Seasonality, phytoplankton succession and the biogeochemical impacts of an autumn storm in the northeast Atlantic Ocean
Seasonality, phytoplankton succession and the biogeochemical impacts of an autumn storm in the northeast Atlantic Ocean
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DOI：
10.1016/j.pocean.2016.02.001
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发表时间：
2016-03
影响因子：
4.1
通讯作者：
Stuart C. Painter;M. Finlay;Victoria S. Hemsley;Adrian P. Martin
中科院分区：
文献类型：
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作者：
Stuart C. Painter;M. Finlay;Victoria S. Hemsley;Adrian P. Martin
通过对浮游植物化学分类分布、分类单元特定颗粒生物量浓度和浮游植物丰度的研究，探讨了东北大西洋秋季风暴通过后的生物地球化学后果。化学分类表明，浮游植物群落以纳米浮游生物（2 ~ 20 μm）为主，平均占群落的75±8%。微浮游（20 ~ 200 μm）和微浮游（<2 μm）分别占21±7%和4±3%，其中硅藻（53±17%）和鞭毛藻（47±17%）的比例几乎相等。总叶绿素-a （CHLa = CHLa + Divinyl CHLa）浓度在22 ~ 677 ng L−1之间，DvCHLa对CHLa的贡献较小，在<1% ~ 13%之间。暴雨期间DvCHLa的贡献增大，表层混合层加深，混合层营养物浓度增加，浮游植物群落垂直混合，导致表层叶绿素浓度在暴雨后升高。微浮游生物是对变化条件的快速反应，其色素标记显示比例突然增加了4倍，但这种增加在风暴后没有持续。雨前和雨后的主要副色素为19′- hex，浓度为48 ~ 435 ng L−1，占总类胡萝卜素浓度的44%。随附的扫描电子显微镜结果支持基于色素的分析，但也提供了对纳米和微型浮游生物群落的详细了解，这些群落在风暴前和风暴后采样期间被证明是高度变化的。在风暴前和风暴后，纳米浮游生物仍占主导地位，但在营养物和叶绿素浓度最高的时期，微型浮游生物的比例达到峰值。关于风暴驱动的富营养化事件导致的秋季水华促进表层浮游植物生长的经典描述应该随着对风暴驱动的水柱垂直重组和常驻浮游植物群落的作用的更多理解而得到缓和。至关重要的是，在这种情况下，我们没有观察到综合叶绿素、颗粒有机碳或生物源二氧化硅浓度的变化，尽管我们也观察到表面叶绿素浓度增加了~ 50%，这表明叶绿素浓度的表面增强很可能是来自下方，而不是由原位生长引起的。虽然没有直接测量，但没有证据表明与这场风暴有关的出口通量增加。这些观测结果对越来越多地利用远程平台上的叶绿素荧光来确定年度生产力期后期的海洋生产力以及对风暴混合作出反应的做法具有影响。
Phytoplankton chemotaxonomic distributions are examined in conjunction with taxon specific particulate biomass concentrations and phytoplankton abundances to investigate the biogeochemical consequences of the passage of an autumn storm in the northeast Atlantic Ocean. Chemotaxonomy indicated that the phytoplankton community was dominated by nanoplankton (2–20 μm), which on average represented 75 ± 8% of the community. Microplankton (20–200 μm) and picoplankton (<2 μm) represented 21 ± 7% and 4 ± 3% respectively with the microplankton group composed of almost equal proportions of diatoms (53 ± 17%) and dinoflagellates (47 ± 17%). Total chlorophyll-a (TCHLa = CHLa + Divinyl CHLa) concentrations ranged from 22 to 677 ng L−1, with DvCHLa making minor contributions of between <1% and 13% to TCHLa. Higher DvCHLa contributions were seen during the storm, which deepened the surface mixed layer, increased mixed layer nutrient concentrations and vertically mixed the phytoplankton community leading to a post-storm increase in surface chlorophyll concentrations. Picoplankton were rapid initial respondents to the changing conditions with pigment markers showing an abrupt 4-fold increase in proportion but this increase was not sustained post-storm. 19′-HEX, a chemotaxonomic marker for prymnesiophytes, was the dominant accessory pigment pre- and post-storm with concentrations of 48–435 ng L−1, and represented 44% of total carotenoid concentrations. Accompanying scanning electron microscopy results support the pigment-based analysis but also provide detailed insight into the nano- and microplankton communities, which proved to be highly variable between pre-storm and post-storm sampling periods. Nanoplankton remained the dominant size class pre- and post-storm but the microplankton proportion peaked during the period of maximum nutrient and chlorophyll concentrations. Classic descriptions of autumn blooms resulting from storm driven eutrophication events promoting phytoplankton growth in surface waters should be tempered with greater understanding of the role of storm driven vertical reorganization of the water column and of resident phytoplankton communities. Crucially, in this case we observed no change in integrated chlorophyll, particulate organic carbon or biogenic silica concentrations despite also observing a ∼50% increase in surface chlorophyll concentrations which indicated that the surface enhancement in chlorophyll concentrations was most likely fed from below rather than resulting from in situ growth. Though not measured directly there was no evidence of enhanced export fluxes associated with this storm. These observations have implications for the growing practice of using chlorophyll fluorescence from remote platforms to determine ocean productivity late in the annual productivity period and in response to storm mixing.