Towards balancing the oceanic Ni budget
Towards balancing the oceanic Ni budget
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DOI：
10.1016/j.epsl.2020.116461
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发表时间：
2020-10
影响因子：
5.3
通讯作者：
S. Little;C. Archer;James McManus;J. Najorka;A. Wegorzewski;Derek Vance
中科院分区：
文献类型：
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作者：
S. Little;C. Archer;James McManus;J. Najorka;A. Wegorzewski;Derek Vance
镍同位素是一种新的和有前途的示踪剂的化学过去的海洋环境，但实现这种示踪剂的潜力，需要全面了解镍埋藏在海洋沉积档案的控制。在20世纪70年代首次认识到的Ni海洋收支中的一个突出难题是已知的海洋输入和输出的主要不平衡：Ni的沉积输出远远大于输入（河流，灰尘）。最近，人们还认识到，输出也比输入重得多。在这项研究中，我们发现东太平洋富锰沉积物的镍同位素组成较轻（δ 60 Ni NIST SRM 986 =− 0.2至− 0.8‰），而铁锰结壳（约为+1.6 ‰）。这些数据表明，同位素重镍的成岩再活化导致了显著的海底镍通量（估计为0.6 - 2.3× 10 8 mol/yr），其量级与河流通量相似。成岩再活化的镍可能发生通过锰氧化物溶解和沉淀的周期，与相关的镍吸附和释放，或在矿物学转变的水钠锰矿钙锰矿。保留同位素轻镍的铁氧化物或富铁自生粘土的次要作用也提出了。总的来说，同位素重镍（约+3 ‰）的海底通量可以平衡海洋镍的收支，指出成岩作用是镍之谜的关键缺失部分。
Nickel isotopes are a novel and promising tracer of the chemistry of past ocean environments, but realisation of this tracer's potential requires a comprehensive understanding of the controls on Ni burial in the marine sedimentary archive. An outstanding puzzle in the marine budget of Ni, first recognised in the 1970s, is a major imbalance in the known inputs and outputs to and from the ocean: the sedimentary outputs of Ni are much larger than the inputs (rivers, dust). Much more recently, it has also been recognised that the outputs are also considerably isotopically heavier than the inputs. In this study, we find light Ni isotope compositions (δ 60 Ni NIST SRM986=− 0.2 to− 0.8‰) for Mn-rich sediments from the eastern Pacific compared to Fe-Mn crusts (at about+ 1.6‰). These data suggest that diagenetic remobilisation of isotopically heavy Ni leads to a significant benthic Ni flux (estimated at 0.6− 2.3× 10 8 mol/yr), similar in magnitude to the riverine flux, to the ocean. Diagenetic remobilisation of Ni may occur either via cycles of Mn-oxide dissolution and precipitation, with associated Ni sorption and release, or during mineralogical transformation of birnessite to todorokite. A minor role for retention of isotopically light Ni by Fe oxides or Fe-rich authigenic clays is also proposed. Overall, a benthic flux of isotopically heavy Ni (at about+ 3‰) can balance the marine Ni budget, pinpointing diagenesis as a key missing piece of the Ni puzzle.