“Normal bioluminescence is when the waves light up or there’s a trail of light behind you,” Dr. Lemmens said. “You see that two or three times a year. This was different. The sea was lit, but the waves were black. That made it really eerie. It gave the idea that the light was coming from a deeper level.”

The crew lowered a bucket into the water and pulled up a sample that contained several pinpoints of light that glowed steadily until the water was stirred; then, the points suddenly went dark. That response, the new paper notes, is contrary to “normal” bioluminescence.

Ms. McKinnon said her first awareness of the glow came around 9 p.m. local time and that it intensified during the night, lasting until dawn. The satellite observations revealed that the glowing patch south of Java, Indonesia’s most populous island, persisted for at least 45 nights and grew to be larger in size than the collective areas of Vermont, New Hampshire, Massachusetts, Rhode Island and Connecticut.