Tuesday, June 23, 2015

An underwater crater or not?

Image of multibeam bathymetry in northern Alaska Gyre.

Jump from 6074 to 3472m in just a few seconds.

A couple of days ago, while conducting our cross-gyre section, we were surprised to find a >6000 m crater underneath the ship as seen in the underway multibeam bathymetry display, but not on any chart. Well, after much initial excitement, we have concluded that this must be an artifact of anomalous multibeam behavior induced by a nearby (very steep) seamount. We saw another crater later on and turned back briefly to verify and better map it. Upon return, while steaming at a slower charting speed of 8 knots (rather than >11 as before), we could not find it!! Instead, only a  steep seamount that agreed with the 1 minute Smith&Sandwell topography was present. To all oceanographers: Have you seen this type of multibeam behavior before?