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11.
在东亚和东南亚第四系对比中,有关的几条界限,本文建议如后。采用Globorotalia truncatulinoides的初现位作为本区海相第四系的下界,其位置大致在古地磁Olduvai亚时的下界,时间约为距今1.9Ma。在南中国海、东海及沿岸地区,发现了以G.truncatulinoides的初现位为代表的一系列有意义的生物事件,如Pulleniatina finalis的初现位,Globigerinoides obliquus和Globoquadrina altispira的灭绝位,以及Globorotalia menardii和Pulleniatina obliquloculata壳体旋向的变化。此界限在东亚和东南亚也是相当稳定的。在陆相地层中,以泥河湾组为代表,狭义的泥河湾动物群(相当于晚维拉方动物群)所在地层的底界,其古地磁位置为Olduvai亚时的底界。以此作为陆相第四系的下界,与上述海相第四系底界一致。 以古地磁布容/松山界线作为中更新世和早更新世的界限,其年代为0.73MaB.P.。中国中更新世的标准地层周口店组,其底界恰为布容/松山的转换面,北京猿人的年代为0.60—0.23MaB.P.。在洛川黄土剖面上,布容/松山界线为古土壤S_7的底界。雷琼地区中更新统下部的北海组的底界也是布容/松山界线,所产的玻璃陨石的裂变径迹年龄为0.687—0.733MaB.P.。在黄海,布容/松山界线是第Ⅶ海侵层的顶界。通过岩石地层标志,以及动物群、古人 相似文献
12.
资料显示,在整个台湾以东海区内磁异常几乎全为负磁异常,磁异常分块现象明显。通过对本海区的磁力资料进行分析和研究,表明本海区的地磁异常表现为明显的条带状异常特征。由于受板块差异性运动的影响,以加瓜海脊为界,东西两侧具有不同的磁条带方向,在加瓜海脊以东,磁条带为NW-SE向(120°),而在加瓜海脊以西则为近东西向(80°)。加瓜脊以西地区的扩张时间为45~38Ma,相当于19~16号磁条带;而加瓜脊以东地区的扩张时间为40~35Ma,相当于17~13号磁条带。加瓜脊以西的磁条带相对于以东的磁条带要老,由此推断出加瓜脊以西相对于东侧发生了北向位移。 相似文献
13.
Temperature data at different layers of the past 45 years were studied and we found adiploe mode in the thermocline layer (DMT): anomalously cold sea temperature off the coast of Sumatra and warm sea temperature in the western Indian Ocean. First, we analyzed the temperature and the temperature anomaly (TA) along the equatorial Indian Ocean in different layers. This shows that stronger cold and warm TA signals appeared at subsurface than at the surface in the tropical Indian O-cean. This result shows that there may be a strong dipole mode pattern in the subsurface tropical Indian Ocean. Secondly we used Empirical Orthogonal Functions (EOF) to analyze the TA at thermocline layer. The first EOF pattern was a dipole mode pattern. Finally we analyzed the correlations between DMT and surface tropical dipole mode (SDM), DMT and Nino 3 SSTA, etc. and these correlations are strong. 相似文献
14.
东亚冬夏季风对热带印度洋秋季海温异常的响应 总被引:5,自引:0,他引:5
利用多年的Reynolds月平均海表温度资料和NCEP/NCAR全球大气再分析资料,分析了热带印度洋秋季海表温度距平(SSTA)与后期东亚冬夏季风强度变化的关系。结果表明,热带印度洋秋季SSTA的主要模态是全区一致(USB)型和偶极子(IOD)型,USB型模态主要代表热带印度洋秋季SSTA的长期变化趋势,而IOD型模态主要反映热带印度洋秋季SSTA的年际变化。热带印度洋秋季海温气候变率中既存在着明显的ENSO信号,也有独立于ENSO的变率特征,独立于ENSO的热带印度洋秋季SSTA变化的主要模态仍是USB型和IOD型。前期秋季USB模态与东亚冬季风及东亚副热带夏季风之间为负相关关系;与前期正(负)IOD模态相对应,南海夏季风强度偏弱(强),而东亚副热带夏季风强度偏强(弱)。USB型和IOD型模态对后期东亚冬、夏季风强度变化的影响是独立于ENSO的,但ENSO起到了调节二者相关显著程度的作用。 相似文献
15.
