ANDRILL Program - MIS and SMS Project Outcomes

The ANDRILL Program is a multinational collaboration between the Antarctic programs of Germany, Italy, New Zealand and the United States to investigate the climate and tectonic history of Antarctica by recovering deep sediment and rock cores from the basins beneath floating shelves (e.g., McMurdo and Ross Ice Shelves) and adjacent sea ice that served as a drilling platform for the McMurdo Ice Shelf (MIS) Project and Southern McMurdo Sound (SMS) Project, respectively, which represent the ANDRILL McMurdo Sound Portfolio (MSP). ANDRILL’s McMurdo Sound Portfolio, which primarily involved two drilling campaigns in 2006 and 2007, achieved significant operational and technological successes: (1) two deepest drill holes in Antarctica; (2) first deep-core recovery beneath an ice shelf (85 m-thick), ~900 mbsl; (3) high-quality 1000 m-long drill core; 98% recovery); (4) first hydrofracture experiment for measuring in-situ intraplate stress in Antarctica; and (5) development and deployment of new core-visualization and data-management software [e.g., CoreRef, PsiCat, Corelyzer] that have been widely adopted (e.g., by the International Continental Drilling Program (ICDP) and the International Ocean Discovery Program (IODP) European Science Operator [ESO]). Scientific results have been published in a diverse assortment of high impact journals and special volumes of papers.

The McMurdo Ice Shelf (MIS) Project (2006) recovered a 1285 m-long core record of climate and ice sheet variability spanning the last 13 million years from beneath the MIS (Naish et al., 2007; Naish et al., 2008). Well-dated cyclic variations in this core (Wilson et al., 2012b) link the extent of the West Antarctic Ice Sheet (WAIS) to orbital-scale climate cycles; 40-kyr cycles paced by obliquity during the Pliocene and early Pleistocene were replaced by 100-kyr cycles in the late Pleistocene (McKay et al., 2009; Naish et al., 2009). This provides the first direct evidence of a dynamic marine-based ice sheet in the Ross Embayment that periodically contracted onto terrestrial West Antarctica during the early Pliocene. Complementary simulations using ANDRILL’s coupled ocean-ice sheet numerical models (Pollard and DeConto, 2009) indicate similar timing and magnitude of WAIS behavior. The geological data and modeling imply a significant thermal regime change of the WAIS during the late Pliocene, coincident with global cooling in oxygen isotope records and the onset of Northern Hemisphere glaciations, and confirm past fluctuations of the WAIS and its collapse during the early Pliocene and during “superinterglacial” warmth of Marine Isotope Stage 31 (MIS-31) and other sustained Pleistocene interglacial periods.

The Southern McMurdo Sound (SMS) Project (2007) recovered a 1138.54 m (98% recovery) record of climate and ice sheet variability spanning the early and middle Miocene (20 to 14.5 Ma), including the sustained global warmth known as the mid-Miocene Climate Optimum. A cyclical history of environmental variation influenced by climate, glacial advance/retreat cycles, and water depth variation is placed within a well-developed chronostratigraphic framework allowing the comparison of Antarctic events with those identified in distal proxy records from deep-sea stable isotope and sea-level reconstructions. The SMS record preserves numerous glacial-interglacial cycles grouped into stratigraphic intervals that reflect three broad modes of AIS character and behavior. Marine and terrestrial fossils preserved in these strata suggest climate conditions similar to that of southern Patagonia and southwestern New Zealand today, influenced by high sediment discharge from river run-off, and high coastal turbidity. This dynamic response of Antarctic climate continues to present a challenge for numerical climate and ice sheet models, which generally fail to produce this range of variability at presumed levels of Miocene atmospheric CO2.

An integrated numerical modeling effort was established in advance of drilling both ANDRILL cores to provide regional perspectives and insight as the cores were recovered. Model development provided new tools to test ANDRILL-specific data-driven hypotheses, to link the ANDRILL drill sites with other paleoenvironmental records, and to provide mechanistic explanations for the observed climate and ice sheet variability. Primary model advances included a new continental ice sheet-shelf model; a coupled Global Climate Model (GCM) ice sheet model; a nested, high-resolution Antarctic Regional Climate Model (RCM) coupled to the ice sheet-shelf model, sub-model components including water-isotope capability in the GCM, linked Antarctic vegetation models; Glacial Isostatic Adjustment (GIA) Earth models for fingerprinting Antarctic ice contributions to past sea level, and sub- and englacial sediment transport capable of making comparisons between model results and sediment provenance studies. The associated model codes have been used by numerous national and international partners and collaborators.