Fluxes and foraminifera fluxes of sediment traps in the Peru-Chile Current

Time-series sediment traps were deployed 180 km off the Chilean coast at 30°S in the Peru-Chile Current during the El Niño period 1991/1992 (6 months) and during the 'normal' period 1993/1994 (12 months). Under normal conditions in 1993/1994 the particle fluxes display a pronounced seasonal cycle marked by a settling phytoplankton bloom in September, intermediate fluxes until January, and low fluxes between January and July. This seasonal pattern is also reflected in stable isotope data, measured on the planktic foraminifera species Neogloboquadrina pachyderma (dex.) and Globigerina bulloides, which indicate persistent upwelling conditions between August and February followed by a stratified water column between March and July. The total flux under normal conditions amounts to 65.1 g m**-2 a**-1, with the main flux constituents contributing 47.6% (carbonate), 26.4% (lithogenic matter), 17.4% (biogenic opal), and 8.6% (organic matter), respectively. Based on these particle flux data the export production has been estimated to be 42 gC m**-2 a**-1. Although the main flux event in September was not sampled in the El Niño period 1991/1992, the available record from November 1991 to April 1992 allows an interesting comparison with the fluxes of the normal year. The total amount of fluxes and the timing of minor flux events are very similar under normal and under El Niño conditions. However, increased proportions of organic carbon and lithogenic matter under El Niño conditions are interpreted to reflect faster sedimentation and preferred scavenging of organic matter by elevated lithogenic fluxes rather than increased productivity. The higher lithogenic fluxes under El Niño conditions are probably due to increased precipitation and terrestial runoff in the arid to semiarid northern part of Chile.1991/1992年厄尔尼诺（El Niño）期间（为期6个月），以及1993/1994年“正常”气候时段（为期12个月），研究人员于秘鲁-智利海流（Peru-Chile Current）区域内智利海岸外180公里、南纬30°处布设了时间序列沉积物捕集器（Time-series sediment traps）。1993/1994年正常气候状态下，颗粒物通量（particle flux）呈现显著的季节性周期：9月出现沉降型浮游植物水华（phytoplankton bloom），通量维持中等水平至次年1月，1月至7月间通量处于低位。这一季节性模式同样反映在针对浮游有孔虫（planktic foraminifera）物种厚壳新抱球虫右旋型（Neogloboquadrina pachyderma (dex.)）与泡抱球虫（Globigerina bulloides）的稳定同位素（stable isotope）分析数据中，结果显示8月至2月间存在持续的上升流（upwelling）环境，3月至7月则为层化水柱（stratified water column）环境。正常气候状态下的总通量（total flux）可达65.1 g·m⁻²·a⁻¹，主要通量组分占比分别为：碳酸盐（carbonate）47.6%、陆源碎屑物（lithogenic matter）26.4%、生物成因蛋白石（biogenic opal）17.4%，以及有机质（organic matter）8.6%。基于上述颗粒物通量数据，研究估算得到的输出生产力（export production）为42 gC·m⁻²·a⁻¹。尽管1991/1992年厄尔尼诺时段未采集到9月的主要通量事件，但1991年11月至1992年4月的有效记录仍可与正常年份的通量数据开展颇具科学价值的对比。正常年份与厄尔尼诺年份的总通量规模及次要通量事件的发生时间均极为相似。不过，厄尔尼诺时段内有机碳与陆源碎屑物占比的提升，被认为反映了更快的沉积速率以及陆源碎屑通量升高对有机质的优先吸附清除（scavenging），而非生产力提升。厄尔尼诺时段较高的陆源碎屑通量，可能源于智利北部干旱至半干旱区域的降水增加与地表径流增强。