ZMT - Leibniz Zentrum für Marine Tropenforschung

Radium (Ra) is an element that is widely used in the study of oceanographic processes. Ra is produced by the decay of particle-bound thorium isotopes, mainly in the sediments, and diffuses into the water column. Ra is less affected by biological processes and inputs, mixing, and decay are the main factors controlling its distribution. There are a number of Ra isotopes with different half-lives, but the quartet 223Ra(T1/2= 11.4 days), 224Ra (T1/2= 3.6 days), 226Ra (T1/2= 1600 years), and 228Ra (T1/2= 5.7 years) are the most commonly used in ocean studies.

Therefore, the aim of the present project is to use Ra isotopes to determine in detail the sources, fluxes and sinks of trace elements (TEs) in the water column along a 23°S zonal section in the South Indian Ocean (SIO), one of the least studied ocean regions. The combination of TEs and Ra measurements will allow an understanding of the supply pathways of TEs to the SIO from the atmosphere, continent (mainly the Zambezi River), sediments (on continental slopes), and ocean crust (hydrothermalism of the Indian Ocean Ridge).

The study is based on samples collected on the German research vessel SONNE during the SO-308 expedition scheduled for November-December 2024 in the SIO from the coast of Mozambique via Madagascar to Australia. Our investigations will be part of the internationally coordinated GEOTRACES programme.

The results will contribute to a better understanding of material fluxes between continents and oceans and their impact on ecosystems and climate, as well as providing fundamental scientific results on tropical and subtropical marine regions.