What’s the patch?
Posted by sogasex on March 11, 2008
By David Ho, LDEO
SO GasEx has four broad categories of projects that together contribute to the overall goals of the experiment: There are those that revolve around (or rather, inside) the Lagrangian tracer patch; those that measure atmospheric fluxes of gases; those that involve autonomous buoys; and those that measure optical properties of the water.
Four days ago, we injected ca. 4800 L of 3He and SF6 infused seawater to create the tracer patch. It was a team effort, headed by Kevin Sullivan from NOAA/AOML. En route to the study site from Punta Arenas, we filled the 4800 L tank on the fantail with seawater. We then infused the tank with tracers by bubbling SF6 through it for a day, and then 3He for a few hours before the injection. While I had previously referred to the tracer infusion during the SAGE Experiment as a “Symphony of Bubbles“, we used a smaller pump and shorter length of “fizzy hose” during this infusion. It’s more accurately characterized as a “Quartet of Bubbles”.
The injection took place over ca. 12 hour period, during which the ship went around a GPS drifter following waypoints that Matt Reid (LDEO) and I were generating with a program that Matt had written. The injection started at 8:30p, and both of us had been up almost the whole day so staying up for another 12 hours wasn’t easy. Various people came in and out of the Hydro Lab throughout the night to talk to us, and while I can’t remember many of those conversations, I remember thinking that things made less and less sense with time.
Despite the difficult of staying up for 12 hours to generate waypoints and guide the ship, I think Matt and I had the easy job. Someone had be outside on the fantail to watch the inject hose, and make sure that the flow rate out of the tank was constant. We had no shortage of volunteers for this job, and these people are the real heros. Remember, it was cold, damp, and dark, much like winter in Scandinavia. Kevin started, and was out there for nearly 3 hours. Steve Archer took the next watch for 2 hours, and I know he wasn’t watching albatrosses because it was pitch black outside. When I went outside to check on him after more than an hour, he was just standing there like one of those Emperor Penguins in Antarctica on a cold winter night. Then, Pete Strutton (the toe rubber), Sarah Purkey (NOAA/PMEL), and Paul Schmieder (LDEO) took successive turns, until Kevin came back in the morning to finish the job.
After the injection, we retrieved the GPS drifter and deployed the MAPCO2 buoy and three drifters in the presumed center of the patch. Then, we started surveying the fruit of our labor. That was another long affair, taking almost 24 hours. In the end, a picture emerged of the initial patch. It was still a bit streaky, and had shifted slightly to the southeast, consistent with the movement of the MAPCO2 buoy and the currents as measured by the ADCP.
Kevin Sullivan with the GPS drifter
Quartet of Bubbles during the tracer tank infusion
The injection track
The patch after a day, with the injection track in white (Figure courtesy of Pete Strutton).