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This study attempts to analyse paleoceanographic changes in the Central Indian Ocean (Deep Sea Drilling Project Site 237), linked to monsoon variability as well as deep-sea circulation during the Plio-Pleistocene. We used factor and cluster analyses of census data of the 34 most dominant species of benthic foraminifera that enabled us to identify five biofacies: Astrononion umbilicatulum–Uvigerina proboscidea (Au–Up), Pullenia bulloides–Bulimina striata (Pb–Bs), Globocassidulina tumida–Nuttallides umbonifera (Gt–Nu), Gyroidinoides nitidula–Cibicides wuellerstorfi (Gn–Cw) and Cassidulina carinata–Cassidulina laevigata (Cc–Cl) biofacies. Knowledge of the environmental preferences of modern deep-sea benthic foraminifera helped to interpret the results of factor and cluster analyses in combination with oxygen and carbon isotope values. The biofacies indicative of high surface productivity, resulting from a stronger South Equatorial Current (Au–Up and Pb–Bs biofacies), dominate the early Pliocene interval (5.6–4.5 Ma) of global warmth. An intense Indo-Pacific ‘biogenic bloom’ and strong Oxygen Minimum Zone extended to intermediate depths (1000–2000 m) over large parts of the Indian Ocean in the early Pliocene. Since 4.5 Ma, the food supply in the Central Indian Ocean dropped and fluctuated while deep waters were corrosive (biofacies Gt–Nu, Gn–Cw). The Pleistocene interval is characterized by an intermediate flux of organic matter (Cc–Cl biofacies). 相似文献
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We investigate Pacific Decadal Oscillation (PDO) signals recorded by two bimonthly resolved coral δ18O series from La Réunion and Ifaty (West Madagascar), Indian Ocean from 1882 to 1993. To isolate the main PDO frequencies,
we apply a band pass filter to the time series passing only periodicities from 16 to 28 years. We investigate the covariance
patterns of the coral time series with sea surface temperature (SST) and sea level pressure (SLP) of the Indian and Pacific
Oceans. In addition, the empirical orthogonal functions of the filtered SST and SLP fields (single and coupled) are related
to the filtered coral times series. The covariance maps show the typical PDO pattern for SST and SLP, confirming the coupling
between the Indian and Pacific Oceans. Both corals show the strongest signal in boreal summer. The La Réunion (Ifaty) coral
better records SST (SLP) than SLP (SST) pattern variability. We suggest that the filtered La Réunion coral δ18O represents δ18O of seawater that varies with the South Equatorial Current, which, in turn, is linked with the SST PDO. The filtered Ifaty
coral δ18O represents SST and is remotely linked with the SLP PDO variability. A combined coral record of the Ifaty and La Réunion
boreal summer δ18O series explains about 64% of the variance of the coupled SST/SLP PDO time series.
AGU OS06 special issue “Ocean’s role in climate change—a paleo perspective”. 相似文献
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根据1993年1─2月“实验3”号考察船在霍尼亚拉港（瓜达尔卡纳尔岛）至关岛的断面观测的温、盐度资料，分析了该断面上的地转流结构，计算了南赤道流及北赤道逆流的地转流流速和流量。结果表明：在纬线方向上E向流与W向流呈带状分布，在垂向上也多为E向流与W向流交替出现。在南赤道流和北赤道逆流中都夹有与主流向相反的流动，它们的流量分别约占主流向流量的1／3和1／5。文章还将分析计算结果与手头掌握的文献报道的结果作了比较。 相似文献
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The Simple Ocean Data Assimilation (SODA) package is used to better understand the variabilities of surface current transport in the Tropical Pacific Ocean from 1950 to 1999. Seasonal variation, internnual and decadal variability analyses are conducted on the three major surface currents of the Tropical Pacific Ocean: the North Equatorial Current (NEC), the North Equatorial Countecurrent (NECC), and the South Equatorial Current (SEC). The transport of SEC is quite larger than those of NEC and NECC. The SEC has two maximums in February and August. The NEC has a small annual variation. The NECC has a maximum in October and is very weak in March and April. All currents have remarkable interannual and decadal variabilities. The variabilities of the NEC and the SEC related to the winds over them well, but the relationship between the NECC and the wind over it is not close. Analysis related to El Niño-Southern Oscillation (ENSO) suggests that before El Niño (La Niña) the SEC is weaker (stronger) and the NECC is stronger (weaker), after El Niño (La Niña) the SEC is stronger (weaker) and the SEC is weaker (stronger). There is no notable relationship between the NEC and ENSO. 相似文献
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分级集合滤波(Hierarchical Ensemble Filter,HEF)和采样误差修正(Sampling Error Correction,SEC)局地化算法能够使采样误差取得极小值,且不需要给出距离的定义。为了检验其理论优势,基于集合卡尔曼滤波(Ensemble Kalman Filter,En KF)方法同化模拟雷达资料,通过与Gaspari-Cohn(GC)局地化算法对比,分析不同局地化算法对En KF同化效果的影响。结果表明,HEF和SEC局地化算法的雷达回波在水平和垂直方向上均强于GC局地化算法。HEF局地化算法各个变量的离散度最高,均方根误差最低;SEC局地化算法离散度略低,均方根误差略高;GC局地化算法离散度最低,均方根误差最高。相比于GC局地化算法,HEF和SEC局地化算法的冷池强度减弱,面积减小,下沉气流的速度和范围增大,雹霰混合比的大小和覆盖面积增大。通过模拟发现,HEF局地化算法模拟的北侧对流中心最强,SEC局地化算法模拟的南侧对流中心最强,且模拟出(40 km,60 km)处的强对流中心。HEF局地化算法模拟的冷池强度最强,HEF和SEC局地化算法基本上模拟出北侧的雹霰混合比高值区。这表明HEF局地化算法有效地改进了基于GC局地化算法的En KF雷达资料同化效果,SEC局地化算法减小了计算量,是HEF局地化算法较好的近似。 相似文献
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The structure of the upper ocean and surface atmospheric conditions are described during a ship cruise across the central Indian Ocean from December 1995 to January 1996. In situ data on currents, temperature, salinity and surface heat fluxes are described and compared with expected climatological values. Thermocline uplift in the 6-7°S latitude band is linked to the cyclonic shear of near-surface currents. A comparison of quiescent and windy periods demonstrates that evaporative fluxes become amplified near cyclonic vortices fed by southerly meridional winds. The ocean density structure is influenced by salinity gradients, driven by the precipitation-evaporation balance. Near the inter-tropical convergence zone (ITCZ), freshwater fluxes create a stable surface layer and helps to maintain the eastward equatorial counter-current. An analysis of the atmospheric boundary layer from NCEP re-analysis data seeks to place the in situ results into the context of weather conditions at the time of the cruise. Further studies of this kind will improve our understanding of relationships between the Indian Ocean monsoon and surrounding climates. 相似文献
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