Particle dynamics are an essential component of global ocean biogeochemistry as they transport essential nutrients, carbon, and other reactive elements and compounds from the surface ocean to depth in the water column. The North Pacific Ocean is characterized by spatial and temporal variations in particle export mediated by a diverse food web and variations in environmental conditions, such as oxygenation. Here we explored temporal variability in the downward flux of particulate carbon (PC) and nitrogen (PN) using ²³⁸U²³⁴Th disequilibria, sediment traps and in situ pumps in winter, spring and summer at the time-series site Station ALOHA, a region characterized by a well-defined summer export pulse that influences the composition and structure of the biological community within the mesopelagic zone. We further explored spatial variability in PC and PN fluxes along a latitudinal gradient (17.5°-5°N x 150°W) that transitions from a low to high productivity region influenced by equatorial upwelling, with several stations further characterized by a shallow (~ 130 m) oxygen minimum zone. Winter PC and PN fluxes at 150 m at Station ALOHA were low, while summer and spring fluxes were significantly higher, coinciding with a seasonal export pulse associated with diazotrophs. PC and PN fluxes along the 155°W transect were also low at 150 m and similar to those measured at Station ALOHA in winter. At Station ALOHA zooplankton impart a greater influence over both small and large PC (and PN) fluxes in February relative to September or May, when heterotrophic bacteria play a proportionally larger role in particle remineralization and cycling. Along the transect stations, PC fluxes were too low to discern any clear trends with latitude, likely due to El Niño conditions at the time of sampling. Where vertical water column profiles of PC and PN fluxes were available, PC (and PN) fluxes were found to peak in the subsurface at 8°N (50 m) and 5°N (75 m) with zooplankton grazing and microbial remineralization following patterns similar to those found in February at Station ALOHA. Combined, these results support the hypothesis that small and large particles contribute to mesopelagic carbon demand depending on season, with smaller particles having greater contributions to mesopelagic food webs when surface derived particle export is low.

粒子动力学是全球海洋生物地球化学的重要组成部分，因为它们将必需的养分，碳以及其他反应性元素和化合物从海洋表层运送到水柱深处。北太平洋的特征是，不同食物网和环境条件（例如充氧）介导的颗粒出口的时空变化。在这里，我们使用²³⁸ U ²³⁴探索了颗粒碳（PC）和氮（PN）向下通量的时间变化冬季，春季和夏季在时间序列站点Station ALOHA上存在失衡，沉积物陷阱和原位泵，该地区的特征是确定的夏季出口脉冲影响了中古生境区内生物群落的组成和结构。我们进一步探索了受纬向梯度（17.5°-5°N x 150°W）影响的PC和PN通量的空间变异性，该梯度从赤道上流的影响从低生产率区域过渡到了高生产率区域，其中几个台站的特征还在于其较浅（〜 130 m）氧气最小区域。ALOHA站150 m处的冬季PC和PN通量较低，而夏季和春季的通量则明显较高，这与重氮菌相关的季节性出口脉动相吻合。155°W断面的PC和PN通量在150 m处也很低，与冬季在ALOHA站测得的相似。相对于9月或5月，在2月份，异养细菌在颗粒再矿化和循环中起着更大的作用，在2月份，ALOHA浮游动物对小型和大型PC（和PN）通量都产生了更大的影响。沿横断面站，PC的通量太低，无法识别出任何明显的纬度趋势，这可能是由于采样时的厄尔尼诺现象造成的。在可获得PC和PN通量的垂直水柱剖面的地方，发现PC（和PN）通量在8°N（50 m）和5°N（75 m）处达到峰值，并遵循浮游动物放牧和微生物再矿化的模式与二月份在车站ALOHA上发现的相似。结合起来