Field Update: Nov. 21, 2010

We’re lowering a video camera into the hole today to explore the ice shelf, and also to see what we can learn about the seafloor below. The video camera is enclosed in a pressure vessel attached to a frame with another pressure vessel providing lighting to allow the camera to see. We rig the system up to look down as we lower the frame, and then on separate runs, we rig it the other way – to see up. The pictures you’ll see in the following sections are a combination of these two viewpoints, but the objective is to give you a tour down the ice hole, through the bottom of the ice shelf, to the seafloor, and then back up again. We go where no one has gone before! It should be fun and very interesting too!

Of course, given the state of our technology, these will be “blind” trips – the camera will be recording, but we won’t be able to see what the camera sees until we download the data after recovering it back to the surface. There’s no real time data transmission to the surface like we would get with a remotely operated vehicle. From the coring, we’ve learned how far it is to the water line in the ice hole – about 41 meters – and how far it is to the base of the ice shelf – about another 219 meters below the water line. We also know the depth from the base of the ice shelf to the seafloor – another 538 meters.

We start lowering the camera and lighting on the frame. As it descends it gets smaller and smaller and eventually it disappears in the hole below.

A water hose is in the hole connected to a pump placed below the water line at 41 meters. This was placed in a separately melted hole, but when we opened up the main hole the two holes melted together and connected.

The camera frame has a measuring stick on it with distances marked with black and white stripes. This allows us to measure the diameter of the hole.

We lower the camera to the water surface at 41 meters and then enter the water while continuously recording these first observations from the hole. We travel down through the 219 meters from the water surface to the base of the ice shelf and every minute the camera is capturing more information about the layers of ice that we have melted through in our journey downward as well as giving us glimpses of what these layers of ice contain in terms of sediments and rock fragments that have been transported 100’s of kilometers from their source region in the Transantarctic Mountains. This part of the Ross Ice Shelf is sourced from the Byrd Glacier, which flows through the mountains and then enters into the Ross Ice Shelf. The ice from Byrd Glacier is sandwiched between ice coming from adjacent glaciers, as well as ice flowing from further south along Siple Coast, where a series of major ice streams are located. When the ice that forms the shelf melts it deposits these sediment layers on the seafloor below, so we are very interested in this process, because it links the glaciology with the preserved geological record.

As we descend deeper we approach the depth of the base of the ice shelf and emerge into the open water in the ice shelf cavity, which is isolated from the atmosphere by the overlying ice and are connected to the main Ross Sea to the north by currents that sweep across the continental shelf and enter the ice shelf cavity on their way south. The ice shelf is also affected by tides and tidal currents, which sweep around the area in a clockwise motion.

We want to know if the base of the ice shelf is rough or flat, whether it exhibits processes that are indicative of melting or freezing, and whether there are strong currents at the boundary just below the ice shelf. These are all unknowns that we hope to learn about from the measurements this year.

We see from the depth indicator on the cable in the MECC that we are below the bottom surface of the ice shelf. We wonder what the camera is seeing down there. Does the ice hole get smaller as it reaches the bottom of the ice? Does the cable get pulled to the side by the strength of the currents? We imagine what the conditions below might be like as the camera continues downward into the eternal night of the abyss. From the gravity core we recovered we know there are sponges and other creatures on the seafloor, but what will the camera reveal? These and many other questions swirl through the minds of the people in the lab as they watch and wait for the camera to complete its mission. In the water below, the light shines into the blackness of the water below the ice shelf, falling downward at the speed of the cable.

Suddenly, the cable stops, the line goes slack, and the load cell indicates that the weight on the line has decreased. We’ve reached the seafloor!!

We decide to stay for a while, letting the camera record while the ice shelf slowly drifts above the bottom at about 2 m/day laterally. We hope we will see something cool, and worry that the camera could have run out of batteries, or that we may have hit a rock and damaged the system. What will be revealed when the camera comes back up? After a while, we start to pull back on the line and gradually ascend back up through the water column. We notice a sharp jump when we reach the bottom of the ice shelf, perhaps indicating that the camera frame may have caught on the base of the ice shelf when it attempted to go back inside the ice hole. We’ll know soon.

The line spools onto the drum, wrap after wrap dripping wet and icing up a bit after coming out of the cold water in the ice hole. Will be able to see the condition of the ice hole, which has been open for several days? Will we see ice crystals forming in the open hole as the hole begins to freeze again? What will it look like? We wait with anticipation of what we will find out. It takes another 40 minutes of winding the line, but gradually the system comes up through the hole and breaks the water surface below. In another few minutes it will be back at the surface and we can start to take it apart and remove the camera to download the data to a computer so we can watch the video. We recover the camera and find that it isn’t damaged – good news!

We’ve travelled back in time as we’ve descended through the ice to the base of the ice shelf and then returned through time to get back to the surface.

We’re excited to see what we will learn and glad to share it with others. Now comes the hard part – What does the data tell us? What does it mean?

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