Fig. 4

Geomagnetic field intensities plotted as a function of longitude and latitude over the period of time the PTT was at the surface as it drifted across the western North Atlantic Ocean. The bands on the 3-D surface indicate iso-contours of 1000 nT. Note that even with the plotted crustal magnetic anomalies (from World Digital Magnetic Anomaly Map, WDMAM), the slope of the surface of the plot is relatively smooth and hence provides a good estimate of position