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

NSF Award Abstract:
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.