International Ocean Discovery Program Expedition 374 Scientific Prospectus

Observations from the past several decades indicate that the Southern Ocean is warming significantly and that Southern Hemisphere westerly winds have migrated southward and strengthened due to increasing atmospheric CO2 concentrations and/or ozone depletion. These changes have been linked to thinning of Antarctic ice shelves and marine terminating glaciers. Results from geologic drilling on Antarctica’s continental margins show late Neogene marine-based ice sheet variability, and numerical models indicate a fundamental role for oceanic heat in controlling this variability over at least the past 20 My. Although evidence for past ice sheet variability has been observed in marginal settings, sedimentological sequences from the outer continental shelf are required to evaluate the extent of past ice sheet variability and the role of oceanic heat flux in controlling ice sheet mass balance. International Ocean Discovery Program (IODP) Expedition 374 proposes a latitudinal and depth transect of six drill sites from the outer continental shelf and rise in the eastern Ross Sea to resolve the relationship between climatic/oceanic change and West Antarctic Ice Sheet (WAIS) evolution through the Neogene and Quaternary. This location was selected because numerical ice sheet models indicate that it is highly sensitive to changes in ocean heat flux and sea level. The proposed drilling is designed for optimal data-model integration, which will enable an improved understanding of the sensitivity of Antarctic Ice Sheet mass balance during warmer-thanpresent climates (e.g., the early Pliocene and middle Miocene). Additionally, the proposed transect links ice-proximal records from the inner Ross Sea continental shelf (e.g., ANDRILL sites) to deepwater Southwest Pacific drilling sites/targets to obtain an ice-proximal to far-field view of Neogene climate and Antarctic cryosphere evolution. The proposed scientific objectives directly address Ocean and Climate Challenges 1 and 2 of the 2013–2023 IODP Science Plan. Drilling Neogene and Quaternary strata from the Ross Sea continental shelf-to-rise sedimentary sequence is designed to achieve five scientific objectives: 1. Evaluate the contribution of West Antarctica to far-field ice volume and sea level estimates. 2. Reconstruct ice-proximal atmospheric and oceanic temperatures to identify past polar amplification and assess its forcings/feedbacks. 3. Assess the role of oceanic forcing (e.g., sea level and temperature) on Antarctic Ice Sheet stability/instability. 4. Identify the sensitivity of the AIS to Earth’s orbital configuration under a variety of climate boundary conditions. 5. Reconstruct eastern Ross Sea bathymetry to examine relationships between seafloor geometry, ice sheet stability/instability, and global climate. To achieve these objectives, we will (1) use data and models to reconcile intervals of maximum Neogene and Quaternary Antarctic ice advance with far-field records of eustatic sea level change; (2) reconstruct past changes in oceanic and atmospheric temperatures using a multiproxy approach; (3) reconstruct Neogene and Quaternary ice margin fluctuations in datable marine continental slope and rise records and correlate these records to existing inner continental shelf records; (4) examine relationships among WAIS stability/instability, Earth’s orbital configuration, oceanic temperature and circulation, and atmospheric pCO2; and (5) constrain the timing of Ross Sea continental shelf overdeepening and assess its impact on Neogene and Quaternary ice dynamics. Schedule for Expedition 374 International Ocean Discovery Program (IODP) Expedition 374 is based on IODP drilling Proposals 751-Full2, 751-Add, and 751Add2 (available at http://iodp.tamu.edu/scienceops/expeditions/ross_sea_ice_sheet_history.html). Following evaluation by the IODP Scientific Advisory Structure, the expedition was scheduled for the research vessel (R/V) JOIDES Resolution, operating under contract with the JOIDES Resolution Science Operator (JRSO). At the time of publication of this Scientific Prospectus, the expedition is scheduled to start in Wellington, New Zealand, on 4 January 2018 and to end in Wellington, New Zealand, on 8 March. A total of 63 days will be available 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 the JOIDES Resolution can be found at http://iodp.tamu. edu/publicinfo/drillship.html. Introduction Drilling eastern Ross Sea outer continental shelf-to-rise sedimentary sequences will provide a direct record of Neogene to Quaternary West Antarctic Ice Sheet (WAIS) evolution and improve understanding of associated climate forcings/feedbacks. In combination with model sensitivity tests, tectonic considerations, and the well-developed seismic stratigraphic framework of the Ross Sea, proposed drilling will enable researchers to determine if the large far-field Neogene sea level estimates (20–60 m) (cf. Miller et al., 2005, 2012; Naish and Wilson, 2009) reflect changes in Antarctic ice volume (Figure F1). The proposed continental shelf-to-rise transect in an area of demonstrated climate sensitivity (Figures F2, F3, F4) allows for improved understanding of ocean–ice sheet interactions on orbital to million year timescales. The onset of the Neogene (23 Ma; Oligocene/Miocene [O/M] boundary) is characterized by an abrupt increase in Antarctic ice volume attributed to changes in Earth’s orbital parameters (Naish et al., 2001; Zachos et al., 1997) and declining atmospheric CO2 (Figure F1) (Pagani et al., 2005). Following the O/M glaciation, both nearand far-field proxy records indicate a period of sustained (~3°C warmer than present) (You et al., 2009) warmth and carbon cycle reorganization (e.g., Foster et al., 2012; Vincent and Berger, 1985), referred to as the Middle Miocene Climatic Optimum (MMCO; ~17–15 Ma) (Flower and Kennett, 1994; Shevenell et al., 2004). During the MMCO, polar amplification of temperature is suggested (Feakins et al., 2012; Lewis et al., 2008; Shevenell et al., 2004; Warny et al., 2009) but not yet successfully modeled (e.g., You et al., 2009). The MMCO was immediately followed by an interval of Antarctic ice growth and cooling, termed the Middle Miocene Climate Transition (MMCT; 14.2–13.8 Ma), as observed in both far-field benthic foraminifer δ18O records and ice-proximal data (Figure F1) (Cramer et al., 2009; Flower and Kennett, 1994; Holbourn et al., 2007; Kennett, 1977; Shevenell et al., 2008, 2004; Zachos et al., 2001) and is believed to have resulted in the extinction of the Antarctic tundra vegetation (Lewis et al., 2008). Although ice expansion has traditionally been inferred in East Antarctica, Ross Sea seismic evidence also suggests WAIS expansion (Bart, 2003). However, the timing of the Ross Sea event, WAIS development, and