Quaternary Paleoceanography of the Ross Sea, Antarctica based on Benthic and Planktic Foraminifera (Site U1523)

The West Antarctic Ice Sheet (WAIS) is currently thinning and retreating because of shifting oceanic currents transporting warmer waters to the ice margin, coupled with rising sea level. Previous geologic drilling projects into the sediments of the Ross Sea that potentially record the history of the WAIS (DSDP Leg 28, RISP, MSSTS, Cape Roberts Drilling Project, ANDRILL), as well as modeling studies (Pollard and DeConto, 2009), show considerable variability of the ice-sheet extent during the late Neogene and Quaternary including ice sheet collapse during times of extreme warmth.

The International Ocean Discovery Program (IODP) Expedition 374 sailed to the Ross Sea in 2018 to study the history of the WAIS over the past 20 million years. Site U1523 is located on the outermost continental shelf with a water depth of 828 m. A primary objective at this site is to investigate past changes in the Antarctic Slope Current and use the cores to correlate records of ice sheet advance and retreat. The preliminary shipboard age model indicates a disconformity has removed a portion of the lower Pleistocene.

Foraminiferal assemblages are generally dominated by planktic species through much of the Pleistocene, although there is a stepped increase in the percent benthics beginning in the mid-Pleistocene transition, particularly after MIS 11. Foraminiferal abundances vary greatly through the uppermost Pliocene and Pleistocene section cored at Site U1523 with peak planktic foraminiferal abundances during what could be interglacial Marine Isotope Stages 5e and 31, as well as in the interval ~2 Ma. Much lower foraminiferal abundances and frequent barren samples in the diatom-rich uppermost Pliocene may be a consequence of very high sedimentation rates and/or dissolution. The planktics are dominated by Neogloboquadrina pachyderma with rare N. incompta and very rare Globigerina bulloides and Turborotalita quinqueloba. The presence of Globoconella inflata and Globigerinoides ruber in a sample close to the Pliocene/Pleistocene boundary signals the incursion of much warmer waters at the edge of the Ross Sea continental shelf. Benthic assemblages are dominated by Trifarina earlandi and Globocassidulina subglobosa. T. earlandi is indicative of shelf-edge conditions and strong currents.