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Pelagic productivity changes in the equatorial area fo the northwest Indian Ocean during the last 400,000 years

机译：近40万年来印度洋西北赤道上层生产力的变化。

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Major and selected trace element (Al, Fe, Mg, K, Ba,P, Mn, V, Cu, Ni, and Ti) records were analyzed in two coresrecovered from the northwestern Indian Ocean (core MD 90940on the Madingley Rise and core MD 85668 in the Somali Basin)order to monitor the sedimentary response to pelagicproductivityin this area during the last 400,000 years.Geochemical proxies such as bulk mass accumulation rate (MAR),Al-normalized major and trace element contents, major and traceelement MARs were compared to biologic markers ofpalaeoproductivity: a new radiolarian index (rad ratio), and thevariations of foraminiferal and radiolarian assemblages. Specialattention being paid to the barium record, a sequential leachingprocedure determined the main Ba-carrier fraction in the sediment,and thus, the amount of biogenic barium. The 'blue ocean'sedimentation on the Madingley Rise (core MD 90940) ischaracterized by a low MAR and an insignificant terrigenous input.The bulk MAR variations are directly related to the variations ofthe rad ratio,reflecting a direct link between surface productivityand pelagic sedimentation at this site. In this sediment, barium ismainly found as barite and can be considered as apalaeoproductivity proxy. In the Somali Basin (core MD 85668),the terrigenous inputs are relatively higher, but the bulk MARvariations are still related to the variations of surface productivity.No barite was found and barium is mainly linked to the terrigenousinput. A comparison of the two pelagic sites of the Madingley Riseand the Somali Basin points out the differences between thebarium records at both sites. Despite the location of both cores inthe pelagic domain, the geochemical record, and especially thebarium one, is dufferent form one core to the other. Thecomparison of the variations of the bulk MAR, which reflects thevariations of the surface productivity, presents significantdiscrepancies between both sites. In the 'blue ocean' (core MD90940), the productivity peak values are mainly recorded duringglacial intervals, but their maximum values are observed duringinterglacial isotope Stage 9. In the Somali Basin (core MD 85668),high bulk MAR periods occurred during glacial isotope stages. Theinterglacial episode of high productivity recorded on theMadingley Rise, the absence of significant variations ofproductivity at the 8/7 transition in the Somali basin, as well as theabsence of a time lag between both records indicate that thesurface productivity is, in this area, controlled more by the localvariations of the palaeoceanographic patterns than the globalclimatic changes, e.g. the glacial/interglacial alternations. 1999Elsevier Science B.V.All rights reserved.
机译：在从印度洋西北部发现的两个岩心中（主要是选定的痕量元素（Al，Fe，Mg，K，Ba，P，Mn，V，Cu，Ni和Ti）记录进行了分析（Madingley Rise的MD 90940核心和MD的核心）索马里盆地85668）为了监测该地区过去40万年来沉积对上层生产力的响应。对地球化学代理，如堆积质量累积率（MAR），Al归一化的主要和微量元素含量，主要和微量元素MARs进行了比较。古生产力的生物学标记：新的放射虫指数（弧度比）以及有孔虫和放射虫组合的变化。特别注意钡的记录，通过连续浸出过程确定了沉积物中主要的Ba载体含量，从而确定了生物成因钡的含量。 Madingley Rise（MD 90940的核心）上的``蓝色海洋''沉积物的特征是MAR较低且陆源输入微不足道.MAR的大量变化与辐射比的变化直接相关，反映了地表生产力与上层沉积物之间的直接联系这个网站。在这种沉积物中，钡主要是重晶石，可以看作是远古生产力的代表。在索马里盆地（MD 85668，核心），陆源输入相对较高，但大量的MAR变化仍与地表生产力的变化有关。未发现重晶石，钡主要与陆源输入有关。对Madingley Rise和索马里盆地的两个中上层站点进行的比较指出，这两个站点的钡记录之间存在差异。尽管两个岩心都位于上层海域，但地球化学记录，尤其是钡，是一个岩心与另一个岩心的区别。反映表面生产力变化的整体MAR的变化比较表明，这两个位置之间存在显着差异。在“蓝海”（MD90940核心）中，生产力峰值主要记录在冰川间隔期间，但在冰期同位素第9阶段观察到了其最大值。在索马里盆地（MD 85668核心）中，冰川同位素发生了高散装MAR时期阶段。在Madingley Rise上记录了高生产力的冰期事件，在索马里盆地8/7过渡期生产力没有显着变化，而且两个记录之间都没有时间滞后，这表明该地区的地表生产力受到更多的控制通过古海洋学模式的局部变化而不是全球气候变化，例如冰川/冰川间的交替。 1999 Elsevier Science B.V.保留所有权利。

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