The South Indian Ocean - Biogeochemical studies on water masses, nutrient and stable isotope distribution, and particulate matter in an oligotrophic ocean region

Abstract

This thesis presents biogeochemical element cycling processes in the less explored oligotrophic subtropical gyre of the South Indian Ocean. A detailed water mass analysis was conducted by using physical water column profiles that were basis to understand the complex distribution of nutrients and stable isotope signals in order to identify the sources and transformation processes in the nitrogen cycle. Furthermore, a five-year sediment trap experiment (2015-2019) was carried out in order to assess the particulate organic carbon (POC) export below the euphotic zone, further into the ocean interior, and its final accumulation in the deep-sea sediments. This constitutes to the organic carbon pump and is a central part of the global carbon cycle. Thus, these investigations contribute to the baseline knowledge on nitrogen and carbon cycle processes and its budgets in oligotrophic areas that are most likely expand under global warming and thus getting even more important on a global scale during the next decades.