Ice Rafted Debris

By far, the best place on the ship to work is the aft control room. It offers eight large windows that look out over the water so you can watch the ice or keep your eye on the horizon when the seasickness starts to kick in. While it is a hub of activity when coring devices are being used (all the gears and controls on the left-hand side of the photo are used to operate the various winches that lower the empty corer down to the seafloor and haul the full corer back out again), often its only occupants are those who are looking for a quiet space to work, nap or watch whatever movies and TV shows they downloaded before the trip began.

The aft control room on the R/V Nathaniel B. Palmer icebreaker
The aft control room on the R/V Nathaniel B. Palmer icebreaker provides a view of the starboard and back decks, as well as the water. Multiple winches on the ship can be raised and lowered from this room. It is also one of the best places to get work done.

I was in the aft control room, working away on yesterday's blog post, pausing occasionally to look out at the face of the Pine Island Glacier, when I noticed a dark blemish on an approaching iceberg. My first thought was, "Seal!" and I grabbed my camera and hurried out on deck to get a closer look. It was almost impossible to tell for sure, but it didn't quite look like a seal, so my second thought was, "Treasure chest!" and I hurried back inside to load the picture onto my computer and zoom in, wondering if "finders keepers" applied to things floating on the ice and how long it would take to deploy a zodiac to go and retrieve it.

Ice rafted debris floats by the R/V Nathaniel B. Palmer icebreaker
A large piece of rock trapped on an iceberg, known as Ice Rafted Debris, floats by between the R/V Nathaniel B. Palmer and the face of the Pine Island Glacier in the Amundsen Sea, Antarctica.

Disappointingly, the object I saw would only be thought of as a treasure by a very small subset of the population (although a substantial number of people on this ship would consider themselves part of that subset). It is something called Ice Rafted Debris - small rocks and bits of sediment that get trapped in a glacier as it scours (or scrapes) the face of a continent, and are then carried off to sea by the chunk of ice into which they become frozen. When we take long cores of sediment from the bottom of the ocean, we often find pebbles buried many meters deep, and the explanation for them is that they were dropped by an iceberg floating above - former ice rafted debris that gets dumped when its raft melts. This piece was unusually large and it is hard to imagine where it came from and where it will end up. Eventually, the ice holding it will melt and this large boulder (or still, maybe, treasure chest) will sink to the bottom of the Amundsen Sea, likely never to be seen again. Fortunately, I got a decent picture to remember it by.

Dr. Ali Graham looks out a porthole on the R/V Nathaniel B. Palmer
Dr. Ali Graham watches a piece of ice rafted debris float by the R/V Nathaniel B. Palmer icebreaker in the Amundsen Sea.

Author
Date
Location
Onboard the R/V Nathaniel B. Palmer icebreaker in the Amundsen Sea at the face of the Pine Island Glacier.
Weather Summary
Gray skies and scattered snow showers with light winds.
Temperature
1.2˚C
Wind Speed
13.1 knots out of the north
Wind Chill
-9.1˚C

Comments

Matthew Pearce

Hi Sarah, Thanks for the posting on Ice Rafted Debris and your expedition, what a fascinating adventure. Be safe!