{"title":"加利福尼亚湾 Guaymas 盆地富含有机质的海洋沉积物中溶解铵的氮同位素深度同质化以及铵在融入可膨胀层硅酸盐过程中的 15N 富集现象","authors":"","doi":"10.1016/j.chemgeo.2024.122203","DOIUrl":null,"url":null,"abstract":"<div><p>Sedimentary nitrogen isotopic ratios are used as a proxy for ancient biogeochemical cycles on Earth's surface. It is generally accepted that sediment hole tops record primary signatures because organic nitrogen (ON) is predominant in this part of the hole. In contrast to such early to middle diagenetic stages, it is well known that heavier nitrogen isotope <sup>15</sup>N tends to enrich in sedimentary rocks during later diagenetic and metamorphic stages. However, there are some critical gaps in our understanding of nitrogen isotopic alteration associated with abiotic processes during early-middle diagenesis. In this study, we examined the isotope ratios of ammonium nitrogen in interstitial water (IW) and total nitrogen (TN), including exchangeable ammonium and mineral nitrogen, in the solid-phase of organic-rich-sediment recovered by International Ocean Discovery Program (IODP) Expedition 385 cores drilled in the Guaymas Basin, Gulf of California, that contained ammonium-rich IW. The isotopic ratios (δ<sup>15</sup>N value) of TN are the most variable with depth compared to any other type of nitrogen. This variation can be interpreted as reflecting changes in the water mass environment in the basin caused by glacial–interglacial climate changes, modifying the δ<sup>15</sup>N values of the marine primary producers. Thus, the δ<sup>15</sup>N value of TN is a proxy for environmental change in the basin, while each component of TN shows different trends. The δ<sup>15</sup>N values of IW and exchangeable ammonium did not exhibit significant changes with depth, but the latter values are about 3 ‰ enriched in <sup>15</sup>N. This may be due to advective transport of solute into adjacent layers followed by the formation of an isotopic equilibrium between IW and exchangeable ammonium in the case of fast sediment accumulation rate. The δ<sup>15</sup>N value of exchangeable ammonium is the highest among the other types of nitrogen with one exception, where the δ<sup>15</sup>N value of TN is the highest. The calculated δ<sup>15</sup>N values of ON based on mass balance are almost the same as those of associated TN in the shallow sediment layers (< 150 m below seafloor), but the difference in the δ<sup>15</sup>N values of TN and ON are significant in the deeper layers, where proportions of ON contents are <50%. In particular, in the layer where the δ<sup>15</sup>N value of TN is the highest, that of ON shows an even higher value and the difference reaches 3.5 ‰. The δ<sup>15</sup>N values of mineral nitrogen are similar to that of IW ammonium except the surface layers. Under such conditions, when δ<sup>15</sup>N value of TN is intermediate between those of mineral nitrogen and exchangeable ammonium, calculated δ<sup>15</sup>N value of ON is close to that of TN. On the other hand, if δ<sup>15</sup>N value of TN is out of the range between mineral nitrogen and exchangeable ammonium, it causes further difference in δ<sup>15</sup>N value of ON. It means that the fluctuation of δ<sup>15</sup>N values of TN is reduced relative to those of ON through depth. It has been considered that δ<sup>15</sup>N value of TN in sediment is similar to that of ON, and changes in the δ<sup>15</sup>N value of TN due to diagenesis are limited, but in such environment ON fluctuations over depth may be slightly underestimated.</p></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":null,"pages":null},"PeriodicalIF":3.6000,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0009254124002833/pdfft?md5=4440969361a4e0aee934c44a01661752&pid=1-s2.0-S0009254124002833-main.pdf","citationCount":"0","resultStr":"{\"title\":\"Nitrogen isotope homogenization of dissolved ammonium with depth and 15N enrichment of ammonium during incorporation into expandable layer silicates in organic-rich marine sediment from Guaymas Basin, Gulf of California\",\"authors\":\"\",\"doi\":\"10.1016/j.chemgeo.2024.122203\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>Sedimentary nitrogen isotopic ratios are used as a proxy for ancient biogeochemical cycles on Earth's surface. It is generally accepted that sediment hole tops record primary signatures because organic nitrogen (ON) is predominant in this part of the hole. In contrast to such early to middle diagenetic stages, it is well known that heavier nitrogen isotope <sup>15</sup>N tends to enrich in sedimentary rocks during later diagenetic and metamorphic stages. However, there are some critical gaps in our understanding of nitrogen isotopic alteration associated with abiotic processes during early-middle diagenesis. In this study, we examined the isotope ratios of ammonium nitrogen in interstitial water (IW) and total nitrogen (TN), including exchangeable ammonium and mineral nitrogen, in the solid-phase of organic-rich-sediment recovered by International Ocean Discovery Program (IODP) Expedition 385 cores drilled in the Guaymas Basin, Gulf of California, that contained ammonium-rich IW. The isotopic ratios (δ<sup>15</sup>N value) of TN are the most variable with depth compared to any other type of nitrogen. This variation can be interpreted as reflecting changes in the water mass environment in the basin caused by glacial–interglacial climate changes, modifying the δ<sup>15</sup>N values of the marine primary producers. Thus, the δ<sup>15</sup>N value of TN is a proxy for environmental change in the basin, while each component of TN shows different trends. The δ<sup>15</sup>N values of IW and exchangeable ammonium did not exhibit significant changes with depth, but the latter values are about 3 ‰ enriched in <sup>15</sup>N. This may be due to advective transport of solute into adjacent layers followed by the formation of an isotopic equilibrium between IW and exchangeable ammonium in the case of fast sediment accumulation rate. The δ<sup>15</sup>N value of exchangeable ammonium is the highest among the other types of nitrogen with one exception, where the δ<sup>15</sup>N value of TN is the highest. The calculated δ<sup>15</sup>N values of ON based on mass balance are almost the same as those of associated TN in the shallow sediment