US GEOTRACES GP17-OCE and GP17-ANT: Sources and Rates of Trace Element and Isotope Cycling Derived from the Radium Quartet

GEOTRACES计划的目标是“确定控制海洋中痕量元素和同位素(TEI)分布的过程和通量，并确定这些分布对不断变化的环境条件的敏感性”。这一雄心勃勃的目标需要协调一致的海洋实地工作，以收集样本，同时测量地球主要海洋盆地的许多元素。然而，如果不同时测量放射性示踪剂，如可以提供海洋输入时间尺度的镭同位素，这些全面的全球痕量元素浓度图就无法得到正确的解释。在这一项目中，调查人员将测量南美洲南端和南极洲之间的南大洋中镭同位素的丰度和分布，包括对南极沿海海洋环境的详细描述。该项目将支持一名博士后助理研究人员，并让两名本科生研究人员参与巡航后分析。拟议研究的主要动机是利用四组镭(Ra)同位素(224Ra、223Ra、228Ra、226Ra)，在即将到来的美国GEOTRACES GP17-OCE和GP17-ANT探险期间，能够识别TEI的来源和通量量化。Ra同位素的测量将使该小组能够解决与海洋边缘和海底边界过程有关的几个关键问题，以及它们在向海洋生态系统供应和输送TEI方面的作用，包括：(1)从南极和巴塔哥尼亚大陆边缘向外以及包括高营养低叶绿素(HNLC)南大洋的TEI横向输送的速率是多少？(2)与南极冰川融水有关的TEI通量是什么？以及(3)与太平洋-南极海脊中性漂浮的热液羽流有关的TEI输送的时间尺度是什么？边界输入被认为是海洋中包括铁在内的许多关键TEI的主要来源，然而，TEI浓度必须与输入和运移速率相结合，以确定它们对海洋生物地球化学循环的影响。大范围的Ra同位素半衰期(3.66天至1600年)使得可以在与海洋混合过程有关的时间尺度上量化TEI的传输过程。建议的RATEI耦合测量将允许实现由GEOTRACES PI测量的众多TEI分布的全部价值。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The goal of the GEOTRACES program is to “identify processes and quantify fluxes that control the distribution of trace elements and isotopes (TEIs) in the ocean and to establish the sensitivity of these distributions to changing environmental conditions”. This ambitious objective requires coordinated seagoing field work for collection of samples to measure many elements simultaneously across the earth’s major ocean basins. However, these comprehensive global concentration maps for trace elements cannot be properly interpreted without concurrent measurement of radioactive tracers like radium isotopes that can provide time scales of their ocean input. In this project, the investigators will measure the abundance and distribution of radium isotopes in the Southern Ocean between the southern tip of South America and Antarctica, including a detailed characterization of the Antarctic coastal marine environment. The project will support a postdoctoral research associate and involve two undergraduate student researchers in post-cruise analyses.The main motivation of the proposed research is to utilize the quartet of radium (Ra) isotopes (224Ra, 223Ra, 228Ra, 226Ra) to enable source identification and flux quantification of TEIs during the forthcoming US GEOTRACES GP17-OCE and GP17-ANT expeditions. Measurement of Ra isotopes will allow the team to address several key questions related to ocean margin and benthic boundary processes and their role in supplying and transporting TEIs to marine ecosystems including: (1) What are the rates of lateral transport of TEIs from the Antarctic and Patagonian continental margins out to and including the high nutrient low chlorophyll (HNLC) Southern Ocean? (2) What are the TEI fluxes associated with Antarctic glacial meltwater? and (3) What are the time scales of TEI transport associated with Pacific-Antarctic Ridge neutrally buoyant hydrothermal plumes? Boundary inputs are considered to be the dominant source of many key TEIs to the ocean including iron, however, TEI concentrations must be coupled with input and transport rates to determine their effect on marine biogeochemical cycles. The wide range of Ra isotope half-lives (3.66 days to 1600 years) allow for the quantification of TEI transport processes on time scales relevant to ocean mixing processes. The proposed coupled Ra-TEI measurements will allow the full value of the distribution of numerous TEIs as measured by GEOTRACES PIs to be realized.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.