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1.
In the recent decades， a large amount of anthropogenic heat has been absorbed and stored in the Southern Ocean. Results from observations and climate models' simulations both show that the Southern Ocean displays large warming in the upper and subsurface ocean that maximizes at 45°~40°S. However， the underlying mechanisms and evolution processes of the Southern Ocean temperature changes remain unclear， leaving the Southern Ocean to be a hotspot of climate change studies in the recent years. The present study summarized the current progress in the observations and numerical modeling of long-term temperature changes in the Southern Ocean. The effects of changes in wind， surface heat flux， sea-ice and other factors on the ocean temperature changes were presented， along with the introduction to the role of oceanic mean circulation and eddies. The present study further proposed that a deepening of the understanding in the Southern Ocean temperature change may be achieved by investigating the fast and slow responses of the Southern Ocean to external radiative forcing， which are respectively associated with the fast adjustments of the ocean mixed-layer and the slow evolution of the deep ocean. Specifically， the striking and fast mixed-layer ocean warming north of 50°S is tightly related to the surface heat absorption over upwelling regions and wind-driven meridional heat transport， resulting in enhanced warming around 45°S. While in the slow response of the Southern Ocean temperature， the enhanced ocean warming shifts southward and downward， mainly associating with the heat transfer from oceanic eddies. The Southern Ocean temperature has pronounced climatic effects on many aspects， such as global energy balance， sea-level rise， ocean stratification changes， regional surface warming and atmospheric circulation changes. However， large model biases/deficiencies in simulating the present-day climatology and essential ocean dynamic processes last in generations of climate models， which are the main challenge in advancing our understanding in the mechanisms for the Southern Ocean climate changes. Therefore， to achieve reliable future projections of the Southern Ocean climate， substantial efforts will be needed to improve the model performances and physical understanding in the relative role of various processes in ocean temperature changes at different time scales. 相似文献
2.
地质界追寻华南洋的研究已有40年历史,在已有研究基础上,通过《中国区域地质志·江西志》《中国矿产地质志·江西卷》及《华南洋?滨太平洋构造演化与成矿》专题对中新元古代华南洋的地质特征与相关地质构造及成矿问题有了进一步的认识:凭祥?歙县?苏州结合带与金沙江?红河结合带在河内市北面相连,为中新元古代华南洋的消亡潜没地带,构成了扬子板块与新厘定的华夏?东南亚板块分界（简称金沙江?红河?歙县?苏州结合带）,现今是一条向南弯曲的纬向构造带;华南洋是扬子古板块与华夏?东南亚古板块间的中新元古代大洋,约闭合于820± Ma,板块碰撞发生了晋宁运动,扬子陆块与华夏?东南亚陆块基本固结,并连为一体;该区印支期以来为欧亚板块重要组成部分,新元古代晚期815± Ma至早古生代形成华南裂谷系,晚古生代以来先后受特提斯构造域、古太平洋构造域复合形成了中国南部及邻区高原、大陆、海域、岛弧的地质构造格局;在华南洋潜没地带的基础上经不断发展演化形成了以S、I型两大岩浆成矿系列为特色的钨锡铜金多金属贵稀金属“金沙江?红河?钦州湾?杭州湾”巨型成矿带。 相似文献
3.
It is summarized based on previous studies that warm and salty Atlantic Water (AW) brings huge amount of heat into Arctic Ocean and influences oceanic heat distribution and climate. Both heat transportation and heat release of AW are key factors affecting the thermal process in Eurasian Basin. The Arctic circumpolar boundary current is the carrier of AW, whose flow velocity varies to influence the efficiency of the warm advection. Because the depth of AW in Eurasian Basin is much shallower than that in Canadian Basin, the upward heat release of AW is an important heat source to supply sea ice melting. Turbulent mixing, winter convention and double-diffusion convention constitute the main physical mechanism for AW upward heat release, which results in the decrease of the Atlantic water core temperature during its spreading along the boundary current. St. Anna Trough, a relatively narrow and long trough in northern continental shelf of Kara Sea, plays a key role in remodeling temperature and salinity characteristics of AW, in which the AW from Fram Strait enters the trough and mixes with the AW from Barents Sea. Since the 21st Century, AW in the Arctic Ocean has experienced obvious warming and had the influence on the physical processes in downstream Canada Basin, which is attributed to the anomalous warming events of AW inflowing from the Fram Strait. It is inferred that the warming AW is dominated by a long-term warming trend superimposed on low frequency oscillation occurring in the Nordic Seas and North Atlantic Ocean. As the Arctic Ocean is experiencing sea ice decline and Arctic amplification, the role of AW heat release in response to the rapid change needs further investigation. 相似文献
4.
