Petrological Characteristics and Genesis of the Central Indian Ocean Basin Basalts

The Central Indian Ocean Basin （CIOB） basalts are plagioclase-rich, while olivine and pyroxene are very few. The analyses of 41 samples reveal high FeOT （～10-18 wt%） and TiO 2 （～1.4-2.7 wt%） indicating a ferrobasaltic composition. The basalts have high incompatible elements （Zr 63-228 ppm; Nb ～1-5 ppm; Ba ～15-78 ppm; La ～3-16 ppm）, a similar U/Pb （0.02-0.4） ratio as the normal midoceanic basalt （0.16±0.07） but the Ba/Nb （12.5-53） ratio is much larger than that of the normal midoceanic ridge basalt （～5.7） and Primitive Mantle （9.56）. Interestingly almost all of the basalts have a significant negative Eu anomaly （Eu/Eu＊=0.78-1.00） that may have been a result of the removal of feldspar and pyroxene during crystal fractionation. These compositional variations suggest that the basalts were derived through fractional crystallization together with low partial melting of a shallow seated magma.

Physical Properties,Morphology and Petrological Characteristics of Pumices from the Central Indian Ocean Basin

About 400 pumice clasts collected from the Central Indian Ocean Basin（CIOB）were studied for their morphology and were classified based on their shape and size.A majority of the samples range between1 cm and 36 cm and in the Zinggs shape diagram plot in the equant and oblate fields.The Corey Shape Factor for most of the samples is close to 0.7,which is common for volcaniclastic material. The physical properties such as density,specific gravity,void ratio,porosity,moisture content and degree of saturation,were determined for 30 pumice samples.Density varies from 0.21 to 0.74 g/cm^3 specific gravity 1.84 to 3.27,void ratio 2.21 to 10.67,porosity 67%to 91%,moisture content during sinking 0.44 to 2.35 and degree of saturation varies from 26.5%to 86%.Binocular and electron microscopy studies reveal that 60%of the vesicles are elongated,30%are spherical and 10%are fibrous.Petrography of the pumices exhibits vitrophyric texture with phenocrysts of feldspars and clinopyroxenes.X-ray diffractrogram and mineral analyses confirm plagioclase to be a major phase, while quartz and orthoclase are not uncommon.Todorokite is commonly present in the ferromanganese oxide coating present over some of the pumices.This paper also delves into some details concerning the controversial origin of the pumices and glass shards in the CIOB.

Implications of REE incorporation and host sediment influence on the origin and growth processes of ferromanganese nodules from Central Indian Ocean Basin

This study presents new major,trace and REE data for thirty-five ferromanganese nodules recovered from areas representing three different sediment types(siliceous,red clay and their transition zone)in the Central Indian Ocean Basin(CIOB)to address their genetic aspects,classification,growth rate,nature of host sediments and influence of REE in the processes of nodule formation.The nodules from CIOB are mostly either hydrogenetic(metals coming from oxygenated bottom water)and diagenetic(metals coming from suboxic sediment pore water)or a combination of both,depending on the source of supply of metal.However,a number of biogeochemical processes mediate this supply of metals which again changes from time to time,making the nodule growth process highly dynamic.This study suggests that at the initial stage of nodule growth,host sediments do not play much role in controlling the growth processes for which REEs can enter both Mn and Fe oxyhydroxide phases equally.Thus,the bottom water signature is imprinted in these early formed nodules irrespective of their host sediment substrate but with gradual growth and burial in the sediment,the main mode of metal enrichment becomes diagenetic through sediment pore water.This tends to increase the concentration of Mn,Ni and Cu over other elements which are retained in the sediment fraction.Among the REEs,Ce concentration of the nodules shows significant positive anomaly due to variation in redox potential and hence its magnitude can be used to get an idea about the metal enrichment procedure and the genetic type of the nodules.However,based on host sediment only,not much difference is found in the magnitude of Ce anomaly in these nodules.On the other hand,discrimination diagram,based on HFSE and REY chemistry,indicates that most of these nodules are of diagenetic origin under oxic condition with a trend towards hydrogenetic field.Further,the genetic type of the ferromanganese nodules from the CIOB are more effectively differentiated by a combination of their major and trace element concentrations rather than solely based on their REE or HFSE chemistry or host sediment substrate.

