Going a Little Overboard
Posted by sogasex on March 11, 2008
By Christopher Sabine, NOAA/PMEL
Most of the blog entries so far have focused on the shipboard measurements, but we also have equipment in the ocean drifting with the tracer patch. The variety of projects on the ship requires that time be shared between different measurements approaches. Sometimes the ship is steaming around surveying the patch with the underway instruments. Sometimes we are sitting on station making an optical or CTD cast. Sometimes we are facing into the wind to make atmospheric measurements. And, sometimes we are racing away from the patch to empty the ship’s holding tanks. One of my projects for this expedition was to deploy a drifting buoy with a string of instruments below it that can make uninterrupted measurements in the patch, no matter what the ship is off doing (see buoy diagram below). The MAPCO2 buoy measures carbon dioxide and a variety of biological and physical properties at the surface that help us understand the exchange of CO2 between the ocean and the atmosphere. Below the buoy is a string of instruments, such as the SAMI-CO2 systems (see DeGrandpre blog), making similar measurements throughout the water column down to 100 m. Most of the instruments take readings every half hour, 24/7.
To help keep the buoy in the tracer patch we have a series of six drogues in line with the instruments. Drogues are large canvas tubes 3 feet in diameter and 30 feet long. The tubes have holes in like Swiss cheese to allow the water to flow in and around the material (see picture below). These drogues provide drag in the water so that the wind doesn’t blow the buoy out of the patch. They also appear to provide a fun house for the local penguins that like swimming in and out of the obstacle course.
To keep track of how the buoy is doing, we transmit some of the key measurements (CO2 partial pressure, salinity, sea surface temperature, wind speed, and buoy location) back to the ship to compare with the shipboard measurements. Well, actually they go from the buoy up to an Iridium satellite in space, down to the United States where the data are posted to the internet, transmitted back up to space and eventually back to the ship that is sitting just a few kilometers away from the buoy. It seems a little overboard, but it is the most reliable way of keeping the data flow coming to the ship.
It’s commonly referred to as a holy sock drogue, but it’s more like a holy stocking
This is a diagram of the entire length of the MAPCO2 buoy. By the way, you deserve a prize for scrolling down this far.