Biological hotspots along the West Antarctic Peninsula (WAP) are characterized by high phytoplankton productivity and biomass as well as spatially focused penguin foraging activity. While unique physical concentrating processes were identified in one of these hotspots, understanding the mechanisms driving the blooms at these locations is of high importance. Factors posited to explain the blooms include the upwelling of macronutrientand micronutrient-enriched modified Upper Circumpolar Deep Water (mUCDW) and the depth of the mixed layer influencing overall light availability for phytoplankton. Using shipboard trace-metal clean incubation experiments in three different coastal biological hotspots spanning a north-south gradient along the WAP, we tested the Canyon Hypothesis (upwelling) for enhanced phytoplankton growth. Diatoms dominated the Southern region, while the Northern region was characterized by a combination of diatoms and cryptophytes. There was ample concentration of macronutrients at the surface and no phytoplankton growth response was detected with the addition of nutrient-enriched mUCDW water or iron solution to surface waters. For all treatments, addition of mUCDW showed no enhancement in phytoplankton growth, suggesting that local upwelling of nutrient-enriched deep water in these hotspots was not the main driver of high phytoplankton biomass. Furthermore, the dynamics in the photoprotective pigments were consistent with the light levels used during these incubations showing that phytoplankton are able to photoacclimate rapidly to higher irradiances and that in situ cells are low light adapted. Light availability appears to be the critical variable for the development of hotspot phytoplankton blooms, which in turn supports the highly productive regional food web. Coastal waters of the West Antarctic Peninsula (WAP) support a highly productive ecosystem and have been historically associated with large, diatom-dominated phytoplankton blooms (Nelson and Smith 1991; Prézelin et al. 2004; Smith et al. 2008). Additionally the WAP has several “biological hotspots” located at particular locations along the WAP continental shelf (Schofield et al. 2013) that are associated with the major penguin rookeries (Fraser and Trivelpiece 1996; Erdmann et al. 2011). Rapid changes in atmospheric and oceanic temperatures over the past six decades have had significant effects on the WAP ecosystem (Ducklow et al. 2012). Summer chlorophyll concentrations have declined about 12% over the past three decades (Montes-Hugo et al. 2009), accompanied with a shift in the community structure from larger diatoms to smaller celled (< 20 μm) cryptophytes (Moline et al. 2004; Montes-Hugo et al. 2009). Seasonal phytoplankton dynamics have been linked to the timing of sea ice retreat (Ducklow et al. 2012; Rozema et al. 2017; Schofield et al. 2017). Increased phytoplankton production is often observed in the spring along the retreating ice edge, where ample supply of nutrients at the surface *Correspondence: filipa.carvalho@noc.ac.uk This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Additional Supporting Information may be found in the online version of this article.

中文翻译：

---

测试峡谷假设：评估南极半岛西部企鹅觅食热点浮游植物生长的光和营养控制

西南极半岛 (WAP) 沿线的生物热点具有高浮游植物生产力和生物量以及空间集中的企鹅觅食活动的特点。虽然在这些热点之一中发现了独特的物理浓缩过程，但了解驱动这些位置水华的机制非常重要。假定可以解释水华的因素包括常量营养素和富含微量营养素的改良上环极深水 (mUCDW) 的上升流，以及影响浮游植物整体光照可用性的混合层深度。在沿 WAP 跨越南北梯度的三个不同沿海生物热点中使用船上痕量金属清洁孵化实验，我们测试了峡谷假设（上升流）以增强浮游植物生长。南部地区以硅藻为主，而北部地区则以硅藻和隐生植物相结合为特征。地表有充足的常量营养素浓度，在向地表水中添加富含营养的 mUCDW 水或铁溶液后，未检测到浮游植物生长反应。对于所有处理，添加 mUCDW 均未显示浮游植物生长增强，这表明这些热点中富含营养的深水的局部上升流并不是高浮游植物生物量的主要驱动因素。此外，光保护色素的动态与这些孵化过程中使用的光照水平一致，表明浮游植物能够快速适应更高的辐照度，并且原位细胞适应低光。光的可用性似乎是热点浮游植物大量繁殖的关键变量，这反过来又支持了高产的区域食物网。南极半岛西部 (WAP) 的沿海水域支持着高产的生态系统，并且在历史上一直与以硅藻为主的大型浮游植物大量繁殖有关（Nelson 和 Smith 1991；Prézelin 等，2004；Smith 等，2008）。此外，WAP 有几个“生物热点”，位于 WAP 大陆架沿线的特定位置（Schofield 等人，2013 年），与主要企鹅栖息地相关（Fraser 和 Trivelpiece 1996 年；Erdmann 等人，2011 年）。过去六十年来，大气和海洋温度的快速变化对 WAP 生态系统产生了重大影响（Ducklow 等人，2012 年）。在过去的 30 年中，夏季叶绿素浓度下降了约 12%（Montes-Hugo 等人，2009 年），伴随着群落结构从较大的硅藻转变为较小的细胞（< 20 微米）隐生植物（Moline 等人，2004 年； Montes-Hugo 等人，2009 年）。季节性浮游植物动态与海冰退缩的时间有关（Ducklow 等人，2012 年；Rozema 等人，2017 年；Schofield 等人，2017 年）。浮游植物产量增加经常在春季沿着退缩的冰缘观察到，那里表面有充足的营养供应 *通讯：filipa.carvalho@noc.ac.uk 这是一篇根据知识共享署名许可条款的开放获取文章，允许在任何媒体中使用、分发和复制，前提是原始作品被正确引用。