Abstract:
Barium (Ba) serves as a tracer for export production, freshwater inputs and ocean chemistry in both modern and past oceans. However, the marine Ba budget remains largely uncertain, particularly regarding the hydrothermal input of Ba, which hinders the understanding of Ba cycling. Furthermore, recent studies have suggested a modern source-sink imbalance of Ba isotopes (δ138Ba) in the ocean, with sources (0.1-0.2‰) being overall isotopically heavier than the sinks (0.0-0.1‰). Nevertheless, this budget estimation has not accounted for the hydrothermal source of Ba. In this study, we present the first investigation of Ba and its isotopes in the Rainbow non-buoyant hydrothermal plume on the Mid-Atlantic Ridge based on a GEOTRACES compliant cruise (M176/2) in September 2021. The concentrations and isotopic signatures of dissolved and labile particulate Ba in the non-buoyant hydrothermal plume can be explained by conservative mixing between the Ba-enriched hydrothermal component and North Atlantic Deep Water. By extrapolating our data to the vent fluid endmember, we find that there is negligible removal of Ba and insignificant modification of Ba isotopic signatures from the vent fluid endmember to the non-buoyant hydrothermal plume, revealing that the Rainbow hydrothermal system introduces isotopically light Ba to the deep Atlantic Ocean (-0.16‰). We estimate that hydrothermal inputs contribute 10-18% of the total Ba inputs to the ocean, suggesting that this input could help balance the Ba isotopic budget of the oceans.
Bio:
Dr. ZHANG Zhouling obtained her Ph.D. degree from Xiamen University in 2020. She then started working at GEOMAR Helmholtz Centre for Ocean Research Kiel as a post-doctoral researcher in July 2020. She is a chemical oceanographer and her research focuses on isotope geochemistry, including the application of non-traditional stable isotopes (such as silicon and barium) and radiogenic isotopes (such as neodymium and hafnium) in tracing the modern oceanic processes. For example, she uses radiogenic neodymium isotopes to trace ocean circulation or terrestrial inputs, and stable silicon isotopes to trace diatom productivity or silicate weathering/reverse weathering. Her research areas cover a wide range, from estuaries, coastal seas to the open ocean. She has been actively involved in the international program GEOTRACES, with her current project associated with the GEOTRACES transect GP21 in the South Pacific Ocean.
