Isotopic characterisation of nutrient dynamics and UCDW behaviour in the west Antarctic Peninsula sea ice environment

This research project aims to examine the ways in which ongoing climate change and sea ice decline at the west Antarctic Peninsula (WAP) are impacting upon nutrient budgets and biogeochemical cycling throughout the region.

The WAP is an ecologically important region of high primary productivity, and nutrient cycling is known to be crucial to phytoplankton production and its relationship with CO2 dynamics. Upper circumpolar deep water (UCDW) is understood to constitute the principal source of nutrients to surface waters throughout the WAP region. UCDW incurs at the shelf break and is transported across the continental shelf, so that nutrients can be supplied to the mixed layer by vertical mixing. This source of nutrients fuels high productivity in coastal regions, with implications for the biological uptake of atmospheric CO2.

Available evidence suggests that sea ice variability can drastically impact phytoplankton biomass and nutrient utilisation in surface waters during the summer growing seasons, but the mechanisms underlying this interaction remain to be fully understood. Sea ice melt and meteoric freshwater inputs can promote phytoplankton blooms by stabilising the upper ocean sufficiently to provide a well-lit surface environment conducive to growth. However, such stratified conditions can also inhibit productivity and the magnitude of the bloom by restricting the resupply of nutrients to the mixed layer. Superimposed onto large interannual variability in chlorophyll, macronutrients and the physical environment, there are strong indications of long-term sea ice decline along the WAP and a concomitant decline in productivity.

This research project seeks to understand the changes in nutrient biogeochemistry underlying these changes in productivity in the WAP sea ice zone, and addresses the central hypothesis that a climate-induced reduction in sea ice and stratification will result in drastic declines in primary production and nitrate utilisation in the surface environment. Such conditions would lead to a simultaneous reduction in the capacity of the oceanic CO2 sink during summer and generate an increased pool of unutilised nitrate in surface waters over the shelf, both of which would hold profound implications for global biogeochemical cycles.

This study will comprise three components:
1. A time-series study over three austral summer growing seasons in Ryder Bay, WAP, to examine temporal changes in fixed nitrogen budgets and cycling, in relation to interannual variability in sea ice, water column structure and productivity.
2. A ship-based transect from the shelf break to Marguerite Bay to examine deep water behaviour and its impact on the supply of nutrients to high productivity coastal regions.
3. Ship-based sampling across the wider WAP shelf region to examine spatial variability in nutrient dynamics, productivity, sea ice and physical oceanography, and give a broader context to the time-series study.

A suite of biogeochemical measurements pertinent to nutrient budgets and cycling will be made during each component of the study. Comprehensive ancillary physical and biological data are available from project partners, to examine productivity and environmental variables alongside these nutrient measurements. A fixed nitrogen budget will be constructed for the WAP shelf on an annual basis and its interannual variability examined in the context of ongoing sea ice losses and changes in phytoplankton productivity.

Nutrient biogeochemistry is central to the relationship between productivity and oceanic uptake of atmospheric CO2, so this study has broad and far-reaching implications for the role of the Southern Ocean CO2 system in regulating global climate. This study will also help to predict the future response of the oceans to ongoing climate change at the wider scale by giving insight into the climatic impacts on nutrient cycling and productivity in the fastest-warming marine environment on Earth.

The most important Impact of this research project will be communication of the key findings and the importance of the oceans and polar regions, in general, to the general public. This will contribute to the knowledge base that informs national and international decision-making, and policy for the Southern Ocean. Impact activities proposed herein will also contribute to public knowledge and quality of life through engagement with cutting-edge research and internationally-relevant science.

The key user community will consist of teachers and students at a number of secondary schools across the UK, as well as members of the general public. One such school will be South Wigston High School in Leicestershire, where a series of visits will build on the already strong relationship between the school and the Fellow. Science workshops will develop the Fellow's previous Outreach work at the school, by demonstrating the practical science behind the knowledge exhibited in previous visits. These science education activities are intended to teach relevant practical science skills and raise the profile of science in student communities. Working with teachers and students will allow the content of the workshops to be incorporated into science teaching programmes and to benefit the maximum number of students, both during the visits and into the future. These science workshops will also be of direct benefit to student development within the school by providing a platform for the school-wide "Science Leaders" scheme. A letter of support from Head Teacher, Mr Gary Toward, demonstrates the school's engagement in this proposal. Whilst communication and plans for Impact activities at South Wigston High School are most advanced, a number of other schools will also benefit from science education and public engagement activities to encourage students to study science at University and to inform and inspire the next generation of polar scientists and enthusiasts.

Members of the general public will also be catered for through engagement events at museums and science centres conducted by the Fellow and in collaboration with the UK Polar Network (see pathways to impact).