Geoffrey P. Glasby Bruce Mountain Theckethottathil C. Vineesh Virupaxa Banakar Ramesh Rajani Xiangwen Ren 《Resource Geology》2010,60(2):165-177
Co-rich Mn crusts from four different locations of the world ocean have been studied to understand the role of dissolved oxygen of the ambient seawater in the formation of Co-rich Mn crusts. WOCE (World Ocean Circulation Experiment) oxygen profiles of modern seawater in the Equatorial North Pacific Ocean, Equatorial South Indian Ocean and the North East Atlantic Ocean have been evaluated with respect to the occurrence of Co-rich Mn crusts at depths ranging from 1500 to 3200 m. The oxygen content at these depths varied from ∼90–240 µmol/kg. The oxygen minimum zone (OMZ), with oxygen contents in the range ∼45–100 µmol/kg, is located in the depth range 800–900 m in these regions. The age of the ocean crust on which seamounts formed is in the range 80.3–180 Ma. Profiles of the oxygen contents of seawater with depth in the oceans are shown to be extremely useful in establishing the optimum conditions for the formation of Co-rich Mn crusts. The use of WOCE oxygen profiles to study geochemical processes in the oceans is highly recommended. 相似文献
5.
西北太平洋各边缘海及其相应俯冲系统受深部构造活动等地质条件的控制,热流变化较大。在收集整理该区域最新的热流数据基础上,重点探讨西北太平洋俯冲带热结构相关理论、边缘海大洋岩石圈热演化理论模型和局部高异常热流的影响因素,总结了西北太平洋边缘海热流所反映的地质意义。研究结果表明,在西北太平洋“沟-弧-海”体系中,从“沟”到“弧”再到“边缘海”,热流密度呈“低-高-较高”的变化趋势,弧后地区整体表现为“均一高热”特征;千岛海沟、日本海沟和琉球海沟热流密度值在30.0 mW/m2左右,而对应的岛弧值为其2~3倍。弧后热流大小受到汇聚型俯冲带热结构的影响,俯冲带脱水作用导致的弧后上地幔黏度变化,地震速度降低,岩石圈弹性厚度减薄,引起小尺度地幔对流,形成弧后“均一高热”的热状态。热流的时空分布与岩石圈年龄也有关,随着岩石圈年龄增大,地表热流密度值会随之降低,热流密度值大小和离散性与其形成时间大致呈负相关。鄂霍次克海形成时代(30~65 Ma)较早,其热流密度值(86.8 mW/m2)和离散性(标准差3.727)相对较低;冲绳海槽目前还处于扩张阶段,其热流密度值(139.0 mW/m2)和离散性(标准差7.001)较高。浅层的地下水循环、断裂活动,深层的地幔部分熔融岩浆活动、弧后小尺度地幔对流、俯冲带拐角流等对局部异常热流起到一定程度的控制作用。 相似文献
6.
S. Ya. Sergin 《Doklady Earth Sciences》2016,469(2):892-894
We consider chemical reactions for the appearance of water during the formation of the planet from cosmic gas and dust material to explain the early geological existence of the Earth’s hydrosphere. This process is fully supported by the resources of the initial substances and thermal energy. Thus, the concept of V.I. Vernadsly about the geological eternity of the World Ocean and ancient age of the oceanic lithosphere is supported. The identical high location of the ancient and modern continental platforms under the conditions of continual isostatical equilibrium in the asthenosphere–lithosphere–hydrosphere gives grounds to conclude that the ocean water depth is stable. Taking this into account, we can consider that the geological evolution of the Earth began in the conditions of the existence of the World Ocean when the mass of the hydrosphere only slightly exceeded the modern one. 相似文献
7.
