Seasonal dynamics of midwater zooplankton and relation to particle cycling in the North Pacific Subtropical Gyre
Seasonal dynamics of midwater zooplankton and relation to particle cycling in the North Pacific Subtropical Gyre
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DOI：
10.1016/j.pocean.2020.102266
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发表时间：
2020-03-01
影响因子：
4.1
通讯作者：
Drazen, Jeffrey C.
中科院分区：
文献类型：
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作者：
Hannides, Cecelia C. S.;Popp, Brian N.;Drazen, Jeffrey C.
中层浮游动物是开阔海洋中生物地球化学转化的主要媒介，但其特征和活动仍然知之甚少。在这里，我们评估中层水浮游动物生物量，氨基酸（AA）特定的稳定同位素组成（三角洲N-15值）使用特定化合物的氨基酸同位素分析（CSIA-AA），营养位置，和元素组成在北太平洋副热带环流（NPSG）。我们专注于浮游动物收集在冬季，春季和夏季评估中层水营养动态的季节性周期。我们第一次发现，中层浮游动物强烈响应生产和出口的季节性变化在NPSG。在夏季，当从真光层的出口升高，这种“夏季脉冲”材料被迅速输送到深处，CSIA-AA表明，大颗粒（> 53 μ m）占主导地位的食物网基地的浮游动物在整个中层水域，并在很大程度上甚至进入上层深海区。在冬季，当出口量低时，中层中层的浮游动物继续依赖大颗粒基底资源，但中层下层和深层上层的常驻浮游动物转而将较小的颗粒（0.7-53 μ m）纳入其食物网基础，甚至是小颗粒池的一个子集。中层浮游动物的迁移模式也随季节而变化，与冬季在上层混合层中被压缩相比，夏季在透光层中的迁移者在夜间分布更均匀。在夏末，中层区较深的浮游动物迁移也减少了，这可能是由于在这个季节，在深度可获得的大颗粒物质的数量增加。我们观察到的活动和营养动力学的季节性变化驱动适度更大的生物量在夏季比冬季通过中层区。相反，中层浮游动物的碳（C），氮（N）和磷（P）的组成不随季节变化。相反，我们发现随着深度的增加，C：N，C：P和N：P比率增加，这可能是由于蛋白质结构和有机P化合物的减少以及储存脂质随深度的增加。我们的研究强调了小型浮游动物摄食策略的重要性和多样性在NPSG中间沃茨。许多小型浮游动物，如oncaeid和oithonid桡足类，能够获得小颗粒资源的深度，并可能是微生物循环和深居微型游泳生物物种之间的重要营养环节，也依赖于小颗粒为基础的食物网。我们观察到的中层浮游动物营养响应出口驱动的变化，在深度的粒子场中层代谢和出口的C深海有重要的影响。
Midwater zooplankton are major agents of biogeochemical transformation in the open ocean; however their characteristics and activity remain poorly known. Here we evaluate midwater zooplankton biomass, amino acid (AA)-specific stable isotope composition (delta N-15 values) using compound-specific isotope analysis of amino acids (CSIA-AA), trophic position, and elemental composition in the North Pacific Subtropical Gyre (NPSG). We focus on zooplankton collected in the winter, spring, and summer to evaluate midwater trophic dynamics over a seasonal cycle. For the first time we find that midwater zooplankton respond strongly to seasonal changes in production and export in the NPSG. In summer, when export from the euphotic zone is elevated and this 'summer pulse' material is transported rapidly to depth, CSIA-AA indicates that large particles (> 53 mu m) dominate the food web base for zooplankton throughout the midwaters, and to a large extent even into the upper bathypelagic zone. In winter, when export is low, zooplankton in the mid-mesopelagic zone continue to rely on large particle basal resources, but resident zooplankton in the lower mesopelagic and upper bathypelagic zones switch to include smaller particles (0.7-53 mu m) in their food web base, or even a subset of the small particle pool. Midwater zooplankton migration patterns also vary with season, with migrants distributed more evenly at night through the euphotic zone in summer as compared to being more compressed in the upper mixed layer in winter. Deeper zooplankton migration within the mesopelagic zone is also reduced in late summer, likely due to the increased magnitude of large particle material available at depth during this season. Our observed seasonal change in activity and trophic dynamics drives modestly greater biomass in summer than winter through the mesopelagic zone. In contrast midwater zooplankton carbon (C), nitrogen (N), and phosphorus (P) composition does not change with season. Instead we find increasing C:N, C:P, and N:P ratios with greater depths, likely due to decreases in proteinaceous structures and organic P compounds and increases in storage lipids with depth. Our study highlights the importance and diversity of feeding strategies for small zooplankton in NPSG mid waters. Many small zooplankton, such as oncaeid and oithonid copepods, are able to access small particle resources at depth and may be an important trophic link between the microbial loop and deep dwelling micro-nekton species that also rely on small particle-based food webs. Our observed midwater zooplankton trophic response to export-driven variation in the particle field at depth has important implications for midwater metabolism and the export of C to the deep sea.