热带印度洋偶极子发生和演变机制的数值研究 总被引:5,自引:0,他引:5
对中国科学院大气物理研究所(IAP)大气科学和地球流体力学数值模拟国家重点实验室(LASG)发展的第三代海洋模式(L30T63 OGCM)进行了改进。分析了该模式1959年1月—1998年12月的40a积分结果,以此研究热带印度洋偶极子发生、发展和消亡的物理机制。对数值模拟结果的分析表明,赤道印度洋表面异常东风引起的异常环流结构是偶极子发生、发展的主要动力学原因,其表面异常东风转换为异常西风所引起的异常环流结构调整是偶极子消亡的主要动力学原因;海气界面热通量异常的交换对热带印度洋海表温度距平偶极子模态的形成和演变起着重要的作用;垂直输送作用是热带印度洋次表层海温偶极子模态发生和演变的主要物理机制。 相似文献
16.
Dissolved and particulate samples were collected to study the distribution of thorium isotopes (234Th, 232Th and 230Th) in the water column of the Indian sector of the Southern Ocean (from 42°S to 47°S and from 60°E to 66°E, north of the Polar Front) during Austral summer 1999. Vertical profiles of excess 230Th (230Thxs) increases linearly with depth in surface water (0–100 m) and a model was applied to estimate a residence time relative to the thorium scavenging (τscav). Low τscav in the Polar Front Zone (PFZ) are found, compared to those estimated in the Subtropical Front Zone (STZ). Changes in particle composition between the PFZ and STZ could influence the 230Thxs scavenging efficiency and explain this difference. An innovative coupling between 234Th and 230Thxs was then used to simultaneously constrain the settling velocities of small (0.6–60 μm) and large (above 60 μm) particles. Although the different hydrological and biogeochemical regimes visited during the ANTARES IV cruise did not explain the spatial variation of sinking velocity estimates, our results indicate that less particles may reach the seafloor north (60 ± 2 m d− 1, station 8) than south of the Agulhas Return Current (119 ± 23 and 130 ± 5 m d− 1 at stations 3 and 7, respectively). This information is essential for understanding particle transport and by extension, carbon export. In the deep water column, the 230Thxs concentrations did not increase linearly with depth, probably due to lateral transport of North Atlantic Deep Water (NADW) from the Atlantic to the Indian sector, which renews the deep waters and decreases the 230Thxs concentrations. A specific 230Thxs transport model is applied in the deep water column and allows us to assess a “travel time” of NADW ranging from 2 to 15 years. 相似文献
17.
We present magnetic field data collected over the Mid-Atlantic Ridge in the vicinity of the Atlantis Fracture Zone and extending out to 10 Ma-old lithosphere. We calculated a magnetization distribution which accounts for the observed magnetic field by performing a three-dimensional inversion in the presence of bathymetry. Our results show the well-developed pattern of magnetic reversals over our study area. We observe a sharp decay in magnetization from the axis out to older lithosphere and we attribute this decay to progressive low temperature oxidation of basalt. In crust which is 10 Ma, we observe an abrupt increase in magnetic field intensity which could be due to an increase in the intensity of magnetization or thickness of the magnetic source layer. We demonstrate that because the reversal epoch was of unusually long duration, a two-layer model comprised of a shallow extrusive layer and a deeper intrusive layer with sloping polarity boundaries can account for the increase in the amplitude of anomaly 5. South of the Atlantis Fracture Zone, high magnetization is correlated with bathymethic troughts at segment end points and lower magnetization is associated with bathymetric highs at segment midpoints. This pattern can be explained by a relative thinning of the magnetic source layer toward the midpoint of the segment. Thickening of the source layer at segment endpoints due to alteration of lower oceanic crust could also cause this pattern. Because we do not observe this pattern north of the fracture zone, we suggest it is a result of the nature of crustal formation process where mantle upwelling is focused. South of the fracture zone, reversals along discontinuity traces only continue to crust 2 Ma old. In crust >2 Ma, we observe bands of high, positive magnetization along discontinuity traces. We suggest that within the discontinuity traces, a high, induced component of magnetization is produced by serpentinized lower crust/upper mantle and this masks the contribution of basalts to the magnetic anomaly signal. 相似文献
18.
