Polar Bear Sightings and Our Expedition’s End

October 1, 2008 · Filed Under Journey · Comment

Jessica Robertson, U.S. Geological Survey Public Affairs Specialist

On Monday I saw three more polar bears! First we saw two bears cuddled together on a piece of multi-year ice. As we passed by, they took a swim in the ocean. To come back to the surface after diving into the water, they had to break through a thin layer of sea ice. We saw some ice and water splash up, and then they appeared again. At one point, one of the bears was sliding across the thin ice, and accompanying this post are some pictures of them lying on and walking along the thin ice. About a half-hour later, we saw another polar bear strolling along the ice. He was farther away, and when he occasionally took a dip in the ocean, everyone would look around at each other trying to figure out where it went. This was an exciting sight, especially in the final days of our journey.

This chapter in our effort to map the Arctic seafloor has come to an end. Several of us are departing Healy today and heading back home. We are taking turns loading into the helicopter and heading back to the airport in Barrow, Alaska.

The past couple days have been spent cleaning and packing, but the hardest part has been saying goodbye. Spending a month at sea brings close friendships and memories that will last a lifetime. I am going to miss all of the friends I have made along the way, but I am sure we will keep in touch!

The U.S. Coast Guard has certainly made our journey on Healy pleasant. The collaboration between the U.S. and Canada in this endeavor has been very successful, enhancing the ability of both countries to collect data in this remote area. When we first saw Louis appear through the fog a few weeks ago, I will never forget the excitement that filled our ship as our joint expedition began. As we watched Louis sail away a couple of days ago, it was a bit lonely peering out and seeing only the endless sea ice and water again.

In the end, we are one large step closer to mapping the Arctic seafloor and understanding the underlying geology.

I want to thank and express my appreciation to those who helped me understand the research and operations onboard Healy, as well as everyone who contributed to making this site available.

If you have any questions about this expedition, please contact me at jrobertson (at) usgs.gov. Remember, I will no longer have access to my healy.polarscience.net account.

Don’t forget to check back for video footage too!

Jessica Robertson

: Two polar bears taking a swim in the Arctic Ocean.

: Polar bears swimming in the Arctic Ocean.

: Polar bears in the Arctic Ocean. One polar bear is swimming and the other one is walking along young ice.

: Polar bears watching our ship sail by.

: Two polar bears cuddled up at the edge of a piece of multi-year ice.

: The polar bear to the left is lying down on young sea ice while the other one takes a swim.

: You can tell this is a piece of multi-year ice by the bright blue color underneath.

: Pieces of multi-year sea ice in the Arctic.

: Piece of multi-year sea ice in the Arctic.

: A polar bear is taking a stroll along the Arctic sea ice. This bear was spotted by itself.

: The entire science crew onboard Healy poses for a picture. We may look a little cold since, in addition to the chilly Arctic temperature, it was snowing that day.

: The entire science group and U.S. Coast Guard crew during our expedition on Healy.

: Every member of the science crew received the U.S. Coast Guard Arctic Service Medal certifying that, in support of polar research above the Arctic Circle, we served aboard U.S. Coast Guard Cutter Healy.

Tags: photos, polar bears, sea ice

Making Bubbles in the Ocean with an Airgun

September 14, 2008 · Filed Under Journey · Comment

Jessica Robertson, U.S. Geological Survey Public Affairs Specialist

We saw a polar bear and cub today! First we saw the tracks, and finally we spotted them. They were about two miles away, so I couldn’t get a close-up picture. Those on the bridge were peering through their binoculars trying to tell the crowd gathered together on the bow where to look. It took a while to find them, and when we did, it was truly spectacular!

Now, on to science. I learned today that Louis is using airguns, which create an acoustic sound signal under water, to image the geologic structure of the sub-seafloor. Even more interesting, scientists used to use dynamite to generate this sound source before airguns were developed! The airgun pulse is heard by everyone onboard Louis and shakes the fantail when set off. These airguns are also called air hammers or pneumatic sound sources.

So how do the airguns work? The gun has two chambers—a release chamber with vents at the top and a pressure chamber underneath. The pressure chamber contains compressed air at a pressure of 1,800 pounds per square inch. A piston is located between the two chambers and when triggered, it shoots into the release chamber, letting air out of the pressure chamber and into the ocean through the vents. The piston slams down and closes before water can come in. This whole process takes about 10 milliseconds. There are three airguns towed behind the ship at one time and they are fired about every 20 seconds.

The resulting air bubble emits energy waves into the seafloor. A signal bounces back, much like an echo sounder, helping image the underlying geologic structure. So, how are the resulting signals recorded? Louis has a streamer about 100 meters long trailing behind in the ocean. Within the streamer are 16 hydrophone channels, which listen for the waves’ return signals. Scientists also deploy sonobuoys behind the ship, each with an attached hydrophone. The hydrophone transmits the signal from the airguns back to the ship by radio. The sonobuoys drift freely behind the ship for several hours before they self-scuttle and sink to the bottom.

In a previous blog, I discussed how Healy is also imaging the geologic structure of the Arctic sub-seafloor. What’s the difference between the instruments on the two ships? The sub-bottom seismic reflection profiler, which is used on Healy, emits lower energy waves and can reach at most 100 meters into the sediment. The airguns, however, can penetrate 100 times further, reaching through sediment up to 10 kilometers thick.

At one point yesterday, Louis was stuck in the ice, and one would think they could just back up and ram forward to break through, right? In this situation, however, that would not be the most productive solution. Since the streamer is behind the ship, backward movement would tangle it with the propellers and disrupt data collection. In the end, Healy altered their track, made a circle around Louis, and set it free. This shows one of the many benefits of this joint expedition, as they will help us if put in a similar situation.

From the cold,

Jessica Robertson

: Polar bear tracks and remains from their last meal.

: Airguns are deployed by Louis earlier in the expedition. The airguns are a cylinder shape, constructed with heavy stainless steel, and range from 12 to 48 inches in height and 6 to 12 inches in diameter.