Doklady Earth Sciences - Statistical analysis of heat flow values measured in transform faults of the equatorial part of the Atlantic Ocean has been performed. Owing to the calculation using the... 相似文献
8.
Meteorological fields variability over the Indian seas in pre and summer monsoon months during extreme monsoon seasons 总被引：1，自引：0，他引：1
U. C. Mohanty R. Bhatla P. V. S. Raju O. P. Madan A. Sarkar 《Journal of Earth System Science》2002,111(3):365-378
In this study, the possible linkage between summer monsoon rainfall over India and surface meteorological fields (basic fields
and heat budget components) over monsoon region (30‡E-120‡E, 30‡S30‡N) during the pre-monsoon month of May and summer monsoon
season (June to September) are examined. For this purpose, monthly surface meteorological fields anomaly are analyzed for
42 years (1958-1999) using reanalysis data of NCEP/NCAR (National Center for Environmental Prediction/National Center for
Atmospheric Research). The statistical significance of the anomaly (difference) between the surplus and deficient monsoon
years in the surface meteorological fields are also examined by Student’s t-test at 95% confidence level.
Significant negative anomalies of mean sea level pressure are observed over India, Arabian Sea and Arabian Peninsular in the
pre-monsoon month of May and monsoon season. Significant positive anomalies in the zonal and meridional wind (at 2 m) in the
month of May are observed in the west Arabian Sea off Somali coast and for monsoon season it is in the central Arabian Sea
that extends up to Somalia. Significant positive anomalies of the surface temperature and air temperature (at 2 m) in the
month of May are observed over north India and adjoining Pakistan and Afghanistan region. During monsoon season this region
is replaced by significant negative anomalies. In the month of May, significant positive anomalies of cloud amount are observed
over Somali coast, north Bay of Bengal and adjoining West Bengal and Bangladesh. During monsoon season, cloud amount shows
positive anomalies over NW India and north Arabian Sea.
There is overall reduction in the incoming shortwave radiation flux during surplus monsoon years. A higher magnitude of latent
heat flux is also found in surplus monsoon years for the month of May as well as the monsoon season. The significant positive
anomaly of latent heat flux in May, observed over southwest Arabian Sea, may be considered as an advance indicator of the
possible behavior of the subsequent monsoon season. The distribution of net heat flux is predominantly negative over eastern
Arabian Sea, Bay of Bengal and Indian Ocean. Anomaly between the two extreme monsoon years in post 1980 (i.e., 1988 and 1987)
shows that shortwave flux, latent heat flux and net heat flux indicate reversal in sign, particularly in south Indian Ocean.
Variations of the heat budget components over four smaller sectors of Indian seas, namely Arabian Sea, Bay of Bengal and west
Indian Ocean and east Indian Ocean show that a small sector of Arabian Sea is most dominant during May and other sectors showing
reversal in sign of latent heat flux during monsoon season. 相似文献
9.
The millennial‐scale asynchrony of Antarctic and Greenland climate records during the last glacial period implies that the global climate system acts as a bipolar see‐saw driven by either high‐latitudinal and/or near‐equatorial sea‐surface perturbations. Based on the results of recent modelling of generic Heinrich and Dansgaard–Oeschger scenarios, we discuss the possibility that oscillations of the deep‐ocean conveyor may have been sufficient to cause this bipolar see‐saw. The bipolar climate asynchrony in our scenarios is caused by the toggle between North Atlantic heat piracy and South Atlantic counter heat piracy. Ocean circulation has an enhanced sensitivity to the northern deep‐water source as the North Atlantic Deep Water (NADW) cannot enter the Southern Ocean at depths shallower than the bottom of the Drake Passage. Any shoaling of the NADW can, therefore, increase the northward incursion of Antarctic Bottom Water (AABW), and trigger an interhemispheric climate oscillation. As hundreds of years are required to warm the respective high latitudes, the observed climate lead and lags between the two hemispheres can be explained entirely by the variability of the meridional overturning and by the corresponding change in the oceanic heat transport. Accordingly, it is entirely feasible for the global climate to work like a pendulum, which theoretically could be controlled by pushing at either of the deep‐water sources. Our model scenarios suggest that it is entirely feasible for the bipolar climate see‐saw to be controlled solely by variations in NADW formation. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
10.