Lithospheric Structure Model of Central Indian Ocean Basin Using Ocean Bottom Seismometer Data

The intense deformation zone in the central Indian Ocean, south of Indian continent is one of the most complex regions in terms of its structure and geodynamics. The deformation zone has been studied and debated in 1990s for its genesis. It was argued that deformation is mainly confined to sedimentary and oceanic crustal layers, while the large wave length geoidal anomalies, on which the deformation region lies, called for deeper sources. The inter connection between deeper and the shallower sources is found missing. The current study focuses on the complexities of this region by analyzing OBS （ocean bottom seismometer） data. The data acquired by five OBS systems along a 300 km long south-north profile in the CIOB （central Indian Ocean basin） have been modeled and the crustal and sub-crustal structure has been determined using 2-D tomographic inversion. Four subsurface layers are identified representing the sediment column, upper crustal layer, lower crustal layer and a sub-crustal layer （upper mantle layer）. A considerable variation in thickness as well as velocity at all interfaces from sedimentary column to upper mantle is observed which indicates that the tectonic forces have affected the entire crust and sub-crustal configuration. The sediments are characterized by higher velocities （2.1 kin/s） due to the increased confining pressure. Modeling results indicated that the velocity in upper crust is in the range of 5.7-6.2 km/s and the velocity of the lower crust varies from 7.0-7.6 km/s. The velocity of the sub-crustal layer is in the range of 7.8-8.4 km/s. This high-velocity layer is interpreted as magmatic under-plating with strong lateral variations. The base of the 7.0 km/s layer at 12-15 km depth is interpreted as the Moho.

Geochemical characteristics of REY-rich pelagic sediments from the GC02 in central Indian Ocean Basin

As a potential mineral resource, the clay minerals enriched in rare earth elements including yttrium（REY） in the deep sea have been attracting great attention. However, the enrichment mechanism of REY remains unclear. To understand the geochemical characteristics and factors controlling REY enrichment in zeolite clay in the deep sea, we conducted mineral identification by XRD, major and trace element measurements by XRF and REY analyses by ICP-MS on a 1.4-m-long sediment core（GC02） located in the Central Indian Oceanic Basin（CIOB）. The main findings include：（1） the core sediments in GC02 possess elevated REY contents and exhibited a strong negative Ce anomaly, an apparent MREE bulge and positive Y anomaly. These were comparable with typical REY-rich clays in the Pacific Ocean, indicating the similar REY enrichment mechanism and the presence of REY-rich clays in the CIOB;（2） in comparison with the dataset from the Wharton Basin and DSDP site 213, the higher content of REY and stronger PAAS（Post Archean Australian Shale） normalization patterns in the GC02 sediments were likely caused by the weaker impact of terrigenous materials of GC02. The CIOB was suggested to be a promising place hosting REY rich pelagic sediments.

Tropical Indian Ocean Basin Mode recorded in coral oxygen isotope data from the Seychelles over the past 148 years

The tropical Indian Ocean （TIO） displays a uniform basin-wide warming or cooling in sea surface temperature （SST） during the decay year of E1 Nifio-Southern Oscillation （ENSO） events. This warming or cooling is called the tropical Indian Ocean Basin Mode （IOBM）. Recent studies showed that the IOBM dominates the interannual variability of the TIO SST and has impacts on the tropical climate from the TIO to the western Pacific. Analyses on a 148-year-long monthly coral δ28O record from the Seychelles Islands demonstrate that the Seychelles coral δ18O not only is associated with the local SST but also indicates the interannul variability of the basin-wide SST in the TIO. Moreover, the Seychelles coral δ180 shows a dominant period of 3-7 years that well represents the variability of the IOBM, which in return is modulated by the inter-decadal climate variability The correlation between the Seychelles coral dlSO and the SST reveals that the coral δ18O lags the SST in the eastern equato- rial Pacific by five months and reaches its peak in the spring following the mature phase of ENSO. The spatial pattern of the first EOF mode indicates that the Seychelles Islands are located at the crucial place of the IOBM. Thus, the Seychelles coral δ80 could be used as a proxy of the IOBM to investigate the ENSO teleconnection on the TIO in terms of long-time climate variability.

