DATASETS - Pervasive iron limitation at subsurface chlorophyll maxima of the California Current

R and Python code for processing these datasets are available from: 10.5281/zenodo.1495504 <strong>Abstract: </strong>Subsurface chlorophyll maximum layers (SCMLs) are nearly ubiquitous in stratified water columns and exist at horizontal scales ranging from the submesoscale to the extent of oligotrophic gyres. These layers of heightened chlorophyll and/or phytoplankton concentrations are generally thought to be a consequence of a balance between light energy from above and a limiting nutrient flux from below, typically nitrate (NO3). Here we present multiple lines of evidence demonstrating that iron (Fe) limits or with light colimits phytoplankton communities in SCMLs along a primary productivity gradient from coastal to oligotrophic offshore waters in the southern California Current ecosystem. SCML phytoplankton responded markedly to added Fe or Fe/light in experimental incubations and transcripts of diatom and picoeukaryote Fe stress genes were strikingly abundant in SCML metatranscriptomes. Using a biogeochemical proxy with data from a 40-y time series, we find that diatoms growing in California Current SCMLs are persistently Fe deficient during the spring and summer growing season.We also find that the spatial extent of Fe deficiency within California Current SCMLs has significantly increased over the last 25 y in line with a regional climate index. Finally, we show that diatom Fe deficiency may be common in the subsurface of major upwelling zones worldwide. Our results have important implications for our understanding of the biogeochemical consequences of marine SCML formation and maintenance.用于处理本数据集的R语言与Python代码可从以下地址获取：10.5281/zenodo.1495504 **摘要：** 次表层叶绿素最大值层（Subsurface Chlorophyll Maximum Layers, SCMLs）几乎普遍存在于分层水体中，其水平尺度范围从亚中尺度直至寡营养环流的全域尺度。这类叶绿素浓度或浮游植物浓度升高的层位，通常被认为是上方光照能量与下方限制性营养盐通量（通常为硝酸盐NO₃）之间达到平衡的结果。本研究通过多维度证据证实：在南加利福尼亚流生态系统中，沿从近岸到寡营养远海的初级生产力梯度，次表层叶绿素最大值层内的浮游植物群落受到铁（Iron, Fe）的限制，或与光照共同产生限制作用。在实验培养中，次表层叶绿素最大值层的浮游植物对添加的铁或铁/光照组合呈现出显著响应；同时，该层位的宏转录组中，硅藻与微微型真核生物的铁胁迫基因转录本丰度极高。通过结合40年时间序列数据的生物地球化学代用指标分析，我们发现加利福尼亚流次表层叶绿素最大值层中的硅藻在春夏季生长季持续处于铁缺乏状态。我们还发现，过去25年间，加利福尼亚流次表层叶绿素最大值层中铁缺乏的空间范围随区域气候指数变化出现显著扩张。最后，我们证实硅藻铁缺乏现象可能普遍存在于全球主要上升流区的次表层水体中。本研究结果对于理解海洋次表层叶绿素最大值层形成与维持的生物地球化学效应具有重要意义。