MOOMZ 5 - our first complete section

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).

Classic Winter Conditions on the Oregon Shelf

Here's the first section from Glider Bob's Oregon shelf mission. This is our fourth season of making Oregon shelf observations. During the winter, the surface layer is typically well-mixed down to 80 m, the pycnocline slopes downward toward the coast intersecting the bottom near the shelfbreak, and there is a small lense of fresh water very near shore from rain and run-off from small local rivers, and the currents are relatively strong and to the north. In this section, there is also a slight run up the shelf along the bottom of salty dense water, lead by some small scale variability that looks reminiscent of nonlinear internal waves a la the observations by Klymak and Moum (2004).

Oregon Coast Seaglider Data

I've been tinkering around with Seaglider data that was collected off of the Oregon coast from September - November 2008. SG130 is equipped with a WET Labs ECO-Puck, which provides us with estimates of Chlorophyll-a concentration (biomass proxy), colored dissolved organic matter (CDOM) fluorescence, and the particulate backscattering coefficient at 660 nm (proxy for particle load, particulate carbon, etc.). The Seaglider also has an oxygen sensor, which will be of great value when seasonal coastal hypoxia sets in again.

At any rate, here is a preliminary plot of data collected along an east/west transect, at apprximately 43.7 N. A large plume of particles being advected off of the shelf is evident in the backscattering data (middle plot on right - ignore the bathymetry for now). More plots to come in the near future!

MOOMZ 4

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.

MOOMZ 3

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.

MOOMZ 2

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.


I'm tuning the roll a little bit and dialing back the vbd:
cmdfile:
$C_VBD,2720
$C_ROLL_DIVE,2500
$C_ROLL_CLIMB,2400
$GO

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

http://gliderfs.coas.oregonstate.edu/sgliderweb/seagliders/sg157/current/procdat/index.php?

Microbial Oceanography of the Oxygen Minimum Zone (MOOMZ)

Two OSU Seagliders (sg157 and sg158) were deployed on Friday Mar 6, 2009 off the coast of Iquique, Chile. sg158 was recovered yesterday, but sg157 remains, collecting observations of temperature, salinity, density, currents, chlorophyl, backscatter, CDOM and dissolved oxygen. sg157 will continue to fly a cross-shelf section from about the 200 m isobath to 100 km offshore until July or August.


Currently, sg157 is headed offshore toward 71 W in deep water, making full dives to 1000 m. sg157 is completing dives too quickly, about 180 minutes vs. 330 minutes optimally, which I think is due to the max pitch at +/- 30 degrees. However, the overall flight seems well tuned; I'm getting good low pitch and roll bias numbers.

sg157 is having some altimeter issues, when it comes up onto the slope, getting false returns, and turning around too soon. I'll continue to work on that the next time we come on shore.