Biogeochemistry of marine dissolved organic sulfur: quantification, distribution, molecular composition, and reactivity

• Main Author: Ksionzek, Kerstin
• Format: Thesis
• Language: unknown
• Published: 2019
• Subjects: Southern Ocean; Weddell Sea
• Online Access: https://epic.awi.de/id/eprint/51462/; https://hdl.handle.net/10013/epic.56b8a8c1-d160-4dde-9fa4-b5a3598be4a3

Dissolved organic matter (DOM) is ubiquitous in natural waters and plays a central role in the biogeochemistry of riverine, estuarine and marine environments. The heteroatomic fraction of DOM consists mainly of nitrogen, phosphorous, and sulfur. While the biogeochemical cycling of C, N, and P has been intensely studied, dissolved organic sulfur (DOS) has been only marginally addressed. Nevertheless, it is an essential element for marine primary production and organic sulfur compounds play a critical role in biogeochemistry, ecology, and climate processes. The analysis of DOS quantity and distribution in marine environments as well as its chemical characterization is of urgent need to further understand the underlying processes of DOS biogeochemistry. This study is based on more than 600 samples from different marine environments, from the surface to the deep ocean, and thus, represents the so far most comprehensive dataset of DOS in the ocean. Within this thesis, a basin-scale distribution of extractable DOS in the East Atlantic Ocean, the Atlantic sector of the Southern Ocean, and the Weddell Sea is presented. A first conservative global inventory of the marine non-volatile DOS stock was calculated using a combination of state-of-the-art approaches. The results suggest that the marine DOS inventory is by far the largest oceanic reservoir of organic sulfur (OS), exceeding the atmospheric stock and the volatile marine DOS by several orders of magnitude. Decades of research on the marine DOS cycle have focused on only ~2 % of the total OS inventory (DMSP cycle). The marine DOS distribution and stoichiometry was compared to radiocarbon age of dissolved organic carbon (DOC), suggesting a primarily autochthonous biogenic origin and an active involvement of this DOS in the microbial loop - similar to organic nitrogen. The contribution of the sulfur-containing amino acid methionine to extractable DOS was found to be only ~2 %. Additionally, ultrahigh-resolution mass spectrometry identified a diverse suite of sulfur ...