热带太平洋海洋环流与暖池的结构特征、变异机理和气候效应 总被引：3，自引：0，他引：3
热带西太平洋暖池是引发强烈的大气对流、驱动Walker环流和Hadley环流系统的主要热源之一,对全球、尤其是东亚气候有重要影响。针对我国在提升气候预测水平方面的重大和迫切需求,国家重点基础研究发展计划项目"热带太平洋海洋环流与暖池的结构特征、变异机理和气候效应"于2011年7月正式立项。项目拟解决的关键科学问题包括:①调控暖池形成和变异的海洋环流多尺度相互作用过程;②海洋动力过程在暖池热盐结构变异中的作用及其机理;③暖池变异对不同类型El Nio影响机理的异同和对东亚季风变异的调制机理。围绕上述关键科学问题,项目将以暖池变异为中心,关注影响和控制暖池结构与变异的关键海洋过程,以及暖池海气相互作用影响ENSO循环、东亚季风年际变异的过程和机理,重点组织开展以下3个方面有针对性的调查研究:①热带太平洋环流和暖池的结构和变异特征;②热带太平洋环流与暖池相互作用的关键过程和机理;③暖池变异的海洋—大气耦合过程及其气候效应。在此基础上,项目将力争阐明暖池影响东亚季风和我国气候变异的过程、机理与敏感区,改进模式的混合参数化方案,提出有效提高ENSO预报技巧的同化方案,为我国短期气候预测能力的提高提供科学支撑。 相似文献
11.
The aim of the present study is to understand the impact of oceanic heat potential in relation to the intensity of tropical cyclones (TC) in the Bay of Bengal during the pre-monsoon (April–May) and post-monsoon (October–November) cyclones for the period 2006–2010. To accomplish this, the two-layer gravity model (TLGM) is employed to estimate daily tropical cyclone heat potential (TCHP) utilizing satellite altimeter data, satellite sea surface temperature (SST), and a high-resolution comprehensive ocean atlas developed for Indian Ocean, subsequently validated with in situ ARGO profiles. Accumulated TCHP (ATCHP) is estimated from genesis to the maximum intensity of cyclone in terms of minimum central pressure along their track of all the cyclones for the study period using TLGM generated TCHP and six-hourly National Centre for Environmental Prediction Climate Forecast System Reanalysis data. Similarly, accumulated sea surface heat content (ASSHC) is estimated using satellite SST. In this study, the relationship between ATCHP and ASSHC with the central pressure (CP) which is a function of TC intensity is developed. Results reveal a distinct relationship between ATCHP and CP during both the seasons. Interestingly, it is seen that requirement of higher ATCHP during pre-monsoon cyclones is required to attain higher intensity compared to post-monsoon cyclones. It is mainly attributed to the presence of thick barrier layer (BL) resulting in higher enthalpy fluxes during post-monsoon period, where as such BL is non-existent during pre-monsoon period. 相似文献
12.
