Marine magnetics data collected by the U.S. Geological Survey in U.S. Atlantic Seaboard in 2014 (Geographic, WGS84, point shapefile 2014-011-FA_mag.shp)

Under normal data collection conditions, the magnetometer is deployed and remains deployed until the end of data collection. Magnetic data collection had interruptions and data gaps during the MGL1407 cruise, mostly because the magnetometer needed to be recovered during the deployment and recovery of seismic equipment, which happened multiple times on the cruise (initial deployment on Julian Day JD235, passage of hurricane Cristobal on Julian Day JD238, and a medevac on Julian Day JD241). The data coincide with all seismic lines, as well as additional tracks that include a test segment prior to the start of seismic acquisition (Julian Day JD234), and tracks laid out to avoid hurricane Cristobal.
Three calibration loops were conducted on August 28, 2014 (Julian day JD240) to test the consistency of magnetometer readings at the loop crossings. The loop pattern was started at 10:24 UTC and finished at 11:23 UTC, resulting in four points of crossing. During the daily review of the magnetometer data, noise was observed in the 1-minute smoothed data plots from JD 246 starting at approximately 21:00 UTC (JD 246.8). At 14:30 on JD 247 the G-882 was powered down and retrieved to check all connectors and cables. As the G-882 neared the boat, a large collection of seaweed was visible on the tow cable where it meets the G-882. The seaweed was cleared, and the G-882 was brought on deck. Upon opening the nose assembly, a white, granular precipitate was seen on the protective housing to the male/female 8-pin connector. The precipitate was cleared and the male and female connectors separated for inspection. The pins were cleaned with a wire brush, and some dialectic grease applied to the connection. The nose assembly was returned to its original state, with the G-882 set in the CG tow position and the unit was redeployed to 220 m behind the ship. During MGL1407, the magnetometer displayed low signal levels. These low signals may have been caused by the connector corrosion (north of latitude 36o) or sub-optimal sensor positioning relative to the Earth’s magnetic field vector. Many of these noisy and low sensor values coincide with the ship course of 230-240 degree azimuth. They can be noted at JD 246 04:00 and JD 248 02:30. On JD 254 when seismic data collection ended and the G-882 was brought on board for the last time, more white precipitate was on the outside of the connector housing.