Data_Sheet_1_The Importance of Mesozooplankton Diel Vertical Migration for Sustaining a Mesopelagic Food Web.xls

We used extensive ecological and biogeochemical measurements obtained from quasi-Lagrangian experiments during two California Current Ecosystem Long-Term Ecosystem Research cruises to analyze carbon fluxes between the epipelagic and mesopelagic zones using a linear inverse ecosystem model (LIEM). Measurement constraints on the model include 14C primary productivity, dilution-based microzooplankton grazing rates, gut pigment-based mesozooplankton grazing rates (on multiple zooplankton size classes), 234Th:238U disequilibrium and sediment trap measured carbon export, and metabolic requirements of micronekton, zooplankton, and bacteria. A likelihood approach (Markov Chain Monte Carlo) was used to estimate the resulting flow uncertainties from a sample of potential flux networks. Results highlight the importance of mesozooplankton active transport (i.e., diel vertical migration) in supplying the carbon demand of mesopelagic organisms and sequestering carbon dioxide from the atmosphere. In nine water parcels ranging from a coastal bloom to offshore oligotrophic conditions, mesozooplankton active transport accounted for 18–84% (median: 42%) of the total carbon transfer to the mesopelagic, with gravitational settling of POC (12–55%; median: 37%), and subduction (2–32%; median: 14%) providing the majority of the remainder. Vertically migrating zooplankton contributed to downward carbon flux through respiration and excretion at depth and via mortality losses to predatory zooplankton and mesopelagic fish (e.g., myctophids and gonostomatids). Sensitivity analyses showed that the results of the LIEM were robust to changes in nekton metabolic demand, rates of bacterial production, and mesozooplankton gross growth efficiency. This analysis suggests that prior estimates of zooplankton active transport based on conservative estimates of standard (rather than active) metabolism are likely too low.

本研究采用从加州洋流生态系统长期生态系统研究巡航中的准拉格朗日实验获得的广泛生态和生物地球化学测量数据，利用线性逆生态系统模型（LIEM）分析了上混层与中层之间的碳通量。模型测量约束包括14C初级生产力、基于稀释的微型浮游动物摄食速率、基于肠道色素的中型浮游动物摄食速率（针对多个浮游动物体型类别）、234Th:238U不均衡和沉积陷阱测量的碳输出，以及微型浮游动物、浮游动物和细菌的代谢需求。采用似然方法（马尔可夫链蒙特卡洛）估计了从潜在通量网络样本中产生的结果流量不确定性。研究结果突出了中型浮游动物主动运输（即昼夜垂直迁移）在满足中层生物碳需求以及从大气中固碳方面的重要性。在从近岸水华到近海寡营养条件的不等九个水团中，中型浮游动物主动运输占到了总碳输送到中层的18-84%（中位数：42%），而颗粒有机碳的沉降（12-55%；中位数：37%）和俯冲（2-32%；中位数：14%）提供了剩余大部分。垂直迁移的浮游动物通过在深处的呼吸和排泄以及通过死亡损失到捕食性浮游动物和中层鱼类（如灯笼鱼和隆头鱼）的方式，对向下碳通流作出了贡献。敏感性分析表明，LIEM的结果对浮游动物代谢需求、细菌生产速率和中型浮游动物总生长效率的变化具有鲁棒性。此分析表明，基于保守的（而非主动的）代谢标准估计的浮游动物主动运输的先前估计可能过低。