樽海鞘大量繁殖导致南大洋的被动碳输出大幅增加
Salp blooms drive strong increases
in passive carbon export in the Southern Ocean
作者：Moira Décima, Michael R. Stukel, Scott D. Nodder, Andrés Gutiérrez-Rodríguez, Karen E. Selph, Adriana Lopes dos Santos, Karl Safi, Thomas B. Kelly, Fenella Deans, Sergio E. Morales, Federico Baltar, Mikel Latasa, Maxim Y. Gorbunov, Matt Pinkerton
期刊：Nature Communications
The Southern Ocean contributes substantially to the global biological carbon pump (BCP). Salps in the Southern Ocean, in particular Salpa thompsoni, are important grazers that produce large, fast-sinking fecal pellets. Here, we quantify the salp bloom impacts on microbial dynamics and the BCP, by contrasting locations differing in salp bloom presence/absence. Salp blooms coincide with phytoplankton dominated by diatoms or prymnesiophytes, depending on water mass characteristics. Their grazing is comparable to microzooplankton during their early bloom, resulting in a decrease of ~1/3 of primary production, and negative phytoplankton rates of change are associated with all salp locations. Particle export in salp waters is always higher, ranging 2- to 8- fold (average 5-fold), compared to non-salp locations, exporting up to 46% of primary production out of the euphotic zone. BCP efficiency increases from 5 to 28% in salp areas, which is among the highest recorded in the global ocean.
Figure 1. Patterns in carbon export flux
Mean±std of a export fluxes of particulate organic carbon (POC), b carbon flux due to recognizable salp fecal pellets (FP), c relative contribution of intact salp FP to POC flux. Colors and symbols for experimental cycles are denoted in the legend in (a). d Ratio of POC flux between Salp and non-salp locations, with three comparisons for SA waters, and one for ST waters. Doted line indicates a ratio of 1. e EZ ratio, the ratio of POC flux: net primary production (NPP), as a function of T100 (POC flux at EZ+100m/POC flux). Numbers indicate locations compared in ref. 3: 1—North Atlantic Bloom Experiment (NABE) (spring, temperate North Atlantic), 2—Kiwi 7, 3—Kiwi 8 (Polar Front, Pacific sector, Southern Ocean), 4—K2 - D1 (subarctic NW Pacific), 5—K2 - D2 (subarctic, NW Pacific), 6—ALOHA (subtropical, central North Pacific), 7—EqPac (tropical, central Pacific), 8—OSP – Aug (summer, NE Pacific), 9—OSP – May (spring, NE Pacific). Circles are proportional to magnitude of NPP (see legend insert). Results from this study are in color: blue indicates non-salp locations, red indicates salp cycles during the SalpPOOP experiment.
南大洋对全球生物碳泵（简称BCP）有很大贡献。生活在南大洋中的樽海鞘，尤其是纽鳃樽，是一种重要的植食性动物，能产生快速沉降的大颗粒粪球。本文通过对比几个存在樽海鞘大量繁殖现象和不存在该现象的地区，量化分析了樽海鞘大量繁殖对微生物动态和全球生物碳泵产生的影响。樽海鞘的大量繁殖与以硅藻和定鞭金藻为主的浮游植物的繁殖相吻合，都取决于水团特征。在大量繁殖的初期，樽海鞘的掠食能力与微型浮游动物相当，这导致初级生产力下降了约1/3，且浮游植物的负生长率也与所有樽海鞘生存的海域有关系。相较于没有樽海鞘的区域，有该生物生存的水体颗粒物输出往往更高，是前者的2-8倍（平均为5倍），能将高达46%的初级生产力运输到透光层之外。在有樽海鞘的海域内，全球生物碳泵效率从5%提高到了28%，是全球海洋中这一数值的最高纪录之一。
(实习生申澳编译)