Arne P. Willner Stuart N. Thomson Johannes Glodny Hans‐Joachim Massonne Rolf L. Romer Cees R. van Staal Alexandre Zagorevski 《地学学报》2019,31(1):1-10
Following Appalachian orogenesis, metamorphic rocks in central Newfoundland were exhumed and reburied under Tournaisian strata. New zircon fission‐track (ZFT) ages of metamorphic rocks below the Tournaisian unconformity yield post‐depositionally reset ages of 212–235 Ma indicating regional fluid‐absent reheating to at least ≥220°C. Post‐Tournaisian sedimentary thicknesses in surrounding basins show that burial alone cannot explain such temperatures, thus requiring that palaeo‐geothermal gradients increased to ≥30–40°C/km before final late Triassic accelerated cooling. We attribute these elevated palaeo‐geothermal gradients to localized thermal blanketing by insulating sediments overlying radiogenic high‐heat‐producing granitoids. Late Triassic rifting and magmatism before break up of Pangaea likely also contributed to elevated heat flow, as well as uplift, triggering late Triassic accelerated cooling and exhumation. Thermochronological ages of 240–200 Ma are seen throughout Atlantic Canada, and record rifting and basaltic magmatism on the conjugate margins of the Central Atlantic Ocean preceding the onset of oceanic spreading at ~190 Ma. 相似文献
13.
A sea ice model which contains Hibler's (1979, 1980) dynamics and Parkinson & Washington's (1979) thermodynamics is used to simulate the seasonal cycle of sea ice motion, thickness,compactness and growth rate in the Arctic Ocean under mean annual climatological forcing. Furthermore, it is used to investigate the air-sea heat flux and mean annual heat state over the entire Arctic Ocean. 相似文献
14.
North-eastern China and surrounding regions host some of the best examples of Phanerozoic juvenile crust on the globe. However, the Mesozoic tectonic setting and geodynamic processes in this region remain debated. Here we attempt a systematic analysis of the spatio-temporal distribution patterns of ore deposits in NE China and surrounding regions to constrain the geodynamic milieu. From an evaluation of the available geochronological data, we identify five distinct stages of ore formation: 240–205 Ma, 190–165 Ma, 155–145 Ma, 140–120 Ma, and 115–100 Ma. The Triassic (240–205 Ma) magmatism and associated mineralisation occurred during in a post-collisional tectonic setting involving the closure of the Paleo-Asian Ocean. The Early-Mid Jurassic (190–165 Ma) events are related to the subduction of the Paleo-Pacific Ocean in the eastern Asian continental margin, whereas in the Erguna block, these are associated with the subduction of the Mongol–Okhotsk Ocean. From 155 to 120 Ma, large-scale continental extension occurred in NE China and surrounding regions. However, the Late Jurassic magmatism and mineralisation events in these areas evolved in a post-orogenic extensional environment of the Mongol–Okhotsk Ocean subduction system. The early stage of the Early Cretaceous events occurred under the combined effects of the closure of the Mongol–Okhotsk Ocean and the subduction of the Paleo-Pacific Ocean. The widespread extension ceased during the late phase of Early Cretaceous (115–100 Ma), following the rapid tectonic changes resulting from the Paleo-Pacific Oceanic plate reconfiguration. 相似文献
15.
《International Geology Review》2012,54(8):985-1006
The Tianshan–Xingmeng molybdenum belt is part of a larger E–W-trending metallogenic belt in northern China. Most of these molybdenum deposits occur as porphyry or porphyry-skarn type, but there are also some vein-type deposits. Following systematic Re-Os dating of molybdenite from four deposits and comparisons with two previously dated deposits, we conclude that molybdenum mineralization in the Tianshan–Xingmeng Orogenic Belt resulted from hydrothermal activity linked to the emplacement of granitoid stocks. Three pulses of granitoid magmatism and Mo mineralization have been recognized in this study, corresponding to tectonic events in the Tianshan–Xingmeng Orogenic Belt. We identify five distinct stages of Mo mineralization events in the Tianshan–Xingmeng Orogenic Belt: 320–250 Ma, 250–200 Ma, 190–155 Ma, 155–140 Ma, and 140–120 Ma. Late Palaeozoic (320–250 Ma) Mo mineralization was closely related to closure of the Palaeo-Asian Ocean and collision between the Siberia and Tarim cratons. Triassic (250–200 Ma) Mo mineralization occurred in a post-collisional tectonic setting. The Early–Middle Jurassic (190–155 Ma) Mo mineralization was related to subduction of the Palaeo-Pacific Ocean on the eastern Asian continental margin, whereas in the Erguna block, the Mo mineralization events were associated with the subduction of the Mongol–Okhotsk Ocean. From 155 to 120 Ma, large-scale continental extension occurred in the Tianshan–Xingmeng Orogenic Belt and surrounding regions. However, the Late Jurassic (150–140 Ma) Mo mineralization events in these areas evolved in a post-orogenic extensional environment of the Mongol–Okhotsk Ocean subduction system. The Early Cretaceous (140–120 Ma) Mo mineralization occurred under the combined effects of the closure of the Mongol–Okhotsk Ocean and subduction of the Palaeo-Pacific Ocean. 相似文献
16.
