Hi Rich: First off, congratulations on your progress! It looks like you’re only some 170 nautical miles from the ice exclusion zone!  The ice exclusion zone has grown from your last race, and the main reason is that the number of icebergs sailing around the Southern Ocean has been growing over time.  We’ve been keeping track of them using satellites since 1976, and in that time, the number of icebergs tracked each year has climbed from fewer than 10 to more than 45!

You see, the icebergs are born, or calved, by breaking off of the large glaciers in Antarctica that normally slowly flow toward the ocean.  The speed of this flow has increased a lot in the past couple of decades, likely because of the warming of both the atmosphere and the ocean.  It’s not simple to figure out just how this is happening, though, and it takes a lot of painstaking work in really cold and difficult conditions.  For example, just in these past couple of months, scientists working in Antarctica have found massive cracks forming in the Pine Island Glacier, one of the major ice streams that create icebergs.

It is normal for cracks to form at the edges of the glacier when icebergs are calved, but the cracks that were just detected are in the middle of the glacier.  This means that something is weakening the glacier in a place that we thought should be stable.  The scientists in the field think that warming ocean water is getting underneath the glacier, between the ice and the bedrock below, and melting it from there.  In 2013 and 2015, chunks that are 20-30 kilometers in length (think six times the area of Manhattan!) broke off the Pine Island Glacier, and have been drifting in the Southern Ocean since, slowly melting and breaking off into smaller chunks that are called growlers and bergy bits.

Another reason for the larger ice exclusion zone is the winds.  This year there has been a persistent wind pattern that has made the icebergs drift further away from Antarctica.  As they float away, these icebergs are being tracked via satellites because they cause a big hazard to shipping – something that you know all too well!  Various agencies world wide use the satellite tracking data to put out notices to mariners to warn ships about these hazards, and this is how the race organizers decide where to draw the ice exclusion zone.

– Question submitted by Rich, from Great American IV