We finished the first dye release experiment today. It lasted a little under 24 hours, and was very successful. We were able to stay with the dye despite strong currents 40 cm/s. The goal for the glider survey was to fly a coherent pattern relative to a translating drifter. While we were piloting the glider I thought we were doing horribly, but when I plotted the relative trajectory I was pleasantly surprised (see the two figures). We ran right over the drifter!
We recovered doug around 1 pm today – blazing hot sun, but nice and calm. The recovery went smoothly, and when we lifted the glider out of the water a dozen fish took off swimming every which way! They were hiding out under our glider. I’ve heard of this happening, but it was still cool to see it.
We found a new survey site and started pumping dye around 6:30, finished around 8pm and deployed the glider at 9pm. We used Chris’s quick release – not because we needed to, but because we had brought it with us, so why not use it. It worked great.
Doug was deployed at 17:32 today (dinner time: spaghetti with meatballs and sausage!).
We deployed in the “normal” fashion from doug’s cart off the starboard side of the ship; the Hatteras is pretty low to the water and it is very calm. I slid doug off and Chris kept doug away from the side of the ship with the pole.
We are conducting a 24-hr survey, after which we will recover and prepare to redeploy tomorrow evening.
Doug is struggling to stay in position relative to the drifters – currents are surprisingly strong (20 cm/s dive-averaged), but we are in the general vicinity!
Doug is on three hour call ins now to try to make some headway on the drifters. Chris will pilot starting at midnight. I will help him get started and nap between calls.
Other ops are going well. Brian Guest (WHOI Tech) had an under water camera and filmed the dye being deployed at 25 m depth – very cool! The water is so clear you could also see it from the surface.
As part of the Lateral Mixing Project, Glider Doug and Glider Russ set sail out of Beaufort NC on the R/V Cape Hatteras Monday morning. During the vessel’s seven day cruise the multi-organization science team will run several trial experiments characterizing the way upper ocean waters mix laterally. Experiments will utilize dye to trace the currents, sensors to follow the dye’s path and Lagrangian floats to ride the current. Gliders will run survey lines relative to one of the floats characterizing the water properties that move the float and the mixing currents.
Results from this trial cruise will prepare for the team for the full run next summer that will include three coordinated research vessels, airplane-based LIDAR and our Slocum gliders. Results from the experience will help us understand a fundamental feature of energy transmission through the ocean and help us create better computer models.
In the run up to the Ocean Sciences meeting next week, I have been exploring the Chilean Seaglider data from the March 2009 deployment in more detail. As far as I know, our Seagliders are the only ones currently in use that have PAR (photosynthetically active radiation) sensors on them, so I wanted to highlight some of those data on my poster. One process that I wanted to look for was daytime fluorescence quenching (DFQ) in the surface waters. Before I get into DFQ, let me back up a bit…
Chlorophyll-a is a pigment used by plants (and algae) during photosynthesis. It is what gives plants their green color. When a chlorophyll molecule has more incoming light than it can effectively shuttle into the process of photosynthesis, it has two ways to get rid of the excess radiation: it can release it as heat, or re-emit the light as fluorescence. Fluorescence by Chlorophyll-a is one thing that we measure with the Seagliders, and is often used as a proxy for plant biomass in the ocean. The first order assumption is: more fluorescence = more chlorophyll pigment = more biomass. However, biology being what it is (inherently complex, and therefore, FUN), there are many factors that can add significant variability in the relationship between fluorescence and pigment concentration (let alone biomass). Some of these may be community composition, light history of the cells (changes in mixed layer depth or stratification, e.g.), nutrient limitation and other stressors.
Now, back to DFQ. When the sun is high during the midday, the amount of incoming solar radiation is often much higher than the amount that phytoplankton cells in the surface waters can effectively process. When this happens, the cells basically throw up their hands (if they had hands), cry uncle (if they had uncles), and start to dissipate the excess energy as heat rather than fluorescence. So, what we would observe in this scenario would be decreased fluorescence during noon hours relative to the amount of chlorophyll pigment that is present, or daytime fluorescence quenching. Profiles of chlorophyll concentration or chlorophyll absorption during this same time period would not show a decrease in the amount of chlorophyll present in the water column, so interpretations of surface fluorescence data have to be carefully considered. This is where the PAR sensor on the Seaglider makes it’s contribution.
