A Water mass analysis and Exploration of linkS between phytoplankton, bacteria and trace MEtals along the South West INdian GEOTRACES Section – AWESOME-SWINGS

The AWESOME SWINGS project combines several complementary approaches:
- The SWINGS oceanographic cruise, to acquire direct measurements at sea and collect samples,
- Analyses of trace elements and isotopes (TEI), used as tracers to characterize water masses and biogeochemical processes,
- Modeling approaches (OMPA, biogeochemical and circulation models) to reconstruct dynamics and quantify fluxes,
- International databases (GEOTRACES, GLODAP, eWOCE, etc.) to extend the analysis to regional and global scales.

The project aims to deliver several major scientific advances:
- Improved characterization of Subantarctic Water Types (SWT) through TEI and isotopic tracers,
- More precise quantification of biogeochemical fluxes (carbon, nutrients, trace metals) in the Southern Ocean,
- Development and validation of innovative analytical tools and models (OMPA approaches, isotopic databases, data–model coupling),
- Production of cross-cutting knowledge useful to the scientific community for studying biogeochemical cycles and the biological carbon pump.

All available data from the GEOTRACES database will be used and subjected to the same methodological approaches (e.g., PMF, OMPA) in order to obtain a more global view of phytoplankton uptake and bacterial remineralization processes.

Scientific papers are currently being written.

The Southern Ocean is considered to be the main sink for anthropogenic carbon in the global ocean and a hub for the redistribution of physical and biogeochemical properties between the Atlantic, Pacific and Indian Oceans. However, the sources, sinks and processes controlling the distribution of vital micronutrients (Fe, Cu, Ni, Mn, Co, Zn, also known as trace metals, TM) remain poorly understood to date. The multidisciplinary oceanographic campaign SWINGS was conducted in early 2021 with 47 scientists from 7 countries on board the N/O Marion Dufresne (MD229, GEOTRACES section GS02, 11 January to 8 March 2021). Together, we proposed to elucidate the sources, transformations and sinks of TMs along a section crossing key areas of the Southern Ocean at 32 stations. Over 8000 samples were collected, providing a major breakthrough in understanding and quantifying dissolved particle exchange, a recognised lock for elemental cycling modelling. One year later, this huge harvest of samples keeps about 80 scientists from 21 international laboratories and 7 countries busy, including 7 PhD students from UBO, Brest (1), SU, Paris (2), UPS, Toulouse (1), AMU, Aix-Marseille (1), Liverpool (1) and Florida International (1), in order to i) establish the relative importance of sedimentary, atmospheric and hydrothermal sources of TMs in the Indian sector of the Southern Ocean, ii) study the internal cycles of the trace elements: biogenic uptake, remineralisation, particle fate and export, and iii) quantify the transport of TM by the Antarctic Circumpolar Current and the numerous fronts at the confluence of the Indian and Atlantic Oceans. The SWINGS project is a major French contribution to the international GEOTRACES program, whose data management policy is to make data available in open access as soon as possible after acquisition.
The current request focuses on the recruitment of three qualified postdoctoral researchers (409500€) to carry out specific data exploration on the following tasks:
1) Conducting an analysis of the water masses along the GS02/SWINGS section, combining hydrographic and macronutrient data through an extended optimal multiparametric analysis. This will be of great benefit in interpreting the observed distributions of dissolved and particulate trace elements north and south of the polar front, particularly in the Fawn Trough which is a major pathway for the Antarctic Circumpolar Current
2) Study of the links between phytoplanktonic, macronutrient and metal distribution and activity in two contrasting regions, north and south of the Polar Front. Statistical tools will be used.
3) Exploration of the metabolic strategies of the microbial community for the acquisition and upstream processing of nutrient trace metals. Bioinformatics will be used to study the 44 metagenomes from the main water bodies, from the surface to the deep ocean, with respect to trace metal distributions.
The rest of the requested funds will be devoted to the dissemination of the main results in scientific articles (publication costs: 13500€) and workshops (3000€). Administrative costs are estimated at 55380€.