Physical Processes of Shelf-Open Ocean Exchange and their ......downwelling, water-mass boundary...

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