Iceberg - Clive Cussler

Frozen inside a million-ton mass of ice is the charred remains of a long-missing luxury yacht, which vanished en route to a secret rendezvous. The only clue to the ship's priceless--and missing--cargo: nine ornately carved rings and the horribly burned bodies of its crew. Reissue.
High seas explorer Dirk Pitt must stop an American millionaire from using impoverished nations for his own personal experiments in this #1 New York Times-bestselling action adventure series.

A routine survey mission over the North Atlantic exposes a missing luxury yacht frozen inside a million-ton mass of ice. The ship had vanished en route to a secret White House rendezvous, making it the responsibility of the National Underwater and Marine Agency to find out what happened. In other words, it's time for Dirk Pitt to cut his sunny, California vacation short and get back to work.

Of course, when Pitt arrives on the scene and discovers the charred remains of the entire crew, who burned alive but never left their posts, he begins to suspect the tragic loss of the ship to be only the first, deliberate step in a far more sinister plan.