ANDRILL: ANtarctic geological DRILLing
CH science objectives
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Coulman High Project
Science Objectives
ANDRILL proposes to drill two ~900 meter holes into lowest Miocene to Paleogene sediments beneath the Ross Ice Shelf, on the Coulman High (CH) in the Ross Embayment, Antarctica (Figs. 1 & 2). Recovery of the targeted strata will provide a new, high-quality stratigraphic record from a period when atmospheric CO2 was comparable to concentrations projected for the next century. Of particular relevance is the response of the Polar Regions to elevated levels of greenhouse gases and the impact that regional amplification of surface temperatures have on the cryosphere.
The ANDRILL CH project proposes to better understand:
• How the Antarctic region responded to elevated levels of atmospheric CO2,
• How ice sheets behaved in the warmer climates, and
• When West Antarctica rifted apart and sank beneath the seas.
Ross iceshelf img
Fig 1
Figure 1. Regional overview of Ross Sea area showing structural basins (green) and highs. Lower inset box (CH) includes location of proposed drill sites (1 & 2), seismic lines including Figure 3 (red), and 2003 and 2010 ice edges (purple and green). Regional seismic correlations lines that carry stratigraphic control from DSDP Sites 270, 272, and 273 in the Eastern Basin and Central Trough to CH are shown in blue. Upper inset map shows location of the region on the Antarctic continent, as well as the location of recent drilling during IODP Expedition 318 (blue box) on the Wilkes Land margin. MIS and SMS are ANDRILL sites in the Victoria Land Basin.
Fig 2 img
Figure 2. Regional detail of CH study area on MODIS image (250 m resolution) from November 2010 showing locations of: i) CH-1, CH-2 drill sites (yellow); ii) NBP0301 marine seismic line array (multicolored); iii) correlation path to CH from DSDP sites 270, 272, 273 (heavy red line); iv) USGS marine seismic lines 403/404; v) locations of previous drill sites MIS, SMS, CRP, CIROS (green/blue stars); vi) and the polar traverse route (heavy black line), Coulman High traverse route (thin brown line), Ross Island, McMurdo Station, Scott Base (labeled).
An integrated data-model science approach will offer new insight into the onset, early evolution, and subsequent behavior of ice sheets in Antarctica in response to underlying tectonic change, landscape evolution, orbital forcing, and varying levels of atmospheric CO2. In 2003 and 2004 a marine multichannel seismic grid was completed across CH as close as 500 m from the front of the Ross Ice Shelf (Fig. 2). The ice shelf front has since advanced north and now sits over several marine seismic lines providing a platform from which to drill into seafloor sites located on those lines. Selected drill sites (Figs. 3 & 4) target an upper sector of ~600 m of laterally continuous sediments and and an underlying 350 - 850 m of faulted sedimentary and basement rocks. Seismic correlation from Deep Sea Drilling Project Sites 270, 272 and 273 to the CH sites implies that the section predates 19 Ma (Fig. 2).
Figure 3. Structural and stratigraphic interpretation of high resolution multichannel 22-fold seismic line NBP-0301-1A0 (upper panel not interpreted; lower our interpretation; location Figs. 1 and 2) showing (i) proposed drilling locations (SP 2240, CH-1; SP 1870, CH-2); (ii) stratified section Coulman High Sequence 2 (CHS2) above the Coulman High Major Unconformity (CHMU), below which are faulted section CHS1 and acoustic basement. A local unconformity (CHlu) divides CHS1 into upper and lower units. Unconformity RSU5A can be traced north to below DSDP site 273 (Figs. 1 and 2), which constrains the Coulman High sequences to be early Miocene or older.
Fig 3 img
RSU5A and reflectivity differences divide CHS2 into three subunits a,b,c. The chosen sites target <600 m of stratified sediments underlain by CHMU. The section below CHMU comprises 350 – 850 m of faulted sediments and basement. Acoustic basement is interpreted to be from 700 to >1500 m below the sea floor. Total proposed maximum drilling depth with optimum conditions for each location is approximately 800-900 mbsf. Depths computed using interval velocities from stacking velocities.
Fig 4 img
Figure 4. CH seismic stratigraphic nomenclature at drill sites CH-1 and CH-2. The target unconformity CHMU is ~600 m below sea floor at CH-1 and ~350 m at CH-2. RSU5A is older than RSU5, which is >21 Ma. Interpreted CO2 levels (Greenhouse- Icehouse) based on age model from seismic correlation and CO2 history (Fig. 2). RSU5a = Ross Sea Unconformity 5A; CHMU = Coulman High Major Unconformity; CHS = Coulman High Sequence.
Examining sediments deposited during the targeted time intervals offers a window into the range of environments and ecosystems in the Ross Sea region during warm, high-CO2 “greenhouse” conditions that dominated the Eocene and cooler, moderate- to low-CO2 conditions that developed during the Oligocene. Direct information on physical, biological, and paleoenvironmental conditions on the Antarctic margin will allow new constraints to be placed on estimates of ice volume variability, marine and terrestrial temperatures, timing and nature of major tectonic episodes, and development of Antarctica’s marine, terrestrial, and sea-ice biota, as well as model simulations of past and future climates and ice sheets. Results of the CH Project will enhance understanding of (1) high-latitude marine and terrestrial coastal environments and climate during the Eocene, prior to the onset of continental-scale glaciation; (2) the transition to a widely glaciated Antarctic continent; (3) the influence of climate change and vertical tectonics in West Antarctica on the early development and subsequent variability of the Antarctic cryosphere; (4) the magnitude and frequency of ice volume changes under moderate to low levels of atmospheric CO2 and the impact of these changes on global and regional sea level; (5) the evolution of polar surface (sea and land) temperatures and magnitude of polar amplification during periods of past global warmth; and (6) timing of Antarctic tectonic episodes and the development of Ross Sea sedimentary basins.
Project activities will yield new data from the Antarctic region, allowing more complete assessment of past changes in Earth’s ocean-ice-climate system, consistent with goals outlined in the 2011 National Research Council report Future Science Opportunities in Antarctica and the Southern Ocean. Project science goals closely align with those of other international programs, including the new science plan for the International Ocean Discovery Program (IODP). New knowledge of Antarctic ice sheet behavior during past intervals of warmer-than-present conditions will enhance understanding of possible future changes. These results will be available for consideration by the Intergovernmental Panel on Climate Change (IPCC). A new Drilling Startegy will allow the recovery of high-quality sediment cores below a fast-moving ice shelf (~2 m/day), expanding the range of potential future drilling targets.