Nitrate-Nitrite Isotopic Exchange: Unveiling Its Influence on Isotope Effect Estimates in Nitrate Assimilation in the Cosmonaut Sea, Antarctica

IF 3.3 2区 地球科学 Q1 OCEANOGRAPHY
Xueli Ba, Jun Zhao, Minfang Zheng, Mengya Chen, Jiawen Kang, Jiashun Hu, Shunan Cao, Jianfeng He, Min Chen
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Interestingly, incorporating this exchange reaction significantly altered the estimated isotope effect of nitrate assimilation for both nitrogen and oxygen based on the Rayleigh model in the nitrate-only system. This raises questions about the reliability of previous estimates in assessing nitrate consumption in the Southern Ocean, suggesting that the nitrate + nitrite system may provide a more accurate representative of nitrate uptake. 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引用次数: 0

Abstract

Recent insights into isotopic exchange between nitrate and nitrite have introduced complexities to our understanding of the nitrogen cycle in the Southern Ocean. This study highlights unusual isotopic compositions in the mixed layer of the Cosmonaut Sea characterized by notably low δ15N and high δ18O values in nitrite. These anomalies challenge our expectations regarding isotopic behavior within cycling pathways, highlighting the significant role of isotopic exchange between nitrate and nitrite. Interestingly, incorporating this exchange reaction significantly altered the estimated isotope effect of nitrate assimilation for both nitrogen and oxygen based on the Rayleigh model in the nitrate-only system. This raises questions about the reliability of previous estimates in assessing nitrate consumption in the Southern Ocean, suggesting that the nitrate + nitrite system may provide a more accurate representative of nitrate uptake. Additionally, spatial variations in the nitrate assimilation isotope effect ( ε NO 3 + NO 2 ${\varepsilon }_{{\text{NO}}_{3}+{\text{NO}}_{2}}$ ) both for nitrogen and oxygen were also observed, with higher ε NO 3 + NO 2 15 ${}^{15}{\varepsilon }_{{\text{NO}}_{3}+{\text{NO}}_{2}}$ and ε NO 3 + NO 2 18 ${}^{18}{\varepsilon }_{{\text{NO}}_{3}+{\text{NO}}_{2}}$ values north of the southern boundary (SB) and lower values to the south. The reduced ε NO 3 + NO 2 15 ${}^{15}{\varepsilon }_{{\text{NO}}_{3}+{\text{NO}}_{2}}$ and ε NO 3 + NO 2 18 ${}^{18}{\varepsilon }_{{\text{NO}}_{3}+{\text{NO}}_{2}}$ values south of the SB may be primarily driven by elevated iron concentrations as indicated by the positive relationship between ε NO 3 + NO 2 18 ${}^{18}{\varepsilon }_{{\text{NO}}_{3}+{\text{NO}}_{2}}$ and △Si/△N, a proxy for iron limitation, rather than by nitrification, phytoplankton composition, vertical mixing, or light availability. This study uses dual isotopes of nitrate and nitrite to evaluate isotopic exchange effects on nitrate assimilation, specifically for oxygen, enhancing our understanding of the Southern Ocean's role in the global nitrogen cycle.

硝酸盐-亚硝酸盐同位素交换:揭示其对南极宇航员海硝酸盐同化同位素效应估计的影响
最近对硝酸盐和亚硝酸盐之间同位素交换的见解使我们对南大洋氮循环的理解变得更加复杂。该研究强调了宇航员海混合层中不同寻常的同位素组成,其特征是亚硝酸盐的δ15N值低,δ18O值高。这些异常挑战了我们对循环路径中同位素行为的预期,突出了硝酸盐和亚硝酸盐之间同位素交换的重要作用。有趣的是,加入这种交换反应显著地改变了基于瑞利模型的硝酸盐系统中氮和氧的硝酸盐同化的同位素效应。这就提出了先前评估南大洋硝酸盐消耗的可靠性的问题,表明硝酸盐+亚硝酸盐系统可能提供更准确的硝酸盐吸收代表。此外,硝态氮同化同位素效应(ε no3 + no2)的空间变化{{\text{NO}}_{3}+{\text{NO}}_{2}}$),具有较高的ε no3 + no2 15${}^{15}{\varepsilon}_{{\text{NO}}_{3}+{\text{NO}}_{2}}$和ε no3 + no218 ${}^{18}{\varepsilon}_{{\text{NO}}_{3}+{\text{NO}}_{2}}$值在南边界(SB)以北,低值在南边界(SB)以南。还原后的ε no3 + no2 15${}^{15}{\varepsilon}_{{\text{NO}}_{3}+{\text{NO}}_{2}}$和ε no3 + no218 ${}^{18}{\varepsilon}_{{\text{NO}}_{3}+{\text{NO}}_{2}}$值可能主要是由铁浓度升高引起的NO 3 + NO 2 18 ${}^{18}{\varepsilon}_{{\text{NO}}_{3}+{\text{NO}}_{2}}$和△Si/△N,一个铁限制的代理,而不是通过硝化作用,浮游植物组成,垂直混合,或光的可用性。 本研究利用硝酸盐和亚硝酸盐的双同位素来评估同位素交换对硝酸盐同化的影响,特别是对氧的同化,增强了我们对南大洋在全球氮循环中的作用的认识。
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来源期刊
Journal of Geophysical Research-Oceans
Journal of Geophysical Research-Oceans Earth and Planetary Sciences-Oceanography
CiteScore
7.00
自引率
13.90%
发文量
429
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