Physical processes related to bio-optical properties on the

1
Physical processes related to bio-optical
properties on the New York Bight inner
continental shelf
Grace C. Chang1, Tommy D. Dickey1, Oscar
Schofield2
1Ocean Physics Laboratory, University of
California, Santa Barbara 2Institute of Marine
and Coastal Sciences, Rutgers University
Contact Information grace_at_icess.ucsb.edu
http//www.opl.ucsb.edu/

• 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 39.35oN, 74.08oW
• 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

• 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 39.46oN, 74.26oW
• 15 m water depth
• Intensive profiling (twice per hour) during July
  and August

Observations - Offshore
Observations - Inshore
(2)
(1)
Comparison between the ratio of
at-w(412)at-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.
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 180o phase,
respectively). Coherence is significant between
chl-a and a(412) at near-surface depths (0o
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 (-180o
phase). Surprisingly, a(412) and a(676) are not
significantly coherent with dissolved oxygen.
Coherence between chlorophyll-a and beam c,
a(412), a(676), temperature, salinity, and
density. Coherence is significant between
chlorophyll-a and optical properties (0o phase)
but not with hydrographic properties.
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).
(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).

• 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.

Comparison between the difference of
at-w(676)-at-w(650) and salinity-1 showing that
low salinity estuarine runoff does not influence
absorption of phytoplankton.
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 (180o phase).
Coherence is significant between a(676) and
temperature at middle and bottom depths (180o
phase).
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).
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 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).
Comparison between b(412) and salinity-1 showing
that low salinity estuarine runoff does not
influence scattering.