Constraints on crustal and mantle structure of the oceanic plate south of Iceland from ocean bottom recorded Rayleigh waves

From April to July 2002 we carried out a deployment of 6 ocean bottom seismometers and 4 ocean bottom hydrophones in the North Atlantic south of Iceland. During the deployment period we recorded clear Rayleigh waves from 2 regional and 14 teleseismic earthquakes. This corresponds to a Rayleigh wave detection rate of nearly 92% for events with M_W ≥ 6.06.0 and epicentral distance less than 110°, close to detection rate estimates based on noise level variability. We measured Rayleigh wave event-station group dispersion and inter-station phase dispersion for one Mid-Atlantic Ridge event. The group dispersion curve is sensitive to the structure of the North-East Atlantic with an average age of  39 Myr. The phase dispersion curve is sensitive to the structure just south of Iceland (average plate age 33 Myr). Both dispersion curves indicate faster velocities than previously postulated for oceanic plate generated at the Reykjanes Ridge. A grid search approach was used to constrain the range of models fitting the data. The high velocity seismic lid just south of Iceland in the model for the phase dispersion path is slower or thinner than in the group dispersion model, which averages over a larger area and a somewhat older plate age, but the velocities in the low velocity half space are similar. We further consider the residual bathymetry in the experimental area. The residual anomaly decreases by 300–400 m from the Reykjanes Ridge to the  30 Myr old plate south of Iceland. This decrease can be explained by the disappearance of a mantle thermal anomaly associated with the Iceland plume. Both the residual bathymetry and the surface wave data are thus consistent with the notion that the southward spreading of the Icelandic plume is channelised underneath the Reykjanes Ridge and does not spread far outside this channel.Based on the experience from the pilot experiment, we estimate that a minimum recording time of 13–15 months in favourable weather conditions (April–September) is required to record enough data to map the spreading plume with surface waves, and to produce a tomographic image to a depth of 1000 km using body waves. This can be achieved by a continuous deployment of at least  20 months, or by two or three deployments during the spring and summer of consecutive years.     

Truncated flame structures within a deposit of the Indian Ocean Tsunami: evidence of syn‐sedimentary deformation

This study reveals the three‐dimensional morphology and syn‐sedimentary formation processes of a deformation structure termed ‘truncated flame structures’ which is found in a terrestrial tsunami deposit in southern Thailand that formed during the 2004 Indian Ocean Tsunami. The structure was found at the boundary between a lower fine‐grained layer and an upper coarse‐grained layer that are related to two runup events. In order to confirm the morphology of the structure, the authors excavated two trenches and an opencast pit. When viewed in a cross‐section oriented parallel to the direction of the runup current, the deformed boundary has an irregularly bulging profile, similar to that observed in flame structures. The protruding structures are inclined towards the downstream direction of the runup current, and are truncated horizontally along their upper surface by parallel laminations in the overlying layer. When viewed in a cross‐section oriented perpendicular to the current direction, it appears that parts of the upper layer descend into the lower layer as lobate masses. In places, these masses are completely detached from the main part of the upper layer, forming circular or elliptical shapes. The contact between the lower layer and the main part of the upper layer is a planar truncation surface. Opencast excavation of the contact surface revealed that the deformed structures have flat, sinuous horseshoe crests that open in a downstream direction. It is possible for the runup current to generate shear stress such that it deforms the boundary into a truncated flame structure. Moreover, the observations made in this study indicate the syn‐sedimentary development of the structure: deformation and truncation occurred simultaneously in association with the runup current that formed the upper layer. Truncated flame structures can be used as a criterion in identifying the syn‐sedimentary deformation of substrate: the structures are indicative of unidirectional flow with sufficiently high shear velocity to deform unconsolidated substrate. As in the present case, the truncated flame structures may be characteristic of tsunami events that involve strong unidirectional currents on land due to the extraordinarily long wave period of tsunamis, rather than other events such as storm surges or flooding.     

North Indian Ocean warming and sea level rise in an OGCM

The variability in the long-term temperature and sea level over the north Indian Ocean during the period 1958–2000 has been investigated using an Ocean General Circulation Model, Modular Ocean Model version 4. The model simulated fields are compared with the sea level observations from tide-gauges, Topex/Poseidon (T/P) satellite, in situ temperature profile observations from WHOI moored buoy and sea surface temperature (SST) observations from DS1, DS3 and DS4 moored buoys. It is seen that the long (6–8 years) warming episodes in the SST over the north Indian Ocean are followed by short episodes (2–3 years) of cooling. The model temperature and sea level anomaly over the north Indian Ocean show an increasing trend in the study period. The model thermocline heat content per unit area shows a linear increasing trend (from 1958–2000) at the rate of 0.0018 × 10¹¹ J/m² per year for north Indian Ocean. North Indian Ocean sea level anomaly (thermosteric component) also shows a linear increasing trend of 0.31 mm/year during 1958–2000.     

