2.2.1 McMurdo Ice Shelf Project (MIS)

Response of Antarctic ice sheets to projected greenhouse warming of up to 5.8°C by the end of the century is not known. Models on which predictions are based need to be constrained by geological data of the ancient ice sheets during times when Earth is known to have been warmer than today. The marine-based West Antarctic Ice Sheet (WAIS) and its fringing ice shelves are hypothesized (Clark et al., 2002; Weaver et al., 2003; Stocker, 2003) and documented (Scherer et al., 1998) to have collapsed during past "super-interglacial" warm extremes when global sea-level was more than 5 m higher than today. Recent collapse of small ice shelves along the Antarctic Pennisula (Doake and Vaughn, 1991; Skvarca, 1993; Rott et al., 1996; Vaughn and Doake, 1996; Doake et al., 1998; Rott et al., 1998; Skvara et al., 1999; Rott et al., 2002) highlights the vulnerability of these glacial components to global warming. The Ross Ice Shelf (RIS) appears to represent one of the most vulnerable elements of the WAIS system. Future demise of the RIS, on timescales of decades to centuries, may well provide an important precursor to eventual WAIS collapse. The key aim of this research project is to determine past ice shelf responses to climate forcing, including variability at a range of timescales. To achieve this aim ANDRILL will drill a stratigraphic hole from a platform located on the northwest corner of the Ross Ice Shelf in the McMurdo Ice Shelf (MIS) sector, east of Hut Point Peninsula, Ross Island. Drilling will be undertaken in the austral summer of 2006-2007. The primary target for the MIS site is a 1200 m-thick body of Plio-Pleistocene glacimarine, terrigenous, volcanic, and biogenic sediment that has accumulated in the Windless Bight region of flexural moat basin surrounding Ross Island (Harwood et al., 2002). A single ~1000 m-deep drill core will be recovered from the bathymetric and depocentral axis of the moat in approximately 900 m of water. The drilling technology will utilize a sea-riser system in a similar fashion to the CRP, but will employ a combination of soft sediments coring tools and continuous wireline diamond-bit coring. Innovative new technology, in the form of a hot-water drill and over-reamer, will be used to make an access hole through ~200 m of ice and to keep the riser free and unfrozen during drilling operations.

Paleoclimatic, paleoceanic, and tectonic objectives at MIS are to:

  • determine the timing of RIS-WAIS development relative to major ice expansion of northern hemisphere ice sheets c. 3.0 to 2.5 million years ago
  • describe the nature of grounding-line and calving-line variability during both the last glacial cycle and the Plio-Pleistocene climate cycles
  • document RIS behavior during the past interglacial warm climatic optima (e.g. Marine Isotope Stages 5e, 11, 31), and interstadial warm periods
  • establish sedimentological and biological evidence for RIS collapse and their correspondence to melt-water discharge
  • understand the effect of RIS collapse on the global thermohaline ocean conveyor
  • assess the phase relationship between RIS collapse, or partial collapse and northern hemisphere climatic events
  • provide the detailed history of the Ross Island volcanic complex
  • understand the flexural response of continental lithosphere to volcanic loading
  • propose a history of Pliocene faulting
  • establish temporal relationships between volcanism, ice volume, local sea level, and eustasy
  • document and describe the regional stress regime

2.2.2 Southern McMurdo Sound Project (SMS)

During the austral summer of 2007 the ANDRILL Program will drill from a sea-ice platform in southern McMurdo Sound to obtain new information about the Neogene Antarctic cryosphere and evolution of Antarctic rift basins. Target strata are middle Miocene to Quaternary in age (~17 Ma to present) and span several key steps in the evolution of Antarctic climate. Fault- and flexure-related subsidence associated with rifting and volcanic loading has provided accommodation space adjacent to the rising Transantarctic Mountains (TAM) that achived a sediment history of this important region, which is also influenced by three significant components of the Antarctic cryospheric system: the East Antarctic Ice Sheet (EAIS), Ross Ice Shelf (RIS)/ West Antarctic Ice Sheet (WAIS), and the Ross Embayment sea-ice. The Southern McMurdo Sound Project (SMS) drillcore will also record a tectonic history of the Antarctic Rift system (Victoria Land Basin VLB), the TAM and the Erebus Volcanic Province. The key aim of the SMS Project is to establish a robust history of the Neogene Antarctic ice sheet variation and climate evolution that can be integrated into continental and global records toward a better understanding of Antarctica’s role in the past, present and future global system.

To achieve this aim, one drillhole (>1000 m) will sample a sequence of strata identified on seismic lines and inferred to represent a lower Miocene and younger sequence of seismic units that expand basinward. Several distinct seismic packages are identified. These units are separated by distinct seismic reflection surfaces, three of which appear to be regional erosional surfaces. This drillhole will recover a composite thickness of >1000 m of strata that lie stratigraphically above the lower Miocene section recovered at the top of the nearby Cenozoic Investigations in the Western Ross Sea (CIROS) -1 drillcore, and above the 1400 m composite section covered by the CRP (~34 to 17 m) (Davey et al., 2001; Florindo et al., 2005). Drilling technology will utilize a sea-riser system and continuous wire-line diamond-bit coring to ensure high-percentage core recovery similar to that obtained by the CRP (e.g. 98% of 939 m in the CRP-3 drillhole).

The recovery of lower to middle Miocene Antarctic stratigraphic sequences is required to evaluate the history derived from global proxy records that invoke a change from a warm climate optimum (~17 Ma) to the onset of major cooling (~14 Ma) and the formation of a quasi-permanent ice sheet on East Antarctica. Secondary target strata of the Pliocene and Pleistocene age from a distal marine setting will complement and build on coastal and fjord sediment records from Dry Valley Drilling Project (DVDP) -10, -11, and CIROS-2 drillcores that are interpreted to reflect repeated Late Neogene alternation between ’interglacial’ and ’glacial’ conditions. The SMS site is well-connected to the grid of seismic lines in the VLB; hence the recovered sections will provide excellent chronostratigraphic control for regional seismic surfaces and units important for interpreting regional stratal architecture and for dating Neogene and younger subsidence and rift fault history.

Paleoclimatic, paleoceanic, and tectonic objectives at SMS are to:

  • document the initial onset and subsequent history of sea-ice presence/absence
  • document the evolution and demise of Neogene terrestrial vegetation
  • document the evolution of terrestrial vegetation during the Neogene
  • establish a local Late Neogene sea-level record
  • test whether stable cold-polar climate conditions persisted for the last 15 m.y.
  • document melt-water discharge events from the adjacent Dry Valley/TAM system
  • construct a composite event history of glacial and interglacial events across a coastal to deep basin transect
  • provide chronostratigraphic control for the regional seismic framework in the western Ross Sea
  • develop provenance and exhumation proxies within Neogene sediment from the TAM
  • document and describe the regional stress regime