Tidal eddies in a semi-enclosed basin: a model study

A modeling study has been carried out to support a Marine Management Plan for the Gulf of Kachchh, India and here the hydrodynamic part of the programme is described. The hydrodynamic model accurately predicts the tides and tidal currents present in the Gulf and these have been validated with the measured data, albeit at only a few locations. The time averaged residual currents obtained from the model for one lunar cycle clearly reproduce the complex, small-scale, topographically induced flows with several eddies. The existence of a dynamic barrier along Sikka-Mundra section, which divides the Gulf into two distinct dynamic systems, is very evident. The model is further used to predict the movement of surface floating particles launched at different locations in the Gulf, as an aid to determining floating pollutants. The results indicate that industries discharging wastes upstream of the barrier should use extreme caution, as these will remain in the vicinity for at least one lunar cycle.     

The Feeding Apparatus in four Pacific Tube Blennies (Te/eos fei: Chaenopsidae):

Abstract. Tube blennies ( Chaenopsidae ) have the largest relative mouth size compared with other blennioids. Their peculiar oral jaw apparatus may be interpreted as adaptation towards opportunistic feeding, making a wide spectrum of prey types and sizes accessible for these "hemisessile" fishes.
Three sympatric species of Gulf of California Acanthemblemaria show different, though overlapping habitat and microhabitat utilization, but are nearly identical in feeding. Accordingly, sizes and shapes of the oral jaw apparati are very similar in the species under consideration. Possible reasons for this apparent lack of ecomorphological divergence are discussed.     

Foldbelts with early salt withdrawal and diapirism: Physical model and examples from the northern Gulf of Mexico and the Flinders Ranges, Australia

A physical experiment shows that shortening applied to existing diapirs and minibasins produces anomalous structural styles that are unlike those of more typical foldbelts. Strong minibasins remain largely undeformed while weak diapirs localize contractional strain. Short diapirs form the cores to folds and thrusted folds, whereas tall diapirs are squeezed and often welded, commonly leading to the extrusion of allochthonous material. Key features of the model are observed in real examples. In the northern Gulf of Mexico passive margin, minibasins were originally separated by a polygonal pattern of deep salt ridges, with diapirs located at ridge intersections. Gravity spreading resulted in squeezed diapirs (and associated allochthonous salt) connected by variably oriented contractional, extensional, and strike-slip structures. In the Flinders Ranges convergent-margin foldbelt of South Australia, preexisting diapirs were squeezed, welded, and thrusted, with anticlines plunging away in multiple directions, so that minibasins are surrounded by highly variable structures. A different geometry is observed in La Popa Basin, Mexico, where squeezing of a linear salt wall produced a vertical weld with diapirs at the terminations, rather than the culmination. In all areas, foldbelt geometries are strongly influenced by the preestablished salt-minibasin architecture.     

北部湾潮汐潮流的三维数值模拟

基于二阶湍流闭合模型计算涡动粘性系数的POM三维水动力模式,采用细网格,考虑6个岛屿、海底摩擦系数进行划片取值,模拟北部湾潮汐潮流.所得潮汐调和常数与81个实测站比较,绝对平均误差:K₁分潮振幅为46cm,迟角为9°;O₁分潮振幅为56cm,迟角为7°;M₂分潮振幅为62cm,迟角为15°.由模拟结果分析出该海区潮汐、潮流、余水位和潮余流,以及水平速度垂直分布等特征.     

Benthic Denitrification in the Gulf of Bothnia

Denitrification was measured over an 8-month period in the Bothnian Bay and the Bothnian Sea, the two northernmost basins of the Baltic Sea. The recorded rates varied between 0 and 0·94 mmol N m⁻²day⁻¹. In the Bothnian Sea, a seasonal pattern could be discerned with high rates in spring, no rate in summer and a moderate rate in winter. In the Bothnian Bay, no such seasonality was observed. It is suggested that denitrification in the Gulf of Bothnia is regulated by sediment nitrification. Calculation of annual mean rates of denitrification gave that the amount of nitrogen consumed by denitrification corresponded to 1·45×10⁴tons N year⁻¹for the Bothnian Bay and 3·45×10⁴tons N year⁻¹for the Bothnian Sea. A comparison with total N input (river runoff, point sources and atmospheric deposition) to the two basins showed that the proportion of N removed through denitrification amounted to 23% for the Bothnian Bay and 31% for the Bothnian Sea.     

Plio-Pleistocene microtephra in DSDP site 231, Gulf of Aden

We reconstruct a Plio-Pleistocene microscopic tephrostratigraphy for DSDP Site 231 in the Gulf of Aden. Systematic microtephrostratigraphy increases the potential for identifying tephra horizons for regional stratigraphic correlation and age control, as well as providing information about eruptive histories. Microtephra reveal three main pulses of volcanism c. 4.0–3.2 Ma, 2.4 Ma and 1.7–1.3 Ma, corresponding to peaks in volcanic activity recorded in the East African Rift System. Previous studies of DSDP Site 231 have reported six visible tephra horizons (up to 25 cm thick) with geochemical compositions matching East African tuffs. We find 68 additional microtephra horizons through microscopic examination of 1050 samples (each integrating c. 3 ka) in over 200 m of marine sediments. We report the major and minor element geochemical compositions of individual glass shards in six of these microtephra horizons and establish a robust correlation at 168.73 m to the Lokochot Tuff (3.58 Ma), which together with previously identified tephra, provides a tightly constrained chronostratigraphy for the mid Pliocene.