Impact of Tropical Indian Ocean Temperature on the Ozone Layer in East Asia

Based on the reanalysis data of monthly mean sea surface temperature (SST) from British Hadley Center and ozone mass mixing ratio from National Aeronautics and Space Administration (NASA) during 1980-2015, two indexes IOBI and IODI of the main modes characterizing SST changes in the tropical Indian Ocean——Indian Ocean Basin (IOB) and Indian Ocean Dipole (IOD) were calculated firstly, and then the correlation of SST anomaly (SSTA) in the tropical Indian Ocean and ozone mass mixing ratio in the stratosphere over East Asia from 1980 to 2015 was analyzed. Besides, the impact of SST changes in the tropical Indian Ocean on the distribution of ozone layer in East Asia was discussed. The results show that SST changes in the tropical Indian Ocean had significant effects on stratospheric ozone distribution in East Asia, and it was consistent with the temporal changes of IOB and IOD. IOBI and IODI had a certain correlation with stratospheric ozone changes in East Asia, with a particularly significant correlation in the lower stratosphere (70 hPa) and middle stratosphere (40 hPa) especially during spring and autumn.

Role of the Oceanic Channel in the Relationships between the Basin/Dipole Mode of SST Anomalies in the Tropical Indian Ocean and ENSO Transition

The relationships between the tropical Indian Ocean basin （IOB）/dipole （IOD） mode of SST anomalies （SSTAs） and ENSO phase transition during the following year are examined and compared in observations for the period 1958-2008. Both partial correlation analysis and composite analysis show that both the positive （negative） phase of the lOB and IOD （independent of each other） in the tropical Indian Ocean are possible contributors to the E1 Nino （La Nifia） decay and phase transition to La Nifia （El Nifio） about one year later. However, the influence on ENSO transition induced by the IOB is stronger than that by the IOD. The SSTAs in the equatorial central-eastern Pacific in the coming year originate from subsurface temperature anomalies in the equatorial eastern Indian and western Pacific Ocean, induced by the IOB and IOD through eastward and upward propagation to meet the surface. During this process, however the contribution of the oceanic channel process between the tropical Indian and Pacific oceans is totally different for the IOB and IOD. For the IOD, the influence of the Indonesian Throughflow transport anomalies could propagate to the eastern Pacific to induce the ENSO transition. For the IOB, the impact of the oceanic channel stays and disappears in the western Pacific without propagation to the eastern Pacific.

The Southwest Indian Ocean Thermocline Dome in CMIP5 Models:Historical Simulation and Future Projection

Using 20 models of the Coupled Model Intercomparison Project Phase 5 （CMIP5）, the simulation of the Southwest Indian Ocean （SWIO） thermocline dome is evaluated and its role in shaping the Indian Ocean Basin （IOB） mode following E1 Nifio investigated. In most of the CMIP5 models, due to an easterly wind bias along the equator, the simulated SWIO thermocline is too deep, which could further influence the amplitude of the interannual IOB mode. A model with a shallow （deep） thermocline dome tends to simulate a strong （weak） IOB mode, including key attributes such as the SWIO SST warming, antisymmetric pattern during boreal spring, and second North Indian Ocean warming during boreal summer. Under global warming, the thermocline dome deepens with the easterly wind trend along the equator in most of the models. However, the IOB amplitude does not follow such a change of the SWIO thermocline among the models; rather, it follows future changes in both ENSO forcing and local convection feedback, suggesting a decreasing effect of the deepening SWIO thermocline dome on the change in the IOB mode in the future.

Remote forcing of Indian Ocean warming on Northwest Pacific during El Nio decaying years:a FOAM model approach

This paper attempts to analyze in detail the remote influence of the Indian Ocean Basin warming on the Northwest Pacific （NWP） during the year of decaying E1 Nifio. Observation data and the Fast Ocean- Atmosphere coupled Model 1.5 were used to investigate the triggering conditions under which the remote influence is formed between the positive sea surface temperature （SST） anomaly in the North Indian Ocean and the Anomalous Northwest Pacific anticyclone （ANWPA）. Our research show that it is only when there is a contributory background wind field over the Indian Ocean, i,e., when the Indian Summer Monsoon （ISM） reaches its peak, that the warmer SST anomaly in the North Indian Ocean incites significant easterly wind anomalies in the lower atmosphere of the Indo-West tropical Pacific. This then produces the remote influence on the ANWPA. Therefore, the SST anomaly in the North Indian Ocean might interfere with the prediction of the East Asia Summer Monsoon in the year of decaying E1 Nifio. Both the sustaining effect of local negative SST anomalies in the NWP, and the remote effect of positive SST anomalies in the North Indian Ocean on the ANWPA, should be considered in further research.

