WORKSHOP ON HYPOXIA IN NARRAGANSETT BAY
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WORKSHOP ON HYPOXIA IN NARRAGANSETT BAY OCTOBER 2 , 2006 - FIELDWORK IN SUPPORT OF HYDRODYNAMIC MODELS. Large Scale CTD Surveys - Deacutis, Murray, Prell Moored + Vessel-based Circulation Studies – Kincaid, Bergondo Towed Undulator Surveys - Ullman

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WORKSHOP ON HYPOXIA IN NARRAGANSETT BAY OCTOBER 2 , 2006 - FIELDWORK IN SUPPORT OF

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WORKSHOP ON HYPOXIA IN NARRAGANSETT BAY

OCTOBER 2 , 2006

- FIELDWORK IN SUPPORT OF

HYDRODYNAMIC MODELS

  • Large Scale CTD Surveys - Deacutis, Murray, Prell

  • Moored + Vessel-based Circulation Studies – Kincaid, Bergondo

  • Towed Undulator Surveys - Ullman

  • Moored Vertical Profilers – Vaudrey, Kremer


“The Day Trippers”

– Large Scale CTD Surveys 2006

Survey Dates :

Neap Tide Surveys :

6/6/06, 7/6/06, 8/3/06,8/31/06

Spring Survey : 8/11/06


PRN 1

PRS 07

http://www.geo.brown.edu/georesearch/insomniacs/


Deanna Bergondo & Chris Kincaid – Bottom Mounted ADCP Sites


Providence River Bottom Mounted ADCPs

Influenced by wind


Providence River Bottom Mounted ADCPs

Outflow

Inflow


Providence River Bottom Mounted ADCPs

Outflow

Inflow


Providence River Bottom Mounted ADCPs


Summary Bottom Mounted Results

  • EYC shallows – average surface flow to North

    • Influenced by prevailing winds

  • Two layer flow in EYC and Conimicut channels

    • Southward winds enhance return flow

    • Northward winds stall return flow


  • Physics: Observations & Modeling

    Acoustic Doppler Current Profilers - C Kincaid

    Bottom mounted

    Ship mounted

    Data coverage:

    Excellent temporal

    Poor Spatial

    Data coverage:

    Good spatial

    Poor Temporal


    Results: Providence River

    Prevailing outflow - shallow, western side shipping channel

    Prevailing inflow - deep, eastern side shipping channel

    Series of weak, recirculation eddies in shallow edges

    Strong wind-induced water column response/reorientation

    Physics:

    Goal to characterize circulation, mixing, flushing, transport, etc

    Methods are Observations & Modeling


    Bay Circulation Data Summary: Model boundary conditions

    18 underway surveys: summer vs winter


    Bay Circulation Data Summary: Model boundary conditions

    18 underway surveys: summer vs winter

    1.5 years of BM-ADCP data


    Bay Circulation Data Summary: Model boundary conditions

    Summer: strong long-shore flow

    bottom

    surface


    Bay Circulation Data Summary: Model boundary conditions

    Summer: prevailing (depth-averaged) counter-clockwise flow

    Summer: strong long-shore flow


    Bay Circulation Data Summary: Model boundary conditions

    Summer: prevailing (depth-averaged) counter-clockwise flow (CCF)

    Dominant exchange through mouth

    Summer: strong long-shore flow


    Bay Circulation Data Summary: Model boundary conditions

    Strong wind-induced exchanges


    Bay Circulation Data Summary: Model boundary conditions

    Extent of counter

    Wind

    Strong wind-induced exchanges

    SE winds enhance CCF, trigger RIS intrusion


    Bay Circulation Data Summary: Model boundary conditions

    Extent of counter

    Spatial extend of CCF

    ?

    ?

