Gravity at sea

This is a review article on the types of gravity-measuring instruments used or tested at sea since 1903, on the various extraneous accelerations that affect sea measurements, and on results obtained in several gravity surveys using one type of meter. Free-air gravity anomaly maps are included of: (1) the Gulf of Mexico; (2) a strip west of the coast from northern California to the southern tip of Alaska; and (3) north of Hawaii. Hypothetical crustal and subcrustal sections, consistent with gravity anomalies and seismic refraction data, are included for selected regions.     

Conflict at sea

Naval conflict has been less important in the second half of the twentieth century than in the first. Navies have operated in support of armies or as instruments of coercive diplomacy. There has been only one true naval war. Conflict in the Falklands was typical because it was local, limited and unexpected. These are likely features in future, for total war at sea seems so pointless that it could only arise by accident, a risk increased by some naval activities in peace. But the motives and the capacities for local and limited conflict at sea are proliferating.     

Rationalization at sea

UNCLOS is only part of intergovernmental efforts to make sense of the new circumstances offshore. The secretariats of the various UN component organs and agencies have always cooperated on the potential of the marine dimension. Plans and policies are evolving, coastal states are getting encouragement to see the sea as an aspect of foreign policy deserving regional collaboration, and a modest rationalization of global interests is taking shape, albeit slowly.     

Modeling vertical motion at ocean fronts: Are nonhydrostatic effects relevant at submesoscales?

Through a suite of three-dimensional, high-resolution numerical modeling experiments, we examine the role of nonhydrostatic effects on O(1 km) submesoscale processes at ocean fronts, with particular focus on the vertical velocity field. Several differences between nonhydrostatic and hydrostatic models are pointed out using a framework that enables precise comparison, but it is difficult to identify categorical differences between the model solutions at the grid resolutions afforded. The instantaneous vertical velocity structure is sensitive to the model choice and, even more so, to grid resolution, but the average vertical flux is similar in both hydrostatic and nonhydrostatic cases.When a frontal region with horizontal density gradients is perturbed by wind, a profusion of submesoscale, O(1 km), secondary circulation features develops in the upper 50 m. Narrow, elongated cells of intense up- and down-welling are found to occur close to the surface, overlying broader regions of weaker up- and down-welling associated with the mesoscale meanders of the baroclinically unstable front. The submesoscale down-welling is considerably stronger than up-welling and is concentrated in 1–2 km width filaments within which velocities can attain magnitudes as high as 200 m day⁻¹. The submesoscale features are found to be robust at horizontal grid resolutions varying between 1 and 0.25 km and exist even in the hydrostatic model. Submesoscale circulation is difficult to observe or resolve in coarser resolution circulation models, but is likely to play a significant role in the exchange of energy and properties between the surface ocean and thermocline. Possible mechanisms for the generation of these features are investigated in a follow-on paper.     

Sequence of facies at a Holocene storm-dominated regressive barrier at Praia de Leste,southern Brazil

Along the coast at Praia de Leste, southern Brazil (25° 41’ S latitude), a positive sedimentary budget and a lowering of the sea level following the postglacial maximum has given rise to a progradational strandplain barrier that is 3–5 km wide. Sand quarries that lie 3.5 km from the present-day coastline have provided material from exceptional outcrops of 75% of the sequence of Holocene barrier facies. Five facies associations have been identified, which correspond to the inner shelf, the lower, middle and upper shorefaces, and the foreshore. The architecture of the facies shows a regressive sequence that overlies an erosional surface and downlapping Pleistocene sediments. At Praia de Leste, the facies association has a thickness of 14 m and is deposited between 2 m above and 12 m below mean paleo sea level. The barrier corresponds to a coastal environment that is characterised by medium to low wave energy under the additional influence of episodic storm events. The sequence at the Praia de Leste barrier differs from the sequence of clastic shoreline facies found elsewhere in two main ways. The first difference is the high content of fine sediment and plant debris, released at around the same time as the formation of the barrier from large estuarine systems, and the second is the predominance on the middle and lower shorefaces of swaley cross-stratified sand facies with abundant plant debris. We also describe two further characteristics of the barrier at Praia de Leste. First, the swaley cross-stratified sand represents a component of onshore transport that resulted in the accumulation of sediment transported from the shelf. Second, the beach step has been well preserved, thereby allowing the continuous tracing of seaward-dipping, low-angle cross-stratification to a sigmoidal cross-stratified beach-step sandy facies. Finally, we have herein been able to improve the precision of the sequence of formation of the depth of the facies, by making reference to paleo sea level during the formation of the barrier, rather than to present-day mean sea level.     