环印度洋地区被动陆缘盆地构造沉积演化及其对成藏要素的控制作用

环印度洋周缘被动陆缘盆地油气资源潜力巨大,是当前世界油气勘探的热点地区之一。本文基于IHS商业数据库和前人研究成果等资料,厘定了环印度洋地区被动陆缘盆地构造演化史,分析了构造演化对盆地充填结构和成藏要素的影响,并利用蒙特卡洛模拟法评估了盆地油气资源潜力,优选了有利勘探区带。研究结果表明,环印度洋地区被动陆缘盆地经历了3期构造演化阶段,依次为裂前期、同裂谷期和被动陆缘期。根据盆地演化的主导阶段,研究区内被动陆缘盆地可分为拉张边缘裂前发育型、拉张边缘断坳叠置型、拉张边缘坳陷发育型和转换边缘断坳叠置型。盆地内烃源岩主要发育于裂前期—被动陆缘早期,不同地区的主力烃源岩层系不同;储集岩主要发育于裂前期—被动陆缘晚期;区域盖层则主要发育于被动陆缘期。资源评价结果显示,研究区内重点被动陆缘盆地待发现石油、天然气和凝析油可采资源量(均值)分别为4.49×10^(8) t,15.86×10^(12) m^(3)和5.23×10^(8) t,折合成油当量137.69×10^(8) t。澳大利亚西北陆架北卡那封盆地裂前中—上三叠统区带、东非地区鲁伍马盆地北部和坦桑尼亚盆地南部中白垩统—新近系三角洲-深水扇区带是最有潜力的勘探区带。

北大西洋和热带印度洋海温的协同作用对松花江流域暖季降水年代际变化的影响

利用松花江流域100站降水资料、NCEP/NCAR再分析资料、哈得来中心海温资料等,运用多种统计方法和数值模拟分析了1975—2020年松花江流域暖季(5—9月)降水的年代际变化特征及其与北大西洋和热带印度洋海温的关系。研究表明,松花江流域暖季降水具有明显的年代际变化特征,20世纪90年代中后期发生了明显的年代际转变,由多雨阶段转为少雨阶段。年代际尺度上,暖季北大西洋马蹄型(North Atlantic Horseshoe,NAH)海温模态和印度洋海盆一致型(Indian Ocean Basin,IOB)海温模态分别与同期松花江流域降水呈显著的负相关和正相关关系,相关系数分别为-0.77和0.68。20世纪90年代中期之前,NAH模态负位相的海温异常在欧亚中高纬度地区激发纬向波列,将异常波能量传递到东北亚地区,在日本海至贝加尔湖地区产生异常气旋式环流;同时,IOB模态正位相的海温异常通过激发开尔文波,引起中国南海到孟加拉湾地区异常反气旋式环流,该异常反气旋式环流在东亚沿海激发出太平洋-日本型(PJ)波列,使得松花江流域出现异常气旋式环流。两者的共同作用使北太平洋水汽输送至松花江流域,有利于松花江流域降水偏多;20世纪90年代中期之后,NAH(IOB)模态由负位相(正位相)转为正位相(负位相),在NAH正位相和IOB负位相的协同影响下,松花江流域出现异常反气旋式环流,导致该区域降水偏少。

