Benthic foraminiferal assemblages and paleoproductivity reconstructions for the last 550 kyr of the Ontong Java Plateau, western equatorial Pacific

We analyzed foraminiferal and nannofossil assemblages and stable isotopes in samples from ODP Hole 807A on the Ontong Java Plateau in order to evaluate productivity and carbonate dissolution cycles over the last 550 kyr (kilo year) in the western equatorial Pacific. Our results indicate that productivity was generally higher in glacials than during interglacials, and gradually increased since MIS 13. Carbonate dissolution was weak in deglacial intervals, but often reached a maximum during interglacial to glacial transitions. Carbonate cycles in the western equatorial Pacific were mainly influenced by changes of deep-water properties rather than by local primary productivity. Fluctuations of the estimated thermocline depth were not related to glacial to interglacial alternations, but changed distinctly at ~280 kyr. Before that time the thermocline was relatively shallow and its depth fluctuated at a comparatively high amplitude and low frequency. After 280 kyr, the thermocline was deeper, and its fluctuations were at lower amplitude and higher frequency. These different patterns in productivity and thermocline variability suggest that thermocline dynamics probably were not a controlling factor of biological productivity in the western equatorial Pacific Ocean. In this region, upwelling, the influx of cool, nutrient-rich waters from the eastern equatorial Pacific or of fresh waters from rivers have probably never been important, and their influence on productivity has been negligible over the studied period. Variations in the inferred productivity in general are well correlated with fluctuations in the eolian flux as recorded in the northwestern Pacific, a proxy for the late Quaternary history of the central East Asian dust flux into the Pacific. Therefore, we suggest that the dust flux from the central East Asian continent may have been an important driver of productivity in the western Pacific.

为评估西赤道太平洋过去550千年（kyr）的生产力与碳酸盐溶解周期，我们分析了翁通爪哇海台ODP 807A孔样品中的有孔虫和纳米化石（nannofossil）组合及稳定同位素。结果表明，冰期生产力总体高于间冰期，且自海洋同位素阶段13（MIS 13）以来逐渐上升。碳酸盐溶解在冰消期较弱，但常在间冰期向冰期转换期间达到峰值。西赤道太平洋的碳酸盐旋回主要受深水性质变化影响，而非局地初级生产力。估算的温跃层深度（thermocline depth）波动与冰期-间冰期交替无关，但在约280 kyr时发生显著变化。此前，温跃层相对较浅，其深度波动振幅较大、频率较低；280 kyr之后，温跃层变深，波动振幅减小、频率升高。生产力与温跃层变异性的这些差异模式表明，温跃层动力学（thermocline dynamics）可能并非西赤道太平洋生物生产力的控制因素。在该区域，上升流、来自东赤道太平洋的低温富营养水输入或河流淡水输入可能从未发挥重要作用，且在研究期内对生产力的影响可忽略不计。推断的生产力变化总体上与西北太平洋记录的风尘通量波动密切相关，后者是东亚中部风尘输入太平洋晚第四纪历史的代用指标。