The Offshore New Harbor Project: Investigating the Greenhouse World to Icehouse World Transition

The Offshore New Harbor (ONH) Project is to study sediments deposited in Antarctica during the transition from the Greenhouse World (34-100 Ma) to Icehouse World (<34 Ma). The ONH Project is part of the Antarctic Geological Drilling Program called ANDRILL. ANDRILL aims to recover stratigraphic intervals for interpreting Antarctica’s climate and glacial history over the past 50 million years.

The goal of the Offshore New Harbor Project is to address two widely recognized but unresolved issues regarding Antarctica’s history: 1) the Paleogene cryospheric (>34 million years ago) development in Antarctica; and 2) the abrupt climate shift across the Eocene/Oligocene transition (circa 34 million years ago).

Offshore New Harbor is located off the eastern coast of East Antarctica in the western Ross Sea.  It is situated on the eastern edge of the Victoria Land Basin, which is one of several sedimentary basins in the Ross Sea. These basins permitted thick sedimentary successions to be deposited and preserved. It is along the margin of the Victoria Land Basin that we expect to first image and then core sedimentary archives deposited during the Greenhouse World.

Base map showing Antarctica on the left. The inset shows the Victoria Land Basin that lies offshore of east Antarctica in the Ross Sea.

Figure courtesy of ANDRILL and the ANDRILL Science Management Office.

 

Why drill at offshore New Harbor?
Previous seismic and borehole projects in the New Harbor and Southern McMurdo Sound provide a regional setting.

The upper figure is a map of Antarctica, with inset showing the eastern portion of the Ross Sea.  The lower figures show the McMurdo Sound area that includes Ross Island (brown landmass to the right, the Ross Ice Shelf (in the gray) and the East Antarctic continent on the left side of each figure. . The stratigraphic architecture of sediment fill of the western Victoria Land Basin in McMurdo Sound is known from an array of existing single and multichannel marine seismic data shown in black lines (Wong and Christoffel, 1981; Bartek and Anderson, 1991; Anderson and Bartek, 1992; Baretk et al., 1996; Brancolini et al., 1995; Melhuish et al., 1995; Hamilton et al., 2001; Wilson et al., 2004; Horgan et al., 2005). The offshore New Harbor area is labeled in red.

In the inset are the ANDRILL drilling sites for the McMurdo Ice Shelf and Southern McMurdo Sound projects as well as sea-ice seismic lines (TS-05-1 and TS-05-2, fall, 2005) are shown for reference. Note that the dashed blue line shows the typical sea-ice break out during the austral summer, while the solid dark blue line shows the extent of the sea ice break out in early 2007.

Figures courtesy of ANDRILL and the ANDRILL Science Management Office.

 

Previous seismic and borehole projects in the New Harbor and Southern McMurdo Sound provide a regional setting. This includes seismic studies (e.g.. Polar Duke, 1990, Italian seismic survey, 1991, Nathaniel B. Palmer, 2004) and continuous long coreholes (e.g., CIROS-1 upper Eocene, L. & U. Oligocene, lower Miocene, MSSTS-1 U. Oligocene, L. Miocene, DVDP-15 lower Miocene, Southern McMurdo Sound Drilling Project (2007)

Why offshore New Harbor?
While there have been a number of successful drilling expeditions in Antarctica, currently there are no cored sediments older than ~37 Ma from Antarctica.

This figure shows the ages of the recovered sediments, shown by the colored bars. On the right are sea level and ice volume estimates from Pekar and Christie-Blick (2008) between 16 and 34 Ma and Miller et al. (2005) between 16- Recent and 34 to 65 Ma.

ONH is an ideal locale to tackle these questions because existing data suggest substantial strata deposited during Eocene time and across the Eocene/Oligocene boundary; and “mid” Oligocene are preserved updip of current borehole locations (CIROS-1). This interpretation is based on previous low-resolution seismic data that suggests late Eocene strata at CIROS-1 dips 10-20˚. This implies that strata at the base of CIROS-1 truncates against younger strata at a depth of ~200 meters below sea floor, 2-4 kilometers updip of CIROS-1. The ONH seismic survey will use and improve upon new over-sea-ice seismic reflection surveying techniques that employ a Generator-Injector (GI) air gun seismic source and a snow streamer.

The figure above is from a multi channel seismic line from Davey et al. (1989), with a single channel seismic line IT91-71. The CIROS-1 borehole location is shown as well as the placement of the interpreted stratigraphic units (REF, 1999) as well as seismic interpretations. Clear highly dipping reflectors that truncate at the more gently dipping reflectors dated as late Oligocene and early Miocene.

The Offshore New Harbor Seismic and Gravity Expedition (October-December, 2008)
In late 2008, The Offshore New Harbor Project will conduct a multichannel seismic reflection and gravity survey to investigate the stratigraphic and tectonic history of westernmost Southern McMurdo Sound from the Greenhouse World (Eocene) to the start of the Icehouse World (Oligocene). This year’s survey represents an important step for identifying future drilling targets for the Antarctic Geological Drilling (ANDRILL) Program. ANDRILL aims to recover stratigraphic intervals for interpreting Antarctica’s climate and glacial history over the past 50 million years.

 

 

 

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