What’s the patch?

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).

Going a Little Overboard

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.

Peaks and Valleys at Sea

By Bruce Hargreaves, Lehigh University

Peaks and valleys are familiar features of land. But these terms can also describe properties of ocean waters. Different colors (wavelengths) of sunlight that cause us to marvel at the sight of a rainbow can also tell us how the ocean may influence climate change.

The energy of the sun fuels the metabolism of phytoplankton (and through food web connections, most living organisms in the sea). On this cruise a collection of old and new methods for measuring absorption of light by photoplankton is combined with simultaneous measurements of metabolism, carbon dioxide concentrations, and satellite data.

The biological oceanographers on this cruise are seeking to learn more about how phytoplankton metabolism can soak up carbon dioxide from the atmosphere, and how satellites might some day be able to measure this process across the entire surface of the world oceans. Bob Vaillancourt and Veronica Lance, with colleague John Marra (all from LDEO, Columbia University), are using several methods to measure photosynthesis and light absorption by phytoplankton. I am making several types of optical measurements, including a new method to measure the absorption of light by freshly collected phytoplankton to compare with measurements of frozen or chemical extracted samples.

An absorption spectrum of the pigments of the phytoplankton community from our study site shows characteristic peaks and valleys. The broad peak in the middle of this chart absorbs blue light to provide most of the energy for photosynthesis. The smaller peak on the right side absorbs red light. The valley between these two peaks transmits green light (the green color we expect to see in living plants is the result of this valley). The prominent peak at the left side of the chart represents a natural sunscreen chemical produced by phytoplankton that live near the surface where UV-B radiation can cause damage. Phytoplankton from a depth of 30 meters had less absorption by this chemical. At our study site where this sample was collected the phytoplankton were equally abundant at 10 and 30 meters but were scarce at a depth of 80 meters (the sun is too weak at that depth to support life).