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1. Expedition 397T Scientific Prospectus: Transit and Return to Walvis Ridge Hotspot

   https://doi.org/10.14379/iodp.sp.397T.2022  

   Sager, W.W. ; Hoernle, K. ; Blum, P. ( July 2022 , Scientific prospectus)

   During International Ocean Discovery Program (IODP) Expedition 391, the Tristan-Gough-Walvis Ridge (TGW) hotspot track was cored in December 2021–February 2022. Its overarching objective was to recover basaltic rock from TGW edifices to understand the evolution of Walvis Ridge and related guyots. Significant cuts to the Expedition 391 operational plan were necessary as a result of lost time due to COVID-19 mitigation procedures. Because the R/V JOIDES Resolution will pass over Walvis Ridge during the transit from Cape Town, South Africa, to Lisbon, Portugal, prior to IODP Expedition 397, the 3 week transit provides an opportunity to drill one or two holes that were planned but not cored during Expedition 391. The transit schedule indicates that ~7 days of ship time will be available for this effort. Coring will be attempted at one or two sites, depending on weather and operational difficulties. The first site to be cored will be proposed Site GT-6A on the flank of the Gough track ridge. If time permits, coring will also be done at proposed Site TT-3A on the Tristan track, completing the proposed transect across the three chains of the Walvis Ridge guyot province. Two operational strategies are planned to address the limited timemore »available. First, the ~164 m thick (Site GT-6A) and ~146 m thick (Site TT-3A) sediment sections will be drilled without coring to ~20 m above basement. Primary Site GT-6A, which is ~1.1 km upslope from alternate Site GT-4A, was specifically proposed because of its reduced sediment thickness.« less
2. Scientific Prospectus Addendum: Dynamics of the Pacific Circumpolar Current (DYNAPACC)

   https://doi.org/10.14379/iodp.sp.383add.2018  

   Lamy, F. ; Winckler, G. ; Alvarez Zarikian, C.A. ( October 2018 , Scientific prospectus)

   This addendum to the International Ocean Discovery Program (IODP) Expedition 383 Scientific Prospectus (Dynamics of the Pacific Antarctic Circumpolar Current; Lamy et al., 2018) addresses the results of the safety review of 10 new proposed drill sites by the IODP Environmental Protection and Safety Panel (EPSP) on 4–6 September 2018 and a change to the operations plan and the end port call for Expedition 383. Because of an adjustment to the R/V JOIDES Resolution 2018–2019 operations schedule, the end port for Expedition 383 has changed from Valparaiso, Chile, to Punta Arenas, Chile. Therefore, at the time of publication of this addendum, the expedition is scheduled to start and end in Punta Arenas, Chile. The dates of the expedition remain unchanged from the original Expedition 383 Scientific Prospectus (Lamy et al., 2018), from 20 May to 20 July 2019. The change in port reduces the distance and hence the transit time between the last drill site in the central South Pacific and the port in Chile, providing ~3 additional days for scientific drilling operations. For that reason, a new proposed primary site (CSP-7A) in the central South Pacific has been added to the original operations plan from Lamy et al. (2018),more »bringing the total number of primary sites planned for Expedition 383 to seven (Figures F1, F2, F3, F4). The current operations plan and time estimates include 5 days of port call activities, 38.2 days of operations, and 17.7 days of transit.« less
3. Expedition 359 Scientific Prospectus Addendum: Sea Level, Currents, and Monsoon Evolution in the Indian Ocean

   https://doi.org/10.14379/iodp.sp.359add.2015  

   Betzler, C. ; Eberli, G.P. ; Alvarez Zarikian, C.A. ( April 2015 , Scientific prospectus)

   This addendum to the Expedition 359 Scientific Prospectus (Betzler et al., 2014) addresses a modification to the scientific objectives and operations plan of the expedition. After consultation with and direction from the U.S. National Science Foundation (NSF), the Ancillary Proposal 849-APL will not be implemented as part of Expedition 359, and consequently the proposed sites (KK-03A and KK-03B) originally planned for scientific drilling in the Kerala-Konkan Basin have been dropped from the operations plan. Two new sites are proposed and described in this addendum, and a revised operations strategy and time estimates for seven primary sites in the Maldives archipelago are presented (Fig. F1). Also detailed in this addendum is an extension to the total penetration depth at primary proposed Site MAL-02A from 560 to 1010 meters below seafloor (mbsf). All other details contained within the original Scientific Prospectus published by the International Ocean Discovery Program in November 2014 (Betzler et al., 2014) remain the same. A summary of the primary sites targeted for Expedition 359 is shown in Table T1. The operations strategy and time estimates for the primary sites are presented in Table T2.
4. Expedition 367/368 Scientific Prospectus Addendum: South China Sea Rifted Margin

   https://doi.org/10.14379/iodp.sp.367368add.2016  

   Sun, Z. ; Stock, J. ; Jian, Z. ; Larsen, H.-C. ; Alvarez Zarikian, C.A. ; Klaus, A. ( November 2016 , Scientific prospectus)

   This addendum to the Scientific Prospectus of the International Ocean Discovery Program (IODP) South China Sea Rifted Margin Expeditions 367 and 368 (Sun et al., 2016) addresses a change of port-of-call and a two-day extension to Expedition 368 and modifications to some of the primary and alternate sites for both expeditions. As of the date of publication of this addendum, Expedition 368 is scheduled to start in Hong Kong on 9 April 2017 and end in Shanghai on 11 June. The two-day extension allows for the additional transit to Shanghai at the end of the expedition without taking time away from scientific drilling operations.
5. Expedition 397T Preliminary Report: Return to Walvis Ridge Hotspot

