{"title":"水团混合和热液过程对南太平洋溶解钕同位素分布和浓度的影响","authors":"Henning Waltemathe , Torben Struve , Matthias Rehbein , Katharina Pahnke","doi":"10.1016/j.epsl.2024.118846","DOIUrl":null,"url":null,"abstract":"<div><p>The isotope composition of dissolved neodymium (Nd) in seawater, expressed as ε<sub>Nd</sub>, serves as a valuable geochemical tracer for the provenance and mixing of water masses in the ocean. However, challenges arise in the application due to additional Nd sources and isotope exchange at ocean boundaries and suspended particles of hydrothermal and lithogenic origin, which are not fully understood. In this study, we present seawater Nd concentrations [Nd] and ε<sub>Nd</sub> obtained from a deep-water (>1500 m water depth) zonal transect across the oligotrophic South Pacific gyre sampled during R/V Sonne cruise SO245, GEOTRACES process study GPpr09. Across 8 stations, dissolved [Nd] range from 10.8 to 31.1 pmol/kg with a characteristic pattern of increasing [Nd] at all stations, while our ε<sub>Nd</sub> results from -3.9 to -8.5 show pronounced zonal differences between the eastern and western part of the transect. We compare our measured data with values predicted from optimum multiparameter analysis (OMPA) of water masses to quantify the non-conservative influence on ε<sub>Nd</sub> and [Nd] along our transect. Our detailed analysis demonstrates that the deep water ε<sub>Nd</sub> distribution is dominated by conservative mixing of Upper and Lower Circumpolar Deep Water, Pacific Deep Water and Antarctic Intermediate Water, with 66% of all samples falling within ±0.6 epsilon units (i.e., the propagated uncertainty range derived from endmember compositions and analytical uncertainty) of the ε<sub>Nd</sub> predicted from conservative water mass mixing. In contrast, our [Nd] results reveal a pronounced deficit relative to concentrations predicted from water mass mixing (up to ∼10 pmol/kg). By excluding other influencing factors such as surface particle rain and boundary scavenging, we ascribe the [Nd] deficit to enhanced scavenging by hydrothermal particles in particular in PDW. This is consistent with the striking similarity of the [Nd] deficit and the distribution of δ<sup>3</sup>He as an indicator of hydrothermal activity along our transect. These findings highlight the decoupling of [Nd], modulated heavily by non-conservative processes, from the mainly conservative behaviour of ε<sub>Nd</sub> in the deep South Pacific.</p></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":null,"pages":null},"PeriodicalIF":4.8000,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0012821X24002796/pdfft?md5=b6c9dff32b12e176c3255d7f52bdf32b&pid=1-s2.0-S0012821X24002796-main.pdf","citationCount":"0","resultStr":"{\"title\":\"Influence of water mass mixing and hydrothermal processes on the distribution of dissolved Nd isotopes and concentrations in the South Pacific\",\"authors\":\"Henning Waltemathe , Torben Struve , Matthias Rehbein , Katharina Pahnke\",\"doi\":\"10.1016/j.epsl.2024.118846\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>The isotope composition of dissolved neodymium (Nd) in seawater, expressed as ε<sub>Nd</sub>, serves as a valuable geochemical tracer for the provenance and mixing of water masses in the ocean. However, challenges arise in the application due to additional Nd sources and isotope exchange at ocean boundaries and suspended particles of hydrothermal and lithogenic origin, which are not fully understood. In this study, we present seawater Nd concentrations [Nd] and ε<sub>Nd</sub> obtained from a deep-water (>1500 m water depth) zonal transect across the oligotrophic South Pacific gyre sampled during R/V Sonne cruise SO245, GEOTRACES process study GPpr09. Across 8 stations, dissolved [Nd] range from 10.8 to 31.1 pmol/kg with a characteristic pattern of increasing [Nd] at all stations, while our ε<sub>Nd</sub> results from -3.9 to -8.5 show pronounced zonal differences between the eastern and western part of the transect. We compare our measured data with values predicted from optimum multiparameter analysis (OMPA) of water masses to quantify the non-conservative influence on ε<sub>Nd</sub> and [Nd] along our transect. Our detailed analysis demonstrates that the deep water ε<sub>Nd</sub> distribution is dominated by conservative mixing of Upper and Lower Circumpolar Deep Water, Pacific Deep Water and Antarctic Intermediate Water, with 66% of all samples falling within ±0.6 epsilon units (i.e., the propagated uncertainty