I was checking on how the Argo Floats we helped get ready were down south and saw that 3 were missing! They hadn't come back up to the surface to send off data for nearly 3 weeks. Feeling a little concerned and being the responsible person that I am, I pointed this out - only to get the reply "Carol, I'm not sure whether you're familiar with the way the "ice-avoiding" floats work"
These three Floats are down around the Ross Ice Shelf.
From early autumn to late spring every year
Antarctica’s sea ice almost doubles the size of the continent!
This means though that Argo Floats in this area get
caught under the ice. If they hit or rub up against floating ice they can be
damaged or destroyed.
So they avoid ice (sounds like a good plan!)
There are especially designed ice-sensing floats that
check the ocean temperature each time they ascend. If the temperature gets very
close to the freezing point, the float will stop heading towards the surface at
5-10 m depth and go back to its parking depth, and try again 7-10 days later.
The float stores its profile data in memory. There
is enough memory in this type of float to store as many as 68 profiles
(although it is usually doesn't need to store more than 40 profiles between
contacts with the satellite) Data transmission through the Iridium system is
quite fast and each profile can be uploaded in no more than 2 minutes.