The Transport group has centered their efforts on a cross-shelf observational line, critical locations of which appear in the graphic in Fig. 12. The backbone of the line are three moorings, labeled A, B, and K tower (now N7) at which several key environmental parameters are being measured. The nominal depths of the stations are 5 m (A), 10 m (B), and 20 m (K tower). N7 tower is also the site of a tower maintained by the United States Air Force (USAF), whose cooperation has been instrumental in the success of the instrument deployments described herein. The structure and dimensions of N7 tower (formerly known as K tower) appear in Fig. 1.
Standard surface meteorological observations are being obtained at a height of 2 m. Direct flux measurements will be obtained at a height of 19 m, in keeping with the requirements necessary to compute the needed forcing parameters. Radiometers will also be placed at 19 m and sea surface temperature (SST) measurements via radiation will occur at 19 m. A camera will also be placed at 19 m to record the physical setting at regular intervals. Redundant wind observations are made from wind sensors on the south tower side at multiple levels, facing in the direction of the predominant winds (see Fig. 11). Temperature and relative humidity sensors are placed as shown to allow for gradient-method flux calculations for comparison with the direct flux measurements. The data are scheduled to be broadcast in real-time via a line of sight connection back to the FSU Coastal and Marine Laboratory (FSUCML). Meteorological data from the tower will be available in raw and quality-controlled form without use restrictions (Figure 11 also shows some temperature and dew point data following initial deployment in summer 2008).
An acoustic Doppler current profiler (ADCP) has been obtaining continuous velocity measurements at N7 tower since April, 2007 and wave state since April 2008. The ADCP is placed about 200 m from the tower and is rotated with a twin ADCP on a monthly schedule (the swap permits downloading of data and cleaning and servicing of the instrument). We plan to cable this instrument to the tower to permit real-time broadcasting of the data to the FSUCML. The necessary equipment has been purchased and is undergoing testing at the moment. Included in this array are processors for the wave observations. Two internally recording SeaBird Electronics conductivity-temperature sensors are attached to N7 tower, one near the surface and one at mid-depth. Four such instruments are now in our possession; they will be rotated on a quarterly schedule. Both A and B moorings are in place, and consist of bottom-mounted Acoustic Wave And Current (AWAC) ADCPs, and YSI 6600 probes. The latter are equipped with Light (PAR), temperature, depth, conductivity, oxygen, chlorophyll a, turbidity and ph sensors and have been installed in bottom-mounts at stations A, B and C. The fourth probe is used to swap the instrument at K-Tower, at least one more probe is needed to permit exchanging the instruments at stations B and A. As biofouling is intense and cleaning on site is not an option, instruments need to be exchanged in order to ensure uninterrupted data collection. In addition, a probe logging colored dissolved organic matter (CDOM) and a nitrate nutrient sensor were installed at the N7-tower bottom mound near the ADCP. Initial testing and calibration of all this equipment has been completed and data are now being collected by all sensors.
Monthly cruises along the line in Fig. 12 began in April, 2007. Five hydrographic stations are occupied along the line. At each, CTD (conductivity, temperature, depth) profiles of temperature, salinity, and pressure are obtained, along with YSI profiles of oxygen and pH. Water samples are collected with Niskin bottles at 3 water depths. The water samples are filtered (Whatman GF/F) on-site into precombusted glass vials and acidified to pH = 2 for DOC and DON analysis in Dittmar's lab at FSU with a state-of-the-art Shimadzu TOC-V-TNM-1 analyzer. In addition to the element analysis, continuous monitoring of colored dissolved organic matter (CDOM) is performed at K-tower. This continuous monitoring will provide a unique data set of DOC and DON in the northern Gulf of Mexico, and the effect of major events (e.g., hurricanes) should be detectable.