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Physical Processes of Shelf-Open Ocean Exchange and their Influence on
Upwelling EcosystemsJack Barth
College of Oceanic & Atmospheric SciencesOregon State University
Marine Ecosystems and Climate: Modeling and Analysis of Observed Variability
NCAR, Boulder, COAugust 5, 2009
Outline
•coastal ocean fronts
•physical processes of shelf-deep ocean exchange wind-driven Ekman transport
• offshore, onshore intrinsic hydrodynamic instability
• eddies, jets and filaments flow-topography interaction wind stress curl high-frequency motions (internal tide)
• ecosystem impacts shelf hypoxia carbon export larval connectivity
California Current Canary Current
Humboldt CurrentBenguela Current
Coastal Upwelling Ecosystems
1% of surface area, but > 20% of wild caught seafood
Retrograde
e.g., buoyancy driven,shelf-break front,downwelling,water-mass boundary
Prograde
e.g., wind-driven,upwelling,western boundary current(e.g., Gulf Stream)
isopycnal
Two types of fronts
Courtesy of Jane Huyer (OSU)
Barth et al. (JGR, 2005)
Coastal Upwelling Front and Jet
23 Jan 2003
Distance (km)
downwellingfront
well-mixed
S
T
σE-Wvel
N-Svel
downwellingjet
23 Jan 2003Coastal downwelling front and jet
contours ofnorth(red)-south(blue)current speed in cm/s
Courtesy of J. Barth (OSU)
Satellite SST on 12 July 1999
Sharples and Simpson (2001)
Tidal mixing Tidal mixing fronts in the fronts in the
Irish SeaIrish Sea
Tidal Mixing FrontsTidal Mixing Fronts
Tidal fronts occur when surface heating (or other source of stratification) is overcome by mixing
these boundaries between cold and warm water can be seen from space
Deep water, tidal ellipses
small
shallow water, tidal ellipses
large
H/u3 smallH/u3 large
Simpson and James (1986)
SST fronts h/u3 = constant
Sharples and Simpson (2001)
satellite SST and chlorophyllon
12 July 1999
Probability density of SST fronts.
(Ullman and Cornillon, 1999)
Tidal Mixing Front on Georges Bank
Shelfbreak front all along Middle Atlantic Bight
Shelfbreak Front
Barth et al. (1998)
Wind Forcing and Large-Scale Circulation
Huyer (1983)
North Pacific High&
Continental Low
Seasonal cycleof winds
Sea-surfacetemperature
upwelling spring transition
Seasonal cycleof winds
Sea-surfacetemperature
windvariability
wind-drivenupwelling
drives ocean productivity
chlorophyll
Courtesy of Ted Strub (OSU)
temperature
Plankton bloom near Port
Orford, Oregon
B. Menge (OSU)
2006Massive phytoplankton blooms
Courtesy of B. Menge (OSU)
ecosystem impacts on
mid- to inner-shelf
30-50 km
The continental margin
Adapted from Hart and Currie (1960)
What happenson the
“inner shelf?”
CrossCross--shelf circulationshelf circulation-- Relationship between crossRelationship between cross--shelf flow and wind stressshelf flow and wind stress
Given steady, linear flow with no pressure gradient, the alongGiven steady, linear flow with no pressure gradient, the along--shelf shelf momentum balance can be approximated asmomentum balance can be approximated as
In shallow waters, where Ekman transport is not fully developed,In shallow waters, where Ekman transport is not fully developed, this becomes:this becomes:
Where:Where:U = measured transport (mU = measured transport (m22ss--11)) oo = reference density (1025 kgm= reference density (1025 kgm--33))
= stress (Nm= stress (Nm--22)) f = Coriolis (1.03x10f = Coriolis (1.03x10--44 ss--11 at 45at 45ooN)N)And: And:
a = fraction of full Ekman transport presenta = fraction of full Ekman transport presentb = timeb = time--series mean transport series mean transport (m(m22ss--11))
(m2s-1) (Lentz, 2001)(Lentz, 2001)
(m2s-1) (Ekman, 1905)(Ekman, 1905)
Lentz (2001); Kirincich et al. (2005)
…… but inner shelf can be efficiently flushed but inner shelf can be efficiently flushed by timeby time--dependent wind forcingdependent wind forcing
2
2
V zuAfv
tu
2
2
V zvAfu
tv
Kirincichand Barth(JPO, 2009)
Strub and James (2000)
Average summer SST and SSH
Submesoscale frontal instabilities and eddies
46
45
44
43
42
41
(relative vorticity)/f from numerical circulation model
X. Capet and co-workers
Horizontal scales of variability
Coastal capes and bays200-300 km
Baroclinic instabilitytraditional ~ mesoscale
50-100 km
Rossby radius
frontal ~ submesoscale10-20 km
R
R
LL2
Castelao et al. (2006)
Probability of detecting a SST front (4-yr average)
from GOES imagery
Castelao et al. (2006)
Probability of detecting a SST front (4-yr average)
from GOES imagery
Cross-shelf transport (mass, heat, salt, nutrients, carbon, larvae, eggs, …)
Barth et al. (2002)
~20% of shelf production5 events like this per year = benthic carbon mineralization rate
Flow-topography interaction off Oregon
HecetaBank
Barth et al. (2005)
Flow-topography interaction off Oregon
lat, N
HF radarsHF radars
Moorings (ADP, Moorings (ADP, T, S)T, S)
graphic design: A. Kurapov
Data Assimilation: Model + Data = Optimized Solution (3D+Time)
The CoOP-sponsored Coastal Ocean Advances in Shelf Transport (COAST) project (2000-2004)
Barth et al. (2005)
29 May – 1 June 2001
T (°C) chl (mg/m³)ADCP velocity
plankton “incubator”contributes to hypoxia!
