374: Ross Sea West Antarctic Ice Sheet History

Figure 1. Bathymetric map with Expedition 374 sites and previous Deep Sea Drilling Program Leg 28, ANDRILL sites, as well as Cape Roberts Project (CRP) sites. Ross Sea bathymetry is from the International Bathymetric Chart of the Southern Ocean (Arndt et al., 2013a, 2013b). Existing seismic network is from the Antarctic Seismic Data Library System and includes some single-channel seismic-reflection profiles (McKay et al., 2019). Figure from IODP Expedition 374 Summary.

Expedition 374 took place from 4 January to 8 March 2018, during which five sites were drilled in the eastern Ross Sea of Antarctica, ranging from the outer continental shelf to the continental  slope and rise (Fig. 1). Three sites (U1521, U1522, and U1523) were on the continental shelf, while U1524 and U1525 were from the continental rise and slope, respectively (Fig. 1).

The study of western Antarctica and the Ross Sea region  is crucial because computer models have shown this area is  highly sensitive to changes in ocean temperature and sea level. The West Antarctic Ice Sheet (WAIS) contains a vast amount of ice, and its complete melting could result in a 4.3 meter rise in global sea level (Patterson et al., 2012). Therefore, by understanding how the ice sheet in this region has changed in the past, researchers can predict how it may change in the future under different climate conditions, which can better prepare societies  for the inevitable future (McKay et al., 2019). 

The primary objective of Expedition 374 was to comprehend how the evolution of the WAIS during the Neogene (23–2.58 million years ago) and Quaternary (2.58 million years ago to Recent) geologic periods relates to changes in climate and oceanic conditions. Scientists wanted to determine the contribution of West Antarctica to overall ice volume and sea level rise, comprehend past polar temperature changes and causes of such changes in temperatures, understand the effect of changes in ocean temperature and sea level on the stability of the Antarctic Ice Sheet, determine how the Earth’s position in its orbit influences the stability of the Antarctic Ice Sheet under different climate conditions, and analyze the relationship between seafloor geometry in the eastern Ross Sea and the stability of the ice sheet and global climate.

Despite challenges such as drifting sea ice and mechanical vessel failure during drilling at Site U1524, the team managed to retrieve significant recoveries. Although about 39% of operational days at sea were lost, making it challenging to achieve all the proposed goals of Expedition 374. Regardless, the recovered samples can still be effectively compared with those from other sites, such as U1522, U1525, and sites from similar projects like the Antarctic Geological Drilling Project (ANDRILL). The goal is to create a continental shelf to rise transect of the Pliocene (5.33–2.58 million years ago) to the Pleistocene (2.58–0.017 million years ago) periods, which is an essential component of the expedition’s overall objectives.

Figure 2: (a) Lithostratigraphic column for Site U1524, with the position of the studied tephra layer highlighted in red. From left to right: Depth of the core, with ‘0’ representing the sediment-water interface, in units of meters below sea floor; core numbers; core recovery (black indicates depths where sediment was recovered, white indicates intervals where no sediments were recovered); age is how old the sediments are; Lith. unit indicates the major types of lithologies, or sediment types, that were recovered; and graphic lithology is the visual description of the different sediment types. (b) Core photographs of Section 374-U1524A-6H-2A and detail of the rhyolite tephra studied in this work. The scale is in cm (Di Roberto et al., 2021). Figure from Di Roberto et al., (2021).

During Expedition 374, 1292.70 meters of cores were recovered from five drill sites spanning the early Miocene (~15 million years ago) to late Quaternary (Recent). The sediments in the Ross Sea near Antarctica were studied by several scientists to gain insights into the history of the West Antarctic Ice Sheet (WAIS). A study by King et al., (2022) focused on how ice and ocean currents interacted during past ice ages (about 2.4 million years ago) to estimate the future extent of the ice sheets and help improve future models of the ice sheet. The study also   fostered an understanding of how the ice sheet formed and grew under different oceanographic conditions. Also, findings from Expedition 374 inspired a new WAIS drilling project that will predict how the ice sheet will respond to future global warming scenarios, including how melting of the ice could contribute to sea-level rise, based on how the ice sheet responded to warming scenarios in the geologic past (Patterson et al., 2012).

In 2022, a study by Lelieveld analyzed sediments from Expedition 374 to investigate how the Antarctic Ice Sheets impacted sea level variations and vegetation changes during the Miocene Period (23–5.33 million years ago) in the Ross Sea. The Miocene Period is a time when atmospheric carbon dioxide levels were much higher than today, and reached levels projected for the coming decades. As such, the Miocene Period is a good geologic analogue for how Earth systems behave and change under increased greenhouse gasses and increased warming. The study found that despite the climate being conducive to higher-order plants, the region’s vegetation was dominated by shrubs and tundra due to the reduced land available for plant growth caused by erosion resulting from glacial advances of the West and East Antarctic Ice Sheets. Another study presented geological evidence of large WAIS expansions from sediment samples obtained during Expedition 374 (Marschalek et al., 2021). The findings from Marschalek et al. (2021) supported the hypothesis  that during the intensely warm Miocene Period , East Antarctica experienced significant ice loss, which contradicted the view of other scientists who suggested that the ice in East Antarctica mostly remained intact during this period of time.

