IODP Expedition 329: Life and Habitability Beneath the Seafloor of the South Pacific Gyre

Abstract

Integrated Ocean Drilling Program (IODP) Expedition 329 made major strides toward fulfilling its objectives. Shipboard studies documented (1) fundamental aspects of habitability and life in this very low activity subseafloor sedimentary ecosystem and (2) first-order patterns of habitability within the igneous basement. A broad range of postexpedition studies will complete the expedition objectives. Throughout the South Pacific Gyre (SPG; Sites U1365–U1370), dissolved oxygen and nitrate are present throughout the entire sediment sequence, and sedimentary microbial cell counts are lower than at all previously drilled IODP/ Ocean Drilling Program (ODP)/Deep Sea Drilling Program (DSDP) sites. In contrast, at Site U1371 in the upwelling zone just south of the gyre, detectable oxygen and nitrate are limited to the top and bottom of the sediment column, manganese reduction is a prominent electron-accepting process, and cell concentrations are higher than at the same depths in the SPG sites throughout the sediment column. Geographic variation in subseafloor profiles of dissolved and solid-phase chemicals are consistent with the magnitude of organic-fueled subseafloor respiration declining from outside the gyre to the gyre center. <br><br> Chemical profiles in the sedimentary pore water and secondary mineral distributions in the basaltic basement indicate that basement alteration continues on the timescale of formation fluid replacement, even at the sites with the oldest basement (84–120 Ma at Sites U1365 and U1366). <br><br> doi:<a href="http://dx.doi.org/10.2204/iodp.sd.15.01.2013" target="_blank">10.2204/iodp.sd.15.01.2013</a>

Radiolytic Hydrogen Production in the Subseafloor Basaltic Aquifer

“…Potassium is typically concentrated in such alteration minerals as smectite and zeolite, as well as K-feldspar ( Alt and Teagle, 2003 ; Bartetzko, 2005 ). Shipboard logs of natural gamma radiation (NGR) show clear evidence of such K concentration at alteration fronts in Site U1365 basalt ( D’Hondt et al, 2011 , 2013 ). However of the three radionuclides, K contributes the least to total H 2 production because it only produces β and γ radiation when it decays.…”

Faculty Opinions recommendation of Subseafloor life and its biogeochemical impacts.

“…For these calculations, diffusivities are from Schulz 104 , corrected for in situ temperature at Sites 1226 and U1370 (temperature was assumed constant at Site 984, where in situ temperature was not measured). Porosities and in situ temperature data are from shipboard measurements of the respective drilling expeditions [105][106][107] (available at http://sedis.iodp. org).…”

“…org). Sedimentation rates are from the shipboard age models generated for each drill site [105][106][107] .…”

An Improved Method for Extracting Viruses From Sediment: Detection of Far More Viruses in the Subseafloor Than Previously Reported

“…Samples from offshore Shimokita, Japan, representing organic-rich hemipelagic sediments were collected from frozen cores collected during the Chikyu Shakedown Cruise CK06-06 at Site C9001 Hole C (Aoike, 2007). South Pacific Gyre samples representing organic poor, oligotrophic sediments were taken from frozen cores collected during IODP Expedition 329 at Sites U1366, U1367, and U1368 (D’Hondt et al, 2011, 2013, 2015). Iron mat sediment samples were collected from Tarama Knoll in the Okinawa Trough during cruise YK17-17 (Makita, 2017).…”