the lowering rate. For casts < 400 meters an hour of ship time is required. Deeper casts are 

 proportionally longer with >3000 m casts requiring 4 to 5 hours of ship time. The LAPS package 

 has a pinger and can approach within 5 m of the bottom. Multiple casts can be performed within 

 short (e.g. 24 hour) time periods to acquire data on diel variability. 



We envision sampling on cross-shelf and slope lines in conjunction with the CTD, 

 chemistry and biological sampling, as well as sampling at mooring locations (particularly the two 

 sediment trap moorings). Because the LAPS is autonomous with respect to power requirements 

 and requires no special equipment, LAPS profiles can follow CTD casts on section lines. 



METHODS AND PLATFORMS 



The LAPS as developed for the OMP is an autonomous system consisting of two major 

 subsystems deployed on a rigid frame that is lowered from a ship using a hydrowire. One 

 subsystem consists of a pair of video camera/strobe/battery systems which are independent of 

 each other. The strobe light output is synchronized to its camera such that the camera records a 

 full second of video (Hi-8, 400 line resolution) within which a single frame is illuminated by the 

 strobe. The strobe light output is collimated and baffled to produce a defined slab of light 

 oriented perpendicular to the camera. One of the cameras will be set to record the low range 

 (>250 um) of the particle field while the other camera will record the high end (>1 mm). These 

 parameters can be adjusted to the conditions. The second subsystem consists of a Sea-Bird Seacat 

 CTD mated to a Wet Labs ac-3 meter. This subsystem is used to measure physical parameters 

 (T, S, pressure) as well as beam attenuation and fluorescence. Merging the data sets from the 

 two subsystems is accomplished by time syncing. Any oceanographic research vessel capable of 

 supporting a multidisciplinary research effort is sufficient as a platform for the LAPS. 



STRENGTHS AND LIMITATIONS OF PROPOSED RESEARCH 



Video based systems for measuring aggregate abundance are necessary because aggregate 

 resuspension ('rebound') occurs at benthic shear stresses significantly lower than required to 

 resuspend sediment, resulting in a decoupling of aggregate transport from traditionally measured 

 optical properties such as beam transmission, as observed on the slope in the Gulf of Mexico 

 where aggregate nepheloid layers are found in the absence of a transmissometer nepheloid layer 

 (Gardner and Walsh, 1990; Walsh and Gardner, 1992). In the shelf/slope environment rebound 

 of aggregates and subsequent downslope transport and settling may be a significant mechanism 

 for export of shelf organic carbon, potentially explaining the discrepancy between benthic oxygen 

 demand on the slope and overlying production (J.J. Walsh et al, 1991; Janhke et al., 1993). The 

 LAPS allows for the measurement of aggregate abundance and size distribution on spatial and 

 temporal scales approaching synopticity (i.e. multiple profiles per day closely spaced along the 

 ship track). This capability is required to asses the along shelf and cross shelf/slope variability 

 of the OMP field area. 



120 



