1. Quantifying Advective Nutrient Fluxes and Their Impact on Coastal Phytoplankton Blooms in a Complex Coastal Ocean
关键词Tags: phytoplankton; vertical structure phytoplankton; vertical structure
摘要：沿海海洋初级生产主要由浮游植物大量繁殖驱动，其规模和时间由物理和生物地球化学过程决定。圣巴巴拉海峡是一个多产且地形复杂的盆地，位于加利福尼亚洋流系统内，其中主要的养分输送机制是风驱动的上升流和水平平流。然而，它们对观察到的浮游植物生物量变异性的相对贡献的量化仍然未知。在这项研究中，开发了平流养分通量的指标，并研究了它们对浮游植物水华预测的影响。通过推导原位硝酸盐测量与遥感和再分析数据之间的经验关系，以高时空分辨率生成地表和地下硝酸盐浓度图。 这些场与表面电流测量和垂直速度估计相结合，产生水平和垂直平流硝酸盐通量的指标。平流硝酸盐通量指标、硝酸盐浓度、速度和养分输送机制的常见物理海洋学代理（风应力和水平压力梯度）的时间序列与通道平均海面叶绿素浓度的时间序列一起进行评估。机制代理和速度都捕获了季节性叶绿素变化，但无法预测年际变化。与其他探索的指标相比，平流硝酸盐通量指标更多地解释了观察到的区域叶绿素浓度的变化。特别是，它们可以更准确地捕捉春季大型开花的规模和秋季小型开花的发生情况。 总体而言，这项研究阐明了驱动水华变异的主要机制，并强调了估计局部尺度养分通量的重要性。
Abstract: Coastal ocean primary production is driven largely by phytoplankton blooms, the magnitude and timing of which are determined by physical and biogeochemical processes. The Santa Barbara Channel is a productive and topographically complex basin located within the California Current System, where the dominant nutrient delivery mechanisms are wind‐driven upwelling and horizontal advection. However, quantification of their relative contributions to observed phytoplankton biomass variability remains unknown. In this study, metrics for advective nutrient fluxes are developed and their impact on predictions of phytoplankton blooms is investigated. Maps of surface and subsurface nitrate concentrations are produced at high spatiotemporal resolution by deriving empirical relationships between in situ nitrate measurements and remotely sensed and reanalysis data. These fields are combined with surface current measurements and vertical velocity estimates to produce metrics for horizontal and vertical advective nitrate fluxes. Time series of advective nitrate flux metrics, nitrate concentrations, velocities, and common physical oceanographic proxies for nutrient delivery mechanisms (wind stress and horizontal pressure gradients) are evaluated alongside time series of channel‐averaged sea surface chlorophyll concentrations. Both the mechanism proxies and velocities capture seasonal chlorophyll variations but fail to predict interannual changes. Advective nitrate flux metrics explain more of the observed variability in regional chlorophyll concentrations than the other metrics explored. In particular, they more accurately capture the magnitude of major spring blooms and the occurrence of minor fall blooms. Overall, this research elucidates the dominant mechanisms driving bloom variability and highlights the importance of estimating nutrient fluxes on local scales.