Constraining the sources of nitrogen fueling export production in the Gulf of Mexico using nitrogen isotope budgets
Constraining the sources of nitrogen fueling export production in the Gulf of Mexico using nitrogen isotope budgets
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DOI：
10.1093/plankt/fbab049
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发表时间：
2021-08
影响因子：
2.1
通讯作者：
A. Knapp;Rachel K. Thomas;M. Stukel;T. Kelly;M. Landry;K. Selph;E. Malca;T. Gerard;J. Lamkin
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作者：
A. Knapp;Rachel K. Thomas;M. Stukel;T. Kelly;M. Landry;K. Selph;E. Malca;T. Gerard;J. Lamkin
海洋表层沃茨中氮的有效性影响着光合作用的速率和海洋生态系统的结构。尽管溶解无机氮浓度低，在贫营养沃茨的出口生产是比较营养丰富的地区。先前的观察提高了二氮（N2）固定供应的N支持在墨西哥湾的出口生产的一个重要部分的可能性。在这项研究中，地球化学工具被用来量化地下硝酸盐和N2固定的相对和绝对重要性，作为2017年5月和2018年5月在贫营养墨西哥湾新的N燃料出口生产的来源。将硝酸盐的同位素组成（“δ 15 N”）与在每次持续2至4天的5个沉积物捕集器部署期间收集的沉降颗粒氮的δ 15 N进行比较，表明通常没有检测到N2固定，并且大多数（≥80%）出口生产由地下硝酸盐支持。此外，没有发现上层海洋溶解有机氮和悬浮颗粒氮浓度和/或δ 15 N的梯度，这将表明在这些池中积累了显着的N2固定通量，与低束毛藻属一致。丰饶。最后，比较真光层内和真光层以下捕获的沉降颗粒氮的δ 15 N表明，在晚春，再生氮的δ 15 N低于沉降氮。
The availability of nitrogen (N) in ocean surface waters affects rates of photosynthesis and marine ecosystem structure. In spite of low dissolved inorganic N concentrations, export production in oligotrophic waters is comparable to more nutrient replete regions. Prior observations raise the possibility that di-nitrogen (N2) fixation supplies a significant fraction of N supporting export production in the Gulf of Mexico. In this study, geochemical tools were used to quantify the relative and absolute importance of both subsurface nitrate and N2 fixation as sources of new N fueling export production in the oligotrophic Gulf of Mexico in May 2017 and May 2018. Comparing the isotopic composition (“δ15N”) of nitrate with the δ15N of sinking particulate N collected during five sediment trap deployments each lasting two to four days indicates that N2 fixation is typically not detected and that the majority (≥80%) of export production is supported by subsurface nitrate. Moreover, no gradients in upper ocean dissolved organic N and suspended particulate N concentration and/or δ15N were found that would indicate significant N2 fixation fluxes accumulated in these pools, consistent with low Trichodesmium spp. abundance. Finally, comparing the δ15N of sinking particulate N captured within vs. below the euphotic zone indicates that during late spring regenerated N is low in δ15N compared to sinking N.