A seasonal study of dissolved cobalt in the Ross Sea, Antarctica: micronutrient behavior, absence of scavenging, and relationships with Zn, Cd, and P
A seasonal study of dissolved cobalt in the Ross Sea, Antarctica: micronutrient behavior, absence of scavenging, and relationships with Zn, Cd, and P
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南极洲罗斯海溶解钴的季节性研究：微量营养素行为、清除的缺乏以及与 Zn、Cd 和 P 的关系
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发表时间：
2010
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通讯作者：
G. R. DiTullio
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作者：
M. Saito;T. Goepfert;A. Noble;Erin M. Bertrand;P. Sedwick;G. R. DiTullio
抽象的。本文报道了2005-2006年夏季和2006年春季罗斯海冰穴中钴的分布。总溶解钴（dCo）的垂直分布与可溶性活性磷酸盐（PO 43 −）相似，dCo和PO 43 −在整个水柱中显示出显著的相关性（r2 = 0.87，164个样本）。一个强烈的季节性信号dCo观察，与大多数春季样品的浓度范围从45-85 pM，而夏季dCo值低于这些水平的生物活动耗尽。夏季巡航的地表样带数据显示，浓度处于这一季节性变化的低范围（约30 pM dCo），在PO 43 −贫化至约0.1 μM的某些区域，观测到的浓度低至20 pM。这两个复杂的Co，定义为强有机配体结合的dCo的分数，和不稳定的Co，定义为不结合这些配体的dCo的分数，通常观察到在整个水柱中的显着浓度。这与在其他海洋区域的真光层中观察到的不稳定Co的耗尽形成对比，表明在罗斯海中Co的生物利用度要高得多。根据溶解浓度计算的生态化学计量为37.6 μmol Co：mol−1 PO 43 −，与在亚北极太平洋观测到的数值相似，但比热带太平洋东部和赤道大西洋的数值低约10倍。溶解的钴和锌的生态化学计量表明，在罗斯海的浅水沃茨中，相对于钴，锌的总体使用量更大，Co：PO 43 −/Zn：PO 43 −的比例为1：17。这些观察到的化学计量与文化研究中估计的值的比较表明，锌是一个关键的微量营养元素，可能会影响浮游植物的多样性在罗斯海。与此相反，所观察到的生态化学计量的钴低于在实验室培养实验中进行的真核浮游植物的生长所需的值，在没有添加锌，这意味着需要显着的锌营养的锌-钴形成酶。溶解的Co：PO 43 −关系中缺乏明显的扭结，这与之前在罗斯海观察到的Zn：PO 43 −和Cd：PO 43 −扭结形成对比。一个过度吸收机制扭结的形成提出了作为一个主要的驱动程序的Cd：PO 43-扭结，其中锌和镉的吸收超过所需的最佳增长发生在底部的真光区，并没有明确的钴扭结发生，因为它的丰度太低，过量吸收。一个不寻常的特点，在罗斯海的钴地球化学是一个明显缺乏的钴清除过程，推断从dCo去除真光层以下的情况。我们假设，这种垂直分布反映了低速率的钴清除锰氧化细菌，可能是由于锰稀缺，相对于每年的深冬混合在罗斯海的时间尺度。因此，一氧化碳在罗斯海表现出类似营养物的行为，与其他海洋区域的混合型行为相反，这可能会增加海洋一氧化碳库存和效用作为古海洋学代理。
Abstract. We report the distribution of cobalt (Co) in the Ross Sea polynya during austral summer 2005–2006 and the following austral spring 2006. The vertical distribution of total dissolved Co (dCo) was similar to soluble reactive phosphate (PO43−), with dCo and PO43− showing a significant correlation throughout the water column (r2 = 0.87, 164 samples). A strong seasonal signal for dCo was observed, with most spring samples having concentrations ranging from ~45–85 pM, whereas summer dCo values were depleted below these levels by biological activity. Surface transect data from the summer cruise revealed concentrations at the low range of this seasonal variability (~30 pM dCo), with concentrations as low as 20 pM observed in some regions where PO43− was depleted to ~0.1 μM. Both complexed Co, defined as the fraction of dCo bound by strong organic ligands, and labile Co, defined as the fraction of dCo not bound by these ligands, were typically observed in significant concentrations throughout the water column. This contrasts the depletion of labile Co observed in the euphotic zone of other ocean regions, suggesting a much higher bioavailability for Co in the Ross Sea. An ecological stoichiometry of 37.6 μmol Co:mol−1 PO43− calculated from dissolved concentrations was similar to values observed in the subarctic Pacific, but approximately tenfold lower than values in the Eastern Tropical Pacific and Equatorial Atlantic. The ecological stoichiometries for dissolved Co and Zn suggest a greater overall use of Zn relative to Co in the shallow waters of the Ross Sea, with a Co:PO43−/Zn:PO43− ratio of 1:17. Comparison of these observed stoichiometries with values estimated in culture studies suggests that Zn is a key micronutrient that likely influences phytoplankton diversity in the Ross Sea. In contrast, the observed ecological stoichiometries for Co were below values necessary for the growth of eukaryotic phytoplankton in laboratory culture experiments conducted in the absence of added zinc, implying the need for significant Zn nutrition in the Zn-Co cambialistic enzymes. The lack of an obvious kink in the dissolved Co:PO43− relationship was in contrast to Zn:PO43− and Cd:PO43− kinks previously observed in the Ross Sea. An excess uptake mechanism for kink formation is proposed as a major driver of Cd:PO43− kinks, where Zn and Cd uptake in excess of that needed for optimal growth occurs at the base of the euphotic zone, and no clear Co kink occurs because its abundances are too low for excess uptake. An unusual characteristic of Co geochemistry in the Ross Sea is an apparent lack of Co scavenging processes, as inferred from the absence of dCo removal below the euphotic zone. We hypothesize that this vertical distribution reflects a low rate of Co scavenging by Mn oxidizing bacteria, perhaps due to Mn scarcity, relative to the timescale of the annual deep winter mixing in the Ross Sea. Thus Co exhibits nutrient-like behavior in the Ross Sea, in contrast to its hybrid-type behavior in other ocean regions, with implications for the possibility of increased marine Co inventories and utility as a paleooceanographic proxy.