Oxygen consumption rates in subseafloor basaltic crust derived from a reaction transport model

Nitrogen cycling in the deep sedimentary biosphere: nitrate isotopes in porewaters underlying the oligotrophic North Atlantic

“…In contrast to well-studied ocean margin sediments, oxygen (O 2 ) and nitrate (NO − 3 ), two powerful oxidants of organic carbon, penetrate deeply into the sediment underlying oligotrophic ocean waters (D'Hondt et al, , 2015Murray and Grundmanis, 1980;Rutgers van der Loeff et al, 1990;Sachs et al, 2009;Røy et al, 2012;Fischer et al, 2009). Furthermore, in the sediments overlying relatively young and permeably ocean crust, O 2 and NO − 3 are also supplied via upward diffusion from oxic and nitrate-replete fluids flowing through basaltic basement as has been shown for the North Pond site, which is located on the western flank of the Mid-Atlantic Ridge (Orcutt et al, 2013;Ziebis et al, 2012). At North Pond, where the sediment cover is thin (< ∼ 25 m), O 2 penetrates the entire sediment column; where sediment thickness is elevated, conditions become anoxic at mid-depths.…”

“…While a majority of seafloor subsurface biosphere research has focused on aspects of sedimentary carbon, sulfur, and iron cycles, the potential role of N in supporting subsurface microbial activity has been largely unexplored. Despite exceedingly oligotrophic conditions, life persists and evidence for active heterotrophic and autotrophic microbial communities in North Pond sediments is mounting (Ziebis et al, 2012;Picard and Ferdelman, 2011;Orcutt et al, 2013).…”

IODP Expedition 336: initiation of long-term coupled microbiological, geochemical, and hydrological experimentation within the seafloor at North Pond, western flank of the Mid-Atlantic Ridge

“…Sediments were intensely sampled for geochemical pore water analyses and microbiological work. Shipboard determination of dissolved oxygen concentrations in the pore waters indicate pronounced C-shaped profiles, indicating diffusion of oxygen into the sedimentary pile from both the water-sediment and sediment-basement interfaces and oxygen consumption by aerobic microbial activity within the sediments (Orcutt et al, 2013). Expedition 336 installed fully functional observatories in two newly drilled holes (U1382A and U1383C).…”

IODP Deep Biosphere Research Workshop report – a synthesis of recent investigations, and discussion of new research questions and drilling targets

“…New techniques for assessing the activity and whole genomic material from individual microbial cells have opened up the possibility of discovering new capabilities in living native subsurface cells (Morono et al, 2011;Lloyd et al, 2013), and by employing new chemical indicators for sporulated cells, researchers now have the tools to distinguish between dormant and metabolically active populations (Lomstein et al, 2012). Finally, the third domain of life, Eukarya (specifically fungi), is also now known to be active in the subseafloor and, likely, to play an important role in the degradation of organic matter in subseafloor sediment (Biddle et al, 2005;Edgcomb et al, 2011;Orsi et al, 2013a). Such studies have fostered a new level of understanding of subseafloor microbiology and have laid the foundation for future investigations of important subseafloor microbial processes.…”

“…Notable exceptions include models applied to sediments from the Demerara Rise (Arndt et al, 2006) and the eastern equatorial Pacific (Wang et al, 2008). A RTM has recently been applied to quantify the rates of microbial catabolism in deep-sea hydrothermal vent chimneys , and similar types of models were used to constrain oxygen consumption patterns in upper oceanic crust (Orcutt et al, 2013) and North Pacific Gyre (Røy et al, 2012). Both bioenergetic and RTM strategies for understanding the deep biosphere functions are restricted by the availability of physiochemical data produced by the IODP.…”