We measured sedimentation fluxes around JA06 Seamount (Xufu Guyot; 19°30′N, 158°00′E) as part of an environmental baseline survey in Japan’s exploration area for cobalt-rich crusts in the subtropical northwest Pacific. Sinking particles were collected at the flat top (sediment trap depths: 900 and 1,000 m) and northeastern base (sediment trap depths: 1,000 and 4,720 m) of the seamount from June 2016 to April 2017. Total mass fluxes were very low, with average values of 4.3–4.9 and 9.3 mg m⁻² d⁻¹ in the shallow traps at the flat top and base, respectively, which is consistent with an oligotrophic system. The lower fluxes at the flat top probably reflect lower productivity of siliceous microplankton, such as diatoms. However, we were unable to substantiate any potential mechanisms for this difference in productivity and cannot evaluate whether this is representative of typical conditions. When combined with previous observations at two adjacent seamounts, our results indicate widespread seasonality in sediment fluxes with a peak in late summer (August–September). However, satellite data indicate that summer is the season with the lowest primary production. This discrepancy could be explained either by phytoplankton blooms fueled by symbiotic nitrogen fixation that only cause minor increases in surface-ocean chlorophyll or short-lived blooms induced by passing typhoons under thick cloud cover. At the base site, we also analyzed material and element transport rates from shallow to deep waters. Half of the organic matter and >80% of the carbonate in sinking particles was not degraded in the water column, suggesting that most of the regeneration of these materials occurs near or on the sediment surface. Furthermore, four major processes appeared to control elemental fluxes in the area: lithogenic (Al, Ti, Fe), carbonate (Mg, Ca, Sr), biogenic (+scavenging) (Ni, Zn, Cd, Pb), and scavenging (V, Mn, Co, Cu, rare earth elements) processes. The estimation of excess flux based on the composition of upper continental crust demonstrated that >85% of total Mn, Co, Ni, Cu, Zn, Cd, and Pb fluxes were attributable to scavenging (+biogenic uptake). Scavenging-dominant metal fluxes are likely ubiquitous in the oligotrophic open ocean.

作为日本基线地区亚热带西北太平洋富钴结壳勘探环境基线调查的一部分，我们测量了JA06海山（徐福圭亚特； 19°30′N，158°00′E）周围的沉积通量。从2016年6月至2017年4月，在海山的平顶（沉积物陷阱深度：900和1,000 m）和东北基部（沉积物陷阱深度：1,000和4,720 m）收集下沉颗粒。总的通量非常低，平均值为4.3–4.9和9.3 mg m ^-2  d ^-1在平坦的顶部和底部的浅陷阱中，这与贫营养系统是一致的。平顶较低的通量可能反映了硅质浮游生物（如硅藻）的较低生产率。但是，我们无法证实任何导致生产率差异的潜在机制，也无法评估这是否代表典型条件。当与先前在两个相邻海山的观测结果相结合时，我们的结果表明沉积物通量具有广泛的季节性，夏末（8月至9月）达到峰值。但是，卫星数据表明，夏季是初级产量最低的季节。这种差异可以用共生固氮促进浮游植物的开花来解释，这种共生固氮只会使表层海洋的叶绿素有少量增加，或者是由于台风在厚厚的云层覆盖下导致的短暂开花。在基地，我们还分析了从浅水到深水的物质和元素传输速率。下沉颗粒中的一半有机物和碳酸盐中的> 80％在水柱中没有降解，这表明这些物质的大部分再生发生在沉积物表面附近或表面。此外，似乎有四个主要过程可以控制该区域的元素通量：致岩性（Al，Ti，Fe），碳酸盐（Mg，Ca，Sr），生物成因（+清除）（Ni，Zn，Cd，Pb）和清除（ V，Mn，Co，Cu，稀土元素）工艺。基于上部大陆壳的成分估算的过剩通量表明，总的Mn，Co，Ni，Cu，Zn，Cd和Pb通量中> 85％归因于清除（+生物吸收）。在贫营养的开放海洋中，占主导地位的金属通量很可能普遍存在。