印度洋海盆模对南北半球太平洋副热带高压非对称的影响及机制

副热带高压对于我国天气气候具有重要影响,它的形成受到印度洋海温异常的影响,但其中的影响机制并不十分清楚。因此,本文利用1980-2020年NCEP/NCAR再分析资料,研究了印度洋海盆模(Indian Ocean Basin Model,IOBM)异常偏强对于太平洋副热带高压的影响;然后从能量角度分析IOBM引起南北半球太平洋海域副热带高压不对称性的物理机制;最后利用GFDL AM2.1模式进行模拟验证。为了说明印度洋海温异常对副热带高压的独立作用,对ENSO信号进行了滤除。结果表明:(1)夏季的印度洋暖海温暖异常会激发东传的Kelvin波,在西北太平洋地区低层出现反气旋异常,使西太副高较常年偏强,我国南海到菲律宾东部降水偏少;冬季IOBM正位相时,澳洲地区东风异常,热带西太平洋地区有大范围的降水负异常。印度洋海盆模对太平洋副热带高压非对称结构的影响在环流和降水场上均有体现。(2)根据能量诊断结果发现IOBM正位相时,夏季西北太平洋低层季风风场辐合区与扰动动能增长区相重合,有利于该地反气旋异常发展,从而使得副高偏强;冬季澳洲地区季风的风场辐合区与扰动动能增长区不能很好地配合,没有明显的反气旋异常。(3)利用数值模式模拟得到的结果能够验证沿赤道对称的印度洋海温异常在西太平洋地区引起的反气旋性环流和降水异常,无论位置还是强度都表现出极强的不对称性。因此,印度洋海盆模(IOBM)对于太平洋副热带高压南北半球非对称结构的形成具有重要作用,并进而对东亚及澳洲地区降水的异常分布产生影响,这为印度洋海盆模对西太副高的影响提供了理论基础。

印度洋偏暖对春末夏初西天山极端降水的影响研究

利用NOAA(美国国家海洋和大气管理局)气候预测中心的逐日格点降水资料分析了春末夏初(5、6月)天山极端降水时空变化以及印度洋海盆一致模(IOBM)影响极端降水的机制。结果表明:春末夏初天山极端降水变化具有明显的空间差异,西天山地区极端降水显著增加,其他区域极端降水变化不显著。诊断分析和数值模式模拟结果表明,春末夏初西天山地区极端降水增加与同期IOBM正异常促进冷暖气流在西天山地区交汇有关。IOBM正异常,一方面有利于东欧至中亚北部反气旋异常加强,促进冷空气向南输送。另一方面使得印度洋海温非均匀增暖,产生异常垂直环流,其下沉支使阿拉伯海和印度半岛产生反气旋异常,异常反气旋和偏南气流共同促进印度洋暖湿水汽向西天山输送,从而有利于西天山地区极端降水增加。

夏季伊朗高原和热带印度洋热力异常与同期塔里木盆地降水的可能联系

基于1979-2019年日本气象厅提供的地表感热与大气环流再分析资料,美国国家海洋和大气管理局提供的月均海表温度数据和国家气象信息中心提供的月降水数据,分析了夏季伊朗高原感热和热带印度洋海温与同期塔里木盆地降水的可能联系.奇异值分解分析表明,两个地区热力异常均与塔里木盆地夏季降水联系紧密,可以通过影响500 hPa风场和水汽输送来调制塔里木盆地夏季降水的变化.当伊朗高原感热和热带印度洋海温均偏强(弱)时,对应中亚上空受异常气旋(反气旋)控制,蒙古高原上空为反气旋(气旋)控制,二者共同作用塔里木盆地上空盛行异常偏南(北)风,形成有利(不利)的动力条件;同时印度半岛上空受异常反气旋(气旋)环流控制,中亚上空为异常气旋(反气旋),阿拉伯海水汽可(不可)由以上两个系统两步输送至新疆上空,导致盆地夏季降水整体偏多(少).当伊朗高原和热带印度洋热力异常反相变化时,盆地降水空间差异性较大,部分区域降水偏多,部分地区降水偏少.

热带印度洋海温与西北地区东部降水关系研究

利用西北地区东部1961 2009年99个气象测站逐月降水量资料,以及Hardley中心逐月海表面温度(SST)资料,采用最大协方差分析(MCA)、相关、回归等统计方法,考虑扣除ENSO(El Ni珘noSouthern Oscillation)影响后,分析了西北地区东部降水量和热带印度洋SST之间年际、年代际变化关系。结果表明:前期冬、春季持续异常的热带印度洋海盆模与西北地区东部5月降水异常主模态存在显著正相关关系,通常超前1~2个季节的暖(冷)海盆模对应5月西北地区东部降水偏多(少),并且这种显著关系存在年代际差异,20世纪70年代中期之前两者关系不显著,之后两者关系加强,通过了0.05显著性水平检验。热带印度洋海盆模对西北地区东部5月降水的影响可能是热带印度洋海盆模"电容器"效应的一种具体体现。

