Impact of phytoplankton on the biogeochemical cycling of iron in subantarctic waters southeast of New Zealand during FeCycle
Impact of phytoplankton on the biogeochemical cycling of iron in subantarctic waters southeast of New Zealand during FeCycle
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FeCycle期间浮游植物对新西兰东南部亚南极水域铁生物地球化学循环的影响
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
P. Boyd
中科院分区：
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作者：
R. McKay;S. Wilhelm;J. Hall;D. Hutchins;M. Al;C. Mioni;S. Pickmere;D. Porta;P. Boyd
在2003年夏季，我们跟踪了一个补丁的地表水注入示踪剂六氟化硫，但没有添加铁，通过亚大洋沃茨超过10天，以表征和量化藻类铁池和通量，构建一个详细的地球化学收支。营养概况的特点是这个补丁作为一个高硝酸盐，低油酸，低叶绿素（HNLSiLC）的水质量缺乏溶解铁。铁缺乏的生理指标（Fv/Fm < 0.25，铁氧还蛋白指数< 0.2）和船载富铁试验证实了低铁条件。在FeCycle期间，微微型浮游植物（0.2-2 μm）和微型浮游植物（2-20 μm）对叶绿素的贡献均大于40%。而picophytoplankton占总初级生产力的0.50%，他们负责大部分的社区铁吸收混合层。因此，微微型浮游植物的55 Fe：14 C吸收比例最高（中位数：17 μmol：mol），而较大的藻类尺寸组分的55 Fe：14 C吸收比例下降到105 μmol：mol。浮游植物的铁收支表明，微型浮游植物是藻类铁的最大库（>90%），这与浮游植物对铁的高需求（约80%）是一致的。然而，通过草食动物再生的铁仅满足总藻类铁需求的约20%。当我们包括由细菌回收的铁时，这个铁再生期增加到藻类铁需求的40%。作为回收物，而不是新的，铁主导了远洋铁预算（博伊德等人，2005年），这是极不可能的新铁的供应将纠正藻类铁的需求和供应之间的不平衡。造成这种不平衡的原因可能包括高估了放射性示踪技术对藻类铁的吸收，或者缺乏对其他铁再生过程的考虑。综上所述，看来，藻类铁的吸收不能仅仅通过藻类铁的回收来支持，并可能需要从异养途径再生的铁“补贴”。
During austral summer 2003, we tracked a patch of surface water infused with the tracer sulfur hexafluoride, but without addition of Fe, through subantarctic waters over 10 days in order to characterize and quantify algal Fe pools and fluxes to construct a detailed biogeochemical budget. Nutrient profiles characterized this patch as a high‐nitrate, low‐silicic acid, low‐chlorophyll (HNLSiLC) water mass deficient in dissolved Fe. The low Fe condition was confirmed by several approaches: shipboard iron enrichment experiments and physiological indices of Fe deficiency (Fv/Fm < 0.25, Ferredoxin Index < 0.2). During FeCycle, picophytoplankton (0.2–2 μm) and nanophytoplankton (2–20 μm) each contributed >40% of total chlorophyll. Whereas the picophytoplankton accounted for ∼50% of total primary production, they were responsible for the majority of community iron uptake in the mixed layer. Thus ratios of 55Fe:14C uptake were highest for picophytoplankton (median: 17 μmol:mol) and declined to ∼5 μmol:mol for the larger algal size fractions. A pelagic Fe budget revealed that picophytoplankton were the largest pool of algal Fe (>90%), which was consistent with the high (∼80%) phytoplankton Fe demand attributed to them. However, Fe regenerated by herbivory satisfied only ∼20% of total algal Fe demand. This iron regeneration term increased to 40% of algal Fe demand when we include Fe recycled by bacterivory. As recycled, rather than new, iron dominated the pelagic iron budget (Boyd et al., 2005), it is highly unlikely that the supply of new Fe would redress the imbalance between algal Fe demand and supply. Reasons for this imbalance may include the overestimation of algal iron uptake from radiotracer techniques, or a lack of consideration of other iron regeneration processes. In conclusion, it seems that algal Fe uptake cannot be supported solely by the recycling of algal iron, and may require an Fe “subsidy” from that regenerated by heterotrophic pathways.