Climatic Influences on Coastal/Estuarine Physical Oceanography…and Possible Interdisciplinary Implications Dan Codiga URI/GSO

1. Climatic Influences on
Coastal/Estuarine
Physical Oceanography
…and Possible Interdisciplinary
Implications
Dan Codiga
URI/GSO

2. Coastal and Estuarine
Physical Oceanography
 Key processes
 Currents, circulation: transport rates & pathways
 Competition b/w stratification and vertical mixing
 Exchange: Advective and dispersive transfers
b/w estuarine (fresher) & coastal (saltier)
 Systems are highly dynamic/variable on
numerous timescales: tidal (~<1 day),
weather-event (3-6 days), spring-neap
(14-28 days), seasonal, inter-annual,
… climatic

3. Local Laboratories:
Estuaries, Coastal Seas/Sounds, the Shelf
Dominant river inputs Examples
Ex 3
later in talk
Ex 1
Ex 2

4. Satellite Sea-Surface Temperature
(AVHRR averaged 2004-2008, Codiga & Ullman 2010 OSamp Part I)
WINTER SPRING
Long
Island
Sound
outflow
a nt ront
oy w F
Bu tflo
Ou
SUMMER FALL

5. In a few days, changing winds &/ river runoff can
dramatically reposition the buoyant outflow front
WINTER SPRING
vent
W eather-e
shifts
SUMMER FALL

6. Climate-Sensitive Influences
 River runoff (precipitation)
 Strength and persistence of stratification
 Strength of estuarine exchange circulation
 Offshore extent of freshening
 Wind speed; and Wind direction
 Vertical mixing; Surface cooling; Upwelling
flow strength; Estuarine exchange strength;
Transport pathways
 Surface heating
 Distributions of temperature, stratification
 Storm frequency and intensity
 Extreme events

7. Estuarine exchange circulation
Estuarine
River input
Up exchange
Estuary Less More
Dense dense Ocean
Head
(Lines of constant density)
 Exchange commonly 10-30X river input
 Exchange increases as river input
increases, and as stratification increases
 Density structure maintained by complex
interaction between advection and mixing

8. Asymmetric Response to Wind
Down-estuary wind Up-estuary wind
Up
Before
After
•Strengthened stratification •Weakened stratification
•Wind-driven vertical mixing •Wind-driven vertical mixing
less effective more effective
•Enhanced exchange flow •Reduced exchange flow
Mixing is sensitive to alignment of wind
relative to estuary axis In LIS: Whitney and Codiga JPO, In press
Wilson and Wang, Submitted

9. Expected trends & possible
consequences
 Increased streamflow/precipitation & surface heating
 Stronger stratification, increased estuarine exchange rate
 Possible transition from mixed estuary to partially stratified,
or from partially stratified toward salt wedge
 Larger offshore extent of freshening/stratification
 Changed mean wind direction
 Increased/decreased vertical mixing and estuarine
exchange, depending on alignment with local estuary axis
 Decreased mean wind speed
 In estuaries, weaker mixing
 On shelf, weaker upwelling circulation
 Increased storminess
 More frequent extreme events, more rapid dispersion

10. Potential Interdisciplinary Drivers
 Higher river flow
 (Estuaries) Increased stratification, nutrient load, primary productivity…
increased spatial extent and intensity of hypoxia
 (Shelf) Greater offshore extent of freshening influence… potential new
transport pathways and geographic extent of HABs
 Decreased mean wind speed
 (Shelf) Weaker upwelling circulation, reduced primary productivity
 Different rates of dispersal, transport and flushing
 Changed wind direction (relative to shoreline geometry)
 (Estuaries) Altered vertical mixing
 New transport pathways & rates
 Increased storminess
 More rapid dispersal of waterborne materials
 More frequent habitat alterations (salinity, temperature)

11. Three examples
 Estuarine exchange flow between Long
Island Sound and coastal ocean
 Rhode Island Sound extreme event: Deep
pulse of slope water from ~100km to south
 Inter-annual variability of Narragansett Bay
stratification and hypoxia

12. Long Island Sound Exchange
Codiga and Aurin, CSR 2007
 Several years 8-times daily ADCP transects (ferry)
 Transport strongest in summer, when stratified
 Increased river runoff should increase stratification
 Suggests future exchange flow will be stronger
 Shorter estuary flushing time – could ameliorate hypoxia
 Contrasts expected enhanced hypoxia due to increased stratification

13. Fall 2009 Deep Slope-water
Intrusion to Rhode Island Sound
 Warm
salty water
with T & S
well higher
than
climatic
averages
(based on
decades of
observ’ns)
Ullman & Codiga 2010 OSamp Part II

14. Buoy time
series
during fall
cooling
Ullman & Codiga 2010
OSamp Part II
 Sudden arrival, present for ~weeks
 T & S values imply origin over continental slope
~100+ km south
 Possible Gulf Stream ring/streamer remnant
 Ecological implications (larval transport, habitat, …)

15. Narragansett Bay Inter-Annual
Streamflow/Hypoxia Variability
 Springtime
streamflow good
predictor of
summer
stratification and
hypoxia
 Wet conditions
enhance hypoxia
 Suggests
worsening future
Codiga et al 2009, Estuar. Coast. hypoxia