What does an Iceberg look like underwater?
April 10, 2009
Sea temperature: 0.0°C
Air temperature: -0.5°C
What does an iceberg look like underwater? ROV IceCUBE has recorded
several hours of video footage underneath the icebergs being studied in
this expedition, and has uncovered surfaces with pockmarks, linear
crevices, caves, and jutting spires. Glimpses of crustaceans like krill
and amphipods, jellyfish, chains of salps, and fish that seem to blend
in with the ice punctuated the videos. Some of the dimpled suncups of
the iceberg’s undersea surface have harbored filaments of algae.
Caves and ledges imaged by ROV IceCUBE during a dive underneath
a iceberg in the Weddell Sea. The nozzle in the foreground was used to
collect water samples with the ROV that were pumped back to the ship via
tubing that was attached to the vehicle's tether. Stripes on the iceberg
indicate land-derived materials incorporated into the iceberg.
Today the ROV IceCUBE successfully completed its final dive of the expedition,
exploring a two-kilometer-long tabular iceberg. The ROV, configured with
biological sampling devices for the Robison lab, spent nearly three
hours in the waters around the iceberg. Although the tether handlers on
deck had to cope with falling snow as they reeled the ROV’s lifeline in
and out, the vehicle experienced favorable diving conditions and water
clarity. One major accomplishment was the completion of vertical
transects at the face of the iceberg and two distances away from it.
During a transect, the ROV is maneuvered forward over a given
distance—in this case, a diagonal line from the depth of the bottom of
the iceberg to the surface—and observations are recorded. Today’s
transects included both a video record and a plankton net tow for each.
Back at MBARI, the Robison lab will analyze the video to identify and
count species and features that were encountered. Tonight on the ship,
they are sorting the samples collected with the plankton nets, which
catch smaller organisms that may not be visible on the video.
During an ROV dive, pilot Craig Dawe controls the vehicle using
a lapbox. Engineer Paul McGill monitors system functions and
communicates with the bridge and tether handlers on the deck. Stephanie
Bush and Rob Sherlock operate the cameras and video system.
Photo by Debbie Nail Meyer
The last water collections and CTD casts are taking place tonight as the
data collection part of the expedition ends. To stay on schedule, the
Palmer will begin the transit back to Punta Arenas tomorrow morning. The
trip will take several days and includes time for weather delays in the
notorious Drake Passage. The barometer is already dropping and we are
anticipating some rough seas for the trip ahead. The swell is already
more noticeable tonight as the ship rises and falls while on station.
— Debbie Nail Meyer