The nitrogen cycle in Arctic and Antarctic macroalgae

The nitrogen cycle is chronically being altered in marine and terrestrial ecosystems in the economic world (Ohkouchi et al., 2015): these changes can be monitored using stable nitrogen isotope ratios (Delta 15N). However, our knowledge of the nitrogen cycle in high-latitude polar environments is poor. The greatest variation of Delta 15N in the modern world from a single ecosystem has been recorded in the pristine environment of Antarctica (Wada et al., 1981).

Research groups are now starting to investigate nitrate concentration and Delta15N in the desert soils of Antarctica (Diaz et al., 2020). Nitrogen isotopic changes in polar sedimentary cores suggest major shifts between glacial and interglacial periods (Ai et al., 2020), which may represent wetting and drying of desert soils around Antarctica. Abundant microbiological communities exist in snow ice ("green ice"; Gray et al., 2020) and their impact on the nitrogen cycle is currently not known.

There is clearly a gap in our knowledge of the nitrogen cycle in Antarctic. Future climate predictions indicate a loss of Arctic and Antarctic ice, which could have a catastrophic impact on the nitrogen cycle in the region. Our understanding of nitrogen cycle in the Arctic region is more thoroughly understood (e.g., Pajares & Ramos, 2019) in comparison to the Antarctic.

The Antarctica is highly sensitive to climate change, and thus a more thorough understanding of the nitrogen cycle in Antarctica is required to predict the environmental impact that glacial ice sheet loss will have on the surrounding ecosystems. This PhD will focus on the delicate environment between the ice and deep marine sedimentary system, the coastal ecosystem, specifically macroalgae.

This PhD will consist of three research work-packages (WP1-3):

Work Package 1 (WP1): To collect and archive macroalgae from the Antarctic Peninsula and Svalbard (Arctic Circle) in various museums around the UK (World Museum, Liverpool; National Museum of Wales; Royal Botanic Garden of Edinburgh; Natural History Museum in London). Their existing macroalgae herbaria have none or very few specimens from Antarctica.

Collecting samples from these climate-sensitive environments will be valuable for future research and education. The specimens collected will be archived and made into a web database from which scientists around the world can request samples for scientific research.

Work Package 2 (WP2): To conduct a nitrogen isotope study of different macroalgae species around the coastal environment from the locations used in WP1. In Antarctica, Himantothallus will definitely be collected: it has blades up to 20m in length and could provide seasonal/historical records of Delta 15N. In the Arctic, various kelp species will be collected. In addition, soil, sediment, ice/water and guano samples will be collected to characterise sources and sinks in the local nitrogen cycle.

Work Package 3 (WP3): SeDeltalect macroalgae samples will be returned to Durham University for experimental work. Experiments will be conducted to mimic future climate states, such as increasing temperature, light and/or nutrients (e.g., nitrate vs ammonia). The macroalgae will be monitored and measured over several months to determine their response.