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61.
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. 相似文献
62.
银川盆地中更新世以来的孢粉记录及古气候研究 总被引:8,自引:1,他引:8
银川盆地中更新世以来的孢粉记录及据此所重建的古气候参数,揭示了该区中更新世以来的古气候演变特征,其演变经过了温湿→凉湿→温和→冷湿→温干→凉较湿→冷湿→温干→凉润→温较干→温干的变化,并与新疆地区,黄土高原以及深海δ^18O曲线进行了对比,结果表明,各地的古环境变化大致同步,该区由于位置靠西,邻近沙漠,最近地质历史时期的区域性干旱特色明显。 相似文献
63.
胶莱盆地发育演化及其油气前景探讨 总被引:5,自引:0,他引:5
根据胶莱盆地区域地质特征,地球动力学背景及盆地中、新生代沉积特征分析,论述盆地的发育和演化阶段,并对胶莱盆地含油气前景进行探讨。 相似文献
64.
Matsumoto Takeshi Goslin Jean Lagabrielle Yves Ruellan Etienne Tanahashi Manabu 《Marine Geophysical Researches》1997,19(1):37-53
A surface ship gravity survey was carried out in the northern part of the North Fiji Basin during the NOFI cruise by the R/V l'Atalante in August-September, 1994. The two ridges inside the study area, the South Pandora Ridge and the Tripartite Ridge, present different structures and states of isostatic equilibrium in terms of gravity anomaly and its tectonic implications. The former is supported by a restoring force of an imaginary elastic plate in the crust and the latter by the Airy type isostasy. These characteristics can be derived from the difference in magmatic activity, as influenced by the difference in lithospheric structure. The latter is characterised by greater active magmatism and hydrothermalism underneath the ridge than the former. Such a difference in the magmatic activity and the horizontal scale of the shallow subsurface structure is derived from the difference in the stiffness or viscosity of the lithosphere beneath the two ridges. 相似文献
65.
66.
刘希林 《海洋地质与第四纪地质》1995,15(3):93-104
泥石流扇的平面形态可用规划的几何图形来模拟。在研究了中国西南地区小江流域和意大利东北部阿尔卑斯山区的52个泥石流扇的基础上,本文提出了两种泥石流扇的平面形态:中国西南地区的“等腰三角形+半圆形”泥石流扇和意大利东北部的“几何扇”。用统计分析建立了两组泥石流扇和泥石流流域之间的形态度量关系。通过两个研究区域的对比,两个流域参数:流域面积和主沟比降确定为影响泥石流扇平面形态和面积的最重要的因素。 相似文献
67.
本文采用1985年12月12日至1986年2月8日“向阳红14”号调查船在太平洋调查所获海洋水文气象资料,计算了四种热交换量。结果表明:海-气热输送与天气系统和海洋水文条件关系密切。冬季,在各种天气系统条件下西太平洋及中太平洋的大气主要是从海洋得到热量,其中以黑潮流经的海域最为明显,而热交换的方式主要是海洋以潜热的形式把热量输送给大气。 相似文献
68.
The recent sea-ice reduction in the Arctic Ocean is not spatially uniform, but is disproportionally large around the Northwind
Ridge and Chukchi Plateau compared to elsewhere in the Canada Basin. In the Northwind Ridge region, Pacific Summer Water (PSW)
delivered from the Bering Sea occupies the subsurface layer. The spatial distribution of warm PSW shows a quite similar pattern
to the recent ice retreat, suggesting the influence of PSW on the sea-ice reduction. To understand the regionality of the
recent ice retreat, we examine the dynamics and timing of the delivery of the PSW into this region. Here, we adopt a two-layer
linearized potential vorticity equation to investigate the behavior of Rossby waves in the presence of a topographic discontinuity
in the high latitude ocean. The analytical results show a quite different structure from those of mid-latitude basins due
to the small value of β. Incident barotropic waves excited by the sea-ice motion with large annual variation can be scattered
into both barotropic and baroclinic modes at the discontinuity. Since the scattered baroclinic Rossby wave with annual frequency
cannot propagate freely, a strong baroclinic current near the topographic discontinuity is established. The seasonal variation
of current near the topographic discontinuity would cause a kind of selective switching system for shelf water transport into
the basin. In our simple analytical model, the enhanced northward transport of summer water and reduced northward transport
of winter water are well demonstrated. The present study indicates that these basic dynamics imply that a strengthening of
the surface forcing during winter in the Canada Basin could cause sea-ice reduction in the Western Arctic through the changes
of underlying Pacific Summer Water. 相似文献
69.
70.
Abstract. Peyssonnelia bed distribution on continental shelf bottoms of the Balearic Islands (Western Mediterranean) ranges from 40 to 90 m depth. Different species of Peyssonnelia dominate these bottoms and, according to multivariate techniques, two main assemblages have been distinguished: the Peyssonnelia rosa-marina beds and the Peyssonnelia sp. beds, together with some transition samples between Peyssonnelia and maërl beds. Erect red algae are always abundant. Although average yearly irradiance reaching these beds is only 6.4-0.3% of subsurface irradiance, the species richness averages 45 species per sample (1600 cm2 ) and mean biomass is 2835 g dw. m-2 . The high carbonate content of the living algae of these bottoms suggests that they are important contributors to the production of sediments in the Balearic continental shelf. 相似文献