Physical and biogeochemical controls on seasonal iron, manganese, and cobalt distributions in Northeast Atlantic shelf seas
Physical and biogeochemical controls on seasonal iron, manganese, and cobalt distributions in Northeast Atlantic shelf seas
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DOI：
10.1016/j.gca.2023.03.023
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发表时间：
2023-03
影响因子：
5
通讯作者：
Xue‐Gang Chen;Dagmara Rusiecka;M. Gledhill;A. Milne;A. Annett;Aaron Joseph Beck;A. Birchill;M. Lohan;S. Ussher;E. Achterberg
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作者：
Xue‐Gang Chen;Dagmara Rusiecka;M. Gledhill;A. Milne;A. Annett;Aaron Joseph Beck;A. Birchill;M. Lohan;S. Ussher;E. Achterberg
溶解的（<0.2 μm）痕量金属（dTM），包括铁（Fe），锰（Mn）和钴（Co），是限制许多海洋区域浮游植物生长的微量营养素。在这里，我们提出的空间和季节分布的dFe，dMn，和dCo的东北大西洋大陆边缘（凯尔特海），沿着一个横断面横跨大陆架和两个离架横断面沿着峡谷和支线。大陆架上的沃茨显示出更高的dTM浓度（dFe 0.07-6.50 nmol L-1，平均1.41 ± 0.96 nmol L-1，n = 138; dMn 0.868-14.8 nmol L-1，2.75 ± 2.37 nmol L-1，n = 148; dCo 54.8-217 pmol L−1，109 ± 32 pmol L−1，n = 144）比在斜率上（dFe 0.03-1.90 nmol L-1，0.65 ± 0.43 nmol L-1，n = 454; dMn 0.223-1.14 nmol L-1，0.58 ± 0.20 nmol L-1，n = 458; dCo 27.3-122 pmol L−1，71.7 ± 11.7 pmol L−1，n = 441），归因于低盐度端元的强dTM贡献，即，河流流量底栖沉积输入通过还原溶解（特别是dFe和dMn），划定了短命的镭（Ra）同位素活动（223 Raxsand 224 Raxs），只有突出的一个站（站点A）的特点是细沉积物。在大陆坡，dMn在深度的水平主要是由不溶性锰氧化物的形成和地中海流出沃茨的入侵。与此相反，dFe和dCo浓度在深度平衡的再生下沉的有机颗粒和清除去除的矿化。此外，底部和中间云状层沿着斜坡说明了升高的dTM浓度和Ra同位素活性。雾状层的存在是特别显着的沿着的峡谷样带相对于支线，证明了斜坡地形的重要性上的dTM到东北Atlantic Ocean.As一个季节性分层的陆架海，dTM和营养盐的陆架上表现出同步的季节变化，表明除了源效应的生物过程的影响。表层dFe和dCo在夏季由于生物吸收的增强而减少，而次表层dFe和dCo在夏秋季由于下沉有机颗粒的矿化而升高。与此相反，表面dMn的水平主要控制的季节性变化的光还原，而次表面dMn的浓度是相对恒定的全年。河流和底栖来源，地形控制和生物过程的综合影响形状的DTM分布的季节性变化。这种dTM和生物活动的季节变化可以影响东北大西洋大陆边缘的生物碳泵，并可能通过大陆边缘和开阔洋之间的动态dTM交换进一步影响大西洋的碳循环。
Dissolved (<0.2 μm) trace metals (dTMs) including iron (Fe), manganese (Mn), and cobalt (Co) are micronutrients that (co-) limit phytoplankton growth in many ocean regions. Here, we present the spatial and seasonal distributions of dFe, dMn, and dCo on the Northeast Atlantic continental margin (Celtic Sea), along a transect across the shelf and two off-shelf transects along a canyon and a spur. Waters on the continental shelf showed much higher dTM concentrations (dFe 0.07–6.50 nmol L−1, average 1.41 ± 0.96 nmol L−1, n = 138; dMn 0.868–14.8 nmol L−1, 2.75 ± 2.37 nmol L−1, n = 148; dCo 54.8–217 pmol L−1, 109 ± 32 pmol L−1, n = 144) than on the slope (dFe 0.03–1.90 nmol L−1, 0.65 ± 0.43 nmol L−1, n = 454; dMn 0.223–1.14 nmol L−1, 0.58 ± 0.20 nmol L−1, n = 458; dCo 27.3–122 pmol L−1, 71.7 ± 11.7 pmol L−1, n = 441), attributed to strong dTM contributions from a low-salinity endmember, i.e., riverine discharge. Benthic sedimentary input via reductive dissolution (especially for dFe and dMn), delineated by short-lived radium (Ra) isotopic activities (223Raxsand224Raxs), was only prominent at a station (Site A) characterized by fine sediments. On the continental slope, dMn levels at depth were mainly determined by the formation of insoluble Mn oxides and the intrusion of Mediterranean Outflow Waters. In contrast, dFe and dCo concentrations at depth were balanced by the regeneration from remineralization of sinking organic particles and scavenging removal. In addition, bottom and intermediate nepheloid layers along the slope illustrated both elevated dTM concentrations and Ra isotopic activities. The presence of nepheloid layers is especially significant along the canyon transect relative to the spur transect, demonstrating the importance of slope topography on the off-shelf transport of dTMs into the Northeast Atlantic Ocean.As a seasonal stratified shelf sea, dTMs and nutrients showed synchronized seasonal variations on the shelf, indicating the influence of biological processes in addition to source effects. Surface dFe and dCo were depleted in summer due to enhanced biological uptake, while sub-surface dFe and dCo were elevated in summer and autumn ascribed to the remineralization of sinking organic particles. In contrast, surface dMn levels were predominantly controlled by the seasonal variations in photoreduction, while sub-surface dMn concentrations were relatively constant throughout the year. The combined effects of fluvial and benthic sources, topographical controls, and biological processes shape the seasonal variations of dTM distributions. Such seasonal variations in dTMs and biological activities can affect the biological carbon pump on the Northeast Atlantic continental margin, and may further influence the carbon cycle in the Atlantic Ocean via the dynamic dTM exchange between continental margins and the open ocean.