Quantifying and disentangling the fluxes of chemical element sources and sinks in the Arctic Ocean system – FLUXARC

The FLUXARC project aims at contributing to the monitoring of rapid climate-driven changes currently occurring in the Arctic Ocean. More specifically, FLUXARC’s general goal is to tackle the sources and sinks of chemical elements to the Arctic Ocean, which remain poorly constrained despite their involvement in making this area a key parameter for the Earth’s climate. Through an innovative geochemical approach combining the analysis of beryllium and thorium isotopes in marine samples of various Arctic areas, I have a threefold ambition:
o disentangle and quantify, in Arctic sea ice, the fraction of chemical elements coming from atmospheric deposition (i.e., from “above”) from the fraction coming from river discharge and remobilization of shelf and bottom sediment (i.e., from “the sides/bottom”);
o quantify the transfer of these chemical fractions through sea ice melting in the water column and the contribution of these indirect supplies through sea ice melting relatively to direct chemical supplies from the atmosphere and “the sides/bottom”;
o assess the origin and fluxes of particulate matter in the Arctic Ocean.

I recently developed a method allowing the combined analysis of long-lived or stable beryllium (Be) and thorium (Th) isotopes in marine polar samples, building on the assumption that their distinct sources – atmospheric for Be-10, continental for Be-9 and Th-232, oceanic for Th-230 – and different affinity to particles and particle composition can be powerfully used to better constrain the sources and sinks of chemical elements to the rapidly changing Arctic Ocean and specifically answer to the aforementioned goals.

My project is based on the analysis of samples coming from two oceanographic cruises (the Canadian Arctic GEOTRACES cruise and the REFUGE-ARCTIC cruise, conducted in 2015 and 2024, respectively) that focused on the western exit of the Arctic Ocean waters to the Atlantic Ocean, through the Canadian Arctic Archipelago and Nares Strait. These Arctic areas include the whole diversity of sources that characterize the Arctic Ocean: a large proportion of continental shelf, with shallow straits, channels, and fjords, fed by riverine and glacial supplies. Glacial supplies are either from terrestrial origin (Ellesmere Island and Greenland glaciers mainly) or first-year and multiyear sea ice.

The combined analyses of Be and Th isotopes in Arctic seawater, sea ice and various sources (glacier, river, sediment) will allow me, together with the elemental ratios and isotopic signatures from the sources, to refine our understanding of chemical element sources and sinks of the Arctic Ocean. Through the coupling of these analyses to complementary trace elements and isotopes included in these two aforementioned cruises, FLUXARC will provide the first quantification of the atmospheric, sea ice, glacier, riverine, and sediment fluxes of a large array of elements and isotopes entering the Arctic Ocean, differentiating also between dissolved and solid fractions (sources). The dissolved-particulate fates of the same elements and isotopes in the marine realm will be established (sink). In the end, a well-documented budget of these chemical species will be proposed. The harvest of data provided by the FLUXARC consortium and his collaborators will offer exciting modelling prospects.