Empirical links between trace metal cycling and marine microbial ecology during a large perturbation to Earth's carbon cycle

Abstract

Available online xxxx Editor: D. Vance Keywords: oceanic anoxic event (OAE2) trace metal drawdown geochemistry anoxia euxinia biomarkersUnderstanding the global redox state of the oceans and its cause-and-effect relationship with periods of widespread organic-carbon deposition is vital to interpretations of Earth's climatic and biotic feedbacks during periods of expanded oceanic oxygen deficiency. Here, we present a compilation of new and published data from an organic-rich locality within the proto-North Atlantic Ocean during the Cenomanian-Turonian boundary event that shows a dramatic drawdown of redox-sensitive trace elements. Iron geochemistry independently suggests euxinic deposition (i.e., anoxic and sulfidic bottom waters) for the entire section, thus confirming its potential as an archive of global marine metal inventories. In particular, depleted molybdenum (Mo) and vanadium (V) concentrations effectively record the global expansion of euxinic and oxygen-deficient but non-sulfidic waters, respectively. The V drawdown precedes the OAE, fingerprinting an expansion of oxygen deficiency prior to an expansion of euxinia. Molybdenum drawdown, in contrast, is delayed with respect to V and coincides with the onset of OAE2. Parallel lipid biomarker analyses provide evidence for significant and progressive reorganization of marine microbial ecology during the OAE in this region of the proto-North Atlantic, with the smallest relative eukaryotic contributions to total primary production occurring during metal-depleted intervals. This relationship may be related to decreasing supplies of enzymatically important trace elements. Similarly, box modeling suggests that oceanic drawdown of Mo may have approached levels capable of affecting marine nitrogen fixation. Predictions of possible nitrogen stress on eukaryotic production, locally and globally, are consistent with the low observed levels of Mo and a rise in 2-methylhopane index values during the peak of the OAE. At the same time, the environmental challenge presented by low dissolved oxygen and euxinia coincides with increased turnover rates of radiolarian clades, calcareous nanofossils, and foraminifera, suggesting that the temporal patterns of anoxia/euxinia and associated nutrient limitation may have contributed to the fabric of OAE2-related turnover.

A model for the oceanic mass balance of rhenium and implications for the extent of Proterozoic ocean anoxia

“…During the Toarcian OAE, for example, the Re and Mo enrichments of ORM are muted, indicating drawdown of the oceanic Re and Mo reservoirs in response to expanded anoxia (Pearce et al, 2008;Owens et al, 2016). Conversely, during the Cretaceous OAEs 1a and 2, which were associated with LIP emplacement, Re concentrations of ORM are often not muted and are mildly correlated with excursions to higher Os concentrations and unradiogenic 187 Os/ 188 Os, suggesting delivery of magmatic Re (and Os) to seawater in sufficient quantities to offset the increased burial of Re (and Os) into anoxic sediments (Turgeon and Creaser, 2008;Bottini et al, 2012;du Vivier et al, 2014;Kendall, 2014).…”

Patterns of local and global redox variability during the Cenomanian–Turonian Boundary Event (Oceanic Anoxic Event 2) recorded in carbonates and shales from central Italy

“…Understanding the dynamics of de‐oxygenation during this short‐lived event, estimated as lasting between 450 kyr and 900 kyr (Arthur & Premoli‐Silva, ; Kuhnt et al ., ; Sageman et al ., ; Voigt et al ., ; Eldrett et al ., ; Batenburg et al ., ), and similar organic carbon burial events throughout Earth history, has been a major priority in the search to unravel the climate forcing, biological feedbacks and related redox dynamics of the ocean during biotic extinction events (Bambach, ). There is mounting evidence for widespread anoxic and specifically euxinic conditions during OAE 2 based on diverse geochemical proxies for local bottom‐water redox at multiple locations (Brumsack, ; Turgeon & Brumsack, ; Jenkyns et al ., ; van Bentum et al ., ; Pearce et al ., ; Lu et al ., ; Hetzel et al ., ; Owens et al ., , ; Westermann et al ., ; Dickson et al ., ; Goldberg et al ., ), including evidence for photic‐zone euxinia (Sinninghe Damsté & Köster, ; Kuypers et al ., ; Pancost et al ., ; van Bentum et al ., ). Numerical ocean modelling suggests that 50% (by volume) of the global ocean was anoxic during the OAE (Monteiro et al ., ).…”

Two pathways for thiosulfate oxidation in the alphaproteobacterial chemolithotrophParacoccus thiocyanatusSST

“…In nature, sulfur exists in a wide range of oxidation states (-2 to +6), and in doing so passes through a complex variety of 50 biogeochemical processes (Luther et al, 1985). Sulfur cycling, in diverse ecosystem, essentially involves sulfur compounds syntrophy (i.e., inter-microbial transfer of various redox states of sulfur), physicochemically or biochemically intermingled with the transformation dynamics of carbon, nitrogen, iron and other metals (Cutter and Kluckhohn 1999;Mopper and Kieber 2002;Owens et al 2016). Among the various reduced states of sulfur, thiosulfate constitutes a key junction in the 55 network of sulfur-species transformations in diverse ecosystems, such as marine sediments (Jorgensen, 1990a;Thamdrup et al, 1994), freshwater sediments (Jorgensen, 1990b), meromictic lakes (Kondo et al, 2000) and hot spring waters (Xu et al, 1998).…”