62 46 S
43 52 W
21 knot winds
high clouds with diffuse sun
smooth, gently rolling seas
Around 3 a.m. this morning, the last CTD cast was completed to end a very successful day of science.
After we completed our work on the eastern side of the Palmer Peninsula, we sailed NE towards the South Orkney Islands. We arrived at the first mooring site off the South Orkney Islands on Saturday 3/5 just after sunset.
These moorings, deployed by Lamont Doherty Earth Observatory of Columbia University, measure and record temperatures and currents in the water column deep in the ocean. These instruments were placed here in the Jane Basin because this deep basin acts as a conduit from the Weddell Sea into the world's oceans. Deployed in 2001, in water between 3500 & 4500 meters deep, these columns of instruments may have recorded any changes in deep ocean circulation that might have occurred as the Larsen B ice shelf broke up in early 2002.
At mooring 1 near the South Orkneys, we were unable to get a repeatable set of responses from the mooring. Rough seas and ship position may have contributed to this. As time was tight, we moved south through the night to arrive at mooring 2 just at daybreak on Sunday. Mooring recovery is done during daylight hours to make it easy to spot the mooring once it arrives on the surface.
At mooring 2 (positions are carefully recorded when the moorings are deployed), the signal sent from the ship was immediately acknowledged by the releases, and so the code to release was sent. Rising through 3500+ meters of water takes over an hour, and the ship stands off to avoid getting fouled in the mooring as it comes to the surface. By using the "acknowledge" feature of the releases, codes are sent multiple times during the ascent phase, and the time it takes for the signal to return to the ship is used to calculate the current depth of the mooring.
A large crowd on the bridge works to spot the mooring once it reaches the surface, assisted by flashing strobe and radio beacon that are mounted atop the mooring. Once spotted, the ship pulls near, lines are thrown over the side to snag the mooring and attach it to the large winch that pulls it slowly on board. As it is brought on, individual instruments are removed one by one and taken to the lab, where computers begin downloading and backing up the stored data.
Once mooring 2 was on board, we headed further south to mooring 3's position. Arriving late in the afternoon, the signals were quickly sent, and there were smiles all around when these releases also immediately responded. With dusk coming on, the mooring was spotted on the surface, and the second recovery of the day began.
With the quick recovery of the first mooring, it was decided to try to refurbish the instruments from that mooring during the transit to mooring 3 and, if all went well at #3, redeploy a new mooring at that site. During the transit, the data from temperature sensors was downloaded, the EPROM memory modules from the current meters were replaced, new battery packs were put in the remote releases, strobe and radio beacons and a lot of Scotch Brite pads were used to clean the corrosion from various fittings and mounting hardware.
Once #3 was on board and after a short break for dinner, a new mooring was deployed in the approximate position that # 3 was recovered from. This was configured the same as the one we recovered except for the addition of a sediment trap at the top of the column. The moorings are deployed by streaming them out on the sea surface behind the ship until the anchor weight is the last item on deck. As the ship passes slowly over the desired location, the anchor is dropped in, and it pulls the entire column of instruments that is strung out on the surface down with it. The flashing strobe beacon was visible on the surface for 7 minutes after the anchor weight was dropped, giving you a feel for just how big these moorings are.
A very tired and very happy Bruce Huber of Lamont sat down for a quick bite to eat at midnight only to rush off for the final CTD cast of the voyage.
We are now headed NW from our final position, which was about as far south as the northern end of the Prince Gustav Channel and 300 nautical miles to the east. Plans are for us to arrive in Punta Arenas on Saturday March 12th.
After a long and rough Drake crossing, we are currently in the calm waters of the Straits of Magellan moving towards the dock in Punta Arenas. Plans call for us to arrive tomorrow morning. Currently we are doing 6.8 knots as we fight the outgoing tide; once it turns we may see speeds near 17 knots, per the captain.
LMG05-02 was an extremely successful scientific venture in many ways. Along with true exploration of a previously unvisited area, we collected significant data that will add to our understanding of the marine geology, ocean chemistry, and climatic history of this area. Planning for next year's cruise is already underway, with plans to target & examine in great detail some specific areas of interest discovered on this voyage.
From all of us on the Laurence M. Gould, we hope you have enjoyed our travels as much as we have. Be sure to catch up with the students who were on this trip to get a first hand account of the cutting edge science and research that they were involved in every day.
I'd like to thank everyone for the kind notes I received about the web updates and the images.
Cheers to everyone, Dave
-commentary provided by Dave Tewksbury, geology technician at Hamilton College