前寒武纪—寒武纪边界处的海洋缺氧事件

前寒武纪—寒武纪 ( PC— C)边界处两个明显不同演化阶段的地层主要根据以下几点事区别 :1可视后生动物组合的变化 ;2化石埋藏条件的变化 ;3痕迹化石组合的变化 ;4寒武纪最早期海洋沉积物中生物扰动强度的增加。生物的这种不连续性归因于生物大量灭绝以及软体生物化石埋藏窗的关闭。有不少迹象表明埃迪卡拉动物群不断减少和有骨骼的无脊椎动物群的出现之间发生了地层超覆 ,这些迹象包括在寒武纪沉积物中发现了埃迪犬拉动物群 ,弄清了寒武纪大爆炸之前没有出现生物大量灭绝事件。另一方面 ,有人认为富营养的底层缺氧水团向上贯穿运动导致生…     

Tidal pump at the shelf edge

Material transport through the shelf edge to the deep ocean determines the fate of particulate matter generated in productive coastal seas. In stratified estuaries, onshore flow in the bottom layer generally keeps particulate matter generated in the upper layer and settled down to the bottom layer within the estuaries. AT the shelf edge of Tokyo Bay under the condition of average onshore flow in the bottom layer, we observed higher vertical sediment flux during ebb than flood tidal currents. The on-shelf and off-shelf differences in turbulent mixing and water depth mainly cause such difference in sediment flux. We propose to call this export process of particulate matter the tidal pump at the shelf edge.     

Fault patterns at outer trench walls

Profiles across subduction-related trenches commonly show normal faulting of the outer trench wall. Such faulting is generally parallel or sub-parallel to the trench and is ascribed to tension in the upper part of the oceanic plate as it is bent into the subduction zone. A number of authors have noted that outer trench wall faulting may involve re-activation of the oceanic spreading fabric of the subducting plate, even when the trend of this fabric is noticeably oblique to the extensional stress direction. However, one previous review of outer trench wall fault patterns questioned the occurrence of a consistent link between fault orientation and such controlling factors. This latter study predated the widespread availability of swath bathymetry and longrange sidescan sonar data over trenches. Based only on profile data, it was unable to analyse fault patterns with the accuracy now possible. This paper therefore re-examines the relationship between outer trench wall faulting and the structure of the subduction zone and subducting plate using GLORIA and Seabeam swath mapping data from several locations around the Pacific and Indian Oceans. The principal conclusions is that the trend of outer trench wall faults is almost always controlled by either the subducting slab strike or by the inherited oceanic spreading fabric in the subducting plate. The latter control operates when the spreading fabric is oblique to the subducting slab strike by less than 25–30°; in all other cases the faults are parallel to slab strike (and parallel or sub-parallel to the trench). Where the angle between spreading fabric and slab strike is close to 30°, two fault trends may coexist; evidence from the Aleutian Trench indicates a gradual change from spreading fabric to slab strike control of fault trend as the angle between the two increases from 25 to 30°. The only observed exception to the above rule of fault control comes from the western Aleutian Trench, where outer trench wall faults are oblique to the slab strike, almost perpendicular to the spreading fabric, and parallel to the convergence direction. Re-orientation of the extensional stress direction due to right-lateral shear at this highly oblique plate boundary is the best explanation of this apparently anomalous observation.     

