Ken’s posterous

Current Location: lat:-73.1986, lon:-114.9596
 
Sailing south toward the Getz Ice Shelf
 
Weather: Gray skies, gray sea, -0.5C (Air), -0.01C (Water)
 
Moods: Excited to finally leave Pine Island Bay and do something new (although new really just means more CTDs and more mooring deployments).
 
Note about last image: Photo of me taking sextant reading by Katie Leonard (I hear multiple of her friends and family might be reading this).
 
I was asked to provide more info about the sextant reading. We took 18 samples across the front of the ice shelf. By "we" I mean Katie Leonard and Chris Little (author of the other NBP09-01 blog). I helped with the first few and then went to bed, most of the transect happened on their shift. An example one went something like this:
 
 * Date: ...
 * Time: ...
 * Lat: ...
 * Lon: ...
 * Radar dist: 0.18 nautical miles
 * Sextant: 8 deg 8.6 min
 * Note: Caves just north of ship, elephant seals spotted nearby.
 
After we were done, we began the analysis. The math is pretty basic trigonometry:
 
1) Convert the distance from nautical miles to meters (333)
2) Convert the angle to degrees (8.1)
3) Convert degrees to radians (0.14)
 
Draw a triangle, knowing one angle and side:
 
 
  __----|
  __-- |
  __--- |
  __--- | h = ?
 o) theta = 0.14 |
-|- -------------------|
 ^ d = 333
 
I'm not sure how that looks to you readers but as I write it I have drawn a person on the left, and a vertical line on the right.
 
In general, tangent = opposite/adjacent
 
So tan(theta) = h/d
 
we want to solve for h so multiply both sides by d and you get
 
h = d * tan(theta)
 
  = 320 * tan( 0.14 )
 
  = 45.1 m high
 
We took a additional steps to make sure things were more accurate. For example, the radar measured 333m but we corrected for the distance between where the radar took its measurement and where we took our measurement, which was not directly under the radar, and about 10 meters closer to the ice shelf.
 
As you can see by plugging in 310 instead of 320, we were close enough that a 10 m error makes a significant difference in the height of the ice shelf.
 
310 * tan( 0.14 ) = 43.7 m
 
Further analysis will refine the equation to take into account the height of the radar and the height of the average observer eye above sea level. We could even take into account the difference in eye height between Chris, Katie, and I, but I do not think that will make much of a difference.

Location: lat:-73.877, lon:-116.827
 
Weather: Stormy. Big waves, two or so meters. Whitecaps. Boat is rocking. Too much motion and to erratic to open the side doors and lower the CTD.
 
Also, we just saw the strangest thing: A fishing boat.
 
Prior to yesterday I thought we were very much alone.
 
We are around 1,200 miles (equivalent New York to somewhere around Kansas) to the bases on the peninsula, where there are a few small scientific outposts (Palmer and Rothera Station, among others).
 
We are more than 1,500 miles from the big base at McMurdo and Ross Island.
 
We are almost 2000 miles from our port in Punta Arenas, Chile, which is around 7 days of non-stop sailing to get home.
 
We are a mere 1,100 miles from the South Pole. That is equivalent to New York to the southern tip of Florida. I thought the closest human beings to us were at the South Pole.
 
When you are in this type of location, you definitely feel a sense of isolation and being alone (and you take safety very seriously).
 
But this morning as we sailed toward our CTD waypoint there was a fishing boat sitting there. It was from New Zealand, and we presume it was fishing for Toothfish / Monkfish / Chilean Sea Bass. It was a very strange sight to see.

Yesterday was different. We parked the boat in some fast ice (ice locked to land) and had an ice party. We put out the gangplank and were allowed off the boat. Penguins came over to inspect us.
 
The reason for this was we needed 12 hours to deploy an Ice Tethered Profiler (ITP), and Ice Mass Balance buoy (IMB), and take an ice core. The ITP is a buoy sitting on multi-year ice that will hopefully last another two years in current position. The buoy is just in case the ice melts or breaks apart. Hanging off the ice/buoy is a 750 m tether and a small robot that twice a day climbs up and down the tether collecting oceanographic data. When it is at the top it uses an inductive modem to relay the data to the surface base which sends it home via Iridium modem. You should be able to see the buoy we deployed here: http://www.whoi.edu/itp
 
The ship crane lowered several hundred pounds of equipment onto the ice including a snowmobile. A route was scouted almost three miles away from the boat, and we towed all the gear out there. The ITP deployment design allows two people with just a wrench and a screwdriver to deploy a ~ 400 pound anchor and 800 m cable (also weighing hundreds of pounds). Photos will come later.
 
While we set up the ITP another team installed an Ice Mass Balance system. The IMB is a sensor suite that measures approximately the top meter of water, the ice and snow from water to air, and then the top meter of air. It gives a complete picture of the ice-ocean-atmosphere interface. Couple that with the 800m data from the ITP and it is quite an impressive data set.
 
It was nice to get off the boat for 10 hours and to do some hard physical labor. And while we worked we watched the nose and gigantic soft black eyes of a seal that used our ice holes as a breathing hole.

Me using sextant to measure angle Pine Island Glacier fills vertically in field of view. Distance provided by ship radar. Geometry provides height.

Current location is lat:-72.981, lon:-111.356
 
Photo location is somewhere NW of Pine Island Bay.

And we're off... We're done with Pine Island Glacier and Pine Island Bay. We're sailing west toward the Thwaites Glacier Tongue, and beyond to Getz. For the next three week we'll do a loop west and back to somewhere near here, then a bit over a week of sailing back northeast to Punta Arenas.

Image is approximately 5 mm across. See recent post "PIG Macro" to compare and contrast scales.

Yesterday we did a transect along the face of the glacier. Every 15 minutes we fired an XBT down to measure temperature, pinged the bottom of the ice shelf with our multibeam bathymetric mapper, used the radar to get the distance from the ice shelf, and used a sextant (old school!) to measure the angle the ice shelf fills in our field of view. With a bit of geometry we now have a rough estimate of the height and draft of the ice shelf. The temperature data crosses the boundary below the ice shelf draft, and we can see how the open bay interacts with the water under the shelf.
 
In other news, I think tomorrow is the half-way point of the cruise. For those of you out there anxious to see those of us down here once again, you are beyond half-way. We left you four or five days before the cruise began and will see you much sooner after it has ended.