Geochemistry of surface sediment samples from the South Atlantic Ocean

The aim of the present study is an evaluation of the applicability of biogenic barium as a proxy for productivity. For this purpose, 190 surface sediment samples from the South Atlantic Ocean were analysed for their barium and aluminium concentrations. Biogenic barium is estimated by subtracting the calculated terrigenous barium (obtained from the terrigenous Ba/Al ratio and the amount of Al in the sample) from the total Ba content in the sample. Based on the accumulation rates of biogenic barium, export production is estimated using three different algorithms proposed by [Paleoceanography 7 (1992) 163, doi:10.1029/92PA00181; Global Biogeochem. Cycles 9 (1995) 289, doi:10.1029/95GB00021; Geomar. Report 38 (1995) 105]. Primary productivity was calculated from these different export productions and compared with measurements of recent primary productivity in the overlying surface waters. Only the primary productions calculated on the basis of the algorithm of [Paleoceanography 7 (1992) 163, doi:10.1029/92PA00181] yield productivity values comparable to those existing in ocean surface waters. This study further reveals that it is not sufficient to use a constant, generally applicable organic carbon/biogenic barium ratio, as is postulated by [Global Biogeochem. Cycles 9 (1995) 289, doi:10.1029/95GB00021]. This ratio has to be assessed regionally. For the sediments of the Cape Basin in the eastern South Atlantic Ocean, a new algorithm is developed which gives plausible primary productivities for the overlying surface waters.

本研究旨在评估生源钡（biogenic barium）作为生产力代用指标的适用性。为达成该目标，我们对采自南大西洋的190份表层沉积物样品开展了钡与铝浓度分析。生源钡的计算方法为：从样品总钡含量中扣除通过陆源Ba/Al比值与样品铝含量推导得到的陆源钡含量。基于生源钡的堆积速率，本研究采用[Paleoceanography 7 (1992) 163, doi:10.1029/92PA00181; Global Biogeochem. Cycles 9 (1995) 289, doi:10.1029/95GB00021; Geomar. Report 38 (1995) 105]提出的三种不同算法，对海洋输出生产力进行估算。随后，基于上述不同输出生产力结果计算初级生产力，并将其与上覆表层水体的现代初级生产力实测值进行对比。分析结果显示，仅采用[Paleoceanography 7 (1992) 163, doi:10.1029/92PA00181]算法计算得到的初级生产力数值，与海洋表层水体的现有生产力水平具有可比性。本研究进一步发现，直接沿用[Global Biogeochem. Cycles 9 (1995) 289, doi:10.1029/95GB00021]中提出的通用恒定有机碳/生源钡比值并不充分，该比值需结合区域特征进行评估。针对南大西洋东部开普盆地的沉积物，本研究开发了一种全新算法，可为其上覆表层水体提供合理的初级生产力估算结果。