Coastal sources, sinks and strong organic complexation of dissolved cobalt within the US North Atlantic GEOTRACES transect GA03
Coastal sources, sinks and strong organic complexation of dissolved cobalt within the US North Atlantic GEOTRACES transect GA03
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DOI：
10.5194/bg-14-2715-2017
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发表时间：
2016-12
期刊：
影响因子：
4.9
通讯作者：
A. Noble;D. Ohnemus;N. Hawco;P. Lam;M. Saito
中科院分区：
文献类型：
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作者：
A. Noble;D. Ohnemus;N. Hawco;P. Lam;M. Saito
抽象的。钴是金属微量营养素中最稀缺的一种，表现出复杂的生物地球化学循环。本文研究了2010年和2011年秋季美国北大西洋地学考察样带(GA03/3_e)中溶解钴的分布、化学形态和生物地球化学。确定了北大西洋钴的两个主要地下来源。其中更突出的是从热带北大西洋东部非洲海岸发出的一大股钴，可能是由于还原溶解、生物吸收和再矿化以及风尘沉积而与氧最小区(OMZ)重合。在氧气水平高于亚氧水平的OMZ中出现这种羽流，意味着溶解的钴羽流持续存在的阈值很高。另一个主要的地下来源来自上拉布拉多海水，由于这些水团与西部边缘的再悬浮沉积物相互作用或来自更上游的输送，可能会携带高浓度的钴。钴的次要来源来自尘埃、沿海地表水和中大西洋海脊沿线的热液系统。钴化学形态的全深度剖面显示，即使在尘埃沉积较高的地区，地表水中也几乎完全络合。然而，在真光带下方观察到的不稳定钴表明，强钴结合配体的存在并不超过那里的总钴浓度，这意味着中层不稳定钴来自下沉有机质的再矿化。在上层水体中，总钴与磷酸盐、活性钴与磷酸盐之间存在相关性，显示出对钴循环有很强的生物影响。在北美海岸外的西部边缘，不再观察到这种与磷酸盐的相关性，而是观察到钴与盐度之间的关系，反映了沿海输入过程对钴分布的重要性。在深水中，总钴和不稳定钴的浓度都低于中等深度水域，这表明清扫可以从水柱中去除不稳定的钴。还将总的和不稳定的钴分布与之前公布的南大西洋地学调查系统兼容的地带性样带(CoFeMUG，GAc01)进行了比较，以辨别区域生物地球化学差异。总而言之，这些大西洋地区的研究突出了总钴和不稳定钴的动态生态化学计量比。由于越来越多的人为使用和随后释放的钴有可能压倒海洋中的自然钴信号，因此比以往任何时候都更重要的是建立对海洋中钴分布的基线了解。
Abstract. Cobalt is the scarcest of metallic micronutrients and displays a complex biogeochemical cycle. This study examines the distribution, chemical speciation, and biogeochemistry of dissolved cobalt during the US North Atlantic GEOTRACES transect expeditions (GA03/3_e), which took place in the fall of 2010 and 2011. Two major subsurface sources of cobalt to the North Atlantic were identified. The more prominent of the two was a large plume of cobalt emanating from the African coast off the eastern tropical North Atlantic coincident with the oxygen minimum zone (OMZ) likely due to reductive dissolution, biouptake and remineralization, and aeolian dust deposition. The occurrence of this plume in an OMZ with oxygen above suboxic levels implies a high threshold for persistence of dissolved cobalt plumes. The other major subsurface source came from Upper Labrador Seawater, which may carry high cobalt concentrations due to the interaction of this water mass with resuspended sediment at the western margin or from transport further upstream. Minor sources of cobalt came from dust, coastal surface waters and hydrothermal systems along the Mid-Atlantic Ridge. The full depth section of cobalt chemical speciation revealed near-complete complexation in surface waters, even within regions of high dust deposition. However, labile cobalt observed below the euphotic zone demonstrated that strong cobalt-binding ligands were not present in excess of the total cobalt concentration there, implying that mesopelagic labile cobalt was sourced from the remineralization of sinking organic matter. In the upper water column, correlations were observed between total cobalt and phosphate, and between labile cobalt and phosphate, demonstrating a strong biological influence on cobalt cycling. Along the western margin off the North American coast, this correlation with phosphate was no longer observed and instead a relationship between cobalt and salinity was observed, reflecting the importance of coastal input processes on cobalt distributions. In deep waters, both total and labile cobalt concentrations were lower than in intermediate depth waters, demonstrating that scavenging may remove labile cobalt from the water column. Total and labile cobalt distributions were also compared to a previously published South Atlantic GEOTRACES-compliant zonal transect (CoFeMUG, GAc01) to discern regional biogeochemical differences. Together, these Atlantic sectional studies highlight the dynamic ecological stoichiometry of total and labile cobalt. As increasing anthropogenic use and subsequent release of cobalt poses the potential to overpower natural cobalt signals in the oceans, it is more important than ever to establish a baseline understanding of cobalt distributions in the ocean.