DataSheet_1_Oligotrophic Phytoplankton Community Effectively Adjusts to Artificial Upwelling Regardless of Intensity, but Differently Among Upwelling Modes.docx

Artificial upwelling has been proposed as a means of enhancing oceanic CO2 sequestration and/or raising fishery yields through an increase in primary production in unproductive parts of the ocean. However, evidence of its efficacy, applicability and side effects is scarce. Here we present part of the results of a 37-day mesocosm study conducted in oligotrophic waters off the coast of Gran Canaria. The goal was to assess in situ the effects of artificial upwelling on the pelagic community. Upwelling was simulated via two modes: i) a singular deep-water pulse and ii) a recurring supply every 4 days; each mode at four different intensities defined by the total amount of nitrate added: approx. 1.5, 3, 5.7, and 11 µmol L-1. In this study we focus on the phytoplankton response through size-fractionated 14C primary production rates (PP), Chlorophyll a and biomass. We observed increases in PP, accumulated PP, Chlorophyll a and biomass that scaled linearly with upwelling intensity. Upwelling primarily benefitted larger phytoplankton size fractions, causing a shift from pico- and nano- to nano- and microphytoplankton. Recurring deep-water addition produced more biomass under higher upwelling intensities than a single pulse addition. It also reached significantly higher accumulated PP per unit of added nutrients and showed a stronger reduction in percentage extracellular release with increasing upwelling intensity. These results demonstrate that oligotrophic phytoplankton communities can effectively adjust to artificial upwelling regardless of upwelling intensity, but differently depending on the upwelling mode. Recurring supply of upwelled waters generated higher efficiencies in primary production and biomass build-up than a single pulse of the same volume and nutrient load.

人工上升流被提议作为一种增强海洋二氧化碳封存能力以及通过增加海洋生产力从而提高渔业产量的手段。然而，关于其有效性、适用性及潜在副作用的证据相对匮乏。在本研究中，我们展示了在加那利岛海岸外贫营养水域进行的一项为期37天的中尺度生态系统研究的一部分结果。研究旨在现场评估人工上升流对浮游生物群落的影响。上升流通过两种模式进行模拟：i) 单次深水脉冲和ii) 每4天重复一次的供应；每种模式在四种不同的强度下进行，这些强度由添加硝酸盐的总量决定：大约1.5、3、5.7和11 µmol L-1。在本研究中，我们重点关注通过尺寸分级14C初级生产率（PP）、叶绿素a和生物量来评估浮游植物的反应。我们观察到初级生产率、累积初级生产率、叶绿素a和生物量的增加与上升流强度呈线性关系。上升流主要有利于较大的浮游植物尺寸分级，导致从原核和纳米浮游植物向纳米和微浮游植物转变。反复的深水添加在更高的上升流强度下产生的生物量比单次脉冲添加更多。它还达到了显著更高的累积初级生产率，并且随着上升流强度的增加，细胞外释放的百分比减少更为明显。这些结果表明，贫营养浮游植物群落能够有效地适应人工上升流，不论上升流强度如何，但适应方式因上升流模式而异。反复供应上升流水源在初级生产效率和生物量积累方面比相同体积和养分负荷的单次脉冲具有更高的效率。