Southern Ocean Iron Experiment (SOFeX) Cruise
January 5 - February 26, 2002
Skip to Log Entry from the USCGC Polar Star
February 14, 2002: Day 41
Position: 66 degrees, 1 minutes South, 172 degrees, 7 minutes West
R/V Melville Log Entry: Although yesterday was sunny and relatively warm, I woke this morning to find the decks and equipment covered in a thick layer of snow. We set up for a series of stations across the patch from West to East in our last of our "transpatch profiles". Snowballs flew across the deck for the first casts. Even the Captain landed a few on some deserving scientists taking cover on the fantail
As you recall, we are in the middle of a dynamic and drifting ocean. In order to stay with the experimentally enriched waters, we have employed the use of a drifting buoy, anchored to the water column with a big drogue. The buoy, developed by MBARI scientists and engineers comes fully loaded with all kinds of instrumentation and an GPS receiver. We have on board a radio connected to a computer that talks to the buoy, downloads the sensor data and it’s position. The idea is that this buoy floats along with the experiment. In reality, there are many forces that act on the buoy (waves, wind, current, tides, etc…) and it always moves outside of the Patch, sooner or later. We had already had to reposition it once because it had drifted outside range of the packet radio.
We had not been able to raise our Inside station Lagrangian navigational buoy by radio for 20 hours. We were getting sensor data downloaded via radio transmission but no position. This meant that the buoy was out wandering by itself and not telling anyone where it was going and as such, was of little use and at great risk of getting lost forever. This is the same way in which the previous buoy failed and the timing at the end of our station was terrible. The Polar Star was on its way and we both planned to occupy an inside station together. It was like having your kids call in and tell you what they were doing but not tell you where they were and you have the relatives coming over. We needed to survey but we also needed to know where we were in this drifting sea of green. The ship’s ADF (automatic direction finder) was almost useless. It would squawk like a chicken and beat its wings when we got within a kilometer, but gave no clue which direction the buoy lay, its bearing indicator swinging 360 degrees.
The calm seas provided ideal conditions to search for the wandering MBARI drifter, D1. We were reaching a point in our schedule where three nights ship time had been devoted to the recovery of this drifter. This was to be our last. It had been sending all its sensor data but refusing to include its position. This was likely because it could not find a navigational satellite during its short wake up period. Our instructions were to reprogram the buoy over the radio (if we could make contact) and command it to turn full on and stay on for at least half an hour. This is somewhat risky because such a maneuver will rapidly drain the batteries and the buoy would go dead. Yet without a position we stood little chance of recovering it. We plotted its last known position (of over a week ago) and superimposed the drift pattern of its twin, D2, then we looked at the difference between D2 drift and the drift of the optical buoy deployed nearby, closed our eyes, flipped a coin and picked a point on the chart. (photo caption: Wendy Wang and the Wayward Widget. Wendy’s coordinates (and Mike’s keen eyesight) helped to recover the wayward MBARI drifter.)
It was getting late and our transect line was running in the direction of the buoy’s last known position. We decided to break off and search for the buoy while the weather was good and there was still ample light. Heading to it’s last known position, we directed the ship in the direction of the net drift and the chicken started to squawk and flap it’s wings (they really gotta get a better ADF).
Kenneth Coale, Chief Scientist
USCGC Polar Star Log Entry: t's rendezvous time! We caught up with the Melville in the early morning hours today.
In the months spent organizing this third cruise, much sleep was lost pondering what if we arrived and there was no patch, or what if we could not find the patch, or what if our cruise schedule overlapped too much or too little with the Melville or what if we were too early or late, or "what if".....
Well today, all those "what if's" disappeared, as we could see for ourselves using the measurements on board the Polar Star that the patch was maintaining high levels of phytoplankton (measured as chlorophyll fluorescence) and that there was enough of the original SF6 tracer still around to define the in and out patch locations. The Melville had taken good care of our patch and guided us to a "hot spot" where the day's activities centered around sampling within a nautical mile of the same location on both ships. These comparisons will be valuable in interpreting both the compatibility of our methods, and for one point in time, provide some of the most detailed small-scale spatial coverage of the patch.
To obtain today's samples, much of our day was spent hanging single sampling bottles on a wire or Kevlar line that was hung over the side of the ship. Our CTD/Rosette sampler, that puts 24 bottles over the side in one go, could not be deployed because of weather. So rather than collect 24 samples in less than one hour, we spent 4-5 hours collecting 9 of 10 sample bottles (one failed and came back open) the old fashioned way, hanging sets on a single wire and dropping a weighted "messenger" down the wire to trip, or close each bottle. This is hard work and a cold job today, but a necessary alternative when the Rosette cannot be used.
Being within a short distance of the Melville also meant that we could catch up with our colleagues directly on VHF radio, and learn first hand about the goings on at the site. The words, "RV Melville, this USCG Cutter Polar Star, do you copy, over..." were uttered by many a pair of scientists today in our quest to determine just what had gone on during the last week at the site and what would be most productive in the coming week. So, while Valentines Day was poorly celebrated by many of us who found ourselves far from our loved ones, it did seem like a bit of a holiday.
As of tonight, we are left on our own as the Melville heads North. We wish her well.
Tonight, we have set our sites on a large-scale survey centered around the "hot spot" that the Melville has led us to here at 66 South, 172 West. Using today's results and this survey, we will refine our sampling strategies for the days ahead. We are expecting many hot and cold spots as the patch is hardly uniform and many small scale features emerge in the surface and subsurface data.
Today's people shot is of Ed Abraham, our top patch tracker from New Zealand, sitting in his corner lab where he measures phytoplankton properties in a continuous seawater line. The phytoplankton that have flourished as a result of the iron enrichment, have different optical properties that Ed can detect with his specialized on line instrumentation.
That's all from the Polar Star. From now on, we are on our own now in the Southern patch.