Optical signatures of estuarine outflow plumes

1
Optical signatures of estuarine outflow plumes

• Dynamics of plumes
• Chesapeake Bay
• Hudson River
• Mobile Bay
• Optical Instrument - ac9
• Optical characteristics of plume and
  upwelling states.

Hyperspectral characterization of the coastal
ocean. D.Johnson R.Arnone J.Miller A.Weidemann V.
Haltrin Naval Research Laboratory Stennis Space
Center
2
Three Estuarine/River Plumes
Hudson River
Chesapeake Bay
Mobile Bay
3
Chesapeake Bay Outflow Plume
Upwelling State Plume dissipates
Plume State Down-welling winds
Moored ac9
4
Visible plume front propagating down the
coast. Distinguishable by color contrast and
roughness contrast.
5
Cross-Section Chesapeake Bay Outflow May
Upwelling State plume dissipates
Plume State Down-welling
6
Collecting InherentOptical Properties
AC9 9 wavelengths (412-715 nM)
Total Beam Attenuation c(l) a(l) b(l)
Absorption a ag ap... (aw)
Scattering b c - a
Filter the absorption tube ag afiltered
7
Example absorption spectrum from ac9
Total with water
Total Measured
Particulate
Dissolved
8
Time series from mooring
Inherent Optical Properties surrogate
CDOM (gelbstoff)
Chlorophyll
Particulates
9
Hudson River Plume July
Plume State.Upwelling.Dissipation
10
Cross Section Hudson River
Upwelling State plume dissipates
Plume State down-welling
11
Absorption Spectra (a) Hudson River Outflow
12
Scattering Spectra (b) Hudson River Outflow
13
Mobile Bay outflow May
Salinity
ag(412)
14
Mobile Bay Outflow
Absorption Spectra (a)
Scattering Spectra (b)
15
Summary

• Estuary/river outflow plumes are an effective
  source of high optical variability on the
  continental shelf.
• Linear pump with storm time scale (2-6 days).
• Chesapeake Bay and Hudson distribute gt 100 km
  along coast.
• Some act as distributed pumps (Mobile
  Bay/Mississippi Sound).
• High loads of chlorophyll, sediments and
  dissolved organics in plumes produce distinctive
  IOP signatures.
• Upwelling state optical signatures can mask plume
  state signatures - the challenge is to separate
  the two.