    Wind

    Strong wind-induced exchanges

    SE winds enhance CCF, trigger RIS intrusion


    Bay Circulation Data Summary: Model boundary conditions

    Extent of counter

    Winter: Strong 2-layer flow

    RIS water from southwest


    Bay Circulation Data Summary: Model boundary conditions

    Mt. Hope Bay circulation/exchange

    /mixing study. ADCP, tide gauges

    (Deleo, 2001)

    Extent of counter

    Bay-RIS exchange study (98-02)


    Bay Circulation Data Summary: Model boundary conditions

    Narragansett Bay Commission: Providence & Seekonk Rivers

    Mt. Hope Bay circulation/exchange

    /mixing study. ADCP, tide gauges

    (Deleo, 2001)

    Extent of counter

    Bay-RIS exchange study (98-02)


    This project: Mid-Bay focus

    Narragansett Bay Commission: Providence & Seekonk Rivers

    Mt. Hope Bay circulation/exchange

    /mixing study. ADCP, tide gauges

    (Deleo, 2001)

    Extent of counter

    Summer, 07: 4 month deployment (Outflow pathways)

    Bay-RIS exchange study (98-02)


    This project: Mid-Bay focus

    Outflow, inflow, exchange between Bay sub-regions

    Narragansett Bay Commission: Providence & Seekonk Rivers

    Mt. Hope Bay circulation/exchange

    /mixing study. ADCP, tide gauges

    (Deleo, 2001)

    Extent of counter

    Summer, 08: Deep return flow processes

    Bay-RIS exchange study (98-02)


    High-Resolution Surveys of Hydrography, Currents, and Vertical Mixing

    Dave Ullman (GSO)

    • Objectives:

      • Provide high resolution sections of physical

      • and biological parameters for assessment and

      • calibration of hydrodynamic and ecological models.

      • Estimate vertical turbulent mixing rates.

    • Methodology:

      • Towed undulating vehicle measuring hydrographic

      • parameters and turbulent microstructure.

      • Shipboard ADCP measuring currents.


    Acrobat

    Microstructure

    Sensors.

    Towed Undulating Vehicle

    • Towed vehicle sensors:

    • Temperature

    • Conductivity

    • Pressure

    • Oxygen concentration

    • Chlorophyll fluorescence

    • Nitrate concentration

    • Microscale conductivity

    • (turbulent mixing)

    • Ship-mounted ADCP:

    • Velocity profiles


    Along-channel sections suggest dynamical importance of the “narrows” at Conimicut

    Rapid variability in depth of

    thermocline, halocline over short

    distances.

    Conimicut


    Coordinate origin

    Conimicut Pt.

    Intensive Sampling, Conimicut Region

    • Carried out repeated tows over approximately a full tidal cycle

    • along black line shown on bathymetry map:

      • August 11, 2005 (Neap): 18 lines

      • August 18, 2005 (Spring): 20 lines


    Flood Tide Eddies

    • Commonly observed just south of narrows at Conimicut on flood tide.

    • Cause as yet unknown.

    • Potential to be an important horizontal dispersal mechanism.

    Aug. 11, 2005 early flood

    Clockwise eddy in

    near-surface current

    (blue vectors)

    Extends down

    to ~7 m depth.

    East Component (m/s)

    North Component (m/s)

    Conimicut

    south


    Acrobat

    Signature of Eddies in Hydrographic Fields?

    T

    Doming of isolines in upper water

    column in eddy region.

    S

    ADCP

    Eddy

    East Component (m/s)

    O2

    Chl-a

    North Component (m/s)

    NO3


    Vertical Mixing Estimates

    • Methodology:

      • Compute variance of conductivity gradient.

      • Apply corrections for salinity contributions

      • and sensor response to get temperature

      • gradient variance.

      • Dissipation rate of temperature gradient

      • fluctuations (T) is proportional to variance.

      • Estimate vertical temperature gradient ( )

      • from CTD sensors on acrobat.

      • Turbulent thermal eddy diffusivity

      • computed from T and gradient:

    • Micro-conductivity Sensor on Acrobat:

    • Measures conductivity at scales of O(1cm).

    • Sampled at 1024 Hz.