Flow-topographyInteraction
Coas
tal u
pwel
ling
jet
Newport
Florence
Heceta Bank Coos Bay
Astoria
Hypoxia Zone
125 124.8 124.6 124.4 124.243.9
44.1
44.3
44.5
44.7
Longitude (°W)
Latit
ude
(°N
)
50
Heceta Bank
Stonewall Bank
HH-Line
NH-Line
0% 1-25% 26-50% 51-75%76-100%
SH-Line
70100200300400
Newport
100
500
B
Florence
A
124
Crab Mortality Classes
Percentage of Pots0 50 100
Grantham et al. (2004)
Significant fish and Dungeness crab die-offs in 2002
B
C
July 2002
Normal Inner-ShelfRockfish Community
Mesoscale activity and larval connectivity
Sotka et al. (2004)
Barnacles: genetic similarity
driftersreleasedhere
driftersreleasedhere
Princeton Ocean Model (POM)
Domain:Extension: 250 x 400 kmResolution: 1.5 kmVertical resolution: 31 σ-layersN-S: periodic; W: open
wind
D
Castelao and Barth (2006)
Numerical Model
Several topographies used, differing in the value of D
22
22
DfHNBu ~
2
2
radiusbankradiusRossby
Model forced by constant winds
fyu
xv
Ro||
~onacceleratiCoriolis
termsnonlinear
Castelao and Barth (2006)
If Bu small (Rossby radius > bank radius), flow follows topographyIf Bu large (Rossby radius < bank radius), flow can’t follow topography
If Ro small (weak flow), flow follows topographyIf Ro large, flow inertially “overshoots” topographic bends
Bu = 1.10 Bu = 0.38
larger
bank
oC
Flow response to steady upwelling favorable winds
= 0.12Pa
Surface velocities and temperature
Castelao and Barth (2006)
Sx
D
Increase bank radius
Stronger upwelling
winds
Sx
Burger number
Ros
sby
num
ber
Sx
Internal Rossby radius
Oregon values
D ~ 15 km
Ro ~ 0.13 - 0.33
Bu ~ 0.7 – 1.1
Castelao and Barth (2006)
Chelton et al. (2004)
Goal: Investigate the importance of curl-driven upwelling for jet separation
4-year average
(Aug 99 – Jul 03)
Satellite wind curl
Chelton et al. (2004)
).(^
fkw
Perlin et al. (2004)
6
6.5
7
7.5
8
8.5
9
9.5
10
10.5
11
11.5Day: 110
x−km
°C
−150 −100 −50 0
Nearshore wind curl influences coastal jet separation and fronts in the California Current System
Day: 70
x−km
y−km
−150 −100 −50 0100
150
200
250
300
350
400
450
−
modeledwinds
modeled circulation
Castelao and Barth (2007)
Sx
[ Note: angle of wind maximumto coast does not matter]
40 50 60 70 80 90 100 1100
10
20
30
40
50
60
70
80
Time (days)
Sx
basic caseno cape
Need the cape to get jet separation; wind maximum with curl alone won’t do it
Castelao and Barth (2007)
Time (days)
No cape
cape + wind curl
Am
ount
of s
epar
atio
n (S
x) (k
m)
40 50 60 70 80 90 100 1100
10
20
30
40
50
60
70
80
Time (days)
Sx
basic caseno curl uniform
x−km
y−km
−200 0
100200300400500
x−km−200 0
−1
0
1
x 10−6
x−km
N m−3
−200 0
y−km
Basic case
100200300400500
no curl
−0.2
−0.1
0 uniform
Pa
Wind maximum with no curl or uniform wind = delayed separation
Time (days)
Castelao and Barth (2007)
cape + wind curl
Am
ount
of s
epar
atio
n (S
x) (k
m)
Seasonal cycleof winds
Sea-surfacetemperatureHow might
winds change?
