A Zonal Pathway for NADW in the South Atlantic

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.     

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

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.     

Size-Fractionated Primary Production Estimated by a Two-Phytoplankton Community Model Applicable to Ocean Color Remote Sensing

In order to estimate primary production from ocean color satellite data using the Vertical Generalized Production Model (VGPM; Behrenfeld and Falkowski, 1997), we propose a two-phytoplankton community model. This model is based on the two assumptions that changes in chlorophyll concentration result from changes of large-sized phytoplankton abundance, and chlorophyll specific productivity of phytoplankton tends to be inversely proportional to phytoplankton size. Based on the analysis of primary production data, P _opt ^B , which was one parameter in the VGPM, was modeled as a function of sea surface temperature and sea surface chlorophyll concentration. The two-phytoplankton community model incorporated into the VGPM gave good estimates in a relatively high productive area. Size-fractionated primary production was estimated by the two-phytoplankton community model, and P _opt ^B of small-sized phytoplankton was 4.5 times that of large-sized phytoplankton. This result fell into the ranges observed during field studies.     

Long-term Sensor Drift Found in Recovered Argo Profiling Floats

We recovered three Argo profiling floats after 2 to 2.5 years of operation, and recalibrated their temperature, conductivity, and pressure sensors. The results demonstrate that these floats exhibited a significant drift in salinity of −0.0074 to −0.0125, primarily due to the conductivity sensor drift. Combined with the recalibration result for another previously recovered float, the indication is that the negative salinity drift increases nearly in proportion to the operating period of floats. The increasing rate is −0.0041 (±0.0015) year⁻¹, which yields a salinity drift of −0.016 (±0.006) for the expected float lifetime of four years. The present result suggests that reducing the float surfacing time would improve the accuracy of the salinity measurements.     

印度东南部海岸拉梅斯沃勒姆滨外保克湾底层水特征对底栖有孔虫的影响

有孔虫生活在海洋和半咸水环境。底栖有孔虫的存在很大程度上受物理因素（深度、温度、光量、水体扰动）、化学因素（盐度、溶解氧和可用元素）和生物因素（食物供给量和底层沉积物特征）的制约。研究人员对印度东、西岸现代底栖有孔虫生态学和分布状态进行了研究。Ｎａｉｄｕ等在对Ｖｉｓａｋｈａｐａｔｎａｍ港复合体有孔虫进行分析后提出 ,可以将有孔虫作为海洋污染的指示物。ＳｒｅｅｎｉｖａｓａＲａｏ等采用Ｑ模式系数分析对尼赞伯德讷姆湾有孔虫的分布进行了研究 ,确认此区域存在４种组合 ,受不同环境条件的影响。Ｋｈａｒｅ等对门格…     

Experimental study on loss factor for corrugated plates by bandwidth method

The material loss factor for technically orthotropic plates was measured by half-power bandwidth method. Rectangular and trapezoidal corrugated plates of steel were considered. A simple isotropic steel plate was also considered for comparison of the results. The concept of single degree of freedom system was adopted. The tests were undertaken at very low frequency range (0–100) Hz. The plate models were suspended freely with two wires to minimize or prevent excessive extraneous energy dissipation. Out of plane point force, random in nature was applied to the top middle of the plates and the responses were measured from the middle point of the plates by FFT analyzer using miniature small mass accelerometer as sensor. The aim of these tests is to investigate the effects of bending rigidity and mode orders over material loss factor. The values of estimated modal damping loss factors are compared and tabulated for the plates models considered. Natural frequencies of some of the initial modes of the plates are also presented.It is observed that the higher the value of bending rigidity of the plates, the larger the values of loss factor of it. There was a significant increase in value of loss factor in corrugated plates to that of the isotropic plate.     

Simple determination of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) using solid-phase microextraction and gas chromatography-mass spectrometry

Solid-phase microextraction (SPME) is a simple, sensitive and less destructive method for the determination of dimethylsulfide (DMS) in seawater. Combined with detection by gas chromatography-mass spectrometry (GC-MS), the method had sufficient sensitivity (minimum detectable concentration of DMS was 0.05 nM), and practical levels of reproducibility (relative standard deviation ≤7%) and linearity (r ² > 0.995) over a wide concentration range (0.5 to 910 nM). The protocol developed was applied to a Sagami Bay water sample to determine concentrations of DMS and DMSP, and in situ DMSP-lyase activity.     

Eddy Shedding from the Kuroshio Bend at Luzon Strait

TOPEX/POSEDIENT-ERS satellite altimeter data along with the mean state from the Parallel Ocean Climate Model result have been used to investigate the variation of Kuroshio intrusion and eddy shedding at Luzon Strait during 1992–2001. The Kuroshio penetrates into the South China Sea and forms a bend. The Kuroshio bend varies with time, periodically shedding anticyclonic eddies. Criteria of eddy shedding are identified: 1) When the shedding event occurs, there are usually two centers of high Sea Surface Height (SSH) together with negative geostrophic vorticity in the Kuroshio Bend (KB) area. 2) Between the two centers of high SSH there usually exists positive geostrophic vorticity. These criteria have been used to determine the eddy shedding times and locations. The most frequent eddy shedding intervals are 70, 80 and 90 days. In both the winter and summer monsoon period, the most frequent locations are 119.5°E and 120°E, which means that the seasonal variation of eddy shedding location is unclear.     

Geodynamics of the deep sedimentary basin of the Caspian Sea region: paragenetic correlation of seismicity and mud volcanism

In this paper we analyze seismic regime and earthquake depth distribution and correlation of seismicity and mud volcanism in the Azerbaijan and the Caspian Sea region. For the present region we have calculated accurate source locations, seismic activity, earthquake repetition and released earthquake energy parameters. It is shown that the active tectonic processes in the region are concentrated within the thick sedimentary cover that we consider as a general source of contemporary stress and a main structural element responsible for the origin of regional earthquakes. The correlation of seismicity and mud volcanism is of paragenetic character.     

Comparison of TOPEX/POSEIDON Altimeter Derived Wind Speed and Wave Parameters with Ocean Buoy Data in the North Indian Ocean

Results of comparison exercises carried out between the state-of-the-art TOPEX/POSEIDON altimeter-derived ocean surface wind speed and ocean wave parameters (significant wave height and wave period) and those measured by a set of ocean data buoys in the North Indian Ocean are presented in this article. Altimeter-derived significant wave height values exhibited rms deviation as small as ±0.3 m, and surface wind speed of ±1.6 m/s. These results are found consistent with those found for the Pacific Ocean. For estimation of ocean wave period, the spectral moments-based semiempirical approach, earlier applied on GEOSAT data, was extended to TOPEX/POSEIDON. For this purpose, distributions of first four years of TOPEX/POSEIDON altimeter data and climatology over the North Indian Ocean were analyzed and a new set of coefficients generated for estimation of wave period. It is shown that wave periods thus estimated from TOPEX/POSEIDON data (for the subsequent two years), when compared with independent data set of ocean data buoys deployed in the North Indian Ocean, exhibit improved accuracy (rms ~ ±1.4 nos) over those determined earlier with GEOSAT data.