Chang and Dickey 1998 Workshop Paper

Observations of internal solitary waves (ISWs) were obtained on a continental shelf during the Coastal Mixing and Optics (CMO) experiment. High-frequency, high-energy bursts were seen in north-component current data and temperature data, as well as in chlorophyll a concentration and beam c data. ISWs resulted in vertical pumping of biogenic and non-biogenic material, as observed in the optical data. Tidal phase and direction, and strength of stratification have a direct influence on the formation and characteristics of ISWs. Introduction Observations of high-energy, large-amplitude solitary waves on continental shelves are common (e.g., Sandstrom et al. [1989]). The interaction of tides with the continental shelf edge during periods of stratification leads to the formation of internal tides. These internal tides are modified over time into non-linear, high-energy bursts, called internal solitary waves (ISWs), or solitons. ISWs are important to vertical transport and mixing of biogenic and non-biogenic components in the water column [Weidemann et al., 1996]. These high-energy bursts bring nutrients and phytoplankton into or out of the euphotic layer, resulting in blooms or death. ISWs also resuspend sediment from the ocean bottom [Bogucki et al., 1997]. Methods The site of the Coastal Mixing and Optics (CMO) experiment was the "Mud Patch" of the Mid-Atlantic Bight (MAB) continental shelf. We collected high temporal resolution time-series of physical and optical data at four depths (14, 37, 52, and 68 m) using instruments on bio-optical systems (BIOPS) [Chang et al., 1997] on a mooring and a tripod. BIOPS instruments used in this study include: 1) PAR sensors, 2) stimulated fluorometers, 3) temperature sensors, and 4) beam transmissometers (660 nm). The sampling rate was eight times per hour. This paper focuses on observations obtained during our fall 1996 CMO mooring deployment between Julian Day (JD) 224 and 244 (August 11 and 31). Oregon State University (OSU) scientists deployed several physical instruments on a subsurface mooring [Boyd et al., 1997]. An uplooking RD Instruments Acoustic Doppler Current Profiler (ADCP) at 65 m, and temperature and salinity sensors at several depths were used in this study. ADCP current data were obtained every two minutes between 3 and 55 m with 4 m bins. Brunt Vaisala frequency (N^2(z), expressed in s^-2) was calculated between depths where subsurface mooring temperature data were available. All data used in this study were band-pass filtered between 10 minutes and one hour to highlight high-frequency ISWs.