海上溢油的处置

全世界每年流入海洋的石油多达数百万吨，超过了海洋的自净能力，造成污染。本文综述了海上溢油的处置技术，包括石油入海后的处理和回收技术以及海上溢油的最终处置技术。     

地幔边界区的钻探

近年来发现在洋中脊不同地区 ,玄武质熔岩是非均一的 ,证明地幔源的成分是不一样的。研究地球化学省之间的边界区成为当前迫切的问题 ,因为一方面这使我们能查明上地幔的成分和物理参数 ,另一方面可以弄清其中发生的过程。表现明显的此类边界之一位于澳大利亚和南极洲之间的中印度洋中脊区 ,在该区这一边界与所谓澳大利亚—南极洲不整合区相吻合。这是全球洋中脊体系最深的 (4～ 5ｋｍ)区域之一 ,这里存在着非常冷的地幔和相应的薄地壳。已进行的地质研究工作表明 ,由边界区向西和向东 ,一系列元素 (Ｓｒ、Ｎｄ、Ｐｂ)的同位素成分有着实质…     

Entanglement of pinnipeds at Marion Island

During the period April 1991–March 1996, 10 entangled Antarctic fur seals Arctocephalus gazella, 28 entangled Subantarctic fur seals A. tropicalis and one entangled southern elephant seal Mirounga leonina were observed at Marion Island, Southern Ocean. Entanglement of fur seals was estimated at between 0.01 and 0.15% of the combined population of both species.     

利用海岸线的海洋遥感图像控制点(GCP)自动匹配法

研究一种利用海岸线自动确定海上地面控制点(GCP)的方法.借助边缘检测技术提取海岸线,将海岸线的点全部作为控制点的备选集合,利用相关松弛法寻找同名点,建立一种可靠判别机制来保证海岸线上GCP的正确性,通过平均法和插值法求取海上GCP的值.利用本方法可以方便地得到分布密集的GCP值,其中海上GCP值具有子像元精度.同时研究了一种新的几何变换方法,即用插值法直接求取需校正图像的几何变换坐标,随着插值密度的增加,求得海上GCP值的点就越多,最后使所有点的坐标值通过插值方法计算得到,代替二元n次方程组进行空间坐标变换,使遥感图像的几何配准误差在某种程度上达到0,利用该方法对海洋遥感资料进行几何配准,可以提高配准的精度和节省机时,为遥感资料的动态监测和数据库建设创造了有利条件.     

鸭绿江口的潮汐特征

对1985年和1996年鸭绿江口6个站位的水位数据进行调和分析,结果显示,鸭绿江口的潮汐以半日潮为主,M2 分潮占优.此外,潮高日不等和涨落潮历时不等的现象较为显著,与实测水位结果一致;由口门向上游方向潮差逐渐减小,落潮历时增大,涨潮历时减小,且落潮历时长于涨潮历时.最下游枢岛验潮站的平均海平面为0.08 m;最上游丹东站为1.14 m(1985);从下游至上游平均海平面呈现增大趋势,主要原因是鸭绿江口为向上游迅速束窄的狭长形喇叭口,大面潮水涌入后水位被束窄抬升所致.利用调和常数计算的潮位与观测数据基本吻合,表明研究区观测期间水位主要受潮汐作用的控制.     

Inclinometric Observations at the Korchagin Deposit

Izvestiya, Atmospheric and Oceanic Physics - The aim of this work is to analyze the results of geodeformation monitoring at the Korchagin oil, gas, and condensate deposit in the Caspian Sea. The...     

Wave setup at Tristan da Cunha

Wave setup was investigated using data from tide gauges in a small harbour at the island of Tristan da Cunha in the South Atlantic Ocean. Frequent examples of wave setup were found during the period 1986–1992, but were much less apparent after 1992, following extensions to the two breakwater arms of the harbour. The unambiguous association of wave setup with the several-decimetre spikes in Tristan sea level, which can persist for a day or so, are a warning that signals related to wave setup could also occur in other tide gauge records, where the wave setup signal could perhaps be misinterpreted as wind setup within the overall storm surge. One conclusion is that, in spite of the difficulties of access to Tristan da Cunha and its ever-present hostile wave climate, the island is undoubtedly now worthy of a permanent tide-gauge installation, which would be an important contribution to the global sea-level network.