Expedition 374 also contributed to providing valuable information on the history of a volcano! A study by Di Roberto et al., (2021) examined a layer of volcanic ash, known as tephra, found in marine sediments in Antarctica’s Ross Sea (Figure 2). The tephra was estimated to be around 1.3 million years old and matched a deposit discovered at Chang Peak volcano, located 1,300 km away from the study site. This discovery adds a new reference point for dating and correlating early Pleistocene records in West Antarctica.


Di Roberto, A., Scateni, B., Di Vincenzo, G., Petrelli, M., Fisauli, G., Barker, S.J., Del Carlo, P., Colleoni, F., Kulhanek, D.K., McKay, R., De Santis, L., and the IODP Expedition 374 Scientific Party, 2021. Tephrochronology and provenance of an early Pleistocene (Calabrian) tephra from IODP Expedition 374 Site U1524, Ross Sea (Antarctica). Geochemistry, Geophysics, Geosystems, 22(8):e2021GC009739. https://doi.org/10.1029/2021GC009739

King, M.V., Gales, J.A., Laberg, J.S., McKay, R.M., De Santis, L., Kulhanek, D.K., Hosegood, P.J., and Morris, A., 2022. Pleistocene depositional environments and links to cryosphere-ocean interactions on the eastern Ross Sea continental slope, Antarctica (IODP Hole U1525A). Marine Geology, 443:106674. https://doi.org/10.1016/j.margeo.2021.106674

Lelieveld, N.J.C., 2022. Antarctic paleoenvironment and vegetation reconstructions during the early and middle Miocene using biomarkers from Ross Sea sediment drill cores [MS thesis]. Victoria University of Wellington, Wellington, NZ. https://openaccess.wgtn.ac.nz/articles/thesis/Antarctic_paleoenvironment_and_vegetation_reconstruction_during_the_early_and_middle_Miocene_using_biomarkers_from_Ross_Sea_sediment_drill_cores/21554862

Marschalek, J.W., Zurli, L., Talarico, F., van de Flierdt, T., Vermeesch, P., Carter, A., Beny, F., Bout-Roumazeilles, V., Sangiorgi, F., Hemming, S.R., Pérez, L.F., Colleoni, F., Prebble, J.G., van Peer, T.E., Perotti, M., Shevenell, A.E., Browne, I., Kulhanek, D.K., Levy, R., Harwood, D., Sullivan, N.B., Meyers, S.R., Griffith, E.M., Hillenbrand, C.D., Gasson, E., Siegert, M.J., Keisling, B., Licht, K.J., Kuhn, G., Dodd, J.P., Boshuis, C., De Santis, L., McKay, R.M., and the IODP Expedition 374 Scientists, 2021. A large West Antarctic Ice Sheet explains early Neogene sea-level amplitude. Nature, 600(7889):450-455. https://doi.org/10.1038/s41586-021-04148-0

McKay, R.M., De Santis, L., Kulhanek, D.K., Ash, J.L., Beny, F., Browne, I.M., Cortese, G., Cordeiro de Sousa, I.M., Dodd, J.P., Esper, O.M., Gales, J.A., Harwood, D.M., Ishino, S., Keisling, B.A., Kim, S., Kim, S., Laberg, J.S., Leckie, R.M., Müller, J., Patterson, M.O., Romans, B.W., Romero, O.E., Sangiorgi, F., Seki, O., Shevenell, A.E., Singh, S.M., Sugisaki, S.T., van de Flierdt, T., van Peer, T.E., Xiao, W., Xiong, Z., the Expedition 374 Scientists, 2019. Expedition 374 summary. In: Proceedings of the International Ocean Discovery Program, 374: College Station, TX (International Ocean Discovery Program). https://doi.org/10.14379/iodp.proc.374.101.2019.

Patterson, M.O., Levy, R.H., Kulhanek, D.K., van de Flierdt, T., Horgan, H., Dunbar, G.B., Naish, T.R., Ash, J., Pyne, A., Mandeno, D., Winberry, P., Harwood, D.M., Florindo, F., Jimenez-Espejo, F.J., Läufer, A., Yoo, K.-C., Seki, O., Stocchi, P., Klages, J.P., Lee, J.I., Colleoni, F., Suganuma, Y., Gasson, E., Ohneiser, C., Flores, J.-A., Try, D., Kirkman, R., Koch, D., and the SWAIS 2D Science Team, 2022. Sensitivity of the West Antarctic Ice Sheet to +2 °C (SWAIS 2C). Scientific Drilling, 30:101-112. https://doi.org/10.5194/sd-30-101-2022

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