We have several links to waterfalls here...
HF Appendix - The RadioReference Wiki
This is outside the ham bands (altho MARS ops often are), so I don't think this is a ham-related mode, but you never know. This looks like about 6975 khz (is that right?); did you check the UDXF logs for possible IDs?
The short bursts suggest something along the lines of a PACTOR mode, but that is a WAG
Mike
