Disentangling marine, soil and plant organic carbon contributions to continental margin sediments: A multi-proxy approach in a 20,000 year sediment record from the Congo deep-sea fan
Disentangling marine, soil and plant organic carbon contributions to continental margin sediments: A multi-proxy approach in a 20,000 year sediment record from the Congo deep-sea fan
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DOI：
10.1016/j.gca.2008.10.016
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发表时间：
2009
影响因子：
5
通讯作者：
J. Weijers;Stefan Schouten;E. Schefuß;R. Schneider;J. Damsté
中科院分区：
文献类型：
--
作者：
J. Weijers;Stefan Schouten;E. Schefuß;R. Schneider;J. Damsté
刚果深海扇(GEOB 6518-1岩心)是世界上最大的深海河流扇之一，其20 kyr长的沉积物序列被分析为散体和分子代用品，以重建自上次冰川盛期以来对这些沉积物的海洋、土壤和植物有机碳(OC)的贡献。C/N比和δ13Corg分别为10~12.5Corg和−24.5~−21‰VPDB。以海洋衍生的烯烃和陆地衍生的奇数正构烷烃为分子代用品，其浓度在0.2~4μg/g干重沉积物之间变化。此外，还使用了分支与类异戊二烯四醚(BIT)指数，该指数是土壤有机质输入的替代指标，在该岩心中的变化范围为0.3至0.5。基于不同个体代表的二元混合模型的应用表明，由于有机碳的异质性，对陆地有机碳输入的估计差异高达50%。应用δ~(13)Corg含量、C/N比和BIT指数的三端元混合模型，能够区分土壤和植物有机质作为沉积有机碳库的独立贡献者。结果表明，近20年来，深海扇体沉积物中海洋有机碳占总有机碳的20%~40%，土壤有机碳约占总有机碳的一半(∼平均为45%)。这表明，土壤有机碳代表了输送到扇沉积物中的大部分陆源有机碳。在过去的20年里，植物和土壤有机碳组分的积累速率变化了高达5倍的变化，并且与泥沙积累速率密切相关。它们在17kyr BP左右开始增加，在年轻的仙女木时期下降，在全新世早期达到峰值，在全新世晚期达到较低的值。这一模式与过去中非湿度和刚果河流量的恢复相吻合，揭示了中非降水模式对刚果深海扇陆源有机碳沉积的主导控制作用。海洋有机碳堆积速率与沉积物堆积速率关系不大，与陆源部分相比，随时间的变化很小。这些变化可能是由于在沉积速率较高的时期加强了保存，以及由于风力驱动的上升流导致初级生产力相对较小的波动。
A 20kyr long sediment sequence from the Congo deep sea fan (core GeoB 6518-1), one of the world’s largest deep sea river fans, has been analysed for bulk and molecular proxies in order to reconstruct the marine, soil and plant organic carbon (OC) contributions to these sediments since the last glacial maximum. The bulk proxies applied, C/N ratio and δ13Corg, ranged from 10 to 12.5 and from −24.5 to −21‰ VPDB, respectively. As molecular proxies, concentrations of marine derived alkenones and terrestrial derived odd-numbered n-alkanes were used, which varied between 0.2 and 4μg/g dry weight sediment. In addition, the branched vs. isoprenoid tetraether (BIT) index, a proxy for soil organic matter input, was used, which varied from 0.3 to 0.5 in this core. Application of binary mixing models, based on the different individual proxies, showed estimates for terrestrial OC input varying by up to 50% due to the heterogeneous nature of the OC. Application of a three end-member mixing model using the δ13Corgcontent, the C/N ratio and the BIT index, enabled the distinction of soil and plant organic matter as separate contributors to the sedimentary OC pool. The results show that marine OC accounts for 20% to 40% of the total OC present in the deep sea fan sediments over the last 20kyr and that soil OC accounts for about half (∼45% on average) of the OC present. This suggests that soil OC represents the majority of the terrestrial OC delivered to the fan sediments. Accumulation rates of the plant and soil OC fractions over the last 20kyr varied by a factor of up to 5, and are strongly related to sediment accumulation rates. They showed an increase starting at ca. 17kyr BP, a decline during the Younger Dryas, peak values during the early Holocene and lower values in the late Holocene. This pattern matches with reconstructions of past central African humidity and Congo River discharge from the same core and revealed that central African precipitation patterns exert a dominant control on terrestrial OC deposition in the Congo deep sea fan. Marine OC accumulation rates are only weakly related to sediment accumulation rates and vary only little over time compared to the terrigenous fractions. These variations are likely a result of enhanced preservation during times of higher sedimentation rates and of relative small fluctuations in primary production due to wind-driven upwelling.