter Island were considerably higher and likely reflect a long-hypothesized upwelling in that area and close coupling between the benthos and autochthonous production. In the Bering Sea, a drop in benthic biomass in 1994 compared with previous measurements (1974–1993) may support earlier observations that document a decline in biomass that began between the 1980s and 1990s in the Chirikov Basin and south of St. Lawrence Island. The results of this study indicate that the benthos is an excellent long-term indicator of both local and physical advective processes. In addition, this work provides further evidence that secondary production on arctic shelves can be significantly augmented by reduced carbon advected from highly productive adjacent shelves.     

三种常用声速算法的比较

在近几年的西太平洋调查中使用了SV Plus声速测量仪,共获取了46个站点的声速剖面,并基于同步观测的CTD数据,利用3种常用的声速算法计算了这些站点的声速剖面。所有这些站点的测深度均超过1500m,而且调查时间为3个不同的季节。CTD数据计算得到的声速剖面与声速测量仪器观测的声速剖面的比较表明,在三种算法中,Chen和Millero算法在积分平均意义上是最好的。当定点比较时,在水深大于800m或者小于200m的范围内,Wilson算法较好;在其他水深范围内,Chen和Millero的算法的计算结果和实际测量结果较为一致。     

海洋监测即时信息服务的设计与实现

提出了海洋监测即时服务的框架,并对该框架下的海洋监测即时服务应用系统的设计概要、系统组成和功能做了介绍。依据该框架研发即时服务应用系统在多个台站和终端用户得到应用,系统运行良好,为海洋监测信息的即时服务提供了保障。     

北海狮水下声信号类型分析

以水族馆内圈养的北海狮为研究对象,利用长达29 h的连续被动声学观测数据,对北海狮水下声信号类型进行了研究。共检测出22 689个水下声信号,对时长、最小频率、最大频率和峰值频率这4个声学参数采用聚类分析方法将信号分为10种类型:单脉冲(SP)、哨声(WS)、咕咕声(GG)、咚咚声(DS)、狗吠声(BK)、吼叫声(WY)、嗡嗡声(BZ)、撞击声(BG)、单频声(SF)以及咩咩声(BT)。该分类方式涵盖了北海狮92.6%的水下发声。北海狮水下声信号时长的均值为5~1 244 ms,峰值频率一般小于10 kHz。10种类型信号的占比各有不同,BK,BT和BG信号的比例较高;SP,WS和BZ信号的比例次之;DS,WY,SF和GG信号的比例较低。对北海狮水下声信号类型的分析能帮助了解北海狮的声行为特征,对野外北海狮的声学观测具有重要的指导价值。