Lack of redox cycling for nickel in the water column of the Eastern tropical north pacific oxygen deficient zone: Insight from dissolved and particulate nickel isotopes
Lack of redox cycling for nickel in the water column of the Eastern tropical north pacific oxygen deficient zone: Insight from dissolved and particulate nickel isotopes
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DOI：
10.1016/j.gca.2021.07.004
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发表时间：
2021-09
影响因子：
5
通讯作者：
Shun‐Chung Yang;Rachel L. Kelly;X. Bian;T. Conway;Kuo‐Fang Huang;T. Ho;Jacquelyn A. Neibauer;R. Keil;J. Moffett;S. John
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文献类型：
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作者：
Shun‐Chung Yang;Rachel L. Kelly;X. Bian;T. Conway;Kuo‐Fang Huang;T. Ho;Jacquelyn A. Neibauer;R. Keil;J. Moffett;S. John
海洋缺氧区（ODZs）促进了独特的浮游生物群落和氧化还原环境，影响了海洋中生物必需微量金属的循环。在这里，我们使用溶解和颗粒镍浓度和同位素的测量，调查生物和非生物过程控制镍循环在世界上最大的ODZ，位于热带北太平洋东部（ETNP）。我们观察到溶解的Ni浓度和整个水柱的同位素组成（δ 60 Ni）之间存在负相关关系，在1000米以上，Ni浓度从大约3 nmol kg − 1增加到8 nmol kg− 1，而δ 60 Ni值从大约+1.6‰下降到+1.4‰。这些垂直模式的特点是亚热带的北太平洋和南太平洋，可以解释为相结合的物理混合的水团和生物吸收和输出，无论是与所有的镍生物可利用或单独的生物可利用和非生物可利用的镍池。尽管在其他臭氧破坏区和富氧沃茨中观察到了额外的镍循环过程的证据，如硫化物沉淀或通过Fe/Mn氧化还原化学的镍吸附/解吸，但我们在ETNP的氧化还原跃层或低氧沃茨中没有发现这些证据。事实上，在ETNP观测到的溶解态[Ni]和δ 60 Ni之间的关系与在北太平洋和南太平洋其他地方报道的结果相似，通常落在表层水端元（溶解态[Ni] = 2 nmol kg− 1和δ 60 Ni = +1.7‰）和深水端元（溶解态[Ni] = 6-10 nmol kg− 1和δ 60 Ni = ~+1.4‰）之间的混合线上。虽然这一表层水端元与大西洋的端元相似，但太平洋的深层端元比大西洋深层镍重约0.1‰。这种微妙的同位素差异表明同位素重镍同位素在深海中逐渐积累，与最近的证据表明，在早期成岩作用期间的重镍再活化。最后，在ETNP中，颗粒δ 60 Ni通常比溶解Ni池轻约0.5‰，这种模式在真光层和氧化还原跃层中是一致的，表明真光层的生物输出是颗粒Ni到深海的主要来源。
Marine oxygen deficient zones (ODZs) promote unique plankton communities and redox environments which impact the cycling of biologically essential trace metals in the ocean. Here we use measurements of dissolved and particulate Ni concentrations and isotopes to investigate the biotic and abiotic processes controlling Ni cycling in the world’s largest ODZ, located in the Eastern Tropical North Pacific (ETNP). We observed a negative correlation between dissolved Ni concentrations and isotopic composition (δ60Ni) throughout the water column, such that Ni concentrations increased from roughly 3 nmol kg−1to 8 nmol kg−1over the upper 1000 m, while δ60Ni values decreased by 0.2‰ from about +1.6‰ to +1.4‰. These vertical patterns are characteristic of both the subtropical North and South Pacific, and can be explained by a combination of physical mixing of water masses and biological uptake and export, either with all of the Ni being bioavailable or with separate bioavailable and non-bioavailable Ni pools. Although evidence for additional Ni cycling processes such as sulfide precipitation or Ni sorption/desorption through Fe/Mn redox chemistry have been observed in other ODZs and euxinic waters, we found no clear evidence for these in either the redoxcline or low oxygen waters of the ETNP. Indeed, the relationship between dissolved [Ni] and δ60Ni observed in the ETNP is similar to results reported elsewhere in the subtropical North and South Pacific, falling generally on a mixing line between a surface water endmember (dissolved [Ni] = 2 nmol kg−1and δ60Ni = +1.7‰) and a deep-water endmember (dissolved [Ni] = 6–10 nmol kg−1and δ60Ni = ~+1.4‰). While this surface water endmember is similar to that of the Atlantic, the deep endmember in the Pacific is approximately 0.1‰ heavier than deep Atlantic Ni. This subtle isotopic difference suggests gradual accumulation of isotopically heavy Ni isotopes in the deep ocean, consistent with recent evidence of heavy Ni remobilization during early diagenesis. Lastly, in the ETNP, particulate δ60Ni is generally ~0.5‰ lighter than the dissolved Ni pool, and this pattern is consistent across both the euphotic zone and redoxcline, suggesting that biological export from the euphotic zone is the primary source of particulate Ni to the deep ocean.