10Be and barium concentrations of sediment core GeoB1008-3

Particle reactive elements are scavenged to a higher degree at ocean margins than in the open ocean due to higher fluxes of biogenic and terrigenous particles. In order to determine the influence of these processes on the depositional fluxes of 10Be and barium we have performed high-resolution measurements on sediment core GeoB1008-3 from the Congo Fan. Because the core is dominated by terrigenous matter supplied by the Congo River, it has a high average mass accumulation rate of 6.5 cm/kyr. Biogenic 10Be and Ba concentrations were calculated from total concentrations by subtracting the terrigenous components of10Be and Ba, which are assumed to be proportional to the flux of Al2O3. The mean Ba/Al weight ratio of the terrigenous component was determined to be 0.0045. The unusualy high terrigenous 10Be concentrations of 9.1 * 10**9 atoms/g Al2O3 are either due to input of particles with high10Be content by the Congo River or due to scavenging of oceanic 10Be by riverine particles. The maxima of biogenic 10Be and Ba concentrations coincide with maxima of the paleoproductivity rates. Time series analysis of the 10Be and of Ba concentration profiles reveals a strong dominance of the precessional period of 24 kyr, which also controls the rates of paleoproductivity in this core. During the maxima of productivity the flux of biogenic Ba is enhanced to a larger extent than that of biogenic 10Be. Applying a model for coastal scavenging, we ascribe the observed higher sensitivity of Ba to biogenic particle fluxes to the fact that the ocean residence time of Ba is approximately 10 times longer than that of 10Be.相较于开阔大洋，海洋边缘区域的颗粒反应性元素被清除的程度更高，这是由于生源颗粒与陆源颗粒的通量更高。为明确上述过程对铍-10（¹⁰Be）与钡（Ba）沉积通量的影响，我们对取自刚果扇的岩芯GeoB1008-3开展了高分辨率测量。该岩芯的物质主要由刚果河供给的陆源物质构成，其平均质量堆积速率高达6.5厘米/千年。 我们通过总浓度扣除陆源铍-10与钡的组分，计算得到了生源铍-10与钡的浓度；其中陆源组分的占比被假定与三氧化二铝（Al₂O₃）的通量成正比。经测定，陆源组分的钡铝重量比均值为0.0045。陆源铍-10浓度异常偏高，达9.1×10⁹原子/克三氧化二铝，这一现象可归因于两种可能：一是刚果河输入了铍-10含量较高的颗粒，二是河流颗粒对海洋铍-10产生了清除作用。 生源铍-10与钡的浓度峰值与古生产力速率峰值相吻合。对铍-10与钡的浓度剖面开展时间序列分析后发现，其主导周期为24千年的岁差周期，而该周期同样控制了本岩芯的古生产力速率。在古生产力峰值期，生源钡的通量增幅大于生源铍-10的通量增幅。通过应用沿岸清除模型，我们将观测到的钡对生源颗粒通量更高的敏感性归因于：钡的海洋滞留时间约为铍-10的10倍。