How partial melts of mafic lower crust affect ascending magmas at oceanic ridges

We present experiments showing that the lower oceanic crust should melt efficiently and quickly when heated by hot ascending magmas. Average plagioclase–olivine and plagioclase–augite pairs from the lower crust at the Southwest Indian Ridge have melt–mineral saturation boundaries at 1,190 and 1,154°C, respectively, and melt rapidly (>0.01 mm/h) at 50°C or more above these temperatures. Melting experiments performed on olivine–plagioclase and augite–plagioclase mineral pairs from actual oceanic lower crustal rock samples and under conditions applicable to a MOR setting (1,220–1,330°C, 1 atm, quartz–fayalite–magnetite oxygen buffer, 0.25–24 h) indicate that the resulting disequilibrium melts are linear mixes of the mineral compositions. The rates of melting are slower than the rate of heat-diffusion into a sample and are approximated as:

Relics of the Mozambique Ocean in the central East African Orogen: evidence from the Vohibory Block of southern Madagascar

The Vohibory Block of south‐western Madagascar is part of the East African Orogen, the formation of which is related to the assembly of the Gondwana supercontinent. It is dominated by metabasic rocks, which have chemical compositions similar to those of recent basalts from a mid‐ocean ridge, back‐arc setting and island‐arc setting. The age of formation of protolith basalts has been dated at 850–700 Ma by U–Pb SHRIMP analysis of magmatic cores in zircon, pointing to an origin related to the Neoproterozoic Mozambique Ocean. The metabasic rocks are interpreted as representing components of an island arc with an associated back‐arc basin. In the early stage of the Pan‐African orogeny, these rocks experienced high‐pressure amphibolite to granulite facies metamorphism (9–12 kbar, 750–880 °C), dated at 612 ± 5 Ma from metamorphic rims in zircon. The metamorphism was most likely related to accretion of the arc terrane to the margin of the Azania microcontinent (Proto‐Madagascar) and closure of the back‐arc basin. The main metamorphism is significantly older than high‐temperature metamorphism in other tectonic units of southern Madagascar, indicating a distinct tectono‐metamorphic history.     

夏半年热带太平洋中部型海温异常与热带印度洋海盆模对同期中国东部降水的共同影响

利用1961—2013年NCEP/NCAR再分析资料和Had ISST月平均海表面温度资料,分析了夏半年热带太平洋中部型海温异常与热带印度洋海盆模(Indian Ocean Basin M ode,IOBM)的特征,并研究了不同位相配置时二者对同期中国东部气候的共同影响。结果表明:1)太平洋中部型海温异常指数与印度洋海盆模指数几乎相互独立。太平洋中部型海温异常与IOBM同位相变化(记为PPNN事件)和反位相变化(记为PNNP事件)时,热带印太地区海温异常分别呈三级型和偶极型分布。2)不同位相配置对中国东部地区降水异常的影响及其影响机制存在显著差异:当发生PPNN事件时,水汽从海洋性大陆(Maritime Continent,MC)地区向江淮流域输送;热带海温异常引起大气产生Gill型响应,维持了中国东部的环流异常;M C地区通过经向三圈异常垂直环流引起江淮流域降水异常增多。发生PNNP事件时,Gill型环流响应中心西移,长江流域降水偏少,水汽辐散;同时MC地区对流层低层准定常Rossby波能传播也有利于长江流域扰动的维持。这些结果对深刻认识中国东部地区夏半年降水异常成因和印度洋/太平洋海温异常不同分布的作用具有重要意义。     

Sea surface heights obtained from Modular Ocean Model simulation and comparison with Topex/Poseidon data for the Indian Ocean

The Modular Ocean Model (MOM) is perhaps the most versatile ocean model available today for the simulation of the large scale circulation of the ocean. The Topex/Poseidon altimeter which has been operating since September 1992 has been providing sea surface heights (SSH) of the accuracy of 5–10 cms with a repeat cycle of 10 days. We examine in this paper, the SSH in the Indian Ocean obtained from a global simulation of MOM with a resolution of 1° in the longitude, 1/3° in the latitude between 30°S and 30°N and 20 levels in the vertical with climatological windforcing and restoring conditions on temperature and salinity. They are compared with the SSH from the Topex/Poseidon altimeter after suitable filtering in the time domain to remove smaller time and length scales. In addition, unfiltered data from both sources are analysed by estimating the cross-spectral density to find the coherence and crossphase at different frequencies. The agreement between the two, over most of the Northern Indian Ocean, especially the Arabian Sea and the Bay of Bengal is quite good.     

海洋生态系统动力学浅说

讨论了海洋生态系统动力学的研究目的，任务和特点。阐述了它的基本理论问题，此外，协同性，可预报性，突变性以及稳定性是人们关切的问题也是海洋生态系统动力学理论研究的重要内容。并对海洋生态系统动力学模型及模拟的基本概念和了描述，进而说明建模时要注意抽象与简化。最后就我国开展海洋生态系统动力学研究提出了一点看法。     

大洋钻探（ODP）与测井地质研究

ＯＤＰ是ＤＳＤＰ的继续，它验证了岩石层板块构造理论，揭示出晚中生代以来的全球气候变化过过程，还带动了一批新学科，如层序地层学，锶同位素地层学的出现，使地质学从零星的描述发展到地球系统研究阶段。同时，使测井技术层次由油气，煤炭测井上升到测井地质的成因研究。     

中国海与现代科学技术

中国既是一个大陆国家又是一个海洋国家，约３００万平方公里的海域与６５００多个岛屿如同陆地资源一样为中国人民提供了舟辑之便与渔盐之利，还蕴藏着丰富的矿产资源。