90-day Monitoring Report - National Marine Fisheries Service - NOAA

Figure 1. Location of the Coakley marine geophysical survey in the Arctic Ocean (LGL EA, 2011).
The purpose of the study is to collect seismic reflection data across the transition from the
Chukchi Shelf to the Chukchi Borderland to image the structures that separate these two large
continental blocks. The data from this study will be used to test existing tectonic models and
develop new constraints on the development of the Amerasian Basin, and will substantially
advance the knowledge about the Mesozoic history of this basin. In addition, the seismic data
collected will enable the formulation of new tectonic models for the history of this region, which
will be used to improve our understanding of the surrounding continents.
2.1.1. Energy Source
The acoustic source used during the Coakley 2D marine geophysical survey in the Arctic Ocean
consisted of one towed airgun array and one hydrophone streamer cable. The array was
deployed centrally astern of the vessel. While only one array was firing at a time, two arrays
were interchanged when maintenance was needed so that production could continue. The
airguns arrays were towed at a depth of six meters and were situated either 83.3 meters or
103.3 meters from the Navigational Reference Point (NRP), which was located on the PSO
observation tower. Whenever the arrays were exchanged the PAM operator would notify the
visual PSOs so that they were always aware of the safety radii. The first acoustic source array
that was deployed was being towed at a depth of nine meters, however it was noticed that the
IHA was granted for an array towed at six meters depth and the array was switched out at 20:45
UTC on 15 September 2011 for an array towed at six meters depth.
UME04085
R.V Marcus G. Langseth
L-DEO/NMFS
05 January 2012
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