Characterizing the K-isotope compositions of marine sediments is a necessary step to using this novel isotope system to investigate K cycling both in the ocean system and in subduction zones. Here we report data for 70+ samples in order to characterize the K-isotope compositions of deep-sea sediments for two drill sites in the western Pacific: (1) IODP Site C0011 adjacent to the Nankai Trough and southwest Japan arc and (2) Site 1149 adjacent to the Izu-Bonin trench and arc. Variation in ${\mathrm{\delta }}^{41}\mathrm{K}$ at both sites is mostly subtle, reflecting a consistently strong contribution of K from sources that have ${\mathrm{\delta }}^{41}\mathrm{K}$ similar to the upper continental crust (UCC). Yet, in detail, the mean ${\mathrm{\delta }}^{41}\mathrm{K}$ at both sites is about 0.05 to 0.10‰ lower than the recently proposed best estimate for UCC (${\mathrm{\delta }}^{41}\mathrm{K}$ = -0.44‰). We infer that the slightly low mean ${\mathrm{\delta }}^{41}\mathrm{K}$ values relative to UCC are likely caused by secondary processes acting on the volcanogenic component of the sediments, though chemical weathering of (non-volcanogenic) terrigenous materials may also play a role. We measured a very low ${\mathrm{\delta }}^{41}\mathrm{K}$ value (-1.33 ± 0.04‰) for one discrete ash layer at Site C0011, so volcanoclastic materials may lower the ${\mathrm{\delta }}^{41}\mathrm{K}$ values of the bulk sediments, despite only accounting for a small fraction of the K in the sediments. Correlations between ${\mathrm{\delta }}^{41}\mathrm{K}$, Cr/Al, and K/Al in the upper sediments of Site 1149 were used to investigate mixing between volcanic ash and terrigenous materials. This approach indicates that mixing of isotopically light volcanic ash (with ${\mathrm{\delta }}^{41}\mathrm{K}$ about -0.75‰) and terrigenous materials (about -0.46‰) can account for the observed variation in ${\mathrm{\delta }}^{41}\mathrm{K}$ values in these sediments. In addition, we observe that at Site C0011 K isotopes exhibit a shift from UCC-like compositions in the upper sediments to slightly lighter compositions (by ∼0.08‰) ∼250 meters below the seafloor. This shift in ${\mathrm{\delta }}^{41}\mathrm{K}$ coincides with an abrupt change in certain physical properties (induration and porosity) of the sediments that may relate to the extent of weathering/degradation of the dispersed volcaniclastics, with more extensively weathered materials present in the lower sediments. Finally, we find evidence for variable admixture of a high ${\mathrm{\delta }}^{41}\mathrm{K}$ silicic volcanic ash in the lowermost sediments at Site C0011, supporting the view that heterogeneous volcaniclastics can give rise to significant ${\mathrm{\delta }}^{41}\mathrm{K}$ variations in marine sediments.

表征海洋沉积物的 K 同位素组成是使用这种新型同位素系统研究海洋系统和俯冲带中 K 循环的必要步骤。在这里，我们报告了 70 多个样品的数据，以表征西太平洋两个钻探地点的深海沉积物的 K 同位素组成：(1) IODP Site C0011 毗邻南海海槽和日本西南部弧，以及 (2)站点 1149 毗邻伊豆-博宁海沟和弧。变化${\mathrm{\delta }}^{41}\mathrm{ķ}$在这两个地点大多是微妙的，反映了来自有来源的 K 的持续强大贡献${\mathrm{\delta }}^{41}\mathrm{ķ}$类似于上大陆地壳（UCC）。然而，详细地说，平均${\mathrm{\delta }}^{41}\mathrm{ķ}$在这两个地点都比最近提出的 UCC 最佳估计值低约 0.05 至 0.10‰（${\mathrm{\delta }}^{41}\mathrm{ķ}$= -0.44‰)。我们推断略低的均值${\mathrm{\delta }}^{41}\mathrm{ķ}$相对于 UCC 的值可能是由作用于沉积物的火山成分的次生过程引起的，尽管（非火山）陆源物质的化学风化也可能起作用。我们测量了一个非常低的${\mathrm{\delta }}^{41}\mathrm{ķ}$现场 C0011 的一个离散灰层的值 (-1.33 ± 0.04‰)，因此火山碎屑材料可能会降低${\mathrm{\delta }}^{41}\mathrm{ķ}$大量沉积物的值，尽管仅占沉积物中 K 的一小部分。之间的相关性${\mathrm{\delta }}^{41}\mathrm{ķ}$、Cr/Al 和 K/Al 在 Site 1149 的上部沉积物中被用来研究火山灰和陆源物质之间的混合。这种方法表明，同位素轻火山灰（与${\mathrm{\delta }}^{41}\mathrm{ķ}$约-0.75‰）和陆源材料（约-0.46‰）可以解释观察到的变化${\mathrm{\delta }}^{41}\mathrm{ķ}$这些沉积物中的值。此外，我们观察到在 C0011 站点，K 同位素表现出从上层沉积物中的类似 UCC 的成分转变为在海底以下 250 米处稍轻的成分（约 0.08‰）。这种转变${\mathrm{\delta }}^{41}\mathrm{ķ}$与沉积物的某些物理性质（硬结和孔隙度）的突然变化相吻合，这可能与分散的火山碎屑的风化/降解程度有关，下部沉积物中存在更广泛的风化物质。最后，我们找到了高变量混合的证据${\mathrm{\delta }}^{41}\mathrm{ķ}$地点 C0011 最下部沉积物中的硅质火山灰，支持异质火山碎屑可以产生显着${\mathrm{\delta }}^{41}\mathrm{ķ}$海洋沉积物的变化。