• strength*• direction• seasonality*• persistence
*examples in next slides
spring transition
Huyer and Smith (1978)
Spring Transition Fall Transition
ac-cumulatewind
Cumulative Wind Stress as measure of amount of upwelling
Spring transition
Falltransition
Interannualvariability
inwind stress
Cumulativewind stresssince Spring
Transition
2005
2000
Equatorward,Upwellingfavorable
Barth/Pierce (OSU)
Spring transitionInterannualvariability
inwind stress
Cumulativewind stresssince Spring
Transition
Equatorward,Upwellingfavorable
Falltransition
Barth et al. (2007)
late, weak upwelling in 2005
led to warm ocean temperatures
Barth et al. (2007)
PISCO
late, weak upwelling in 2005
led to low nutrients and chlorophyll
Barth et al. (2007)
long-termaverage
PISCO
0
50
100
150
200
050
100150200250300350400450500
0
25
50
75
100
125
150
recr
uits
/day
0
100
200
300
400
500
0
50
100
150
200
Month
1 2 3 4 5 6 7 8 9 10 11 12
0
20
40
60
80
100
120
0
100
200
300
0
50
100
150
200
0
10
20
30
40
50
60
Month
1 2 3 4 5 6 7 8 9 10 11 120
2
4
6
8
10
12
2005Long-term
Cape Meares45.47 N
Fogarty Creek44.84 N
Boiler Bay44.83 N
Seal Rock44.50 N
Yachats Beach44.32 N
Strawberry Hill44.25 N
Tokatee Klootchman44.20 N
Cape Arago43.31 N
Cape Blanco42.84 N
Rocky Point42.72 N
Mytilus spp.and unprecedented low recruitment !
mussels (Mytilusspp.)
Barth et al. (2007)
PISCO
2005Long-term
Jun-Aug: -83%
and unprecedented low recruitment !
barnacles(Balanus glandula)
Barth et al. (2007)
PISCO
2005Long-term
020406080
100120140
Cape Meares
020406080
100120140
Fogarty Creek
0
20
40
60
80
0
50
100
150
200
250
300Seal RockBoiler Bay
recr
uits
/day
020406080
100120140160
0
20
40
60
80
100Yachats Beach
0
20
40
60
80
100
Strawberry Hill
020406080
100120140
Tokatee Klootchman
Month
0 1 2 3 4 5 6 7 8 9 10 11 12 13
0
20
40
60
80
Month
0 1 2 3 4 5 6 7 8 9 10 11 12 13
0
10
20
30
40
50
2005Long-term
Cape Arago
Cape Blanco Rocky Point
Balanus glandula
year x season p = 0.008
year p = 0.002season p<0.0001
NS year x season p<0.0001
year x season p<0.0001
year x season p=0.027
NS
year x season p<0.0001
year x season p=0.045
year x season p=0.007
May-Jul: -66%
Upwellingfavorable
Lack of upwelling early in 2005
2005
Barth et al. (2007)
Led to poorplankton growth and marine die-offs
… and poorsalmon returns in 2008
March 14, 2008
Barth et al. (2007)
44.6N = Oregon
20-30 day oscillations
Win
d St
ress
(N m
-2)
The culprit? Strong intraseasonal wind oscillations and an anomalously southern Jet Stream location
Barth et al. (2007)
The culprit? Strong intraseasonal wind oscillations and an anomalously southern Jet Stream location
Jet StreamPosition
May 2005
July 2005
2005
2006
Supercharged upwelling of 2006two extremes
in the lastseveral years !
Led to massive plankton blooms and hypoxia
Upwellingfavorable
Summary - Shelf-Deep Ocean Exchange wind forcing
• Ekman transport • offshore, onshore• curl-driven• changing w/climate?
intrinsic hydrodynamic instability• eddies, jets and filaments
flow-topography interaction
• ecosystem impacts shelf hypoxia carbon export larval connectivity