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2006 Expedition to Antarctica

Week 2

Monday, April 17

Currently at 65° 53' S, 61° 03' W
Temp. -1.8 C, Location off Larsen B, SCAR Inlet Ice Shelf


At present we are conducting multibeam operations and swath mapping a portion of the seafloor off the remaining Larsen B ice shelf that clings to SCAR inlet. Just two months ago this region lay beneath the ice shelf but the calving of giant iceberg A 54 has opened yet another chasm in the sub ice shelf seafloor within the embayment.

The previous two days we conducted seismic reflection and multibeam work in the open water just along the southern border of iceberg A-54, which provided the only open water along our proposed dip section line (a line that runs across the orientation of strata within the basin). The Italian OGS group along with Raytheon staff did a fantastic job of bringing the system to life and we collected excellent data showing dipping strata and active faulting.
 

Figure 1: cutting new sea ice around Robertson Island. In such conditions we can't collect multibeam or seismic data so we are searching for open water in which to work as we head south.
   
Figure 2: open water often develops along the downwind side of large icebergs such as A-54 (see figure 3). We took advantage of this lead to run our seismic line which was over 45 nm long.
   
Figure 3: the 'over-the-side' aspect of seismic operations consists of a gas injection 'gun' which is suspended in the water by the large red floats and a streamer. The gun is filled with compressed air that is burst open every 10 seconds. The acoustic pulse travels to the seafloor and within, reflecting off layers beneath the seafloor. These reflected layers return to the ship and are received by the streamer, a long line of hydrophones that can detect a small echo in the water.

 
Figure 4: the echoes are replayed back in the lab and amplified to produce a seismic section, which is a cross section of the seafloor depicting the stratigraphy (layering) and structure (folds and faults). Here Dr. Michele Rebesco of the OGS  Italy team is examining the first data returns from the system.
   
Figure 5: A satellite image shows the position of the ship as of AM April 19th as well as our approximate path across the NW Weddell Sea.

Friday, April 21

We have completed our first set of data collection within the SCAR Inlet and Exasperation Inlet. Seismic data collected yesterday included a complete cross section of the sedimentary basin that lay beneath the former Larsen Ice Shelf. We are now headed to the Larsen C Ice Shelf to recover a mooring. As we occupied our first bottom station early this AM students were excited to finally see some mud and we collected a fine sediment core. This location was under the remnant Larsen B ice shelf until just 2 months ago when the huge iceberg A-54 calved away.
 

Figure 1: View of the Oscar II Coast along the trough of the Crane Glacier. Our swath mapping has revealed a tremendous submarine valley that reaches depths of over 1200 m (3600')and extends to the calving front of the Crane Glacier.
   
Figure 2: We could not complete our work here in the Antarctic without the dedication of talented technicians from Raytheon Polar Services. This includes our two IT persons, Kathleen Gavahan and Isaiah Norton, shown here in front of the Crane Glacier.
   
Figure 3: With mud in the grab sampler Cathleen Dale (Montclair State Univ.), Taylor Burt (Hamilton College), and Sarah Garner (Southern Illinois University) go to work subsampling the sediments recovered from 1600 below the surface and just in front of the Larsen B ice shelf that in SCAR inlet. The grab came up about 6:00 in the morning just before the sun came up.

Saturday, April 22

We are trying to get as much work done before the weather changes on us and we are particularly concerned about the wind. We are working in the northern and western end of Exasperation Inlet, a apt name since the ice choked waters in the NW corner have prevented us from one of our goals of collecting a jumbo piston core. In the last day we have completed a swath survey of the outer Crane Trough which should allow us to more accurately asses the cold seep system and locations from which to sample it. Ice is forming before our eyes, as first the water becomes a thick syrupy fluid, then a slushy surface forms into small pancake ice, which becomes larger and congeals into a uniform grease ice layer that progressively thickens. It's troublesome to our data collection even though the Palmer passes through the slush with ease, as the fine ice crystals wash under the hull and play havoc with our multibeam system. This means it takes us twice as long to complete a single track of sway data, as we first have to clear a channel, (hope the winds don't pick up) and then retrace our course to get bathymetric data.
 

Figure 1: Niki West (Colgate University), Kim Roe (Hamilton College), and Molly Rosig (Montclair State) start to pick apart our first kasten core, a fine box of muck collected from beneath the Larsen B remnant ice shelf in SCAR Inlet. Each set of samples taken, and there may be hundreds from a single meter of core, is designated for one type of analysis. For instance grain size and geochemistry at Hamilton, diatoms at Colgate, magnetic minerals at Montclair State, and forams to Southern Illinois. Later we hope to collect some microbial mats for Mike McCormick (Hamilton College).


-- Commentary provided by Chief Scientist Eugene Domack