热带印度洋海温海盆一致模的变化规律及其对东亚夏季气候影响的回顾

近十几年,热带印度洋对全球气候的作用越来越受到关注。本文从热带印度洋气候态特征、海温海盆一致模的变化规律以及对东亚夏季气候的影响方面回顾了这些研究工作,并且对这些研究以及存在的不足做了系统的总结。

2016年我国梅雨异常特征及成因分析

利用国家气候中心梅雨监测资料和NCEP再分析资料,对2016年我国梅雨异常特征及其大尺度环流成因进行了分析。结果表明:(1)2016年我国梅雨有明显的区域特征,其中江南区入梅偏早14天,与1995年并列成为1951年以来入梅最早的年份,出梅偏晚11天,梅雨期(量)偏长(多),但梅雨期日平均降水量偏少;长江区入梅和出梅均偏晚,梅雨期接近常年,但梅雨量偏多一倍以上,梅雨量和梅雨期日平均降水量分别为1951年以来历史同期第三和第二高值;江淮区入梅、出梅及梅雨期接近常年,但梅雨量偏多。(2)对流层高、中、低层环流系统冬夏季节性调整和转变显著提前的共同作用,导致了2016年江南区入梅显著偏早;东亚副热带西风急流、西太平洋副热带高压(副高)和东亚夏季风涌在7月中旬阶段性地南落导致了江南区和长江区出梅偏晚。(3)受到前冬超强厄尔尼诺衰减和春、夏季热带印度洋全区一致海温模态偏暖的影响,梅雨期副高异常偏强,副高西南侧转向的水汽输送异常偏强,并在长江区和江淮区与北方弱冷空气辐合,造成梅雨量异常偏多。

2016年汛期气候预测效果评述及主要先兆信号与应用

2016年汛期预测较好把握了"全国气候年景状况总体差,降水偏多,涝重于旱,洪涝灾害比1983年重,但比1998年轻"的总趋势,准确预测了长江流域降水异常偏多和严重的汛情,对2016年东部地区季节内雨季进程"华南前汛期开始早,南海夏季风5月第5候爆发,长江中下游入、出梅晚且雨量明显多,及华北雨季开始晚、雨量接近常年到略偏多"的预测与实况也一致。对台风强度强,活跃程度前弱后强的预测与实况基本吻合,对夏季全国大部气温正常到偏高,尤其是我国西北大部气温异常偏高及盛夏江南华南阶段性高温热浪的预测也接近实况。但对我国北方地区降水的预测存在较大偏差,未能正确预测华北降水异常偏多和7—8月东北地区明显少雨。2016年汛期预测中重点考虑了冬季超强El Nino事件及其衰减后热带印度洋海温接力作用对夏季风环流的影响,认为夏季尤其是夏季前期西太平洋副热带高压强度异常偏强,位置明显偏西,东亚副热带夏季风强度弱,这些都直接造成长江中下游地区降水明显偏多。

2016年夏季我国东部降水异常特征及成因简析

2016年夏季(6~8月),我国东部降水呈南、北两条多雨带,长江中下游和华北大部降水均较常年同期明显偏多。其中,6—7月的降水主要发生在长江流域,而8月发生显著转折,除了华南地区降水偏多外,我国东部大部地区降水都较常年同期明显偏少。6—7月长江流域的降水偏多主要是受到偏强、偏西的西太平洋副热带高压(以下简称副高)的影响,副高脊线位置总体接近常年,但南北摆动较大,阶段性偏南对应了长江流域降水明显偏多的时段。同时,菲律宾附近低层异常反气旋环流导致来自副高西侧的水汽通量异常辐合区主要位于长江中下游。热带印度洋全区一致暖海温在超强El Nino衰减年的持续发展是导致上述环流异常的重要外强迫因子。8月,副高发生断裂,西北太平洋对流层低层转为异常气旋性环流控制,水汽输送异常辐散区控制我国东部大部地区,长江流域持续高温少雨。8月的热带大气季节内振荡(Madden-Julian Oscillation,MJO)活动偏强,MJO东传至西太平洋并持续长达25 d,为历史少见。异常的MJO活动是导致8月热带和副热带大气发生转折的重要原因。