Expedition 390/393 Scientific Prospectus: The South Atlantic Transect
International Ocean Discovery Program Scientific Prospectus
Portions of this work may have been published in whole or in part in other IODP documents or publications. This IODP Scientific Prospectus is based on precruise JOIDES Resolution Facility advisory panel discussions and scientific input from the designated Co-Chief Scientists on behalf of the drilling proponents. During the course of the cruise, actual site operations may indicate to the Co-Chief Scientists, the Expedition Project Manager/Staff Scientist, and the Operations Superintendent that
... perintendent that it would be scientifically or operationally advantageous to amend the plan detailed in this prospectus. It should be understood that any substantial changes to the science deliverables outlined in the plan presented here are contingent upon the approval of the IODP JRSO Director and/or JOIDES Resolution Facility Board. Abstract The South Atlantic Transect (SAT) is a multidisciplinary scientific ocean drilling project that comprises two International Ocean Discovery Program (IODP) expeditions (390, October-December 2020, and 393, April-June 2021). These expeditions will recover complete sedimentary sections and the upper ~250 m of the underlying oceanic crust along a slow/intermediate spreading rate Mid-Atlantic Ridge crustal flow line at ~31°S. The sediments along this transect were originally spot cored more than 50 y ago during Deep Sea Drilling Project Leg 3 to help verify the theories of seafloor spreading and plate tectonics. Given dramatic advances in drilling technology and analytical capabilities since Leg 3, many high-priority scientific objectives can be addressed by revisiting the transect. The SAT expeditions will target six primary sites on 7, 15, 31, 49, and 61 Ma ocean crust, which will fill critical gaps in our sampling of intact in situ ocean crust with regards to crustal age, spreading rate, and sediment thickness. These sections are required to investigate the history of the low-temperature hydrothermal interactions between the aging ocean crust and the evolving South Atlantic Ocean and quantify past hydrothermal contributions to global geochemical cycles. The transect traverses the previously unexplored sediment-and basalt-hosted deep biosphere beneath the South Atlantic Gyre from which samples are essential to refine global biomass estimates and investigate microbial ecosystems' responses to variable conditions in a low-energy gyre and aging ocean crust. The drilling operations will include installation of reentry cones and casing to establish legacy boreholes for future basement hydrothermal and microbiological experiments. The transect is also located near World Ocean Circulation Experiment Line A10, providing access to records of carbonate chemistry and deepwater mass properties across the western South Atlantic through key Cenozoic intervals of elevated atmospheric CO 2 and rapid climate change. Reconstruction of the history of the deep western boundary current and deepwater formation in the Atlantic basins will yield crucial data to test hypotheses regarding the role of evolving thermohaline circulation patterns in climate change and the effects of tectonic gateways and climate on ocean acidification. Schedule for IODP Expeditions 390 and 393 International Ocean Discovery Program (IODP) Expeditions 390 and 393 are based on IODP drilling Proposal 853-Full2 and 853-Add (available at http://iodp.tamu.edu/scienceops/expeditions/south-_atlantic_transect.html). Following evaluation by the IODP Scientific Advisory Structure, the expeditions were scheduled for the R/V JOIDES Resolution, operating under contract with the JOIDES Resolution Science Operator (JRSO). At the time of publication of this Scientific Prospectus, Expedition 390 is scheduled to start in Rio de Janeiro, Brazil, on 5 October 2020 and end in Cape Town, South Africa, on 5 December. Expedition 393 is scheduled to start in Cape Town on 6 April 2021 and to end in Rio de Janeiro on 6 June. A total of 61 days will be available for each expedition for the transit, drilling, coring, and downhole measurements described in this report (for the current detailed schedule, see http://iodp.tamu.edu/scienceops). Further details about the facilities aboard JOIDES Resolution can be found at http://iodp.tamu.edu/labs/index.html.