We continued to have communication problems with SG157, so we decided to call on our Chilean colleagues to help with a rescue on July 10th. The Seaglider was close to the coast at the time, so the pilot worked to keep it as close as possible to the port of Iquique despite a current pushing it to the south.
The plan was to have a student, Nadin, fly from Concepcion to Iquique to help with the recovery, since he helped us with the deployments and recoveries back in March. We communicated with our Chilean colleagues mostly via Email, so sometimes things were happening there faster than we could follow. It turns out that before Nadin could get from Concepcion to Iquique, the Chilean Navy was already on sight and recovering our glider! Jack’s words were, “Chilean Navy to the rescue!” We were all surprised that they had gotten involved, but I guess it’s not every day that a misbehaving Seaglider needs to be rescued off of the Chilean coast. We were (are!) very grateful for their assistance, and they did a great job on the recovery. By the time they got the glider back to shore, Nadin was able to get there and shut the glider off with the magnet. All’s well that ends well in the world of Seagliders!
We received this clipping from a Chilean newspaper yesterday (click for bigger)…
I spent some time today looking at patterns of CDOM along our glider sections. As an introduction, CDOM is colored dissolved organic matter, also known as “yellow substance,” “gilvin,” and “gelbstoff.” CDOM is a subset of the pool of dissolved organic material in the ocean (and lakes, streams, estuaries, etc.) that is optically active (i.e. has color). CDOM appears yellow or brown to the eye depending on it’s concentration, it absorbs light very strongly in the blue region of the spectrum, and fluoresces in the blue as well. CDOMs optical characteristics enable us to monitor it’s concentration and distribution with a fluorometer on the Seaglider (WET Labs ECO-Puck; CDOM fluorescence excitation/emission at 370/460 nm). CDOM is an important parameter to keep track of for many reasons (see excellent review by P. Coble, Chem. Rev., 2007, 107, 402-418), but for our purposes we are primarily interested in monitoring the variability of sources and sinks of carbon in the OMZ.
Here is a plot of all of the CDOM-depth profiles from our most recent complete section, Line 11, with oxygen concentration in color. The red line is a running average at each depth bin.
A couple of things pop out right away. CDOM is degraded by sunlight very quickly, which is evident here in the surface data. That’s just a good double-check that the fluorometer is working. Second, there appears to be (maybe?) two discrete pools of CDOM – one associted with phytoplankton production and degredation in the chlorophyll maximum (photic zone, high O2), and one associated with the microbial community in the OMZ (low light/aphotic & hypoxic). However, it is impossible to tell from these data alone if the source of the CDOM in the OMZ is local or if it was derived from far away sources and has been transported with the water mass. Collecting water samples for CDOM spectral absorption measurements will tell us a great deal about the nature and origin of CDOM in this area. It’s also important to remeber that not all CDOM is fluorescent, so we are actually looking at a sub-pool (the fluorescent bits) of a sub-pool (the colored bits) of the pool of dissolved carbon. However, the CDOM data that we are able to collect autonomously could be very instructive when considered in conjuncion with other variables like chlorophyll, backscattering, and physical indecies of mixing and mass transport.
This is just a first-look at the data, and I’m still trying to get my head around it. Feedback in the comments is encouraged!
Here is a plot of the upper 400 meters of the latest seaglider section off of Iquique (27 March – 07 April 2009, onshore to offshore track). On a hunch I plotted salinity contour lines on top of the oxygen (upper right) and backscattering (middle right) data. It seems that there is tight coupling between salinity and both O2 and bb. Before seeing these data, I would have guessed that variability in the deep oxycline would be driven by intrusions of water masses with different density and oxygen characteristics. Likewise with the bottom boundary of the intermediate depth scattering maximum. However, given what we see here, the story seems to be a bit more interesting than that! Why would salinity be more influential than density in regulating these distributions?
Dive 236 uploaded new science file to decrease energy consumption and match buoyancy energy rate.
// Science for OSU sg157 and/or sg158 with PAR sensor
/depth time sample gcint
50 4 1111 60
150 4 1111 120
250 16 1110 180
600 52 1110 300
1000 104 1100 360
The projected recovery date is currently end of July, this may buy us some more time.
Seaglider 157 recently completed it’s first complete onshore to offshore section, and the data are fantastic! As you saw in the profiles, the oxycline is consistently very near the surface, ranging from 30 to 75 meters depth. Becasue the oxycline is so shallow, we often observe a second chlorophyll peak within hypoxic waters (oxygen below 20 umol/kg or 1 mL/L). We also see consistently elevated backscattering signals throughout the OMZ, from the oxycline to about 300 meters depth. We hypothesize that this signal is at least partially derived (if not mostly) from enhanced microbial activity in the OMZ, and look forward to ship-based sampling to test this idea. We have observed these same features in data from Apex profiling floats that were released in the area last March (Whitmire et. al., in prep.; link to data, link to plot).
Yeah, Anatoli! He got the dive speeds down from 180 minutes to 260 minutes (30 cm/s to 10 cm/s), and the results is extended mission duration and better vertical resolution in the profile data! Check out the latest profiles and you’ll see a much clearer picture of the small scale subsurface maxima in chl or DO:
Here’s the cmdfile that did the trick:
A new ratio for D_TGT and T_DIVE (not 3 anymore) and limiting the buoyancy range from 200 down to 100 with MAX_BUOY. This slows the dive thru buoyancy without altering the range.
sg157 continues to head offshore almost to 71 W now. For the last ten dives (85-95), sg157 has been collecting chl, backscatter and cdom observations over the entire 1000 m. I have now turned off the optics after 600 m depth. This deep water should have minimal signals (i.e. zeros), and will provide a means for Amanda to estimate drift in the optical measurements.
The oxygen minimum is still clear, but the layer seems to be getting thinner (250 m vs. 300 m). My plan is to continue offshore until sg157 exits the OMZ or 71.5 W.
sg157 continues to make full 1000 m dives on its way offshore. The top of the OMZ has been deepening in the offshore direction, and now the top is at about 100 m. Measurements from the upcast (red) are more reliable due to the large time constant associated with the DO sensor.
And, per Amanda’s request I’m going to turn on the optics for the full depth for a few dives.
// Science for OSU sg130 initial deployment
//depth time sample gcint
50 4 111 60
100 4 111 120
250 8 111 180
600 48 111 300
1000 96 111 300
See sg157 full observations