    Example Vertical Diffusivity Section

    From a single tow on Aug. 18, 2005.

    Spring tide conditions, ebb flow.

    Colors: log10(KT) (m2/s)

    Lines: t (kg/m3)

    • Conimicut narrows:

      • KT~10-4 - 10-3 m2/s

      • (strong vertical mixing)

    south


    Tidally Averaged Vertical Turbulent Diffusivity

    Colors: log10(KT) (m2/s)

    Lines: t (kg/m3)

    Aug. 11 (neap)

    Aug. 18 (spring)

    • Turbulent mixing appears to be enhanced in the Conimicut area.

    • Slightly stronger mixing on spring tides:

      • Neap average = 2.9x10-5 m2/s.

      • Spring average = 3.5x10-5 m2/s.


    Future Interaction with Modelers

    • Compare observations to ROMS model output:

      • Tidal eddies

        • Present in model?

        • If so, what is the mechanism by which they form?

          (Examine model momentum balance)

        • How do they affect horizontal property transport?

      • Vertical mixing

        • How does magnitude of model vertical mixing

          (computed by turbulence closure submodel) compare

          with observed mixing rates?

        • Can observations be used to tune model turbulence

          parameterizations?

      • Stratification

        • Is model vertical stratification of similar magnitude

          as observed?


    J. Kremer & J. Vaudrey

    Profiling Units

    4 Locations

    Field’s Point

    Bullocks Reach Buoy

    east of Conimicut Point Light

    Warwick Neck

    Sampling Set-Up

    sample every 15cm in the vertical

    1 profile every 3 hours

    deployed for ~ 2 weeks

    3 Deployments

    June, July, September


    Temperature

    oC

    depth off the bottom (m)

    Salinity

    ppt

    Dissolved

    Oxygen

    mg/L

    day of deployment (day 1 = 8/31/06)

    east of Conimicut Light


    Warwick Neck

    Temperature

    oC

    depth off the bottom (m)

    Salinity

    ppt

    Dissolved

    Oxygen

    mg/L

    day of deployment (day 1 = 6/27/06; day 16 = 7/13/06)


    END


    Hydrodynamic Model

    Grid Resolution: 100 m

    Grid Size: 1024 x 512

    Vertical Layers: 20

    River Flow: USGS

    Winds: NCDC

    Tidal Forcing: ADCIRC

    Open Boundary


    Modeling Exchange Between

    Biological Model Grids

    DYE_01

    DYE_02

    DYE_03

    DYE_06

    DYE

    04

    DYE

    05

    DYE_07

    DYE_09

    DYE_08


    Dye Experiment


    Dye Experiment


    Dye Experiment


    Model-Data Comparison

    Salinity - Phillipsdale

    Model

    Salinity (ppt)

    Data

    Time (days)


    Model-Data Comparison


    Seekonk River Bottom Mounted ADCPs


    Goal: Understand chemistry, biology and physics

    of the Bay, at all points in the Bay, for all time


    Goal: Understand chemistry, biology and physics

    of the Bay, at all points in the Bay, for all time

    Goal 2: Understand coupled processes given any

    combination of external forcing conditions


    Numerical Model

    Equations

    Momentum balance x & y directions:

    u + vu – fv = f + Fu + Du

    t x

    v + vv + fu = f + Fv + Dv

    ty

    Potential temperature and salinity :

    T+ vT = FT + DT

    t

    S + vS = FS + DS

    t

    The equation of state:

    r= r (T, S, P)

    Vertical momentum:

    f = - r g

    z ro

    Continuity equation:

    u+v+w = 0

    x y z

    Initial Conditions

    Forcing Conditions

    ROMS Model

    Regional Ocean

    Modeling System

    Output


    Narragansett Bay Commission: Providence & Seekonk Rivers

    3 month BM-ADCPs


    Narragansett Bay Commission: Providence & Seekonk Rivers

    3 month BM-ADCPs

    Underway ADCPs


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