Jelly biomass sinking speed reveals a fast carbon export mechanism

Sinking of gelatinous zooplankton biomass is an important component of the biological pump removing carbon from the upper ocean. The export efficiency, e.g., how much biomass reaches the ocean interior sequestering carbon, is poorly known because of the absence of reliable sinking speed data. We measured sinking rates of gelatinous particulate organic matter (jelly-POM) from different species of scyphozoans, ctenophores, thaliaceans, and pteropods, both in the field and in the laboratory in vertical columns filled with seawater using high-quality video. Using these data, we determined taxon-specific jelly-POM export efficiencies using equations that integrate biomass decay rate, seawater temperature, and sinking speed. Two depth scenarios in several environments were considered, with jelly-POM sinking from 200 and 600 m in temperate, tropical, and polar regions. Jelly-POM sank on average between 850 and 1500 m/d (salps: 800-1200 m/d; ctenophores: 1200-1500 m/d; scyphozoans: 1000-1100 m d; pyrosomes: 1300 m/d). High latitudes represent a fast-sinking and low-remineralization corridor, regardless of species. In tropical and temperate regions, significant decomposition takes place above 1500 m unless jelly-POM sinks below the permanent thermocline. Sinking jelly-POM sequesters carbon to the deep ocean faster than anticipated, and should be incorporated into biogeochemical and modeling studies to provide more realistic quantification of export via the biological carbon pump worldwide.胶质浮游动物生物量的沉降是海洋上层碳移除生物泵（biological pump）的重要组成部分。当前学界对其输出效率——即有多少生物量能够抵达海洋深部以实现碳封存——的认知仍较为匮乏，核心原因在于缺乏可靠的沉降速度数据。本研究通过高质量视频记录，在野外及实验室的海水填充垂直柱中，测量了钵水母纲、栉水母动物、海樽纲以及翼足类不同物种来源的胶质颗粒有机物（gelatinous particulate organic matter, jelly-POM）的沉降速率。基于上述实测数据，我们结合整合了生物量衰减速率、海水温度与沉降速度的计算公式，确定了类群特异性的jelly-POM输出效率。本研究针对两类深度情景展开分析，分别模拟胶质颗粒有机物在温带、热带与极地海域从200米及600米水深处开始沉降的过程。胶质颗粒有机物的平均沉降速率介于850~1500米/天之间（其中樽海鞘：800~1200米/天；栉水母动物：1200~1500米/天；钵水母纲：1000~1100米/天；火体虫：1300米/天）。无论物种类型如何，高纬度海域均构成了快速沉降且再矿化（remineralization）程度较低的通道。在热带与温带海域，除非胶质颗粒有机物沉降至永久温跃层（permanent thermocline）以下，否则在1500米水层以上便会发生显著的分解过程。沉降中的胶质颗粒有机物向深海封存碳的速度远超此前预期，因此相关研究应将其纳入生物地球化学与模型研究范畴，以更真实地量化全球范围内生物碳泵（biological carbon pump）介导的碳输出通量。