Field activities 07001 and 08002: The SB-424 towfish (07001) and Chirp 3200 transducers (08002) were mounted on a rigid pole, approximately 1 and 0.5 m, respectively, below the sea surface on the starboard side of the R/V Rafael. Position data were provided by a RTK-GPS navigation receiver located directly above the interferometric sonar head that was mounted from the bow of the R/V Rafael. Athough the horizontal offsets between the seismic-reflection sources and the RTK-GPS navigation receiver were not corrected in the sonar setup, this distance was less than 3 m, and the resulting positional accuracy during each field activity is assumed to be ± 10 m.
Seismic-reflection data acquisition 07001: Chirp seismic data were collected using an EdgeTech Geo-Star FSSB sub-bottom profiling system and an SB-424 towfish (4-24 kHz), which was mounted on a rigid pole on the starboard side of the R/V Rafael of Woods Hole, MA. Edgetech J-Star and Triton Imaging Inc. SB-Logger seismic acquisition software was used to control the Geo-Star topside unit, digitally log trace data in EdgeTech JSF and SEG-Y Rev. 1 formats, respectively, and record GPS navigation coordinates to the JSF or SEG-Y trace headers. Data were acquired using a 0.25-s shot rate, a 10-ms pulse length, and a 4 to 16 kHz frequency sweep. Recorded trace lengths were approximately 250 ms. Northwest-southeast oriented tracklines were spaced between 75 and 100 m apart.
Seismic-reflection data acquisition 07002: Chirp seismic data were collected using an EdgeTech Geo-Star FSSB sub-bottom profiling system and an SB-0512i towfish (0.5-12 kHz), which was mounted on a catamaran and towed astern of the R/V Megan T. Miller of Port Jefferson, NY. Edgetech J-Star seismic acquisition software was used to control the Geo-Star topside unit, digitally log trace data in the EdgeTech JSF format, and record GPS navigation coordinates to the JSF trace headers. Data were acquired using a 0.25-s shot rate, a 5-ms pulse length, and a 0.5 to 8 kHz frequency sweep. Recorded trace lengths were approximately 250 ms. Northwest-southeast oriented tracklines were spaced between 100 m and 1 km apart, while northwest-southeast oriented tracklines were spaced between 1 and 3.5 km apart.
Seismic-reflection data acquisition 08002: Chirp seismic data were collected using a dual frequency (3.5 and 200 kHz) Knudsen Engineering Limited Chirp 3200 system with transducers mounted on a rigid pole on the starboard side of the R/V Rafael of Woods Hole, MA. Knudsen SounderSuite seismic acquisition software was used to control the Chirp 3200 system, digitally log trace data in the SEG-Y Rev. 1 format, and record GPS navigation coordinates to the SEG-Y trace headers. Data were acquired using a 0.25 or 0.5-s shot rate, a 1 or 2-ms pulse length, and a peak frequency of 3.5 kHz. Recorded trace lengths were approximately 67 and 135 ms. Northwest-southeast oriented tracklines were spaced between 60 and 150 m apart.