Collaborative Research: US GEOTRACES GP17-ANT: Nitrogen isotope dynamics on the Amundsen Sea continental margin

南极洲大陆架是一个动态的、往往具有生物生产力的极地环境，对海洋循环、营养物质和碳循环具有全球重要性。由于其高纬度位置和南极近端冰盖的影响，南极大陆架在持续的全球变暖下将迅速发生变化。然而，人们对南极大陆架的自然状态知之甚少，之前的研究表明，这种环境已经随着时间的推移而发生了变化，这也预示着它未来可能会如何变化。这项研究将利用氮的天然同位素来研究南极大陆架上氮循环的运作。氮是生命的关键营养物质，限制了许多环境中的生物生产力，并提供了海水中生物生长和分解之间的平衡的整体观点。氮同位素测量，结合美国地理轨迹GP17-ANT探险队的其他测量，将确定南极大陆架的一段生物生产力的主要来源和汇-阿蒙森海架-可能特别容易随着南极冰盖融化的加速而发生变化。这些测量还将提供关键的基线信息，以支持利用沉积物岩芯和其他档案重建过去的变化。该项目将培训研究生和本科生，并支持一名早期职业博士后研究人员。美国地理跟踪公司GP17-ANT探险队将提供机会，在阿蒙森海架上产生微量元素和同位素的补充数据集，阿蒙森海架是一个南极边缘环境，以丰富的海冰、融化的冰架和高效的多尼阿为特征。对于GP17-ANT的所有站，将测量硝酸盐的氮和氧同位素比率的全深度剖面，以及几个有代表性的站的总溶解氮的氮同位素比率，以深入了解氮源和水柱中的循环。此外，将从比标准方法所允许的更深的深处测量GEOTRACES大容量泵样本的悬浮颗粒氮同位素比，以调查再生和实地真相，并将深海珊瑚氮同位素比作为古替代指标的应用。最后，将从表层沉积物样本中测量大量沉积物和硅藻结合的氮同位素比率，为正在进行的使用较长沉积物岩心的古海洋重建提供地面真实资料。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 continental shelf of Antarctica is a dynamic and often biologically productive polar environment, with global importance for ocean circulation, nutrient and carbon cycling. Due to its high latitude location and the impacts of the proximal Antarctic ice sheet, the Antarctic continental shelf stands to change quickly under ongoing global warming. Yet the natural state of the Antarctic continental shelf is poorly known, and previous research suggests that this environment has changed through time, which would also signal how it may change in the future. This study will investigate the operation of the nitrogen cycle on the Antarctic continental shelf, using the natural isotopes of nitrogen. Nitrogen is a critical nutrient for life, limits biological productivity in many environments, and provides a holistic view of the balance between biological growth and decomposition in ocean waters. The nitrogen isotope measurements, combined with the other measurements of the U.S. GEOTRACES GP17-ANT expedition, will determine the major sources and sinks of biological productivity on a segment of the Antarctic continental shelf – the Amundsen Sea shelf – that may be particularly susceptible to change as Antarctic ice sheet melting accelerates. The measurements will also provide key baseline information to support the reconstruction of past changes using sediment cores and other archives. The project will train graduate and undergraduate students and support one early career postdoctoral researcher.The U.S. GEOTRACES GP17-ANT expedition will provide the opportunity to generate complementary data sets of trace elements and isotopes on the Amundsen Sea shelf, an Antarctic margin environment characterized by abundant sea ice, melting ice shelves, and highly productive polynyas. For all stations of GP17-ANT, full depth profiles of the nitrogen and oxygen isotope ratios of nitrate will be measured, along with nitrogen isotope ratios of total dissolved nitrogen at a few representative stations to provide insight into nitrogen sources and cycling in the water column. Moreover, suspended particle nitrogen isotope ratios will be measured from the GEOTRACES high-volume pump samples from deeper depths than standard methods allow, to investigate regeneration and ground-truth the application of deep-sea coral nitrogen isotope ratios as a paleo-proxy. Lastly, from surface sediment samples, bulk sediment and diatom-bound nitrogen isotope ratios will be measured, providing ground-truthing for ongoing paleo-oceanographic reconstructions using longer sediment cores.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.