Seawater‐particle interactions of rare earth elements and neodymium isotopes in the deep central Arctic Ocean

• Published in: Journal of Geophysical Research: Oceans
• Main Authors: Paffrath, Ronja, Pahnke, Katharina, Böning, Philipp, Rutgers Van Der Loeff, Michiel, Valk, Ole, Gdaniec, Sandra, Planquette, Helene
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union (AGU) 2021
• Subjects: Arctic Ocean; rare earth elements; neodymium isotopes; GEOTRACES; particles; hydrothermal vents; Arctic; Gakkel Ridge; Kara Sea; Climate change; Sea ice
• Online Access: https://archimer.ifremer.fr/doc/00705/81716/86324.pdf; https://archimer.ifremer.fr/doc/00705/81716/86326.pdf; https://doi.org/10.1029/2021JC017423; https://archimer.ifremer.fr/doc/00705/81716/

In the central Arctic Ocean, dissolved rare earth element concentrations ([dREE]) and the neodymium (Nd) isotope compositions are constant throughout the deep water column (>1000 m water depth), indicating unique conditions among the ocean basins and therefore requiring an investigation of seawater-particle interactions. Here, we present the first high resolution particulate REE and Nd isotope data from the Arctic Ocean and discuss the possible seawater-particle processes affecting the Arctic Ocean. Our results show that particulate [REE] are on the same order of magnitude as in other ocean basins, suggesting that particle composition is the main cause for a lack of pREE release to the dissolved pool. The lithogenic fraction dominates throughout the water column while the biogenic material contribution is very small. This paucity of biogenic material results in reduced particle-seawater exchanges of REEs and Nd isotopes. Moreover, we note only slight differences in the dissolved Nd isotope composition between the Eurasian and Canadian Basins. This is due to the different source regions supplying different dissolved and particulate Nd isotope signatures to both basins. The dissolved [REE] and Nd isotope composition of Atlantic waters are modified during their flow paths through contributions from the Kara Sea, lowering the salinity and increasing [dREE] and dNd isotope compositions. Hydrothermal influence from the Gakkel Ridge on dissolved and particulate [REE] and Nd isotopes could not be detected. Plain Language Summary The Arctic Ocean is strongly affected by climate change. Due to rising temperatures, the sea-ice is melting und the river input is increasing. This will also change the chemical composition of the Arctic Ocean and biological activity, since many trace elements added by rivers are essential for algal growth. In order to understand these changes and effects, the environmental conditions and processes need to be understood. We investigated rare earth element concentrations and neodymium isotope compositions in seawater and in suspended particles in the central Arctic Ocean. The data show that the release of rare earth elements from particles to seawater is lower in the Arctic Ocean than in other ocean basins and that this is due to the lower amount of biogenic relative to terrestrial-derived particles in the Arctic Ocean. This leads to constant dissolved rare earth element concentrations in the Arctic water column, in contrast to increasing concentrations with depth in other oceans. We further investigated the potential modification of rare earth elements and neodymium isotopes in the hydrothermally influenced deep waters over the Gakkel Ridge. In this study, we did not find an impact of the hydrothermal activity on rare earth elements or the neodymium isotope composition