The evolution of early diagenetic signals in Bering Sea subseafloor sediments in response to varying organic carbon deposition over the last 4.3 Ma
The evolution of early diagenetic signals in Bering Sea subseafloor sediments in response to varying organic carbon deposition over the last 4.3 Ma
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DOI：
10.1016/j.gca.2013.01.025
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发表时间：
2013-05
影响因子：
5
通讯作者：
L. Wehrmann;S. Arndt;C. März;T. Ferdelman;B. Brunner
中科院分区：
文献类型：
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作者：
L. Wehrmann;S. Arndt;C. März;T. Ferdelman;B. Brunner
由于有机质输入量和质量的变化，深海海底海洋沉积物中的瞬态孔隙水和固相特征很常见，但往往难以解释。我们将综合海洋钻探计划（IODP）远征323站点U1341（白令海鲍尔斯岭）的高分辨率孔隙水和固相数据与反反应输运模型相结合，研究了这些深海海底沉积物中成岩信号的演化和潜在保存。我们探索这些信号如何反映鲍尔斯岭海底有机物沉积和反应性的主要变化。反演结果表明，2.51 ~ 2.58 ma以前，极不稳定有机质的高沉积通量可能与地表水初级生产力的增加有关。相关的有机分解硫酸盐还原速率的升高促进了低硫酸盐浓度，甲烷生成的开始，因此硫酸盐还原与甲烷的厌氧氧化（AOM）耦合。硫酸盐枯竭导致生物源重晶石溶蚀，表现为低Ba/Al比值的沉积层段。形成了两个硫酸盐-甲烷过渡带（SMTZs），其中高速率的AOM控制了硫酸盐的消耗，这是由来自上方海水和下方深层来源的硫酸盐流入维持的。在随后的~ 13万年中，这两个SMTZs的位置发生了非同步移动，直到甲烷生成和AOM下降。现今的硫酸盐浓度和硫同位素剖面仍然反映了反应性有机质脉冲的影响。它们还记录了更新世中晚期一段反应性有机质沉积非常低的时期，这可能与初级生产力非常低有关，导致沉积物中的微生物碳周转很少。我们的研究表明，结合深海海底沉积物固相记录的生物地球化学特征与反反应-输运模型对瞬态孔隙水信号的分析，可以对过去的深海生物圈过程和海洋盆地的古生产力有新的认识。
Transient pore-water and solid-phase signatures in deep subseafloor marine sediments, resulting from changes in both the amount and the quality of the organic matter input, are common but often difficult to interpret. We combined high-resolution pore-water and solid-phase data from Integrated Ocean Drilling Program (IODP) Expedition 323 Site U1341 (Bowers Ridge, Bering Sea) with inverse reaction-transport modeling to examine the evolution and potential preservation of diagenetic signals in these deep subseafloor sediments. We explore how these signals reflect major changes in the deposition and reactivity of organic matter to the seafloor at Bowers Ridge. Results of the inverse model approach reveal that 2.51–2.58Ma ago a high deposition flux of extremely labile organic matter, probably linked to increased surface water primary productivity, affected this site. Associated elevated organoclastic sulfate reduction rates facilitated low sulfate concentrations, the onset of methanogenesis, and consequently sulfate reduction coupled to the anaerobic oxidation of methane (AOM). Sulfate depletion caused the dissolution of biogenic barite reflected by a sedimentary interval with low Ba/Al ratios. Two sulfate–methane transition zones (SMTZs) evolved where high rates of AOM controlled sulfate consumption which was sustained by the influx of sulfate from seawater above and a deep source below. The positions of both SMTZs shifted non-synchronously over the subsequent ∼130,000yrs, until methanogenesis and AOM declined. The present-day sulfate concentration and sulfur isotope profiles still reflect the impact of the reactive organic matter pulse. They also record a period of very low reactive organic matter deposition during the middle to late Pleistocene, probably linked to very low primary productivity, resulting in little microbial carbon turnover in the sediment. Our study shows that combining biogeochemical signatures recorded in the solid-phase of deep subseafloor sediments with the analysis of transient pore-water signals by inverse reaction-transport modeling yields new insights into past deep biosphere processes and the paleoproductivity of marine basins.