    Sager, W. ; Blum, P. ( December 2022 , Preliminary report)

   International Ocean Discovery Program Expedition 397T sought to address the shortage of drilling time caused by COVID-19 mitigation during Expedition 391 (Walvis Ridge Hotspot) by drilling at two sites omitted from the earlier cruise. A week of coring time was added to a transit of JOIDES Resolution from Cape Town to Lisbon, which would cross Walvis Ridge on its way north. These two sites were located on two of the three seamount trails that emerge from the split in Walvis Ridge morphology into several seamount chains at 2°E. Site U1584 (proposed Site GT-6A) sampled the Gough track on the east, and Site U1585 (proposed Site TT-4A) sampled the Tristan track on the west. Together with Site U1578, drilled on the Center track during Expedition 391, they form a transect across the northern Walvis Ridge Guyot Province. The goal was to core seamount basalts and associated volcanic material for geochemical and isotopic, geochronologic, paleomagnetic, and volcanologic study. Scientifically, one emphasis was to better understand the split in geochemical and isotopic signatures that occurs at the morphologic split. Geochronology would add to the established age progression but also give another dimension to understanding Walvis Ridge seamount formation by giving multiple ages atmore »the same sites. The paleomagnetic study seeks to establish paleolatitudes for Walvis Ridge sites for comparison with those published from hotspot seamount chains in the Pacific, in particular to test whether a component of true polar wander affects hotspot paleolatitude. Hole U1584A cored a 66.4 m thick sedimentary and volcaniclastic section with two lithostratigraphic units. Unit I is a 23 m thick sequence of bioturbated clay and nannofossil chalk with increasing volcaniclastic content downhole. Unit II is a >43 m thick sequence of lapillistone with basalt fragments. Because the seismic section crossing the site shows no evidence as to the depth of the volcaniclastic cover, coring was terminated early. Because there were no other shallow nearby sites with different character on existing seismic lines, the unused operations time from Site U1584 was shifted to the next site. The seismic reflector interpreted as the top of igneous rock at Site U1585 once again resulted from volcaniclastic deposits. Hole U1585A coring began at 144.1 mbsf and penetrated a 273.5 m thick sedimentary and volcaniclastic section atop a 81.2 m thick series of massive basalt flows. The hole was terminated at 498.8 mbsf because allotted operational time expired. The sedimentary section contains four main units. Unit I (144.1–157.02 mbsf) is a bioturbated nannofossil chalk with foraminifera, similar to the shallowest sediments recovered at Site U1584. Unit II (157.02–249.20 mbsf), which is divided into two subunits, is a 92.2 m thick succession of massive and bedded pumice and scoria lapillistone with increased reworking, clast alteration, and tuffaceous chalk intercalations downhole. Unit III (249.20–397.76 mbsf) is 148.6 m thick and consists of a complex succession of pink to greenish gray tuffaceous chalk containing multiple thin, graded ash turbidites and tuffaceous ash layers; intercalated tuffaceous chalk slumps; and several thick coarse lapilli and block-dominated volcaniclastic layers. Befitting the complexity, it is divided into eight subunits (IIIA–IIIH). Three of these subunits (IIIA, IIID, and IIIG) are mainly basalt breccias. Unit IV (397.76–417.60 mbsf) is a volcanic breccia, 19.8 m thick, containing mostly juvenile volcaniclasts. The igneous section, Unit V (417.60–498.80 mbsf) is composed of a small number of massive basaltic lava flows. It is divided into three lithologic units, with Unit 2 represented by a single 3 cm piece of quenched basalt with olivine phenocrysts in a microcrystalline groundmass. This piece may represent a poorly recovered set of pillow lavas. Unit 1 is sparsely to highly olivine-clinopyroxene ± plagioclase phyric massive basalt and is divided into Subunits 1a and 1b based on textural and mineralogical differences, which suggests that they are two different flows. Unit 3 also consists of two massive lava flows with no clear boundary features. Subunit 3a is a 10.3 m thick highly clinopyroxene-plagioclase phyric massive basalt flow with a fine-grained groundmass. Subunit 3b is a featureless massive basalt flow that is moderately to highly clinopyroxene-olivine-plagioclase phyric and >43.7 m thick. Alteration of the lava flows is patchy and moderate to low in grade, with two stages, one at a higher temperature and one at a low temperature, both focused around fractures. The Site U1585 chronologic succession from basalt flows to pelagic sediment indicates volcanic construction and subsidence. Lava eruptions were followed by inundation and shallow-water volcaniclastic sediment deposition, which deepened over time to deepwater conditions. Although the massive flows were probably erupted in a short time and have little variability, volcaniclasts in the sediments may provide geochemical and geochronologic data from a range of time and sources. Chemical analyses indicate that Site U1585 basalt samples are mostly alkalic basalt, with a few trachybasalt flow and clast samples and one basaltic trachyandesite clast. Ti/V ratios lie mostly within the oceanic island basalt (OIB) field but overlap the mid-ocean-ridge basalt (MORB) field. Only a handful of clasts from Site U1584 were analyzed, but geochemical data are similar. Paleomagnetic data from Site U1585 indicate that the sediments and basalt units are strongly magnetic and mostly give coherent inclination data, which indicates that the basaltic section and ~133 m of overlying volcaniclastic sediment is reversely polarized and that this reversal is preserved in a core. Above this, the rest of the sediment section records two normal and two reversed zones. Although there are not enough basalt flows to give a reliable paleolatitude, it may be possible to attain such a result from the sediments.« less