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30 October 2007: Prepared for OCB data system by Nancy Copley (Biology Dept, WHOI) and Cyndy Chandler, BCO-DMO (MCG Dept, WHOI).
Contact: Jim Ledwell (WHOI)
The tracer injection sled for the EDDIES project lowered to the target potential density surface and then towed along that surface at 0.5 m/s while the tracer is injected. The sled is neutrally buoyant and is towed at the end of a 2-meter tether attached to the end of the CTD cable, which removes much of the ship motion. To follow lower frequency displacements of the target surface, the winch is controlled automatically with feedback from a SeaBird 911plus CTD system (Ledwell et al., 1998). The CTD has dual pumped C/T sensors mounted at the front of the sled to sample water not perturbed by the thermal wake of the sled. Also with the CTD was the same WET Labs fluorometer that had been used on Survey 1 on the Oceanus CTD/Rosette system. On the injection sled are also mounted injection orifices, pumps, batteries, fluid reservoirs, and control electronics for the injection. No injection sled data were reported for this cruise.
The sampling sled is similar to the injection sled in that it carries the same SeaBird 9 CTD and the WET Labs fluorometer. It is mounted directly at the end of the CTD cable, with no tether, and with an array of integrating samplers above and below it (Ledwell et al. 1998). It is oriented into the flow with wedge-shaped panels on the aft end, and is also controlled to stay as near as possible to a target isopycnal surface.
Ledwell, J. R., A. J. Watson, and C. S. Law, Mixing of a tracer in the pycnocline, J. Geophys. Res., 103 (C10), pp. 21,499-21,529, 1998.
Data from the casts with the injection and sampling sleds are divided into downcast, flights along the target surface, and upcasts, indicated by "down", "flight" and "up" in the filenames, respectively.
Thirteen casts were done with the sampling sled on this cruise. Casts 5 and 12 were for calibration only. The others were all part of the tracer survey, and are labeled sampling tows 1 through 11. There are 13 sampler casts, 001 through 013. Data from cast 1 are reported separately because the CTD unit was configured with two fluorometer sensors, a WET Labs ECO-AFL/FL and a Chelsea Instruments fluorometer. Chlorophyll-a estimates from the Chelsea fluorometer for the first scan reported from each downcast were set to 'nd', because the values were erroneously high (2600-3200).
The sled sampling events as reported in the cruise event log are:
# cruise: OC415-4 EDDIES Tracer 2 # event date time lon lat cast ev_type comments --------------------------------------------------------------------------- 200508310100 20050831 0100 -70.845 29.882 1 Sampler Tow 200508311230 20050831 1230 -69.845 29.711 1 Sampler End Tow 200509010100 20050901 0100 -70.784 29.791 2 Sampler Tow 200509011200 20050901 1200 -70.518 29.727 2 Sampler End Tow 200509020100 20050902 0100 -70.723 29.808 3 Sampler Tow 200509021200 20050902 1200 -70.436 29.737 3 Sampler End Tow 200509030100 20050903 0100 -70.720 29.726 4 Sampler Tow 200509031200 20050903 1200 -70.425 29.614 4 Sampler End Tow 200509040030 20050904 0030 -70.408 29.922 5/6 Sampler Tow/Cast 200509041130 20050904 1130 -70.193 30.095 5/6 Sampler End Tow 200509050130 20050905 0130 -70.578 29.735 7/6 Sampler Tow/Cast 200509051200 20050905 1200 -70.289 29.685 7/6 Sampler End Tow 200509060100 20050906 0100 -70.453 29.821 8/7 Sampler Tow/Cast 200509061130 20050906 1130 -70.276 30.027 8/7 Sampler End Tow 200509080230 20050908 0230 -70.453 29.821 9/8 Sampler Tow/Cast 200509081330 20050908 1330 -70.276 30.027 9/8 Sampler End Tow 200509090030 20050909 0030 -70.544 29.696 10/9 Sampler Tow/Cast 200509091200 20050909 1200 -70.776 29.762 10/9 Sampler End Tow 200509100030 20050910 0030 -70.559 29.712 11/10 Sampler Tow/Cast 200509101200 20050910 1200 -70.926 29.853 11/10 Sampler End Tow 200509110100 20050911 0100 -70.181 29.875 11/12 Sampler Tow/Cast 200509111230 20050911 1230 -70.421 29.722 11/12 Sampler Recovery
The primary variables added to the database from the original SAM_00?_*.mat files are:
scan scan number
yearday time in decimal days, referenced to 0 at start of 2005
lat decimal degrees north
lon decimal degrees east (negative in our case)
temp0 temperature, primary sensor pair (T90, deg C))
temp1 temperature, secondary sensor pair (T90, deg C))
cond0 conductivity, primary sensor pair
cond1 conductivity, secondary sensor pair
press pressure (dbar)
v0 Chelsea Instruments fluorometer voltage
v5 Wetlabs fluorometer voltage (only for Cast 001)
sampl Sampler status: 1=ON; 0=OFF (estimated)
and the derived variables are:
sal0 Salinity, primary sensor pair
sal1 Salinity, secondary sensor pair
Wetl Chlorophyll from WetLabs fluorometer on Cast 1
Wetl = 3.5334*v5 - 0.3250, with v5 in volts
fluor_chla Chlorophyll from Chelsea Instruments fluorometer voltage, v0, (mg/m3):
inter-calibrated with the WetLabs fluorometer used on cast 1
Salinity Calibration
A few salinity samples were taken during the tows during OC415-4.
The mean values should be subtracted from sal0, and potential temperature and potential density should be recalculated accordingly.
| Cruise | Name | No. of samples | Mean S - Autosal | Std. Dev. |
| OC415-4 | Tracer 2 | 6 | 0.0040 | 0.0034 |
PI notes pertaining to the Seabird 911plus CTD unit
24 scans were averaged, so data were recorded at 1 hz.
A correction for the thermal mass effect was made with coefficients:
a = 0.027300, b = 0.100000
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