layers (< 150 m below seafloor), but the difference in the δ<sup>15</sup>N values of TN and ON are significant in the deeper layers, where proportions of ON contents are <50%. In particular, in the layer where the δ<sup>15</sup>N value of TN is the highest, that of ON shows an even higher value and the difference reaches 3.5 ‰. The δ<sup>15</sup>N values of mineral nitrogen are similar to that of IW ammonium except the surface layers. Under such conditions, when δ<sup>15</sup>N value of TN is intermediate between those of mineral nitrogen and exchangeable ammonium, calculated δ<sup>15</sup>N value of ON is close to that of TN. On the other hand, if δ<sup>15</sup>N value of TN is out of the range between mineral nitrogen and exchangeable ammonium, it causes further difference in δ<sup>15</sup>N value of ON. It means that the fluctuation of δ<sup>15</sup>N values of TN is reduced relative to those of ON through depth. It has been considered that δ<sup>15</sup>N value of TN in sediment is similar to that of ON, and changes in the δ<sup>15</sup>N value of TN due to diagenesis are limited, but in such environment ON fluctuations over depth may be slightly underestimated.</p></div>\",\"PeriodicalId\":9847,\"journal\":{\"name\":\"Chemical Geology\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":3.6000,\"publicationDate\":\"2024-06-01\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"https://www.sciencedirect.com/science/article/pii/S0009254124002833/pdfft?md5=4440969361a4e0aee934c44a01661752&pid=1-s2.0-S0009254124002833-main.pdf\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Chemical Geology\",\"FirstCategoryId\":\"89\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0009254124002833\",\"RegionNum\":2,\"RegionCategory\":\"地球科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q1\",\"JCRName\":\"GEOCHEMISTRY & GEOPHYSICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Chemical Geology","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0009254124002833","RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
Nitrogen isotope homogenization of dissolved ammonium with depth and 15N enrichment of ammonium during incorporation into expandable layer silicates in organic-rich marine sediment from Guaymas Basin, Gulf of California
Sedimentary nitrogen isotopic ratios are used as a proxy for ancient biogeochemical cycles on Earth's surface. It is generally accepted that sediment hole tops record primary signatures because organic nitrogen (ON) is predominant in this part of the hole. In contrast to such early to middle diagenetic stages, it is well known that heavier nitrogen isotope 15N tends to enrich in sedimentary rocks during later diagenetic and metamorphic stages. However, there are some critical gaps in our understanding of nitrogen isotopic alteration associated with abiotic processes during early-middle diagenesis. In this study, we examined the isotope ratios of ammonium nitrogen in interstitial water (IW) and total nitrogen (TN), including exchangeable ammonium and mineral nitrogen, in the solid-phase of organic-rich-sediment recovered by International Ocean Discovery Program (IODP) Expedition 385 cores drilled in the Guaymas Basin, Gulf of California, that contained ammonium-rich IW. The isotopic ratios (δ15N value) of TN are the most variable with depth compared to any other type of nitrogen. This variation can be interpreted as reflecting changes in the water mass environment in the basin caused by glacial–interglacial climate changes, modifying the δ15N values of the marine primary producers. Thus, the δ15N value of TN is a proxy for environmental change in the basin, while each component of TN shows different trends. The δ15N values of IW and exchangeable ammonium did not exhibit significant changes with depth, but the latter values are about 3 ‰ enriched in 15N. This may be due to advective transport of solute into adjacent layers followed by the formation of an isotopic equilibrium between IW and exchangeable ammonium in the case of fast sediment accumulation rate. The δ15N value of exchangeable ammonium is the highest among the other types of nitrogen with one exception, where the δ15N value of TN is the highest. The calculated δ15N values of ON based on mass balance are almost the same as those of associated TN in the shallow sediment layers (< 150 m below seafloor), but the difference in the δ15N values of TN and ON are significant in the deeper layers, where proportions of ON contents are <50%. In particular, in the layer where the δ15N value of TN is the highest, that of ON shows an even higher value and the difference reaches 3.5 ‰. The δ15N values of mineral nitrogen are similar to that of IW ammonium except the surface layers. Under such conditions, when δ15N value of TN is intermediate between those of mineral nitrogen and exchangeable ammonium, calculated δ15N value of ON is close to that of TN. On the other hand, if δ15N value of TN is out of the range between mineral nitrogen and exchangeable ammonium, it causes further difference in δ15N value of ON. It means that the fluctuation of δ15N values of TN is reduced relative to those of ON through depth. It has been considered that δ15N value of TN in sediment is similar to that of ON, and changes in the δ15N value of TN due to diagenesis are limited, but in such environment ON fluctuations over depth may be slightly underestimated.
期刊介绍:
Chemical Geology is an international journal that publishes original research papers on isotopic and elemental geochemistry, geochronology and cosmochemistry.
The Journal focuses on chemical processes in igneous, metamorphic, and sedimentary petrology, low- and high-temperature aqueous solutions, biogeochemistry, the environment and cosmochemistry.
Papers that are field, experimentally, or computationally based are appropriate if they are of broad international interest. The Journal generally does not publish papers that are primarily of regional or local interest, or which are primarily focused on remediation and applied geochemistry.
The Journal also welcomes innovative papers dealing with significant analytical advances that are of wide interest in the community and extend significantly beyond the scope of what would be included in the methods section of a standard research paper.