Breaking Ice and Making Waves

Thursday, February 6, 2014

Waking up to ice!

Waking up to ice, the view outside of our porthole.

Tuesday:  Today’s day shift awoke to a wonderful surprise; we’ve entered the ice! The transition was swift, and even our colleagues working the night shift last night were surprised by how fast the ice accumulated. For those of us working today’s day shift, it has been a beautiful sight. While stunning, the ice can interfere with our seismic CHIRP data so when ice is present, a more careful watch must be kept on the Knudsen monitor in order to be sure that no data are lost.

The appearance of sea ice also has had ramifications for the two marine mammal observers on board. Now that the sea ice has reached a density of greater than 50%, a constant mammal watch must be kept. We must be cognizant of the marine mammal species present in order to reduce the impact of the ship’s icebreaking and seismic operations on these observations. All research members will assist with the sightings because it is impossible for our two designated observers to spot all of the wildlife present. Now that we have entered the ice, each person spends two hours of their shift on the bridge, identifying the animals or “takes.”  So instead of standing just one two-hour watch during our shift, logging ship data and watching the computer monitors, each of us now also stands an additional two-hour watch focused on observing marine mammals. A large assortment of animals has been sighted already, including Crabeater seals, Emperor and Adélie penguins, and several varieties of petrels. Even though the landscape is dominated by ice, there is high faunal diversity.

In addition to the mammal watches, we have begun seismic operations. This involves deploying two high-pressure air guns and a seismic streamer into the water behind the ship. The streamer and the air guns are buoyant and remain attached to the back deck, following the Nathaniel B Palmer like a tail. This system is designed to help map the seafloor topography as well as define the sedimentary layers and bedrock beneath the seafloor. The high-pressure guns release large air bubbles, sending high-energy waves through the water to the seafloor and below that then reflect back towards the ship. These waves are then picked up by the hydrophones in the streamer and, based on the known velocities of the waves, the distance that the wave traveled from the gun back to the streamer can be determined.

Waiting for seismic data

Waiting anxiously for seismic data.

Seismic operations are best in ice-free, open water for accurate depth records and good resolution, so the disturbance and noise created when the ship is ice breaking can skew seismic measurements. Thus, the icebergs that were so exciting to see in the morning became a hindrance in the afternoon. Even though the seismic guns and the streamer were ready to go in the early evening on Tuesday, we had to wait until we reached the polynya, or open water, before seismic data collection could begin. The path to open water caused us to depart from our originally planned course but the captain and mates skillfully steered us through the remaining ice and got us back on track shortly. There was a collective sigh of relief in the Forward Dry Lab when seismic data began to transmit properly, and the seismic guns and streamer remained in operation for 16 hours, firing through Tuesday’s night shift into the following day shift. The collected information is now being used to determine the exact location for dredge sites, which will be our next sampling objective. After the flurry of activity of our first scientific operations on board, there is a feeling of satisfaction at the productivity of the last two shifts and an excitement to continue to our next instrument deployment.

(Just a note for those of you receiving email notifications of our new posts: images are easier to upload and format after the new text post is initialized so after the email notification, please allow about 10 minutes for picture uploads before visiting our site.  Thanks for your interest in our blog!)

Sea ice at sunset.

Floating sea ice at sunset.

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