Abstract
Anoxic marine sediments contribute a significant amount of dissolved iron (Fe2+) to the ocean which is crucial for the global carbon cycle. Here, we investigate iron cycling in four Arctic cold seeps where sediments are anoxic and sulfidic due to the high rates of methane-fueled sulfate reduction. We estimated Fe2+ diffusive fluxes towards the oxic sediment layer to be in the range of 0.8 to 138.7 μmole/m2/day and Fe2+ fluxes across the sediment-water interface to be in the range of 0.3 to 102.2 μmole/m2/day. Such variable fluxes cannot be explained by Fe2+ production from organic matter–coupled dissimilatory reduction alone. We propose that the reduction of dissolved and complexed Fe3+ as well as the rapid formation of iron sulfide minerals are the most important reactions regulating the fluxes of Fe2+ in these cold seeps. By comparing seafloor visual observations with subsurface pore fluid composition, we demonstrate how the joint cycling of iron and sulfur determines the distribution of chemosynthesis-based biota.
Highlights
Iron is a critical micro-nutrient for marine phytoplankton and photosynthesis in the surface ocean (e.g., Boyd et al 2000)
Sediment cores were recovered by various techniques: box corer (BC), multicorer (MC), and gravity corer (GC) as well as push corer (PC) and blade corer (BLC) using a remotely operated vehicle (ROV) onboard R/V Helmer Hanssen
We focus on the following reactions/processes that contribute to the cycling of iron in the sediments of the investigated cold seeps: (1) the release of Fe2+ from dissimilatory iron reduction (DIR), (2) the release of Fe2+ from other reactions such as the reduction of dissolved Fe3+, (3) precipitation of iron sulfide minerals, and (4) oxidation of Fe2+ in the sediments as a result of biological disturbance
Summary
Iron is a critical micro-nutrient for marine phytoplankton and photosynthesis in the surface ocean (e.g., Boyd et al 2000). In the absence of organic ligands, Fe(OH) is the primary inorganic aqueous iron species at pH 8 whereas Fe2+ dominates the aqueous iron pool under anoxic conditions (Raiswell and Canfield 2012). Fe2+ is mostly produced through the reductive dissolution of iron (oxyhydr)oxide driven by the decomposition of particulate organic matter (POC) (or dissimilatory iron reduction (DIR), hereafter) (Lovley and Phillips 1988). The rates of Fe2+ production through this process depend on factors such as the quantity/type of organic matter, bottom seawater dissolved oxygen concentration (Lyons and Severmann 2006; Dale et al 2015), the reactivity of different iron minerals (Raiswell and Canfield 1998; Larsen and Postma 2001), and solution pH (Straub et al 2001).
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
