Redox evolution during Eemian and Holocene sapropel formation in the Black Sea

authored by: Antje Wegwerth, Sebastian Eckert, Olaf Dellwig, Bernhard Schnetger, Silke Severmann, Stefan Weyer, Annika Brüske, Jérôme Kaiser, Jürgen Köster, Helge W. Arz, Hans Jürgen Brumsack
Abstract: The Black Sea repeatedly experienced major hydrographic changes during glacial-interglacial transitions, with alternating limnic and brackish stages. While the redox conditions during the present Holocene brackish period (since ~ 9,000 yr BP) have been intensively studied, the redox evolution during the last interglacial, the Eemian (~ 128,000-120,000 yr BP), remains largely unexplored. With its at least 3 °C warmer climate and an up to 10 m higher global sea level, the Eemian could open a window into the future development of the Black Sea. This study provides a detailed comparison of the Black Sea redox evolution during Eemian and Holocene sapropel formation. We show that the redox conditions and associated geochemical processes in the Black Sea water column can strongly deviate from the Holocene when sea level and climate conditions are different. Mo/Al and Re/Mo as well as Mo and Fe isotope proxies record a comparatively uniform rise of the Eemian redoxcline culminating in pronounced euxinia. This scenario strongly contrasts with weaker euxinic conditions during the Holocene Unit II sapropel (~ 8,000-2,500 yr BP). Higher Mo/TOC ratios during the Eemian and Mo inventory considerations suggest a higher Eemian Mo availability, possibly due to an improved connection to the Mediterranean Sea. We conclude that higher temperatures, productivity, sea level-associated salinity changes, and corresponding higher sulphide levels were ultimately responsible for enhanced trace metal enrichment during the Eemian Black Sea sapropel stage.
Organisation(s): Institute of Mineralogy
Geochemistry
External Organisation(s): Leibniz Institute for Baltic Sea Research Warnemünde (IOW)
Carl von Ossietzky University of Oldenburg
Rutgers University
Type: Article
Journal: Palaeogeography, Palaeoclimatology, Palaeoecology
Volume: 489
Pages: 249-260
No. of pages: 12
ISSN: 0031-0182
Publication date: 01.01.2018
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: Oceanography, Ecology, Evolution, Behavior and Systematics, Earth-Surface Processes, Palaeontology
Sustainable Development Goals: SDG 13 - Climate Action
Electronic version(s): https://doi.org/10.1016/j.palaeo.2017.10.014 (Access: Closed)