Particulate organic carbon and nitrogen concentrations and fluxes at time series station DYNAPROC

Sinking particles were collected every 4 h with drifting sediment traps deployed at 200 m depth in May 1995 in a 1-D vertical system during the DYNAPROC observations in the northwestern Mediterranean sea. POC, proteins, glucosamine and lipid classes were used as indicators of the intensity and quality of the particle flux. The roles of day/night cycle and wind on the particle flux were examined. The transient regime of production from late spring bloom to pre-oligotrophy determined the flux intensity and quality. POC fluxes decreased from, on average, 34 to 11 mg/m**2/d, representing 6-14% of the primary production under late spring bloom conditions to 1-2% under pre-oligotrophic conditions. Total protein and chloroplast lipid fluxes correlated with POC and reflected the input of algal biomass into the traps. As the season proceeded, changes in the biochemical composition of the exported material were observed. The C/N ratio rose from 7.8 to 12. Increases of serine (10-28% of total proteins), total lipids (7-9 to 14-28% of POC) and reserve lipids (1-5 to 5-22% of total lipids) were noticeable, whereas total protein content in POC decreased (20-27 to 18-7%). N-acetyl glucosamine, a tracer of fecal pellet flux, showed that zooplankton grazing was a major vector of downward export during the decaying bloom. Against this background pattern, episodic events specifically increased the flux, modifying the quality and the settling velocity of particles. Day/night signals in biotracers (POC, N-acetyl glucosamine, protein and chloroplast lipids) showed that zooplankton migrations were responsible for sedimentation of fresh material through fast sinking particles (V=170-180 m/d) at night. Periodic signatures of re-processed material (high lipolysis and bacterial biomass indices) suggested that other zooplankton fecal pellets or small aggregates, probably of lower settling velocities (V<170 m/d), contributed to the flux during calm periods. At the beginning of the experiment, during the development of a prymnesiophyte bloom in the upper layers, the sterol signal with no periodicity enabled us to estimate high particle settling velocities (>=600 m/d) likely related to large aggregate formation. A wind event increased biotracer fluxes (POC, protein, chloroplast lipids). The rapid transmission of surface signals through extremely fast sinking particles could be a general feature of particle fluxes in marine areas unaffected by horizontal advection.

1995年5月，在地中海西北部开展的DYNAPROC观测计划期间，研究人员于一维垂向系统的200米水深位置部署漂流沉积物捕集器，每4小时采集沉降颗粒样品。本研究以颗粒有机碳（Particulate Organic Carbon, POC）、蛋白质、葡萄糖胺以及脂类组分作为颗粒通量强度与品质的指示指标，考察了昼夜周期与风力作用对颗粒通量的影响。春季末藻华向贫营养化前期转变过程中的生产瞬态过程，决定了通量的强度与品质。POC通量平均从34 mg/m²/d降至11 mg/m²/d，其占春季末藻华时期初级生产的比例为6%~14%，而在贫营养化前期则降至1%~2%。总蛋白质与叶绿体脂类通量与POC通量相关，可反映藻类生物量向捕集器的输入情况。随着季节推进，输出物质的生化组成发生显著变化：碳氮比从7.8升至12；丝氨酸占总蛋白质的比例（10%~28%）、总脂类占POC的比例（7%~9%升至14%~28%）以及储备脂类占总脂类的比例（1%~5%升至5%~22%）均明显升高，而POC中的总蛋白质占比则从20%~27%降至7%~18%。N-乙酰葡萄糖胺作为粪球粒通量的示踪剂，表明在藻华衰退期，浮游动物摄食是向下输出有机质的主要途径。在此背景模式下，突发性事件会特异性提升颗粒通量，并改变颗粒的品质与沉降速度。生物示踪剂（POC、N-乙酰葡萄糖胺、蛋白质与叶绿体脂类）中的昼夜信号显示，浮游动物垂直迁移是夜间通过快速沉降颗粒（沉降速度V=170~180 m/d）输送新鲜有机质发生沉降的原因。再加工物质的周期性特征（高脂解作用与细菌生物量指标）表明，其他浮游动物粪球粒或小型聚集体（沉降速度可能更低，V<170 m/d）在静稳期对通量有贡献。实验初期，上层水体出现定鞭藻藻华，无周期性的甾醇信号可用于估算较高的颗粒沉降速度（≥600 m/d），该现象大概率与大型聚集体的形成有关。一次风力事件提升了生物示踪剂通量（POC、蛋白质、叶绿体脂类）。地表信号通过超快速沉降颗粒实现快速传递，这可能是不受水平平流影响的海洋区域颗粒通量的普遍特征。