Water Level Sensor Physical processes related to bio-optical properties on the New York Bight inner continental shelf Grace C. Chang 1, Tommy D. Dickey 1, Oscar Schofield 2 1 Ocean Physics Laboratory, University of California, Santa Barbara; 2 Institute of Marine and Coastal Sciences, Rutgers University Introduction Hyperspectral Coastal Ocean Dynamics Experiment (HyCODE) was designed to improve our understanding of the diverse processes controlling inherent optical properties (IOPs) in the coastal ocean in order to develop operational ocean color algorithms in both the optically-shallow and optically-deep ocean. Objectives Determine how temporal and spatial variability in IOPs are affected by: Coastal physical and biological dynamics (upwelling/downwelling, fronts, filaments, eddies, blooms, etc.) and larger scale circulation patterns. Wave fields. Water column stratification and current shears. Near surface and near bottom mixing. Diurnal and seasonal biological and physical cycles Riverine and runoff inflows. Methods – Offshore Mooring Site of HyCODE is the New Jersey continental shelf, inner New York Bight, Middle Atlantic Bight Offshore mooring at o N, o W ~24 m water depth Two mooring deployments from May 2000 – July 2000 and July 2000 – September 2000 Temperature and conductivity sensors, fluorometers, transmissometers, and ADCP sampled once per minute PAR sensors sampled eight times per hour HydroScat-6 and ac-9 sampled once per hour Observations - Offshore Comparison between the difference of a t-w (676)- a t-w (650) and salinity -1 showing that low salinity estuarine runoff does not influence absorption of phytoplankton. Results - Offshore Tidal cycles (semi-diurnal and diurnal) are important to physical and optical properties. Diel cycle important to bio-optical properties. Estuarine and river flows greatly influence bio- optical properties. Near-surface optical signals mostly from dissolved matter. Results - Inshore Low-frequencies dominate hydrographic and bio- optical properties. Tidal oscillations important to near-bottom absorption. Optical properties are generally not significantly coherent with biological or hydrographic properties. Inshore is well-mixed and more dynamic (presence of southward coastal jet) than offshore. Methods – Inshore Nodes Site of HyCODE is the New Jersey continental shelf, inner New York Bight, Middle Atlantic Bight CTD and optical profiling nodes and an ADCP Temperature, depth, salinity, optical backscatter, and dissolved oxygen sensors, fluorometer, transmissometer, and ac-9 Inshore nodes at o N, o W ~15 m water depth Intensive profiling (twice per hour) during July and August The dominant transport direction is toward the southwest. The M2 semi-diurnal tidal period is the most important signal in the north and east current velocities. The O1 diurnal tidal period is of lesser importance. Time series of temperature, salinity, and density show interesting features: (1) pulses of low-salinity water on ~4 day cycles at 5m and (2) possible buoyant plumes. Dominant time scales of variability are the tidal frequencies (M2 & O1) and the surface temperature diel signal (D). (1) (2) (a and c) Time series of chlorophyll-a derived from fluorometers. (b and d) Temporal variability of chlorophyll-a (I = Inertial, M2 = semi-diurnal tide, D = diel). Time series of absorption, scattering, and beam attenuation coefficient. Dominant time scales of variability of absorption ratios (right column) are the diel signal (D) and the semi- diurnal tide (M2). Coherence between chlorophyll-a and beam c, a(412), a(676), temperature, salinity, and density. Coherence is significant between chlorophyll-a and optical properties (0 o phase) but not with hydrographic properties. Coherence between a(412) and a(676) with hydrographic properties. Coherence is significant between a(412) and temperature at middle and bottom depths and with salinity and density at near-surface depths (180 o phase). Coherence is significant between a(676) and temperature at middle and bottom depths (180 o phase). Comparison between the ratio of a t-w (412):a t-w (676) and salinity -1 showing the influence of low salinity estuarine runoff on bio-optical properties, specifically, absorption of dissolved matter and/or detritus. Comparison between b(412) and salinity -1 showing that low salinity estuarine runoff does not influence scattering. Observations - Inshore Time series of hydrographic and bio-optical properties from the profiling nodes. Tidal variability is important to hydrographic properties at the near-surface and near-bottom. Low-frequency variability of absorption ratios (right column) dominates all depths. Dominant time scales of variability for absorption ratios at the near bottom are the diel signal (D) and the semi-diurnal tide (M2). Coherence between chlorophyll-a with hydrographic and optical properties. Coherence is significant between chl-a and temperature and salinity at near-bottom depths (0 and 180 o phase, respectively). Coherence is significant between chl-a and a(412) at near-surface depths (0 o phase). Surprisingly, chl-a is not significantly coherent with a(676). Coherence between a(412) and a(676) with hydrographic properties and dissolved oxygen. Coherence is significant between a(412) and a(676) with salinity at mid-water depths (-180 o phase). Surprisingly, a(412) and a(676) are not significantly coherent with dissolved oxygen. Acknowledgements This work was supported by: Special thanks to Derek Manov and Frank Spada for engineering support and to Song Jiang for data processing. Contact Information: