ROC Meeting 21st February 2006 - UEA

The Antarctic Circumpolar Productivity Belt (Ito et al. GRL, 2005)

RATIONALE

General Paradigm for Export ProductionIn the Global Ocean

EquatorHigh

LatitudesHigh

Latitudes

CaCO3 DominatedSilicate

Dominated

Silicate

Dominated

(Surface [CHL] from Seawifs)

Observed Circumpolar Productivity Belt

Southern Ocean Meridional Circulation

Speer et al. , JPO, 2000

Wind

Global Ocean Nutrient Distribution

NADW

AABW

AAIW

SAMW

www.ewoce.org

Southern Ocean Nutrient Distribution

Southern Ocean Vertical Circulation

W @ 220 m (10-6 m s-1)

a)

b)

a) = (ET) Ekman Transport (Wind Driven)

b) = Residual Vertical Circulation = ET – Eddy-Flux

Up

Southern Ocean Export Production

Export Production @ 220 mW @ 220 m (10-6 m s-1)

MolSi m-2 yr-1

MolC m-2 yr-1

45 S

Schlitzer DSR II, 2002(gC m-2 yr-1)

Ito et al. GRL, 2005

Southern Ocean Export Production

Decoupling Iron from P and Si

Fe*(PO4) = Fe – (RFe:P)PO4

Fe*(Si) = Fe – (RFe:Si)PO4

(RFe:P) = 10-4 for small phytoplankton

(RFe:P) = 10-3 for diatoms

Parekh et al., GBC, 2005

Aeolian Dust Input

Dutkiewicz et al. ,GBC, 2005

From Mahowald et al., 2003 (mmol Fe m-2 yr-1)

Fe*> 0

Fe*< 0

Fe*< 0

Southern Ocean & Fe*

Fe*< 0 Fe limits PP

Fe*> 0Macro-Nuts limit PP

ACC

Fe*< 0 Fe limits PP

Fe*> 0 Si, P limit PP

Aeolian Dust Aeolian DustWind

UpwellingDeep

Ocean

Ekman Layer

Diatoms rule Non-diatoms ruleVE

ResidualCirculation

ACC

Fe*< 0 Fe limits PP

Fe*> 0 Si, P limit PP

Aeolian Dust Aeolian DustWind

UpwellingDeep

Ocean

Ekman Layer

Diatoms rule Non-diatoms ruleVE

ExportProduction

ExportProduction

ResidualCirculation

SO Dust Input & Global (I)Low Dust Input

High Dust Input

Dutkiewicz et al. ,GBC, 2005

Dutkiewicz et al. ,GBC, 2005

ΔPP (HD –LD)gC m-2 yr-1

SO Dust Input & Global (II)

Confirms Sarmiento et al., Nature, 2004 Role of SAMW for global ocean PP

Open Questions & Directions

1) Vertical Circulation, only driver for ACPB ?

2) If not Ballast Effect , Aggregation, or whatelse ?

3) If Climate Change causes an Ecosystem Shift, Positive or Negative feedback ?

NOT THAT SIMPLE !!!!

(Other factors might change: wind, dust input)

Ciao

Southern Ocean Nutrient Distribution