The identification of syn- and late-orogenic flysch deposits, extending from the Betic Cordillera to the Southern Apennines, assists in the reconstruction of the tectonic-sedimentary evolution of the perimediterranean chains. A microplate was located between the European and African Plates during the Late Jurassic–Early Cretaceous, bordered northwards by the Piemontese Ocean and southwards by another (North Africa ‘Flysch’ Basin or Maghrebian) Ocean. The Piemontese Ocean and the northern margin of the microplate were structured from the Late Cretaceous to the Eocene to create an Eo-alpine Chain. The southern margin of the microplate was deformed in the Aquitanian, when the internal areas of the Maghrebian Ocean were characterized by syn-orogenic flysch deposits. This episode culminated with metamorphism (25–22 Ma) and nappe emplacement, which destroyed the former palaeogeography and created an orogenic belt (AlKaPeCa). Afterwards, a lower Burdigalian late-orogenic cycle started in the deformed area, which as a result of the opening of the Algero-Provençal Basin, caused the fragmentation of the AlKaPeCa, its thrusting on the ‘Flysch’ Basin and the collision with the North Africa and South Iberia Margins. These latter were folded and thrusted, the ‘Flysch’ Units pushed over the External Domain and also back-thrusted. Langhian late-orogenic deposits suture the new tectonic features. Finally, the whole orogen was thrust onto the foredeep during the Middle–Late Miocene. 相似文献
17.
《Gondwana Research》2014,26(4):1517-1534
Trapped between the Siberian Craton to the north, and the Tarim and North China blocks to the south, the Mongol–Okhotsk Belt represents a young portion of the Central Asian Orogenic Belt. The Andean-type orogeny was caused by the closure of the Mongol–Okhotsk Ocean, whose timing and mode of geodynamic evolution still needs to be clarified in more detail. This paper investigates the lithostratigraphic units of the Gorkhi Formation, which are comprised in the Hangay–Hentey terrane representing the accretionary prism of the northern continental margin of the Mongol–Okhotsk Ocean. In the tectonically disrupted slices of the Gorkhi Formation we identify a typical ocean plate stratigraphy with pelagic to hemipelagic and turbiditic sequences. Locally, shallow marine limestones are found associated with mafic volcanic rocks. XRF and LA–ICPMS measurements of these volcanic rocks clearly indicate an OIB signature. The geochemistry together with lithostratigraphic observations permit us to reconstruct the evolution of a seamount, ranging from its growth in shallow water depths and drowning due to subduction-related subsidence linked with subsequent radiolarian chert, hemipelagic shale and turbiditic sandstone cover sedimentation. Calc-alkaline felsic dikes later intruded the accreted silt and sandstone deposits. Standard sandstone provenance analysis, detrital zircon U–Pb laser ablation ICP-MS dating and Hf isotope ratios in the sandstones document a prevailing continental volcanic arc sourcing during Carboniferous from the northern margin of the Mongol–Okhotsk Ocean. 相似文献
18.
