Cindy Byers: Mapping in the ice! May 11, 2018

NOAA Teacher at Sea
Cindy Byers
Aboard NOAA Ship Fairweather
April 29 – May 13

Mission: Southeast Alaska Hydrographic Survey

Geographic Area of Cruise: Southeast Alaska

Date: May 11, 2018

Weather from the Bridge:

Latitude:57°43.3 N
Longitude:133°35.5 W
Sea Wave Height: 0
Wind Speed: 5 knots
Wind Direction: variable
Visibility:3 nautical miles
Air Temperature: 11.5°C
Sky:100% cloud coverage

Science and Technology Log

The area that NOAA Ship Fairweather is surveying is Tracy Arm and Endicott Arm.  These are fjords, which are glacial valleys carved by a receding (melting) glacier.  Before the surveying could begin the launches(small boats) were sent up the fjords, in pairs for safety, to see how far up the fjord they could safely travel.  There were reports of ice closer to the glacier. Because the glacier is receding, some of the area has never been mapped. This is an area important for tourism, as it is used by cruise ships.  I was assigned to go up Endicott Arm towards Dawes Glacier.

Almost as soon as we turned into the arm, we saw that there was ice. As we continued farther, the ice pieces got more numerous. We were being very careful not to hit ice or get the launch into a dangerous place.  The launch is very sturdy, but the equipment used to map the ocean floor is on the hull of the boat and needs to be protected. We were able to get to within about 8 kilometers of the glacier, which was very exciting.

The launches have been going out every day this week to map areas in Tracy Arm.  I have been out two of the days doing surveying and bottom sampling. During this time I have really enjoyed looking at the glacial ice.  It looks different from ice that you might find in a glass of soda. Glacial ice is actually different.  It is called firn.  What happens is that snow falls and is compacted by the snow that falls on top of it. This squeezes the air out of of the snow and it becomes more compact.  In addition, there is some thawing and refreezing that goes on over many seasons. This causes the ice crystals to grow. The firn ends up to be a very dense ice.

Glaciers are like slow moving rivers.  Like a river, they move down a slope and carve out the land underneath them. Glaciers move by interior deformation, which means the ice crystals actually change shape and cause the ice to move forward, and by basal sliding, which means the ice is sliding on a layer of water.

The front of a glacier will calve or break off.  The big pieces of ice that we saw in the water was caused by calving of the glacier.  What is also very interesting about this ice is that it looks blue. White light, of course, has different wavelengths. The red wavelengths are longer and are absorbed by the ice.  The blue waves are shorter and are scattered. This light does not get far into the ice and is scattered back to your eyes. This is why it looks blue.

Meltwater is also a beautiful blue-green color.  This is also caused by the way that light scatters off the sediment that melts out of the glacial ice.  This sediment, which got ground up in the glacier is called rock flour.

Mapping and bottom sampling in the ice

NOAA Ship Fairweather has spent the last four days mapping the area of Tracy Arm that is accessible to the launches.  This means each boat going back and forth in assigned areas with the multibeam sonar running. The launches also stop and take CTD (Conductivity, Temperature and Depth) casts.  These are taken to increase the accuracy of the sound speed data.

Today I went out on a launch to take bottom samples. This information is important to have for boats that are wanting to anchor in the area. Most of the bottom samples we found were a fine sand.  Some had silt and clay in them also. All three of these sediment types are the products of the rocks that have been ground up by ice and water. The color ranged from gray-green to tan. The sediment size was small, except in one area that did not have sand, but instead had small rocks.

The instrument used to grab the bottom sediment had a camera attached and so videos

were taken of each of the 8 bottom grabs. It was exciting to see the bottom, including some sea life such as sea stars, sea pens and we even picked up a small sea urchin.  My students will remember seeing a bottom sample of Lake Huron this year. The video today looked much the same.

Personal Log

I have seen three bears since we arrived in Holkham Bay where the ship is anchored.  Two of them have been black. Today’s bear was brown. It was very fun to watch from our safe distance in the launch.

I have really enjoyed watching the birds too.  There are many waterfowl that I do not know. My students would certainly recognize the northern loons that we have seen quite often.  

I have not really talked about the three amazing meals we get each day. In the morning we are treated to fresh fruit, hot and cold cereal, yogurt, made to order eggs, potatoes, and pancakes or waffles. Last night it was prime rib and shrimp.  There is always fresh vegetables for salad and a cooked vegetable too. Carrie is famous for her desserts, which are out for lunch and dinner. Lunches have homemade cookies and dinners have their own new cake type. If we are out on a launch there is a cooler filled with sandwich fixings, chips, cookies, fruit snacks, trail mix, hummus and vegetables.  

The cereal and milk is always available for snacks, along with fresh fruit, ice cream, peanut butter, jelly and different breads.  Often there are granola bars and chips. It would be hard to ever be hungry!