International Ocean Discovery Program (IODP) Expedition 357 successfully cored an east-west transect across the southern wall of Atlantis Massif on the western flank of the Mid-Atlantic Ridge (MAR) to study the links between serpentinization processes and microbial activity in the shallow subsurface of highly altered ultramafic and mafic sequences that have been uplifted to the seafloor along a major detachment fault zone.The primary goals of this expedition were to (1) examine the role of serpentinization in driving hydrothermal systems, sustaining microbial communities, and sequestering carbon; (2) characterize the tectonomagmatic processes that lead to lithospheric heterogeneities and detachment faulting; and (3) assess how abiotic and biotic processes change with variations in rock type and progressive exposure on the seafloor.To accomplish these objectives, we developed a coring and sampling strategy centered on the use of seabed drills-the first time that such systems have been used in the scientific ocean drilling programs.This technology was chosen in the hope of achieving high recovery of the carbonate cap sequences and intact contact and deformation relationships.The expedition plans also included several engineering developments to assess geochemical parameters during drilling; sample bottom water before, during, and after drilling; supply synthetic tracers during drilling for contamination assessment; acquire in situ electrical resistivity and magnetic susceptibility measurements for assessing fractures, fluid flow, and extent of serpentinization; and seal boreholes to provide opportunities for future experiments.endipitously able to generate a high-resolution (20 m per pixel) multibeam bathymetry map across the entire Atlantis Massif and the nearby fracture zone, MAR, and eastern conjugate, taking advantage of weather and operational downtime.This will assist science party members in evaluating and interpreting tectonic and mass-wasting processes at Atlantis Massif.

Downhole logging 34 Paleomagnetism 35 References V o l u m e 3 5 725 November, and the vessel immediately began to transit toward Site M0071.In summary, nine coring attempts were made in Hole M0068B to a maximum depth of 9.60 m with 66.04% recovery. Site M0075Cores were recovered from two holes at Site M0075 (proposed Site AM-03A), with an average site recovery of 45.46%.The water depth was 1568.00 m with no tidal range.An additional CTD cast that was conducted over the Mid-Atlantic Ridge was linked to this site (Hole M0075X).The water depth at this location was ≈4222 m.The total time spent on station was 1.67 days. Hole M0075AAt 0300 h on 14 November 2015, the vessel turned onto an eastsoutheast course for Site M0075.The vessel settled into DP mode at 0800 h; however, the swell (>4 m) was prohibitive for the deployment of either drill.At 0838 h, a CTD cast was begun.At 1003 h, the CTD was 2.4 m off the bottom and the first three Niskin bottles were fired.Two further Niskin bottles were fired on the way up, with a final one fired near the surface (see Table T5 in the Expedition 357 summary chapter [Früh-Green et al., 2017c]).The CTD was recovered on deck by 1102 h.Having completed the CTD, the sea state was still too rough to deploy either drill, so the vessel moved off site at 1111 h on 14 November to conduct an additional CTD cast over the Mid-Atlantic Ridge (Hole M0075X).The vessel returned to Site M0075 on 28 November at 0625 h from Hole M0071C.The RD2 was initially deployed at 0654 h.However, after repositioning three times because of the angle of the rig on landing, the RD2 had to return to deck at 0912 h because of a minor oil leak.The RD2 was redeployed at 1058 h and landed on the seafloor at 1153 h.Coring commenced at 1210 h, and the first core run was completed by 1320 h.Core Barrel 2 was loaded into the BHA at 1356 h, but at 1400 h, the RD2 suffered a sensor cable fault and we had to abandon the hole, returning the drill to deck at 1500 h.The vessel held position for rig repairs.By 1700 h, the cable was changed out, but a hydraulic leak in the top drive was discovered.The only option was to exchange the top drive for another one, which would take approximately 18 h.The fault with the MeBo, suffered during Hole M0071C operations immediately prior to Hole M0075A operations, was a hydraulic slip ring inside the top drive assembly that was not repairable at sea, so the MeBo could not be deployed.Because repairs to the RD2 would take some time, we decided to leave the site and continue running the multibeam survey.The vessel departed the site at 2013 h on 28 November.In summary, one coring attempt was made in Hole M0075A to a maximum depth of 1.72 m with 37.79% recovery.

This chapter documents the primary procedures and methods employed by the operational and scientific groups during the offshore and onshore phases of International Ocean Discovery Program (IODP) Expedition 357. This information concerns only shipboard and Onshore Science Party (OSP) methods described in the site chapters. Methods for postexpedition research conducted on Expedition 357 samples and data will be described in individual scientific contributions. Detailed drilling and engineering operations are described in the Operations section of each site chapter.

G.L. Früh-Green, B.N. Orcutt, S.L. Green, C. Cotterill, S. Morgan, N. Akizawa, G. Bayrakci, J.-H. Behrmann, C. Boschi, W.J. Brazelton, M. Cannat, K.G. Dunkel, J. Escartin, M. Harris, E. Herrero-Bervera, K. Hesse, B.E. John, S.Q. Lang, M.D. Lilley, H.-Q. Liu, L.E. Mayhew, A.M. McCaig, B. Menez, Y. Morono, M. Quéméneur, S. Rouméjon, A. Sandaruwan Ratnayake, M.O. Schrenk, E.M. Schwarzenbach, K.I. Twing, D. Weis, S.A. Whattam, M. Williams, and R. Zhao2

G.L. Früh-Green, B.N. Orcutt, S.L. Green, C. Cotterill, S. Morgan, N. Akizawa, G. Bayrakci, J.-H. Behrmann, C. Boschi, W.J. Brazelton, M. Cannat, K.G. Dunkel, J. Escartin, M. Harris, E. Herrero-Bervera, K. Hesse, B.E. John, S.Q. Lang, M.D. Lilley, H.-Q. Liu, L.E. Mayhew, A.M. McCaig, B. Menez, Y. Morono, M. Quéméneur, S. Rouméjon, A. Sandaruwan Ratnayake, M.O. Schrenk, E.M. Schwarzenbach, K.I. Twing, D. Weis, S.A. Whattam, M. Williams, and R. Zhao2