Basaltoids of the Vendian–Cambrian Kulbyurstyug volcanic complex in the eastern part of Kuznetsk Alatau have a high content of titanium (TiO2 3–4 wt %). They are relatively enriched with LILE and HFSE (Ba 360–900, Zr 160–726, Nb 66–101, ΣREE up to 225–329 ppm), and demonstrate a fractionated spectrum of REEs (La/Yb ～ 13–17), high Nb/U (44–66), and low Th/Ta and Th/Nb. These features are comparable with derivatives of OIB (Ocean Island Basalts) magmatism. The rock geochemistry suggests the possible formation of an initial mafic melt in the garnet-bearing peridotite mantle with 2–4% degree of melting and the presence of a small amount of spinel. By the age and composition, the studied volcanics are correlated with the OIB magmatism products, occurring in the adjacent Gorny Altai and also considered to be derivatives of intraplate magmatism of Riphean–Early Cambrian age. This magmatism was caused by plume activity during formation of the Paleo-Asian Ocean. 相似文献
19.
Bioavailable iron in the Southern Ocean: the significance of the iceberg conveyor belt 总被引：1，自引：0，他引：1
Productivity in the Southern Oceans is iron-limited, and the supply of iron dissolved from aeolian dust is believed to be the main source from outside the marine reservoir. Glacial sediment sources of iron have rarely been considered, as the iron has been assumed to be inert and non-bioavailable. This study demonstrates the presence of potentially bioavailable Fe as ferrihydrite and goethite in nanoparticulate clusters, in sediments collected from icebergs in the Southern Ocean and glaciers on the Antarctic landmass. Nanoparticles in ice can be transported by icebergs away from coastal regions in the Southern Ocean, enabling melting to release bioavailable Fe to the open ocean. The abundance of nanoparticulate iron has been measured by an ascorbate extraction. This data indicates that the fluxes of bioavailable iron supplied to the Southern Ocean from aeolian dust (0.01–0.13 Tg yr-1) and icebergs (0.06–0.12 Tg yr-1) are comparable. Increases in iceberg production thus have the capacity to increase productivity and this newly identified negative feedback may help to mitigate fossil fuel emissions. 相似文献
20.
This paper reports new petrological, geochemical and isotopic data for Carlsberg Ridge Basalts (CRB) of northwest Indian Ocean and evaluates their petrogenetic aspects in the context of the geochemical and tectonic evolution of the Indian Ocean mantle. The CRB samples exhibit tholeiitic to transitional composition of precursor melts derived by high degree, shallow level partial melting of a spinel peridotite mantle source. CRB reflects distinct E-MORB affinity with selective enrichment in incompatible trace elements. Higher values of Zr/Hf (33.8–47.3) and Zr/Sm (24.9–36.4) in conjunction with lower Nb/Ta (1.7–7.3) ratio corroborate their origin from an enriched mantle source. Negative Nb anomalies with lower Nb/Y (0.04–0.11) and Zr/Y (2.5–3.5) conform to a non-plume origin of these basalts. Higher Zr/Nb (25.5–71.5) and Th/Nb (0.6–0.42) compared to OIB substantiate contributions from recycled subduction-processed components in the source mantle. Lower Nb/U (6.2–37.9) values with higher Ba/Nb (6.1–21.9), Ba/Th (27.7–147.5), Zr/Nb (25.5–71.5) and Th/Nb (0.6–0.42) compared to OIB and N-MORB attest to role of a metasomatized oceanic lithosphere that recycled into the depleted upper mantle attributing to the source heterogeneity. Sr-Nd isotopic signatures (87Sr/86Sr: 0.702668 to 0.702841 and 143Nd/144Nd: 0.512972 to 0.513068) of CRB suggest a HIMU source component preserved in the northwest Indian Ocean Ridge mantle. The compositional diversity of the Indian Ocean mantle can be translated in terms of periodic refertilization of depleted N-MORB type mantle through delamination and recycling of oceanic (HIMU component) and continental lithosphere (EM I component) concurrent with Neoproterozoic-Palaeozoic amalgamation and Jurassic dispersal of Gondwana Supercontinent respectively. This study complies with the derivation of CRB from a geochemically heterogeneous Indian Ocean mantle that experienced a protracted residence beneath the Gondwana Supercontinent prior to the opening of Indian Ocean and trapped recycled metasomatized oceanic lithosphere genetically linked with multiple stages of paleo-ocean closure and continental convergence during Gondwana assembly. 相似文献