The ridge located between 31° S and 34°30′S is spreading at a rate of 35 mm yr−1, a transitional velocity between the very slow (≤20 mm yr−1) opening rates of the North Atlantic and Southwest Indian Oceans, and the intermediate rates (60 mm yr−1) of the northern limb of the East Pacific Rise, and the Galapagos and Juan de Fuca Ridges. A synthesis of multi-narrow beam,
magnetics and gravity data document that in this area the ridge represents a dynamically evolving system. Here the ridge is
partitioned into an ensemble of six distinct segments of variable lengths (12 to 100 km) by two transform faults (first-order
discontinuities) and three small offset (< 30 km) discontinuities (second-order discontinuities) that behave non-rigidly creating
complex and heterogeneous morphotectonic patterns that are not parallel to flow lines. The offset magnitudes of both the first
and second-order discontinuities change in response to differential asymmetric spreading. In addition, along the fossil trace
of second-order discontinuities, the lengths of abyssal hills located to either side of a discordant zone are observed to
lengthen and shorten creating a saw-toothed pattern. Although the spreading rate remains the same along the length of the
ridge studied, the morphology of the spreading segments varies from a deep median valley with characteristics analogous to
the rift segments of the North Atlantic to a gently rifted axial bulge that is indistinguishable from the shape and relief
of the intermediate rate spreading centers of the East Pacific Rise (i.e., 21°N). Like other carefully surveyed ridge segments
at slow and fast rates of accretion, the along-axis profiles of each ridge segment are distinctly convex upwards, and exhibit
along-strike changes in relief of 500m to 1500 between the shallowest portion of the segment (approximate center) and the
segment ends. Such spatial variations create marked along-axis changes in the morphology and relief of each segment. A relatively
low mantle Bouguer anomaly is known to be associated with the ridge segment characterized by a gently rifted axial bulge and
is interpreted to indicate the presence of focused mantle upwelling (Kuo and Forsyth, 1988). Moreover, the terrain at the
ends of each segment are known to be highly magnetized compared to the centers of each segment (Carbotte et al, 1990). Taken
together, these data clearly establish that these profound spatial variations in ridge segment properties between adjoining
segments, and along and across each segment, indicate that the upper mantle processes responsible for the formation of this
contrasting architecture are not solely related to passive upwelling of the asthenosphere beneath the ridge axis. Rather,
there must be differences in the thermal and mechanical structure of the crust and upper mantle between and along the ridge
segments to explain these spatial variations in axial topography, crustal structure and magnetization. These results are consistent
with the results of investigations from other parts of the ridge and suggest that the emplacement of magma is highly focused
along segments and positioned beneath the depth minimum of a given segment. The profound differences between segments indicate
that the processes governing the behavior of upwelling mantle are decoupled and the variations in the patterns of axis flanking
morphology and rate of accretion indicate that processes controlling upwelling and melt production vary markedly in time as
well. At this spreading rate and in this area, the accretionary processes are clearly three-dimensional. In addition, the
morphology of a ridge segment is not governed so much by opening rate as by the thermal structure of the mantle which underlies
the segment. 相似文献
19.
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
20.
Seasonal Variability of Near-Surface Heat Budget of Selected Oceanic Areas in the North Tropical Indian Ocean 总被引:1,自引:0,他引:1
The results obtained from an Ocean General Circulation Model (OGCM), the Modular Ocean Model 2.2, forced with the National
Center for Environmental Prediction/National Center for Atmospheric Research reanalysis data, and observational data have
been utilized to document the climatological seasonal cycle of the upper ocean response in the Tropical Indian Ocean. We address
the various roles played by the net surface heat flux and the local and remote ocean dynamics for the seasonal variation of
near-surface heat budget in the Tropical Indian Ocean. The investigation is based in seven selected boxes in the Arabian Sea,
Bay of Bengal and the Equatorial Indian Ocean. The changes of basin-wide heat budget of ocean process in the Arabian Sea and
the Western Equatorial Indian Ocean show an annual cycle, whereas those in the Bay of Bengal and the Eastern Equatorial Indian
Ocean show a semi-annual cycle. The time tendency of heat budget in the Arabian Sea depends on both the net surface heat flux
and ocean dynamics while on the other hand, that in the Bay of Bengal depends mainly on the net surface flux. However, it
has been found that the changes of heat budget are very different between western and eastern regional sea areas in the Arabian
Sea and the Bay of Bengal, respectively. This difference depends on seasonal variations of the different local wind forcing
and the different ocean dynamics associated with ocean eddies and Kelvin and Rossby waves in each regional sea areas. We also
discuss the comparison and the connection for the seasonal variation of near-surface heat budget among their regional sea
areas.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献