Feb
15

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.

Section 3 Chl-a and PAR bins

Section 3 Chl-a and PAR bins

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…

Jul
21
Filed Under (Chile, gliders, Ha ha, Iquique, OMZ, seagliders, SG157) by Amanda Whitmire on 21-07-2009

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)…

Chilean newspaper article on the SG157 recovery

Chilean newspaper article on the SG157 recovery

We’re famous!

Jun
11
Filed Under (Chile, gliders, Iquique, MOOMZ, OSU, power, seagliders, SG157) by shearmar on 11-06-2009
Energy usage plot for sg157 since the beginning of the deployment.

Energy usage plot for sg157 since the beginning of the deployment.

We’ve been experimenting with some power saving strategies on sg157 this week. In the plot of energy consumption, you can see that the blue 10V battery is draining a lot faster than the red 24V battery. The 10V battery powers the onboard computer and the scientific sensors. The 24V battery mainly powers the buoyancy pump. So, our energy consumption for science is rapidly outpacing our energy consumption for flying.

How to fix that? Shut off the science sensors! So we tried that starting MondayJun 08 by uploading a one-line science file:

// Science for OSU sg157 and/or sg158 with PAR sensor
/depth  time    sample  gcint
1000    600     0000    600

This file determines that from the surface to 1000 m the sampling interval is 600 seconds (10 minutes), none of the sensors are turned on (0000), and the guidance and control interval (time between steering) is also 600 seconds. This had an immediate affect:

10V battery energy usage by sensor, major consumers are optics and TT8 (computer)

10V battery energy usage by sensor, major consumers are optics and TT8 (computer)

Notice the major drop near dive 540. This is great, it extended our mission duration from end of August to end of October! Nevermind the fact we are no longer collecting data … and this had an added complication of suddenly erratic flying by the glider. With the glider checking in only every 10 minutes to steer and make flying decisions, sg157 would fly past 1000 m, go to deep and rocket up to the surface in what I’m assuming is an emergency manuever.

Anatoli did some experimentning, and now we are flying with shorter gcints and the CT sensor on, consuming only slightly more power than everything off, and having no more erratic dives.

May
11
Filed Under (gliders, Iquique, seagliders, SG157) by Amanda Whitmire on 11-05-2009

Hey all – just realized that Seaglider 157 made it’s 400th dive off of Iquique on Saturday (9 May, 2009). Very exciting! The glider is now on it’s usual onshore-offshore route, about 2/3 the way through the seventh ~135 km, cross-shore transect. The eastern south Pacific oxygen minimum zone has never been sampled over these time and space scales, so I hope you all can share some of my enthusiasm for these unprecedented data. Now, if we could just find a research vessel so that we could get out there and do some discrete sampling…

Anyhow – thanks to everyone involved for your continued efforts.

Apr
19
Filed Under (Chile, energy, gliders, power, seagliders, SG157) by shearmar on 19-04-2009

I’m trying a drastic change in the science file to see if I can make any impact on the energy consumption. Right now the power remaining should get us to end of July, and this may work well for the timing of a MOOMZ cruise, but if the cruise gets delayed further having sg157 last as long as possible will be a priority. Here’s the new science:
// Science for OSU sg157 and/or sg158 with PAR sensor
/depth time sample gcint
50 4 1111 60
150 4 1111 120
250 52 1110 180
600 104 1110 300
1000 104 1100 360

Apr
13
Filed Under (Chile, gliders, Iquique, OMZ, seagliders, SG157) by Amanda Whitmire on 13-04-2009

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?

Apr
08
Filed Under (Chile, gliders, Iquique, MOOMZ, OMZ, seagliders, SG157) by shearmar on 08-04-2009

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.

Mar
25
Filed Under (Chile, gliders, Iquique, OMZ, seagliders, SG157) by Amanda Whitmire on 25-03-2009
Full profile (0-1000m) below \/, surface to 400 meters above /\

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).

Mar
17
Filed Under (Chile, gliders, Iquique, MOOMZ, OMZ, seagliders, SG157) by shearmar on 17-03-2009

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:
$D_TGT,990
$T_DIVE,470
$T_MISSION,390
$HEAD_ERRBAND,30
$ROLL_ADJ_DBAND,3
$ROLL_ADJ_GAIN,0.03
$ALTIM_PING_DEPTH,400
$ALTIM_PING_DELTA,20
$ALTIM_SENSITIVITY,4
$MAX_BUOY,100
$SM_CC,300
$C_VBD,2630
$C_PITCH,2500
$C_ROLL_DIVE,2500
$C_ROLL_CLIMB,2400
$GO

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.

Mar
14
Filed Under (Chile, gliders, Iquique, MOOMZ, OMZ, seagliders, SG157) by shearmar on 14-03-2009

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.