Help me remember the name or author of this short story [View all]

When I was a teenager in the mid-90's, I recall reading a short story in Analog or Asimov about a future in which a massive comet hit Earth and threw it's orbit into a wide ellipse, so much so that the oceans froze solid for much of the year, only thawing for a few short months as the planet re-approached the sun. To survive, humanity had genetically engineered itself into aquatic creatures that could survive being frozen solid in the ice. There was also an offshoot species of human that evolved large gills to filter-feed on plankton, the only other complex organism to survive and form the base of the food chain.

I keep thinking it sounds like a Stephen Baxter story, but can't find it. Anyone know what I'm talking about?