Below is a plot that shows the effect of DFQ on the fluorescence signal. I took the Seaglider data from each dive or climb, and median binned the data in ten meter surface bins from 0-10m, 10-20m, 20-30m, and 30-40m. I plotted PAR in black, and Chl-a in green, and plotted both vs. time (day of year) on the x-axis. This is one transect of data.
You can see that DFQ is quite apparent in the 0-10m and 10-20m bins, but the effect starts to fade and is hardly visible deeper in the water column. Neat, eh?
The next step, which I probably won’t get to before the conference, is to look into where and when DFQ is more pronounced, and relate this variability to the physical environment of the cells. One place to start would be to look at the mixed layer depth in order to estimate the daily integrated PAR that the surface community is getting. It seems obvious, but can I relate a shallower mixed layer depth with higher DFQ using in situ data? That would be pretty exciting! There are caveats, of course. The existence of a mixed layer doesn’t establish that mixing is actually taking place, etc., but the effort is worth making with these unprecedented data…
We’re back in the water off Oregon. Now we are in our winter sampling mode, where we get one out-in section and then recover at the first chance the weather gives us.
The outbound section shows a big slug of warm, (super) high chlorophyll in the offshore surface layer. This is may be associated with the icky HAB (Akashiwo sanguinea) that created a foam that dissolved the water-proofing oils from seabirds and was killing them as a result (http://www.oregonlive.com/news/index.ssf/2009/10/killer_foam_was_it_a_freak_eve.html).
Jack Barth and our Oregon shelf glider observations feature prominently on the NSF website (http://www.nsf.gov/news/special_reports/deadzones/index.jsp). The report describes how our continual presence in the Oregon coastal ocean via gliders has helped reveal the unprecedented extent and severity of hypoxia in the Pacific Northwest.
I was checking out the latest plots from SG130 yesterday, and I noticed a very interesting feature. The glider is a ways south of Newport, over 100 km offshore, heading northbound. In the last several profiles, in addition to a surface chlorophyll peak (~50 m), there appears a second chlorophyll maximum around 200 meters. Check it out:
The feature shows up in the backscattering data, too, and is not associated with any change in water mass characteristics (temperature or salinity). Is the deep chlorophyll max (DCM) an older surface bloom that has been advected offshore and is now sinking out? It would be neat to look at the glider and satellite data going back in time to see if I could track the origin of this DCM. Time to hit the literature and refresh my memory on the coastal dynamics of summer phytoplankton blooms off of Oregon. Any thoughts from our readers on origins of this feature, and whether or not it is an annual occurrence? I’ve got SG130 data from last summer, too…
IMHO, if you name your glider Waldo, you are asking for trouble …
Let’s hope they find it.
After performing a very nice “butterfly” pattern during the MOOMZ cruise, we sent sg158 offshore to start cross-shelf transects. Shortly after that, we started getting loads of roll retries and even a few roll errors – this means the internal motors were trying to shift the batteries and execute a roll to turn the glider and the motors either did not respond enough or did not respond at all. We panicked a bit a called Fritz at UW. He gently chided us for not digging a little deeper into the log files, and then suggested some glider magic:
Create a pdoscmds.bat file with these 3 lines and let the glider execute it during next phone call:
This ran the glider through a series of tests on the roll mechanism. Things seemed ok, but the problem continued to worsen as we made more and more dives. Eventually, the glider was stuck rolled partially to the starboard side, meaning all dives now executed as a slow clockwise spiral on the way down and counterclockwise spiral on the way up with no real control of heading.
Now, this meant sg158 had to be recovered. It wasn’t in imminent danger, but it was way (30+ nautical miles) offshore. Once again, Gadiel Alarcon sprang into action (on a Saturday and Sunday no less), and late on Sunday August 23 sg158 was safely recovered and brought back to Iquique.
On Monday, Laura emailed with Ruben Moraga at UNAP and they got sg158 turned off and stowed away. Now we’ll need to get the gliders shipped back to the US to replace sg157’s batteries and figure out what went wrong with sg158.