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Dye release test cruise on R/V Elakha, 13 April 2001


Participants

Perry York (operator), Jack Barth, Murray Levine, Steve Pierce, Michael Ott, John Lyman, Andy Dale.

Conditions

Wind: Weak (~3 kt), variable direction, following two weeks of largely upwelling-favorable winds (data from buoy 46050).

Wave height: 11-14 ft (we hit the peak!), but almost all was swell, so working conditions were good.

Click on a station for CTD data

Cruise photos

Abbreviated chronology (local times) Observations

CTD had WetStar Chlorophyll fluorometer, transmissometer and the new Seapoint fluorescein fluorometer.

We spent most time around three miles offshore in 60-65m of water (cruisetrack.ps). ADCP velocities largely to the E/NE, at ~0.1-0.2 m/s. It is not clear whether conditions could be categorised as upwelled or downwelled.

Curiously, CTD casts show a temperature minimum at 10-20m and maximum around 20-30m (CTD 1 etc.). Jay suggests that this must be an alongshore effect, and it was not evident in CTDs from 2 April 11th (Leah Feinberg).

The Seapoint fluorescein fluorometer performed smoothly. On deck and in surface waters the signal was either noisy or zero (in direct sunlight) due to ambient light hitting the detector window, since we had the instrument in an open (flow through) configuration. This effect was confined to the upper 10m. It is easy to switch to pumped configuration, or the manual from Seapoint suggests a baffle to shield from ambient light.

Florescein response showed no correlation with chlorophyll and a slight response to turbidity in the bottom boundary layer (CTD 4). This is probably due to autofluorescence (should be corrected when the detector window is changed to acrylic). In any case, this signal was lower than expected background fluorescence levels.

It was disappointing not to detect any fluorescein except for while actually pumping it, when it was seen intermittantly (we were moving slowly so the dye should have streamed out away from the fluorometer). cruisetrack.ps shows CTD cast positions vs predicted dye positions at CTD times, assuming a current of 0.2 m/s to the NE. It would have taken luck to find the dye! Post-processed ADCP (Steve) suggests that maybe the currents were slightly weaker than this and more to the E.

Dye Release Equipment/Method

The diffuser (PVC pipe) was attached to the rear of the minibat with two hose clamps, then the hose to the yoke with three ponytail holders and plenty of slack (37.jpg). This was very simple and seemed to work well. As the minibat was lowered, a ponytail holder was used to attach the hose to the line each 2-3 m .. also seemed to work well, although need 4 people to do this (one on MB winch, one paying out hose, one holding hose to wire, and one attaching ponytail holders). Cable tends to pull away from boat (maybe better without wings on MB?). Hose attachment would be very difficult in rougher conditions.

The pumps and plumbing performed well, although some redesign will make it easier to flush the tank and hose. Pump rate was 3-4 gallons/min when either pumping out through hose (~200ft) and diffuser, or sucking from a short hose over the side to flush the tank. Sucking through the diffuser did not seem to work.

Problems to resolve

- Minibat not flying well. Jay says we should have been able to get to 35m or so with 100m of cable. I need to check that set-up is exactly as Jay had it (including weighting and cable routes). Also, could drill out yoke mounting holes to give more flexibility.

- Minibat cable needs reterminating after getting caught in block.

- Dye plumbing redesign:

- Think about hose handling .. this is a little difficult.

- Need simple algorithms for navigation / turns etc so these are easily communicated to Perry.