range derived from endmember compositions and analytical uncertainty) of the ε<sub>Nd</sub> predicted from conservative water mass mixing. In contrast, our [Nd] results reveal a pronounced deficit relative to concentrations predicted from water mass mixing (up to ∼10 pmol/kg). By excluding other influencing factors such as surface particle rain and boundary scavenging, we ascribe the [Nd] deficit to enhanced scavenging by hydrothermal particles in particular in PDW. This is consistent with the striking similarity of the [Nd] deficit and the distribution of δ<sup>3</sup>He as an indicator of hydrothermal activity along our transect. These findings highlight the decoupling of [Nd], modulated heavily by non-conservative processes, from the mainly conservative behaviour of ε<sub>Nd</sub> in the deep South Pacific.</p></div>\",\"PeriodicalId\":11481,\"journal\":{\"name\":\"Earth and Planetary Science Letters\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":4.8000,\"publicationDate\":\"2024-07-03\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"https://www.sciencedirect.com/science/article/pii/S0012821X24002796/pdfft?md5=b6c9dff32b12e176c3255d7f52bdf32b&pid=1-s2.0-S0012821X24002796-main.pdf\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Earth and Planetary Science Letters\",\"FirstCategoryId\":\"89\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0012821X24002796\",\"RegionNum\":1,\"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":"Earth and Planetary Science Letters","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0012821X24002796","RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
Influence of water mass mixing and hydrothermal processes on the distribution of dissolved Nd isotopes and concentrations in the South Pacific
The isotope composition of dissolved neodymium (Nd) in seawater, expressed as εNd, serves as a valuable geochemical tracer for the provenance and mixing of water masses in the ocean. However, challenges arise in the application due to additional Nd sources and isotope exchange at ocean boundaries and suspended particles of hydrothermal and lithogenic origin, which are not fully understood. In this study, we present seawater Nd concentrations [Nd] and εNd obtained from a deep-water (>1500 m water depth) zonal transect across the oligotrophic South Pacific gyre sampled during R/V Sonne cruise SO245, GEOTRACES process study GPpr09. Across 8 stations, dissolved [Nd] range from 10.8 to 31.1 pmol/kg with a characteristic pattern of increasing [Nd] at all stations, while our εNd results from -3.9 to -8.5 show pronounced zonal differences between the eastern and western part of the transect. We compare our measured data with values predicted from optimum multiparameter analysis (OMPA) of water masses to quantify the non-conservative influence on εNd and [Nd] along our transect. Our detailed analysis demonstrates that the deep water εNd distribution is dominated by conservative mixing of Upper and Lower Circumpolar Deep Water, Pacific Deep Water and Antarctic Intermediate Water, with 66% of all samples falling within ±0.6 epsilon units (i.e., the propagated uncertainty range derived from endmember compositions and analytical uncertainty) of the εNd predicted from conservative water mass mixing. In contrast, our [Nd] results reveal a pronounced deficit relative to concentrations predicted from water mass mixing (up to ∼10 pmol/kg). By excluding other influencing factors such as surface particle rain and boundary scavenging, we ascribe the [Nd] deficit to enhanced scavenging by hydrothermal particles in particular in PDW. This is consistent with the striking similarity of the [Nd] deficit and the distribution of δ3He as an indicator of hydrothermal activity along our transect. These findings highlight the decoupling of [Nd], modulated heavily by non-conservative processes, from the mainly conservative behaviour of εNd in the deep South Pacific.
期刊介绍:
Earth and Planetary Science Letters (EPSL) is a leading journal for researchers across the entire Earth and planetary sciences community. It publishes concise, exciting, high-impact articles ("Letters") of broad interest. Its focus is on physical and chemical processes, the evolution and general properties of the Earth and planets - from their deep interiors to their atmospheres. EPSL also includes a Frontiers section, featuring invited high-profile synthesis articles by leading experts on timely topics to bring cutting-edge research to the wider community.